Misplaced Pages

#768231

134-789: The Compact Muon Solenoid ( CMS ) experiment is one of two large general-purpose particle physics detectors built on the Large Hadron Collider (LHC) at CERN in Switzerland and France . The goal of the CMS experiment is to investigate a wide range of physics, including the search for the Higgs boson , extra dimensions , and particles that could make up dark matter . CMS is 21 metres long, 15 m in diameter , and weighs about 14,000 tonnes. Over 4,000 people, representing 206 scientific institutes and 47 countries, form

268-400: A {\displaystyle a} , and τ p {\displaystyle \tau _{\mathrm {p} }} decreases with increasing a {\displaystyle a} . Acceleration gives rise to a non-vanishing probability for the transition p → n + e + ν e . This was a matter of concern in

402-487: A Hilbert space , which is also treated in quantum field theory . Following the convention of particle physicists, the term elementary particles is applied to those particles that are, according to current understanding, presumed to be indivisible and not composed of other particles. Ordinary matter is made from first- generation quarks ( up , down ) and leptons ( electron , electron neutrino ). Collectively, quarks and leptons are called fermions , because they have

536-402: A microsecond . They occur after collisions between particles made of quarks, such as fast-moving protons and neutrons in cosmic rays . Mesons are also produced in cyclotrons or other particle accelerators . Particles have corresponding antiparticles with the same mass but with opposite electric charges . For example, the antiparticle of the electron is the positron . The electron has

670-502: A quantum spin of half-integers (−1/2, 1/2, 3/2, etc.). This causes the fermions to obey the Pauli exclusion principle , where no two particles may occupy the same quantum state . Quarks have fractional elementary electric charge (−1/3 or 2/3) and leptons have whole-numbered electric charge (0 or 1). Quarks also have color charge , which is labeled arbitrarily with no correlation to actual light color as red, green and blue. Because

804-427: A zinc sulfide screen produced at a distance well beyond the distance of alpha-particle range of travel but instead corresponding to the range of travel of hydrogen atoms (protons). After experimentation, Rutherford traced the reaction to the nitrogen in air and found that when alpha particles were introduced into pure nitrogen gas, the effect was larger. In 1919, Rutherford assumed that the alpha particle merely knocked

938-1058: A " Theory of Everything ", or "TOE". There are also other areas of work in theoretical particle physics ranging from particle cosmology to loop quantum gravity . In principle, all physics (and practical applications developed therefrom) can be derived from the study of fundamental particles. In practice, even if "particle physics" is taken to mean only "high-energy atom smashers", many technologies have been developed during these pioneering investigations that later find wide uses in society. Particle accelerators are used to produce medical isotopes for research and treatment (for example, isotopes used in PET imaging ), or used directly in external beam radiotherapy . The development of superconductors has been pushed forward by their use in particle physics. The World Wide Web and touchscreen technology were initially developed at CERN . Additional applications are found in medicine, national security, industry, computing, science, and workforce development, illustrating

1072-449: A bare nucleus, consisting of a proton (and 0 neutrons for the most abundant isotope protium 1 H ). The proton is a "bare charge" with only about 1/64,000 of the radius of a hydrogen atom, and so is extremely reactive chemically. The free proton, thus, has an extremely short lifetime in chemical systems such as liquids and it reacts immediately with the electron cloud of any available molecule. In aqueous solution, it forms

1206-613: A candidate to be a fundamental or elementary particle , and hence a building block of nitrogen and all other heavier atomic nuclei. Although protons were originally considered to be elementary particles, in the modern Standard Model of particle physics , protons are known to be composite particles, containing three valence quarks , and together with neutrons are now classified as hadrons . Protons are composed of two up quarks of charge + ⁠ 2 / 3 ⁠ e each, and one down quark of charge − ⁠ 1 / 3 ⁠ e . The rest masses of quarks contribute only about 1% of

1340-485: A charge pulse in the strips, at right angles to the wire direction. Because the strips and the wires are perpendicular, we get two position coordinates for each passing particle. In addition to providing precise space and time information, the closely spaced wires make the CSCs fast detectors suitable for triggering. Each CSC module contains six layers making it able to accurately identify muons and match their tracks to those in

1474-436: A few measurement points. Each measurement is accurate to 10 μm, a fraction of the width of a human hair. It is also the inner most layer of the detector and so receives the highest volume of particles: the construction materials were therefore carefully chosen to resist radiation. The CMS tracker is made entirely of silicon: the pixels, at the very core of the detector and dealing with the highest intensity of particles, and

SECTION 10

#1732772874769

1608-416: A form-factor related to the two-dimensional parton diameter of the proton. A value from before 2010 is based on scattering electrons from protons followed by complex calculation involving scattering cross section based on Rosenbluth equation for momentum-transfer cross section ), and based on studies of the atomic energy levels of hydrogen and deuterium. In 2010 an international research team published

1742-452: A fourth generation of fermions does not exist. Bosons are the mediators or carriers of fundamental interactions, such as electromagnetism , the weak interaction , and the strong interaction . Electromagnetism is mediated by the photon , the quanta of light . The weak interaction is mediated by the W and Z bosons . The strong interaction is mediated by the gluon , which can link quarks together to form composite particles. Due to

1876-548: A front size of 22 mm × 22 mm and a depth of 230 mm. They are set in a matrix of carbon fibre to keep them optically isolated, and backed by silicon avalanche photodiodes for readout. The ECAL, made up of a barrel section and two "endcaps", forms a layer between the tracker and the HCAL. The cylindrical "barrel" consists of 61,200 crystals formed into 36 "supermodules", each weighing around three tonnes and containing 1,700 crystals. The flat ECAL endcaps seal off

2010-576: A further factor of 100 down to 1,000 events per second. These are then stored on tape for future analysis. Data that has passed the triggering stages and been stored on tape is duplicated using the Grid to additional sites around the world for easier access and redundancy. Physicists are then able to use the Grid to access and run their analyses on the data. There are a huge range of analyses performed at CMS, including: The term Compact Muon Solenoid comes from

2144-829: A long and growing list of beneficial practical applications with contributions from particle physics. Major efforts to look for physics beyond the Standard Model include the Future Circular Collider proposed for CERN and the Particle Physics Project Prioritization Panel (P5) in the US that will update the 2014 P5 study that recommended the Deep Underground Neutrino Experiment , among other experiments. Proton A proton

2278-459: A lower collision energy of 10 TeV but this was prevented by the 19 September 2008 shutdown. When at this target level, the LHC will have a significantly reduced luminosity, due to both fewer proton bunches in each beam and fewer protons per bunch. The reduced bunch frequency does allow the crossing angle to be reduced to zero however, as bunches are far enough spaced to prevent secondary collisions in

2412-430: A negative electric charge, the positron has a positive charge. These antiparticles can theoretically form a corresponding form of matter called antimatter . Some particles, such as the photon , are their own antiparticle. These elementary particles are excitations of the quantum fields that also govern their interactions. The dominant theory explaining these fundamental particles and fields, along with their dynamics,

2546-484: A neutral hydrogen atom , which is chemically a free radical . Such "free hydrogen atoms" tend to react chemically with many other types of atoms at sufficiently low energies. When free hydrogen atoms react with each other, they form neutral hydrogen molecules (H 2 ), which are the most common molecular component of molecular clouds in interstellar space . Free protons are routinely used for accelerators for proton therapy or various particle physics experiments, with

2680-418: A new muon system in CMS, in order to complement the existing systems in the endcaps. The forward region is the part of CMS most affected by large radiation doses and high event rates. The GEM chambers will provide additional redundancy and measurement points, allowing a better muon track identification and also wider coverage in the very forward region. The CMS GEM detectors are made of three layers, each of which

2814-543: A number of situations in which energies or temperatures are high enough to separate them from electrons, for which they have some affinity. Free protons exist in plasmas in which temperatures are too high to allow them to combine with electrons . Free protons of high energy and velocity make up 90% of cosmic rays , which propagate through the interstellar medium . Free protons are emitted directly from atomic nuclei in some rare types of radioactive decay . Protons also result (along with electrons and antineutrinos ) from

SECTION 20

#1732772874769

2948-465: A proton charge radius measurement via the Lamb shift in muonic hydrogen (an exotic atom made of a proton and a negatively charged muon ). As a muon is 200 times heavier than an electron, resulting in a smaller atomic orbital , it is much more sensitive to the proton's charge radius and thus allows a more precise measurement. Subsequent improved scattering and electron-spectroscopy measurements agree with

3082-418: A proton out of nitrogen, turning it into carbon. After observing Blackett's cloud chamber images in 1925, Rutherford realized that the alpha particle was absorbed. If the alpha particle were not absorbed, then it would knock a proton off of nitrogen creating 3 charged particles (a negatively charged carbon, a proton, and an alpha particle). It can be shown that the 3 charged particles would create three tracks in

3216-697: A proton's mass. The remainder of a proton's mass is due to quantum chromodynamics binding energy , which includes the kinetic energy of the quarks and the energy of the gluon fields that bind the quarks together. The root mean square charge radius of a proton is about 0.84–0.87  fm ( 1 fm = 10  m ). In 2019, two different studies, using different techniques, found this radius to be 0.833 fm, with an uncertainty of ±0.010 fm. Free protons occur occasionally on Earth: thunderstorms can produce protons with energies of up to several tens of MeV . At sufficiently low temperatures and kinetic energies, free protons will bind to electrons . However,

3350-547: A result, they become so-called Brønsted acids . For example, a proton captured by a water molecule in water becomes hydronium , the aqueous cation H 3 O . In chemistry , the number of protons in the nucleus of an atom is known as the atomic number , which determines the chemical element to which the atom belongs. For example, the atomic number of chlorine is 17; this means that each chlorine atom has 17 protons and that all atoms with 17 protons are chlorine atoms. The chemical properties of each atom are determined by

3484-455: A simplistic interpretation of early values of atomic weights (see Prout's hypothesis ), which was disproved when more accurate values were measured. In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases. However, since particles from different gases had different values of charge-to-mass ratio ( q / m ), they could not be identified with

3618-431: A single particle, unlike the negative electrons discovered by J. J. Thomson . Wilhelm Wien in 1898 identified the hydrogen ion as the particle with the highest charge-to-mass ratio in ionized gases. Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge. This

3752-403: A slightly different technology of steel absorbers and quartz fibres for readout, designed to allow better separation of particles in the congested forward region. The HF is also used to measure the relative online luminosity system in CMS. About half of the brass used in the endcaps of the HCAL used to be Russian artillery shells. The CMS magnet is the central device around which the experiment

3886-436: A small amount of key information is used to perform a fast, approximate calculation to identify features of interest such as high energy jets, muons or missing energy. This "Level 1" calculation is completed in around 1 μs, and event rate is reduced by a factor of about 1,000 down to 50 kHz. All these calculations are done on fast, custom hardware using reprogrammable field-programmable gate arrays (FPGA). If an event

4020-435: A wide range of exotic particles . All particles and their interactions observed to date can be described almost entirely by the Standard Model. Dynamics of particles are also governed by quantum mechanics ; they exhibit wave–particle duality , displaying particle-like behaviour under certain experimental conditions and wave -like behaviour in others. In more technical terms, they are described by quantum state vectors in

4154-498: Is a 50 μm thick copper-cladded polyimide foil. These chambers are filled with an Ar/CO 2 gas mixture, where the primary ionisation due to incident muons will occur which subsequently result in an electron avalanche, providing an amplified signal. New particles discovered in CMS will be typically unstable and rapidly transform into a cascade of lighter, more stable and better understood particles. Particles travelling through CMS leave behind characteristic patterns, or "signatures", in

Compact Muon Solenoid - Misplaced Pages Continue

4288-487: Is a lone proton. The nuclei of the heavy hydrogen isotopes deuterium and tritium contain one proton bound to one and two neutrons, respectively. All other types of atomic nuclei are composed of two or more protons and various numbers of neutrons. The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms (which he called "protyles"), based on

4422-425: Is a particle physics theory suggesting that systems with higher energy have a smaller number of dimensions. A third major effort in theoretical particle physics is string theory . String theorists attempt to construct a unified description of quantum mechanics and general relativity by building a theory based on small strings, and branes rather than particles. If the theory is successful, it may be considered

4556-506: Is a silicon-based tracker. Surrounding it is a scintillating crystal electromagnetic calorimeter , which is itself surrounded with a sampling calorimeter for hadrons. The tracker and the calorimetry are compact enough to fit inside the CMS Solenoid which generates a powerful magnetic field of 3.8 T . Outside the magnet are the large muon detectors, which are inside the return yoke of the magnet. For full technical details about

4690-491: Is a stable subatomic particle , symbol p , H , or H with a positive electric charge of +1  e ( elementary charge ). Its mass is slightly less than the mass of a neutron and approximately 1836 times the mass of an electron (the proton-to-electron mass ratio ). Protons and neutrons, each with a mass of approximately one atomic mass unit , are jointly referred to as nucleons (particles present in atomic nuclei). One or more protons are present in

4824-441: Is a unique chemical species, being a bare nucleus. As a consequence it has no independent existence in the condensed state and is invariably found bound by a pair of electrons to another atom. Ross Stewart, The Proton: Application to Organic Chemistry (1985, p. 1) In chemistry, the term proton refers to the hydrogen ion, H . Since the atomic number of hydrogen is 1, a hydrogen ion has no electrons and corresponds to

4958-495: Is built, with a 4 Tesla magnetic field that is 100,000 times stronger than the Earth's. CMS has a large solenoid magnet. This allows the charge/mass ratio of particles to be determined from the curved track that they follow in the magnetic field. It is 13 m long and 6 m in diameter, and its refrigerated superconducting niobium-titanium coils were originally intended to produce a 4  T magnetic field. The operating field

5092-482: Is called the Standard Model . The reconciliation of gravity to the current particle physics theory is not solved; many theories have addressed this problem, such as loop quantum gravity , string theory and supersymmetry theory . Practical particle physics is the study of these particles in radioactive processes and in particle accelerators such as the Large Hadron Collider . Theoretical particle physics

5226-432: Is constructed from crystals of lead tungstate , PbWO 4 . This is an extremely dense but optically clear material, ideal for stopping high energy particles. Lead tungstate crystal is made primarily of metal and is heavier than stainless steel, but with a touch of oxygen in this crystalline form it is highly transparent and scintillates when electrons and photons pass through it. This means it produces light in proportion to

5360-532: Is explained by the Standard Model , which gained widespread acceptance in the mid-1970s after experimental confirmation of the existence of quarks . It describes the strong , weak , and electromagnetic fundamental interactions , using mediating gauge bosons . The species of gauge bosons are eight gluons , W , W and Z bosons , and the photon . The Standard Model also contains 24 fundamental fermions (12 particles and their associated anti-particles), which are

5494-544: Is in model building where model builders develop ideas for what physics may lie beyond the Standard Model (at higher energies or smaller distances). This work is often motivated by the hierarchy problem and is constrained by existing experimental data. It may involve work on supersymmetry , alternatives to the Higgs mechanism , extra spatial dimensions (such as the Randall–Sundrum models ), Preon theory, combinations of these, or other ideas. Vanishing-dimensions theory

Compact Muon Solenoid - Misplaced Pages Continue

5628-615: Is its decay into four muons. Because muons can penetrate several metres of iron without depositing a significant amount of energy, unlike most particles, they are not stopped by any of CMS's calorimeters. Therefore, chambers to detect muons are placed at the very edge of the experiment where they are the only particles likely to register a signal. To identify muons and measure their momenta, CMS uses three types of detector: drift tubes (DT), cathode strip chambers (CSC), resistive plate chambers (RPC), and Gas electron multiplier (GEM). The DTs are used for precise trajectory measurements in

5762-570: Is passed by the Level 1 trigger all the data still buffered in the detector is sent over fibre-optic links to the "High Level" trigger, which is software (mainly written in C++ ) running on ordinary computer servers. The lower event rate in the High Level trigger allows time for much more detailed analysis of the event to be done than in the Level 1 trigger. The High Level trigger reduces the event rate by

5896-434: Is planned to increase the performance and the radiation tolerance of the tracker. This part of the detector is the world's largest silicon detector. It has 205 m of silicon sensors (approximately the area of a tennis court) in 9.3 million microstrip sensors comprising 76 million channels. The Electromagnetic Calorimeter (ECAL) is designed to measure with high accuracy the energies of electrons and photons . The ECAL

6030-512: Is reversible; neutrons can convert back to protons through beta decay , a common form of radioactive decay . In fact, a free neutron decays this way, with a mean lifetime of about 15 minutes. A proton can also transform into a neutron through beta plus decay (β+ decay). According to quantum field theory , the mean proper lifetime of protons τ p {\displaystyle \tau _{\mathrm {p} }} becomes finite when they are accelerating with proper acceleration

6164-471: Is the study of these particles in the context of cosmology and quantum theory . The two are closely interrelated: the Higgs boson was postulated by theoretical particle physicists and its presence confirmed by practical experiments. The idea that all matter is fundamentally composed of elementary particles dates from at least the 6th century BC. In the 19th century, John Dalton , through his work on stoichiometry , concluded that each element of nature

6298-529: Is to aid in pion-photon discrimination. The Hadron Calorimeter (HCAL) measures the energy of hadrons , particles made of quarks and gluons (for example protons , neutrons , pions and kaons ). Additionally it provides indirect measurement of the presence of non-interacting, uncharged particles such as neutrinos . The HCAL consists of layers of dense material ( brass or steel ) interleaved with tiles of plastic scintillators , read out via wavelength-shifting fibres by hybrid photodiodes . This combination

6432-600: Is used to extract the parameters of the Standard Model with less uncertainty. This work probes the limits of the Standard Model and therefore expands scientific understanding of nature's building blocks. Those efforts are made challenging by the difficulty of calculating high precision quantities in quantum chromodynamics . Some theorists working in this area use the tools of perturbative quantum field theory and effective field theory , referring to themselves as phenomenologists . Others make use of lattice field theory and call themselves lattice theorists . Another major effort

6566-470: Is worth noting that for studies of physics at the electroweak scale, the scattering events are initiated by a single quark or gluon from each proton, and so the actual energy involved in each collision will be lower as the total centre of mass energy is shared by these quarks and gluons (determined by the parton distribution functions ). The first test which ran in September 2008 was expected to operate at

6700-587: The Morris water maze . Electrical charging of a spacecraft due to interplanetary proton bombardment has also been proposed for study. There are many more studies that pertain to space travel, including galactic cosmic rays and their possible health effects , and solar proton event exposure. The American Biostack and Soviet Biorack space travel experiments have demonstrated the severity of molecular damage induced by heavy ions on microorganisms including Artemia cysts. CPT-symmetry puts strong constraints on

6834-544: The atomic nuclei are baryons – the neutron is composed of two down quarks and one up quark, and the proton is composed of two up quarks and one down quark. A baryon is composed of three quarks, and a meson is composed of two quarks (one normal, one anti). Baryons and mesons are collectively called hadrons . Quarks inside hadrons are governed by the strong interaction, thus are subjected to quantum chromodynamics (color charges). The bounded quarks must have their color charge to be neutral, or "white" for analogy with mixing

SECTION 50

#1732772874769

6968-448: The center-of-mass energy of the LHC particle accelerator. The CMS detector is built around a huge solenoid magnet. This takes the form of a cylindrical coil of superconducting cable that generates a magnetic field of 4 tesla, about 100 000 times that of the Earth. The magnetic field is confined by a steel 'yoke' that forms the bulk of the detector's weight of 12 500 t. An unusual feature of

7102-594: The constituent quark model, which were popular in the 1980s, and the SVZ sum rules , which allow for rough approximate mass calculations. These methods do not have the same accuracy as the more brute-force lattice QCD methods, at least not yet. The CODATA recommended value of a proton's charge radius is 8.4075(64) × 10  m . The radius of the proton is defined by a formula that can be calculated by quantum electrodynamics and be derived from either atomic spectroscopy or by electron–proton scattering. The formula involves

7236-462: The electron cloud in a normal atom. However, in such an association with an electron, the character of the bound proton is not changed, and it remains a proton. The attraction of low-energy free protons to any electrons present in normal matter (such as the electrons in normal atoms) causes free protons to stop and to form a new chemical bond with an atom. Such a bond happens at any sufficiently "cold" temperature (that is, comparable to temperatures at

7370-414: The hydronium ion , H 3 O , which in turn is further solvated by water molecules in clusters such as [H 5 O 2 ] and [H 9 O 4 ] . The transfer of H in an acid–base reaction is usually referred to as "proton transfer". The acid is referred to as a proton donor and the base as a proton acceptor. Likewise, biochemical terms such as proton pump and proton channel refer to

7504-714: The mean lifetime of a proton for various assumed decay products. Experiments at the Super-Kamiokande detector in Japan gave lower limits for proton mean lifetime of 6.6 × 10  years for decay to an antimuon and a neutral pion , and 8.2 × 10  years for decay to a positron and a neutral pion. Another experiment at the Sudbury Neutrino Observatory in Canada searched for gamma rays resulting from residual nuclei resulting from

7638-405: The nucleus of every atom . They provide the attractive electrostatic central force which binds the atomic electrons. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z ). Since each element is identified by the number of protons in its nucleus, each element has its own atomic number, which determines

7772-423: The radioactive decay of free neutrons , which are unstable. The spontaneous decay of free protons has never been observed, and protons are therefore considered stable particles according to the Standard Model. However, some grand unified theories (GUTs) of particle physics predict that proton decay should take place with lifetimes between 10 and 10 years. Experimental searches have established lower bounds on

7906-439: The silicon microstrip detectors that surround it. As particles travel through the tracker the pixels and microstrips produce tiny electric signals that are amplified and detected. The tracker employs sensors covering an area the size of a tennis court, with 75 million separate electronic read-out channels: in the pixel detector there are some 6,000 connections per square centimetre. The CMS silicon tracker consists of 14 layers in

8040-401: The weak interaction , and the strong interaction . Quarks cannot exist on their own but form hadrons . Hadrons that contain an odd number of quarks are called baryons and those that contain an even number are called mesons . Two baryons, the proton and the neutron , make up most of the mass of ordinary matter. Mesons are unstable and the longest-lived last for only a few hundredths of

8174-529: The (as of October 2011) recently closed Tevatron at Fermilab have provided remarkable insights into, and precision tests of, the Standard Model of Particle Physics. A principal achievement of these experiments (specifically of the LHC) is the discovery of a particle consistent with the Standard Model Higgs boson , the particle resulting from the Higgs mechanism , which provides an explanation for

SECTION 60

#1732772874769

8308-407: The 40 MHz crossing rate would result in 40  terabytes of data a second, an amount that the experiment cannot hope to store, let alone process properly. The full trigger system reduces the rate of interesting events down to a manageable 1,000 per second. To accomplish this, a series of "trigger" stages are employed. All the data from each crossing is held in buffers within the detector while

8442-492: The CMS collaboration who built and now operate the detector. It is located in a cavern at Cessy in France , just across the border from Geneva . In July 2012, along with ATLAS , CMS tentatively discovered the Higgs boson . By March 2013 its existence was confirmed. Recent collider experiments such as the now-dismantled Large Electron-Positron Collider and the newly renovated Large Hadron Collider (LHC) at CERN, as well as

8576-401: The CMS detector is that instead of being built in-situ underground, like the other giant detectors of the LHC experiments, it was constructed on the surface, before being lowered underground in 15 sections and reassembled. It contains subsystems which are designed to measure the energy and momentum of photons , electrons , muons , and other products of the collisions. The innermost layer

8710-506: The CMS detector, please see the Technical Design Report . This is the point in the centre of the detector at which proton -proton collisions occur between the two counter-rotating beams of the LHC . At each end of the detector magnets focus the beams into the interaction point. At collision each beam has a radius of 17 μm and the crossing angle between the beams is 285 μrad. At full design luminosity each of

8844-498: The LHC. The more momentum a particle has the less its path is curved by the magnetic field, so tracing its path gives a measure of momentum. CMS began with the aim of having the strongest magnet possible because a higher strength field bends paths more and, combined with high-precision position measurements in the tracker and muon detectors, this allows accurate measurement of the momentum of even high-energy particles. The tracker and calorimeter detectors (ECAL and HCAL) fit snugly inside

8978-474: The Moon is inside the Earth's geomagnetic tail, and typically no solar wind particles were detectable. For the remainder of each lunar orbit, the Moon is in a transitional region known as the magnetosheath , where the Earth's magnetic field affects the solar wind, but does not completely exclude it. In this region, the particle flux is reduced, with typical proton velocities of 250 to 450 kilometers per second. During

9112-408: The Standard Model during the 1970s, physicists clarified the origin of the particle zoo. The large number of particles was explained as combinations of a (relatively) small number of more fundamental particles and framed in the context of quantum field theories . This reclassification marked the beginning of modern particle physics. The current state of the classification of all elementary particles

9246-571: The aforementioned color confinement, gluons are never observed independently. The Higgs boson gives mass to the W and Z bosons via the Higgs mechanism – the gluon and photon are expected to be massless . All bosons have an integer quantum spin (0 and 1) and can have the same quantum state . Most aforementioned particles have corresponding antiparticles , which compose antimatter . Normal particles have positive lepton or baryon number , and antiparticles have these numbers negative. Most properties of corresponding antiparticles and particles are

9380-580: The barrel at either end and are made up of almost 15,000 further crystals. For extra spatial precision, the ECAL also contains pre-shower detectors that sit in front of the endcaps. These allow CMS to distinguish between single high-energy photons (often signs of exciting physics) and the less interesting close pairs of low-energy photons. At the endcaps the ECAL inner surface is covered by the pre-shower subdetector, consisting of two layers of lead interleaved with two layers of silicon strip detectors. Its purpose

9514-402: The cables from the power converter to the cryostat ) has a value of 0.1 mΩ which leads to a circuit time constant of nearly 39 hours. This is the longest time constant of any circuit at CERN. The operating current for 3.8  T is 18,160  A , giving a stored energy of 2.3  GJ . The job of the big magnet is to bend the paths of particles emerging from high-energy collisions in

9648-414: The central barrel region, while the CSCs are used in the end caps . The RPCs provide a fast signal when a muon passes through the muon detector, and are installed in both the barrel and the end caps. The drift tube (DT) system measures muon positions in the barrel part of the detector. Each 4-cm-wide tube contains a stretched wire within a gas volume. When a muon or any charged particle passes through

9782-465: The central region and 15 layers in the endcaps. The innermost four layers (up to 16 cm radius) consist of 100 × 150 μm pixels, 124 million in total. The pixel detector was upgraded as a part of the CMS phase-1 upgrade in 2017, which added an additional layer to both the barrel and endcap, and shifted the innermost layer 1.5 cm closer to the beamline. The next four layers (up to 55 cm radius) consist of 10 cm × 180 μm silicon strips, followed by

9916-407: The character of such bound protons does not change, and they remain protons. A fast proton moving through matter will slow by interactions with electrons and nuclei, until it is captured by the electron cloud of an atom. The result is a diatomic or polyatomic ion containing hydrogen. In a vacuum, when free electrons are present, a sufficiently slow proton may pick up a single free electron, becoming

10050-399: The cloud chamber, but instead only 2 tracks in the cloud chamber were observed. The alpha particle is absorbed by the nitrogen atom. After capture of the alpha particle, a hydrogen nucleus is ejected, creating a net result of 2 charged particles (a proton and a positively charged oxygen) which make 2 tracks in the cloud chamber. Heavy oxygen ( O), not carbon or fluorine, is the product. This was

10184-480: The coaccelerated frame there is a thermal bath due to Fulling–Davies–Unruh effect , an intrinsic effect of quantum field theory. In this thermal bath, experienced by the proton, there are electrons and antineutrinos with which the proton may interact according to the processes: Adding the contributions of each of these processes, one should obtain τ p {\displaystyle \tau _{\mathrm {p} }} . In quantum chromodynamics ,

10318-597: The constituents of all matter . Finally, the Standard Model also predicted the existence of a type of boson known as the Higgs boson . On 4 July 2012, physicists with the Large Hadron Collider at CERN announced they had found a new particle that behaves similarly to what is expected from the Higgs boson. The Standard Model, as currently formulated, has 61 elementary particles. Those elementary particles can combine to form composite particles, accounting for

10452-438: The decay of a proton from oxygen-16. This experiment was designed to detect decay to any product, and established a lower limit to a proton lifetime of 2.1 × 10  years . However, protons are known to transform into neutrons through the process of electron capture (also called inverse beta decay ). For free protons, this process does not occur spontaneously but only when energy is supplied. The equation is: The process

10586-450: The development of nuclear weapons . Throughout the 1950s and 1960s, a bewildering variety of particles was found in collisions of particles from beams of increasingly high energy. It was referred to informally as the " particle zoo ". Important discoveries such as the CP violation by James Cronin and Val Fitch brought new questions to matter-antimatter imbalance . After the formulation of

10720-420: The different layers, allowing them to be identified. The presence (or not) of any new particles can then be inferred. To have a good chance of producing a rare particle, such as a Higgs boson , a very large number of collisions is required. Most collision events in the detector are "soft" and do not produce interesting effects. The amount of raw data from each crossing is approximately 1  megabyte , which at

10854-432: The endcap disks where the magnetic field is uneven and particle rates are high. CSCs consist of arrays of positively charged "anode" wires crossed with negatively charged copper "cathode" strips within a gas volume. When muons pass through, they knock electrons off the gas atoms, which flock to the anode wires creating an avalanche of electrons. Positive ions move away from the wire and towards the copper cathode, also inducing

10988-482: The experiment are: The ATLAS experiment , at the other side of the LHC ring is designed with similar goals in mind, and the two experiments are designed to complement each other both to extend reach and to provide corroboration of findings. CMS and ATLAS uses different technical solutions and design of its detector magnet system to achieve the goals. CMS is designed as a general-purpose detector, capable of studying many aspects of proton collisions at 0.9–13.6 TeV ,

11122-443: The experimental beampipe. Momentum of particles is crucial in helping us to build up a picture of events at the heart of the collision. One method to calculate the momentum of a particle is to track its path through a magnetic field; the more curved the path, the less momentum the particle had. The CMS tracker records the paths taken by charged particles by finding their positions at a number of key points. The tracker can reconstruct

11256-478: The first experimental deviations from the Standard Model, since neutrinos do not have mass in the Standard Model. Modern particle physics research is focused on subatomic particles , including atomic constituents, such as electrons , protons , and neutrons (protons and neutrons are composite particles called baryons , made of quarks ), that are produced by radioactive and scattering processes; such particles are photons , neutrinos , and muons , as well as

11390-441: The first reported nuclear reaction , N + α → O + p . Rutherford at first thought of our modern "p" in this equation as a hydrogen ion, H . Depending on one's perspective, either 1919 (when it was seen experimentally as derived from another source than hydrogen) or 1920 (when it was recognized and proposed as an elementary particle) may be regarded as the moment when the proton was 'discovered'. Rutherford knew hydrogen to be

11524-458: The forces of its own magnetic field. As the name "Compact Muon Solenoid" suggests, detecting muons is one of CMS's most important tasks. Muons are charged particles that are just like electrons and positrons , but are 200 times more massive. We expect them to be produced in the decay of a number of potential new particles; for instance, one of the clearest "signatures" of the Higgs Boson

11658-418: The gluons, and transitory pairs of sea quarks . Protons have a positive charge distribution, which decays approximately exponentially, with a root mean square charge radius of about 0.8 fm. Protons and neutrons are both nucleons , which may be bound together by the nuclear force to form atomic nuclei . The nucleus of the most common isotope of the hydrogen atom (with the chemical symbol "H")

11792-538: The gravitational interaction, but it has not been detected or completely reconciled with current theories. Many other hypothetical particles have been proposed to address the limitations of the Standard Model. Notably, supersymmetric particles aim to solve the hierarchy problem , axions address the strong CP problem , and various other particles are proposed to explain the origins of dark matter and dark energy . The world's major particle physics laboratories are: Theoretical particle physics attempts to develop

11926-424: The hundreds of other species of particles that have been discovered since the 1960s. The Standard Model has been found to agree with almost all the experimental tests conducted to date. However, most particle physicists believe that it is an incomplete description of nature and that a more fundamental theory awaits discovery (See Theory of Everything ). In recent years, measurements of neutrino mass have provided

12060-433: The interactions between the quarks store energy which can convert to other particles when the quarks are far apart enough, quarks cannot be observed independently. This is called color confinement . There are three known generations of quarks (up and down, strange and charm , top and bottom ) and leptons (electron and its neutrino, muon and its neutrino , tau and its neutrino ), with strong indirect evidence that

12194-429: The later 1990s because τ p {\displaystyle \tau _{\mathrm {p} }} is a scalar that can be measured by the inertial and coaccelerated observers . In the inertial frame , the accelerating proton should decay according to the formula above. However, according to the coaccelerated observer the proton is at rest and hence should not decay. This puzzle is solved by realizing that in

12328-450: The lunar night, the spectrometer was shielded from the solar wind by the Moon and no solar wind particles were measured. Protons also have extrasolar origin from galactic cosmic rays , where they make up about 90% of the total particle flux. These protons often have higher energy than solar wind protons, and their intensity is far more uniform and less variable than protons coming from the Sun,

12462-462: The magnet coil whilst the muon detectors are interleaved with a 12-sided iron structure that surrounds the magnet coils and contains and guides the field. Made up of three layers this "return yoke" reaches out 14 metres in diameter and also acts as a filter, allowing through only muons and weakly interacting particles such as neutrinos. The enormous magnet also provides most of the experiment's structural support, and must be very strong itself to withstand

12596-402: The mass of a quark by itself, while constituent quark mass refers to the current quark mass plus the mass of the gluon particle field surrounding the quark. These masses typically have very different values. The kinetic energy of the quarks that is a consequence of confinement is a contribution (see Mass in special relativity ). Using lattice QCD calculations, the contributions to

12730-2129: The mass of the proton are the quark condensate (~9%, comprising the up and down quarks and a sea of virtual strange quarks), the quark kinetic energy (~32%), the gluon kinetic energy (~37%), and the anomalous gluonic contribution (~23%, comprising contributions from condensates of all quark flavors). The constituent quark model wavefunction for the proton is | p ↑ ⟩ = 1 18 ( 2 | u ↑ d ↓ u ↑ ⟩ + 2 | u ↑ u ↑ d ↓ ⟩ + 2 | d ↓ u ↑ u ↑ ⟩ − | u ↑ u ↓ d ↑ ⟩ − | u ↑ d ↑ u ↓ ⟩ − | u ↓ d ↑ u ↑ ⟩ − | d ↑ u ↓ u ↑ ⟩ − | d ↑ u ↑ u ↓ ⟩ − | u ↓ u ↑ d ↑ ⟩ ) . {\displaystyle \mathrm {|p_{\uparrow }\rangle ={\tfrac {1}{\sqrt {18}}}\left(2|u_{\uparrow }d_{\downarrow }u_{\uparrow }\rangle +2|u_{\uparrow }u_{\uparrow }d_{\downarrow }\rangle +2|d_{\downarrow }u_{\uparrow }u_{\uparrow }\rangle -|u_{\uparrow }u_{\downarrow }d_{\uparrow }\rangle -|u_{\uparrow }d_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }d_{\uparrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\downarrow }u_{\uparrow }\rangle -|d_{\uparrow }u_{\uparrow }u_{\downarrow }\rangle -|u_{\downarrow }u_{\uparrow }d_{\uparrow }\rangle \right)} .} The internal dynamics of protons are complicated, because they are determined by

12864-461: The masses of elementary particles. However, there are still many questions that future collider experiments hope to answer. These include uncertainties in the mathematical behaviour of the Standard Model at high energies, tests of proposed theories of dark matter (including supersymmetry ), and the reasons for the imbalance of matter and antimatter observed in the Universe. The main goals of

12998-497: The models, theoretical framework, and mathematical tools to understand current experiments and make predictions for future experiments (see also theoretical physics ). There are several major interrelated efforts being made in theoretical particle physics today. One important branch attempts to better understand the Standard Model and its tests. Theorists make quantitative predictions of observables at collider and astronomical experiments, which along with experimental measurements

13132-480: The modern theory of the nuclear force, most of the mass of protons and neutrons is explained by special relativity . The mass of a proton is about 80–100 times greater than the sum of the rest masses of its three valence quarks , while the gluons have zero rest mass. The extra energy of the quarks and gluons in a proton, as compared to the rest energy of the quarks alone in the QCD vacuum , accounts for almost 99% of

13266-412: The most powerful example being the Large Hadron Collider . Protons are spin- ⁠ 1 / 2 ⁠ fermions and are composed of three valence quarks, making them baryons (a sub-type of hadrons ). The two up quarks and one down quark of a proton are held together by the strong force , mediated by gluons . A modern perspective has a proton composed of the valence quarks (up, up, down),

13400-440: The movement of hydrated H ions. The ion produced by removing the electron from a deuterium atom is known as a deuteron , not a proton. Likewise, removing an electron from a tritium atom produces a triton . Also in chemistry, the term proton NMR refers to the observation of hydrogen-1 nuclei in (mostly organic ) molecules by nuclear magnetic resonance . This method uses the quantized spin magnetic moment of

13534-438: The neutral hydrogen atom. He initially suggested both proton and prouton (after Prout). Rutherford later reported that the meeting had accepted his suggestion that the hydrogen nucleus be named the "proton", following Prout's word "protyle". The first use of the word "proton" in the scientific literature appeared in 1920. One or more bound protons are present in the nucleus of every atom. Free protons are found naturally in

13668-403: The new small radius. Work continues to refine and check this new value. Since the proton is composed of quarks confined by gluons, an equivalent pressure that acts on the quarks can be defined. The size of that pressure and other details about it are controversial. In 2018 this pressure was reported to be on the order 10  Pa, which is greater than the pressure inside a neutron star . It

13802-416: The nucleon structure is still missing because ... long-distance behavior requires a nonperturbative and/or numerical treatment ..." More conceptual approaches to the structure of protons are: the topological soliton approach originally due to Tony Skyrme and the more accurate AdS/QCD approach that extends it to include a string theory of gluons, various QCD-inspired models like the bag model and

13936-598: The nucleus the proton , after the neuter singular of the Greek word for "first", πρῶτον . However, Rutherford also had in mind the word protyle as used by Prout. Rutherford spoke at the British Association for the Advancement of Science at its Cardiff meeting beginning 24 August 1920. At the meeting, he was asked by Oliver Lodge for a new name for the positive hydrogen nucleus to avoid confusion with

14070-681: The number of (negatively charged) electrons , which for neutral atoms is equal to the number of (positive) protons so that the total charge is zero. For example, a neutral chlorine atom has 17 protons and 17 electrons, whereas a Cl anion has 17 protons and 18 electrons for a total charge of −1. All atoms of a given element are not necessarily identical, however. The number of neutrons may vary to form different isotopes , and energy levels may differ, resulting in different nuclear isomers . For example, there are two stable isotopes of chlorine : 17 Cl with 35 − 17 = 18 neutrons and 17 Cl with 37 − 17 = 20 neutrons. The proton

14204-418: The number of atomic electrons and consequently the chemical characteristics of the element. The word proton is Greek for "first", and the name was given to the hydrogen nucleus by Ernest Rutherford in 1920. In previous years, Rutherford had discovered that the hydrogen nucleus (known to be the lightest nucleus) could be extracted from the nuclei of nitrogen by atomic collisions. Protons were therefore

14338-445: The particle's energy. These high-density crystals produce light in fast, short, well-defined photon bursts that allow for a precise, fast and fairly compact detector. It has a radiation length of χ 0  = 0.89 cm, and has a rapid light yield, with 80% of light yield within one crossing time (25 ns). This is balanced however by a relatively low light yield of 30 photons per MeV of incident energy. The crystals used have

14472-719: The particles in the solar wind are electrons and protons, in approximately equal numbers. Because the Solar Wind Spectrometer made continuous measurements, it was possible to measure how the Earth's magnetic field affects arriving solar wind particles. For about two-thirds of each orbit, the Moon is outside of the Earth's magnetic field. At these times, a typical proton density was 10 to 20 per cubic centimeter, with most protons having velocities between 400 and 650 kilometers per second. For about five days of each month,

14606-498: The paths of high-energy muons, electrons and hadrons (particles made up of quarks) as well as see tracks coming from the decay of very short-lived particles such as beauty or "b quarks" that will be used to study the differences between matter and antimatter. The tracker needs to record particle paths accurately yet be lightweight so as to disturb the particle as little as possible. It does this by taking position measurements so accurate that tracks can be reliably reconstructed using just

14740-483: The photon or gluon, have no antiparticles. Quarks and gluons additionally have color charges, which influences the strong interaction. Quark's color charges are called red, green and blue (though the particle itself have no physical color), and in antiquarks are called antired, antigreen and antiblue. The gluon can have eight color charges , which are the result of quarks' interactions to form composite particles (gauge symmetry SU(3) ). The neutrons and protons in

14874-675: The pressure profile shape by selection of the model. The radius of the hydrated proton appears in the Born equation for calculating the hydration enthalpy of hydronium . Although protons have affinity for oppositely charged electrons, this is a relatively low-energy interaction and so free protons must lose sufficient velocity (and kinetic energy ) in order to become closely associated and bound to electrons. High energy protons, in traversing ordinary matter, lose energy by collisions with atomic nuclei , and by ionization of atoms (removing electrons) until they are slowed sufficiently to be captured by

15008-426: The primary colors . More exotic hadrons can have other types, arrangement or number of quarks ( tetraquark , pentaquark ). An atom is made from protons, neutrons and electrons. By modifying the particles inside a normal atom, exotic atoms can be formed. A simple example would be the hydrogen-4.1 , which has one of its electrons replaced with a muon. The graviton is a hypothetical particle that can mediate

15142-662: The production of which is heavily affected by solar proton events such as coronal mass ejections . Research has been performed on the dose-rate effects of protons, as typically found in space travel , on human health. To be more specific, there are hopes to identify what specific chromosomes are damaged, and to define the damage, during cancer development from proton exposure. Another study looks into determining "the effects of exposure to proton irradiation on neurochemical and behavioral endpoints, including dopaminergic functioning, amphetamine -induced conditioned taste aversion learning, and spatial learning and memory as measured by

15276-400: The proton's mass. The rest mass of a proton is, thus, the invariant mass of the system of moving quarks and gluons that make up the particle, and, in such systems, even the energy of massless particles confined to a system is still measured as part of the rest mass of the system. Two terms are used in referring to the mass of the quarks that make up protons: current quark mass refers to

15410-479: The proton, which is due to its angular momentum (or spin ), which in turn has a magnitude of one-half the reduced Planck constant . ( ℏ / 2 {\displaystyle \hbar /2} ). The name refers to examination of protons as they occur in protium (hydrogen-1 atoms) in compounds, and does not imply that free protons exist in the compound being studied. The Apollo Lunar Surface Experiments Packages (ALSEP) determined that more than 95% of

15544-517: The quarks' exchanging gluons, and interacting with various vacuum condensates. Lattice QCD provides a way of calculating the mass of a proton directly from the theory to any accuracy, in principle. The most recent calculations claim that the mass is determined to better than 4% accuracy, even to 1% accuracy (see Figure S5 in Dürr et al. ). These claims are still controversial, because the calculations cannot yet be done with quarks as light as they are in

15678-444: The real world. This means that the predictions are found by a process of extrapolation , which can introduce systematic errors. It is hard to tell whether these errors are controlled properly, because the quantities that are compared to experiment are the masses of the hadrons , which are known in advance. These recent calculations are performed by massive supercomputers, and, as noted by Boffi and Pasquini: "a detailed description of

15812-581: The relative properties of particles and antiparticles and, therefore, is open to stringent tests. For example, the charges of a proton and antiproton must sum to exactly zero. This equality has been tested to one part in 10 . The equality of their masses has also been tested to better than one part in 10 . By holding antiprotons in a Penning trap , the equality of the charge-to-mass ratio of protons and antiprotons has been tested to one part in 6 × 10 . The magnetic moment of antiprotons has been measured with an error of 8 × 10 nuclear Bohr magnetons , and

15946-455: The relatively compact size of the detector, the fact that it detects muons, and the use of solenoids in the detector. "CMS" is also a reference to the center-of-mass system , an important concept in particle physics. Particle physics Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation . The field also studies combinations of elementary particles up to

16080-436: The remaining six layers of 25 cm × 180 μm strips, out to a radius of 1.1 m. There are 9.6 million strip channels in total. During full luminosity collisions the occupancy of the pixel layers per event is expected to be 0.1%, and 1–2% in the strip layers. The expected HL-LHC upgrade will increase the number of interactions to the point where over-occupancy would significantly reduce track-finding effectiveness. An upgrade

16214-444: The same, with a few gets reversed; the electron's antiparticle, positron, has an opposite charge. To differentiate between antiparticles and particles, a plus or negative sign is added in superscript . For example, the electron and the positron are denoted e and e . When a particle and an antiparticle interact with each other, they are annihilated and convert to other particles. Some particles, such as

16348-622: The scale of protons and neutrons , while the study of combination of protons and neutrons is called nuclear physics . The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) and bosons (force-carrying particles). There are three generations of fermions, although ordinary matter is made only from the first fermion generation. The first generation consists of up and down quarks which form protons and neutrons , and electrons and electron neutrinos . The three fundamental interactions known to be mediated by bosons are electromagnetism ,

16482-463: The signal (the electrons), which are instead picked up by external metallic strips after a small but precise time delay. The pattern of hit strips gives a quick measure of the muon momentum, which is then used by the trigger to make immediate decisions about whether the data are worth keeping. RPCs combine a good spatial resolution with a time resolution of just one nanosecond (one billionth of a second). Gas electron multiplier (GEM) detectors represent

16616-443: The simplest and lightest element and was influenced by Prout's hypothesis that hydrogen was the building block of all elements. Discovery that the hydrogen nucleus is present in other nuclei as an elementary particle led Rutherford to give the hydrogen nucleus H a special name as a particle, since he suspected that hydrogen, the lightest element, contained only one of these particles. He named this new fundamental building block of

16750-485: The surface of the Sun) and with any type of atom. Thus, in interaction with any type of normal (non-plasma) matter, low-velocity free protons do not remain free but are attracted to electrons in any atom or molecule with which they come into contact, causing the proton and molecule to combine. Such molecules are then said to be " protonated ", and chemically they are simply compounds of hydrogen, often positively charged. Often, as

16884-571: The tracker. Resistive plate chambers (RPC) are fast gaseous detectors that provide a muon trigger system parallel with those of the DTs and CSCs. RPCs consist of two parallel plates, a positively charged anode and a negatively charged cathode, both made of a very high resistivity plastic material and separated by a gas volume. When a muon passes through the chamber, electrons are knocked out of gas atoms. These electrons in turn hit other atoms causing an avalanche of electrons. The electrodes are transparent to

17018-411: The tube by the time taken) DTs give two coordinates for the muon's position. Each DT chamber, on average 2 m x 2.5 m in size, consists of 12 aluminium layers, arranged in three groups of four, each with up to 60 tubes: the middle group measures the coordinate along the direction parallel to the beam and the two outside groups measure the perpendicular coordinate. Cathode strip chambers (CSC) are used in

17152-420: The two LHC beams will contain 2,808 bunches of 1.15 × 10 protons. The interval between crossings is 25 ns, although the number of collisions per second is only 31.6 million due to gaps in the beam as injector magnets are activated and deactivated. At full luminosity each collision will produce an average of 20 proton-proton interactions. The collisions occur at a centre of mass energy of 8 TeV. But, it

17286-399: The volume it knocks electrons off the atoms of the gas. These follow the electric field ending up at the positively charged wire. By registering where along the wire electrons hit (in the diagram, the wires are going into the page) as well as by calculating the muon's original distance away from the wire (shown here as horizontal distance and calculated by multiplying the speed of an electron in

17420-630: Was composed of a single, unique type of particle. The word atom , after the Greek word atomos meaning "indivisible", has since then denoted the smallest particle of a chemical element , but physicists later discovered that atoms are not, in fact, the fundamental particles of nature, but are conglomerates of even smaller particles, such as the electron . The early 20th century explorations of nuclear physics and quantum physics led to proofs of nuclear fission in 1939 by Lise Meitner (based on experiments by Otto Hahn ), and nuclear fusion by Hans Bethe in that same year; both discoveries also led to

17554-529: Was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra (More details in Atomic number under Moseley's 1913 experiment). In 1917, Rutherford performed experiments (reported in 1919 and 1925) which proved that the hydrogen nucleus is present in other nuclei, a result usually described as the discovery of protons. These experiments began after Rutherford observed that when alpha particles would strike air, Rutherford could detect scintillation on

17688-481: Was determined to allow the maximum amount of absorbing material inside of the magnet coil. The high pseudorapidity region ( 3.0 < | η | < 5.0 ) {\displaystyle \scriptstyle (3.0\;<\;|\eta |\;<\;5.0)} is instrumented by the Hadronic Forward (HF) detector. Located 11 m either side of the interaction point, this uses

17822-436: Was said to be maximum at the centre, positive (repulsive) to a radial distance of about 0.6 fm, negative (attractive) at greater distances, and very weak beyond about 2 fm. These numbers were derived by a combination of a theoretical model and experimental Compton scattering of high-energy electrons. However, these results have been challenged as also being consistent with zero pressure and as effectively providing

17956-419: Was scaled down to 3.8 T instead of the full design strength in order to maximize longevity. The inductance of the magnet is 14  Η and the nominal current for 4  T is 19,500  A , giving a total stored energy of 2.66  GJ , equivalent to about half-a-tonne of TNT . There are dump circuits to safely dissipate this energy should the magnet quench . The circuit resistance (essentially just

#768231