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47-572: Its discovery was made independently by two research groups, one at the Stanford Linear Accelerator Center , headed by Burton Richter , and one at the Brookhaven National Laboratory , headed by Samuel Ting of MIT . They discovered that they had found the same particle, and both announced their discoveries on 11 November 1974. The importance of this discovery is highlighted by the fact that

94-700: A better representation of the new direction of the lab and the ability to trademark the laboratory's name. Stanford University had legally opposed the Department of Energy's attempt to trademark "Stanford Linear Accelerator Center". In March 2009, it was announced that the SLAC National Accelerator Laboratory was to receive $ 68.3 million in Recovery Act Funding to be disbursed by Department of Energy's Office of Science. In October 2016, Bits and Watts launched as

141-541: A branching ratio is used. In this case, the branching ratio is just the ratio of the branching fractions between two states. To use our example from before, if the branching fraction to state |g⟩ is ⁠ p {\displaystyle p} ⁠ , then the branching ratio comparing the transition rates to |g⟩ and |d⟩ would be ⁠ p 1 − p {\displaystyle {\frac {p}{1-p}}} ⁠ . Branching fractions can be measured in

188-447: A charm + anticharm meson would be like. The group at Brookhaven , were the first to discern a peak at 3.1 GeV in plots of production rates and named the particle the ψ  meson . Ting named it the "J meson" in his simultaneous discovery. Hadronic decay modes of J/ψ are strongly suppressed because of the OZI rule . This effect strongly increases the lifetime of

235-641: A collaboration between SLAC and Stanford University to design "better, greener electric grids". SLAC later pulled out over concerns about an industry partner, the state-owned Chinese electric utility. In April of 2024, SLAC completed two decades of work constructing the world's largest digital camera for the Legacy Survey of Space and Time (LSST) project at the Vera C. Rubin Observatory in Chile. The camera

282-521: A new superconducting accelerator at 4 GeV and two new sets of undulators that will increase the available energy range of LCLS. The advancement from the discoveries using this new capabilities may include new drugs, next-generation computers, and new materials. In 2012, the first two-thirds (~2 km) of the original SLAC LINAC were recommissioned for a new user facility, the Facility for Advanced Accelerator Experimental Tests (FACET). This facility

329-619: A particle and its antiparticle (an electron and positron in the case of positronium). Stanford Linear Accelerator Center SLAC National Accelerator Laboratory , originally named the Stanford Linear Accelerator Center , is a federally funded research and development center in Menlo Park , California , United States . Founded in 1962, the laboratory is now sponsored by the United States Department of Energy and administrated by Stanford University . It

376-524: A sixth smaller detector. About 300 researchers made used of PEP. PEP stopped operating in 1990, and PEP-II began construction in 1994. From 1999 to 2008, the main purpose of the linear accelerator was to inject electrons and positrons into the PEP-II accelerator, an electron-positron collider with a pair of storage rings 2.2 km (1.4 mi) in circumference. PEP-II was host to the BaBar experiment , one of

423-471: A strange quark into a down quark, which were not observed. A 1970 idea of Sheldon Glashow , John Iliopoulos , and Luciano Maiani , known as the GIM mechanism , showed that the flavor-changing decays would be strongly suppressed if there were a fourth quark (now called the charm quark ) that was a complementary counterpart to the strange quark . By summer 1974 this work had led to theoretical predictions of what

470-452: A variety of ways, including time-resolved recording of the atom's fluorescence during a series of population transfers in the relevant states. A sample measuring procedure for a three state Λ -system that includes ground state |g⟩ , excited state |e⟩ , and long-lived state |d⟩ , is as follows: First, prepare all atoms in the ground state. Pump laser, which drives transition between ground state and

517-474: Is a free electron laser facility located at SLAC. The LCLS is partially a reconstruction of the last 1/3 of the original linear accelerator at SLAC, and can deliver extremely intense x-ray radiation for research in a number of areas. It achieved first lasing in April 2009. The laser produces hard X-rays, 10 times the relative brightness of traditional synchrotron sources and is the most powerful x-ray source in

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564-530: Is buried 9 m (30 ft) below ground and passes underneath Interstate Highway 280 . The above-ground klystron gallery atop the beamline , was the longest building in the United States until the LIGO project's twin interferometers were completed in 1999. It is easily distinguishable from the air and is marked as a visual waypoint on aeronautical charts. A portion of the original linear accelerator

611-417: Is evaluated with respect to the baseline provided by the total production of all charm quark-containing subatomic particles, and because it is widely expected that some J/ψ are produced and/or destroyed at time of QGP hadronization . Thus, there is uncertainty in the prevailing conditions at the initial collisions. In fact, instead of suppression, enhanced production of J/ψ

658-448: Is expected in heavy ion experiments at LHC where the quark-combinant production mechanism should be dominant given the large abundance of charm quarks in the QGP. Aside of J/ψ , charmed B mesons ( B c ), offer a signature that indicates that quarks move freely and bind at-will when combining to form hadrons . Because of the nearly simultaneous discovery,

705-463: Is expected to become operational in 2025. The main accelerator was an RF linear accelerator that accelerated electrons and positrons up to 50 GeV . At 3.2 km (2.0 mi) long, the accelerator was the longest linear accelerator in the world, and was claimed to be "the world's most straight object." until 2017 when the European x-ray free electron laser opened. The main accelerator

752-485: Is given, but this term is misleading; due to competing modes, it is not true that half of the particles will decay through a particular decay mode after its partial half-life . The partial half-life is merely an alternate way to specify the partial decay constant λ , the two being related through: For example, for decays of Cs , 98.1% are ε ( electron capture ) or β ( positron ) decays, and 1.9% are β ( electron ) decays. The partial decay constants can be calculated from

799-508: Is now part of the Linac Coherent Light Source. The Stanford Linear Collider was a linear accelerator that collided electrons and positrons at SLAC. The center of mass energy was about 90 GeV , equal to the mass of the Z boson , which the accelerator was designed to study. Grad student Barrett D. Milliken discovered the first Z event on 12 April 1989 while poring over the previous day's computer data from

846-561: Is partially housed on the grounds of SLAC, in addition to its presence on the main Stanford campus. The Stanford PULSE Institute (PULSE) is a Stanford Independent Laboratory located in the Central Laboratory at SLAC. PULSE was created by Stanford in 2005 to help Stanford faculty and SLAC scientists develop ultrafast x-ray research at LCLS. PULSE research publications can be viewed here . The Linac Coherent Light Source (LCLS)

893-595: Is the site of the Stanford Linear Accelerator , a 3.2 kilometer (2-mile) linear accelerator constructed in 1966 that could accelerate electrons to energies of 50 GeV . Today SLAC research centers on a broad program in atomic and solid-state physics , chemistry , biology , and medicine using X-rays from synchrotron radiation and a free-electron laser as well as experimental and theoretical research in elementary particle physics , astroparticle physics , and cosmology . The laboratory

940-659: Is under the programmatic direction of the United States Department of Energy Office of Science. Founded in 1962 as the Stanford Linear Accelerator Center, the facility is located on 172 ha (426 acres) of Stanford University -owned land on Sand Hill Road in Menlo Park, California, just west of the university's main campus. The main accelerator is 3.2 km (2 mi) long, making it the longest linear accelerator in

987-471: The J/ψ; and its excitations are expected to melt. This is one of the predicted signals of the formation of the quark–gluon plasma . Heavy-ion experiments at CERN 's Super Proton Synchrotron and at BNL 's Relativistic Heavy Ion Collider have studied this phenomenon without a conclusive outcome as of 2009. This is due to the requirement that the disappearance of J/ψ mesons

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1034-503: The J/ψ is the only particle to have a two-letter name. Richter named it "SP", after the SPEAR accelerator used at SLAC ; however, none of his coworkers liked that name. After consulting with Greek-born Leo Resvanis to see which Greek letters were still available, and rejecting " iota " because its name implies insignificance, Richter chose "psi" – a name which, as Gerson Goldhaber pointed out, contains

1081-401: The |g⟩ state is ⁠ p {\displaystyle p} ⁠ , then the probability to decay into the other state |d⟩ would be ⁠ 1 − p {\displaystyle 1-p} ⁠ . Further possible decays would split appropriately, with their probabilities summing to 1. In some instances, instead of a branching fraction,

1128-611: The Mark II detector . The bulk of the data was collected by the SLAC Large Detector , which came online in 1991. Although largely overshadowed by the Large Electron–Positron Collider at CERN , which began running in 1989, the highly polarized electron beam at SLC (close to 80% ) made certain unique measurements possible, such as parity violation in Z Boson-b quark coupling. Presently no beam enters

1175-556: The Stanford Synchrotron Radiation Laboratory (SSRL) for synchrotron light radiation research, which was "indispensable" in the research leading to the 2006 Nobel Prize in Chemistry awarded to Stanford Professor Roger D. Kornberg . In October 2008, the Department of Energy announced that the center's name would be changed to SLAC National Accelerator Laboratory. The reasons given include

1222-409: The branching fraction (or branching ratio ) for a decay is the fraction of particles that decay by an individual decay mode or with respect to the total number of particles which decay. It applies to either the radioactive decay of atoms or the decay of elementary particles . It is equal to the ratio of the partial decay constant to the overall decay constant . Sometimes a partial half-life

1269-588: The "quarks", originally with three types or "flavors", called up , down , and strange . (Later the model was expanded to six quarks, adding the charm , top and bottom quarks.) Despite the ability of quark models to bring order to the "elementary particle zoo", they were considered something like mathematical fiction at the time, a simple artifact of deeper physical reasons. Starting in 1969, deep inelastic scattering experiments at SLAC revealed surprising experimental evidence for particles inside of protons. Whether these were quarks or something else

1316-531: The branching fraction and the half-life of Cs (6.479 d), they are: 0.10 d (ε + β ) and 0.0020 d (β ). The partial half-lives are 6.60 d (ε + β ) and 341 d (β ). Here the problem with the term partial half-life is evident: after (341+6.60) days almost all the nuclei will have decayed, not only half as one may initially think. Isotopes with significant branching of decay modes include copper-64 , arsenic-74 , rhodium-102 , indium-112 , iodine-126 and holmium-164 . In

1363-751: The continuation of beam-driven plasma acceleration studies in 2019. The Next Linear Collider Test Accelerator (NLCTA) is a 60-120 MeV high-brightness electron beam linear accelerator used for experiments on advanced beam manipulation and acceleration techniques. It is located at SLAC's end station B. A list of relevant research publications can be viewed here Archived 15 September 2015 at the Wayback Machine . SLAC also performs theoretical research in elementary particle physics, including in areas of quantum field theory , collider physics, astroparticle physics , and particle phenomenology. Branching fraction In particle physics and nuclear physics ,

1410-430: The excited state is then turned on, and a photomultiplier (PMT) is used to count the "blue photon" emitted during the transition. Record the counted blue photon as N . Every time an atom is driven to the excited state, it has probability ⁠ 1 − p {\displaystyle 1-p} ⁠ of decaying to long-lived state. Therefore, while the pump laser is on, more and more atom would end up in

1457-429: The field of atomic, molecular, and optical physics , a branching fraction refers to the probability of decay to a specific lower-lying energy states from some excited state. Suppose we drive a transition in an atomic system to an excited state |e⟩ , which can decay into either the ground state |g⟩ or a long-lived state |d⟩ . If the probability to decay (the branching fraction) into

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1504-573: The first World Wide Web server outside of Europe. In the early-to-mid 1990s, the Stanford Linear Collider (SLC) investigated the properties of the Z boson using the Stanford Large Detector. As of 2005, SLAC employed over 1,000 people, some 150 of whom were physicists with doctorate degrees , and served over 3,000 visiting researchers yearly, operating particle accelerators for high-energy physics and

1551-431: The laser is capable of capturing images with a "shutter speed" measured in femtoseconds, or million-billionths of a second, necessary because the intensity of the beam is often high enough so that the sample explodes on the femtosecond timescale. The LCLS-II project is to provide a major upgrade to LCLS by adding two new X-ray laser beams. The new system will utilize the 500 m (1,600 ft) of existing tunnel to add

1598-433: The long-lived state, where they cannot be addressed by the cooling laser. After all the atoms are in the |d⟩ state, apply repump laser, which drives the transition between |d⟩ and |e⟩ . During this process each atom emits one blue photon. Denote number of emitted blue photon during this process as n . Then the branching fraction for |e⟩ decaying to |g⟩

1645-479: The original name "SP", but in reverse order. Coincidentally, later spark chamber pictures often resembled the psi shape. Ting assigned the name "J" to it, saying that the more stable particles, such as the W and Z bosons had Roman names, as opposed to classical particles, which had Greek names. He also cited the symbol for electromagnetic current j μ ( x ) {\displaystyle j_{\mu }(x)} which much of their previous work

1692-469: The particle and thereby gives it its very narrow decay width of just 93.2 ± 2.1 keV . Because of this strong suppression, electromagnetic decays begin to compete with hadronic decays. This is why the J/ψ has a significant branching fraction to leptons. The primary decay modes are: In a hot QCD medium , when the temperature is raised well beyond the Hagedorn temperature ,

1739-546: The so-called B-Factory experiments studying charge-parity symmetry . The Stanford Synchrotron Radiation Lightsource (SSRL) is a synchrotron light user facility located on the SLAC campus. Originally built for particle physics, it was used in experiments where the J/ψ meson was discovered. It is now used exclusively for materials science and biology experiments which take advantage of the high-intensity synchrotron radiation emitted by

1786-753: The south and north arcs in the machine, which leads to the Final Focus, therefore this section is mothballed to run beam into the PEP2 section from the beam switchyard. The SLAC Large Detector (SLD) was the main detector for the Stanford Linear Collider. It was designed primarily to detect Z bosons produced by the accelerator's electron-positron collisions. Built in 1991, the SLD operated from 1992 to 1998. PEP (Positron-Electron Project) began operation in 1980, with center-of-mass energies up to 29 GeV. At its apex, PEP had five large particle detectors in operation, as well as

1833-605: The stored electron beam to study the structure of molecules. In the early 1990s, an independent electron injector was built for this storage ring, allowing it to operate independently of the main linear accelerator. SLAC plays a primary role in the mission and operation of the Fermi Gamma-ray Space Telescope, launched in August 2008. The principal scientific objectives of this mission are: The Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)

1880-577: The subsequent, rapid changes in high-energy physics at the time have become collectively known as the " November Revolution ". Richter and Ting were awarded the 1976 Nobel Prize in Physics . The background to the discovery of the J/ψ was both theoretical and experimental. In the 1960s, the first quark models of elementary particle physics were proposed, which said that protons , neutrons , and all other baryons , and also all mesons , are made from fractionally charged particles,

1927-578: The world, and has been operational since 1966. Research at SLAC has produced three Nobel Prizes in Physics : SLAC's meeting facilities also provided a venue for the Homebrew Computer Club and other pioneers of the home computer revolution of the late 1970s and early 1980s. In 1984, the laboratory was named an ASME National Historic Engineering Landmark and an IEEE Milestone . SLAC developed and, in December 1991, began hosting

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1974-437: The world. LCLS enables a variety of new experiments and provides enhancements for existing experimental methods. Often, x-rays are used to take "snapshots" of objects at the atomic level before obliterating samples. The laser's wavelength, ranging from 6.2 to 0.13 nm (200 to 9500 electron volts (eV)) is similar to the width of an atom, providing extremely detailed information that was previously unattainable. Additionally,

2021-482: Was called the ψ″; it is now called ψ(3770), indicating mass in MeV/ c . Other vector charm–anticharm states are denoted similarly with ψ and the quantum state (if known) or the mass. The "J" is not used, since Richter's group alone first found excited states. The name charmonium is used for the J/ψ and other charm–anticharm bound states. This is by analogy with positronium , which also consists of

2068-518: Was capable of delivering 20 GeV, 3 nC electron (and positron) beams with short bunch lengths and small spot sizes, ideal for beam-driven plasma acceleration studies. The facility ended operations in 2016 for the constructions of LCLS-II which will occupy the first third of the SLAC LINAC. The FACET-II project will re-establish electron and positron beams in the middle third of the LINAC for

2115-403: Was concentrated on to be one of the reasons. Much of the scientific community considered it unjust to give one of the two discoverers priority, so most subsequent publications have referred to the particle as the " J/ψ ". The first excited state of the J/ψ was called the ψ′; it is now called the ψ(2S), indicating its quantum state. The next excited state

2162-527: Was not known at first. Many experiments were needed to fully identify the properties of the sub-protonic components. To a first approximation, they indeed were a match for the previously described quarks. On the theoretical front, gauge theories with broken symmetry became the first fully viable contenders for explaining the weak interaction after Gerardus 't Hooft discovered in 1971 how to calculate with them beyond tree level . The first experimental evidence for these electroweak unification theories

2209-425: Was the discovery of the weak neutral current in 1973. Gauge theories with quarks became a viable contender for the strong interaction in 1973, when the concept of asymptotic freedom was identified. However, a naive mixture of electroweak theory and the quark model led to calculations about known decay modes that contradicted observation: In particular, it predicted Z boson -mediated flavor-changing decays of

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