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55-455: The construction of the NA48 experimental setup took place early 1990s. The primary physics goal – the search for direct CP violation – was inherited from the predecessor NA31 experiment . The physics data taking runs took place between 1997 and 2001. The discovery of the phenomenon of direct CP violation, one of the most important experimental results obtained at CERN, was announced by

110-478: A K can transform into a K and vice versa. To study the asymmetries between K and K decay rates in the various final states f (f = π π , π π , π π π , π π π , π l ν), the CPLEAR collaboration used the fact that the strangeness of kaons is tagged by the charge of the accompanying kaon. Time-reversal invariance would imply that all details of one of

165-2117: A → 2 → b {\displaystyle a\rightarrow 2\rightarrow b} . This is exactly the case for the kaon where the decay is performed via different quark channels (see the Figure above). In this case we have: M = | M 1 |   e i θ 1   e i ϕ 1 + | M 2 |   e i θ 2   e i ϕ 2 M ¯ = | M 1 |   e i θ 1   e − i ϕ 1 + | M 2 |   e i θ 2   e − i ϕ 2   . {\displaystyle {\begin{alignedat}{3}{\cal {M}}&=|{\cal {M}}_{1}|\ e^{i\theta _{1}}\ e^{i\phi _{1}}&&+|{\cal {M}}_{2}|\ e^{i\theta _{2}}\ e^{i\phi _{2}}\\{\bar {\cal {M}}}&=|{\cal {M}}_{1}|\ e^{i\theta _{1}}\ e^{-i\phi _{1}}&&+|{\cal {M}}_{2}|\ e^{i\theta _{2}}\ e^{-i\phi _{2}}\ .\end{alignedat}}} Some further calculation gives: | M | 2 − | M ¯ | 2 = − 4   | M 1 |   | M 2 |   sin ⁡ ( θ 1 − θ 2 )   sin ⁡ ( ϕ 1 − ϕ 2 ) . {\displaystyle |{\cal {M}}|^{2}-|{\bar {\cal {M}}}|^{2}=-4\ |{\cal {M}}_{1}|\ |{\cal {M}}_{2}|\ \sin(\theta _{1}-\theta _{2})\ \sin(\phi _{1}-\phi _{2}).} Thus, we see that

220-477: A K 1 , and the CP for the particles flipped from −1 to +1, and CP wasn't conserved. The experiment resulted in an excess of 45±9 events around cos(θ) = 1 in the correct mass range for 2-pion decays. This means that for every decay of K 2 into three pions, there are (2.0±0.4)×10-3 decays into two pions. Because of this, neutral K mesons violate CP. The study of the ratio of neutral kaon and neutral anti-kaons production

275-554: A complex phase causes CP violation (CPV) is not immediately obvious, but can be seen as follows. Consider any given particles (or sets of particles)   a   {\displaystyle \ a\ } and   b   , {\displaystyle \ b\ ,} and their antiparticles   a ¯   {\displaystyle \ {\bar {a}}\ } and   b ¯   . {\displaystyle \ {\bar {b}}\ .} Now consider

330-603: A complex phase gives rise to processes that proceed at different rates for particles and antiparticles, and CP is violated. From the theoretical end, the CKM matrix is defined as   V C K M = U u † U d {\displaystyle \ V_{\mathrm {CKM} }=U_{u}^{\dagger }U_{d}} , where U u {\displaystyle U_{u}} and U d {\displaystyle U_{d}} are unitary transformation matrices which diagonalize

385-488: A letter to Chen-Ning Yang and shortly after, Boris L. Ioffe , Lev Okun and A. P. Rudik showed that the parity violation meant that charge conjugation invariance must also be violated in weak decays. Charge violation was confirmed in the Wu experiment and in experiments performed by Valentine Telegdi and Jerome Friedman and Garwin and Lederman who observed parity non-conservation in pion and muon decay and found that C

440-506: A logical possibility that all CP violation was confined to kaon physics. However, this raised the question of why CP violation did not extend to the strong force, and furthermore, why this was not predicted by the unextended Standard Model , despite the model's accuracy for "normal" phenomena. In 2011, a hint of CP violation in decays of neutral D mesons was reported by the LHCb experiment at CERN using 0.6 fb of Run 1 data. However,

495-465: A pressurized hydrogen gas target. A hydrogen gas target was used instead of liquid hydrogen to minimize the amount of matter in the decay volume. The target initially had a radius of 7 cm and subjected to a pressure of 16 bar. Changed in 1994, its radius became equal to 1.1 cm, under a 27 bar pressure. The detector had to fulfill the specific requirements of the experiment and thus had to be able to: Cylindrical tracking detectors together with

550-407: A solenoid field were used to determine the charge signs, momenta and positions of the charged particles. They were followed by the particle identification detector (PID) whose role was to identify the charged kaon. It was compounded by a Cherenkov detector , which carried out the kaon-pion separation; and scintillator s , measuring the energy loss and the time of flight of the charged particles. It

605-517: Is   0.0003   {\displaystyle \ 0.0003\ } times the maximum value of   J max = 1 6 3   ≈   0.1   . {\displaystyle \ J_{\max }={\tfrac {1}{6{\sqrt {3}}}}\ \approx \ 0.1\ .} For leptons, only an upper limit exists:   | J | < 0.03   . {\displaystyle \ |J|<0.03\ .} The reason why such

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660-403: Is baryogenesis , the hypothetical physical process that took place during the early universe that produced baryonic asymmetry, i.e. the imbalance of matter (baryons) and antimatter (antibaryons) in the observed universe. However, baryogenesis is only possible under the following conditions proposed by Andrei Sakharov in 1967: The first experimental test of CP violation came in 1964 with

715-534: Is a stub . You can help Misplaced Pages by expanding it . CP violation In particle physics , CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry ): the combination of C-symmetry ( charge conjugation symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics should be the same if a particle is interchanged with its antiparticle (C-symmetry) while its spatial coordinates are inverted ("mirror" or P-symmetry). The discovery of CP violation in 1964 in

770-541: Is also violated. Charge violation was more explicitly shown in experiments done by John Riley Holt at the University of Liverpool . Oehme then wrote a paper with Lee and Yang in which they discussed the interplay of non-invariance under P, C and T. The same result was also independently obtained by Ioffe, Okun and Rudik. Both groups also discussed possible CP violations in neutral kaon decays. Lev Landau proposed in 1957 CP-symmetry , often called just CP as

825-458: Is different. However, consider that there are two different routes : a ⟶ 1 b {\displaystyle a{\overset {1}{\longrightarrow }}b} and a ⟶ 2 b {\displaystyle a{\overset {2}{\longrightarrow }}b} or equivalently, two unrelated intermediate states: a → 1 → b {\displaystyle a\rightarrow 1\rightarrow b} and

880-426: Is slightly violated during certain types of weak decay . Only a weaker version of the symmetry could be preserved by physical phenomena, which was CPT symmetry . Besides C and P, there is a third operation, time reversal T , which corresponds to reversal of motion. Invariance under time reversal implies that whenever a motion is allowed by the laws of physics, the reversed motion is also an allowed one and occurs at

935-466: Is so close to a symmetry, introduced a great puzzle. The kind of CP violation (CPV) discovered in 1964 was linked to the fact that neutral kaons can transform into their antiparticles (in which each quark is replaced with the other's antiquark) and vice versa, but such transformation does not occur with exactly the same probability in both directions; this is called indirect CP violation. Despite many searches, no other manifestation of CP violation

990-531: Is the Jarlskog invariant :   J = c 12   c 13 2   c 23   s 12   s 13   s 23   sin ⁡ δ   ≈   0.00003   , {\displaystyle \ J=c_{12}\ c_{13}^{2}\ c_{23}\ s_{12}\ s_{13}\ s_{23}\ \sin \delta \ \approx \ 0.00003\ ,} for quarks, which

1045-543: Is thus an efficient tool to understand what happened in the early Universe that promoted the production of matter. CPLEAR is a collaboration of about 100 scientists, coming from 17 institutions from 9 different countries. Accepted in 1985, the experiment took data from 1990 until 1996. Its main aim was to study CP , T and CPT symmetries in the neutral kaon system. In addition, CPLEAR performed measurements about quantum coherence of wave function s , Bose-Einstein correlations in multi- pion states, regeneration of

1100-474: The ν μ beams. Analysis of these observations was not yet precise enough to determine the size of the CP violation, relative to that seen in quarks. In addition, another similar experiment, NOvA sees no evidence of CP violation in neutrino oscillations and is in slight tension with T2K. "Direct" CP violation is allowed in the Standard Model if a complex phase appears in

1155-764: The BaBar experiment at the Stanford Linear Accelerator Center ( SLAC ) and the Belle Experiment at the High Energy Accelerator Research Organisation ( KEK ) in Japan, observed direct CP violation in a different system, namely in decays of the B mesons . A large number of CP violation processes in B meson decays have now been discovered. Before these " B-factory " experiments, there was

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1210-676: The Cabibbo–Kobayashi–Maskawa matrix (CKM matrix) describing quark mixing, or the Pontecorvo–Maki–Nakagawa–Sakata matrix (PMNS matrix) describing neutrino mixing. A necessary condition for the appearance of the complex phase is the presence of at least three generations of fermions. If fewer generations are present, the complex phase parameter can be absorbed into redefinitions of the fermion fields. A popular rephasing invariant whose vanishing signals absence of CP violation and occurs in most CP violating amplitudes

1265-594: The Fitch-Cronin experiment . The experiment involved particles called neutral K-mesons , which fortuitously have the properties needed to test CP. First, as mesons, they're a combination of a quark and an anti-quark, in this case, down and antistrange , or anti-down and strange . Second, the two different particles have different CP values and different decay modes: K 1 has CP = +1 and decays into two pions ; K 2 has CP = −1 and decays into three. Because decays with larger changes in mass occur more readily,

1320-550: The Universe . If this was true, particle s and antiparticle s would have annihilated each other, creating photon s , and thus the Universe would have been only compounded by light (one particle of matter for 10 photons). However, only matter has remained and at a rate of one billion times more particles than expected. What happened then, for the antimatter to disappear in favor of matter? A possible answer to this question

1375-512: The antiproton beam of the LEAR facility – Low- Energy Antiproton Ring which operated at CERN from 1982 to 1996 – to produce neutral kaon s through proton - antiproton annihilation in order to study CP , T and CPT violation in the neutral kaon system. According to the theory of the Big Bang , matter and antimatter would have existed in the same amount at the beginning of

1430-505: The same complex number. We can separate the magnitude and phase by writing M = | M |   e i θ {\displaystyle {\cal {M}}=|{\cal {M}}|\ e^{i\theta }} . If a phase term is introduced from (e.g.) the CKM matrix, denote it e i ϕ {\displaystyle e^{i\phi }} . Note that M ¯ {\displaystyle {\bar {\cal {M}}}} contains

1485-511: The time reversal symmetry violation without any assumption of CPT theorem was done in 1998 by two groups, CPLEAR and KTeV collaborations, at CERN and Fermilab , respectively. Already in 1970 Klaus Schubert observed T violation independent of assuming CPT symmetry by using the Bell–Steinberger unitarity relation. The idea behind parity symmetry was that the equations of particle physics are invariant under mirror inversion. This led to

1540-409: The 1980 Nobel Prize. This discovery showed that weak interactions violate not only the charge-conjugation symmetry C between particles and antiparticles and the P or parity symmetry, but also their combination. The discovery shocked particle physics and opened the door to questions still at the core of particle physics and of cosmology today. The lack of an exact CP-symmetry, but also the fact that it

1595-411: The K 1 decay happens 100 times faster than the K 2 decay. This means that a sufficiently long beam of neutral Kaons will become arbitrarily pure K 2 after a sufficient amount of time. The Fitch-Cronin experiment exploits this. If all the K 1 s are allowed to decay out of a beam of mixed Kaons, only K 2 decays should be observed. If any K 1 decays are found, it means that a K 2 flipped to

1650-399: The collaboration in 1999. The publication of the final result was made in 2001. In addition the experiment made a contribution to studies of rare decays of neutral kaons . The following stage of the experiment (NA48/1) was carried out in 2002 and was devoted to high precision study of rare decays of neutral kaons and hyperons . The next stage (NA48/2) was carried out in 2003–2004 and

1705-962: The conjugate matrix to M {\displaystyle {\cal {M}}} , so it picks up a phase term e − i ϕ {\displaystyle e^{-i\phi }} . Now the formula becomes: M = | M |   e i θ   e + i ϕ M ¯ = | M |   e i θ   e − i ϕ {\displaystyle {\begin{aligned}{\cal {M}}&=|{\cal {M}}|\ e^{i\theta }\ e^{+i\phi }\\{\bar {\cal {M}}}&=|{\cal {M}}|\ e^{i\theta }\ e^{-i\phi }\end{aligned}}} Physically measurable reaction rates are proportional to   | M | 2 {\displaystyle \ |{\cal {M}}|^{2}} , thus so far nothing

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1760-517: The decays of neutral kaons resulted in the Nobel Prize in Physics in 1980 for its discoverers James Cronin and Val Fitch . It plays an important role both in the attempts of cosmology to explain the dominance of matter over antimatter in the present universe , and in the study of weak interactions in particle physics. Until the 1950s, parity conservation was believed to be one of

1815-472: The eigenvalues are given by m 1 2 = A − B x y − C x 2 + y 2 + x 2 y 2 x y , {\displaystyle \mathbf {m_{1}} ^{2}=\mathbf {A} -\mathbf {B} {x \over y}-\mathbf {C} {{\sqrt {x^{2}+y^{2}+x^{2}y^{2}}} \over xy},} CPLEAR experiment The CPLEAR experiment used

1870-1156: The fermion mass matrices M u {\displaystyle M_{u}} and M d {\displaystyle M_{d}} , respectively. Thus, there are two necessary conditions for getting a complex CKM matrix: For a standard model with three fermion generations, the most general non-Hermitian pattern of its mass matrices can be given by M = [ A 1 + i D 1 B 1 + i C 1 B 2 + i C 2 B 4 + i C 4 A 2 + i D 2 B 3 + i C 3 B 5 + i C 5 B 6 + i C 6 A 3 + i D 3 ] . {\displaystyle M={\begin{bmatrix}A_{1}+iD_{1}&B_{1}+iC_{1}&B_{2}+iC_{2}\\B_{4}+iC_{4}&A_{2}+iD_{2}&B_{3}+iC_{3}\\B_{5}+iC_{5}&B_{6}+iC_{6}&A_{3}+iD_{3}\end{bmatrix}}.} This M matrix contains 9 elements and 18 parameters, 9 from

1925-443: The first time. In this experiment, beams of muon neutrinos ( ν μ ) and muon antineutrinos ( ν μ ) were alternately produced by an accelerator . By the time they got to the detector, a significantly higher proportion of electron neutrinos ( ν e ) was observed from the ν μ beams, than electron antineutrinos ( ν e ) were from

1980-418: The fundamental geometric conservation laws (along with conservation of energy and conservation of momentum ). After the discovery of parity violation in 1956, CP-symmetry was proposed to restore order. However, while the strong interaction and electromagnetic interaction are experimentally found to be invariant under the combined CP transformation operation, further experiments showed that this symmetry

2035-798: The most general ones. The perfect way to solve the CPV problem in the standard model is to diagonalize such matrices analytically and to achieve a U matrix which applies to both. Unfortunately, even though the M 2 {\displaystyle \mathbf {M^{2}} } matrix has only 9 parameters, it is still too complicated to be diagonalized directly. Thus, an assumption M 2 R ⋅ M 2 † I + M 2 I ⋅ M 2 † R = 0 {\displaystyle \mathbf {M^{2}} _{R}\cdot \mathbf {M^{2\dagger }} _{I}+\mathbf {M^{2}} _{I}\cdot \mathbf {M^{2\dagger }} _{R}=0}

2090-2018: The parameter number from 9 to 5 and the reduced M 2 {\displaystyle \mathbf {M^{2}} } matrix can be given by M 2 = [ A + B ( x y − x y ) y B x B y B A + B ( y x − x y ) B x B B A ] + i [ 0 C y − C x − C y 0 C C x − C 0 ] ≡ M 2 R + i M 2 I , {\displaystyle \mathbf {M^{2}} ={\begin{bmatrix}\mathbf {A} +\mathbf {B} (xy-{x \over y})&y\mathbf {B} &x\mathbf {B} \\y\mathbf {B} &\mathbf {A} +\mathbf {B} ({y \over x}-{x \over y})&\mathbf {B} \\x\mathbf {B} &\mathbf {B} &\mathbf {A} \end{bmatrix}}+i{\begin{bmatrix}0&{\mathbf {C} \over y}&-{\mathbf {C} \over x}\\-{\mathbf {C} \over y}&0&\mathbf {C} \\{\mathbf {C} \over x}&-\mathbf {C} &0\end{bmatrix}}\equiv \mathbf {M^{2}} _{R}+i\mathbf {M^{2}} _{I},} where A ≡ A 3 , B ≡ B 3 , C ≡ C 3 , x ≡ B 2 / B 3 , {\displaystyle \mathbf {A} \equiv \mathbf {A_{3}} ,\mathbf {B} \equiv \mathbf {B_{3}} ,\mathbf {C} \equiv \mathbf {C_{3}} ,x\equiv \mathbf {B_{2}/B_{3}} ,} and y ≡ B 1 / B 3 {\displaystyle y\equiv \mathbf {B_{1}/B_{3}} } . Diagonalizing M 2 {\displaystyle \mathbf {M^{2}} } analytically,

2145-413: The prediction that the mirror image of a reaction (such as a chemical reaction or radioactive decay ) occurs at the same rate as the original reaction. However, in 1956 a careful critical review of the existing experimental data by theoretical physicists Tsung-Dao Lee and Chen-Ning Yang revealed that while parity conservation had been verified in decays by the strong or electromagnetic interactions, it

2200-573: The processes   a → b   {\displaystyle \ a\rightarrow b\ } and the corresponding antiparticle process   a ¯ → b ¯   , {\displaystyle \ {\bar {a}}\rightarrow {\bar {b}}\ ,} and denote their amplitudes M {\displaystyle {\cal {M}}} and M ¯ {\displaystyle {\bar {\cal {M}}}} respectively. Before CP violation, these terms must be

2255-1248: The real coefficients and 9 from the imaginary coefficients. Obviously, a 3x3 matrix with 18 parameters is too difficult to diagonalize analytically. However, a naturally Hermitian M 2 = M ⋅ M † {\displaystyle \mathbf {M^{2}} =M\cdot M^{\dagger }} can be given by M 2 = [ A 1 B 1 + i C 1 B 2 + i C 2 B 1 − i C 1 A 2 B 3 + i C 3 B 2 − i C 2 B 3 − i C 3 A 3 ] , {\displaystyle \mathbf {M^{2}} ={\begin{bmatrix}\mathbf {A_{1}} &\mathbf {B_{1}} +i\mathbf {C_{1}} &\mathbf {B_{2}} +i\mathbf {C_{2}} \\\mathbf {B_{1}} -i\mathbf {C_{1}} &\mathbf {A_{2}} &\mathbf {B_{3}} +i\mathbf {C_{3}} \\\mathbf {B_{2}} -i\mathbf {C_{2}} &\mathbf {B_{3}} -i\mathbf {C_{3}} &\mathbf {A_{3}} \end{bmatrix}},} and it has

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2310-430: The same effect as diagonalizing an M {\displaystyle M} matrix with 18 parameters. Therefore, diagonalizing the M 2 {\displaystyle \mathbf {M^{2}} } matrix is certainly the most reasonable choice. The M {\displaystyle M} and M 2 {\displaystyle \mathbf {M^{2}} } matrix patterns given above are

2365-530: The same measurement using the full 3.0 fb Run 1 sample was consistent with CP-symmetry. In 2013 LHCb announced discovery of CP violation in strange B meson decays. In March 2019, LHCb announced discovery of CP violation in charmed D 0 {\displaystyle D^{0}} decays with a deviation from zero of 5.3 standard deviations. In 2020, the T2K Collaboration reported some indications of CP violation in leptons for

2420-595: The same rate forwards and backwards. The combination of CPT is thought to constitute an exact symmetry of all types of fundamental interactions. Because of the long-held CPT symmetry theorem, provided that it is valid, a violation of the CP-symmetry is equivalent to a violation of the T-symmetry. In this theorem, regarded as one of the basic principles of quantum field theory , charge conjugation, parity, and time reversal are applied together. Direct observation of

2475-3739: The same unitary transformation matrix U with M. Besides, parameters in M 2 {\displaystyle \mathbf {M^{2}} } are correlated to those in M directly in the ways shown below A 1 = A 1 2 + D 1 2 + B 1 2 + C 1 2 + B 2 2 + C 2 2 , A 2 = A 2 2 + D 2 2 + B 3 2 + C 3 2 + B 4 2 + C 4 2 , A 3 = A 3 2 + D 3 2 + B 5 2 + C 5 2 + B 6 2 + C 6 2 , B 1 = A 1 B 4 + D 1 C 4 + B 1 A 2 + C 1 D 2 + B 2 B 3 + C 2 C 3 , B 2 = A 1 B 5 + D 1 C 5 + B 1 B 6 + C 1 C 6 + B 2 A 3 + C 2 D 3 , B 3 = B 4 B 5 + C 4 C 5 + B 6 A 2 + C 6 D 2 + A 3 B 3 + D 3 C 3 , C 1 = D 1 B 4 − A 1 C 4 + A 2 C 1 − B 1 D 2 + B 3 C 2 − B 2 C 3 , C 2 = D 1 B 5 − A 1 C 5 + B 6 C 1 − B 1 C 6 + A 3 C 2 − B 2 D 3 , C 3 = C 4 B 5 − B 4 C 5 + D 2 B 6 − A 2 C 6 + A 3 C 3 − B 3 D 3 . {\displaystyle {\begin{aligned}\mathbf {A_{1}} &=A_{1}^{2}+D_{1}^{2}+B_{1}^{2}+C_{1}^{2}+B_{2}^{2}+C_{2}^{2},\\\mathbf {A_{2}} &=A_{2}^{2}+D_{2}^{2}+B_{3}^{2}+C_{3}^{2}+B_{4}^{2}+C_{4}^{2},\\\mathbf {A_{3}} &=A_{3}^{2}+D_{3}^{2}+B_{5}^{2}+C_{5}^{2}+B_{6}^{2}+C_{6}^{2},\\\mathbf {B_{1}} &=A_{1}B_{4}+D_{1}C_{4}+B_{1}A_{2}+C_{1}D_{2}+B_{2}B_{3}+C_{2}C_{3},\\\mathbf {B_{2}} &=A_{1}B_{5}+D_{1}C_{5}+B_{1}B_{6}+C_{1}C_{6}+B_{2}A_{3}+C_{2}D_{3},\\\mathbf {B_{3}} &=B_{4}B_{5}+C_{4}C_{5}+B_{6}A_{2}+C_{6}D_{2}+A_{3}B_{3}+D_{3}C_{3},\\\mathbf {C_{1}} &=D_{1}B_{4}-A_{1}C_{4}+A_{2}C_{1}-B_{1}D_{2}+B_{3}C_{2}-B_{2}C_{3},\\\mathbf {C_{2}} &=D_{1}B_{5}-A_{1}C_{5}+B_{6}C_{1}-B_{1}C_{6}+A_{3}C_{2}-B_{2}D_{3},\\\mathbf {C_{3}} &=C_{4}B_{5}-B_{4}C_{5}+D_{2}B_{6}-A_{2}C_{6}+A_{3}C_{3}-B_{3}D_{3}.\end{aligned}}} That means if we diagonalize an M 2 {\displaystyle \mathbf {M^{2}} } matrix with 9 parameters, it has

2530-548: The short-lived kaon component in the matter, the Einstein-Rosen-Podolsky paradox using entangled neutral-kaon pair states and the equivalence principle of general relativity . The CPLEAR detector was able to determine the locations, the momenta and the charges of the tracks at the production of the neutral kaon and at its decay, thus visualizing the complete event. Strangeness is not conserved under weak interactions, meaning that under weak interactions

2585-410: The size of the stopping region small in the detector . Since the proton-antiproton reaction happens at rest, the particles are produced isotropically , and as a consequence, the detector has to have a near-4π symmetry. The whole detector was embedded in a 3.6 m long and 2 m diameter warm solenoidal magnet providing a 0.44 T uniform magnetic field . The antiprotons were stopped using

2640-467: The symmetry of a quantum mechanical system can be restored if another approximate symmetry S can be found such that the combined symmetry PS remains unbroken. This rather subtle point about the structure of Hilbert space was realized shortly after the discovery of P violation, and it was proposed that charge conjugation, C , which transforms a particle into its antiparticle , was the suitable symmetry to restore order. In 1956 Reinhard Oehme in

2695-427: The transformations could be deducible from the other one, i.e. the probability for a kaon to oscillate into an anti-kaon would be equal to the one for the reverse process. The measurement of these probabilities required the knowledge of the strangeness of a kaon at two different times of its life. Since the strangeness of the kaon is given by the charge of the accompanying kaon, and thus be known for each event , it

2750-680: The true symmetry between matter and antimatter. CP-symmetry is the product of two transformations : C for charge conjugation and P for parity. In other words, a process in which all particles are exchanged with their antiparticles was assumed to be equivalent to the mirror image of the original process and so the combined CP-symmetry would be conserved in the weak interaction. In 1962, a group of experimentalists at Dubna , on Okun's insistence, unsuccessfully searched for CP-violating kaon decay. In 1964, James Cronin , Val Fitch and coworkers provided clear evidence from kaon decay that CP-symmetry could be broken. (cf. also Ref. ). This work won them

2805-475: Was dedicated to a large programme of studies of properties of charged kaons, including the search of direct CP violation, studies of rare decays of the charged kaon, and low-energy QCD using final state rescattering . The successor of NA48 is the NA62 experiment , which started data collection in 2015 and is dedicated to further studies of rare decays of the charged kaon. This particle physics –related article

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2860-553: Was discovered until the 1990s, when the NA31 experiment at CERN suggested evidence for CP violation in the decay process of the very same neutral kaons ( direct CP violation). The observation was somewhat controversial, and final proof for it came in 1999 from the KTeV experiment at Fermilab and the NA48 experiment at CERN . Starting in 2001, a new generation of experiments, including

2915-402: Was employed to simplify the pattern, where M 2 R {\displaystyle \mathbf {M^{2}} _{R}} is the real part of M 2 {\displaystyle \mathbf {M^{2}} } and M 2 I {\displaystyle \mathbf {M^{2}} _{I}} is the imaginary part. Such an assumption could further reduce

2970-430: Was observed that this symmetry was not respected, thereby proving the T violation in neutral kaon systems under weak interaction. The neutral kaons are initially produced in the annihilation channels which happen when the 10 anti-protons per second beam coming from the LEAR facility is stopped by a highly-pressurized hydrogen gas target. The low momentum of the antiprotons and the high pressure allowed to keep

3025-579: Was untested in the weak interaction. They proposed several possible direct experimental tests. The first test based on beta decay of cobalt-60 nuclei was carried out in 1956 by a group led by Chien-Shiung Wu , and demonstrated conclusively that weak interactions violate the P-symmetry or, as the analogy goes, some reactions did not occur as often as their mirror image. However, parity symmetry still appears to be valid for all reactions involving electromagnetism and strong interactions . Overall,

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