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| {{Beyond the Standard Model|expanded=Evidence}}
| | Laboratory Manager Byron from Kirkland, enjoys croquet, Live Cam Girls and home brewing. Has toured ever since childhood and has visited many places, such as Historic Monuments of Ancient Nara.<br><br>My site - live sex cam girls ([http://www.xdirekt.com/ Full Statement]) |
| In [[particle physics]], '''CP violation''' (CP standing for '''Charge Parity''') is a violation of the postulated '''CP-symmetry''' (or '''Charge conjugation Parity symmetry'''): the combination of [[C-symmetry]] ([[charge (physics)|charge]] conjugation symmetry) and [[Parity (physics)|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), and then its spatial coordinates are inverted ("mirror" or P symmetry). The discovery of CP violation in 1964 in the decays of neutral [[kaon]]s resulted in the [[Nobel Prize in Physics]] in [[Nobel Prize in Physics#1980s|1980]] for its discoverers [[James Cronin]] and [[Val Fitch]].
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| It plays an important role both in the attempts of [[Physical cosmology|cosmology]] to explain the dominance of [[matter]] over [[antimatter]] in the present [[Universe]], and in the study of [[weak interaction]]s in particle physics.
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| == CP-symmetry ==
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| ''CP-symmetry'', often called just ''CP'', is the product of two [[symmetry in physics|symmetries]]: C for charge conjugation, which transforms a particle into its [[antiparticle]], and P for parity, which creates the mirror image of a physical system. The [[strong interaction]] and [[electromagnetic interaction]] seem to be invariant under the combined CP transformation operation, but this symmetry is slightly violated during certain types of [[weak decay]]. Historically, CP-symmetry was proposed to restore order after the discovery of [[Parity (physics)#Parity violation|parity violation]] in the 1950s.
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| The idea behind parity symmetry is that the equations of particle physics are invariant under mirror inversion. This leads to 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. Parity symmetry appears to be valid for all reactions involving [[electromagnetism]] and [[strong interaction]]s. Until 1956, parity conservation was believed to be one of the fundamental geometric conservation laws (along with [[conservation of energy]] and [[conservation of momentum]]). 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 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.
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| Overall, the symmetry of a [[quantum mechanics|quantum mechanical]] system can be restored if another 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 was the desired symmetry to restore order.
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| Simply speaking, charge conjugation is a simple symmetry between particles and antiparticles, and so CP-symmetry was proposed in 1957 by [[Lev Landau]] as the true symmetry between matter and antimatter.
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| In other words a process in which all particles are exchanged with their [[antiparticle]]s was assumed to be equivalent to the mirror image of the original process.
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| ===CP violation in the Standard Model===
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| "Direct" CP violation is allowed in the Standard Model if a complex phase appears in the [[CKM matrix]] describing [[quark]] mixing, or the [[PMNS matrix]] describing [[neutrino]] mixing. In such a scheme, a necessary condition for the appearance of the complex phase, and thus for CP violation, is the presence of at least three generations of quarks.
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| The reason why this causes CP violation is not immediately obvious, but can be seen as follows. Consider any given particles (or sets of particles) <math>a</math> and <math>b</math>, and their antiparticles <math>\tilde{a}</math> and <math>\tilde{b}</math>. Now consider the processes <math>a \rightarrow b</math> and the corresponding antiparticle process <math>\tilde{a} \rightarrow \tilde{b}</math>, and denote their amplitudes <math>M</math> and <math>\tilde{M}</math> respectively. Before CP violation, these terms '''must be the same''' complex number. We can separate the magnitude and phase by writing <math>M=|M|e^{i\theta}</math>. If a phase term is introduced from (e.g.) the CKM matrix, denote it <math>e^{i\phi}</math>. Note that <math>\tilde{M}</math> contains the conjugate matrix to <math>M</math>, so it picks up a phase term <math>e^{-i\phi}</math>. Now we have:
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| :<math>M=|M|e^{i\theta}e^{i\phi}</math>
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| :<math>\tilde{M}=|M|e^{i\theta}e^{-i\phi}</math>
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| However, physically measurable reaction rates are proportional to <math>|M|^{2}</math>, so far nothing is different. However, consider that there are '''two different routes''' for <math>a \rightarrow b</math>. Now we have:
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| :<math>M = |M_{1}|e^{i\theta_{1}}e^{i\phi_{1}} + |M_{2}|e^{i\theta_{2}}e^{i\phi_{2}}</math>
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| :<math>\tilde{M} = |M_{1}|e^{i\theta_{1}}e^{-i\phi_{1}} + |M_{2}|e^{i\theta_{2}}e^{-i\phi_{2}}</math>
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| Some further calculation gives:
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| :<math>|M|^{2}-|\tilde{M}|^{2}=-4|M_{1}||M_{2}|\sin(\theta_{1}-\theta_{2})\sin(\phi_{1}-\phi_{2})</math>
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| Thus, we see that a complex phase gives rise to processes that proceed at different rates for particles and antiparticles, and CP is violated.
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| ==Experimental status==
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| {{Unreferenced section|date=January 2014}}
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| ===Indirect CP violation===
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| In 1964, [[James Cronin]], [[Val Fitch]] with coworkers provided clear evidence (which was first announced at the 12th [[ICHEP]] conference in [[Dubna]]) that CP-symmetry could be broken. This work won them 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, 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 is so nearly a symmetry, created a great puzzle.
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| 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. The combination of CPT is thought to constitute an exact symmetry of all types of fundamental interactions. Because of the CPT symmetry, a violation of the CP-symmetry is equivalent to a violation of the T symmetry. CP violation implied nonconservation of T, provided that the long-held CPT theorem was valid. In this theorem, regarded as one of the basic principles of [[quantum field theory]], charge conjugation, parity, and time reversal are applied together.
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| ===Direct CP violation===
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| [[File:Kaon-box-diagram.svg|thumb|right|Kaon oscillation box diagram]]
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| [[File:Kaon-box-diagram-alt.svg|thumb|right|The two box diagrams above are the [[Feynman diagram]]s providing the leading contributions to the amplitude of {{Subatomic particle|link=yes|Kaon0}}-{{Subatomic particle|link=yes|Antikaon0}} oscillation]]
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| The kind of CP violation discovered in 1964 was linked to the fact that neutral [[kaon]]s can transform into their [[antiparticle]]s (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.
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| Despite many searches, no other manifestation of CP violation 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]].<ref name="NA48">
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| {{Cite journal
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| |author= NA48 Collaboration, V. Fanti, A. Lai, D. Marras, L. Musa, ''et al.''.
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| |title= A new measurement of direct CP violation in two pion decays of the neutral kaon
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| |journal= [[Physics Letters B]]
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| |volume= 465
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| |issue= 1–4
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| |pages= 335–348
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| |year= 1999
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| |doi= 10.1016/S0370-2693(99)01030-8
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| |arxiv= hep-ex/9909022
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| |bibcode= 1999PhLB..465..335F
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| }}</ref>
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| In 2001, a new generation of experiments, including 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 meson]]s.<ref>
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| {{Cite journal
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| |first= Peter
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| |last= Rodgers
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| |type= magazine
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| |publisher= Institute of Physics
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| |publication-place= Bristol
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| |title = Where did all the antimatter go?
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| |page= 11
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| |date= August 2001
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| |url = http://cdsweb.cern.ch/record/715913
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| |accessdate = 2009-01-22
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| |journal= Physics World (Bristol, England)
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| |postscript= <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}
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| }}</ref> By now a large number of CP violation processes in [[B meson]] decays have been discovered. Before these "[[B-factory]]" experiments, there was a logical possibility that all CP violation was confined to kaon physics. However, this raised the question of why it's ''not'' extended to the strong force, and furthermore, why this is not predicted in the unextended [[Standard Model]], despite the model being undeniably accurate with "normal" phenomena.
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| In 2011, a first indication of CP violation in decays of neutral [[D meson]]s was reported by the [[LHCb]] experiment at [[CERN]].
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| ==Strong CP problem==
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| {{unsolved|physics|Why is the strong nuclear interaction force CP-invariant?}}
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| There is no experimentally known violation of the CP-symmetry in [[quantum chromodynamics]]. As there is no known reason for it to be conserved in QCD specifically, this is a "fine tuning" problem known as the [[Strong CP problem]].
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| QCD does not violate the CP-symmetry as easily as the [[electroweak theory]]; unlike the electroweak theory in which the gauge fields couple to [[chirality (physics)|chiral]] currents constructed from the [[fermion]]ic fields, the gluons couple to vector currents. Experiments do not indicate any CP violation in the QCD sector. For example, a generic CP violation in the strongly interacting sector would create the [[electric dipole moment]] of the [[neutron]] which would be comparable to 10<sup>−18</sup> [[Elementary charge|e]]·[[Metre|m]] while the experimental upper bound is roughly one trillionth that size.
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| This is a problem because at the end, there are natural terms in the QCD [[Lagrangian]] that are able to break the CP-symmetry.
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| :<math>{\mathcal L} = -\frac{1}{4} F_{\mu\nu}F^{\mu\nu}-\frac{n_f g^2\theta}{32\pi^2}
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| F_{\mu\nu}\tilde F^{\mu\nu}+\bar \psi(i\gamma^\mu D_\mu - m
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| e^{i\theta'\gamma_5})\psi</math>
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| For a nonzero choice of the θ angle and the [[chiral quark]] [[mass phase]] θ′ one expects the CP-symmetry to be violated. One usually assumes that the chiral quark mass phase can be converted to a contribution to the total effective <math>\scriptstyle{\tilde\theta}</math> angle, but it remains to be explained why this angle is extremely small instead of being of order one; the particular value of the θ angle that must be very close to zero (in this case) is an example of a [[fine-tuning|fine-tuning problem]] in physics, and is typically solved by [[physics beyond the Standard Model]].
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| There are several proposed solutions to solve the strong CP problem. The most well-known is [[Peccei–Quinn theory]], involving new [[scalar particle]]s called [[axion]]s. A newer, more radical approach not requiring the axion is a theory involving [[multiple time dimensions|two time dimensions]] first proposed in 1998 by Bars, Deliduman, and Andreev.<ref>
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| {{cite journal
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| | author=I. Bars; C. Deliduman; O. Andreev
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| | title = Gauged Duality, Conformal Symmetry, and Spacetime with Two Times
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| | journal = [[Physical Review D]]
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| | volume = 58 | issue = 6 | page= 066004
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| | year = 1998
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| | doi = 10.1103/PhysRevD.58.066004
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| |arxiv = hep-th/9803188 |bibcode = 1998PhRvD..58f6004B }}</ref>
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| The strong CP problem may also be solved within a theory of [[quantum gravity]].
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| ===Little CP problem===
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| The little CP problem is a term coined by [[Lisa Randall]]. It refers to an issue related to the enhanced new physics contributions to the electric dipole moment ([[Electric dipole moment#Dipole moments of fundamental particles|EDM]]) of the neutron in flavor anarchic models.<ref>
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| {{cite journal
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| | title = CP violation and FCNC in a warped A4 flavor model
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| | arxiv=1101.5420|doi= 10.1007/JHEP06(2011)121
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| | year=2011
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| | journal=Journal of High Energy Physics
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| | volume=2011
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| | issue=6
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| | last1 = Kadosh
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| | first1 = Avihay
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| | last2 = Pallante
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| | first2 = Elisabetta
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| |bibcode = 2011JHEP...06..121K }}</ref>
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| ==CP violation and the matter–antimatter imbalance==
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| {{main|Baryogenesis}}
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| {{unsolved|physics|Why does the universe have so much more matter than antimatter?}}
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| The universe is made chiefly of [[matter]], rather than consisting of equal parts of matter and [[antimatter]] as might be expected. It can be demonstrated that, to create an imbalance in matter and antimatter from an initial condition of balance, the [[Sakharov conditions]] must be satisfied, one of which is the existence of CP violation during the extreme conditions of the first seconds after the [[Big Bang]]. Explanations which do not involve CP violation are less plausible, since they rely on the assumption that the matter–antimatter imbalance was present at the beginning, or on other admittedly exotic assumptions.
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| The Big Bang should have produced equal amounts of matter and antimatter if CP-symmetry was preserved; as such, there should have been total cancellation of both—[[protons]] should have cancelled with [[antiproton]]s, [[electrons]] with [[positron]]s, [[neutrons]] with [[antineutron]]s, and so on. This would have resulted in a sea of radiation in the universe with no matter. Since this is not the case, after the Big Bang, physical laws must have acted differently for matter and antimatter, i.e. violating CP-symmetry.
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| The [[Standard Model]] contains at least three sources of CP violation. The first of these, involving the [[Cabibbo–Kobayashi–Maskawa matrix]] in the [[quark]] sector, has been observed experimentally and can only account for a small portion of the CP violation required to explain the matter-antimatter asymmetry. The strong interaction should also violate CP, in principle, but the failure to observe the [[electric dipole moment]] of the [[neutron]] in experiments suggests that any CP violation in the strong sector is also too small to account for the necessary CP violation in the early universe. The third source of CP violation is the [[Pontecorvo–Maki–Nakagawa–Sakata matrix]] in the [[lepton]] sector. Current neutrino experiments are not yet sensitive to experimental observation of CP violation in the lepton sector, but the [[NOνA]] experiment currently under construction could observe some small fraction of possible CP violating phases and proposed neutrino experiments [[Hyper-Kamiokande]] and [[LBNE]] will be sensitive to a relatively large fraction of CP violating phases. Further into the future, a [[neutrino factory]] could be sensitive to nearly all possible CP violating phases.
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| If neutrinos are [[Majorana fermion]]s, the [[Pontecorvo–Maki–Nakagawa–Sakata matrix|PMNS matrix]] could have two independent CP violating phases leading to a fourth source of CP violation within the Standard Model. The experimental evidence for Majorana neutrinos would be the observation of [[Neutrinoless_double_beta_decay#Neutrinoless_double beta_decay|neutrinoless double-beta decay]]. As of September 2013, the best limits come from the [http://www.mpi-hd.mpg.de/ge76/ GERDA] experiment. CP violation in the lepton sector generates a matter-antimatter asymmetry through a process called [[Leptogenesis (physics)|leptogenesis]]. This could become the preferred explanation in the Standard Model for the matter-antimatter asymmetry of the universe once CP violation is experimentally confirmed in the lepton sector.
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| If CP violation in the lepton sector is experimentally determined to be too small to account for matter-antimatter asymmetry, some new [[Physics beyond the Standard Model]] would be required to explain additional sources of CP violation. Fortunately, it is generally the case that adding new particles and/or interactions to the Standard Model introduces new sources of CP violation since CP is not a symmetry of nature.
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| ==See also==
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| *[[B-factory]]
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| *[[LHCb]]
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| *[[BTeV]]
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| *[[Cabibbo–Kobayashi–Maskawa matrix]]
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| *[[Penguin diagram]]
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| ==Notes==
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| {{Reflist}}
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| ==References==
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| {{Refbegin}}
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| *{{cite book | author = Sozzi, M.S. | title = Discrete symmetries and CP violation | publisher = [[Oxford University Press]] | year = 2008 |isbn=978-0-19-929666-8}}
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| * {{cite book | author=G. C. Branco, L. Lavoura and J. P. Silva |title=CP violation |publisher= [[Clarendon Press]] |year=1999 | isbn = 0-19-850399-7}}
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| * {{cite book | author=I. Bigi and A. Sanda |title=CP violation |publisher=[[Cambridge University Press]] |year=1999 |isbn = 0-521-44349-0}}
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| * {{cite book | editor= Michael Beyer | title = CP Violation in Particle, Nuclear and Astrophysics| publisher = [[Springer Science+Business Media|Springer]] | year = 2002 | isbn = 3-540-43705-3}} ''(A collection of essays introducing the subject, with an emphasis on experimental results.)''
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| * {{cite book | author = L. Wolfenstein | title = CP violation | publisher = [[North–Holland Publishing]] | year = 1989 | isbn = 0-444-88081-X }} ''(A compilation of reprints of numerous important papers on the topic, including papers by T.D. Lee, Cronin, Fitch, Kobayashi and Maskawa, and many others.)''
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| *{{cite book | author = David J. Griffiths | title = Introduction to Elementary Particles | publisher = [[John Wiley & Sons]] | year = 1987 | isbn = 0-471-60386-4}}
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| *{{cite journal |last1=Bigi | first1=I. |title=CP Violation — An Essential Mystery in Nature's Grand Design |year=1997 |volume=12 |pages=269–336 |journal=[[Surveys of High Energy Physics]] |arxiv=hep-ph/9712475 |bibcode=1997hep.ph...12475B |doi=10.1080/01422419808228861}}
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| *{{cite journal
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| |author1=Mark Trodden |title=Electroweak Baryogenesis |year=1998 |journal=[[Reviews of Modern Physics]] |volume=71 |issue=5 |pages=1463 |arxiv=hep-ph/9803479 |bibcode = 1999RvMP...71.1463T |doi=10.1103/RevModPhys.71.1463}}
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| * {{cite web | author = Davide Castelvecchi | title = What is direct CP-violation? | url = http://www2.slac.stanford.edu/tip/special/cp.htm | publisher = [[SLAC]] |accessdate = 2009-07-01 }}
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| {{Refend}}
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| ==External links==
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| * [http://cerncourier.com/cws/article/cern/28025 Cern Courier article]
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| {{C, P and T}}
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| {{DEFAULTSORT:Cp Violation}}
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| [[Category:Quantum field theory]]
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| [[Category:Particle physics]]
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| [[Category:Symmetry]]
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| [[Category:Conservation laws]]
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| [[Category:Physics beyond the Standard Model]]
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