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CP violation: The difference between matter and antimatter

CP violation: The difference between matter and antimatter. Gerhard Raven Vrije Universiteit Amsterdam, Subatomic Physics & NIKHEF. Antimatter. 1928: Dirac equation unifies Quantum Mechanics and Special Relativity:. Paul A.M. Dirac.

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CP violation: The difference between matter and antimatter

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  1. CP violation:The difference between matter and antimatter Gerhard Raven Vrije Universiteit Amsterdam, Subatomic Physics & NIKHEF Gerhard Raven

  2. Antimatter 1928: Dirac equation unifies Quantum Mechanics and Special Relativity: Paul A.M. Dirac 1) Negative energy solutions can be seen as particles traveling backwards in time, equivalent to anti-particles traveling forward in time (Feynman & Stückelberg) 2) The # of particles is NOT conserved but #particles - #antiparticles is conserved) Westminster Abbey Gerhard Raven

  3. Discovery of the positron In 1932, Carl Anderson discovers the positron Gerhard Raven

  4. E=mc2: creating Matter and Antimatter When creating matter from energy, always create equal amount of antimatter Gerhard Raven

  5. Big Bang Cosmology Equal amounts of matter & antimatter Matter Dominates ! Gerhard Raven

  6. Searches for Antimatter in the Universe • Universe around us is matter dominated: • Absence of antinuclei amongst cosmic rays • Absence of intense g-ray emission due to annihilation of distant galaxies in collision with antimatter Alpha Magnetic Spectrometer Gerhard Raven

  7. Searches for Antimatter in the Universe The visible universe is very much matter dominated Gerhard Raven

  8. Where did the Antimatter go? Angular Power Spectrum 2.7248K 2.7252K Cosmic Microwave Background WMAP satellite Almost all matter annihilated with antimatter, producing photons… Gerhard Raven

  9. Where did the Antimatter go? • In 1966, Andrei Sakharov showed that the generation of a net baryon number requires: • Baryon number violating processes (e.g. proton decay) • Non-equilibrium state during the expansion of the universe • Violation of C and CP symmetry • Standard Model of particle physics does allow for some CP-violation • However, it is extremely unlikely to be sufficient to explain matter asymmetry in the universe • It means there must be something beyond the SM in CP violation somewhere, so a good place for further investigation Gerhard Raven

  10. Three Important Symmetries: C, P and T • Charge Conjugation, C • Charge conjugation turns a particle into its anti-particle • e +e - , K -K + • Parity, P • Parity reflects a system through the origin. Convertsright-handed coordinate systems to left-handed ones. • Vectors change sign but axial vectors remain unchanged • x  -x , p  -p, butL=xp  L +  • Time Reversal, T • Changes, for example, the direction of motion of particles • t -t • CPT Theorem • One of the most important and generally valid theorems in localquantum field theory. • All interactions are invariant under combined C, P and T • Implies particle and anti-particle have equal masses and lifetimes Gerhard Raven

  11. “Weak” Interactions Gerhard Raven

  12. Weak Force breaks C, breaks P, is CP really OK ? C e-R W- nL P e+L e-L W+ W- nR nR e+R W+ L spin nL R spin • Weak Interaction breaks both C and P symmetry maximally! • Despite the maximal violation of C and P symmetry, the combined operation, CP, seemed exactly conserved… • But, in 1964, Christensen, Cronin, Fitch and Turlay observed CP violation in decays of Neutral Kaons! (1980 Nobel prize) Gerhard Raven

  13. The Standard Model and CP violation • 1973: If there are at least 3 generations of quarks, the Standard Model of particle physics allows for CP asymmetry • All 3 generations have been observed • c: 1974 (Nobel prize 1976) • t: 1975 (Nobel prize 1995) • b: 1977 • t: 1994 • LEP: 1990 – 1995: there are 3 species of (light, left-handed) neutrinos • With 3 generations, there is a single parameter in the SM responsible for all CP violating processes • Very predictive! (in principle) • To explain the observed ratio of baryons to photons, it falls short by ~8 orders of magnitude • Ideal place for further research! Gerhard Raven

  14. Matter-Antimatter Oscillations At t=0 produce a B0 and B0 pair For many such pairs, plot Amix as a function of the decaytime, t t(ps) But B0 B0 goes as fast as B0B0… Oscillation frequency: 0.5/ps, Average B0 lifetime: 1.5 ps Produce with bg=0.56, and measure flight distance (1ps ~ 150 mm) Gerhard Raven

  15. Intermezzo: Interference Interference allows one to determine phase-differences Gerhard Raven

  16. Interference due to B0 B0 oscillations CP Gerhard Raven

  17. Coherent Time Evolution at the (4S) PEP-2 (SLAC) B-Flavor Tagging Exclusive B Meson Reconstruction Vertexing &Time DifferenceDetermination Gerhard Raven

  18. BaBar Silicon Vertex Detector Readout chips Beam bending magnets Beam pipe Layer 1,2 Layer 3 Layer 4 Layer 5 Gerhard Raven

  19. BaBar Detector @ Stanford Linear Accelerator Center (SLAC) Gerhard Raven

  20. Example of a fully reconstructed event • In general, use charges of identified • leptons, • kaons, • soft pions • from the “the rest of the event” to tag B flavour ‘’fish eye’’ view • B0 D*+ p-fast •  D0p+soft • K-p+ EPR! fast B0(Dt) (2S) Ks m+m- p+p- soft At Dt=0 (i.e. when the D*p decay happened), the ‘CP’ B was/would have been a B0 Gerhard Raven

  21. CP violation in the B system is not small! CP violation in B system not small! 220 events caveat: 100 million (4S) decays needed… Gerhard Raven

  22. The Result & The Standard Model Without using sin(2b) One solution for b is consistent with the prediction from the SM The SM has successfully survived its first precision test of CP violation! Standard Model predicts two other distinct phase differences, a and g  Current research aims to measure g using several redundant methods Gerhard Raven

  23. Summary • CP asymmetry is required to generate a universe with • more than just photons… • CP is included in the Standard Model of particle physics • if particles come in (at least) 3 generations • We have now observed all 3 generations! • The Standard Model does not allow sufficient CP asymmetry • to explain the observed baryon to photon ratio • The Standard Model prediction for CP violation has survived • its first experimental precision test • Current research aimed at testing the Standard Model predictions • in various ways • Somewhere the Standard Model must be incomplete… Gerhard Raven

  24. Escher on CP violation… P CP C C P Gerhard Raven

  25. Colliders First collider: 13 cm, 80 KeV, 1931 LHC: 27 km, 14 TeV, 2007 Gerhard Raven

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