VUstudiedag2003

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Published on October 15, 2007

Author: Gourangi

Source: authorstream.com

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:  Antimatter Westminster Abbey 1928: Dirac equation unifies Quantum Mechanics and Special Relativity: 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) Paul A.M. Dirac Discovery of the positron:  Discovery of the positron In 1932, Carl Anderson discovers the positron E=mc2: creating Matter and Antimatter:  E=mc2: creating Matter and Antimatter When creating matter from energy, always create equal amount of antimatter Big Bang Cosmology:  Big Bang Cosmology Equal amounts of matter & antimatter Matter Dominates ! Searches for Antimatter in the Universe:  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 Searches for Antimatter in the Universe:  Searches for Antimatter in the Universe The visible universe is very much matter dominated Where did the Antimatter go?:  Where did the Antimatter go? Almost all matter annihilated with antimatter, producing photons… WMAP satellite Cosmic Microwave Background Where did the Antimatter go?:  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 Three Important Symmetries: C, P and T :  Three Important Symmetries: C, P and T CPT Theorem One of the most important and generally valid theorems in local quantum field theory. All interactions are invariant under combined C, P and T Implies particle and anti-particle have equal masses and lifetimes “Weak” Interactions:  “Weak” Interactions Weak Force breaks C, breaks P, is CP really OK ?:  Weak Force breaks C, breaks P, is CP really OK ? 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) The Standard Model and CP violation:  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! Matter-Antimatter Oscillations:  Matter-Antimatter Oscillations Oscillation frequency: 0.5/ps, Average B0 lifetime: 1.5 ps Produce with bg=0.56, and measure flight distance (1ps ~ 150 mm) Intermezzo: Interference:  Intermezzo: Interference Interference allows one to determine phase-differences Interference due to B0 B0 oscillations:  Interference due to B0 B0 oscillations Coherent Time Evolution at the (4S):  Coherent Time Evolution at the (4S) B-Flavor Tagging Exclusive B Meson Reconstruction Vertexing & Time Difference Determination BaBar Silicon Vertex Detector:  BaBar Silicon Vertex Detector Beam pipe Layer 1,2 Layer 3 Layer 4 Layer 5 Beam bending magnets Readout chips BaBar Detector @ Stanford Linear Accelerator Center (SLAC):  BaBar Detector @ Stanford Linear Accelerator Center (SLAC) Example of a fully reconstructed event:  Example of a fully reconstructed event (2S) Ks  m+m-  p+p- B0  D*+ p-fast  D0p+soft K-p+ ‘’fish eye’’ view fast soft B0(Dt) At Dt=0 (i.e. when the D*p decay happened), the ‘CP’ B was/would have been a B0 EPR! CP violation in the B system is not small!:  CP violation in the B system is not small! CP violation in B system not small! caveat: 100 million (4S) decays needed… 220 events The Result & The Standard Model:  The Result & The Standard Model 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 Summary:  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… Escher on CP violation…:  Escher on CP violation… Colliders:  Colliders First collider: 13 cm, 80 KeV, 1931 LHC: 27 km, 14 TeV, 2007

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