1 Oct 8 th, 2003Gerhard Raven CP violation: The difference between matter and antimatter Gerhard Raven Vrije Universiteit Amsterdam, Subatomic Physics & NIKHEF

2 Oct 8 th, 2003Gerhard RavenAntimatter 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

3 Oct 8 th, 2003Gerhard Raven Discovery of the positron In 1932, Carl Anderson discovers the positron

4 Oct 8 th, 2003Gerhard Raven E=mc 2 : creating Matter and Antimatter When creating matter from energy, always create equal amount of antimatter

5 Oct 8 th, 2003Gerhard Raven Big Bang Cosmology Equal amounts of matter & antimatter Matter Dominates !

6 Oct 8 th, 2003Gerhard Raven Searches for Antimatter in the Universe Universe around us is matter dominated: –Absence of antinuclei amongst cosmic rays –Absence of intense  ray emission due to annihilation of distant galaxies in collision with antimatter Alpha Magnetic Spectrometer

7 Oct 8 th, 2003Gerhard Raven Searches for Antimatter in the Universe The visible universe is very much matter dominated

8 Oct 8 th, 2003Gerhard Raven Where did the Antimatter go? Almost all matter annihilated with antimatter, producing photons… WMAP satellite K2.7252K Cosmic Microwave Background Angular Power Spectrum

9 Oct 8 th, 2003Gerhard Raven Where did the Antimatter go? In 1966, Andrei Sakharov showed that the generation of a net baryon number requires: 1.Baryon number violating processes (e.g. proton decay) 2.Non-equilibrium state during the expansion of the universe 3.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

10 Oct 8 th, 2003Gerhard Raven Three Important Symmetries: C, P and T Parity, P –Parity reflects a system through the origin. Converts right-handed coordinate systems to left-handed ones. –Vectors change sign but axial vectors remain unchanged x   x, p  -p, but L=x  p  L   Charge Conjugation, C –Charge conjugation turns a particle into its anti-particle e   e   K   K  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 local quantum field theory. –All interactions are invariant under combined C, P and T –Implies particle and anti-particle have equal masses and lifetimes

11 Oct 8 th, 2003Gerhard Raven “Weak” Interactions

12 Oct 8 th, 2003Gerhard Raven 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) W+W+ e+Re+R L W+W+ e+Le+L R WW eReR L WW eLeL R P C L R spin

13 Oct 8 th, 2003Gerhard Raven 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)  : 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!

14 Oct 8 th, 2003Gerhard Raven Matter-Antimatter Oscillations Oscillation frequency: 0.5/ps, Average B 0 lifetime: 1.5 ps Produce with  =0.56, and measure flight distance (1ps ~ 150  m) t(ps) At t=0 produce a B 0 and B 0 pair For many such pairs, plot A mix as a function of the decaytime, t But B 0  B 0 goes as fast as B 0  B 0 …

15 Oct 8 th, 2003Gerhard Raven Intermezzo: Interference Interference allows one to determine phase-differences

16 Oct 8 th, 2003Gerhard Raven Interference due to B 0 B 0 oscillations CP

17 Oct 8 th, 2003Gerhard Raven Coherent Time Evolution at the  (4S) B-Flavor Tagging Exclusive B Meson Reconstruction PEP-2 (SLAC) Vertexing & Time Difference Determination

18 Oct 8 th, 2003Gerhard Raven BaBar Silicon Vertex Detector Beam pipe Layer 1,2 Layer 3 Layer 4 Layer 5 Beam bending magnets Readout chips

19 Oct 8 th, 2003Gerhard Raven BaBar Stanford Linear Accelerator Center (SLAC)

20 Oct 8 th, 2003Gerhard Raven Example of a fully reconstructed event  (2S) K s   +  -   +  - B 0  D* +  - fast  D 0  + soft  K -  + ‘’fish eye’’ view fast soft B 0 (  t) At  t=0 (i.e. when the D*  decay happened), the ‘CP’ B was/would have been a B 0 EPR! In general, use charges of identified leptons, kaons, soft pions from the “the rest of the event” to tag B flavour

21 Oct 8 th, 2003Gerhard Raven CP violation in the B system is not small! CP violation in B system not small! caveat: 100 million  (4S) decays needed… 220 events

22 Oct 8 th, 2003Gerhard Raven The Result & The Standard Model Without using sin(2  ) One solution for  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,  and   Current research aims to measure  using several redundant methods

23 Oct 8 th, 2003Gerhard RavenSummary 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…

24 Oct 8 th, 2003Gerhard Raven Escher on CP violation… P P C C CP

25 Oct 8 th, 2003Gerhard RavenColliders First collider: 13 cm, 80 KeV, 1931 LHC: 27 km, 14 TeV, 2007