# Chris Parkes1 Part III CP Violation and K Physics Chris Parkes.

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Chris Parkes1 Part III CP Violation and K Physics Chris Parkes

2 Outline PHENOMENOLOGY AND EXPERIMENTS III.CP violation and Kaon physics T-violation: CPLEAR An angle (phase difference) measurement: CPLEAR ε’ : NA48 Rare kaon decays IV.CP violation and B physics V.CP Violation and D physics VI.Concluding remarks Present status and future ahead

Mixing in the neutral kaon system

Chris Parkes4 Neutral kaon system K 0 – K 0 in nature (1/2)  If CP was conserved:  In nature, CP violated: with  quantifies degree of CP violation flavour eigenstates, CP conjugated

Chris Parkes5 Neutral kaons “identity card”:  Branching fractions: K S :      69%,      31% K L :        21%,        13%,     66%  Mixing parameters: Neutral kaon system K 0 – K 0 in nature (2/2) ~600 times larger! K S  o  o K S  +  - K L  +  -  o K L  o  o  o CP=+1 CP=-1

Chris Parkes6 d s u, c, t WW WW _ s d _ d s WW WW _ s d _ _ _ _ K0K0 K0K0  Neutral kaon mixing - oscillations K0K0 K0K0   Feynman (box) diagrams for neutral kaon mixing: t=0: initial K 0 beam K S decay early Pure K L beam after a while! At t>0: superposition of states

Chris Parkes7 CPLEAR T-invariance (can also think of it in terms of CP violation) Rate difference K o  K o  K o  K o is T violation

8 Experiment at LEAR ring at CERN 1990- 1996 Pions from kaon decay

9 1) Identify K o / K o at production: produced in association with K + /K - 2) Identify K o / K o at decay from charge of lepton:CPLEAR measure Get positron: s d KoKo u d e+e+ ν W+W+ π -π - dd Or electron: s KoKo u e-e- ν W-W- π+π+ Final states f, f are particle /anti-particles

Oscillation 10 t=0t K0K0 K0K0 K0K0 K0K0 K0K0 K0K0

Oscillation & Decay 11 t=0t K0K0 K0K0 K0K0 K0K0 K0K0 K0K0 s d KoKo u d e+e+ ν W+W+ π -π - dd s KoKo u e-e- ν W-W- π+π+

CPLEAR T-Invariance 12 T or equivalently CP is violated by this tiny amount

Chris Parkes13 CPLEAR : decay to CP eigenstate -Illustrate 3 types of CP violation -Measuring an angle (phase difference)

14 1) Identify K o / K o at production: produced in association with K + /K - 2) Decay to π + π - final state reachable from K o and K o CPLEAR – decay to π + π - measure Interference of route with/without oscillations Same final state f in both cases

Oscillation 15 t=0t K0K0 K0K0 K0K0 K0K0 K0K0 K0K0

Oscillation & Decay 16 t=0t K0K0 K0K0 K0K0 K0K0 K0K0 K0K0 Amplitude Rate

Three methods of CP Violation Revisited Rates 17 1.CP violation in decay 2.CP violation in mixing 3.CP violation in interference mixing/decay

18 (since ) Hence we are measuring an angle ϕ +- c.f. B system discussion later

19

NA48: Direct CP Violation

Chris Parkes21  CP violation first seen though existence of decay modes  CP conservation would imply …. but experimentally these parameters are found ~ 10 -3  CP violation due solely to mixing would be independent of the decay to the final state The  and  ’ parameters (1/2)

Chris Parkes22  To separate CP violation in decay from CP violation in mixing, the following is introduced: … to separate the channel-independent term  from the channel-dependent term  ’  Measurement of rates yields The  and  ’ parameters (2/2) Direct CP violation (i.e. in decay) CP violation in mixing K L /K s rates:

Chris Parkes23 The NA48 experiment at CERN (1/2) Study of direct CP violation in the neutral kaon system

Chris Parkes24  Start with a pure K o beam  After a few meters (short time) all K s component decayed  Introduce slab of material in beam  Several reactions can occur with the material: 1)elastic scattering 2)charge exchange 3)Hyperon production  K 0 absorbed more strongly! f amount of K 0 absorbed, f amount of K 0 absorbed Neutral kaon regeneration K s regenerated! A consequence of particle-antiparticle mixing

Chris Parkes25 Measurements of  ’/  : Discovery of Direct CP violation Average: 1.68 ± 0.14  10 -3 Not easy to compare with SM theory - CP violation frontier now in B and D Direct CP Violation

Rare kaon decays

Chris Parkes27 Rare Kaon Decays Look for extremely suppressed decays in SM – where new physics could contribute Precision currently at parts per trillion ! Some interesting modes Standard Model New Physics Example Same experimental signature Very light/massless neutralino – neutral SUSY particle

Chris Parkes28 Mainly (and very) sensitive to V td Predicted B. R. ~ 8x10 -11 One such event Enhancement over SM of central value, but not significant

Chris Parkes29 Rare kaon decays – NA62 (successor to NA48) NA62 at CERN’s SPS currently commissioning, to measure Start after CERN (LHC) accelerator shutdown K+K+ ++ ~11 MHz of K + decays Expect Also Koto expt, Japan

Chris Parkes30 Key Points – Kaon section K s (short lived), K L (long lived) are mixture of K 1 (CP +ve), K 2 (CP –ve) ε quantifies degree of CP violation CPLEAR measurement of T (or equiv. CP) Violation K o  K o  K o  K o CPLEAR CP violation in a CP eigenstate π + π - same final state f, defined Parameter η +- How to measure an angle NA48 Direct CP Violation Difference in CP violation in π + π -, π 0 π 0 Quantified by  ’/  Rare Decays, extremely suppressed in SM, new physics can contribute NA62

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