CP Violation Recent results and perspectives João R. T. de Mello Neto Instituto de Física Universidade Federal do Rio de Janeiro IF – UFRJ, July/2003

Outline Introduction CP Violation in the SM Measurement of β B Factories results Other measurements Hadron colliders (LHCb) New physics Conclusion

Motivations SM with 3 generations and the CKM ansatz can accomodate CP CP is one of the less experimentally constrained parts of SM Observations of CP in the B system can: test the consistency of SM lead to the discovery of new physics Cosmology needs additional sources of CP violation other than what is provided by the SM. CP violation is one of the fundamental phenomena in particle physics CP asymmetries in the B system are expected to be large.

I will not talk about: Kaon physics Strong CP problem; CP violation in the charm sector; CP violation in Cosmology! Concentrate in CP violation in the B sector (Only a small subset!)

CLEO 3 BELLE BTEV ATLASATLAS ? Huge experimental effort Plus hundreds of experimental groups around the World.

Matter – antimatter oscillations decay ordinary ΔB=1 interactions exchange of virtual q (2/3) t : dominant amplitude ΔB=2 V td ΔmdΔmd f B decay constant B B Bag factor

CKM matrix = = mixing phase Weak decay phase mixing phase The quark electroweak eigenstates are connected to the mass eigenstates by the CKM matrix : four parameters A, λ, ρ, η

Unitarity triangles V td V tb  +V cd V cb  +V ud V ub  = 0 (0,0)     V ub   V cb  V td (,)(,) (1,0) V td V ud  +V ts V us  +V tb V ub  = 0  V ub   V td  V ts   In SM: measure all the angles measure all the sides SM: consistency!

CP violation Three possible manifestations of CP violation: Direct CP violation (interference between two decay amplitudes) Indirect CP violation (interference between two mixing amplitudes) CP violation in the interference between mixed and unmixed decays

General time-dependent formalism Interfering amplitudes with different CP-violating (weak) phases can give a non-zero CP asymmetry. For B 0 → f CP : Then, when one of the interfering amplitudes is B-mixing with S C Only one decay amplitude (or all decay amp. same CKM phase): C=0 and S gives clean CKM phase information

Golden modes: –clean theory –“relatively easy” experiment Tree and leading penguin have same phase sin  m  t coeff. measures sin2  cleanly Not just J/  K S : –Also  ’ K S,  c1 K S,  c K S (CP=-1) –J/  K L (CP=+1) –J/  K *0 (Mixed CP) Measuring β

B factories: Belle, BaBar Assimetric colliders at One year: ~ 100 M pairs Belle 132 fb -1 March, 2003 BaBar 117 fb -1 Coherent production

KEKB Luminosity achieved: 1.06 x cm -2 s -1

Babar detector

Mixing and lifetimes Results based on large samples of –Fully or partially reco. hadronic decays –Fully or partially reco. D * l –Dileptons 8K events 12K events 29 fb -1

Δt Distributions  Lifetimes Δt = proper time difference between the decay times of the two B-mesons Δt resolution of ~ same order of magnitude as lifetime  0 =   psec  - =   psec

Lifetimes results summary Belle and BaBar now dominate world averages Improvement by x2 over pre B-factory era Order 1% uncertainty on lifetimes and ratio

Adding Tagging Information  m d =   ps fb -1

1.6K events ~500 signal ev. Clean ~2K K S sample + ~ 500 K L events with ~ 60% purity Event samples

Δ t distributions and asymmetries CP=-1 CP=+1 Events with K S Events with K L

Δt distributions and asymmetries

Summary of sin2b in b  ccs 7.5% precision

B 0 → J/   0 S = - sin2β if no penguin C = 0 if no penguin

Measuring β in b → sss B →  K S  B →  ‘ K S Same CKM structure as J/ψ K S u-penguin down by ~1/50 Expect S=sin2β to 5% Like ϕK S but also u-tree Still, S~sin2b

Measuring β in b → sss

Theoretical especulations sin(2β) = S ϕK = (2.7 σ) from the SM prediction; models from SUSY could explain this result! G.L. Kane et al., PRL Apr.2003 Grossman et al. hep-ph/

SM is alive and well! Confidence levels in the large (rhobar,etabar) plane obtained from the global fit. The constraint from the WA sin2beta (from psi Ks modes) is overlaid. Confidence levels in the large (rhobar,etabar) plane obtained from the global fit. The constraint from the WA sin2beta (from psi Ks modes) is included in the fit.

2007 More data close to theory limit from penguin pollution; Measurement of Δm S improve |V td /V cb | from near cancellation of B d and B s form factor; More data from B→h u lν and B→h c X together with improvement in theory will give some improvement in |V td /V cb | ;

Strategy: new physics! now yr LHCb B d  J/  K S B d  B s  J/  Bs DsKBs DsK statistics!! Goal: Physics beyond the Standard model Measurements which provide a reference case for SM effects; Compare this to channels that might be affected by New Physics; Understand experimental and theoretical systematics to a level where we can draw conclusions.

for larger the B boost increses rapidly Hadronic b production B hadrons at Tevatron b quark pair produced preferentially at low  highly correlated tagging low pt cuts

LHCb Experiment Acceptance : –15-300mrad (bending) –15-250mrad (non-bending) Particle ID –RICH detectors –Calorimeters –Muon Detectors Dedicated B physics Experiment at the LHC –pp collisions at 14TeV RICH1 Z ~ m RICH2 Z ~ m Calorimeters Z ~ m Muon System Z ~ m

One event!

Tracking performance Average efficiency = 92 % Efficiency for p>5GeV >95% Ghost rate p T >0.5 GeV ~ 7%. Mass resolution (~13 MeV) (~13 MeV) for the decay channel B s  D s  + KKπ Momentum resolution:  p/p=0.38% Proper time resolution (42 fs) resolution (42 fs) = 27 tracks/event = 27 tracks/event S. Amato C. Nunes JTMN

Hadron ID : Physics Performance No RICH With RICH n Signal Purity improved from 13% to 84% with RICH n Signal Efficiency 79% n RICH essential for hadronic decays n Example : B s  K + K - n Sensitive to CKM angle 

Muon Identification Muons selected by searching for muon stations hits compatible with reconstructed track extrapolations –Compare track slopes and distance of muon station hits from track extrapolation For P>3GeV/c  eff = 96.7  0.2 %  misid = 2.50  0.04 % M. Gandelman JTMN

Strategies for measurements of CKM angles and rare decays Rare

Measuring β S. Amato C. Nunes JTMN

Measuring β S. Amato C. Nunes JTMN

Systematic errors in CP measurements high statistical precision asymmetries ratios robust production asymmetries tagging efficiencies mistag rate final state acceptance Control channels Monte Carlo Detector cross-checks CP eigenstates L. de Paula

experimental: background with similar topologies theoretical: penguin diagrams make it harder to interpret observables in term of

|P/T|= CP conserving strong phase approximately

Rare B decays flavour changing neutral currents only at loop level very small BR ~ or smaller In the SM: Excellent probe of indirect effects of new physics! SM : BR ~ observation of the decay measurement of its BR LHCb width MeV/c 2 signal backg Franciole S. Amato

A. Ali et al., Phys. Rev. D (2000) Rare B decays Forward-backward asymmetry can be calculated in SM and other models LHCb (1y) H. Lopes LHC Physics – Praga (B. de Paula)

Measuring γ Amplitudes of the charge conjugated process are obtained from the above ones just changing the signal from weak phase.

Measuring γ M. Gandelman K. Akiba

LHCb reach in one year (2 fb -1 ) ChannelYield Precision *  B d  J /  K s 119 k  0.6 o  B s  D s K B d  , B s  KK 8 k 27 k, 35 k  10 o  3 o  Bd  Bd   27 k  5 o - 10 o  B s  J /  128 k  2 o |V td /V ts  B s  D s  72 k  m s up to 58 ps  rare decays B d  K   20 k Numbers being updated for the Physics TDR.

Conclusions LHCb is a second generation beauty CP violation experiment; It is well prepared to make crucial measurements in flavour physics with huge amount of statistics; Impressive number of different strategies for measurements of SM parameters and search of New Physics; CP violation is a cool research topic!! B factories established CP violation in the B sector and are making interesting measurements; Exciting times: understanding the origin of CP violation in the SM and beyond.

SM is alive and being poked !