Section 5: B mesons (what are all those B factory talks really about ?)

Section 5: B mesons (what are all those B factory talks really about ?) :

Bo Bo systems • Decays of Bo Bo are the same, so lifetimes of B1 and B2 are similar • Two types of neutral B mesons: • Bd = (bd) ; Bd = (bd) • Bs = (bs) ; Bs = (bs) • Difference in B1 and B2 lifetimes is small • Difference in B1 and B2 masses is large • Oscillation parameter o o

Mixing (and similarly for Bs) o b d • Dominated by top quark contribution W- u, c, t u, c, t _ _ W+ - b d B0 B0 d b u, c, t _ W+ W- _ _ _ _ u, c, t b d For Bo For Bo s

EPS,2005 Time-dependent probability for a at t=0 to be observed as or at time t Asymmetry  cos(Dmdt) |Dt| (ps) Bd Mixing BELLE 152 106 BB . Full B reconstruction Dmd : a high precision measurement (~1%) dominated by B factories results Dmd = 0.5090.005 ps-1

ms EPS 2005 68%CL ( ) ( ) 95%CL Dms= 22.2 3.1 ps-1 Dms > 14.4 ps-1 at 95%CL Expectation from fits to the Unitarity Triangle Amplitude method search: • LEP, SLD, Tevatron

Bs Mixing - xs • CDF DMs/Gs = xs <60 • SM 22< xs < 31 • Si detector & disp. track trigger • combine with Bd mixing - xd • xs/xd a |Vts/Vtd| (s - theoretical unc.) • constrain side of CKM triangle • Flavour at Decay • Flavour at Production • - other B • proper time wtag backgroundst LHCb st = 43 fs s DMs= 8fs-1 DMs = 10 ps-1

CP Violation in B Decays • TYPES: • 1) neutral to CP eigenstates • 2) neutral to non-CP eigenstates • 3) charged B-decays • CP Possibilities: • Mixing • Decay • Interference between mixing and decay • Channels: • Far too many to discuss! • A few well known ‘benchmark channels’

( ) BdJ/Ks (CP=-1) o c b J/ • Look at decay (l+l-)(+-), Br(BdJ/Ks) ~ 5x10-4 c o o s  K K mixing s d d o Minus for CP odd state

( ) BdJ/Ks (CP=-1) • Asymmetry

golden mode • Dominant penguin contribution : same weak phase ( no direct CP violation) • The only diagram with a different weak phase is suppressed by O(l2)(+OZI) (_) _ B0 tag B0 f B0 B0 f B  charmonium B0 tag C=0 S=sin(2b) New BELLE result for J/K0 (386 106 BB) EPS 2005

Discovery of Direct CP in B system • Look at B-> K+ - • Cf. anti-B->K- + • Tree and Penguin Diagrams • Contribute • Sign of Kaon Tags B • rather than anti-B meson

Hard to interpret in terms of a P in BgKp, or isospin Bgp0p0 BR 5x10-6 No sub-mass constraint Other 2 body backgrounds Penguin Pollution Sin(2a) from Bdgp+p- 0 Tree only: Due to Penguin: a, d, |P/T| Another possibility, clean theory, complex analysis a from Bdgrpgp+p-p0

2b + g Tree only Mixing and decay BR 10-3 But bgu doubly cabibbo suppressed (~ 2% bgc) Bs counterparts g-2dg Similar strength diagrams Larger asymmetry BS BR 10-4 Better Bet (if RICH) Dsp background Benchmark g 0 0 - BdgD*-p+ BsgDsK+

Brief Angles Prospects Summary •  • BdgJ/Ks Measured accurately by BaBar/Belle •  • Bdgp+p-, with |P/T| knowledge. • Bdgrpgp+p-p0, time dep. Dalitz plot •  • As BdgD*-p+ or BsgDsK+ • Bdgp+p- - What is it good for ? Comparing with BsgK+K- •  • BdgJ/, obtain CP eigenstates from angular correlations • Probe higher order unitarity r o o o o o - o o o

The Experiments • B Factories (2000): • BaBar, Belle • (also CLEO) • TeVatron (2001 ): • CDF, D0, (proposed BTev) • LHC (start 2007) • LHCb (also ATLAS,CMS)

Semileptonic decay bgl kaon tag bgcgs jet charge Signal B B Other B B Flavour Tagging use particles accompanying signal B b s s u u e – tagging efficiency w – wrong tagging fraction D=1-2w, Dilution • Identify other b hadron • - deduce initial flavour

Production Asymmetries Initial fraction b , b e , e e.g. detector response asymmetry in magnetic field w , w Final State acceptance Control Channels e.g. measure e,ew,w Precision 10-3 Untaggeda f+ / f- Systematic Errors + -

B Factories: BaBar/PEPII, Belle/KEKB • Asymmetric beams boosted B • Time difference between B decays  z • At decay time on b one bbar (c.f. EPR ‘Paradox’)

Clean environment no additional tracks Initial state B0B0 or B+B- B mesons ~ 20% stot simpler triggering Bs J/Yf Why study CP at a hadron collider ? e+ e- (BaBar) pp(bar) (D0) • Rate • statistics limited channel • Bs DMs • Bs • Extracting g

h = - ln (tan (q/2)) 2 < h<5 LHCb/BTeV for larger |h | B boost bg increases rapidly B quark pair produced preferentially at small q highly correlated Hadronic b production LHC 1012 bb per year (B factories ~ 108)

LHCb Detector • Forward single arm spectrometer • Two RICH detectors for particle ID • Multi-level Trigger system, using displaced vertices • Precision Silicon Vertex Detector • 40MHz beam crossing rate Series of Discs Detectors separated 6cm during injection

Bdgp+p- No identification Purity = 9.5% With pion identification Purity = 85%, Eff. =90%

Section 6: Concluding Remarks on CP Violation :

CKM triangle status, ICHEP 2004 Compatibility obtained between all constraints 2002: first non-trivial compatibility test for CKM triangle Next step to measure alpha and beta angles

Final Comments • CP violation: a fundamental symmetry broken • Good reasons to believe SM is not final answer • Sensitive to new physics • Next Decade • Promises to be v. exciting for CP studies • BaBar/Belle , TeVatron, LHC • Overconstrain CKM triangle

Not the whole picture…. • Do mixing • Not yet observed • Slow oscillations x< 0.01 • Sensitive to new physics • CP violation in the lepton sector • Massive neutrinos  • Neutrino mixing between flavour eigenstates to produce mass eigenstates • Neutrino Oscillations between 3 famillies and CP phase. • Neutrino Factory would produce enough neutrinos for CP violation test. • See Paul’s neutrino course

Further Reading • SLAC-R-504The BaBar Physics Book, • Chapter 1, A CP Violation Primer • CP Violation, Bigi & Sanda, Cambridge University Press, 2000 • FERMILAB-Pub-01/197 B Physics at the Tevatron: Run II and Beyond • CERN 2000-04 Proceedings of the workshop on Standard Model Physics (and more) at the LHC • B Decays Chapter • Hep-ph/9911321, Y. Nir, Lectures at the SLAC Summer Institute (1999)

Section 5: B mesons (what are all those B factory talks really about ?)