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

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Presentation on theme: ": Section 5: B mesons (what are all those B factory talks really about ?)"— Presentation transcript:

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

2 B o B o systems Decays of B o B o are the same, so lifetimes of B 1 and B 2 are similar Two types of neutral B mesons: –B d = (bd) ; B d = (bd) –B s = (bs) ; B s = (bs) Difference in B 1 and B 2 lifetimes is small Difference in B 1 and B 2 masses is large Oscillation parameter oo

3 Mixing Dominated by top quark contribution b d u, c, t WW WW _ d b _ b d WW WW _ d b _ _ _ _ B0B0 B0B0  For B o s (and similarly for B s ) o

4 EPS,2005 Asymmetry  cos(  m d t) |  t| (ps) BELLE BB. Full B reconstruction Time-dependent probability for a at t=0 to be observed as or at time t B d Mixing  m d : a high precision measurement (~1%) dominated by B factories results  m d =  ps -1

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

6 B s Mixing - x s CDF  M s /  s  x s <60 –SM 22< x s < 31 Si detector & disp. track trigger –combine with B d mixing - x d xs/xd  |Vts/Vtd| (  theoretical unc.) –constrain side of CKM triangle Flavour at Decay Flavour at Production - other B proper time  tag background  t LHCb  M s = 10 ps -1  t = 43 fs  M s = 8fs -1

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8 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’

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

10 B d  J/  K s (CP=-1) Asymmetry ( )

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

12 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

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14 Sin(2  ) from B d      Hard to interpret in terms of  –P in    or isospin       0 BR 5x10 -6 No sub-mass constraint –Other 2 body backgrounds Tree only: Due to Penguin:  |P/T| Another possibility, clean theory, complex analysis  from B d         

15 Benchmark  2  +  Tree only –Mixing and decay BR –But b  u doubly cabibbo suppressed (~ 2% b  c) B s counterparts  -2  Similar strength diagrams –Larger asymmetry –B S BR Better Bet (if RICH) –D s  background BsDsK+BsDsK+ BdD*-BdD*- 00-

16 Brief Angles Prospects Summary  –B d  J/  K s Measured accurately by BaBar/Belle  –B d     , with |P/T| knowledge. –B d           time dep. Dalitz plot  –As B d  D * -    or B s  D s K + –B d      - What is it good for ? Comparing with B s       –B d  J/ , obtain CP eigenstates from angular correlations –Probe higher order unitarity  o o o o o o o o -

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

18 Flavour Tagging Semileptonic decayb  l kaon tag b  c  s jet charge B B Signal B Other Bb s s u u use particles accompanying signal B Identify other b hadron - deduce initial flavour  – tagging efficiency w – wrong tagging fraction D=1-2w, Dilution

19 Systematic Errors Production Asymmetries –Initial fraction b, b  e.g. detector response asymmetry in magnetic field w, w Final State acceptance Control Channels –e.g. –measure  w,w –Precision –Untagged  f + / f - + -

20 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’)

21 Clean environment –no additional tracks Initial state –B 0 B 0 or B + B - B mesons ~ 20%  tot –simpler triggering Why study CP at a hadron collider ? B s –J/  e + e - (BaBar) pp (bar) (D0) Rate –statistics limited channel B s  M s B s –Extracting 

22 Hadronic b production  ln (tan (  –  LHCb/BTeV for larger |   boost  increases rapidly B quark pair produced preferentially at small  highly correlated LHC bb per year (B factories ~ 10 8)

23 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

24 BdBd No identification Purity = 9.5% With pion identification Purity = 85%, Eff. =90%

25 : Section 6: Concluding Remarks on CP Violation

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

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28 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

29 Not the whole picture…. D o 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

30 Further Reading SLAC-R-504 The 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 Proceedings of the workshop on Standard Model Physics (and more) at the LHC –B Decays Chapter Hep-ph/ , Y. Nir, Lectures at the SLAC Summer Institute (1999)


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