CP violation in B decays

Transcription

1 CP violation in B decays Philip Clark University of Bristol The BaBar Collaboration

2 Outline Brief introduction to CP violation in the B meson system. The PEP-II storage ring and BaBar detector. Performance of the experiment. Physics results B lifetimes B mixing CP asymmetry Conclusions and future prospects ,943800,84 0,8: !;4,93, /0.,894!00389,908!8#0; 099

3 Why is CP violation interesting? :3/,2039, /0/9405,32,9907,392,9907, , , / / / 48920,8: ,7, % $9,3/,7/4/0,34; ,390$570/ /0503/039 20,8: ,90/94902,880307,9320., :902,97 :3/,2039,25., ,

4 Three types of CP violation in B decays!;4, : :97,2, ,908,70/ !00389,908!;4,9433/0.,..:783 ± /0.,80390,259:/0147,/0.,,3/98!.43:,90,;0/ ,39:/08!;4, /0.,89,3/94:923..:783/0.,8913,89, ,3/

5 More on the types of CP violation 438/07/0.,89413,!00389,9081!, ,3/ /0., ,20,8:7,-06:,3993/0503/039415,80.43; q p A A CP λ η fcp f f CP q p A A f f CP CP CP symmetry is conserved if and only if:- q p =1 A A f f CP CP =1 Im λ = 0 If violated you get CP violation in :- 1. Mixing 2. Decay 3. Interference between decays with and without mixing

6 CKM matrix unitarity: b u l ν Unitarity Triangle B ππ B πρ V ud V ub * α (=ρ,=η) V td V tb * B 0 B 0 mixing B ργ V B Κπ B D 0 cpk ud V * ub γ CP violation V cd V cb * b * * + VcdVcb + VtdVtb c l ν = 0 β B J/ψΚ 0, B ψ(2s)κ S

7 The unitarity triangle (cont.) %08/08,70/ /-20,8: ,39:/ !, ! 20,8:708, , , ,,2-:908 4, ,28944; ,397,30.79., :.9:7041$

8 CP violation in the interference between decays with and without mixing B 0 B 0 B 0 (t) f CP B 0 (t) f CP B 0 B 0 A CP = A(B 0 (t) -> f CP ) 2 - A(B 0 (t) -> f CP ) 2 A(B 0 (t) -> f CP ) 2 + A(B 0 (t) -> f CP ) 2 A CP (t) = - Im(λ) sin( mt) Alternatively:- A CP (t) = - η CP sin(2φ) sin( mt) where φ = α, β, or γ 4790/0., 588 Im(λ) = sin(2β)

9 Existing Constraints on the Unitarity Triangle η Errors are dominated by theoretical uncertainties! m d m s / m d 0.4 ε K 0.2 V ub /V cb Constraints come from - CP violation in K 0 mesons - V ub and V cb measurement - B d and B s mixing ρ 4.07,.07$,5, /07 055

10 The asymmetric B-factory concept 0 Г 0 >=Υ(48 >=.0,384: :97,88902Υ$ > 0;4; /0., , ,;4:7 472, 8/434997,;01,7034:3Υ$708917, ,8:70 9 =µ2 3, , /94 89:/!;4, ,4390-0,2/ ,;0,20,8:7,-0 /89, /0.,,43/090723, #06:708,94730 Г 0.4/07 9, , :73.43; !!,3/%789, Г 0.4/078 94, ,.94708, /

11 The anatomy of a CP event J /Ψ= >=µ + µ e + e - >Υ(4 >Υ(4S) tagging B decays Β= >J /Ψ=Κ s t ~ z / β=γ=c Κ s >=π + π coherent evolution

12 Experimental Approach!74/:.02,3 5,78 # :.94303,!00389,908:.,8 > Ψ= 8 %, / ,;47, /0., /0.,8: ,4390-0,2/ βγ. 425,70 9 /897-: Г,3/ 1 9,0/0;0398 B tagged,3, ;/ ( f + )!;4,943 B tagged ( f - ) η CP sin 2φ sin ( m t)

13 The B meson factory PEP-II 0'(0 0 Г 2(0 0 Г.2 8 ( /,( 083 #0,.0/ 08

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15 BABAR Collaboration: 9 Countries, 72 Institutes China [1/6] Inst. of High Energy Physics, Beijing Germany [3/21] Ruhr U Bochum TU Dresden U Rostock France [5/50] LAPP, Annecy LAL Orsay LPNHE des Universités Paris 6/7 Ecole Polytechnique CEA, DAPNIA, CE-Saclay United Kingdom [10/80] U of Birmingham U of Bristol Brunel University U of Edinburgh U of Liverpool Imperial College Queen Mary & Westfield College Royal Holloway, University of London U of Manchester Rutherford Appleton Laboratory 554 physicists Italy [12/89] INFN Bari INFN Ferrara INFN Frascati INFN Genova INFN Milano INFN Napoli INFN Padova INFN Pavia INFN Pisa INFN Roma INFN Torino INFN Trieste Canada [4/16] U of British Columbia McGill U U de Montréal U of Victoria Norway [1/3] U of Bergen Russia [1/13] Budker Inst., Novosibirsk USA [35/276] Caltech, Pasadena UC, Irvine UC, Los Angeles UC, San Diego UC, Santa Barbara UC, Santa Cruz U of Cincinnati U of Colorado Colorado State Elon College Florida A&M U of Iowa Iowa State U LBNL LLNL U of Louisville U of Maryland U of Massachusets MIT U of Mississippi Mount Holyoke College Northern Kentucky U U of Notre Dame ORNL/Y-12 U of Oregon U of Pennsylvania Prairie View A&M Princeton SLAC U of South Carolina Stanford U U of Tennessee U of Texas at Dallas Vanderbilt U of Wisconsin Yale U

16 Instrumented Flux Return DIRC stand-off box PMTs in water Electro Magnetic Calorimeter Quartz bars Drift Chamber e + (3.1 GeV) - e (9.0 GeV) Silicon Vertex Detector

17 Silicon Vertex Tracker (SVT) 22 Five layer double-sided Si Very low mass Stand-alone tracking device for P T < 120 MeV/c Radiation hard z-resolution of 70µm on CP vertex

18 Drift Chamber %7,.37084:943

19 Detector of Internally Reflected Cherenkov Light (DIRC): Θ c resolution: cosθ c =1/nβ

20 Cherenkov angles for π=and K from D * D 0 π +,==D 0 K - π + π K

21 Electromagnetic calorimeter σ E E 1% = 4 E 1.2% #,/, ,/:8.2!0, % , / '

22 Instrumented Flux Return (IFR) µ ,3/π 1,07,90, # Large solid angle coverage for muon id (P>1 GeV/c) and to detect neutral hadrons (K 0 L )

23 Summary:- unique features of BaBar ,28 70,90,20,3260 µm ; ,7,943 4;0732,35,79.0/0;.0# 4709,382,5805,7,943: GeV/c ,.74:3/8 7,/0/802039,94341,/743./ # 574;/ :.943 ",-9949,0/,9,.4393:4:8,9 7,90,3/-908 0;039809,;07,0 /0,/ : !! 38%0;,

24 BaBar daily recorded luminosity Design value

25 PEP-II/BaBar integrated luminosity

26 Exclusive B reconstruction 302,9.;,7,-08 E = E * 1 2 σ ( E) 25MeV /423,90/-/ :943 s E (GeV) B 0 D * π + (Kπ) m σ 2 * 2 ES = s P B 1 2 ( m ES ) 3MeV /423,90/--0, ,/ m ES (GeV/c 2 )

27 Exclusive B Decays to Charmonium Branching ratios B 0 J/ψK s (π + = π ) 0., 7,3.3 7,.943 PRELIMINARY ψ π Г π π π 1742 ψ Г ψ Г Г ψ Г ψπ B + J/ψK + χ. χ. Г χ.... Г Ψ$ Г Ψ$ Г

28 Exclusive B decays to Charmonium

29 B lifetime measurement B 1 partially reconstructed σ z ~ 140 µm B 2 fully reconstructed σ z ~ µm e e + 9 GeV 3.1GeV z γ B γβcτ B 260 µm Method / 05 βγ.τ Β : :.9,,703: ,8:70.43; /897-: '9,94:3/0789,3/90/ ; :943

30 Reconstructed hadronic B sample 1- B 0 /B 0 B + /B - ±.,3//,908 ±.,3//,908 47/8,70898,250411: :.90/8

31 Resolution function 9 resolution function! :943 :7#$7084: ,8:73 9 8,-4:9 58 %88831.,39.425,70/ ;4:90/9 0:80,7084: t.85,7,209070/,88:2 41/ ,:88,38 20,8:70/.470 9,8 4:9078

32 B Lifetime Measurements B 0 /B 0 B + /B - PRELIMINARY t (ps) τ B 0 = ± (stat) ± (syst) ps [PDG= ± 0.032] t (ps) τ B + = ± (stat) ± (syst) ps [PDG= ± 0.028] τ B +/ τ B 0 = ± (stat) ± (syst) [PDG= ± 0.029]

33 Flavour tagging:- B 0 or B 0 %,90 1,;4:7:8390., , leptons: b l, b l + p*>1.0 GeV/c (e ± ), p*>1.1 GeV/c (µ ± ) k a o ns: b K, b K + NT1 & NT2: b(-1/3) c(+2/3) s(-1/3) W- ν W+ e,µ (-1) Neural network mainly to recover unidentified leptons, slow pions from D*, ε 89, ω ":,9 " ± ± ±,43 ± ± ± % ± ± ± % ± ± ± %49, ± ±

34 An Event of the CP Sample A candidate in the Golden Mode B 0 CP with: J J 0 / ψ KS, K + / ψ µ µ 0 S π + π A negative kaon is found in the decay products of the other B meson, which is therefore tagged as a B z is measured precisely, thanks to the Silicon Vertex Detector 0

35 Mixing and Sin2β analysis procedure Reconstruct one B fully in CP eigenstate or flavour eigenstate Other B partially reconstructed and flavour tagged Measure =z Fit for =t = =z/cγβγ B Mixing:- PDF( t)= exp( t /τ B ) ( 1 ± (1-2ω) cos( m t) ) R( t) CP violation:- PDF( t)= exp( t /τ B ) ( 1 ± (1-2ω) sin2β sin( m t) ) R( t) (1-2ω) is the dilution due to mistag R( t) is the vertex resolution function

36 Detector Effects on CP and Mixing Samples CP events B tagged B tagged Perfect detector Mixing events unmixed mixed + Mistag effect + Vertex resolution effect

37 Mixing result from B flav events Events/ 0.4 ps Unmixed Events Mixed Events BABAR t (ps) Asymmetry BABAR t (ps) M d = ± ± ps -1 (preliminary)

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39 2 Events / 2.5 MeV/c BABAR ( B 0 ) = J/ψ K S K S π + π 2 Events / 2.5 MeV/c BABAR ( B 0 ) = J/ψ K S K S π 0 π Beam-Energy Substituted Mass (MeV/c ) Beam-Energy Substituted Mass (MeV/c ) BaBar golden modes 2 Events / 2.5 MeV/c BABAR ( B 0 ) = ψ(2s) K S K S π + π Beam-Energy Substituted Mass (MeV/c )

40 t distributions of tagged CP events

41 A CP ( t) Golden Modes a) 0 sin2β= 0.25 ± 0.22 (stat) Asymmetry J/Ψ=K L b) sin2β= 0.87 ± 0.51 (stat) Combined: sin2β===0.34 ± 0.20 ± 0.05 t (ps)

42 Our sin2β measurement and the unitarity triangle 4.07,.07$,5, / Allowed blue region obtained with the new sin2β meas.

43 Comparison of Sin2β measurements $2,077478,3/ ,70/,9,809 3σ!

44 PEP-II/BaBar luminosity projections Integrated Lumi [fb-1] Peak Lumi [10**33] Yearly Lumi Cumulative Lumi Peak Lumi mid Yearly Lumi Cumulative Lumi Peak Lumi Year

45 Conclusions and future prospects!!,3/,,7,704507,93,9/083;,:0, :98/: :98443 $ ,3708:98841,7 83β=== ± ± / ± ± :380:3/07, 090,78!,394,..:2:,904;071-! β,=' :- '.- 20,8: $3α /090723,943,3/.43897,39843$3γ $0,7.147/70.9!;4,943