Results of same sign dilepton charge asymmetry from Belle and BaBar

Transcription

1 Results of same sign dilepton charge asymmetry from Belle and BaBar Yoshiyuki Onuki High Energy Physics Experiment Group Tohoku University cpv from b factories to tevatron and lhcb@tohoku University

2 Outline IntroducEon B factories, Belle and BaBar Physics of B d0 B d 0 mixing dilepton charge asymmetry Results of same sign dilepton charge asymmetry from B factories Global fit Conclusions

3 IntroducEon B factories, Belle and BaBar

4 KEKB at KEK KEKB Mt. Tsukuba Belle 8 GeV e - and 3.5 GeV e + ±11mrad crossing on resonance of Υ(4S)~10.58GeV Y(4S) : qq(continuum)= 1:3 Br(Υ(4S) BB)>96% ~1 km in diameter L peak = 2.1 x sec -1 cm -2 >Twice of the design Luminosity! Producing enormous BB pairs copiously B-factory βγ=0.425 Δt=Δz/(βγc)

5 PEP II at SLAC 9 GeV e - and 3.1 GeV e + on resonance of Υ(4S)~10.58GeV L peak = 1.2 x sec -1 cm -2 βγ=0.55

6 30 June April 2008

7 Belle Detector SC solenoid 1.5T Aerogel Cherenkov cnt. n=1.015~1.030 K/π separation 3.5GeV e + CsI(Tl) 16X 0 TOF counter 8GeV e - Tracking + de/dx small cell + He/C 2 H 5 Si vtx. det. 4 lyr. DSSD µ / K L detection 14/15 lyr. RPC+Fe

8 The BaBar Detector Cerenkov Detector (DIRC) 144 quartz bars PMs e- (9 GeV) 1.5 T solenoid Electromagnetic Calorimeter 6580 CsI(Tl) crystals e+ (3.1 GeV) Drift Chamber 40 stereo layers Instrumented Flux Return iron / RPCs (muon / neutral hadrons) Silicon Vertex Tracker 5 layers, double sided strips

9 IntroducEon Physics of B d0 B d 0 mixing dilepton charge asymmetry

10 V qb V * dq B d0 B d 0 mixing V qb u, c, t V * dq u, c, t u, c, t V * V dq qb V dq * u, c, t A general state of neutral B meson can be wri]en as ψ(t) =a(t) Β 0 + b(t) Β 0 We can evolves the state with Schrödinger eq.. i ψ = H The equaeon can ψ be re wri]en the matrics form. i ψ = H ψ The solueon can be found by diagonalizing the matrics. H ψ = λψ V qb

11 B d0 B d 0 mixing The eigen value of the equaeon can be expressed with mass and decay matrics elements supposing CPT invariance. λ ± = Μ ± iγ ± /2 The mass eigenstate are composed of two flavor eigenstates B H = p B 0 + q B 0 B L = p B 0 q B 0 Where p 2 + q 2 =1

12 B d0 B d 0 mixing We can evolve the Eme at t using λ B 0 (t) = f + (t) B 0 + (q/p)f (t) B 0 B 0 (t) = (q/p)f (t) B 0 + f + (t) B 0 Where f ± =[exp( iλ + t)±exp( iλ t)]/2 (q/p) V td /V td*

13 Dilepton charge asymmetry The Eme dependent decay rate for same sign dileptons can be calculated using the equaeons of previous slide as below. Thus, we can get the Eme integrated asymmetry The current prediceons of q/p in the Standard Model are q/p ~ 4 ~ Some NP scenarios indicate to be different with that of the SM

14 Results of same sign dilepton charge asymmetry from B factories E.Nakano et al. Physical Review D 73, (2006) B.Aubert et al. Physical Review Le]ers 96, (2006)

15 Signals Υ(4S) B d0 B d 0 B 0 d B 0 d X l + ν l X l + ν l B 0B 0 d d X + l ν l X + l ν l Charge of lepton from semileptonic decay determines B flavour at decay Eme

16 Cascade decay Also from B + B Backgrounds Direct Lepton l ν l + ν Cascade Lepton b c d Dilepton in which one lepton comes from cascade decay. unmixedb 0 d B 0 d D + l ν l X 0 l + ν l X l + ν l Dilepton in which both lepton come from cascade decay. mixedb 0 d B 0 d D + l ν D + l ν l l X 0 l + ν l X 0 l + ν l Direct lepton and the cascade decay lepton stem from the same B

17 Charmonium J/ψ ll veto ψ(2s) ll veto ConEnuum Backgrounds E.Nakano et al. Phys. Rev. D 73, (2006) All possible combinaeons Casecade background fraceons are fixed at the MC, signal and background fraceon is float and determined with Δz fit. Casecade background fraceons are fixed at the MC and esemated from data.

18 Asymmetry effect from detector Track finding efficiency e: < 0.5% e µ µ:< 0.5% Lepton ideneficaeon e: < 0.5% e µ µ:< 0.5% Hadron misideneficaeon π e K e p e e: 0.8±0.2% µ:0.8±0.2% e: 1.2% for direct lepton w/ higher p 0.8% for direct lepton w/ lower p 0.5% for casecade lepton w/ higher p 0.2% for casecade lepton w/ lower p µ:float in the fit Open circle: NegaEve charge Filled circle: PosiEve charge π µ K µ p µ K µ p e The effect is included in the Lepton ID

19 Data seleceon at Belle Data sample: 85M B pairs Event seleceon: Fox Wolfram moments, at least 5 tracks, vertex in IR, Total Energy, Momentum, Opening angle of two tracks Tight lepton PID Photon conversion and J/ψ veto

20 CorrecEons Efficiency correceon #detected track track finding eff. hadron/lepton raeo (MC) #generated track lepton id eff. lepton id fake rate(data) p * lepton momentum in e + e center of mass θ lab angle between lepton momentum direction and beam axis the in the lab. ConEnuum correceon To suppress the contribueon from conenuum, dilepton candidate yield is wighted by funceon as below. Prob(BB) = f(p 1*, p 2*, θ 1, θ 2, θ ll*, Δz) BB background correceon Casecade background fraceons are fixed at the MC, signal and background fraceon is float and determined to fit for Δz distribueon.

21 Fizng data at Belle Using N ±± (Δz)=N s ±± (Δz) + N b ±± (Δz) dilution factor d( Δz )= N S /N Total ( Δz )

22 Result at Belle A sl = ( 1.1 ±7.9(stat) ± 8.5(syst)) 10 3 q/p = ±0.0040(stat) ± (syst) q/p 1 =(0.5 ±4.0(stat) ± 4.3(syst)) 10 3

23 Data seleceon at BaBar Data sample: 232M B pairs Event seleceon: Fox Wolfram moments, invariant mass, aplanarity, track muleplicity Tight lepton PID Photon conversion and charmonium veto events pass this dilepton seleceon

24 Data fizng at BaBar Likelihood fit function is defined as below fraceon of conenuum ConEnuum term The other term fraceon of B + B B 0 B 0 term Cascade term signal term B + B cascade term B + B term Tau decay term Cascade decay term Where q 1,q 2,f 1 and f 2 are charges and flavors(e,µ)

25 Result at BaBar q/p 1 =( 0.8 ±2.7(stat) ± 1.9(syst)) 10 3

26 Global fit by HFAG and conclusions

27 Average By Heavy Flavour Averaging Group (HFAG) in 2010 Averaged result of CLEO, BABAR and Belle A SL = ± q/p = ± Averaged result of CLEO, BABAR,Belle, ALEPH, OPAL and D0 (and assuming A SL (B s ) = 0) A SL = ± q/p = ± arxiv: v1 [hep ex]

28 Used results to average arxiv: v1 [hep ex]

29 Conclusions Dilepton charge asymmetry had measured at B factory and High energy colliders. These averaged value from B factories is calculated as below by HFAG group. q/p = ± The result is consistent with SM prediceon in the B 0 mixing

30 BaBar fit fraceon Event types in fit: Signal (both leptons, 81% of B pair events) Direct cascade leptons from the two B mesons (9%) Direct cascade leptons from the same B meson (4%) b τ (e or μ) (3%) Charmonium leptons (3%)