For the BaBar Collaboration Measurement of the Amplitude Ratio of B0  J/ K*0 to B0  J/ K*0 (K+-) decays Max Baak NIKHEF, Amsterdam For the BaBar Collaboration APS Meeting Philadelphia, 8 April 2003 Max Baak

Two simple concepts ? 1 2 Wrong-flavor decay Right-flavor decay B0  J/ K * 0 ( ) Right-flavor decay B0  J/ K * 0 ( ) 1 ( ) To tag a K*, use charge of kaon and pion 2 Max Baak

Can sin2ßS and sin2ßL be different? Time-dependent asymmetry for B0  J/ KS,L normally given by - sin2ßS = sin2ßL Can sin2ßS and sin2ßL be different? - SM corrections: (sin2ßS - sin2ßL) ~ 0.01 - Experimental limit: 0.02 ± 0.17 How to find wrong-flavor decays if K0 and K0 mix into CP states?  Use B0 J/ K*0 sample! Same quark-level process. Tag with K*0 K+-. BaBar data Grossman, Ligeti, Kagan Phys.Lett.B538:327 Observed asymmetry sin2S = 0.741  0.067 For different sin2ßS and sin2ßL, need non-zero wrong-flavor decay amplitudes (New Physics) sin2L = 0.723  0.158 Max Baak

B  J/ K*0 time dependent analysis a) unmixed B0(t) J/K*0 B0 Initial state Flavor eigenstate b) mixed B0 With wrong- flavor decays No wrong- flavor decays B0(t) B0 Initial state Flavor eigenstate J/K*0 b) a) b) a) Standard Model Wrong-flavor For final state J/ K*0 replace C  -C , S  -S . J/K*0 Extract wrong-flavor to right-flavor amplitude-ratios  and  from time-dependent fit to B0/B0  J/ K*0 and B0/B0  J/ K*0 =0  C=1, S=0 (standard B0B0 mixing) Max Baak

BaBar Detector e+ (3.1 GeV) e- (9 GeV) z Electromagnetic Calorimeter 6580 CsI(Tl) crystals 1.5 T solenoid e+ (3.1 GeV) Cerenkov Detector (DIRC) 144 quartz bars 11000 PMs e- (9 GeV) Drift Chamber 40 stereo layers z Silicon Vertex Tracker 5 layers, double sided strips SVT: 97% efficiency, 15 mm z hit resolution (inner layers, perp. tracks) SVT+DCH: (pT)/pT = 0.13 %  pT + 0.45 % DIRC: K- separation 4.2  @ 3.0 GeV/c  2.5  @ 4.0 GeV/c EMC: E/E = 2.3 %E-1/4  1.9 % Max Baak

K-p separation with Cerenkov Detector (DIRC) Good kaon-pion separation essential to distinguish between K*0K+- and K*0 K-+ BaBar uses DIRC: Čerenkov light in quartz  angle qc handle on particle ID >9s K/p separation s(qc)  2.2 mrad Momentum range of K and  from K* < 3 GeV Max Baak

Analysis Technique sz ~ 110 mm sz ~ 65 mm U(4s) bg = 0.55 Dt @ Dz/gbc At time of BTAG decay, the 2 B’s are in opposite flavor states K+ Tag B sz ~ 110 mm J/Y Reco B sz ~ 65 mm z U(4s) Dz K*0 bg = 0.55 Dt @ Dz/gbc gbctB @ 260 mm Determine flavor of other B meson BTAG (“tagging”) Fully reconstruct B meson in state J/Y K*0 or J/Y K*0 Reconstruct vertex of BTAG and compute proper time difference Dt Max Baak

Dt distribution of mixed and unmixed events realistic mis-tagging & finite time resolution w J/Y K* pdf (similar for J/Y K*) perfect flavor tagging & time resolution Bflav Mixing pdf D(*) , , a1 sample (Bflav) determines mistag fraction w and resolution function Res w Max Baak

Data Sample [1999-2002]: 82 fb-1 on U(4s) Resonance 3s cut on DE applied signal region E [MeV] Sample Ntagged Purity J/Y K*0 860 96% 856 ‘tight’ kaon selection mES [GeV/c2] Max Baak

Fit Parameters Likelihood Fit Combined unbinned maximum likelihood fit to Dt spectra of B-flavor and J/Y K*0 and J/Y K*0 samples. Analysis performed blind. Fit Parameters C,S,C,S 4 Mistag fractions for B0 and B0 tags 12 Signal resolution function 8 Empirical description of background Dt 24 B lifetime fixed (PDG 2002 value) tB = 1.542 ps Mixing Frequency fixed (PDG) Dmd = 0.489 ps-1 tagged J/Y K* tagged flavor sample 48 total free parameters All Dt parameters extracted from data Correct estimate of the error and correlations Max Baak

WARNING! Fake wrong-flavor decays! Need to minimize this effect K- swapping Doubly mis-IDing both K+ and - for each other fakes a K*0 for a K*0 - From MC: double mis-ID rate wrec = 0.3 % WARNING! Fake wrong-flavor decays! Need to minimize this effect Effect of K- swapping on time-dependent decay distributions? To lowest order sine terms not affected, but cosine terms are. (assuming C, C and S, S are of equal size) mixed up on wrec occasions Determined using MC Coefficient C S Syst. Error  0.004  0.001  0.003 Max Baak

Result C = 1.045 ± 0.058 (stat) ± 0.034 (syst) S = -0.024 ± 0.094 (stat) ± 0.039 (syst) C = 0.966 ± 0.051 (stat) ± 0.034 (syst) S = 0.004 ± 0.090 (stat) ± 0.039 (syst) a) unmixed Entries / 0.6 ps b) mixed Source Error C/C Error S/S Background description 0.019 0.017 t resolution and detector effects 0.016 0.021 Signal mistag fractions 0.013 0.000 md and B (PDG 2002) 0.004 0.006 Monte Carlo statistics 0.015 K swapping 0.001 Tag-side DCKM decays Total 0.034 0.039 c) asymmetry Asymmetry See my next talk! t (ps) Max Baak

Conclusion To be submitted to PRL. No sign for wrong-flavor decays B0 J/ K*0 and B0 J/ K*0 Using the relations: Measured values Standard Model 1 2 3 Assuming common wrong-flavor decay amplitudes for B0 J/ K*0 and B0 J/ K*0 To be submitted to PRL. Max Baak

Backup Slides Max Baak

Cerenkov Particle Identification System (DIRC) Good kaon-pion separation essential to distinguish between K*0K+- and K*0 K-+ DIRC: Čerenkov light in quartz K- separation > 4  for this analysis Transmitted by internal reflection Rings projected in standoff box Detected by PMTs Essential for Kaon ID >2 GeV Max Baak

B Flavor Tagging Methods In BaBar tagging is handled with Neural Nets Information used: Primary lepton Secondary lepton Kaon(s) Soft pions from D* decays Fast charged tracks Mistag fraction w determined with flavor eigen-states sample Bflav (23.7k events, purity 82%) Smallest mistag fraction Tagging category Fraction of tagged events e (%) Wrong tag fraction w (%) Q = e (1-2w)2 (%) Lepton 9.1  0.2 3.3  0.6 7.9  0.3 Kaon+Kpi 16.7  0.2 9.9  0.7 10.7  0.4 Kaon+Spi 19.8  0.3 20.9  0.8 6.7  0.4 Inclusive 20.0  0.3 31.6  0.9 0.9  0.2 ALL 65.6  0.5 28.1  0.7 The errors on C,S,C,S scale with quality Q Max Baak