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Measurement of the Amplitude Ratio of B 0  J/  K *0 to B 0  J/  K *0 (K +  - ) decays

Measurement of the Amplitude Ratio of B 0  J/  K *0 to B 0  J/  K *0 (K +  - ) decays. Max Baak NIKHEF, Amsterdam For the BaBar Collaboration APS Meeting Philadelphia, 8 April 2003. Two simple concepts. Wrong-flavor decay. ?. B 0  J/ K * 0 B 0  J/ K * 0. ( ).

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Measurement of the Amplitude Ratio of B 0  J/  K *0 to B 0  J/  K *0 (K +  - ) decays

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

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

  3. Can sin2ßSand sin2ßL be different? BaBar data • Time-dependent asymmetry for B0 J/ KS,L normally given by • - • sin2ßS = sin2ßL • Can sin2ßSand 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+-. Grossman, Ligeti, Kagan Phys.Lett.B538:327 Observed asymmetry sin2S = 0.741  0.067 For differentsin2ßSand sin2ßL, need non-zero wrong-flavor decay amplitudes (New Physics) sin2L = 0.723  0.158 Max Baak

  4. B  J/ K*0 time dependent analysis B0 Flavor eigenstate With wrong- flavor decays Flavor eigenstate B0(t) B0(t) J/K*0 J/K*0 For final state J/ K*0 replace C  -C , S  -S . Initialstate Initialstate B0 a) a) b) b) J/K*0 B0 Standard Model Wrong-flavor 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) B0 a) unmixed b) mixed No wrong- flavor decays Max Baak

  5. BaBar Detector 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

  6. 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

  7. Analysis Technique 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 gbctB@ 260 mm bg = 0.55 Dt @Dz/gbc Determine flavor of other B meson BTAG (“tagging”) Fully reconstruct B mesonin state J/Y K*0 or J/Y K*0 Reconstruct vertex of BTAG and compute proper time difference Dt Max Baak

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

  9. Data Sample [1999-2002]: 82 fb-1 on U(4s) Resonance 3s cut on DE applied signal region E [MeV] ‘tight’ kaon selection mES [GeV/c2] Max Baak

  10. Likelihood Fit • Combined unbinned maximum likelihood fit to Dt spectraof B-flavor and J/Y K*0 and J/Y K*0 samples. • Analysis performed blind. • All Dt parameters extracted from data • Correct estimate of the error and correlations 48 total free parameters 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 Max Baak

  11. K- swapping WARNING! Fake wrong-flavor decays!Need to minimize this effect mixed up on wrec occasions (assuming C, C and S, S are of equal size) Determined using MC • To lowest order sine terms not affected, but cosine terms are. • 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 % • Effect of K- swapping on time-dependent decay distributions? Max Baak

  12. 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 c) asymmetry Asymmetry See my next talk! t (ps) Max Baak

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

  14. Backup Slides Max Baak

  15. 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

  16. 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 The errors on C,S,C,S scale with quality Q Max Baak

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