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Suppressed Decays of B s Mesons

Suppressed Decays of B s Mesons

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Suppressed Decays of B s Mesons

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  1. Suppressed Decays of Bs Mesons Olga Norniella UIUC On behalf of the CDF collaboration ICHEP, July 22-28, 2010

  2. d d K*0 Vcs s s s K*0 B0 Vcd d c Bs W+ J/ c b c W+ J/ c b Motivation • Most of the Bs suppressed decays have not been observed yet •  Bs J/K*(892) , Bs  J/KS, BsJ/f0, … • Only difference is the Vcd contribution vs the Vcs • All of these modes have the possibility of providing further information on lifetime difference and CP asymmetries in Bs decays. •  Bs  J/ KS is a CP eigenstate, measurement of the lifetime • in this  mode is a direct measurement of Bs (Heavy) •  Bs J/ KS can be used to extract the angle  of unitary triangle • (R. Fleischer, Eur.Phys. J.C10:299-306,1999) •  Bs  J/ K* contains an admixture of CP final states, an angular • analysis can be done to extract sin(2s ) (complementary to Bs J/)

  3. B production at Tevatron • Tevatron is a source of all B-hadron species: Bd, Bu, Bc, Bsand Λb •  At CDF the σb= 29.4 ±0.6 ±6.2 μb (|η| < 1) • Some of them are not produced at the B-factories •  Bs, Bc, B**, Bs**, b, b, b,.. • More decays are accessible thanks to the amount of luminosity collected •  CDF has more than 7.5 fb-1 on tape • CDF has excellent mass resolution, vertex resolution and trigger system for flavor physics

  4. Br(BsJ/ h) N(BsJ/ h) fd = * * Arel Br(B0 J/ h) N(B0J/ h) fs Measurements • Branching ratio measurement • Analysis strategy •  Reconstruct BJ/ K* and BJ/ KS from a large sample of di-muon • (J/  + - decays ) •  Apply specific optimization cuts to remove backgrounds •  Likelihood fit to the invariant mass distribution to get the ratio of yields where h  KS or K* Branching ratio of Bs relative to B0 Fragmentation fractions (from CDF result) Relative Acceptance (from MC) Yield of Bs and B0 events (from data)

  5. J/  J/     K KS c ~ 430 m c ~ 460 m c ~ 2.5 cm B  B K*  - - p p p p Reconstruction • Data from di-muon triggers •  J/ triggers , mainly looking for:  two low pT muons : pT>1.5 GeV/c2  two muons have opposite charge   (between 2 muons) <120 degrees • Reconstruction

  6. BJ/ KS Analysis • Advantage: KS has a long life (c~ 2.5 cm) and • is a narrow resonance • easy to get a pure KS sample • Disadvantage: expecting small Bs signal • important to suppress combinatorial • background contribution • A Neural Network is used to discriminate between signal and combinatorial background  22 different kinematic variables pT , d0, c, helicity angles, mass,..  Trained using Bs MC for Signal and data sideband for BKG Optimization procedure geared towards maximizing efficiency/(1.5 + B)

  7. Fit contributions for BJ/ KS • The invariant mass distribution is fitted with binned Likelihood Signal B0 and Bs decays Background  Partial reconstruction multibody decays where , K or  missing  Combinatorial background  bJ/ contribution Negligible after specific cut 3 Gaussian template extracted from B0 simulation Use m(Bs)-m(B0) for extrapolation Argus function convoluted with a Gaussian Exponential function

  8. Br(BsJ/ KS) N(BsJ/ KS) fd = * * Arel Br(B0 J/ KS) N(B0J/ KS) fs First observation of BsJ/ KS !!! N (B0) = 5954  79 ; N (Bs) = 64  14 ; N(Bs)/N(B0) = 0.0108  0.0019 • The p- value for Bs signal compared to the background hypothesis p-value = 3.85 10-13 or 7.2

  9. BJ/ K* Analysis • Disadvantage: K*is not a long-lived particle and is a wider resonance •  more background contributions to deal with • Advantage: expecting bigger Bs signal •  not necessary sophisticated tools to remove combinatorial background • Rectangular cuts optimization to maximize efficiency/(1.5 + B) • pT (B) >6 GeV/c • Flight distance Lxy (B) >300 m • Impact parameter dxy (B) < 50 m • Fit vertex Probability (B) >0.01 • pT (K+, -) >1.5 GeV/c

  10. Fit contributions for BJ/ K* • Same contributions than in the BJ/ KS analysis plus additional backgrounds Signal B0 and Bs decays • Background •  Partial reconstruction • Combinatorial background • BsJ/ contribution • BsJ/f0 contribution last one is negligible BsJ/  modeled by 2 Gaussians template Extracted from simulation but contribution constrained using data

  11. First observation of Bs J/ K* !!! N (B0) = 9530  110 ; N (Bs) = 151  25 ; N(Bs)/N(B0) = 0.0159  0.0022 • The p- value for Bs signal compared to the background hypothesis p-value = 8.9 10-16 or 8

  12. Systematic uncertainties Difference sources of systematic uncertainties have been considered B J/K* N(Bs)/N(B0) = 0.0159  0.0022 (stat.)  0.0050 (sys.) B  J/KS N(Bs)/N(B0) = 0.0108  0.0019 (stat.)  0.0010 (sys.)

  13. Br(BsJ/ h) N(BsJ/ h) fd = * * Arel Br(B0 J/ h) N(B0J/ h) fs Relative Acceptance Calculation • Relative Acceptance evaluation using simulation • Systematic uncertainties Arel = 1.057  0.010 (stat)  0.263(sys.) B J/K* Arel = 1.012  0.010 (stat)  0.042 (sys.) B  J/KS

  14. Br(BsJ/ h) N(BsJ/ h) fd = * * Arel Br(B0 J/ h) N(B0J/ h) fs Recap of all numbers where h  KS or K* • N(BsJ/ h)/N(B0 J/ h) : • fs/fd from CDF( Phys.Rev. D77, 072003 (2008)) combined with new PDG value for Br(Ds) 0.269  0.033 • Arel : 1.057  0.010 (stat)  0.263 (sys) 1.012  0.010 (stat)  0.042 (sys) 0.0159  0.0022 (stat.)  0.0050 (sys.) B J/K* 0.0108  0.0019 (stat.)  0.0010 (sys.) B  J/KS

  15. Branching Ratios Measurement Br(BsJ/ K*) = 0.062  0.009 (stat.)  0.025 (sys.)  0.008 (frag.) Br(B0 J/ K*) Br(BsJ/ KS) = 0.041  0.007 (stat.)  0.004 (sys.)  0.005 (frag.) Br(B0 J/ KS) • Using PDG values: Br(B0 J/ K*) = (1.33  0.06) * 10-3 Br(B0 J/ K0) = (8.71  0.32) * 10-4 Br(BsJ/ K*) = (8.3  1.2 (stat.)  3.3 (sys.)  1.0 (frag.)  0.4 (PDG))*10-5 Br(BsJ/ K0) = (3.5  0.6 (stat.)  0.4 (sys.)  0.4 (frag.)  0.1 (PDG))*10-5

  16. Summary • Two new Cabibbo and color suppressed decays of Bs mesons have been observed by CDF : BsJ/K*and BsJ/KS • significance greater than 7 • A preliminary measurement of their Branching Ratios relative to the B0 decays have been done •  •  • These modes are going to provide further • information on lifetime difference and • CP asymmetries in Bs decays • CDF is collecting a lot of more events • every hour…so stay tuned because more • decays are coming soon For K*: 0.062  0.009 (stat.)  0.025 (sys.)  0.008 (frag.) For KS: 0.041  0.007 (stat.)  0.004 (sys.)  0.005 (frag.)

  17. Back up

  18. Signals and Background Contributions • Both analysis have some common Background contributions and signals • Signals (B0 and Bs) templates are obtained from simulation (B0 MC) • The same template for B0 and Bs taking into account m=86.8 MeV/c2 • Combinatorial background • Exponential function • (Float in the final fit) • Partial reconstruction contribution for 5 bodies B0 decays • Argus function • m0 cut off ~5.14 • mass (B0)-mass (0)

  19. More Backgrounds • BJ/ K* analysis has more backgrounds that need to be modeled • Bs J/ Templates are obtained from simulation: 2 Gaussians (Fixed in the final fit)  Contribution constrained using Bs J/ data sample • Partial reconstruction contribution for 5 bodies Bs decays •  modeled with another ARGUS function •  m0 cut off at 5.22 GeV/c2 : mass (Bs)-mass(0) •  exponential constant constrained to be identical to the previous one • Background studied but considered negligible contributions • In BJ/ K* analysis: B J/ f0 • In BJ/ Ks analysis: bJ/