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Rare B and D Decays at CDF

Sinéad M. Farrington University of Oxford for the CDF Collaboration HQL 15 th October 2010. Rare B and D Decays at CDF. D edicated rare B and D dimuon triggers Will show B → mm , B → mm h, D → mm Using all muon chambers to | h | 1.1 Tracking capability leads to good mass resolution.

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Rare B and D Decays at CDF

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  1. Sinéad M. Farrington University of Oxford for the CDF Collaboration HQL 15th October 2010 Rare B and D Decays at CDF

  2. Dedicated rare B and D dimuon triggers • Will show B→mm, B→ mmh, D→mm • Using all muon chambers to |h|1.1 • Tracking capability leads to good mass resolution CDF Central Muon Extension (0.6< |h| < 1.0) Central Muon Chambers (|h| < 0.6) 2

  3. Bd,smm 0 3

  4. In Standard Model FCNC decay B  mm heavily suppressed • Standard Model predicts B mm in the Standard Model A. Buras Phys. Lett. B 566,115 • Bd mm further suppressed by CKM coupling (Vtd/Vts)2 • Both are below sensitivity of Tevatron experiments • SUSY scenarios (MSSM,RPV,mSUGRA) boost the BR by up to 100x Observe no events  set limits on new physics Observe events  clear evidence for new physics 4

  5. The Challenge pp collider: trigger on dimuons search region Mass resolution: separate Bd, Bs s(Mmm)~24MeV • Large combinatorial background • Key elements are • select discriminating variables • determine efficiencies • estimate background 5

  6. Methodology • Vertex muon pairs in Bd/Bs mass windows • Unbiased optimisation, signal region blind • Aim to measure BR or set limit: • Reconstruct normalisation mode (B+J/y K+) • Construct Neural Net to select B signal and suppress dimuon background • Measure remaining background • Measure the acceptance and efficiency ratios 6

  7. B mm Neural Net Variables • Proper decay length (l) • Pointing (Da) |fB – fvtx| • Isolation (Iso) 7

  8. Neural Net • Train NN using signal MC and • data sidebands for background • Rather than making a cut on NN value: • Combine results from several • bins of NN output value • Optimise choice of bins by • maximising expected limit on • Bs decay 8

  9. Backgrounds Combinatorial background obtained by extrapolating sidebands to signal region Check this method in same sign dimuon and negative lifetime control regions B→hh backgrounds (h=p/K) evaluated using MC and fake rates measured in data

  10. 3.7 fb-1 Results BR(Bsmm) < 4.3×10-8 @ 95% CL 3.6 90 BR(Bdmm) < 7.6×10-9 @ 95% CL 6.0 90 • World best limits • Will have ~x2 this • dataset by end of 2011 CDF public note 9892 10

  11. s s s s s s b b • B Rare Decays Bm+m- h : • B+ mm K+ • B0mm K* • Bsmmf • FCNC b  sg* • Penguin or box processes in the Standard Model: • Predicted BR(Bsmmf)=1.61x10-6 Rare B Decays: Bd,sm+m-K+/K*/f PRL103:171801,2009 PRD 79:031102,2009 PRD 79:011104,2009 observed at Babar,Belle,CDF not seen until now m- m+ m- m+ hep-ph/0303246 11

  12. Standard Model • Sensitive to Wilson coefficients: can be affected by new physics • Forward backward asymmetry in B0 mm K* decay • Predictions exist for several new physics scenarios Forward Backward Asymmetry • θ = the angle of the lepton with respect to B direction in the dilepton rest frame • s = q2/mB2 C7=-C7SM C9C10=-C9C10SM AFB=-AFBSM

  13. Forward backward asymmetry in B0 mm K* decay • Predictions exist for several new physics scenarios Forward Backward Asymmetry Babar Belle C7=-C7SM C9C10=-C9C10SM AFB=-AFBSM arXiv:0904.0770 arXiv:0804.4412 13

  14. (J/)   B h • Rare decays: B →mm K+/K*0/f • Simple topology: • Vertex two muons with hadron (h=K+/K*0/f) • Require J/y mass window clean normalisation mode • Reject J/y, y’ mass window rare decays sample • Measure the relative BR: Methodology Relative efficiency from MC 14

  15. Candidate invariant mass distributions Results: mass distributions Number of sigma statistical significance: 9.7 8.5 6.3 15

  16. 4.4 fb-1 • Forward backward asymmetry • Unbinned likelihood fit • Angular acceptances taken from MC Results: Asymmetry CDF public note 10047 Asymmetry as function of q2=mass(mm) 2 Expect zero asymmetry in B+ Compatible and competitive with the B factories 16

  17. D mm 17

  18. Highly suppressed decay • Predicted BR ~ 4x10-13 • Can be enhanced in R parity violating SUSY by up to 7 orders of magnitude D→mm Rare Decay 18

  19. Measure branching ratio relative to control channel • Measure muon fake rates in tagged D* samples • Main background is from B decays with cascade D decays D→mm Rare Decay 19

  20. 0.36 fb-1 • Measure branching ratio relative to control channel D→mm Results CDF public note 9226 20

  21. Bd,sm+m-, D m+m- are a powerful probe of new physics • Could give first hint of new physics at the Tevatron • Impacting new physics scenarios’ phase space • B→mm h first observation in Bs mode, first measurement of asymmetry in these decays at hadron collider • Data sample will be x2 by end of 2011, many more results to come! Summary SO(10) Constrained MSSM hep-ph/0507233 Phys. Lett B624, 47, 2005 21

  22. Back-up 22

  23. Gathered ~7.6 fb-1 to date CDF 23

  24. 1)First observation in Bs channel 2) Tests of Standard Model • branching ratios • kinematic distributions (with enough statistics) • Effective field theory for b  s (Operator Product Expansion) • Sensitive to Wilson coefficients, Ci • calculable for many models (e.g. SUSY, technicolor) • Decay amplitude: C9 • Dilepton mass distribution: C7, C9 • Forward-backward asymmetry: C10 Motivations for B→mmh Search 24

  25. Two ways to search for new physics: • direct searches – seek e.g. Supersymmetric particles • indirect searches – test for deviations from Standard Model predictions e.g. branching ratios • In the absence of evidence for new physics • set limits on model parameters Searching for New Physics l+ Z* c02 q l- BR(Bmm)<1x10-7 q c01 q c+ l+ W+ n Trileptons 25

  26. Expected Background • Extrapolate from data sidebands to obtain expected events • Scale by the expected rejection from the likelihood ratio cut • Also include contributions from charmless B decays • Bhh (h=K/p) (use measured fake rates) 26

  27. now Limits on BR(Bd,smm) • BR(Bsmm) < 1.0×10-7 @ 90% CL • < 8.0×10-8 @ 95% CL • BR(Bdmm) < 3.0×10-8 @ 90% CL • < 2.3×10-8 @ 95% CL • These are currently world best limits • The future: • Need to reoptimise after 1fb-1 for • best results • Assume linear background • scaling 27

  28. m b RPV SUSY ~ n l’i23 l i22 m s • SUSY could enhance BR by orders of magnitude • MSSM: BR(B  mm)  tan6b • may be 100x Standard Model B mm in New Physics Models • R-parity violating SUSY: tree level diagram via sneutrino • observe decay for low tan b • mSUGRA: B  mm search complements direct SUSY searches • Low tan b observation of trilepton events • High tan b observation of B  mm • Or something else! A. Dedes et al, hep-ph/0207026 28

  29. Expected Background • Tested background prediction in several control regions and find good agreement OS-: opposite sign muon, negative lifetime SS+: same sign muon, positive lifetime SS-: same sign muon, negative lifetime FM+: fake muon, positive lifetime 29

  30. Likelihood p.d.f.s Input p.d.f.s: Isolation Pointing angle Ct significance New plots*** 30

  31. six dedicated rare B triggers • using all muon chambers to |h|1.1 • Tracking capability leads to good mass resolution • Use two types of muon pairs: central-central central-extension CDF Central Muon Extension (0.6< |h| < 1.0) Central Muon Chambers (|h| < 0.6) 31

  32. B Rare Decays • B+ mm K+ • B0mm K* • Bsmmf • Lbmm L • FCNC b  sg* • Penguin or box processes in the Standard Model: • Rare processes: Latest Belle measurement Bd,smm K+/K*/f hep-ex/0109026, hep-ex/0308042, hep-ex/0503044 observed at Babar, Belle m m m m x10-7 32

  33. 1) Would be first observations in Bs and Lb channels 2) Tests of Standard Model • branching ratios • kinematic distributions (with enough statistics) • Effective field theory for b  s (Operator Product Expansion) • Rare decay channels are sensitive to Wilson coefficients which are calculable for many models (several new physics scenarios e.g. SUSY, technicolor) • Decay amplitude: C9 • Dilepton mass distribution: C7, C9 • Forward-backward asymmetry: C10 Motivations 33

  34. Dedicated rare B triggers • in total six Level 3 paths • Two muons + other cuts • using all chambers to |h|1.1 • Use two types of dimuons: CMU-CMU CMU-CMX • Additional cuts in some triggers: • Spt(m)>5 GeV • Lxy>100mm • mass(m m)<6 GeV • mass(m m)>2.7 GeV Samples (CDF) 34

  35. Signal and Side-band Regions • Use events from same triggers for • B+ and Bs(d) mm reconstruction. • Search region: • - 5.169 < Mmm < 5.469 GeV • - Signal region not used in • optimization procedure s(Mmm)~24MeV Monte Carlo Search region • Sideband regions: • - 500MeV on either side of search region • - For background estimate and analysis • optimization.

  36. MC Samples • Pythia MC • Tune A • default cdfSim tcl • realistic silicon and beamline • pT(B) from Mary Bishai • pT(b)>3 GeV && |y(b)|<1.5 • Bsm+m- • (signal efficiencies) • B+JK+m+m-K+ (nrmlztn efncy and xchks) • B+Jp+m+m-p+ (nrmlztn correction)

  37. SO(10) Unification Model R. Dermisek et al., hep-ph/0304101 • tan(b)~50 constrained by unification • of Yukawa coupling • All previously allowed regions (white) • are excluded by this new measurement • Unification valid for small M1/2 • (~500GeV) • New Br(Bsmm) limit strongly • disfavors this solution for • mA= 500 GeV h2>0.13 mh<111GeV m+<104GeV Excluded by this new result Red regions are excluded by either theory or experiments Green region is the WMAP preferred region Blue dashed line is the Br(Bsmm) contour Light blue region excluded by old Bsmm analysis

  38. Method: Likelihood Variable Choice Prob(l) = probability of Bsmm yields l>lobs (ie. the integral of the cumulative distribution) Prob(l) = exp(-l/438 mm) • yields flat distribution • reduces sensitivity to • MC modeling inaccuracies • (e.g. L00, SVX-z)

  39. Step 4: Compute Acceptance and Efficiencies • Most efficiencies are determined directly from data using inclusive • J/ymm events. The rest are taken from Pythia MC. • a(B+/Bs)= 0.297 +/- 0.008 (CMU-CMU) • = 0.191 +/- 0.006 (CMU-CMX) • eLH(Bs): ranges from 70% for LH>0.9 to • 40% for LH>0.99 • etrig(B+/Bs) = 0.9997 +/- 0.0016 (CMU-CMU) • = 0.9986 +/- 0.0014 (CMU-CMX) Red = From MC Green = From Data Blue = combination of MC and Data • ereco-mm(B+/Bs) = 1.00 +/- 0.03 (CMU-CMU/X) • evtx(B+/Bs) = 0.986 +/- 0.013 (CMU-CMU/X) • ereco-K(B+) = 0.938 +/- 0.016 (CMU-CMU/X)

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