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1 Sinéad M. Farrington University of Oxford for the CDF Collaboration HQL 15 th October 2010 Rare B and D Decays at CDF
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2 Dedicated rare B and D dimuon triggers Will show B→ , B→ h, D→ Using all muon chambers to | | 1.1 Tracking capability leads to good mass resolution 2 CDF Central Muon Extension (0.6< | | < 1.0) Central Muon Chambers (| | < 0.6)
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3 3 B d,s 0
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4 4 B in the Standard Model In Standard Model FCNC decay B heavily suppressed Standard Model predicts A. Buras Phys. Lett. B 566,115 B d further suppressed by CKM coupling (V td /V ts ) 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
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5 5 The Challenge Large combinatorial background Key elements are select discriminating variables determine efficiencies estimate background search region pp collider: trigger on dimuons )~24MeV Mass resolution: separate B d, B s
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6 Vertex muon pairs in B d /B s mass windows Unbiased optimisation, signal region blind Aim to measure BR or set limit: Reconstruct normalisation mode (B + J/ K + ) Construct Neural Net to select B signal and suppress dimuon background Measure remaining background Measure the acceptance and efficiency ratios 6 Methodology
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7 Proper decay length ( ) Pointing ( ) | B – vtx | Isolation (Iso) 7 B Neural Net Variables
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8 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 B s decay
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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= /K) evaluated using MC and fake rates measured in data
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10 Results BR(B s ) < 4.3×10 -8 @ 95% CL 3.6 90 BR(B d ) < 7.6×10 -9 @ 95% CL 6.0 90 ChannelExpectedObserved B s central4 ±13 B s extended2.08 ± 0.784 B d central5.3± 15 B d extended2.78 ± 0.783 3.7 fb -1 World best limits Will have ~x2 this dataset by end of 2011 CDF public note 9892
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11 B Rare Decays B h : B + K + B 0 K * B s FCNC b s * Penguin or box processes in the Standard Model: Predicted BR(B s )=1.61x10 -6 11 Rare B Decays: B d,s K + /K*/ observed at Babar,Belle,CDF PRL103:171801,2009 PRD 79:031102,2009 PRD 79:011104,2009 not seen until now hep-ph/0303246 s s s b s b s s
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12 Sensitive to Wilson coefficients: can be affected by new physics Forward backward asymmetry in B 0 K* decay Predictions exist for several new physics scenarios Forward Backward Asymmetry Standard Model θ = the angle of the lepton with respect to B direction in the dilepton rest frame s = q 2 /m B 2 C 7 =-C 7 SM C 9 C 10 =-C 9 C 10 SM A FB =-A FB SM
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13 Forward backward asymmetry in B 0 K* decay Predictions exist for several new physics scenarios 13 Forward Backward Asymmetry arXiv:0904.0770 arXiv:0804.4412 BabarBelle C 7 =-C 7 SM C 9 C 10 =-C 9 C 10 SM A FB =-A FB SM
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14 Rare decays: B → K + /K *0 / Simple topology: Vertex two muons with hadron (h=K + /K *0 / ) Require J/ mass window clean normalisation mode Reject J/ , ’ mass window rare decays sample Measure the relative BR: Methodology 14 (J/ ) h B Relative efficiency from MC
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15 Candidate invariant mass distributions 15 Results: mass distributions Number of sigma statistical significance: 9.7 8.5 6.3
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16 Forward backward asymmetry Unbinned likelihood fit Angular acceptances taken from MC 16 Results: Asymmetry Asymmetry as function of q 2 =mass( ) 2 Expect zero asymmetry in B + Compatible and competitive with the B factories 4.4 fb -1 CDF public note 10047
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17 D
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18 Highly suppressed decay Predicted BR ~ 4x10 -13 Can be enhanced in R parity violating SUSY by up to 7 orders of magnitude 18 D→ Rare Decay
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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 19 D→ Rare Decay
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20 Measure branching ratio relative to control channel 20 D→ Results 0.36 fb -1 CDF public note 9226
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21 Summary B d,s , D are a powerful probe of new physics Could give first hint of new physics at the Tevatron Impacting new physics scenarios’ phase space B→ h first observation in B s 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! SO(10) hep-ph/0507233 Phys. Lett B624, 47, 2005 Constrained MSSM
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22 Back-up
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23 Gathered ~7.6 fb -1 to date 23 CDF
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24 Motivations for B→ h Search 1) First observation in B s 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, C i calculable for many models (e.g. SUSY, technicolor) Decay amplitude: C 9 Dilepton mass distribution: C 7, C 9 Forward-backward asymmetry: C 10
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25 Searching for New Physics 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 BR(B 1x10 -7 Trileptons l+l+ l-l- l+l+ q q Z* W+W+ q
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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/ ) (use measured fake rates)
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27 now 27 Limits on BR(B d,s ) BR(B s ) < 1.0×10 -7 @ 90% CL < 8.0×10 -8 @ 95% CL BR(B d ) < 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
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28 B in New Physics Models SUSY could enhance BR by orders of magnitude MSSM: BR(B ) tan 6 may be 100x Standard Model R-parity violating SUSY: tree level diagram via sneutrino observe decay for low tan mSUGRA: B search complements direct SUSY searches Low tan observation of trilepton events High tan observation of B Or something else! ’ i23 i22 b s RPV SUSY A. Dedes et al, hep-ph/0207026
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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
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30 Likelihood p.d.f.s Input p.d.f.s: Isolation Pointing angle Ct significance New plots***
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31 six dedicated rare B triggers using all muon chambers to | | 1.1 Tracking capability leads to good mass resolution Use two types of muon pairs: central-central central-extension 31 CDF Central Muon Extension (0.6< | | < 1.0) Central Muon Chambers (| | < 0.6)
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32 B d,s K + /K*/ B Rare Decays B + K + B 0 B s b FCNC b s * Penguin or box processes in the Standard Model: Rare processes: Latest Belle measurement observed at Babar, Belle hep-ex/0109026, hep-ex/0308042, hep-ex/0503044 x10 -7
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33 Motivations 1) Would be first observations in B s and b 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: C 9 Dilepton mass distribution: C 7, C 9 Forward-backward asymmetry: C 10
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34 Samples (CDF) Dedicated rare B triggers in total six Level 3 paths Two muons + other cuts using all chambers to | | 1.1 Use two types of dimuons: CMU-CMU CMU-CMX Additional cuts in some triggers: p t ( )>5 GeV L xy >100 m mass( )<6 GeV mass( )>2.7 GeV
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35 Signal and Side-band Regions Use events from same triggers for B + and Bs(d) reconstruction. Search region: - 5.169 < M < 5.469 GeV - Signal region not used in optimization procedure Sideband regions: - 500MeV on either side of search region - For background estimate and analysis optimization. Search region Monte Carlo )~24MeV
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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 – B s (signal efficiencies) – B+ JK+ K+ (nrmlztn efncy and xchks) – B+ J + (nrmlztn correction)
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37 R. Dermisek et al., hep-ph/0304101 SO(10) Unification Model tan( )~50 constrained by unification of Yukawa coupling All previously allowed regions (white) are excluded by this new measurement Unification valid for small M 1/2 (~500GeV) New Br(Bs limit strongly disfavors this solution for m A = 500 GeV Red regions are excluded by either theory or experiments Green region is the WMAP preferred region Blue dashed line is the Br(Bs ) contour Light blue region excluded by old Bs analysis h 2 >0.13 m + <104GeV m h <111GeV Excluded by this new result
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38 Method: Likelihood Variable Choice Prob( ) = probability of B s yields > obs (ie. the integral of the cumulative distribution) Prob( ) = exp(- /438 m) yields flat distribution reduces sensitivity to MC modeling inaccuracies (e.g. L00, SVX-z)
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39 Step 4: Compute Acceptance and Efficiencies Most efficiencies are determined directly from data using inclusive J/ events. The rest are taken from Pythia MC. (B+/Bs) = 0.297 +/- 0.008 (CMU-CMU) = 0.191 +/- 0.006 (CMU-CMX) LH (Bs): ranges from 70% for LH>0.9 to 40% for LH>0.99 trig (B+/Bs) = 0.9997 +/- 0.0016 (CMU-CMU) = 0.9986 +/- 0.0014 (CMU-CMX) reco- (B+/Bs) = 1.00 +/- 0.03 (CMU-CMU/X) vtx (B+/Bs) = 0.986 +/- 0.013 (CMU-CMU/X) reco-K (B+) = 0.938 +/- 0.016 (CMU-CMU/X) Red = From MC Green = From Data Blue = combination of MC and Data
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