Recent Results on B Physics at D

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Recent Results onB Physics at DØ

• Heriberto Castilla
• Cinvestav-IPN, Mexico City
• Dzero Collaboration
• Les Rencontres de Physique
• De La Valle DAoste
• March 9-15, 2003 at La Thuile, Aosta Valley

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DØ B Physics Program

• B0s mixing Bs?Ds l X, Bs?Ds(n?)
• B Lifetimes
• Average B lifetime b ?J/?X
• ?b lifetime ?b?J/??0
• B0s lifetime and width B0s?J/??
• CP violation in B0d B0s
• Rare decays, cross sections
• Ingredients for a Time-dependent B Physics
  program
• Reconstruct final states
• Reconstruct proper time distribution
• Tag the flavor of the b at production

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The Run II DØ Detector
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Strategy Measure ?jet cross-section
Extract b-content using PTRel Data selection
kinematic cuts pT? gt6 GeV/c, ?? lt0.8
(Muon PT measured in muon system only) ?jet
lt 0.6 , Etcorr gt20 GeV 0.5 cone ?R(jet,?) lt
0.7
B jet Cross Section
Measured in Run1 2-3 times higher
than predictions
?jet
?
pTRel
jet

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Muon jet cross section
Lower in Jet ET so need muon and jet trigger
efficiencies
emuon 55-70
Jet Energy scale Correction 1.8 0.13
Error on Jet Energy scale
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m jet cross section
Jet reco. Eff. 100 E gt 20 GeV ? reco. Eff.
43.70.8(stat)2.2(sys)
Jet resolution dijet pT imbalance ? momentum
resolution from central tracks
Jet quality cuts applied
Data 02/27/02 05/10/02 3.4 pb-1
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B jet cross section
Fit pTrel templates to data in jet ET bins
PTrel for jets with 20 GeV lt ET lt 25 GeV
Data unsmeared using ansatz function
B fraction as a functionof Jet ET
Dominant error is due to jet energy scale
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The J/?

• ? pT gt 1.5 GeV
• J/? pT gt 3.0 GeV
• SMT hitsgt3 CFT hitsgt4

J/?s 75,013
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The J/?

• Reconstructing ?0 ? ??

• ?? ee- conversion
• J/? tracks pT gt 2 GeV
• ? tracks pT gt 1 GeV
• J/? mass window 2.8 3.3 GeV
• J/? and ? vertex constrained

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Exclusive B decays
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Average B Hadron Lifetime
( ) states (prompt) B ? J/?
J/? Sources
decay Prompt PV J/?(B)
SV
Difference
Transverse Decay Length Plot
MC
?B through ??
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Average B Hadron Lifetime

• Transverse Decay Length Plot
• Contributions
• Zero lifetime component
• Prompt J/? signal
• Combinatorial Background
• Both modeled as double Gaussians
• Parameters from J/? sidebands
• Background fraction from fit to J/? peak
• Long lived component
• B ? J/? signal
• Semileptonic Background
• Both modeled as exponentials convoluted with
  gaussians
• Background parameters and normalization
  determined from J/? sideband
• Signal parameters floated

?B 468 7(stat) 22(syst) ?m B fraction
17.30.5 Prompt fraction 82.70.6 (?) 1.561
0.024(stat)0.074(syst) ps
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Charged B Lifetime

• R G1 ? G2
• L Right ? EG (B ?J/? K0)
• P Right ? E1G1 ? E2G2

Right
Left
Signal
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Flavor tagging
Soft Muon Tag
Jet Charge Tagging

• Muon tagger
• must have ?R gt 2.0 separation from reconstructed
  B
• must have pT gt 1.9 GeV/c
• b flavor tagging
• charge of highest-pT muon in event gives
  (opposite-side) B-tag

• Jet charge tagger
• Remove daughter tracks from the reconstructed B
• Remove tracks 2D impact parameter greater than
  0.2cm
• Remove tracks with vtx_z pvtxz gt 2. Cm,
  suppress minimum bias events
• Use tracks left to calculate the jet charge Q by
  weighing on track pT
• Events with Qgt0.2 are counted as tagged, while
  the others are dropped

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B Flavor Tagging
DØ Run-II Preliminary
Soft muons
Average jet charge

• Errors only statistical
• Errors in fractions of signal, bgd events
• in mass window (from fit) are ignored

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Conclusions

• Latest Run IIa D0 B Physics results
• B-jet cross section
• B exclusive decays ( B, B0d in two different
  channels)
• Average B Lifetime
• Preliminary Charged B lifetime measurement
• Understanding Flavor Tagging
• Improvements in the short term future
• Track trigger and Silicon Trigger
• Just the beginning of an exciting DØ B Physics
  program

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Average B Hadron Lifetime
Systematic Uncertainties
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V0 Finding
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Flavor tagging