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Published bySylvia Snow Modified over 9 years ago
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23-09-2004M.Mevius Open and hidden beauty production in 920 GeV proton –nucleus collisions at HERA-B M.Mevius DESY
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23-09-2004M.Mevius Outline the HERA-B experiment open b production upsilon production conclusions
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23-09-2004M.Mevius The HERA-B Detector
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23-09-2004M.Mevius Data Sample Data taking is finished in 2003; analysis is in progress additional: 210 M minimum bias events dilepton trigger: pretriggers high E T ECAL clusters, MUON hits FLT: hardware trigger track finding behind magnet SLT: software trigger track finding behind magnet and in VDS vertex reconstruction online event reconstruction 150 M dilepton trigger events 300 000 J/ (>1000 per hour) 10 000 c 3 500 (2S)
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23-09-2004M.Mevius Dilepton spectra ~ 1600 Long Tracks (Vertex Detector + Tracking System) PID: likelihood, E/p Dilepton Vertex Probability > 1% J/ acceptance: -0.35 < x F < 0.15 muon channel ~ 108,000 J/ → ee σ = 64 MeV/c2 // J/ (2S) electron channelmuon channel ~ 108,000 J/ ee σ = 64 MeV/c2 // J/ (2S) electron channel ~ 177,000 J/ σ = 44 MeV/c 2 ~ 3000 (2S) ~ 1600
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23-09-2004M.Mevius open b production Theoretical uncertainties: –b quark mass 4.5 - 5 GeV –At NLO, scale ( ) dependence Previous measurements do not agree between each other
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23-09-2004M.Mevius pn bb + X b(b) B J/ + X J/ ; e + e - open b production Measurement relative to direct J/ production to minimize trigger/reconstruction uncertainties R = relative efficiency 1 B selection eff. from MC
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23-09-2004M.Mevius open b production B Selection: (30-45% Efficiency) Lepton impact to the wire Distance J/ to wire B Meson has a long life time ( ~ 9 mm at HERA-B kinematics) ~ 0.5 mm dilepton vertex resolution J/ from a B decay will be detached from primary interaction
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23-09-2004M.Mevius open b production Vertex z resolution ~ 500 μm Good agreement between data and MC simulation good separation between direct and detached J/ Cuts optimized simultaneously Background: bb and cc simultaneous semileptonic decays Combinatorial Prompt J/
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23-09-2004M.Mevius open b production C,W,Ti targets Unbinned likelihood fit preliminary 20% sys. error under investigation main contribution: Br(bb J/ X) = 2.32 0.20%
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23-09-2004M.Mevius J/ cross section E771/E789 : scaled to HERA-B cms energy (J/ )=357 ± 2 ± 36 nb/nucleon E771/E789 HERA-B measurement on min. bias data ongoing using E771/E789 result: preliminary
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23-09-2004M.Mevius upsilon production HERA-B s = 41.6 GeV E772 (A=2) E605 (A=64) Several measurements available but unclear situation at s ~ 40GeV HERA-B has good coverage in the central region of collisions ( x F ~ [-0.35,0.15]) Theoretical prediction Hadronization: Possible nuclear suppression ?
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23-09-2004M.Mevius upsilon production pA + X μ +μ- ; e+e- Measurement relative to prompt J/ –Less sensitive to systematic effects Prompt J/ cross section from E771 and E789
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23-09-2004M.Mevius upsilon production 25% W + 75 % C (targets) Mass resolution between 140 and 160 MeV/c 2 Background: Drell-Yan: shape estimated from MC (1S) / (2S) / (3S) relative production fixed to E605 results Random combinatorial: estimated from like sign pairs in data 8
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23-09-2004M.Mevius upsilon production Events Br d /dy y=0 +-+- 33 ± 73.9 ± 1.1 pb/n e+e-e+e- 31 ± 102.9 ± 1.2 pb/n both3.4 ± 0.8 pb/n Both channels are compatible Extrapolation to S = 38.8 GeV yields: Br d /dy y=0 = 2.4 ± 0.9 pb/n –compatible with E605 –(more than 1 ) below E772 and E771
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23-09-2004M.Mevius upsilon production Not used in fit Modified Craigie parameterization to include nuclear suppression (parameter ) Data compatible with no nuclear suppression: = 0.99 0.05
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23-09-2004M.Mevius HERA-B has finished data taking preliminary results: – (bb) : using: (J/ )=357±2±36 nb/nucleon – production: Conclusions
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23-09-2004M.Mevius model dependence Changing PDFs from MRST to CTEQ b quark mass from 4.5 to 5.0 GeV/c 2 QCD renormalization scale from 0.5 o to 2 o Fragmentation functions –Peterson form with from 0.002 to 0.008 –Kartvelishvili form with from 12.4 to 15.0 from 0.125 to 2.0 GeV 2 Fraction of b-baryons produced in the b-hadronization process from 0 to 12% ±1.5% ±1% ±2% ±3% ±1% ±2% Default model: MRST PDF, Peterson FF =0.006 Total: ±5% Studied variations:Sys cont. to (bb )
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23-09-2004M.Mevius 92% of J/ are produced in our x F range J/ from b decays kinematics
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