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Measurement of the bb Production Cross Section in Proton-Nucleus Collisions at Hera-B

Measurement of the bb Production Cross Section in Proton-Nucleus Collisions at Hera-B. P. Kreuzer University of California, Los Angeles For the Hera-B Collaboration.  Motivations  The HERA-B spectrometer and trigger (Y2K)  The Measurement: b  J/(l + l - ) + X

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Measurement of the bb Production Cross Section in Proton-Nucleus Collisions at Hera-B

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  1. Measurement of the bb Production Cross Section in Proton-Nucleus Collisions at Hera-B P. Kreuzer University of California, Los Angeles For the Hera-B Collaboration  Motivations The HERA-B spectrometer and trigger (Y2K) The Measurement: b  J/(l+l-) + X Comparison with Data & QCD Predictions Conclusions ICHEP 2002 Conference Amsterdam, July 27 2002 (hep-ex/0205106 + submit. EPJ C) P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  2. Motivations for a bb cross section measurement at Hera-B 12 (bb ) 70 nb/nucl. at 920 GeV/c (Hera-B) A test for QCD Predictions:  Recent improvements but still large uncertainties ! Fixed Target Data:  Hera-B can extend the experimental panorama by covering both bJ/( e  ) and bJ/(  ) & the non-exploited negative xF region ( ) P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  3. Carbon Titanium The Hera-B Detector (920 GeV p-N interactions) Y2K J/-coverage: -0.25 < xF < 0.15 (now -0.4<xF<0.3) P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  4. The Hera-B Di-lepton Trigger (Y2K) Pretrigger(5 MHz) E_t cut for e, hit coinc.for  Level I(~150 KHz) 2 leptons (ee,) requirement (no tracking ! ) Level II(~12 KHz) 2 tracks in Main Tracker and Vertex Detector (Farms of 240+100 PCs, ~20 Hz output) 9.0 105 di-e &4.5 105 di- events P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  5. The measurement steps 1. Select prompt J/ 2. Select bJ/ Detached Vertex selection Efficiency Relative detection Efficiency 3. Normalize to (pN J/X) Minimize systematic errors & Avoid luminosity dependence using E789/E771g[-0.25 < xF < 0.15] P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  6. Prompt J/ selection Reconstruction based on Trigger tracks + Vertex + Particle ID Electron Channel: Muon Channel: nP= 5710380st280sys nP= 288060 P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  7. Total (prompt) J/ signal Detached b J/ signal upstream | downstream l+ l+ J/ z l- J/ B X IW l- Isolating the b signal (z)  < gct >B (600 mm)(8000 mm) Dz Iw P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  8. Downstream Prompt region Upstream Detached b selection (e channel) Main Bkgd sources: * bb -> (e+ +X)(e-+X) * combinatorial * < 0.2 prompt J/y J/y peak P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  9. Invariant Mass fit Electron channel: Unbinned Likelihood Fit: - Sig. shape from MC, - BKG shape data/MC e+e- invariant mass ( GeV/c2 ) e+e- invariant mass ( GeV/c2 ) Muon channel: Unbinned Likelihood Fit: - Sig. shape from data, - BKG shape from data P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam D(bb ) = nb/nucl (-0.25 < xF < 0.15)

  10. Systematic Uncertainties P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  11. Hera-B compared to other data/theory Hera-B Y2K @ 920 GeV: TOT(bb ) = nb/nucl (92% bJ/in our xF range) The result shows good agreement with recent calculations beyond NLO R. Boncianiet al. (2002), NLO+NLL with latest MRST PDF Nucl.Phys.B529 (1998) N. Kidonakis et al. (2001), NLO+NNLL Phys.Rev D64 (2001) 114001-1 P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  12. Conclusions • B  J/ X  l+l-X observed at Hera-B • Result: • Good compatibility with recent QCD calculations • Outlook 2002/3: O(1000) higher statistics ! • Baseline Physics program - (bb ): expected error 15% (systematic limited) - Charmonium production (J/,y ‘,c ), Atomic number dependence c P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  13. Detector characteristics (I) • Large acceptance: 15-220 mrad in x (bending plane), 15-160 mrad in y (vertical plane)  Target – up to 8 wires inserted into the halo of 920 GeV proton beam (C, Ti) • VDS – Vertex Detector System. Dilepton vertex resolutions: sz  600 mm, sx,y 70 mm • Dipole Magnet- field integral 2.13 Tm • OTR – Outer Tracker. Honeycomb drift cells; wire pitch 5/10 mm; spatial hit resolution 350 mm; Backward hemisfere in CM (negative xF) World largerst honeycomb tracker: 1000 modules, 115000 channels • ITR – Inner Tracker: MicroStrip Gas Chambers, pitch 100 mm, resolution 100 mm; Forward hemisfere in CM (positive xF) World largerst (gas) micro pattern tracker P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  14. Detector characteristics (II) • RICH – Ring Imaging Cherenkov Hodoscope C4F10 radiator gas, 2 planes of PMT 4s separation: e/p p [3.4, 15] GeV/c, p/K p  [12,54] GeV/c • ECAL – Electromagnetic CALorimeter – Sandwich sampling calorimeter (“Shashlik”); Pb and W as converter; 3 regions • MUON detector – 4 tracking stations; Gas pixel chambers, Proportional tube chambers, some with segmented cathodes • DAQ system – High bandwidth, high trigger and logging rates • TRIGGER. - Pretriggers on ECAL & MUON seeds - FLT hardware based on ITR/OTR - SLT software trigger; Tracking+Vertexing; linux farm with 240 nodes  Event reconstruction; on-line, linux farm with 200 nodes P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  15. E866 : 0.955  0.005 E789 + E771 : 356  7  25 nb/nucleon The cross section normalization [-0.25<xF<0.15] Relative detection efficiencies Efficiency of detected vertex selection Number of observed bJ/y and prompt J/y P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  16. Prompt J/: Particle ID / Kinem. PID: E/P + bremsstrahlung Electron Channel: Preliminary! BR=0.340.020.02 PID:  likelihoods from MUON and RICH detectors Muon Channel: P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  17. Optimization procedure: Detached b  J/y cuts Electron Channel Cuts: - z > 0.5cm - e Imp. Param. wire Iw > 200 m , or - Min. dist. @ ZW to any other track > 250 m Muon Channel Cuts: - z > 7.5z - Imp. Param. to wireIw >45m -  “ “ to primary vtx Ip> 160m P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  18. Bkg Bkg Bkg MC =0.810.03 cm RD =1.000.30 cm BKG=0.360.13 cm Systematic checks (e-channel DECAY LENGTH LIKELIHOOD FIT: Different bkg optimization: Downstream Entries / 100 MeV/c2 Dz (cm) Upstream e+e- invariant mass ( GeV/c2 ) P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Mass (ee) (GeV/c2)

  19. e-channel  D(bb ) = nb/N -channel  D(bb ) = nb/N (bb) Determination Simultaneous fit to e+e- & +- (in Hera-B acceptance): Extrapolation to the full xF range: TOT(bb ) = nb/nucleon P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  20. J/y from b decays kinematics 92% of J/y are produced in our xF range P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  21. Based on HQ cross section calculation at NLO+NLL by • M. Mangano, P. Nason and G. Ridolfi, Nucl. Phys. B373 (92) 295 • Latest MRST parton distribution functions (NNLL) for nucleons • Intrinsic kT of interacting partons is gaussian-distributed • with <kT2> = 0.5 GeV2 • b quarks fragmentation given by a Peterson function (e = 0.006) • The b-hadron decays to J/y is controlled by Pythia b production model For the xF and pT distributions of J/y from b decays, we need a model of the b quark production and hadronization Our b production & decay model: 92% of J/y from b decays are produced in our xF range P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  22. Changing PDFs from MRST to CTEQ b quark mass from 4.5 to 5.0 GeV/c2 QCD renormalization scale m from 0.5 mo to 2 mo Fragmentation functions Peterson form with e from 0.002 to 0.008 Kartvelishvili form with ab from 12.4 to 15.0 <kT2> from 0.125 to 2.0 GeV2 Fraction of b-baryons produced in the b-hadronization process from 0 to 12% ±1.5% ±1% ±2% ±3% ±1% ±2% b production model systematics Default model: MRST PDF, Peterson FF e=0.006 Studied variations: Sys cont. to s(bb ) Total: ±5% P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

  23. Essential Bibliography P.Mangano et al., Nucl. Phys. B373 (92) 295 P.NASON, QCD at High Energy, Proc. Of the XX Int. Symp. on Lepton and Photon Interactions at High Energies, hep-ph/0111024 P.NASON et al., Adv. Ser. Direct. High Energy Phys. 15(1998), 609 N. Kidonakis et al., Phys.Rev. D64 (2001) 114001-1 R. Bonciani et al., Nucl.Phys.B529 (1998) 424 T.Alexopoulos et al., Phys.Rev.Lett.82 (1999) 41 D.M.Jansen et al., Phys.Rev.Lett.74 (1995)3118 M.H. Schub et al., Phys.Rev.Lett. D52 (1995) 1307 P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam

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