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Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions

This study analyzes the beauty production in proton-nucleus collisions using the HERA-B detector, focusing on the prompt J/ψ sample. The results show the open and hidden beauty cross sections and their agreement with previous measurements.

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Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions

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  1. Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions Hernan Wahlberg Utrecht University/NIKHEF For the HERA-B Collaboration Hernan Wahlberg, HADRON05

  2. Outline • HERA-B detector • Reference prompt J/ysample for beauty analysis • Open cross section •  ( ) production cross section • Summary Hernan Wahlberg, HADRON05

  3. HERA-B Detector (I) Hernan Wahlberg, HADRON05

  4. HERA-B Detector (II) • Fixed target detector at p ring HERA, DESY • Proton beam at 920 GeV/c (√s = 41.6 GeV) • Interaction rate ~ 5 MHz • Wire targets (different materials: C,W,Ti) in proton halo • Multiple trigger level (Hardware + Software) for lepton pairs • High resolution vertexing (~ 500 mm-longitudinal) • Very good particle ID for e, , , K and p Hernan Wahlberg, HADRON05

  5. Data Sample • HERA-B has finished data taking (March 2003) • Dilepton trigger • Pretriggers: high ET ECAL clusters, MUON hits • FLT (hardware trigger): track finding behind magnet • SLT (software trigger): track finding behind magnet and in silicon detector + vertex reconstruction • 165 M dilepton triggered events • ≈ 300.000 J/Ψ (>1000 per hour to tape) • 3 target wires of different materials • Carbon (A=12, ≈ 64% of total statistics) • Titanium (A=48, ≈ 9%) • Tungsten (A=184, ≈ 27%) Hernan Wahlberg, HADRON05

  6. Reference Prompt J/y Sample • Long tracks (vertex detector + tracking system) • PID: m likelihood , E/p • Dilepton vertex probability > 1% • J/ψacceptance: -0.35 < xF < 0.15 J/y: 148200±500 J/y: 103800±1000 y’: 2600±120 y’: 1700±160 Hernan Wahlberg, HADRON05

  7. Outline • HERA-B detector • Reference prompt J/ysample for beauty analysis • Open cross section •  ( ) production cross section • Summary Hernan Wahlberg, HADRON05

  8. B: Motivation HERA-B 2002 measurement • Theoretical uncertainties: • b quark mass 4.5 - 5 GeV • Production near energy threshold. At NLO, scale (m) dependence. • Need to go beyond NLO • Previous measurements: • Poor statistical precision • Incompatible Hernan Wahlberg, HADRON05

  9. B: Selection Method pA bb + X b(b) B  J/ + X J/  m+m- ; e+e- • B Selection: (~ 40% Efficiency) • Lepton impact to the wire • Distance J/y to wire Hernan Wahlberg, HADRON05

  10. B Meson has a long life time ( ~ 9 mm at HERA-B kinematics) • ~ 0.5 mm dilepton vertex resolution • J/y from a B decay will be detached from primary interaction • Only needed to count detached J/y B selection efficiency from MC • Measurement relative to direct J/ production to minimize trigger/reconstruction uncertainties • R= relative efficiency1 B: Principle of Measurement Hernan Wahlberg, HADRON05

  11. B: Data and MC Samples • Good agreement between data and MC simulation • Good separation between direct and detached J/ Hernan Wahlberg, HADRON05

  12. Downstream Upstream 46.2+8.6-7.9 -0.1±1.4 B: Detached J/ (muons) • Detachment cuts (on significance) optimized blindly and simultaneously: • Δz > 9 σ • Iwl > 2.6 σ • IwJ/Ψ< 9σ • Upstream from target: • unphysical region • Downstream from target: • signal region • Unbinned likelihood fit • Background: • Combinatorial • B doublesemileptonic • No prompt J/ Hernan Wahlberg, HADRON05

  13. B: Detached J/ (electrons) • Detachment cuts (on significance) optimized blindly and simultaneously : • Δz > 10 σ • Iwl > 3.0 σ • IwJ/Ψ< 12σ Upstream Downstream -4.2±1.9 36.9+8.5-7.8 • Upstream from target: • unphysical region • Downstream from target: • signal region • Unbinned likelihood fit • Background: • Combinatorial • B doublesemileptonic • No prompt J/ Hernan Wahlberg, HADRON05

  14. B: Sample Confirmation (I) t = 1.39 ± 0.19 ps • Confirmation of B flavor: • Long lived candidates around J/ψ mass • B lifetime compatible with expectations 1.54 ps (PDG) Hernan Wahlberg, HADRON05

  15. B: Sample Confirmation (II) • Search for additional tracks in a common vertex ( J/+h± ) • Relax detachment cuts • Partially independent sample • Higher purity but lower stat • RΔσ = (4.3±1.0)x10-2compatible with main result (see next slide) • Some fully reconstructed final state events • Ongoing study based on double semileptonic bb decay sample 22 ± 5 Hernan Wahlberg, HADRON05

  16. B: Results (I) • e and μ channels are partially independent • Results agree well within errors • Good control of systematics Hernan Wahlberg, HADRON05

  17. σJ/Ψ = (352 ± 2 ± 26) nb/n (average E789-E771) Weighted average with previous HERA-B measurement (I Abt et al., Eur. Phys. J. C26 (2003) 345) B: Results (II) Cross section in full xF range: Hernan Wahlberg, HADRON05

  18. B: Results (III) • Result compatible with lower limit of theoretical predictions • Compatible with E789 • Ongoing study suggests ~40% higher σ(J/ψ) and consequently σ( ) Hernan Wahlberg, HADRON05

  19. Outline • HERA-B detector • Reference prompt J/ysample for beauty analysis • Open cross section •  ( ) production cross section • Summary Hernan Wahlberg, HADRON05

  20. E772 (A=2) E605 (A=64) HERA-B s = 41.6 GeV :Motivation • Several measurements available but unclear situation at √s ~ 40GeV • Test quarkonium production models • Possible nuclear suppression ? • HERA-B has good coverage in the central region of collisions ( xF ~ [-0.35,0.15]) Hernan Wahlberg, HADRON05

  21. :Method pA  + X   m+m- ; e+e- • Measurement relative to prompt J/y • Less sensitive to systematic effects • Prompt J/y cross section from E771 and E789 Hernan Wahlberg, HADRON05

  22. :Signal   e+e- • Background: • Random combinatorial: estimated by like sign pairs of real data • Drell-Yan: shape estimated from MC • (1S) / (2S) / (3S) relative production fixed to E605 results 75±14   m+m- 30.8±7.4 Hernan Wahlberg, HADRON05

  23. :Preliminary Results • Based on σJ/Ψ = (352 ± 2 ± 26) nb/n (average E789-E771) • Both channels are compatible • Extrapolation to √s = 38.8 GeV yields: Br• d/dyy=0 = 2.3 ± 0.5stat± 0.5syspb/n • compatible with E605 • (more than 1 s) below E772 and E771 Hernan Wahlberg, HADRON05

  24. a-1 : Global Situation • Modified Craigie parameterization to include nuclear suppression (parametera) • Data compatible with no nuclear suppression:  = 0.96  0.05 Hernan Wahlberg, HADRON05

  25. Conclusions (I): B cross section • HERA-B measured (2000+2004) Rσ =(2.8±0.4±0.3)x10-2 • Lifetime of candidates in agreement with expectations • Compatibility between different channels • The complete HERA-B sample (~90 events) is significantly larger than previous fixed target experiments • Based on σJ/Ψ = (352 ± 2 ± 26) nb/n (average E789-E771) • Ongoing fit of existing experimental results on σ(J/) with COM parametrisation to provide absolute bb cross section Hernan Wahlberg, HADRON05

  26. Conclusions (II):  cross section • Preliminary  cross section measurement 3.5 ± 0.8pb/n • In agreement with E605 • Global fit to  data consistent with no nuclear suppression Hernan Wahlberg, HADRON05

  27. Backup Slides Hernan Wahlberg, HADRON05

  28. 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 H1 Coll. T.Sloan et al.,Proc. QCD 2001 Conf., Moriond, March 2001. ZEUS Coll. J.Breitweg et al.,Eur.Phys.J.C18(2001) L3 Coll. M.Acciarri et al.,Phys.Lett.B503(2001) 10 OPAL Coll.OPAL Phys.Note PN455, August 29,2001 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 BIBLIOGRAPHY Hernan Wahlberg, HADRON05

  29. E771/E789 J/ cross section E771/E789 : scaled to HERA-B cms energy (J/)=352 ± 2 ± 26 nb/nucleon HERA–B Preliminary HERA-B measurement on min. bias data ongoing Hernan Wahlberg, HADRON05

  30. 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, W) • 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 hemisphere 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 hemisphere in CM (positive xF) Not used in this analysis (stability issues) Hernan Wahlberg, HADRON05

  31. Detector characteristics (II) • RICH – Ring Imaging Cherenkov Detector 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 Hernan Wahlberg, HADRON05

  32. MUON AND ELECTRON CHANNEL: RELATIVE X-SECTION RESULTS Hernan Wahlberg, HADRON05

  33. 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% Hernan Wahlberg, HADRON05

  34. J/y from b decays kinematics 92% of J/y are produced in our xF range Hernan Wahlberg, HADRON05

  35. HERA-B preliminary : Theory (preliminary) • Theoretical prediction: • NLO + (NNLO+NNNLL) • Uncertainties: • b mass • Renormalization scale m • Compatible with Modified Craigie parameterisation Hernan Wahlberg, HADRON05

  36. Hernan Wahlberg, HADRON05

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