Open and Hidden Beauty in 920 GeV Proton-Nucleus Collisions

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Open and Hidden Beauty in 920 GeV Proton-Nucleus
Collisions

• Hernan Wahlberg
• Utrecht University/NIKHEF
• For HERA-B Collaboration

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Outline

• HERA-B detector
• Reference prompt J/y sample for beauty analysis
• ? ( ) production cross section
• Open cross section
• Summary

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Hera-B Detector
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Reference Prompt J/y Sample
Di-Muon total sample Approx. 177,000 J/y
eventsWidth 44 MeV/c2
Di-Electron total sample Approx. 108,000 J/y
eventsWidth 64 MeV/c2
J/? (ee)
J/? (mm)
?(2S)
?(2S)

• Long Tracks (Vertex Detector Tracking System)
• PID m likelihood , E/p
• Dilepton Vertex Probability gt 1
• J/Y acceptance -0.35 lt xF lt 0.15

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? Motivation

• Several measurements
• available but unclear
• situation at vs 40GeV

• Theoretical prediction
• Hadronization Possible nuclear suppression ?

HERA-B ?s 41.6 GeV

• HERA-B has good
• coverage in the central
• region of collisions
• ( xF -0.35,0.15)

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? Method
pA ?? X ? ? mm- ee-

• Measurement relative to prompt J/y
• Less sensitive to systematic effects
• Prompt J/y cross section from E771 and E789

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? Signal

• 25 W 75 C (targets)
• Mass resolution between 140 and 160 MeV/c2
• 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

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? Preliminary Results
Events Br d?/dy?y0
??- 33 7 3.9 1.1 pb/n
ee- 31 10 2.9 1.2 pb/n
both 3.4 0.8 pb/n

• Both channels are compatible
• Extrapolation to vS 38.8 GeV yields
• Br d?/dy?y0 2.4 0.9 pb/n
• compatible with E605
• (more than 1 s) below E772 and E771

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? Global Situation

• Modified Craigie parameterization to include
  nuclear suppression (parameter a)
• Data compatible with no nuclear suppression
• ? 0.99 ? 0.05

?s (GeV)
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B Motivation

• Theoretical uncertainties
• b quark mass 4.5 - 5 GeV
• At NLO, scale (m) dependence
• Previous measurements do not agree

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B Principle of the Measurement
pA ?bb X b(b) ? B ? J/? Y J/? ? mm- ee-
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B Principle of the Measurement

• 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 count detached J/y
• Measurement relative to prompt J/y
• Prompt J/y cross section from E771 and E789

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B Detached Scheme

• B Selection (30-45 Efficiency)
• Lepton impact to the wire
• Lepton closest distance of approach to primary
• Distance J/y to wire

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B Real Data vs. MC

• Vertex z resolution 500 mm
• Good agreement between real data and MC
  simulation

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B Signal

• Carbon Tungsten targets
• 35 of total sample
• Cuts optimized simultaneously
• Background
• bb and cc simultaneous semileptonic decays
• Combinatorial
• Prompt J/y
• Unbinned likelihood fit

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B Sample Cross Check
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B Preliminary Result

• Only statistical errors
• Good compatibility of two channels
• 1.3 s lower than HERAB (2000)

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B Ongoing studies

• Simultaneous semileptonic decays
• Search of exclusive decays
• Lifetime measurement

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Conclusions

• Events observed in hidden and open beauty in the
  2002-2003 data sample
• Preliminary ? cross section measurement 3.4
  0.8 pb/n
• in agreement with E605
• Global fit to ? data consistent with no nuclear
  suppression
• Preliminary bb cross section measurement (35 of
  the total statistics)
• The complete HERA-B sample will be significantly
  larger than previous fixed target experiments

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Back-up slides
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Essential bibliography
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)
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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
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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

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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 TrackingVertexing linux
  farm with 240 nodes
• ? Event reconstruction on-line, linux farm with
  200 nodes

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b production model systematics
Default model MRST PDF, Peterson FF e0.006
Studied variations
Sys cont. to s(bb )

• 1.5
• 1
• 2
• 3
• 1
• 2

• 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
• ltkT2gt from 0.125 to 2.0 GeV2
• Fraction of b-baryons produced in the
• b-hadronization process from 0 to 12

Total 5
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J/y from b decays kinematics
92 of J/y are produced in our xF range