Open and Hidden Beauty in 920 GeV ProtonNucleus Collisions

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Open and Hidden Beauty in 920 GeV Proton-Nucleus
Collisions

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

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Outline

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

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HERA-B Detector (I)
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HERA-B Detector (II)

• Fixed target detector at p ring HERA, DESY
• Proton beam at 920 GeV/c (vs 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

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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/? (gt1000 per hour to tape)
• 3 target wires of different materials
• Carbon (A12, 64 of total statistics)
• Titanium (A48, 9)
• Tungsten (A184, 27)

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Reference Prompt J/y Sample

• Long tracks (vertex detector tracking system)
• PID m likelihood , E/p
• Dilepton vertex probability gt 1
• J/? acceptance -0.35 lt xF lt 0.15

J/y 148200500
J/y 1038001000
y 2600120
y 1700160
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Outline

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

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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

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B Selection Method
pA ?bb X b(b) ? B ? J/? X J/? ? mm-
ee-

• B Selection ( 40 Efficiency)
• Lepton impact to the wire
• Distance J/y to wire

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B Principle of Measurement
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B Data and MC Samples

• Good agreement between data and MC simulation
• Good separation between direct and detached J/?

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B Detached J/? (muons)

• Detachment cuts (on significance) optimized
  blindly and simultaneously
• ?z gt 9 s
• Iwl gt 2.6 s
• IwJ/? lt 9s

• Upstream from target
• unphysical region
• Downstream from target
• signal region
• Unbinned likelihood fit
• Background
• Combinatorial
• B doublesemileptonic
• No prompt J/?

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B Detached J/? (electrons)

• Detachment cuts (on significance) optimized
  blindly and simultaneously
• ?z gt 10 s
• Iwl gt 3.0 s
• IwJ/? lt 12s

Upstream
Downstream
36.98.5-7.8
-4.21.9

• Upstream from target
• unphysical region
• Downstream from target
• signal region
• Unbinned likelihood fit
• Background
• Combinatorial
• B doublesemileptonic
• No prompt J/?

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B Sample Confirmation (I)
t 1.39 0.19 ps

• Confirmation of B flavor
• Long lived candidates around J/? mass
• B lifetime compatible with expectations 1.54 ps
  (PDG)

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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
• R?s (4.31.0)x10-2 compatible with main result
  (see next slide)
• Some fully reconstructed final state events
• Ongoing study based on double semileptonic bb
  decay sample

22 5
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B Results (I)

• e and µ channels are partially independent
• Results agree well within errors

• Good control of systematics

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B Results (II)
Cross section in full xF range
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B Results (III)

• Result compatible with lower limit of
  theoretical predictions
• Compatible with E789

• Ongoing study suggests 40 higher s(J/?) and
  consequently s( )

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Outline

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

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? Motivation

• Several measurements available but unclear
  situation at vs 40GeV

• Test quarkonium production models
• Possible nuclear suppression ?

• 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
? ? ee-

• 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

7514
? ? mm-
30.87.4
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? Preliminary Results

• Based on sJ/? (352 2 26) nb/n (average
  E789-E771)

• Both channels are compatible
• Extrapolation to vs 38.8 GeV yields
• Br d?/dy?y0 2.3 0.5stat 0.5sys 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
• ? 0.96 ? 0.05

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Conclusions (I) B cross section

• HERA-B measured (20002004) Rs
  (2.80.40.3)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 sJ/? (352 2 26) nb/n (average
  E789-E771)
• Ongoing fit of existing experimental results on
  s(J/?) with COM parametrisation to provide
  absolute bb cross section

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Conclusions (II) ? cross section

• Preliminary ? cross section measurement
• 3.5 0.8 pb/n
• In agreement with E605
• Global fit to ? data consistent with no nuclear
  suppression

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Backup Slides
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BIBLIOGRAPHY
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J/? cross section
E771/E789 scaled to HERA-B cms energy
?(J/?)352 2 26 nb/nucleon
HERAB Preliminary
HERA-B measurement on min. bias data ongoing
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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, 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)

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

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MUON AND ELECTRON CHANNEL RELATIVE X-SECTION
RESULTS
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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
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? Theory (preliminary)

• Theoretical prediction
• NLO (NNLONNNLL)
• Uncertainties
• b mass
• Renormalization scale m
• Compatible with Modified Craigie parameterisation
  

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