Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions

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Open and Hidden Charm Productionin 920 GeV
Proton-Nucleus Collisions
6th International Conference on Hyperons, Charm
Beauty Hadrons Illinois Institute of Technology,
Chicago, IL, June 27 - July 3, 2004

• Ulrich Husemann
• for the HERA-B Collaboration
• Experimentelle Teilchenphysik, Universität
  Siegen

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Outline of the Talk

• HERA-B detector and trigger systems
• Charmonium production
• Open charm production
• Summary

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• Detector Trigger

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The HERA-B Detector
Muon Detector4 layers of gas pixel chambers
(inner) and MWPC with cathode pad readout
(outer), pad-coincidence pretrigger
Top View
920 GeV/c Protons
Magnet
10 m
0 m
20 m
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The Dilepton Trigger
HERA-B detector data is read out and buffered
for 10 ?s(proton bunches cross every 96 ns, 0.5
interactions/BX)
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Data Sample 2002/2003

• Data-taking period October 2002February 2003
• Dilepton trigger require ? 2 electrons or muons
• Trigger performance gt1,000 J/? per hour
• Sample for charmonium studies
• 300,000 J/?
• 10,000 cc
• 3,500 ?(2S)
• Study of beauty production ? see talk by H.
  Wahlberg, B3.8
• Minimum bias trigger minimum activity in
  RICH/ECAL
• 200 million events recorded
• Strangeness and hyperon production
• Pentaquark searches ? see talk by A. Sbrizzi,
  ST.3
• Open charm production

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Dilepton Spectrum Muon Channel
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• Charmonium
• Production

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J/y Production Cross Section

• J/y ? ee / mm signals observed in minimum
  bias data
• Determination of J/y cross section without
  trigger bias(systematic effects currently
  under study)

J/y ? ee
J/y ? mm
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J/y Differential Cross Section pT

• Parametrization? Broad pT coverage, good
  agreement of electron and muon channel

80 of ee sample
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J/y Differential Cross Section xF

• Large acceptance for negative xF (fractional
  longitudinal momentum)
• Parametrization
• Work on systematics ongoing

10 of ee sample
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J/y A-Dependence

• Test of charmonium production models in nuclear
  matter (nonrelativistic QCD initial/final state
  interactions in nucleus)
• Parametrization
• ? lt 1 charmonium suppression by nuclear effects
• HERA-B extract ? from runs with two target wires
  simultaneously (carbon A12, tungsten A184)

• 3 ingredients of A-dependence measurement

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J/y A-Dependence
Preliminary
Preliminary
Sample I
Sample II

• Previous result of FNAL E866 extended to xF
  0.3
• Result from 10 of full mm sample, statistical
  uncertainties only
• Two different combinations of carbon and tungsten
  wires (different acceptances) consistent results
• Work on systematics ongoing

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?(2S) Production

• Measure ?(2S) cross section relative to J/?
  ? reduce systematic uncertainties
• eJ/y/ey(2S) 0.72 (MC)
• Preliminary result (electrons, 30 of full
  statistics)
• Muon channel compatible results

Preliminary
Preliminary
R 0.13 0.02 (stat.)
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cc Production

• Test of charmonium production models fraction
  R(cc) of J/? from radiative decays ?c? J/? ?? m
  m ?

Published result of 2000 data-taking (37074
cc) I. Abt et al., Phys. Lett. B561 (2003) 61
R(?c)0.320.06(stat.)0.04(syst.)
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R(cc) Analysis in 2002/2003

• Signal found in mass difference M(J/? ?) M(J/?)

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• Open Charm
• Production

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Open Charm Production

• Open charm signals in minimum bias data
  (charge-conjugated channels included)

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Open Charm Production
Preliminary
Preliminary
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New Limit on BR(D0????)

• Search for flavor-changing neutral current decay
  D0???? (branching fraction enhanced in some
  SUSY models)
• 3 events in signal regionCurrently best
  upper limitI. Abt et al., hep-ex/0405059, to be
  published in Phys. Lett. B
• Previous limit by CDF BR(D0????) lt 2.5?10-6
  (90 CL) D. Acosta et al.,Phys. Rev. D68 (2003)
  091101

18 events
6 events
3 evt
BR(D0????) lt 2.0?10-6(90 CL)
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Summary Outlook

• HERA-B has finished data-taking
• Analysis of 2002/2003 data in progress
• Charmonium production
• Production cross sections and differential
  distributions
• A-dependence of J/y production HERA-B covers
  xFlt0
• Production ratios y(2S) to J/y, fraction of J/y
  from cc
• Open charm production
• D meson production cross sections and ratios D0,
  D, D
• New limit for FCNC decay D0????
• Outlook
• First results of 2002/2003 run to be published
  soon
• Stay tuned more interesting results to come
• Thanks to HERA-B charmonium open charm working
  groups

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Dilepton Spectrum Electron Channel
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Why Charmonium Production?

• Test of current framework for charmonium
  production models nonrelativistic QCD
  (perturbative expansion in relative quark
  velocities)
• Modification of models via nuclear effects
• Initial state effects, e.g. shadowing, energy
  loss
• Final state effects, e.g. absorption in nuclear
  matter
• Parametrization power law with exponent ?
  ?(xF,pT)? is measure of A-depencence (A
  target atomic mass)? lt 1 charmonium suppression
  by nuclear effects (anomalous suppression
  signature for quark-gluon plasma)

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A-Dependence Theory
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A-Dependence HERA-Bs Contribution

• Measurements in proton-nucleus scattering
  (Fermilab E866/NuSea) as a function of xF

M.J. Leitch et al., Phys. Rev. Lett. 84 (2000)
3256