Open and hidden beauty production in 920 GeV proton

1
Open and hidden beauty production in 920 GeV
proton nucleus collisions at HERA-B

• M.Mevius
• DESY

2
Outline

• the HERA-B experiment
• open b production
• upsilon production
• conclusions

3
The HERA-B Detector
4
Data Sample

• Data taking is finished in 2003 analysis is in
  progress

• 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 VDS
• vertex reconstruction
• online event reconstruction

150 M dilepton trigger events 300 000 J/?
(gt1000 per hour) 10 000 ?c 3 500 ?(2S)
additional 210 M minimum bias events
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Dilepton spectra

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

1600
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open b production

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

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open b production
pn ?bb X b(b) ? B ? J/? X J/? ? mm- ee-
B selection eff. from MC
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open b production
B Meson has a long life time ( 9 mm at HERA-B
kinematics) 0.5 mm dilepton vertex
resolution J/? from a B decay will be detached
from primary interaction
B Selection (30-45 Efficiency) Lepton impact to
the wire Distance J/? to wire
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open b production

• Vertex z resolution 500 µm
• Good agreement between data and MC simulation
• good separation between direct and detached J/?

• Background
• bb and cc simultaneous semileptonic decays
• Combinatorial
• Prompt J/?

Cuts optimized simultaneously
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open b production

• C,W,Ti targets
• Unbinned likelihood fit

preliminary
20 sys. error under investigation main
contribution Br(bb?J/?X) 2.32?0.20
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J/? cross section
E771/E789 scaled to HERA-B cms energy
?(J/?)357 2 36 nb/nucleon
using E771/E789 result
HERA-B measurement on min. bias data ongoing
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upsilon production

• Several measurements
• available but unclear
• situation at ?s 40GeV

• Theoretical prediction
• Hadronization Possible nuclear suppression ?

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

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upsilon production

• pA ?? X
• ? ? µ µ- ee-

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

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upsilon production

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

Random combinatorial estimated from like sign
pairs in data
Drell-Yan shape estimated from MC

• ?(1S) / ?(2S) / ?(3S) relative production fixed
  to E605 results

8
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upsilon production
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 ?S 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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upsilon production
a-1

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

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Conclusions

• HERA-B has finished data taking
• preliminary results
• ?(bb)
• using ?(J/?)357236 nb/nucleon
• ? production

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model dependence
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/? from b decays kinematics
92 of J/y are produced in our xF range