23-09-2004 M.Mevius

Open and hidden beauty production in 920 GeV proton –nucleus

collisions at HERA-B

M.Mevius

DESY

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Outline

the HERA-B experiment

open b production

upsilon production

conclusions

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The HERA-B Detector

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Data Sample

• Data taking is finished in 2003; analysis is in progress

additional: 210 M minimum bias events

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 VDSvertex reconstruction

•online event reconstruction 150 M dilepton trigger events 300 000 J/ (>1000 per hour) 10 000 c

3 500 (2S)

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Dilepton spectra

~ 1600

•Long Tracks (Vertex Detector + Tracking System)•PID: likelihood , E/p•Dilepton Vertex Probability > 1%•J/ acceptance: -0.35 < xF < 0.15

muon channel

~ 108,000 J/ → ee

σ = 64 MeV/c2

/

J/

(2S)

electron channelmuon channel

~ 108,000 J/ ee

σ = 64 MeV/c2

/

J/

(2S)

electron channel

~ 177,000 J/ σ = 44 MeV/c2

~ 3000 (2S)

~ 1600

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open b production

Experiment E p (GeV) s (nb/ nucleon) N Events

E789 800 5 ± 1.5 ± 3 ~ 20

E771 800 43(+27-17)± 7 ~ 6

HERA-B(2000) 920 32(+14-12)(+6-7) ~ 10

Theory Order

N.Kidonakis et al. NLO + NNLL 30 ± 18

R.Bonciani et al. NLO + NLL 25 (+20-13)

• Theoretical uncertainties: – b quark mass 4.5 - 5 GeV– At NLO, scale () dependence

• Previous measurements do not agree between each other

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)/(

1

//

XJbbBrn

nzBRJ

BJbb

ss

pn bb + Xb(b) B J/ + X

J/ ; e+e-

open b production

Measurement relative to direct J/ production to minimize trigger/reconstruction uncertainties

R= relative efficiency1

B selection eff. from MC

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open b production

B Selection: (30-45% Efficiency)Lepton impact to the wire

Distance J/ to wire

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

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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/

Cuts optimized simultaneously

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

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open b production

0.027 0.004 0.005/

bb

J

s

s

• C,W,Ti targets

• Unbinned likelihood fit

preliminary

20% sys. error under investigationmain contribution: Br(bbJ/X) = 2.320.20%

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J/ cross sectionE771/E789 : scaled to HERA-B cms energy s(J/)=357 ± 2 ± 36 nb/nucleon

E771/E789

HERA-B measurement on min. bias data ongoing

using E771/E789 result:

preliminary

9.8 1.4 2.0 nb/nucleonbbs

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upsilon production

HERA-Bs = 41.6 GeV

E772 (A=2)

E605 (A=64)

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

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

• Theoretical prediction Hadronization: Possible

nuclear suppression ?

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upsilon production

pA + X

μ +μ- ; e+e-

/

/0

1( ) = ( / ) / ) J

J effy

d NBr l l Br J l l J

dy N y

s s

• Measurement relative to prompt J/ – Less sensitive to systematic effects

• Prompt J/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:

Drell-Yan: shape estimated from MC

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

Random combinatorial: estimated from like sign pairs in data

8

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upsilon productionEvents Br• ds/dyy=0

+- 33 ± 7 3.9 ± 1.1 pb/n

e+e- 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• ds/dyy=0 = 2.4 ± 0.9 pb/n– compatible with E605– (more than 1 s) below E772 and E771

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upsilon production

Not usedin fit

As

ms

dy

dBr o

o

y

exp)(0

ss

• Modified Craigie parameterization to include nuclear suppression (parameter )

• Data compatible with no nuclear suppression:

= 0.99 0.05

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• HERA-B has finished data taking• preliminary results:

s(bb) :

• using: s(J/)=357±2±36 nb/nucleon

production:

Conclusions

0.027 0.004 0.005/

bb

J

s

s

9.8 1.4 2.0 nb/nucleonbbs

0

( ) = 3.4 0.8 pb/nucleony

dBr l l

dy

s

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model dependence

• Changing PDFs from MRST to CTEQ• b quark mass from 4.5 to 5.0 GeV/c2

• QCD renormalization scale from 0.5 o to 2 o

• Fragmentation functions– Peterson form with from 0.002 to 0.008– Kartvelishvili form with 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%

Default model: MRST PDF, Peterson FF =0.006 22222 GeV/c 0.5kpmGeV/c 4.75m TTbb 0

Total: ±5%

Studied variations: Sys cont. to s(bb )

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92% of J/ are produced in our xF range

J/ from b decays kinematics