July 3 2004 Hernan Wahlberg, BEACH04 1

Open and Hidden Beauty in 920 GeV Proton-Nucleus

Collisions

Hernan WahlbergUtrecht University/NIKHEFFor HERA-B Collaboration

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Outline

• HERA-B detector

• Reference prompt J/ sample for beauty analysis

( ) production cross section

• Open cross section• Summary

bb

bb

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Hera-B Detector

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Reference Prompt J/ SampleDi-Muon total sample:

Approx. 177,000 J/ eventsWidth: 44 MeV/c2

(2S)

J/ ()

Di-Electron total sample: Approx. 108,000 J/eventsWidth: 64 MeV/c2

(2S)

J/ (ee)

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

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: Motivation

• Theoretical prediction– Hadronization: Possible

nuclear suppression ?HERA-Bs = 41.6 GeV

• 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])

E772 (A=2)

E605 (A=64)

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: Method

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

• Prompt J/cross section from E771 and E789

pA + X - ; e+e-

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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

• Both channels are compatible• Extrapolation to √S = 38.8 GeV yields:

Br• d/dyy=0 = 2.4 ± 0.9 pb/n– compatible with E605– (more than 1 ) below E772 and E771

Events Br• d/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

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: Global Situation

• Modified Craigie parameterization to include nuclear suppression (parameter

• Data compatible with no nuclear suppression:

= 0.99 0.05

Not usedin fit

As

ms

dy

dBr o

o

y

exp)(0

s (GeV)

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B: Motivation• Theoretical uncertainties:

– b quark mass 4.5 - 5 GeV– At NLO, scale () dependence

• Previous measurements do not agree

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

E789 800 5 ± 1.5 ± 3 ~ 20

E771 800 43 ± 22 ± 7 ~ 6

HERA-B(2000) 920 32 ± 13 ± 6.5 ~ 10

Theory Order

N.Kidonakis et al. NLO + NNLL 30 ± 18

R.Bonciani et al. NLO + NLL 25 ± 17

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pA bb + Xb(b) B J/ + Y

J/ ; e+e-

B: Principle of the Measurement

)/(

1

//

XJbbBrn

nzBRJ

BJbb

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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/ from a B decay will be detached from primary interaction• Only needed: count detached J/• Measurement relative to prompt J/• Prompt J/cross section from E771 and E789

)/(

1

//

XJbbBrn

nzBRJ

BJbb

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B: Detached Scheme

P P

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

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B: Real Data vs. MC

•Vertex z resolution ~ 500 m •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/

• Unbinned likelihood fit

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B: Sample Cross Check

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•Only statistical errors•Good compatibility of two channels•1.3 lower than HERA–B (2000)

B: Preliminary Result

N/nb12.7 4.23.6bb

n/nb 12.7 : Muons 4.23.6bb

n/nb12.3 3.53.2bb

n/nb 11.5 :Electrons 5.34.5bb

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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

n/nb12.3 3.53.2bb

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Back-up slides

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Essential bibliographyP.NASON, QCD at High Energy, Proc. Of the XX Int. Symp. on Lepton and Photon Interactions at High Energies, hep-ph/0111024P.NASON et al., Adv. Ser. Direct. High Energy Phys. 15(1998), 609H1 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) 10

OPAL Coll. OPAL Phys.Note PN455, August 29,2001

N. Kidonakis et al., Phys.Rev. D64 (2001) 114001-1

D.M.Jansen et al., Phys.Rev.Lett.74 (1995)3118

T.Alexopoulos et al., Phys.Rev.Lett.82 (1999) 41

R. Bonciani et al., Nucl.Phys.B529 (1998) 424

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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: z 600 m, x,y 70 m Dipole Magnet- field integral 2.13 Tm OTR – Outer Tracker. Honeycomb drift cells; wire pitch 5/10

mm; spatial hit resolution 350 m; Backward hemisfere in CM (negative xF)World largerst honeycomb tracker: 1000 modules, 115000 channels

ITR – Inner Tracker: MicroStrip Gas Chambers, pitch 100 m, resolution 100 m; 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

4 separation: e/ p [3.4, 15] GeV/c, /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; Tracking+Vertexing; linux farm with 240

nodes

Event reconstruction; on-line, linux farm with 200 nodes

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b production model systematics

• 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 (bb )

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J/ from b decays kinematics

92% of J/ are produced in our xF range