1. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Measurement of the bb Production Cross Section in Proton-Nucleus Collisions at Hera-B P. Kreuzer University of California, Los Angeles For the Hera-B Collaboration ICHEP 2002 Conference Amsterdam, July 27 2002  Motivations  The HERA-B spectrometer and trigger (Y2K)  The Measurement: b  J/  (l + l - ) + X  Comparison with Data & QCD Predictions  Conclusions (hep-ex/0205106 + submit. EPJ C)

2. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Motivations for a bb cross section measurement at Hera-B ExpTargp Beam  (bb) nb/nucleon Channel E789Au800 (GeV/c) 5.7  1.5  1.3b  J/  (   ) X E771Si800 (GeV/c) bb  (  + +X)(  - +X) 12   (bb )  70 nb/nucl. at 920 GeV/c (Hera-B) Fixed Target Data:  Hera-B can extend the experimental panorama  Recent improvements but still large uncertainties ! by covering both b  J/  ( e  ) and b  J/  (   ) & the non-exploited negative x F region A test for QCD Predictions: ()

3. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam The Hera-B Detector Carbon Titanium Y2K J/  -coverage: -0.25 < x F < 0.15 ( now -0.4<x F <0.3 ) (920 GeV p-N interactions)

4. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam The Hera-B Di-lepton Trigger (Y2K) Pretrigger (5 MHz) E_t cut for e, hit coinc.for  Level I (~150 KHz) 2 leptons (ee,  ) requirement (no tracking ! ) Level II (~12 KHz) 2 tracks in Main Tracker and Vertex Detector 9.0 10 5 di-e & 4.5 10 5 di-  events (Farms of 240+100 PCs, ~20 Hz output)

5. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam The measurement steps Minimize systematic errors & Avoid luminosity dependence Relative detection Efficiency Detached Vertex selection Efficiency  Select prompt J/   Select b  J/   Normalize to  (pN  J/  X) using E789/E771 g [-0.25 < x F < 0.15]

6. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Prompt J/  selection n P = 5710  380 st  280 sys n P = 2880  60 Muon Channel: Electron Channel: Reconstruction based on Trigger tracks + Vertex + Particle ID

7. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Isolating the b signal Total (prompt) J/  signalDetached b  J/  signal J/  l + l -  (  z)   c  B (600  m) (8000  m) IWIW l + J/  B zz X l - upstream | downstream zz IwIw

8. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam * bb -> (e + +X)(e - +X) * combinatorial * < 0.2 prompt J/  Detached b selection (e channel) Prompt region Upstream Downstream J/  peak Main Bkgd sources:

9. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Invariant Mass fit Unbinned Likelihood Fit: - Sig. shape from MC, - BKG shape data/MC e + e - invariant mass ( GeV/c 2 ) Electron channel: Muon channel: Unbinned Likelihood Fit: - Sig. shape from data, - BKG shape from data  (bb ) = nb/nucl (-0.25 < x F < 0.15)

10. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Systematic Uncertainties External (internal) sourcesCh Syst % rr ee 11 BR(bb  J/  X)ee 9 Trigger & detector sim. (  R )ee 5 b production/decay models MRST NNLL Parton Distr. F., Peterson Fragment., Pythia) ee 5 Prompt counting J/  (n p )e5 Prompt J/  MC prod. Mod.ee 2.5 A-dependence in  R   z B ee 1.7 Partial contributione-  17-16 Sources dominated by statistics ChSyst %  +  - bkg fluctuations  +10 -24 e + e - bkg shapee7 e + e - bkg fluctuations e11 Partial contribution e-  Total systematic uncertaintyee +20 % -23 %

11. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam R. Bonciani et al. (2002), NLO+NLL with latest MRST PDF Nucl.Phys.B529 (1998) Hera-B compared to other data/theory The result shows good agreement with recent calculations beyond NLO Hera-B Y2K @ 920 GeV: nb/nucl  TOT (bb ) = (92% b  J/  in our x F range) N. Kidonakis et al. (2001), NLO+NNLL Phys.Rev D64 (2001) 114001-1

12. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam  Outlook 2002/3: O(1000) higher statistics !  Baseline Physics program -  (bb ): expected error 15% (systematic limited) - Charmonium production (J/ ,  ‘,  ), Atomic number dependence Conclusions  B  J/  X  l + l - X observed at Hera-B  Good compatibility with recent QCD calculations  Result: c

13. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam 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 x F ) 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 x F ) World largerst (gas) micro pattern tracker

14. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Detector characteristics (II)  RICH – Ring Imaging Cherenkov Hodoscope C 4 F 10 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

15. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam The cross section normalization E789 + E771 : 356  7  25 nb/nucleon E866 : 0.955  0.005 Relative detection efficiencies Efficiency of detected vertex selection Number of observed b  J/  and prompt J/  [-0.25<x F <0.15]

16. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Prompt J/  : Particle ID / Kinem.  BR =0.34  0.02  0.02 PID: E/P + bremsstrahlung Electron Channel: PID:  likelihoods from MUON and RICH detectors Muon Channel:

17. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Detached b  J/  cuts -  z > 0.5 cm - e  Imp. Param. wire I w > 200  m, or - Min. dist. @ Z W to any other track > 250  m Optimization procedure: Electron Channel Cuts: Muon Channel Cuts: -  z > 7.5  z -   Imp. Param. to wire I w >45  m -   “ “ to primary vtx I p > 160  m

18. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Systematic checks (e-channel DECAY LENGTH LIKELIHOOD FIT: MC =0.81  0.03 cm RD =1.00  0.30 cm BKG =0.36  0.13 cm Different bkg optimization: Upstream Downstream Dz (cm) Mass (ee) (GeV/c 2 ) Bkg e + e - invariant mass ( GeV/c 2 ) Entries / 100 MeV/c 2

19. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam  TOT (bb ) = nb/nucleon  (bb) Determination  Simultaneous fit to e + e - &  +  - (in Hera-B acceptance): Extrapolation to the full x F range: e-channel   (bb ) = nb/N  -channel   (bb ) = nb/N

20. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam J/  from b decays kinematics 92% of J/  are produced in our x F range

21. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam b production model For the x F and p T distributions of J/  from b decays, we need a model of the b quark production and hadronization Our b production & decay model: Based on HQ cross section calculation at NLO+NLL by M. Mangano, P. Nason and G. Ridolfi, Nucl. Phys. B373 (92) 295 Latest MRST parton distribution functions (NNLL) for nucleons Intrinsic k T of interacting partons is gaussian-distributed with = 0.5 GeV 2 b quarks fragmentation given by a Peterson function (  = 0.006) The b-hadron decays to J/  is controlled by Pythia 92% of J/  from b decays are produced in our x F range

22. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam b production model systematics Changing PDFs from MRST to CTEQ b quark mass from 4.5 to 5.0 GeV/c 2 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 from 0.125 to 2.0 GeV 2 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 Total: ±5% Studied variations:Sys cont. to  (bb )

23. P.Kreuzer – BBbar at Hera-B – ICHEP2002 Amsterdam Essential Bibliography P.NASON, QCD at High Energy, Proc. Of the XX Int. Symp. on Lepton and Photon Interactions at High Energies, hep-ph/0111024 P.NASON et al., Adv. Ser. Direct. High Energy Phys. 15(1998), 609 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 M.H. Schub et al., Phys.Rev.Lett. D52 (1995) 1307 P.Mangano et al., Nucl. Phys. B373 (92) 295