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Hera-B Physics Results 2000: Detector Layout Geared towards J/Ψ

This report covers the Hera-B physics results from the year 2000, focusing on the detector layout geared towards J/Ψ particle identification. The commissioning phase had limited statistics due to trigger and detector availability. The layout emphasized good vertexing, charge determination, and detection in the ECAL and muon chambers. The analysis compared results with other experiments, showcasing the acceptance in xF and pT distribution. Nuclear effects were studied using multiple target wires simultaneously, canceling uncertainties. The report also details the identification of χc and the extraction of bb-cross section with Monte Carlo simulations. Overall, the results provide valuable insights into particle physics research.

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Hera-B Physics Results 2000: Detector Layout Geared towards J/Ψ

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  1. Hera-B Physics results • Data of the year 2000 • limited statistics • 2. Commissioning: • trigger and detector not yet fully available • (limited acceptance in xF) • Targets: • Cand Ti • (partially simultaneously) -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  2. General view of Hera-B Rich Trans. rad. det. vertex detector ECAL p e target magnet (2 Tm) muon chambers (/h) inner tracker outer tracker hi-Pt tracker 20 m -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  3. Hera-B detector and trigger layout geared towards J/ : • Based on J/ e+ e- and J/ + - ; • Good vertexing through Si- m strips; • e+ ande- in ECAL; • + and- in Muondetector; • Magnetic field for charge determination. • ECAL is also fine-grain photon detector. • Not used in this part of analysis: • Rich • Inner Tracker • Trans. Rad. Detector -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  4. m+m- inv. Mass: J/ signal before cuts J/ J/ signal after cuts -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  5. e+ e-Invariant mass spectrum (| 1 - E/p| < 0.3) No J/ signal … -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  6. Bremsstrahlung recovery e+ beam e+ magnetic field ECAL -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  7. e+e-Invariant mass spectrum -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  8. e+e-Invariant mass spectrum (012) BR (12) BR (2) BR before background subtraction after background subtraction -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  9. e+e-Invariant mass spectrum with bremsstrahlung requirement Before background subtraction After background subtraction -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  10. J/ production Hera-B has large xF (and good pT ) acceptance xF xF -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  11. pT and xF distribution with e and m sample: -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  12. Comparison with other experiments: -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  13. d N(J/) Fit ansatz: = a * (1 - |xF | )c d xF c = 6.2 + 0.6 - -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  14. Energy dependence of exponent c -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  15. Energy dependence of width pT -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  16. Nuclear effects: Hera-B uses up to 8 different target wires simultaneously (in 2000: C and Ti). Most uncertainties cancel out: can easily measure nuclear exponent a as function of xF or other parameters. Important: goodaccep-tance in negative xF. (use W and C targets…) 2000 2002 -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 16a

  17. cProduction Identification of c through : D M = M(l +l -g ) - M (l +l -) uncertainty in J/ mass essentially cancels: Mc = (MJ/2 + 2Eg EJ/ – 2pgpJ/ ) dMc = dMJ/ = 0.877 dMJ/ d(Mc - MJ/ ) = -0.123 dMJ/ MJ/ Mc Nc Ratio ofJ/fromc : Rc = NJ/ * eg -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  18. DM-spectrum: cc-signal on top of combinatorial background (J/ -- g) -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  19. Nc (relative) Dependency of c reconstruction on ECAL miscalibration ADC shift -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  20. Rc Dependency of Rc on upper limit of tracks: eJ/ varies, but Rc constant. -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 Nvds

  21. Rc Dependency of Rc on upper limit of Ecal clusters: eg varies, but Rc constant. -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002 Nclus

  22. Final result : Rc = 0.321 + 0.064stat+ 0.035syst Comparison ofwith previous experiments -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  23. Rcas function of energy CSM p p CEM NRQCD p-A p p-A p Hera-B -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  24. bb-cross section Previous data Factor 7 -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  25. Method: • tB = 10-12 s • B only long lived decay • intoJ/ • at 920 GeV: lB ~ 1 cm • look for detachedJ/ • normalize using known • cross section and • measured number of J/ • and BR B J/ • no efficiency/trigger/… • knowledge required • (well, “almost not required”…) Monte Carlo -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  26. Invariant di-muon mass spectrum after detached event selection (incl. likelihood-fit). -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  27. Data Monte Carlo Invariant Mass: for downstream and upstream events clear signal of detachedJ/ -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  28. Decay length fit lsignal = 1.0 +/- 0.3 (lMC = 0.83 +/- 0.03) lbackgr. = 0.39 +/- 0.11 -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  29. Single cut optimization on downstream bkgr. Simult. cut optimization on upstream bkgr. Simult. cut optimization on downstream bkgr. -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  30. Final result: s(bb) = 32 +15+ 8syst nb/nucleon -12 stat - Uncertainties: Reference J/ cross sect. 11 % Trigger simulation: 5 % prompt J/ product. models 2.5 % b prod. and decay model 8 % A-dep. ignored 1.7 % prompt J/ counting 5 % b lifetime error 1 % J/  e+e-g 1 % m+m- background shape 20 % m+m- background fluct. 23 % e+e- background shape 14 % e+e- background fluct 11 % Total 24 % – 33 % -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

  31. Conclusion • Results of 2000 limited in statistics • (though competitive: s(bb), Rc ) • Hera-B offers good possibilities: • Simultaneous different targets • small relative uncertainties • large acceptance in - negative - xF; • full event capability: PID, g, … • Improved detector (trigger) in 2002: • high statistics expected -- Th. S. Bauer (NIKHEF) -- ECT -- 18. 6. 2002

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