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PPR chapter 6.5 & D 0 detection

PPR chapter 6.5 & D 0 detection. Andrea Dainese University of Padova. 6.5 Charm and Beauty: update. First part on c and b production at LHC is finalized It will be submitted as a Note in these days Contents: cross sections and yields in Pb-Pb and pp at NLO (Nicola)

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PPR chapter 6.5 & D 0 detection

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  1. PPR chapter 6.5&D0 detection Andrea Dainese University of Padova ALICE Physics Forum - March 11, 2003 Andrea Dainese

  2. 6.5 Charm and Beauty: update • First part on c and b production at LHC is finalized • It will be submitted as a Note in these days • Contents: • cross sections and yields in Pb-Pb and pp at NLO (Nicola) • c and b kinematical distributions and PYTHIA tuning (Nicola) • D and B meson parameterized pT distributions for Pb-Pb NEW • cross sections and yields in p-Pb at NLO NEW • Bjorken-x acceptance for ALICE in pp, Pb-Pb, p-Pb NEW • Present ALICE baseline for c and b production • To be used as an input for simulation studies ALICE Physics Forum - March 11, 2003 Andrea Dainese

  3. Cross sections in p-Pb • Centre of mass energy: • Rapidity shift for p-Pb (Pb-p): • Cross sections at NLO (MNR) calculated for pp w/o and w/ shadowing corrections by R. Vogt • PDF set: MRST (for pp and Pb-Pb the calculation was done with MRST and CTEQ5M, and results were averaged; MRST result were ~10% lower than the average) • shadowing: EKS98 (same as for Pb-Pb) • Extrapolation to p-Pb: • no centrality selection assumed (min. bias collisions) ALICE Physics Forum - March 11, 2003 Andrea Dainese

  4.  5  150 Charm cross sections ALICE Physics Forum - March 11, 2003 Andrea Dainese

  5.  4  160 Beauty cross sections ALICE Physics Forum - March 11, 2003 Andrea Dainese

  6. Accessible x range (1) • Bjorken x = p(parton) / p(proton) • Heavy Quark prod. at LO: • The x range probed depends on: • At central rapidity x1 ~ x2 • Charm has lower mass lower x values • Measurements at forward rapidity lower range in x2 ALICE Physics Forum - March 11, 2003 Andrea Dainese

  7. MUON ARM MUON ARM BARREL BARREL p-Pb and Pb-p allow to cover a broader x range and reach down to x ~ 10-6 in MUON ARM x ~ 10-4 in BARREL handle to Gluon Shadowing same as in pp at 14 TeV! Accessible x range (2) ALICE Physics Forum - March 11, 2003 Andrea Dainese

  8. D0 detection in pp collisions • Generation of signal and background • Tracking and Primary vertex reconstruction in pp • Particle ID in TOF • Secondary vertex selection • Effect of primary vertex resolution • Tuning of selection cuts • Results Estimate of results for p-Pb collisions ALICE Physics Forum - March 11, 2003 Andrea Dainese

  9. Generation Signal • “Signal event” = 1 Pythia pp event with a D0 Kp with K and p in TPC acceptance • Corresponds to 1044 pp Minimum Bias events • Generated 2  106 “signal events” ( = 2.06  109 pp MB evts) • 2.9  106 pp non-diffr. events generated, reconstructed, analyzed using distributed resources and AliEn (only final “ntuple” with D0 candidates copied to Padova) • Correspond to 4.1  106 pp MB events (fraction of non-diffr. events / MB events taken from Pythia: 70 %) Background ALICE Physics Forum - March 11, 2003 Andrea Dainese

  10. in the direction  to the track Impact parameter measurement • Request of two tracks with large impact parameters is one the most important selection criteria SGN BKG ALICE Physics Forum - March 11, 2003 Andrea Dainese

  11. Interaction vertex at the LHC • Position of the beam in (x,y) given by the machine with very high precision (stable for a long time) • “Nominal” size of the beam: • s = 15 mm in Pb-Pb • s = 15 mm in pp (L ~ 1031 cm-2 s-1) • s 150 mm in pp (if L is reduced at ALICE IP to ~ 1029 cm-2 s-1) • The vertex position has to be reconstructed in 3D using tracks • Feasibility study done with two scenarios: • vertex position known with a resolution of 15 mm • vertex position reconstructed with tracks ALICE Physics Forum - March 11, 2003 Andrea Dainese

  12. 3D reconstruction with tracks • Track reconstruction in TPC+ITS • TPC tracking parameterization • ITS Kalman filter (6/6 points) • ITS tracking uses the position of the primary vertex: • (x, y) from beam position (resolution ~ 150 mm) • z from pixels information (resolution ~ 150 mm) • Vertex reconstruction in 2 steps: • VERTEX FINDING: using DCA for track pairs • VERTEX FITTING: (inspired by CMS and ATLAS methods) • give optimal estimate of the position of the vertex • give vertex covariance matrix • give a c2 Internal Note by A.D. and M.Masera almost ready ALICE Physics Forum - March 11, 2003 Andrea Dainese

  13. Tuning of the algorithm • Inspiration: ATLAS TRT TDR • Criterion used to reject mismeasured and secondary tracks from the fit: cut on the maximum contribution to the c2 ci2 < c2max • if c2max is too low too many tracks are rejected and we loose resolution • if c2max is too high bad or secondary tracks enter the fit and we loose resolution • This cut is tuned, as a function of event multiplicity, in order to optimize the resolution ALICE Physics Forum - March 11, 2003 Andrea Dainese

  14. Resolutions VS multiplicity pp min. bias pp with charm ALICE Physics Forum - March 11, 2003 Andrea Dainese

  15. Impact on impact parameter resolution as in Pb-Pb pp with charm pp min. bias ALICE Physics Forum - March 11, 2003 Andrea Dainese

  16. Statistics before selections ALICE Physics Forum - March 11, 2003 Andrea Dainese

  17. Displaced vertex selection ALICE Physics Forum - March 11, 2003 Andrea Dainese

  18. 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c Charm w/o primary vertex reconstruction? What if we did not reconstruct the primary vertex? ALICE Physics Forum - March 11, 2003 Andrea Dainese

  19. 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c Charm with new vertexer • First attempt: all tracks in the event are used to reconstruct the vertex position, only the cut on the maximum c2 is applied ALICE Physics Forum - March 11, 2003 Andrea Dainese

  20. V2 V1 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c 1 < pT < 2 GeV/c 5 < pT < 7 GeV/c Charm with new vertexer • The tracks from the D0 tend to “pull the vertex estimate closer to them” • As a consequence both impact parameters are underestimated For each D0 candidate the primary vertex position is estimated using ALL tracks in the event BUT the two decay products of the D0 NEW STRATEGY ALICE Physics Forum - March 11, 2003 Andrea Dainese

  21. Tuning of selection cuts (1) • As in Pb-Pb, cuts are tuned as a function of pT in order to maximize the significance of the signal ALICE Physics Forum - March 11, 2003 Andrea Dainese

  22. Tuning of selection cuts (2) • The cut on the product of impact parameters has to be carefully studied as a function of pT Low pT D0 poor d0 resolution High pT D0 good d0 resolution ALICE Physics Forum - March 11, 2003 Andrea Dainese

  23. Results – pT integrated ALICE Physics Forum - March 11, 2003 Andrea Dainese

  24. Analysis of the worsening: pointing Both SGN and BKG before this cut lower by ~ 10% (events rejected because # trks < 5) Poorer resolution on cos qp Selected SGN after this cut lower by ~ 20 % ALICE Physics Forum - March 11, 2003 Andrea Dainese

  25. Analysis of the worsening: d0 d0 Both SGN and BKG have broader distributions Cut at  < -25000 mm2 Selected SGN is the ~ same Selected BKG larger by factor ~ 4 ALICE Physics Forum - March 11, 2003 Andrea Dainese

  26. pT distribution • For scenario with primary vertex reconstruction • pT distribution of rec. D0 and SGNC vs pT ~ 20,000 with SGNC > 10 up to 10 GeV/c (1 GeV/c bins) ~ 2,000 D0 in 0.5 < pT < 1 GeV/c with SGNC = 14 ALICE Physics Forum - March 11, 2003 Andrea Dainese

  27. ~ 15 % ~ 35 % ~ 10 % Acceptance and Efficiency ALICE Physics Forum - March 11, 2003 Andrea Dainese

  28.  3  5 Extrapolation of results for p-Pb • Starting point: • Assume same detector performance (tracking, PID) as in pp • Primary vertex known as in Pb-Pb (s ~ 15 mm) • Same values for the cuts as in pp (pessimistic) SGNSELECTED/SGNINITIALand BKGSELECTED/BKGINITIAL same as in pp with primary vertex “known” ALICE Physics Forum - March 11, 2003 Andrea Dainese

  29. Extrapolation for p-Pb • SGNSELECTED larger by factor 5 • BKGSELECTED prop. to (multiplicity)2 larger by factor ~10 • Low pT: • High pT: • Globally: • Complete simulation will be done by R.Grosso on time for the PPR ALICE Physics Forum - March 11, 2003 Andrea Dainese

  30. Conclusions First part of chapter 6.5: “Charm and beauty production at LHC” ready and soon released The rest of the chapter is growing: • Hadronic charm in pp down to pT ~ 0 (“fat” beam won’t manage to kill charm!) • First look at D0 in pA: very promising, complete study is starting • Material from the electron and muon branches will come soon • Collaboration with HLT group started during the coffee break It will be a very tasty heavy flavour chapter! ALICE Physics Forum - March 11, 2003 Andrea Dainese

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