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Charm production at LHC: - th. predictions - exp. sensitivity

Charm production at LHC: - th. predictions - exp. sensitivity. Andrea Dainese University of Padova. Outline. Accessible Bjorken x range NLO charm cross section in pp at 14 TeV Charm as a tool to probe gluon PDFs at small x Measurement of D 0 cross section in ALICE. c. c. Bjorken x.

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Charm production at LHC: - th. predictions - exp. sensitivity

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  1. Charm production at LHC:- th. predictions- exp. sensitivity Andrea Dainese University of Padova HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  2. Outline • Accessible Bjorken x range • NLO charm cross section in pp at 14 TeV • Charm as a tool to probe gluon PDFs at small x • Measurement of D0 cross section in ALICE HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  3. c c Bjorken x • Approx. estimated using LO process HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  4. Bjorken x • For pt 0: • x1~x2 ~ 10-4 at y = 0 • min(x1,x2) ~ 10-5 at y =  3 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  5. Cross section at 14 TeV • NLO pQCD calculation implemented e.g. in program by Mangano, Nason and Ridolfi (hvqmnr*) • large uncertainty (more than factor 2) due to choice of charm mass and scales * M.L.Mangano, P.Nason and G.Ridolfi, Nucl. Phys. B373 (1992) 295 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  6. Cross section at 14 TeV • NLO pQCD calculation implemented e.g. in program by Mangano, Nason and Ridolfi (hvqmnr) • large uncertainty (more than factor 2) due to choice of charm mass and scales • much smaller uncertainty (~20%) from PDFs (thanks to HERA!) ALICE baseline kinematics: PYTHIA tuned to reproduce c pt distr. given by NLO with these params N.Carrer and A.D. hep-ph/0312255 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  7. More charm than expected at LHC? • Global fits of HERA data improved by adding nonlinear corrections to standard DGLAP partonic-evolution equations (K.J.Eskola et al., hep-ph/0211239) • Nonlinear corrections physically arise from gluon recombination at small x (~10-3) • and, at LO, imply larger gluon density (w.r.t. to DGLAP) hep-ph/0310111 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  8. Gluons: DGLAP nonlinear nonlinear (quadratic) correction has “–” sign Q2 evolution is slower low Q2 and x has to be larger than in DGLAP x = 10-3 Q = 2 mc = 2.4 GeV HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  9. Charm: nonlinear/DGLAP vs pt • “Enhancement” limited to pt < 2 GeV/c • Strongly dependent on choice of mass and scale* (Q2) • Varies from 1.5 to 5 • ! Currently calculated only at LO ! * mR = mF = Q HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  10. ALICE: a good charm-buster • Excellent tracking in |h| < 0.9 with impact parameter resolution better than 60 mm for pt> 1 GeV/c • Low field (< 0.5 T) + K ID via time-of-flight exclusive D0 K-p+ down to very low pt (~ 0) • … and more (not covered today): • electron ID in TPC+TRD in |h| < 0.9 • muon arm in 2.5 < h < 4 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  11. L3 Magnet B < 0.5 T: 0.2 T low pt acceptance, 0.5 T pt resolution at high pt HMPID RICH @ high pt TOF PID TRD Electron ID PMD g multiplicity FMD Forward multiplicity TPC Tracking, dEdx ZDC Centrality ITS Low pt tracking Vertexing MUON m-pairs PHOS g,p0 ALICE detector HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  12. D0 K-p+:Selection of D0 candidates • Large combinatorial background • Main selection: displaced-vertex selection • pair of tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex Invariant mass analysis to “count” real D0 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  13. D0 K-p+:Results 0.5 < pt < 1 GeV/c 2 < pt < 2.5 GeV/c 12 < pt < 14 GeV/c HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  14. inner bars: statistical shaded band: systematic D0 K-p+:d2s(D0)/dptdy and ds(D0)/dy ds(D0)/dy for |y| < 1 and pt > 0.5 GeV/c statistical error = 3 % systematic error = 14 % from beauty = 8 % MC corrections = 10% B.R. = 2.4 % sppinel (TOTEM) = 5 % HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  15. syst. (14%) stat. (3%) Comparison to pQCD (1) HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  16. Comparison to pQCD (2) HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  17. Data: mc = 1.2 GeV, Q2 = 4mt2 and enhancement Data: mc = 1.3 GeV, Q2 = mt2 and enhancement How to detect the enhancement due to nonlinear effects? • The idea is that the effect (enh. only at very low pt) cannot be mimicked by NLO pQCD • In practice: consider ratio “Data/Theory” for all reasonable choices of Theory parameters hep-ph/0403098 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  18. S/(S+B) S per 107 Pb-Pb events pt > 2 GeV/c, d0 > 180 mm: 80,000 electrons with S/(S+B) = 90 % Open Beauty in electron channelin ALICE • Inclusive B  e + X: • electron ID + cut on pt + cut on impact parameter • Possible in Pb-Pb with dNch/dy = 6000! • pp case under study (trigger …) HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  19. Conclusions • Charm production at LHC probes the gluon distributions at small-x (~10-4), small-Q2 (~10 GeV2) • where *new* (beyond DGLAP) effects might be lurking • Cross-section “prediction” uncertainties dominated by choice of mass and scales (PDFs quite well constrained by HERA) • ALICE will • measure D pt-differential cross section down to almost 0 • allow sensitive comparison to pQCD predictions HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  20. Back-up slides HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  21. d0K d0 <<0 cos pointing 1 D0 K-p+:Selection of D0 candidates • Main selection: displaced-vertex selection • pair of tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  22. test beam: p id. as e = 1 % p as e < 10% up to 5 GeV/c Open Beauty in electron channel Electron identification in TRD-TPC (pt > 1 GeV/c) + impact parameter in ITS HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  23. this looks better! small effect How do nonlinear effects compare to ALICE sensitivity? ! assuming same enhancement at NLO as at LO ! A.D., R.Vogt, M.Bondila, K.J.Eskola and V.J.Kohlinen, hep-ph/0403098 HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  24. beauty charm misid. p S/(S+B) S per 107 Pb-Pb events pt > 2 GeV/c, d0 > 180 mm: 80,000 electrons with S/(S+B) = 90 % Open Beauty in electron channel • B electron identification: • cut on pt : reject low-pt backgrounds (conversions, dalitz of light mesons) • cut on impact parameter: reject background from D mesons HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

  25. Check min pt of muon for B Lumi for pp Tables with bbbar HERA-LHC Workshop - CERN, March 26, 2004 Andrea Dainese

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