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Investigating heavy quark energy loss with lepton-tagged jets

Investigating heavy quark energy loss with lepton-tagged jets. Jennifer Klay California Polytechnic State University San Luis Obispo. Theoretical Motivation. Transport coefficient. Strong coupling. Casimir factor. Medium size.

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Investigating heavy quark energy loss with lepton-tagged jets

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  1. Investigating heavy quark energy loss with lepton-tagged jets Jennifer Klay California Polytechnic State University San Luis Obispo

  2. Theoretical Motivation Transport coefficient Strong coupling Casimir factor Medium size Quarks (CR=4/3) vs. Gluons (CR=3)  colour charge dependence Gluon(g): self-interacting mediator of strong force Light quark(q): up, down, strange m ~ 300 MeV «Dead-cone» effect for θ0 < mQ/EQ  mass dependence Heavy quark(Q): charm, bottom m ~1-5 GeV Y.L.Dokshitzer and D.E. Kharzeev, Physics Letters B519, 199 (2001) ETD-HIC 2007, Montreal QC

  3. Experimental Landscape STAR, Phys Rev Lett 91, 072304 Di-hadron suppression Photon vs. Hadron suppression Non-photonic electron suppression similar to light hadrons ETD-HIC 2007, Montreal QC

  4. Heavy Quark Production in PYTHIA Pair Creation Leading Order: Back-to-back in azimuth (gluon in (c) causes kinematic shift but cross-sections determined by LO 2 2) Flavour Excitation Scattering of Q(Q) out of initial state into final state by gluon or light quark (Virtuality of hard scatter must be > mQ2) E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000) Gluon Splitting No QQ in hard-scatter, but pair created within parton shower or during the fragmentation process of a gluon or a light quark QCD Process classification: 2, 1, or 0 heavy flavours in hard-scattering final state ETD-HIC 2007, Montreal QC

  5. b-Jet Kinematics in PYTHIA E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000) Normalized to unit area for shape comparison Leading order pairs come out back-to-back  pT Similar results in HERWIG, ISAJET See R.D. Field, Phys. Rev. D65 (2002) 094006 hep-ph/0201112 ETD-HIC 2007, Montreal QC

  6. Lin and Vogt, Nucl.Phys. B544 (1999) 339-354 bB- (38%), B0 (38%), B0s (11%), Λ0b(13%) BlX, BDXlY Bl- (9.30%), BDXl-Y(2.07%) Bl+(1.25%), BDXl+Y(7.36%) bb->dilepton 0.020/event Bl1Xl1l2Y 0.018/event How to find them? Semi-leptonic decay channel provides the signal sources to look for… Find the jet with a B through the e,μ decay and you have your parton… • Backgrounds: • Photonic electrons : 0,  Dalitz, gama conversions  Remove with Minv cut • Mis-identified particles • Leptons from underlying event ETD-HIC 2007, Montreal QC

  7. Lepton Jets at the Tevatron Good agreement between experiment/theory p+p, 1.8 TeV Herwig Simulation: bb di-jets within |η|<1.5 Event selection: (69K e + 15K μ) - di-jet with ETuncorr>15 GeV (<ETparton> ~ 20 GeV) - pT>8 GeV lepton within ΔR < 0.4 - Correction for fake tags In simulation these are due to Gluon-splitting CDF, Phys. Rev. D69 (2004) 072004 hep-ex/0311051 ETD-HIC 2007, Montreal QC

  8. Heavy Quark Correlations at RHIC A. Mischke, SQM2007 trigger side statistical errors only scaled by 2.86 3.83% 54% ~10% charm production ~70% from charm ~30% from beauty essentially from B decays only probe side ETD-HIC 2007, Montreal QC

  9. Jet rate comparison LHC is a jet factory • Full complement of hard observables accessible: • Identified spectra, RAA • Multi-hadron correlations • Jets: Fragmentation function modifications, -jet coincidences, tagged heavy quark jets, … • Quarkonia ETD-HIC 2007, Montreal QC

  10. Large Hadron Collider at CERN Latest Schedule: Summer 2008: commission 14 TeV p+p Winter 2009: first 5.5 TeV Pb+Pb collisions? Lac Leman LHC SPS ALICE CERN ETD-HIC 2007, Montreal QC

  11. Spectrum of jet observables 1/event 106/mo. 50 GeV 10 GeV 20 GeV 100 GeV 200 GeV Jet ET ~ 10-30 GeV Jet ET ~ 50-200 GeV Leading particle Spectra Jet reconstruction RAA Tagged jets (-jet, b-jet) Multi-hadron correlations Fragmentation functions Complementarity with RHIC Exclusive to LHC, completely new regime BUT! Need a trigger ETD-HIC 2007, Montreal QC

  12. Heavy quark jet production Expected N(QQ) per central A+A Collision: RHICLHC Charm 10 250 Bottom 0.055 E. Norrbin & T. Sjostrand, Eur. Phys. J. C17, 137 (2000) A B C ETD-HIC 2007, Montreal QC

  13. Size: 16 x 26 meters Weight: 10,000 tons ALICE TOF TRD HMPID ITS PMD Muon Arm PHOS ALICE TPC ETD-HIC 2007, Montreal QC

  14. Tracking/PID Robust, redundant tracking: 100 MeV/c to 100 GeV/c DpT/pT ITS (Silicon): 4<r<44 cm, 6 layers TPC: 85<r<245 cm, 159 pad rows TRD: 290<r<370 cm, 6 layers Central Pb+Pb p+p B field = 0.5 T  good pattern recognition Long lever arm  good momentum resolution Material budget: vertex outer TPC < 0.1 X0 107 Central Pb+Pb events  p K TPC dE/dx ~5.5-6.5% ETD-HIC 2007, Montreal QC ALICE PPR CERN/LHCC 2003-049

  15. ALICE Electromagnetic Calorimeter • Upgrade to ALICE • ~17 US and European institutions • Current expectations: • 2009 run: partial installation • 2010 run: fully installed and commissioned Lead-scintillator sampling calorimeter Shashlik fiber geometry Avalanche photodiode readout Coverage: ||<0.7, =110° ~13K towers (x~0.014x0.014) Depth ~21 X0 Design resolution: E/E~1% + 8%/√E ETD-HIC 2007, Montreal QC

  16. Acceptance/triggering/rates L = 5 x 1026 cm-2 s-1; t = 106 s; 50 GeV jet Rate ~ 1 Hz ETD-HIC 2007, Montreal QC

  17. Jet triggering with EMCAL A. Mischke and P. Jacobs, ALICE INT-2005-50 • Background rejection ~ factor of 10 • Centrality dependent threshold • Good efficiency above ~60 GeV ETD-HIC 2007, Montreal QC

  18. p+p Pb+Pb    FastJet, M. Cacciari, G. Salaam hep-ph/0512210 N3 Nlog(N) In all cases, a background subtraction method is necessary Geometric nearest neighbor search Jet-finding in Heavy Ion Collisions Cone jet finders Sum energy within cone of R = √(2+2) Conceptually simple Small cones may have own trigger bias  kT algorithms Allow for arbitrary shaped jets  follow the energy flow Less bias on intra-jet shape N3 combinatorics Many methods under investigation in ALICE ETD-HIC 2007, Montreal QC

  19. Cone finder results Pb+Pb: E/E~30% for Ejet = 100 GeV Comparable to p+p Background is subtracted event-by-event using information from outside cone within event and statistical average of background from all events R = 0.3, pT > 2 GeV/c ETD-HIC 2007, Montreal QC

  20. What contributes to resolution? p+p, pure simulation pT cut has modest effect, R more dramatic Intrinsic limit to resolution if “hidden” neutrals (n,K0L,) are excluded Jet resolution is affected by the cuts (R,pT) which are necessary to reduce the background/fluctuations in Pb+Pb hadron calorimetry vs. tracking Trade-off: resolution vs. background rejection ETD-HIC 2007, Montreal QC

  21. Contributions to electron yields • -PYTHIA 6.22 for shapes • -Cross-sections from NLO (Dainese, y<0.9) • Charm: 2.14 mb • Bottom: 0.082 mb • W: 6.5 nb (NLO,Vogt) ALICE EMCAL acceptance W electrons can be distinguished with isolation cuts Calculation by Mark Heinz ETD-HIC 2007, Montreal QC

  22. Electron Identification Studies Electron/pion discrimination via cluster properties Electron p/E Studies by Mark Heinz ETD-HIC 2007, Montreal QC

  23. Electron/Pion Id Combined cuts reduce pion background with small decrease in efficiency p/E Cluster shape Cluster multiplicity ETD-HIC 2007, Montreal QC

  24. Visualizing events in ALICE K+ (pT=8.8GeV) e+ (pT=16.8GeV) b+b scatter, Q2~50 GeV B0 (pT=41.8GeV)  e+ (pT=16.8GeV) + e (pT=3.3GeV) + D- (pT=21.9GeV)  light hadrons (TRD and TOF not shown) ETD-HIC 2007, Montreal QC

  25. Putting it together Investigate the differences in fragmentation distributions for tagged and un-tagged jets How similar/different are they? Pb+Pb only Pb+Pb/p+p Simulation studies in progress for EMCAL review ETD-HIC 2007, Montreal QC

  26. Summary/Outlook High production rate for heavy quarks and jets at LHC LHC Jet Identification in heavy ions opens up new observable for investigating flavor-dependent medium coupling b-tagging via leptons in jet/di-jet events • Experimental requirements • Jet triggering • Good jet-finding for pTjet > 30 GeV in heavy ions • PID/Momentum resolution for eID/jet fragmentation studies • Secondary vertex reconstruction Are you ready? Collisions are just around the corner! ETD-HIC 2007, Montreal QC

  27. Empty ALICE (last year) ETD-HIC 2007, Montreal QC

  28. ALICE ca. 11-July-2007 Installation proceeds apace… ETD-HIC 2007, Montreal QC

  29. Backup ETD-HIC 2007, Montreal QC

  30. Jet-finding Challenges More than one pT > 7 GeV/c particle per event ~1-2 TeV of energy within jet cone of R ~1 Charged particles from Pb+Pb Background* Energy within cone, E(R) Charged particles within jets* Cone radius, R *(Similar for charged + neutral) pT cuts/small cone radii can suppress background, but also influence jet energy resolution Trade-off with hadron calorimetry vs. tracking for jet reconstruction ETD-HIC 2007, Montreal QC

  31. Fluctuations get worse with larger cones Backgrounds • Fluctuations in background energy within jets caused by: • Event-by-event impact parameter variations • Poissonian fluctuations of uncorrelated particles • Correlated particles from other sources (e.g. overlapping low ET jets) • In- and Out-of-Cone fluctuations ETD-HIC 2007, Montreal QC

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