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p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization

p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization. Tsiledakis Georgios University of Heidelberg. 417 th WE-Heraeus-Seminar, June 25 - 28 2008, Bad Honnef. Outline. Introduction

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p t correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization

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  1. pt correlations versus relative azimuth of D-Dbar pairs as a sensitive probe for thermalization Tsiledakis Georgios University of Heidelberg 417th WE-Heraeus-Seminar, June 25 - 28 2008, Bad Honnef

  2. Outline • Introduction • Primordial c-cbar (D-Dbar) correlations for p-p collisions at 14 TeV • The Average Momentum Correlator • Contribution of transverse radial/elliptic flow • Primordial B-Bbar pt correlations • Charm Production in ALICE • D-e pt correlations • e+ - e- pt correlations from D, B decays • Conclusions

  3. Introduction • Higgs mass: electro-weak symmetry breaking. (current quark mass) • QCD mass: Chiral symmetry breaking. (constituent quark mass) • Strong interactions do not affect heavy-quark masses. • Important tool for studying properties of the hot/dense medium at RHIC and LHC. • Test pQCD predictions at RHIC and LHC. Total quark mass (MeV) X. Zhu, M. Bleicher, K.Schweda, H. Stoecker, N. Xu et al., PLB 647 (2007) 366.

  4. Low Energy D-Dbar Meson Pair Correlations D 103/N * dN/d(Df) Df Dbar • Correlation variable studied:  = (D) – (Dbar) • At low energies, D-Dbar production correlated! • Pythia describes these correlations! • How about LHC energies?  (D-Dbar) • E791 : Eur. Phys. J. direct C1 (1999) 4 • WA92 : Phys. Lett. B385 (1996) 487 • NA32 : PLB257 (1991) 519 , PLB302 (1993) 112, PLB353 (1995) 547 For many more details, see: C. Lourenço & H. K. Wöhri, Phys. Rep. 433 (2006) 127.

  5. Charm correlations at LHC • Inp+p: c-cbar are correlated • Flavor creation: back to back • Gluon splitting: forward • Flavor excitation: flat • InPb+Pb: Correlations vanish  frequent interactions among partons !  probe light-quark thermalization !

  6. PYTHIA (v.6_406) 500000 p-p events at √s = 14 TeV 1 pair c-cbar/event no tracking, 100 % efficiency No rapidity cut Fragmentation Pv = 0.75 (default) D p c c p D PYTHIA Settings ALICE PPR vol. II, J. Phys. G: Nucl. Part. Phys. 32 (2006) 1295-2040

  7. Fragmentation of charm quarks into D mesons Primordial D –no decay • c-cbar  D0 + D0bar (61 %) D+ + D- (19 %) Ds+ + Ds- (12 %) Lc+ + Lc-bar (8 %) • Large fraction of c goes to D0 mesons • Measure D0-D0bar correlations! Counts D+ D*+ D0 D*0 Ds+ D*s+ PID N(D0) : N(D+) : N(D*0) : N(D*+) = 1 : 1 : 3 : 3

  8. Primordial D-Dbar angular correlations • Azimuthal correlations survive fragmentation No pt cut • FC away side correlation • FE + GS  flat Df • Rather weak Df dependence • Enhanced correlations • FC back to back • GS forward • FE flat • Strong pt dependence • Correlations sensitive to pt region • Study pt correlations versus Df(DDbar)

  9. Primordial D-Dbar pt correlations D • Incl. pt-distr.  Cumulant x(pt) • 2-dim plot (x(pt)1, x(pt)2) for D-Dbar respectively • Is uniform when no correlations are present Inclusive pt distribution x(pt) Cumulant pt variable x pt (GeV/c)

  10. D-Dbar pt correlations – at full Df pt correlations are dominated by large pt effects (along the diagonal atx1~x2~1) Same event Mixed event

  11. D-Dbar pt correlations – angular dependence Gluon Spitting 0 < Df < 45 45 < Df < 90 90 < Df < 135 135 < Df < 180 Flavor Creation

  12. Measurement of pT Fluctuations using the Average Momentum Correlator • To quantify dynamical pT fluctuations • We define the quantity<pt,1pt,2>. • It is a covariance and an integral of 2-body correlations. • It equals zero in the absence of dynamical fluctuations • Defined to be positive for correlation and negative for anti-correlation. S. Voloshin. V. Koch. H. Ritter, PRC60 (1999) • pt,ifor D • pt,j for Dbar • Nk=1 / 2 / 2 where

  13. Average Momentum Correlator - same event analysis At full Df: <Dpt,1Dpt,2> = 0.1995 +/- 0.006 (GeV/c)2 or Spt~30 % Counts CERES at SPS has measured ~1% fluctuations for charged particles <Dpt,1Dpt,2> = 22.71+/- 0.32 (MeV/c)2 pt (DDbar)~30 GeV/c (GeV/c)2

  14. Average Momentum Correlator – angular dependence Signal Background • At full Df: <Dpt,1Dpt,2> ~ 0.20 (GeV/c)2 • or Spt~30 % • Enhanced correlations • Only FC produces correlations atDf ~ p • Distinction of the baseline at middle Df – flat to 0 • Average Momentum Correlator is a sensitive measure of back to back correlations

  15. Transverse radial flow contribution ptDbar • Assume a fireball created in a coll. from PYTHIA • Expansion produces additional momentum ptf • Attribute to each pt a randomized position • Add the radial flow component vectorially ptf = gbm ptD b = 0, 0.3, 0.6, 0.9 ptDbar Counts ptD pt (GeV/c) E. Cuautle and G. Paic hep-ph/0604246 v2 24 May 2006

  16. Transverse radial flow contribution on <Dpt,1Dpt,2> Radial flow: b = 0, 0.3, 0.6, 0.9 10000 events for b = 0.3, 0.6, 0.9 500k events for b = 0 • Stronger flow introduces anti-correlations around Df = 180o f D f Dbar Dbar D

  17. Elliptic flow contribution • Introduces a cos(2Df) modulation • We introduce the measure fi,j • We calculate the average momentum correlator for • DDbar pairs that have flow 10% and 90% We evaluate the elliptic flow expressed in units of (GeV/c)2

  18. Elliptic flow contribution on <Dpt,1Dpt,2> • realistic amount of elliptic flow does not change correlations !

  19. Primordial D-Dbar angular correlationsat mid-rapidity Full rapidity (500000 events) Mid-rapidity (200000 events) • NLO dominant at LHC • Weak D-Dbar correlation in Df • Measurement of medium modification of this correlation in heavy ion collisions is challenging • FC away side correlation • FE  flat in Df • GS  forward • Use of pt correlator

  20. Average Momentum Correlator for D-Dbarat mid-rapidity Full rapidity (500000 events) Mid-rapidity (200000 events) • At full Df: <Dpt,1Dpt,2> = 0.549+/-0.017 (GeV/c)2 • or Spt~40 % • Stronger signal at mid-rapidity

  21. Charm Production in ALICE using D0 K-p+ ALICE has a barrel system with high precisionvertexing, PID and electron identification (|h| < 0.9)and a forward muon spectrometer (h: 2.5–4.0), down to low pt. Charm production can be studied: • In the electronic and muonic channels D  eX (mX) • In several hadronic decay channels: D0  K , D±  K D0  Kpp, Ds  KKp, Ds    D*  D0p, Lc  pKp • 109 p-p events • Nccbar/event = 0.16 (PPR2) • c-cbar  D0 (61 %) • D0 Kp (4 %) • Eff.(acceptance, reconstruction, selection eff.) ~ 0.005 • S/B ~ 10% • TPC: main tracking device • ITS: high spatial resolution • TRD: good electron PID (high pion rejection) • ToF: extend PID to large pt • #Events with both D0-D0bar < 10 • Looking at semileptonic decays ALICE PPR II, J. Phys. 32 (2006) 1295

  22. Charmed e+/e- correlations • Study e+/e- pt correlations • at the electronic channel D  e + X • BR ~ 15% from D+/-, ~7% from D0 • At low pt the correlation is lost (< 0.5 GeV/c) • At pt > 1 GeV/c survives • Need to apply a pt cut: • 10% e with pt > 1 GeV/c • 1% e with pt > 2 GeV/c • To account the BG from Dalitz, conversions, B semileptonic decays… D e- pt D (GeV/c) pt e- (GeV/c)

  23. Angular correlation of D-e from D  e + X No pt cut pt > 1 GeV/c • Semileptonic-decay e are strongly pt correlated with parent D • e+/e- from D-Dbar decay preserve the original D-Dbar angular correlation to a large extent No pt cut pt > 1 GeV/c

  24. D-e pt correlation Kp<—D0<—D*—c – c— D*—> D0—>e- + X • No pt cut Full rapidity Mid-rapidity • D-e pt correlations survive charm decay

  25. Charmed e+/e- pt correlations e+ + X<—D0<—D*—c – c— D*—> D0—>e-+ X Full rapidity Mid-rapidity Mid-rapidity with pt > 0.5 GeV/c Mid-rapidity with pt > 1 GeV/c • e+ - e- pt correlations at pt > 1 GeV/c survive charm decay

  26. PYTHIA processes for charm/beauty generation f + f’  f + f’ g + g  f + fbar f + g  f + g g + g  g + g D-Dbar Fraction of each process/All processes B-Bbar • GS dominant for D-Dbar • FC dominant for B-Bbar • FE is flat pt (GeV/c)

  27. Primordial B-Bbar angular correlations • At full Df: <Dpt,1Dpt,2> = 2.97 +/- 0.18 (GeV/c)2 or Spt~55 % • GS flat in dN/dDf but strong in small Df using the Average Momentum Correlator • FC back to back • The Average Momentum Correlator is very sensitive to different PYTHIA processes for beauty generation

  28. e+/e- correlations from B decays e+ + X<—B0<—B*—c – c— B*—> B0—>e-+ X • e+/e- from B decays are strongly pt correlated at small and large Df • Need to study background BDe pt B (GeV/c) pt e- (GeV/c) pt > 1 GeV/c

  29. Conclusions e<—D0<—D*—c – c— D*—> D0—>e- • In p+p, heavy q-qbar production is correlated • The Average Momentum Correlator is a sensitive measure • Correlations survive hadronization • e+- e- pt correlations at pt > 1GeV/c survive charm/beauty decay  need TRD for electron ID!  need full simulations within ALICE  study changes in correlations and address light quark thermalization at LHC • <Dpt,1Dpt,2> ~ 0.2(GeV/c)2 for D-Dbar

  30. Backup slides

  31. Measure of mean pT fluctuations • DMpT : variance of MpT dist. • Dp2T : variance of inclusive pT dist. • <N> : mean multiplicity • pT : inclusive (event-averaged) mean pT • Normalizeddynamical fluctuation = 0 for purely statistical fluctuation > 0(< 0) with positive/negative two-particle correlation or dynamical EbyE fluctuation Dimensionless measure SpT • Proportional to mean covariance • of all particle pairs / event • Robust under change of multiplicity due to changes in beam energy and acceptance

  32. c-cbar angular correlations • PYTHIA production • No pt cut • Away side correlation  = (c) – (cbar)

  33. D-Dbar pt correlations - Mixed event analysis Full Df • Uniform populated – no correlations 0 < Df < 45 45 < Df < 90 90 < Df < 135 135 < Df < 180

  34. D-Dbar pt correlations - Same event analysis Full Df Gluon splitting • High pT correlations at small Df 0 < Df < 45 45 < Df < 90 90 < Df < 135 135 < Df < 180

  35. D-Dbar pt correlations - Same event analysis Full Df Flavor excitation • Rather flat 0 < Df < 45 45 < Df < 90 135 < Df < 180 90 < Df < 135

  36. D-Dbar pt correlations - Same event analysis Full Df Pair creation • High pT correlations at big Df 0 < Df < 45 45 < Df < 90 90 < Df < 135 135 < Df < 180

  37. Average Momentum Correlator for same/mixed events Counts Mixed events Same events Counts GeV2 GeV2

  38. Correlation strength for primordial D0 and D0 from D* 50000 • Generate D0, D+/-, Ds (no resonances) with Pv=1 (0.75 default) • Generate D* (only resonances) with Pv=0 and decay them… • correlations survive resonance decay

  39. Elliptic flow contribution on dN/dDF No flow 10% elliptic flow 90% elliptic flow

  40. Radial flow contribution on dN/dDF 10000 b = 0, 0.3, 0.6, 0.8, 0.9 • With increasing b, near-side/away-side peaks are enhanced

  41. Charm Production in ALICE ALICE has a barrel system with high precisionvertexing, PID and electron identification (|h| < 0.9)and a forward muon spectrometer (h: 2.5–4.0), down to low pT. Charm production can be studied: • In the electronic and muonic channels D  eX (mX) • In several hadronic decay channels: D0  K , D±  K D0  Kpp, Ds  KKp, Ds    D*  D0p, Lc  pKp • TPC: main tracking device • ITS: high spatial resolution • TRD: good electron PID (high pion rejection) • ToF: extend PID to large pT • D0 K-p+ the cleanest channel • pair of opposite-charge tracks with large impact parameters • good pointing of reconstructed D0 momentum to the primary vertex ALICE PPR II, J. Phys. 32 (2006) 1295

  42. pt for D-Dbar at full and mid-rapidity Full rapidity (500000 events) Mid-rapidity (200000 events)

  43. Fraction of each process/All processes Full rapidity (100000 events) pt (GeV/c) Mid-rapidity (200000 events)

  44. Number of charmed electrons • 109 p-p events • Nccbar/event = 0.16 (PPR2) • c-cbar  D0 (61%) • c-cbar  D+/- (20%) • D  e + X (15% from D+/-, 7% from D0) • 10% e with pt > 1 GeV/c #events with e+/e- from D0 = 0.16*0.612*0.072*109 ~ 300000 At pt > 1 GeV = 3000 #events with e+/e- from D+/- = 0.16*0.202*0.152*109 ~ 144000 At pt > 1 GeV = 1440 ~ 4500 clean e+/e- pairs with pt > 1 GeV at full rapidity

  45. D-e e+ - e-

  46. At full Df: <Dpt,1Dpt,2> = 2.97 +/- 0.18 (GeV/c)2 • or Spt~55 % Counts B-Bbar (GeV/c)2 • At full Df: <Dpt,1Dpt,2> = 0.2 +/- 0.006 (GeV/c)2 • or Spt~30 % Counts D-Dbar (GeV/c)2

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