1 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 , 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 p t correlations Charm Production in ALICE D-e p t correlations e+ - e- p t correlations from D, B decays Conclusions

3 Introduction Total quark mass (MeV) X. Zhu, M. Bleicher, K.Schweda, H. Stoecker, N. Xu et al., PLB 647 (2007) )Higgs mass: electro-weak symmetry breaking. (current quark mass) 2)QCD mass: Chiral symmetry breaking. (constituent quark mass) éStrong interactions do not affect heavy-quark masses. éImportant tool for studying properties of the hot/dense medium at RHIC and LHC. éTest pQCD predictions at RHIC and LHC.

4 Low Energy D-Dbar Meson Pair Correlations  (D-Dbar)  =  (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  Correlation variable studied: 10 3 /N * dN/d(  ) At low energies, D-Dbar production correlated! Pythia describes these correlations!  How about LHC energies? For many more details, see: C. Lourenço & H. K. Wöhri, Phys. Rep. 433 (2006) 127. D Dbar 

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

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

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

8 Primordial D-Dbar angular correlations  FC  away side correlation  FE + GS  flat   Rather weak  dependence No p t cut  Enhanced correlations  FC back to back  GS forward  FE flat  Strong p t dependence  Correlations sensitive to p t region  Study p t correlations versus  (DDbar)  Azimuthal correlations survive fragmentation

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

10 D-Dbar p t correlations – at full  p t correlations are dominated by large p t effects (along the diagonal at x  x  ) Same event Mixed event

11 D-Dbar p t correlations – angular dependence    Gluon Spitting Flavor Creation

12 Measurement of p T Fluctuations using the Average Momentum Correlator To quantify dynamical p T fluctuations –We define the quantity. –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) / 2 where  p t,i for D  p t,j for Dbar  N k =1

13 Average Momentum Correlator - same event analysis p t (DDbar)~30 GeV/c At full  : = / (GeV/c) 2 or  p t ~30 % Counts CERES at SPS has measured ~1% fluctuations for charged particles  = / (MeV/c) 2 (GeV/c) 2

14 Average Momentum Correlator – angular dependence  Enhanced correlations  Only FC produces correlations at   Distinction of the baseline at middle  – flat to 0  Average Momentum Correlator is a sensitive measure of back to back correlations Signal Background  At full  : ~ 0.20 (GeV/c) 2 or  p t ~30 %

15 Transverse radial flow contribution ptDptD p t Dbar ptDptD p t f =  m  = 0, 0.3, 0.6, 0.9 E. Cuautle and G. Paic hep-ph/ v2 24 May 2006  Assume a fireball created in a coll. from PYTHIA  Expansion produces additional momentum p t f  Attribute to each p t a randomized position  Add the radial flow component vectorially p t (GeV/c) Counts

16 Transverse radial flow contribution on Radial flow:  = 0, 0.3, 0.6, 0.9  Stronger flow introduces anti-correlations around  = 180 o events for  = 0.3, 0.6, k events for  = 0 D Dbar D f f

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

18  realistic amount of elliptic flow does not change correlations ! Elliptic flow contribution on

19 Full rapidity ( events) Mid-rapidity ( events) Primordial D-Dbar angular correlations at mid-rapidity NLO dominant at LHC Weak D-Dbar correlation in  Measurement of medium modification of this correlation in heavy ion collisions is challenging  FC  away side correlation  FE  flat in   GS  forward  Use of p t correlator

20 Average Momentum Correlator for D-Dbar at mid-rapidity  At full  : = / (GeV/c) 2 or  p t ~40 %  Stronger signal at mid-rapidity Full rapidity ( events) Mid-rapidity ( events)

21 Charm Production in ALICE using D 0  K -  + ALICE has a barrel system with high precision vertexing, PID and electron identification (|  | < 0.9) and a forward muon spectrometer (  : 2.5–4.0), down to low p t. Charm production can be studied: In the electronic and muonic channels D  eX (  X) In several hadronic decay channels: D 0  K , D ±  K   D 0  K , D s  KK , D s   D*  D 0 ,  c  pK  ALICE PPR II, J. Phys. 32 (2006) 1295  TPC: main tracking device  ITS: high spatial resolution  TRD: good electron PID (high pion rejection)  ToF: extend PID to large p t  10 9 p-p events  Nccbar/event = 0.16 (PPR2)  c-cbar  D 0 (61 %)  D 0   (4 %)  Eff.(acceptance, reconstruction, selection eff.) ~  S/B ~ 10% #Events with both D 0 -D 0 bar < 10  Looking at semileptonic decays

22 Charmed e+/e- correlations p t D (GeV/c) p t e- (GeV/c) D e- Study e+/e- p t correlations at the electronic channel D  e + X BR ~ 15% from D +/-, ~7% from D 0 At low p t the correlation is lost (< 0.5 GeV/c) At p t > 1 GeV/c survives Need to apply a p t cut: 10% e with p t > 1 GeV/c 1% e with p t > 2 GeV/c To account the BG from Dalitz, conversions, B semileptonic decays…

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

24 D-e p t correlation K  D 0 —>e- + X Full rapidity Mid-rapidity  No p t cut  D-e p t correlations survive charm decay

25 Charmed e+/e- p t correlations Full rapidity Mid-rapidity Mid-rapidity with p t > 0.5 GeV/c Mid-rapidity with p t > 1 GeV/c  e+ - e- p t correlations at p t > 1 GeV/c survive charm decay e+ + X D 0 —>e- + X

26 PYTHIA processes for charm/beauty generation Fraction of each process/All processes f + f’  f + f’ g + g  f + fbar f + g  f + g g + g  g + g GS dominant for D-Dbar FC dominant for B-Bbar FE is flat D-Dbar B-Bbar p t (GeV/c)

27 Primordial B-Bbar angular correlations At full  : = / (GeV/c) 2 or  p t ~55 % GS flat in dN/d  but strong in small  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 p t e- (GeV/c) p t > 1 GeV/c  e+/e- from B decays are strongly p t correlated at small and large   Need to study background B  D  e p t B (GeV/c) e+ + X B 0 —>e- + X

29 Conclusions  In p+p, heavy q-qbar production is correlated  The Average Momentum Correlator is a sensitive measure  Correlations survive hadronization  e + - e - p t correlations at p t > 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 e D 0 —>e- ~ 0.2 (GeV/c) 2 for D-Dbar

30 Backup slides

31 Measure of mean p T fluctuations Normalized dynamical fluctuation  M pT : variance of M p T dist.  p 2 T : variance of inclusive p T dist. : mean multiplicity p T : inclusive (event-averaged) mean p T = 0 for purely statistical fluctuation > 0(< 0) with positive/negative two- particle correlation or dynamical EbyE fluctuation pTpT Dimensionless measure  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 p t cut  Away side correlation  =  (c) –  (cbar)

33 D-Dbar p t correlations - Mixed event analysis  Full      Uniform populated – no correlations

34 Gluon splitting  Full     D-Dbar p t correlations - Same event analysis  High p T correlations at small 

35 Flavor excitation  Full      D-Dbar p t correlations - Same event analysis  Rather flat

36 Pair creation  Full     D-Dbar p t correlations - Same event analysis  High p T correlations at big 

37 Average Momentum Correlator for same/mixed events Mixed events Same events GeV 2 Counts

38 Correlation strength for primordial D0 and D0 from D*  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 50000

39 No flow 10% elliptic flow 90% elliptic flow Elliptic flow contribution on dN/d 

40 Radial flow contribution on dN/d   = 0, 0.3, 0.6, 0.8, 0.9  With increasing  near-side/away-side peaks are enhanced 10000

41 Charm Production in ALICE ALICE has a barrel system with high precision vertexing, PID and electron identification (|  | < 0.9) and a forward muon spectrometer (  : 2.5–4.0), down to low p T. Charm production can be studied: In the electronic and muonic channels D  eX (  X) In several hadronic decay channels: D 0  K , D ±  K   D 0  K , D s  KK , D s   D*  D 0 ,  c  pK  ALICE PPR II, J. Phys. 32 (2006) 1295  D0  K-  + the cleanest channel pair of opposite-charge tracks with large impact parameters good pointing of reconstructed D0 momentum to the primary vertex  TPC: main tracking device  ITS: high spatial resolution  TRD: good electron PID (high pion rejection)  ToF: extend PID to large p T

42 Full rapidity ( events) Mid-rapidity ( events) p t for D-Dbar at full and mid-rapidity

43 Mid-rapidity ( events) Full rapidity ( events) Fraction of each process/All processes p t (GeV/c)

44 Number of charmed electrons  10 9 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 p t > 1 GeV/c #events with e+/e- from D0 = 0.16* * *10 9 ~ At p t > 1 GeV = 3000 #events with e+/e- from D+/- = 0.16* * *10 9 ~ At p t > 1 GeV = 1440 ~ 4500 clean e+/e- pairs with pt > 1 GeV at full rapidity

45 e+ - e- D-e

46 D-Dbar B-Bbar  At full  : = / (GeV/c) 2 or  p t ~55 %  At full  : = 0.2 +/ (GeV/c) 2 or  p t ~30 % Counts (GeV/c) 2