Momentum Kick Model and the Clustering of Heavy Quarks in QGP Cheuk-Yin Wong Oak Ridge National Laboratory

Transcription

1 UCLA Jan 22-24, 2009 Momentum Kick Model and the Clustering of Heavy Quarks in QGP Cheuk-Yin Wong Oak Ridge National Laboratory Introduction to the momentum kick model for the near-side ridge Successes of momentum kick model for light quarks Failures of momentum kick model for heavy quarks Clustering phenomenon of slow heavy quarks Conclusions C.Y.Wong, Phy.Rev.C76,054908( 07) C.Y.Wong, Chinese Phys. Lett.25,3939(08) C.Y.Wong, J. Phys. G35,104085(08) C.Y.Wong, Phy.Rev.C78,064905( 08) C.Y.Wong, arxiv: ( 09) C.Y.Wong, Phys. Rev. C76,014902( 07) 1

2 What is the ridge phenomenon? jet ridge Particles are detected associated with a near-side trigger Δφ=φ (particle)- φ (trigger jet) Δη=η (particle)- φ (trigger jet) Δφ Δη Find: Δφ- Δη correlation Probability distribution P(Δφ, Δη ) is in the form of (i) a jet component (ii) a ridge component. Putschke et al. (STAR) J.Phys..G74 S679( 07) 2

3 Many Ridge Models S.A.Voloshin, Phys. Lett. B632, 490 (`06) C.Y.Wong, Phy.Rev.C76,054908( 07);arXiv: ;arxiv: ( 08) E. Shuryak, C76, (`07) V. S. Pantuev, arxiv: R.C. Hwa, arxiv: Nestor Armesto, Carlos A. Salgado, Urs Achim Wiedemann, Phys. Rev. C 76, (2007) Adrian Dumitru, Yasushi Nara, Bjoern Schenke, Michael Strickland, arxiv: A. Majumder, B. Müller, and S. A. Bass, Phys. Rev. Lett. 99, (2007) R. Mizukawa, T. Hirano, M. Isse, Y. Nara, A. Ohnishi, arxiv: Sean Gavin, Larry McLerran, George Moschelli, arxiv: A. Dumitru,F. Gelis, L. McLerran, and R. Venugoplan, arxiv: many more 3

4 Experimental observations and their implications (i) Ridge yield correlated with N_participants (ii) Ridge yield nearly independent of pt trigger, flavor, baryon, light meson characters of the jet (iii) Brayon/meson ratios in the ridge and in inclusive bulk are similar (iv) T_ridge is similar to T_inclusive but slightly higher ~ ridge particles are medium partons (v) Δφ ~ 0 implies that the ridge particles acquire their azimuthally properties from the jet (vi) jet-(medium parton) interactions are short-ranged because of non-perturbative screening ridge particles are medium partons kicked by the jet and they acquire a momentum kick q along the jet direction 4

5 Schematic picture of the momentum kick model jet ridge Δφ Δη 5

6 The momentum kick model 6

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8 Momentum kick model described well STAR near-side data around Δη~0 Data from STAR Collaboration PRL95,152301(05) & J. Phy. G34, S679 (07) 8

9 Parton momentum distribution at the moment of jet-parton collision 9

10 Ridge yield is a maximum at Δφ~0 10

11 Momentum kick model described well STAR near-side data around Δη~0 Data from STAR Collaboration PRL95,152301(05) & J. Phy. G34, S679 (07) 11

12 Momentum kick model described well STAR near-side data around 2.7< η <3.9 STAR Prelinimary Data Wang et al. arxiv: ( 07) 12

13 Momentum kick model gives the correct prediction for the PHOBOX data Data from Wenger et al.(j.phys.g35,104080( 08) 13

14 ptrig=2-3gev ptrig=3-4gev ptrig=4-5gev PHENIX Data ptrig=5-10gev 14

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16 STAR preliminary heavy quark data CuCu at sqrt(s)=200 GeV 0.15<p t assoc <0.5 GeV η trig <0.7, η assoc <1 G. Wang et al. J.Phys. G35, ( 08) 16

17 STAR preliminary heavy quark data AuAu at sqrt(s)=200 GeV 0.15<p t assoc <1.0 GeV η trig <0.7, η assoc <1 G. Wang et al. J.Phys. G35, ( 08) B. Biritz et al. (DNP talk, Oct. 08) 17

18 CuCu PYTHIA results AuAu Jet component associated with heavy quark is small. G.Wang et al. J.Phys. G35, ( 08) 18

19 Momentum kick model fails to reproduce STAR particle near-side yields associated with heavy quarks Experimnetal large associated particle yield suggests collective medium excitation by heavy quarks 19

20 Clusters surrounding a charge Q in a plasma An external charge Q polarizes the plasma medium Medium charges of the same sign are pulled toward Q. Medium charges of the opposite sign are pushed away from Q. This is the familiar Debye screening with a screening radius r D There is no net change of total medium density, to the first order of (α/r D T). However, the second order term (α/r D T) 2 has the same sign for charges of both signs. There is a net increase in total density surrounding Q. This increase in polarization charges can be large in a dense medium. 20

21 A simple model of charge clustering Q (charge +q) at -R/2 Q (charge q) at R/2 medium: e + (charge +q), e - (charge q) particles interact with an e 1 e 2 /r interaction We assume e + and e - are massless and are fermions. We also assume local thermal equilibrium 21

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24 (b) R (fm) Lattice gauge calcualtions of TS 1 =U 1 -F 1. O. Kaczmarek et al. hep-lat/ r C.Y.Wong,Phys.Rev.C76,014902( 07) 24

25 (1) Simple estimates of heavy quark parton cluster (2) 25

26 Implications of a heavy quark parton cluster The motion of the heavy quark is that of a cluster of particles and not just a single particle. The color charge of the heavy quark is substantially screened by the cluster of medium charges. The clustering will enhance the (heavy-quark)-parton cross section by the presence of associated particles. The degree of clustering will decrease in strength as the p t of the heavy quark increases. Associated near-side cluster yield decreases with increasing heavy quark pt. The cluster of particles show up experimentally as associated particles in coincidence with the heavy quark. These associated particles has characteristics different from those associated with a light quark. 26

27 Conclusions The momentum kick model describes near-side ridge data with light quark triggers provides information on early medium properties and jetmedium interaction fails to describe near-side ridge data with heavy quark (electron) trigger Recent STAR near-side heavy quark jet data observations Number of associated with heavy quark is large CuCu yield is large relative to AuAu yield There exists the clustering of medium particles surrounding heavy quarks We should explore whether parton clustering may be a possible origin of the STAR observation of large number of particles associated with heavy quarks 27

28 Additional details 28

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30 Basic ideas of the momemtum kick model Ridge particles are medium partons kicked by the jet and they acquire a momentum kick q along the jet direction The kicked final partons subsequently materialize as hadrons by parton-hadron duality The ridge particle distribution depends on the initial parton momentum distribution and the magnitude of the momentum kick q. 30

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32 The width in Δφ depends on the magnitude of q. at pt=2 GeV 32

33 To describe experimental data, we need 1. A good description of the jet component 2. A good description of the shape of the normalized initial momentum distribution 3. We can then determine the jet-medium interaction parameters by comparison with data: q, f R <N k >, f J 33

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36 Centrality depedence of R AA & ridge yield 36

37 Distribution of the number of jet-(medium parton) collisions 37

38 The momentum kick model gives a good description of R AA 38

39 Centrality dependence in the momentum kick model 39

40 Energy and mass dependence in the momentum kick model 40

41 Possible evolution scenario of medium partons 41

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