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QGP Formation Signals and Quark Recombination Model

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Presentation on theme: "QGP Formation Signals and Quark Recombination Model"— Presentation transcript:

1 QGP Formation Signals and Quark Recombination Model
Chunbin Yang Central China Normal University Wuhan

2 Outline Heavy ion collisions and QGP formation Anomalies at RHIC
Physics ideas in the recombination model Fragmentation in the recombination model Applications to Au+Au collisions NCQ scaling of flow v2 Violation of the scaling Particle species dependence of Cronin effect Discussions C.B. Yang

3 Hot and Dense Cooling down Initial conditions freezing out
time Hot and Dense Cooling down freezing out Initial conditions and interactions C.B. Yang

4 QGP signal from the bulk?
QGP formation signals Strangeness enhancement Suppression of J/Ψ Dilepton enhancement Direct photon … Parton degree of QGP? QGP signal from the bulk? Experimental probes: 1) Penetrating probes: “jets” energy loss 2) Bulk probes :Elliptic flow, radial flow … C.B. Yang

5 Evidence for the formation of QGP
Single hadron Dihadron Jet quenching Energy loss of jets in medium No suppression for p spectrum C.B. Yang

6 Hadron production mechanisms
Partons are produced in high energy collisions like e++e-, e+p, p+p, p+A,A+A Partons in the final stage of evolution are converted into hadrons HOW? C.B. Yang

7 Traditional models String formation and break for low p T
Fragmentation for high p T The string model may not be applicable to heavy ion collisions Fragmentation failed for central Au+Au collisions C.B. Yang

8 Anomalies at intermediate pT
B/M v2(pT) Jet structure Cronin effect p/ ≈1 v2(baryons) > v2(mesons) not the same as in pp RCPp > RCP Hard to be understood in traditional models C.B. Yang

9 Hadronization by recombination
The colliding system generates quarks and gluons in the phase space The quarks get dressed The dressed quarks recombine into hadrons to the detector C.B. Yang

10 Why Recombination? meson momentum higher yield heavy penalty p1+p2 q
Parton distribution (log scale) (recombine) (fragment) higher yield heavy penalty C.B. Yang

11 Features soft parton density depends on medium
quark momenta add, higher yield for high produced pT hadrons soft parton density depends on medium more quarks for baryons than for mesons enhanced dependence on centrality for baryons when thermal partons are involved C.B. Yang

12 No anomalies in recombination
At intermediate pT, aplenty soft quarks are more important for proton production than for pionsp/1 For baryons, three quarks contribute to the flow, while only two quarks for mesons  v2(baryons) > v2(mesons), quark number scaling Soft and semi-soft recombination  Cronin effect Process dependence of soft partons different jet structure in dA and AA C.B. Yang

13 Recombination models Use just the lowest Fock state
i.e. valence quarks qqqB q qbarM Gluons converted to quarks first The probability for two (three) quarks to form a meson (baryon) is given by a process independent recombination function R C.B. Yang

14 Different implementations
Duke group etc: 6-dimensional phase space using Wigner function from density matrix Oregon group: one-dimensional momentum space using phenomenological recombination function C.B. Yang

15 Duke approach Low pT recombination high pT fragmentation C.B. Yang

16 Texas/Ohio approach Texas A&M/Budapest (Ko, Greco, Levai, Chen)
Monte Carlo implementation (with spatial overlap) Soft and hard partons Soft-hard coalescence allowed Ohio State (Lin, Molnar) ReCo as a solution to the opacity puzzle C.B. Yang

17 Basic formulas in Oregon approach
C.B. Yang

18 Recombination functions
Given by the valon distribution of the hadrons C.B. Yang

19 Determining R R p was determined from CTEQ
From the parton distributions in proton a=b=1.755, c=1.05 at Q2=1GeV2 R  was determined from Drell-Yan processes a=b=0 See Phys. Rev. C 66, C.B. Yang

20 Fragmentation? Recombination?
Answer: NO FRAGMENTATION only RECOMBINATION Fragmentation is not a description of the hadronization process. It uses phenomenological functions D(z) that give the probability of momentum fraction z of a hadron in a parton jet C.B. Yang

21 Fragmentation D(z) q A C.B. Yang

22 Parton shower recombination fragmentation q h Parton shower
Initiating parton (hard) Parton shower (semi-hard) h recombination fragmentation C.B. Yang

23 Recombination for fragmentation
Fragmentation function known from fitting e+e- annihilation data S  V  G  S K G K BKK KKP etc Recombination function known in the recombination model Hwa, Phys. Rev. D (1980). Shower parton distributions K, L, G, Ls, Gs C.B. Yang

24 Fitted results C.B. Yang

25 Shower parton distributions
C.B. Yang

26 Application to Au+Au collisions
Thermalized low pT (soft) partons Hard partons (semi-hard) shower partons Three types of recombination for mesons thermal parton & thermal parton thermal parton & shower parton shower parton & shower parton Joint parton distribution is not factorizable C.B. Yang

27 Hard parton distributions fi(k) can be calculated from
Parton sources Thermal parton distribution is assumed Hard parton distributions fi(k) can be calculated from pQCD nuclear shadowing nuclear geometry C.B. Yang

28 Parton sources Single shower parton distribution is
Joint two (three) shower parton distribution can also be written down C.B. Yang

29  Spectrum (0-10%) C.B. Yang

30 Nuclear modification RAA
C.B. Yang

31 p spectrum C.B. Yang

32 p/ C.B. Yang

33 Centrality dependence
C.B. Yang

34 New physics Thermal-thermal recombination makes p/ increase from very small value to about 1 at pT3GeV/c Thermal-shower recombination plays an important role This recombination can be equivalently regarded as modification of the fragmentation functions C.B. Yang

35 NCQ scaling AMPT model results: Scaling in v2: partonic dof dominant;
No scaling in v2 : hadronic dof dominant => A tool to search for the possible phase boundary! The beam energy dependence of the partonic cross sections will not affect the v2 scaling argument. Important for Beam Energy Scan program. C.B. Yang

36 NCQ scaling violation C.B. Yang

37 Validity of the assumptions?
Why NCQ scaling ? joint distribution φdependence collinear Assumptions: F(p1,p2)=F(p1)F(p2) Validity of the assumptions? C.B. Yang

38 Why NCQ scaling violates?
Because of quark interactions, joint distributions are not products of quark distributions Recombined quarks not necessarily have the same momentum Fluctuations: large n=1,3 terms appears in quarks distributions. They contribute to v2 NCQ at RHIC may be coincident C.B. Yang

39 Application to d+Au collisions
Basic formulas the same as for Au+Au collisions Soft parton distribution the same form, T not temperature but inverse slope No jet quenching Nuclear shadowing a little different from that in Au+Au case C.B. Yang

40 Pion spectrum C.B. Yang

41 Centrality dependence
C.B. Yang

42 Cronin effect Enhancement of hadron spectrum in pA
collisions at high pT Traditional explanation: initial interactions Many soft collisions before the last hard one, each gives a kT kick C.B. Yang

43 Cronin effect Shadowing effect is cancelled partially C.B. Yang

44 Puzzles If Cronin effect is really due to initial interactions, dilepton spectrum should show similar effect. Experimentally, the effect for dilepton is very small, no definite conclusion Species dependence of the Cronin effect C.B. Yang

45 From recombination Medium density depends on centrality
Medium effects are different in meson and baryon production C.B. Yang

46 Proton spectrum T different for different centralities C.B. Yang

47 RCP for proton C.B. Yang

48 RCP for p &  C.B. Yang

49 Discussions QGP signal can be found from the bulk
Hadronization of partons can be described by ReCo for d+Au and Au+Au collisions ReCo naturally explains species dependence, such as baryon enhancement, v2 scaling... Cronin effect can be interpreted as from final state interactions C.B. Yang

50 Discussions Combination with other models, such as hydrodynamics etc, is needed and under development Recombination formulism from pQCD How to calculate the joint distributions? C.B. Yang

51 The End Thank you all! C.B. Yang

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