Effects of minijet degradation on hadron observables in heavy-ion collisions

1. Effects of minijet degradation on hadron observables in heavy-ion collisions Lilin Zhu Sichuan University QPT2013, Chengdu

2. Outline • Introduction • Physicsideasoftherecombinationmodel • New property of minijet distribution • Hadronic spectra • Conclusion QPT2013, Chengdu

3. low intermediate high pT 2 6 pQCD no rigorous theoretical framework hydro Transverse momentum spectra That is where abundant experimental data exist. At intermediate pT recombination model has been successful. QPT2013, Chengdu

4. ReCo models PRL90,202301(03), PRC68,044902(03), ArXiv:1102.5723. • Duke group: • 6-dimensional phase space • using Wigner function from density matrix • Texas A&M/Budapest • Monte Carlo implementation • Soft andhardpartons • Soft-hardcoalescenceis allowed • Oregon group: • one-dimensional momentum space • using phenomenological recombination function PRL90,202302(03), PRC68,034904(03). PRC67,034902(03), PRC70,024905(04). Hwa, QGP4, p.267. CPOD2011, Wuhan

5. T : thermal parton fragmentation S : shower parton Oregon recombination model pT distributions of and p Recombination functions Hwa, Phys. Rev. D (1980). Parton distributions before recombination = T T + T S + SS =T T T + T T S + T SS + SSS QPT2013, Chengdu

6. Parton distributions Thermal partons: T is the inverse slope parameter, not the hydro temperature hard and semihardparton distributions at the medium surface. Integrated over all initial creation points. Shower distribution SPD, Obtained from FF, Hwa-Yang (04) let’s see how to take parton momentum degradation into account QPT2013, Chengdu

7. The process of momentum degradation Calculation in pQCD is not reliable at intermediate q and difficult to account for the nuclear complications at various c and Fries, et al PRC(03) dynamical path length p2 parton distribution at creation point Nuclear complicatioin is in the determination of The degradation of momentum from k to q can be written as a simple exponential Hwa-Yang(10) QPT2013, Chengdu 7

8. Since depends on the nuclear medium and the azimuthal angle, so we could express in terms of angle and centrality c. That is contained in the probability function in relating to The probability of having at and c in the medium QPT2013, Chengdu

9. Mean dynamical path length Whereas depends on , c implicitly, the mean depends on them explicitly. The dynamical effect of energy loss per unit length i=g, q. probability of production of a (semi)hard parton at creation point x0 and y0 determined by fitting nuclear modification factor Hwa-Yang(10) The geometrical path length is weighted by the local density along the trajectory marked by t. not time As the system expands, the density D decreases but t1 increases, so is not very sensitive to the expansion dynamics. QPT2013, Chengdu

10. Mean dynamical path length Points determined from calculation that account for nuclear complications.   QPT2013, Chengdu

11. Minijet distribution at RHIC For calculating the pT spectra of any hadron produced later, we make averaged over minijet distribution, averaged over , initial creation points. No momentum degradation More suppression for gluons than for quarks throughout the whole region. QPT2013, Chengdu

12. Minijet Degradation Factor Increase is rapid at low q. It is analogous to the nuclear modification factor RAA for , but for minijets. Rg is roughly half of Rq, but q and c dependencies are similar in shape. QPT2013, Chengdu

13. parametrization for Tsallis distribution could fit the minijet distribution very well Tt=0.32 is universal; ni depends on parton type. QPT2013, Chengdu

14. pion production The formalism for recombination of thermal and shower partons has been developed previously. Hwa-Yang, PRC(04) Hwa-Zhu, PRC(11) Now we generalize to non-central collisioins, especially show the contributions from various species of semihard partons TT Zhu-Hwa , 1307.3328 TS SS The two shower partons are from the same minijet with momentum q QPT2013, Chengdu

15. proton production TTT TTS TSS SSS QPT2013, Chengdu

16. pion at central collision The inverse slope is adjusted to fit the low pT behavior. T=0.283 GeV. It’s the same value for all hadrons at low pT. SS TT TS The pT of TS and SS are fixed by minijets, whose magnitudes depend on . QPT2013, Chengdu

17. pion Zhu-Hwa, 1307.3328 Only vary C(Npart) for the thermal partons. No parameters are adjusted for the shape of the pT distribution at intermediate and high pT region at all centralities. QPT2013, Chengdu

18. proton Quark minijets are more influential than gluons in the proton distribution at high pT. It is our prediction for proton pT>5 for c > 20%. QPT2013, Chengdu

19. Kaon Good fit out to 9 GeV/c for all centralities. QPT2013, Chengdu

20. p/pi at RHIC • For 0-10% the ratio is very well reproduced. • For 20-40% not as well around the peak. QPT2013, Chengdu

21. at LHC QPT2013, Chengdu

22. pion Pb-Pb collisions at 2.76 TeV RHIC SS TT TS Hwa-Zhu, PRC (11) Zhu-Hwa, 1307.3328 • At LHC minijets are pervasive and their effects dominate the spectra at the low and intermediate pT range. • TS>TT at pT>0.5 GeV/c. QPT2013, Chengdu

23. K/p/Λ spectra (0-5% Central) T=0.38 for thermal partons is higher than 0.283 at RHIC. For p and Λ, TTS>TTT 0-5％ 0-5％ Hwa-Zhu, PRC(11) 0-5％ QPT2013, Chengdu

24. T=0.38 GeV at LHC T=0.283 GeV at RHIC effect of minijets at LHC Due to the abundant production of minijet, TS is elevated going from RHIC to LHC QPT2013, Chengdu

25. new features of momentum degradation of minijets produced at intermediate q before hadronization. • pTand c dependencies of hadronicobservables are well reproduced-- by the minijet approach in the framework of the recombination model • Extension of the study to hyperons production, such as: Omega. • Hadron production at LHC. Summary & outlook QPT2013, Chengdu

26. Thank you! QPT2013, Chengdu

27. backup QPT2013, Chengdu

28. Hwa-Zhu, (12) The good fits support our minijet approach to the treatment of azimuthal anisotropy. QPT2013, Chengdu

29. Determining RFs • 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, 025204 CPOD2011, Wuhan

30. Recombination functions Given by the valon distribution of the hadrons CPOD2011, Wuhan

31. Recombination function known in the recombination model Fragmentation function known from fitting e+e- annihilation data S  V  G  S K G K Hwa, Phys. Rev. D (1980). Shower parton distributions K, L, G, Ls, Gs Biennewies, Kniehl, Kramer Kniehl, Kramer, Pötter Hwa and Yang, PRC70,024904(2004) Recombination model for fragmentation CPOD2011, Wuhan