1. Anomaly of over ratios in Au+Au collision with jet quenching Xiaofang Chen IOPP, CCNU Collaborator: Enke Wang Hanzhong Zhang Benwei Zhang Beijing Mar. 22-24 IOPP1

2. Outline  The introduction of single hadron spectrum in NLO PQCD  The anomaly of and ratios and the two reasons for that  Summary and discussion IOPP Beijing Mar. 22-24 2

3. Jet quenching: Induced by multiple scattering in QGP medium, a parton jet will radiate gluon and lose its energy. IOPP Beijing Mar. 22-24 3

4. Invariant Cross Sections in pp collision LO (Leading order) : One-loop corrections2→3 processes (tree level) 2→2 processes (tree level) NLO (Next to Leading Order ) corrections: Parton distribution function CTEQ,MRS Parton fragmentation function BKK,KKP,AKK A factor K=1.5-2 was putA factor K is no longer needed IOPP Beijing Mar. 22-24 4

5.   We use AKK fragmentation function X.F. Zhang and G. Fai, Phys. Rev. Lett. 89, 272301 (2002)   Considering the shortage of fragmentation function,we introduce a phenomenological multiplication factor to the production of proton. IOPP Beijing Mar. 22-24 5

6. Invariant Cross Sections in AA collision Nuclear thick function Modified parton distribution function Modified fragmentation functions Due to jet quenching Jet quenching in 2 2 and 2→3 processes S.Y. Li and X.N. Wang, Phys. Lett. B527,85(2002). IOPP Beijing Mar. 22-24 6

7. Where, The energy loss of final parton jet the averaged scattering number, IOPP Beijing Mar. 22-24 7

8. the gluon density distribution, In 1-demension expanding medium, the total energy loss is written as a path integration: The energy loss per unit length with detailed balance: (Enke Wang and Xin-Nian Wang, PRL87 (2001) 142301) An energy loss parameter proportional to the initial gluon density IOPP Beijing Mar. 22-24 8

9. No Medium Effect Medium Effect Nuclear Modification Factor: IOPP Beijing Mar. 22-24 9

10. IOPP 10

11. IOPP 11 production rate is dominated by quark jets at high and by gluon jet at low ;while production rate is dominated by gluon jets both in low and high.

12. IOPP Beijing Mar. 22-24 12 Data from STAR collaboration have indicated that and ratios at high in central Au+Au collisions approach those in p+p and d+Au collisions. These observations indicate that, at high,fragmentation in central Au+Au and p+p events is similar and there is no evidence of different energy loss for quarks and gluons in the medium. ATAR Collaboration, J. Adams et al. Phys. Rev. Lett. 97, 152301 (2006)

13. In order to differentiate and,we think come from gluon and quark, come from gluon and antiquark. IOPP Beijing Mar. 22-24 13

14.  Recent studies have shown that elastic scattering of quark and gluon jets in the QGP also leads to an appreciable loss of their energies. in the QGP also leads to an appreciable loss of their energies. S. Wicks, W. Horowitz, M. Djordjevic, and M. Gyulassy, Nucl. Phys. A784,426 (2007) S. Wicks, W. Horowitz, M. Djordjevic, and M. Gyulassy, Nucl. Phys. A784,426 (2007) M.G. Mustafa, Phys. Rev. C 72, 014905 (2005)  Another forms of energy loss maybe exist in the process when parton jets propagate through the QGP medium. propagate through the QGP medium.  The energy loss is calculated in the state of equilibrium,but the QGP may be in non-equilibrium. of equilibrium,but the QGP may be in non-equilibrium. IOPP Beijing Mar. 22-24 14

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17. IOPP 17 Different and ratios due to equal energy losses of gluons and quarks

18. Inelastic scattering:elastic scattering: Flavor conversion : Quark and gluon jets traversing through a quark-gluon plasma not only lose their energy but also can undergo flavor conversion. X.N. Wang and X. Guo, Nucl. Phys. A696, 788(2001); B.W. Zhang, X.N. Wang, and A. Schafer,ibid. A783551(2007) IOPP Beijing Mar. 22-24 18

19. W. Liu, C.M. Ko, and B.W. Zhang PRC75, 051901(2007) We find that conversions between quark and gluon jets indeed lead to an increase in the final number of gluon jets in central heavy ion collisions than in the case without conversions. Arxiv: 0801.0453v1 W. Liu and R. J Fries Jet flavor conversions reduce the number of high transverse momentum quark jets by 30%. of high transverse momentum quark jets by 30%. IOPP Beijing Mar. 22-24 19

20. IOPP 20 Different and ratios due to flavor conversion The AKK fragmentation functions show that gluon fragmentation contribute to 40% of pion production at while more than 80% of proton are from gluon fragmentation. ( S. Albino,B.A. Kniehl and G. Kramer. Nucl.Phys. B725,181(2005) )

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23. IOPP 23 Summary and discussion  We investigate the consequence if gluons lose the same amount of energy in QGP as quarks and demonstrate that it will enhance the and ratios for central Au+Au collision.  We explore the effect of strong jet conversion where a net of quark- to-gluon conversion also result in similar and ratios in central Au+Au and p+p collisions  The exploration presented here is a phenomenological one and why the energy losses of quarks and gluons are equal or a strong jet conversion happened in Au+Au collision still need further intense theoretical investigate.

24. Thank you!