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Anomaly of over ratios in Au+Au collision with jet quenching

Anomaly of over ratios in Au+Au collision with jet quenching. Xiaofang Chen. IOPP, CCNU. Collaborator: Enke Wang Hanzhong Zhang Benwei Zhang. IOPP. Beijing Mar. 22-24. 1. Outline. The introduction of single hadron spectrum in NLO PQCD.

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Anomaly of over ratios in Au+Au collision with jet quenching

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

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

  5. We use AKK fragmentation function • Considering the shortage of fragmentation function,we introduce a phenomenological multiplication factor to the production of proton. X.F. Zhang and G. Fai, Phys. Rev. Lett. 89, 272301 (2002) 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. Nuclear Modification Factor: No Medium Effect Medium Effect IOPP Beijing Mar. 22-24 9

  10. IOPP Beijing Mar. 22-24 10

  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 . IOPP Beijing Mar. 22-24 11

  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) IOPP Beijing Mar. 22-24 12

  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. The energy loss is calculated in the state of equilibrium ,but the QGP may be in non-equilibrium. • Recent studies have shown that elastic scattering of quark and gluon jets • 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) 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. IOPP Beijing Mar. 22-24 14

  15. IOPP Beijing Mar. 22-24 15

  16. IOPP Beijing Mar. 22-24 16

  17. Different and ratios due to equal energy losses of gluons and quarks IOPP Beijing Mar. 22-24 17

  18. Flavor conversion : Inelastic scattering: elastic scattering: 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. We find that conversionsbetween 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. W. Liu , C.M. Ko, and B.W. Zhang PRC75, 051901(2007) Jet flavor conversions reduce the number of high transverse momentum quark jets by 30%. Arxiv: 0801.0453v1 W. Liu and R. J Fries IOPP Beijing Mar. 22-24 19

  20. Different and ratios due to flavor conversion The AKKfragmentation 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) ) IOPP Beijing Mar. 22-24 20

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  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. IOPP Beijing Mar. 22-24 23

  24. Thank you!

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