Jet quenching and direct photon production F.M. Liu 刘刘刘 Central China Normal University, Ch ina T. Hirano University of Tokyo, Jap an K.Werner University of Nantes, Fran ce Y. Zhu 刘刘 Central China Normal Univers ity, China arXiv: hep-ph/0807.4771v2 SQM2008 Beijing Oct 6-10
Jet quenching and direct photon production. F.M. Liu 刘复明 Central China Normal University, China T. Hirano University of Tokyo, Japan K.Werner University of Nantes, France Y. Zhu 朱燕 Central China Normal University, China arXiv: hep-ph/0807.4771v2. - PowerPoint PPT Presentation
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Jet quenching and direct photon production
F.M. Liu 刘复明 Central China Normal University, China
The PHENIX fit of pp spectrum is used for Raa of thermal photons.
PRL 98, 012002 (2007)
A good test for contributions from leading order +fragmentation without Elossin AA collisions.
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Raa: energy loss
• Data is reproduced within theory uncertainty.
• E loss makes about 40% decrease of total photon production
• Centrality independent ? central and peripheral results differ
by less than 5% with Eloss
by about 20% at intermediate pt w/o Eloss
PRL94,232302(2005);J.Phys.G34, S1015-1018,2007
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Jet quenching & bulk volume
• E loss does play a important role in fragmentation contribution and
jet photon-conversion contribution.
• This is centrality-dependent, similar to the suppression to pi0 production.
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Competition btw different sources
Thermal and LO dominate low and high pt region respectively.Raa is not sensitive to E loss, because of the centrality dependence of them.
When collisions move to perpherial, JPC becomes less importantwhile fragmentation becomes more important .
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Information from Thermal photonsEnergy density at plasma center
• High Temp. from fitting a pt spectrum A higher Temp. plasma
• More yields (shines) of thermal photons A bigger-size (longer-life) plasma.
Raa due to thermal source
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V2 of thermal photons
Contrary to hadronic v2 (ideal hydro predicted increase monotonically), the elliptic flow of thermal photons decrease at high pt!
( Information for the earlier evolution of the plasma?)
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Time evolution
• At initial time there is no transverse flow, so v2 vanishes.
• A big fraction of energetic thermal photons are emitted at early time: More than 50\% at pt=3GeV/c and more than 70\% at pt=4GeV/c within the first 0.3fm/c, though the whole evolution time is about 20fm/c.
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Discussion and Conclusion• Parton energy loss does make 40% decrease of Raa(γ)
• Raa(γ) is independent of centrality (within 5% accuracy) because of
1) the dominance of leading order contribution
2) strong suppression to JPC and frag. contributions due to E-loss
• Thermal photons can provide information of the temperature and size of
the plasma via the slope of pt spectrum and the yields.
• The elliptic flow of thermal photons is predicted to first increase and then
decrease with pt, contrary to hadronic v2, which does not carry the early i
nformation of the QGP.
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Thank you!
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purely leading order calculation:
Isosping mixture and nuclear shadowing make an evident decrease.