相对论重离子碰撞中直接光子的产生-Indico

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outline
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pp collisions at extremely high energy (i.e. 14TeV)
Multiple scattering, many Pomerons / strings involved How to treat the afterward secondary scattering?
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Direct photon production
RHIC Au+Au data are explained with 4 sources Hydrodynamic description of the hot dense matter in AA Hydrodynamic treatment of the secondary scattering in pp
Should the secondary interaction be responsible for this deviation?
Saturation makes a decrease of PDF at low x. can not be.
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Secondary scattering in AA
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Direct photon data in pp (ppbar)
Latest PDG review
Present data are generally in good agreement with NLO QCD prediction.
But a tendency for the data to be above (below) the theory for lower (large) pt.
Rapidity
Pomeron number might be very big. We need a post-collision evolution to treat the many-body system.
Question: How to treat the afterward secondary scattering ? on parton level ? or on hadron level? or string interaction? or Pomeron interaction?
Problem: Two-string picture can not explain observables (~100GeV)
1) 2) 3) 4) High multiplicity (multiplicity dis. predicted is too narrow) Increase of mean pt High pt jets Rise of central rapidity density
Usually, a pair of strings are formed via a) longitudinal excitation b) color exchange
hadron production: string fragmentation, i.e.
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pp collisions at high E
Evolution of core region, or huge number of secondary collisions, can be treated with hydrodynamics.
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Hydrodynamic treatment
, p, u , s, B,...( , x, y, z)
2. Fragmentation contribution: High order contribution
dN dN c 1 0 2 dz D ( z , Q ) c /c c 2 2 2 dyd pt cq , g dyd pt zc
q q，g qq
D0 and CDF can only measure pt > 10GeV.
H.J.Drescher et al, Phys.Rept.350,93(2001).
F.M.Liu et al. PRD 67, 034011 (2003)
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pp at extremely high E, ie, E=14TeV
Multiple elementary interactions (Pomerons) in NEXUS/EPOS:
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Results and discussion
pQCD + plasma contribution Is it possible to form a QGP in pp collisions?
PHOS@ALICE will answer.
pt 100Mev~100GeV .
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Particle production in pp
Direct Photon Production in pp collisions at the LHC
F.M. Liu K. Werner
IOPP/CCNU, Wuhan, China Subatech, Nantes, France
Théorie LHC France 06 April 2010
Solution: Multiple scattering becomes important at high energies More Pomerons/strings are added
Pomeron = a pair of strings
Prob ( )， ： Pomeron number
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pp-> gamma with NLO pQCD
W.Vogelsang & M.R.Walley 1997 JPG: 23,A1-A69
1. Leading Order contribution
ຫໍສະໝຸດ Baidu
qq g，qg q
ˆ d dN pp ( LO) 2 2 s ˆ tˆ u ˆ) dxa dxbGa / p ( xa , M )Gb / p ( xb , M ) (ab cd ) ( s 2 ˆ dyd pt dt ab