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Direct photons. Generators aspects.

Direct photons. Generators aspects. Sergey Kiselev, ITEP Moscow, for the ECAL group Introduction Prompt g g from hadron gas. An example Subtraction method Momentum correlations method Low mass e + e - pairs method g from UrQMD g from HSD g from RQMQ

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Direct photons. Generators aspects.

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  1. Direct photons. Generators aspects. • Sergey Kiselev, ITEP Moscow, for the ECAL group • Introduction • Prompt g • g from hadron gas. An example • Subtraction method • Momentum correlations method • Low mass e+e- pairs method • g from UrQMD • g from HSD • g from RQMQ • g from HIJING • Conclusions • Next steps Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  2. Introduction • In A+B collision direct photons - photons that originate during time of the collision, ctAB~ 50-100 fm; po, h,h’ rg/ωg/2g, have ct »ctAB - main origin of non-direct photons. • Quark gluon level: qq  gg, qg  qg, qq(g)  qq(g)g Initial hard NN collisions, pQCD  prompt g. Thermalised QGP stage  thermal g from QGP. • Hadron level: • decays: w  pg, a1  pg, D  Ng, K* Kg, f  hg, r  ppg, . . . • meson scatterings: pp  rg, pr  pg, pK  K*g, Kr  Kg, KK*  pg, pK*  Kg, . . . Thermalised hadron stage  thermal g from hadron gas. • We shell analyze direct photons at the CBM energy, p beam up to 90 GeV, Au beam up to 35 AGeV. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  3. Prompt g : pp data • A Compilation of Data, J. Phys. G,23 (1997) A1 CBM can cover the range √s < 14 GeV Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  4. Prompt g : data fit • Data fit (xT>0.1): Ed3σpp/d3p = 575(√s)3.3 /(pt)9.14pb/GeV2 EPJ C22 (2001) 129 • For A+B: Ed3N/d3p(b) = Ed3σpp/d3p AB TAB(b) = Ed3σpp/d3p Ncoll/ σppin Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  5. Prompt g : yields at CBM • If extrapolation to the CBM energy is correct one can estimate yields. • ~10-4 prompt g with pt > 2 GeV/c per Au+Au central event at 25 AGeV • At beam intensity 109/s + 1% interaction + 10% centrality  prompt g rate100/s Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  6. g from hadron gas. An example • nucl-th/9712048, transport code based on the Walecka-typemodel Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  7. Subtraction method • Direct photon measurement by the subtraction method: WA98 PRL 85 (2000) 3595, PHENIX PRL 94 (2005) 232301 • WA98 subtracted from measured photons those from known hadronic source: from decays of reconstructedpo,h and other hadrons (with some assumption of its yield and spectrum) • At pt > 0,5 GeV/c • from po - 80% • from h - 13% • from w - 2% • from h’ - 1.3% Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  8. Subtraction method – cont. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  9. Momentum correlationsmethod • ggmomentum correlations, WA98 PRL 93 (2004) 022301, STAR nucl-ex/0511055 • gg correlations direct photons • direct photons correlation provide the system sizes at all stages of heavy-ion collisions • Needs larger statistics • Rinv (gg) ≈ 6 fm ≈ Rinv (pp) • emitted in the late, hadron gas, stage of the collision • Thermalcalculations substantialy underestimate the data. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  10. Low mass e+e- pairs method • A novel technique (QM’05): internal conversion of direct photons into e+e-, PHENIX, nucl-ex/0511041 • any source of real g emits also virtual g with very low-mass • gdirect =( g*direct /g*incl.) gincl. Electrons in the central arms were identified by matching charged particle tracks to clusters in the ECAL and to rings in the RICH Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  11. Low mass e+e- pairs – cont. • Measurement for 1 < pT < 5 GeV/c consistent with calculations when thermal photon emission is taken into account (at high pT > 5 it is consistent with a NLO pQCD calculation). Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  12. g from UrQMD • UrQMD (Ultra Relativistic Quantum Molecular Dynamics) Prog. Part. Nucl. Phys. 41 (1998) 225–370. • Phys. Rev. C57 (1998) 3271 “Direct photons in Pb+Pb at CERN-SPS …” • The processes pp  rg, pr  pg were consideredexplicitly using cross sections given in Phys. Rev. D44, (1991) 2774. • the pr  pg and w  pg processes are dominant in the range1 GeV≤ kT ≤ 3 GeV. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  13. g from UrQMD – at CBM • 103 UrQMD Au+Au central events at 25 AGeV • ≈ 14 photons per event. BUT all g are from decays, mainly a1  pg. Where are the processes pp  rg, pr  pg ? • 22 Feb 2006, M. Bleicher “. . . photons should not be calculated within theurqmd, but explicitely outside with a different code.everybody should ignore all processes with photons involved. we will move them out of the model in the next version.” Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  14. g from HSD • HSD (Hadron String Dinamics), Phys. Rep. 308 (1999) 65, 6.6. Direct photons p. 174 • BUT in the file generated for CBM, 103 central Au+Au events at 25 AGeV, there are NO photons at all !? Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  15. g from RQMD • RQMD (Relativistic Quantum Molecular Dynamics)Phys. Rev. C52 (1995) 3291 • 103 Au+Au central, b<3 fm, events at T/A=25 GeV have been generated • ≈5.4 g per event • 2/3 from h’ • 1/3 from w Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  16. g from HIJING • HIJING (Heavy Ion Jet Interaction Generator) Phys. Rev. D 44, (1991) 3501. • Soft processes: FRITIOF • Hard processes: PYTHIA NO rescatterings • 25 AGeV: Error: too low CM energy, 6.982 GeV for event generation. Execution stopped! • BLOCK DATA PYDATA: PARP(2)=6.8 instead 10. • 103 Au+Au central, b<3 fm, events at T/A=25 GeV have been generated • 10.5 g per event • 60% from h’ • 36% from w • 4% from D • Though direct g production(IHPR2(3)=2) is included using PYTHIA, BUT at CBM energy the code does not generate direct g. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  17. Conclusions • There are three main experimental methods to study direct photons. They supplement each other and use ECAL as the main instrument. • CBM: • High intensity beam • Good tracking, e± PID by TRD+RICH+ECAL and g PID by ECAL CBM has good possibility to measure direct photons by all three methods. By momentum correlation method  presentation of K.Mikhailov • Photons from existing transport codes at the CBM energy: We have not transport code with direct photons! Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  18. Next steps • To start feasibility of direct photons study by • Conventional subtraction method • Low mass e+e- pairs method • To implement the direct photons into the HSD/UrQMD code. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  19. Backup Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  20. Quark gluon level Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  21. UrQMD email • Date: Fri, 23 Dec 2005 14:16:27 +0100 • From: marcus bleicher <bleicher@th.physik.uni-frankfurt.de> • To: Serguei Kiselev <kiselev@mail.cern.ch> • Subject: Re: direct photons with UrQMD (fwd) • dear sergey, you can do a photon study with urqmd. • we have done this in • 14) DIRECT PHOTONS IN PB + PB AT CERN SPS FROM MICROSCOPIC TRANSPORT THEORY. By A. Dumitru, M. Bleicher, S.A. Bass, C. Spieles, L. Neise, Horst Stoecker, W. Greiner (Frankfurt U.),. UFTP-449-1997, 1998. 14pp. Published in Phys.Rev.C57:3271-3275,1998 e-Print Archive: hep-ph/9709487 • however, since only the hadronic cross section are explicitely present in urqmd, we used the cross section from kapusta et al (ref 2 in paper above) and folded it with the urqmd collision spectrum. • best regards, merry christmas, marcus Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  22. UrQMD email – cont. • ---------- Forwarded message ---------- Date: Wed, 22 Feb 2006 19:28:07 +0100 • From: bleicher <bleicher@th.physik.uni-frankfurt.de> • To: Xianglei Zhu <zhu@th.physik.uni-frankfurt.de> Subject: Re: [URQMD] ftn15 (fwd) • hm, • yes photons are mesons in urqmd. however, photons should not be calculated within the urqmd, but explicitely outside with a different code. everybody should ignore all processes with photons involved. we will move them out of the model in the next version. cheers, marcus • Xianglei Zhu wrote: • > hi marcus, • > actually i found photon + meson elastic rescattering (also ID 38) are much • > more popular. it is strange, isn't? • > grusse, • > x. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  23. HSD email • Date: Thu, 29 Dec 2005 13:32:33 +0100 • From: Elena Bratkovskaya <Elena.Bratkovskaya@th.physik.uni-frankfurt.de> • To: Serguei Kiselev kiselev@mail.cern.ch • Subject: Re: direct photons with HSD • Dear Sergey, • thank you for the registration as HSD user. • > I plan to study direct photons in • > A+B collisions at E_lab/A ~ 10 - 40 GeV. • > Is it possible to do this with HSD? • In principle - yes, in practice ... you must understand that the open HSD 2.0 code does not include the routines for the direct photon production! The available (by special request) version HSD 2.5 includes dileptons, but NOT the direct photons. So, if someone wants to use the HSD for direct photon production, he has to implement direct photon production channels himself, i.e. to use HSD only as "hadrons generator" (e.g. as UrQMD). Sure, there is no principle difficulties to implement the direct photons in the code, just usual "men-power" problem. If there is a "volunteer" to do that, he can expect to get my help and support. • Sorry for such answer. • Best regards and Happy New Year! • Elena Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  24. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  25. Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  26. Experimental results -3 Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  27. HIJING vs RQMD Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  28. UrQMD Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  29. g from HIJING, 158 AGeV Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  30. g from RQMD, 158 AGeV Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

  31. g from UrQMD, 158 AGeV Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev

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