Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 1 Direct photons. Generators aspects.  Sergey Kiselev, ITEP Moscow, for the ECAL group  Introduction  Prompt    from hadron gas. An example  Subtraction method  Momentum correlations method  Low mass e + e - pairs method   from UrQMD   from HSD   from RQMQ   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, c  ~ fm;  o,  ’   ω  have c »  c   main origin of non- direct photons.  Quark gluon level: qq  g, qg  qqq(g)  qq(g) Initial hard NN collisions, pQCD  prompt  Thermalised QGP stage  thermal from QGP  Hadron level: decays:   , a 1  ,         ,    meson scatterings:   ,                 Thermalised hadron stage  thermal 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  : 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  : data fit  Data fit (x T >0.1): Ed 3 σ pp /d 3 p = 575(√s) 3.3 /(p t ) 9.14 pb/GeV 2 EPJ C22 (2001) 129  For A+B: Ed 3 N/d 3 p(b) = Ed 3 σ pp /d 3 p AB T AB (b) = Ed 3 σ pp /d 3 p N coll / σ pp in

Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 5 Prompt  : yields at CBM  If extrapolation to the CBM energy is correct one can estimate yields.  ~10 -4 prompt  with p t > 2 GeV/c per Au+Au central event at 25 AGeV  At beam intensity 10 9 /s + 1% interaction + 10% centrality  prompt  rate  100/s

Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 6  from hadron gas. An example  nucl-th/ , transport code based on the Walecka-type model

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)  WA98 subtracted from measured photons those from known hadronic source: from decays of reconstructed  o, and other hadrons (with some assumption of its yield and spectrum)  At p t > 0,5 GeV/c from  o  from  from  from ’

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 correlations method   momentum correlations, WA98 PRL 93 (2004) , STAR nucl- ex/  correlations  direct photons direct photons correlation provide the system sizes at all stages of heavy-ion collisions Needs larger statistics  R inv (  ≈ 6 fm ≈ R inv (  emitted in the late, hadron gas, stage of the collision Thermal calculations 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/ any source of real  emits also virtual  with very low-mass  direct   direct   incl. )  incl. 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 5 it is consistent with a NLO pQCD calculation).

Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 12  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   ,   were considered explicitly using cross sections given in Phys. Rev. D44, (1991) the    and    processes are dominant in the range 1 GeV≤ k T ≤ 3 GeV.

Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 13  from UrQMD – at CBM  10 3 UrQMD Au+Au central events at 25 AGeV  ≈ 14 photons per event. BUT all  are from decays, mainly a 1  . Where are the processes   ,   ?  22 Feb 2006, M. Bleicher “... 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.”

Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 14  from HSD  HSD (Hadron String Dinamics), Phys. Rep. 308 (1999) 65, 6.6. Direct photons p. 174  BUT in the file generated for CBM, 10 3 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  from RQMD  RQMD (Relativistic Quantum Molecular Dynamics)Phys. Rev. C52 (1995) 3291  10 3 Au+Au central, b<3 fm, events at T/A=25 GeV have been generated  ≈ 5.4  per event 2/3 from ’ 1/3 from 

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

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 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: origin UrQMDHSDRQMDHIJING prompt---+ BUT - decays+ BUT -+ BUT ? ’, ’, K * meson scatterings+ BUT ---- 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  Date: Fri, 23 Dec :16:  From: marcus bleicher  To: Serguei Kiselev  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 , pp. Published in Phys.Rev.C57: ,1998 e- Print Archive: hep-ph/  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 – cont.  Forwarded message Date: Wed, 22 Feb :28:  From: bleicher  To: Xianglei Zhu 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  Date: Thu, 29 Dec :32:  From: Elena Bratkovskaya  To: Serguei Kiselev  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 ~ 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  from HIJING, 158 AGeV

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

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