11.03.2006Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 1 Direct photons. Generators aspects. Sergey

11.03.2006 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


2

Introduction In A+B collision direct photons - photons that originate during

time of the collision, c~ 50-100 fm; o, ’ω have c»c main origin of non-direct photons.

Quark gluon level: qq g, qg qqq(g) qq(g)Initial hard NN collisions, pQCD prompt Thermalised QGP stage thermal from QGP

Hadron level: decays: , a1 , ,

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.


3

Prompt : pp data A Compilation of Data, J. Phys. G, 23 (1997) A1

CBM can cover the range √s < 14 GeV


4

Prompt : data fit Data fit (xT>0.1):

Ed3σpp/d3p = 575(√s)3.3 /(pt)9.14 pb/GeV2 EPJ C22 (2001) 129

For A+B: Ed3N/d3p(b) = Ed3σpp/d3p AB TAB(b) = Ed3σpp/d3p Ncoll/ σpp

in


5

Prompt : yields at CBM If extrapolation to the

CBM energy is correct one can estimate yields.

~10-4 prompt with pt

> 2 GeV/c per Au+Au central event at 25 AGeV

At beam intensity 109/s + 1% interaction + 10% centrality prompt rate100/s


6

from hadron gas. An example nucl-th/9712048, transport code based on the Walecka-type model


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 reconstructed o, and other hadrons (with some assumption of its yield and spectrum)

At pt > 0,5 GeV/c from o from from from ’


8

Subtraction method – cont.


9

Momentum correlations method momentum correlations,

WA98 PRL 93 (2004) 022301, STAR nucl-ex/0511055 correlations direct

photons direct photons correlation

provide the system sizes at all stages of heavy-ion collisions

Needs larger statistics Rinv (≈ 6 fm ≈ Rinv

( emitted in the late, hadron

gas, stage of the collision Thermal calculations

substantialy underestimate the data.


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

emits also virtual with very low-mass

directdirect

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


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).


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) 2774.

the and processes are dominant in the range 1 GeV≤ kT ≤ 3 GeV.


13

from UrQMD – at CBM 103 UrQMD Au+Au central

events at 25 AGeV ≈ 14 photons per event.

BUT all are from decays, mainly a1 . 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.”


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, 103 central Au+Au events at 25 AGeV, there are NO photons at all !?


15

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 per event 2/3 from ’ 1/3 from


16

from HIJING HIJING (Heavy Ion Jet Interaction

Generator) Phys. Rev. D 44, (1991) 3501. Soft processes: FRITIOF Hard processes: PYTHIANO 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 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 .


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 UrQMD HSD RQMD HIJING

prompt - - - + BUT -

decays + BUT - + BUT ? ’, ’, K*

meson scatterings + BUT - - - -

We have not transport code with direct photons!


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.


19

Backup


20

Quark gluon level


21

UrQMD email Date: Fri, 23 Dec 2005 14:16:27 +0100 From: marcus bleicher <[email protected]> To: Serguei Kiselev <[email protected]> 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


22

UrQMD email – cont.

---------- Forwarded message ---------- Date: Wed, 22 Feb 2006 19:28:07 +0100

From: bleicher <[email protected]> To: Xianglei Zhu <[email protected]> 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.


23

HSD email Date: Thu, 29 Dec 2005 13:32:33 +0100 From: Elena Bratkovskaya <[email protected]> To: Serguei Kiselev [email protected] 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


24


25


26

Experimental results -3


27

HIJING vs RQMD


28

UrQMD


29

from HIJING, 158 AGeV


30

from RQMD, 158 AGeV


31

from UrQMD, 158 AGeV

Documents

11.03.2006Workshop of European Research Group on Ultrarelativistic Heavy Ion Physics, Dubna-ITEP S.Kiselev 1 Direct photons. Generators aspects. Sergey