25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow ...

48
25.01.2007 RELNP seminar, ITEP, S.Kise lev 1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow Introduction Before QM’06 p+p: prompt γ A+B: experimental methods Subtraction method Momentum correlations method Internal conversion method QM’06 high-p t low-p t elliptic flow v 2 γ-h azimuthal correlation Conclusions

description

RELNP seminar, ITEP, S.Kiselev3 Introduction – cont.  Hadron level: meson scatterings: ππ  ργ, πρ  πγ, πK  K * γ, Kρ  Kγ, KK *  πγ, πK *  Kγ,... Thermalised hadron stage  thermal γ from hadron gas  Decay photons: Long lived (c  » c  AB ~ fm) π 0  γγ,   γγ,  ’  ργ/ωγ/2γ Shot lived (c   c  AB ~ fm) ω  πγ, a 1  πγ, Δ  Nγ, K *  Kγ,    γ, ρ  ππγ,...

Transcript of 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow ...

Page 1: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 1

Direct photons. Data review.Sergey Kiselev, ITEP Moscow Introduction Before QM’06

p+p: prompt γA+B: experimental methods

Subtraction method Momentum correlations methodInternal conversion method

QM’06high-pt

low-pt

elliptic flow v2

γ-h azimuthal correlation Conclusions

Page 2: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 2

Introduction Direct photons: not from hadron decays Quark gluon level:

qq gγ, qg qγ, qq(g) qq(g)γ. Initial hard NN collisions, pQCD prompt γ.

Thermalised QGP stage thermal γ from QGP.

Page 3: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 3

Introduction – cont. Hadron level:

meson scatterings: ππ ργ, πρ πγ, πK K* γ, Kρ Kγ, KK* πγ, πK* Kγ, . . .

Thermalised hadron stage thermal γ from hadron gas Decay photons:

Long lived (c » cAB ~ 50-100 fm) π0 γγ, γγ, ’ ργ/ωγ/2γ

Shot lived (c cAB ~ 50-100 fm) ω πγ, a1 πγ, Δ Nγ, K* Kγ, γ, ρ ππγ, . . .

Page 4: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 4

Prompt : pp data A Compilation of Data, J. Phys. G, 23 (1997) A1 Data fit: D.Srivastava, Eur.Phys.J, C22 (2001) 129

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 5

Prompt : data fit

Page 6: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 6

Prompt : other data fit PHENIX

hep-ph/0609037 d3σ/dyd2pT = (√s)5 ·

F(xT,y)

Page 7: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 7

Prompt : data/theoryP.Aurenche et.al, PR D73, 094007 (2006), with PHENIX, D0 dataThe data can be described (accuracy ~ 50%) within the NLO QCD (JETPHOX code), except E706 experiment.

Page 8: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 8

Experimental methods for direct photons

Last years: large progress in experimental techniques to extract direct photons

Direct photons have been revealed by methods: Subtraction method, WA98/2000, PHENIX/2005 Momentum correlation method, WA98/2004 Internal conversion method, PHENIX/2005 External conversion method, PHENIX/2006, QM’06

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 9

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 ’

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 10

Subtraction – WA98

Page 11: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 11

Subtraction – PHENIXPRL 94, 232301 (2005)

.

2

2

//

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inelcollAA

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TAA

TAA

NTddpNdTddpNdpR

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 12

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

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 13

Momentum correlations – WA98 Rinv (≈ 6 fm ≈

Rinv ( emitted in the late,

hadron gas, stage of the collision

Thermal calculations substantialy underestimate the data.

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 14

Internal conversion 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

directdirectincl.) incl.

Electrons in the central arms were identified by matching charged particle tracks to clusters in the ECAL and to rings in the RICH

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 15

Internal conversion - details

32

2222

2

2

2

112141321 )

Mm()m(F

m)

mm(

mm

dmdN

Nee

eeeeee

e

ee

e

ee

ee

Main assumption: the Kroll-Wada (KW) formula, Phys.Rev.98(1955)1355A given reaction produces, instead of real γ, γ* e+e-. For decays:

Nγ – number of real γπo γγ πo γγ* γe+e- I=KW = 0.0059η γγ η γγ* γe+e- I=KW = 0.0081γdirect γ*direct e+e- I=KW = 0.0162 phase space factor =1, if pee

T » mee

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Internal conversion – 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).

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RAA vs pT for direct photons

.

2

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inelcollAA

TNN

AA

TAA

TAA

NTddpNdTddpNdpR

QM’05:High pT direct photonsare not suppressed strong suppression of mesons is not an initialeffect, but a final stateeffect

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 18

Quark Matter 2006 PHENIX data High-pT direct photon

Hard scattering Talk by T.Isobe

Low-pT direct photon Thermal emission from

QGP. Talk by D. Peressounko

Azimuthal anisotropy of direct photon Talk by V.S. Panteuev

γ- h azimuthal correlations Talk by J. Jin

Enter STAR into the game…

Run Year Species s1/2 [GeV ] Ldt

01 2000 Au+Au 130 1 b-1

02 2001/2 Au+Au 200 24 b-1 p+p 200 0.15 pb-1

03 2002/3 d+Au 200 2.74 nb-1 p+p 200 0.35 pb-1

04 2003/4 Au+Au 200 241 b-1 Au+Au 62 9 b-1

05 2004/5 Cu+Cu 200 3 nb-1 Cu+Cu 62 0.19 nb-1 Cu+Cu 22.5 2.7 b-1 p+p 200 3.8 pb-1

06 2006 p+p 200 93.3 pb-1 ?

p+p 62 1.1 pb-1 ?

07 2007 Au+Au 200

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 19

Systematic Study of High-pT Direct Photon Production with the PHENIX Experiment at RHIC

Tadaaki Isobe (CNS, Univ. of Tokyo)for the PHENIX Collaboration

The 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions

at Shanghai, China

Page 20: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

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High-pT direct photons: where are we?

p+p: agreement with NLO pQCD.

Run2 high-pT direct photons in Au+Au: consistent with binary scaled NLO pQCD.

Binary scaling is not obvious. 70% prompt photon + 30% jet

fragmentation at high-pT. Fragmentation photons are

suppressed by jet-quenching effect at RHIC?

Compensated by other contribution?

30% contribution from jet frag.

Phys. Rev. Lett. 94, (2005) 232301

Page 21: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 21

Fraction of fragmentation photons Fraction of fragmentation photons

is evaluated in terms of the fraction of isolated photons in 200GeV p+p collisions.

If energy of cone around a target photon is much less than the energy of photon, the photon is defined as isolated photon.

Isolation cut removes fragmentation (Bremsstrahlung) photons.

Data are consistent with theoretical expectation within the error. hep-ex/0609031

Jet

Theoretical predictions where PHENIX acceptance is taken into account

Page 22: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 22

Parameterization of the p+p data For the calculation of nuclear

modification factor, p+p reference is parameterized using a fitting function.

The fitting works well to parameterize the p+p photon data.

The parameterized photon data show enhancement comparing with NLO pQCD expectation by a factor of more than 20%.

Data Fit

Page 23: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 23

Interaction of hard-scattered parton with dense matter. Compton scattering (jet-photon

conv.) R.J. Fries, Phys.Rev. C72

(2005) 041902 Over estimation at high-pT

S. Turbide, Phys.Rev. C72 (2005) 014906

Reproduce data well Bremsstrahlung

B.G. Zakharov, JETP Lett. 80 (2004) 1

If it is observed, it can be used as hard probe of bulk matter.

Medium induced high-pT direct photons

Jet-quenching effect for fragmentation photons are estimated with AMY formalism.

QGP-ThermalJet-photon

NLO-pQCD

All

Hard scattered parton interacts with gluon in bulk matter

Page 24: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 24

Direct photon RAA

Nuclear modification factor Yield from hard processes can be

scaled with Ncoll (# of collisions). divided by expected (binary scaled)

yield from p+p data.

RAA is consistent with Ncoll scaled p+p reference.

RAA of very high-pT direct photons is below one. A hint of jet-quenching effect for

fragmentation photons? RAA using pQCD shows different

tendency.

.

2

2

//

/)(

inelcollAA

TNN

AA

TAA

TAA

NTddpNdTddpNdpR

First data using p+p data as reference!

Thanks to the more accurate p+p/Au+Au data.

RAA with pQCD

RAA with p+p data

.

2

2

//

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inelcollAA

TNN

AA

TAA

TAA

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 25

Comparison of RAA with theoretical calculation Turbide et al.

Phys. Rev. C72 (2005) 014906 + Private communication. AMY formalism for jet-

quenching effect for fragmentation photons.

Systematically data points are below theoretical prediction.

F. Arleo JHEP 0609 (2006) 015

High-pT suppression due to isospin effect, in addition to jet-quenching and shadowing. BDMPS for jet-

quenching. Medium induced jet-photon is

not taken into account. The suppression of very high-pT

photon is well reproduced.

Page 26: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 26

Summary/T.Isobe Direct photons in 200GeV p+p collisions.

Published final year-3 p+p data. Preliminary year-5 data. Consistent with NLO pQCD within uncertainty.

Direct photons in 200GeV Au+Au collisions. Clear signal of direct photon at high-pT thanks to the strong

suppression of neutral hadrons. Spectra up to 20GeV/c.

First direct photons RAA in 200GeV Au+Au collisions with p+p reference. Almost consistent with binary scaled p+p data. RAA seems to be below one at very high-pT region.

Page 27: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 27

Direct photons at low pt measured in PHENIX

D.Peressounko RRC “Kurchatov institute”

for the PHENIX collaboration

Page 28: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 28

Subtraction and Tagging methods

Measure photon spectrum and remove those photons which make 0 mass with any other

Correct direct photon candidate sample for contribution from 0 decay photons with missing partner and for direct photons with fake partners

Subtract contribution from , etc. decays

Measure yield of inclusive photons corrected for hadron contaminations, conversion, efficiency and acceptance.

Measure spectrum of 0, , etc.

Calculate yield of decay photons and subtract it from the inclusive yield.

Ndir = N

incl - Ndecay

Subtraction Tagging

Page 29: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 29

d+Au collisions: Double ratio

• Internal conversion method provides smaller systematic errors • But not as small as in the case of Au+Au collisions in Run-4 (Large background of external conversion on MVD detector in Run-3)

Page 30: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

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d+Au collisions: Spectrum

Internal conversion extends range of significant points to pt > 2 GeV

Data agrees with pQCD predictions in full pt range

=> No indication for nuclear effects

Page 31: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 31

Au+Au collisions: External conversion

Combining this photon with others measured in EMCAL with loose PID cut, estimate proportion of photons coming from 0 decays

Correct for missing 0 decay partners Subtract , , ’ decay photons Calculate ratio N

all/Ndecay

Use very tight PID cut on EMCAL photons to produce very clean photon sample

Use external photon conversion in beam pipe to produce very clean photon sample

External conversion Tagging

no pair cutwith pair cut

Dal

itz

Conversion

Uses very pure photon sample avoid explicit calculation of 0 spectrum

=>reduce systematic errors

Page 32: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 32

Comparison: Au+Au, central collisions

Spectra agree within errors in entire pt range

Systematic errors are still too large to extract thermal photons.There is room for thermal photons

This is consistent with excess above pQCD reported previously

Page 33: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 33

Two-photon correlations

1

2

1

2rec

e-

e+

External conversion:• No close cluster interference• No hadron contamination

C2 calculated in EMCAL and converted+EMCAL agree =>both effects are under control

Page 34: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 34

Conclusions/D.Peressounko Measurement of direct photon yield at small pt

is very interesting but extremely complicated task

PHENIX has developed a variety of methods for direct photon extraction in p+p, d+Au and Au+Au collisions producing consistent results

Because of the large systematic errors comparison of binary scaled d+Au spectrum with Au+Au does not allow to make a statement on the origin of the excess above pQCD observed in Au+Au.

More precise data are coming…

Page 35: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 35

PHENIX measurements of reaction plane dependence of high pT photons and pions in Au+Au collisions

Vladislav Pantuev, University at Stony Brookfor PHENIX collaboration

Page 36: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 36

Compton AnnihilationIn p+p Hard photons:direct component

q + g + q q + q + g

Photons in A+A

Direct Photons Decay Photons

hard thermal hard+thermal

QGP Hadron gasdirect fragmentation

Preequilibriumphotons

jet--conv.

Medium induced bremsstr.

In A+A picture is much more complicated:

V2=0V2<0V2<0

V2>0V2>0V2>0

Page 37: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 37

There are theoretical predictions with a sizable azimuthal parameter v2 :

S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006)R. Chatterjee et al., PRL 96, 202302 (2006)

Thermal photons are produced throughout the expansion history and reflect quark anisotropy

Jets lose more energy where the medium is thicker - more jet-photon conversions (v2<0), + photons from fragmentation of quenched jets (v2>0)

4

Page 38: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 38

How does PHENIX measure direct photons and v2?

Measure inclusive photon yield, Ninc Measure hadron contribution components 0 and By Monte Carlo calculate and decay background in

inclusive sample, Nbg Calculate direct photon excess over hadron decays, R Measure inclusive and hadron v2 by reaction plane

method Calculate direct photon v2 as R * v2

inc – v2BG

R = N inc / NBG

v2dir =

R – 1Use large statistics Run 4 Au+Au data set

See also poster 86 by Kentaro Miki

5

Page 39: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 39

Step by step calculations:

PHENIX preliminary

PHENIX preliminary

PHENIX preliminary

PHENIX preliminary

6

Page 40: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 40

PHENIX direct photon v2 result

Within statistical and systematic errors v2 is consistent with zero. v2=0 or cancellation of different contributions?

Systematic errors dominantly from R:

Enormous background of decay photons at low pT

7

Page 41: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 41

PHENIX Measurement on High pT h-h and -h Azimuthal Correlations

Jiamin Jin

For the PHENIX collaborationQuark Matter 2006, ShanghaiNov. 18, 2006

Page 42: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 42

Method Construct inclusive -h yield Construct decay -h yield via:

Pair by pair weighted summation convolutes all 0-h pair

contributions from higher pT Weight reflects probability from

kinematics for 0 at given pT to decay into photon in given pT range

Subtraction via:

hdecYhincRYRhdirY

11

# inclusive # inclusive ##decay decay

p+p

R=R=

Page 43: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 43

First direct -h yield in p+p, cmp with PYTHIA!p+p: important baseline measurement!p+p: important baseline measurement!

• data PYTHIA PYTHIA 6.1 kT = 2.5 GeV

• A nice confirmation of our method

PHENIX Preliminary PHENIX Preliminary

Page 44: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 44

•v2 modulated bkgd for inclusive/decay subtracted from each corr. fn under ZYAM assumption (v2 from single measurements)•Near side yield consistent with 0 small fragmentation photon yield

• Away side yield also small, suppressed!?

Au+Au: study medium induced modification!Au+Au: study medium induced modification!

First direct -h yield in Au+Au!1/

Ntri

gdN/

d

(rad) (rad)

1/N

trigdN

/d

Page 45: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 45

Comparison btw Au+Au and p+p

• Hint of away side modification in AuAu!

Black: Au+Au Red: p+p

1/N

trigdN

/d

(rad)

1/N

trigdN

/d

(rad)

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25.01.2007 RELNP seminar, ITEP, S.Kiselev 46

Away side integrated yield• trigger pT dependence• assoc. h pT dependence• centrality dependence + pp

• p+p shows a systematic trend of having higher yields in the away side than Au+Au!

Page 47: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 47

Conclusions/J.Jin

First measurements of high pT direct -h yields in Au+Au/p+p collisions Near side yield ~ 0 Hint of suppression of away side jets in Au+Au Need more statistics to make conclusive

statement Upcoming Au+Au run

Page 48: 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental.

25.01.2007 RELNP seminar, ITEP, S.Kiselev 48

Conclusions High-pt: RAA in 200GeV Au+Au collisions seems to

be below one at very high-pT region. Low-pt: more methods, but errors are still too large.

More precise data are coming… Elliptic flow v2: within statistical and systematic

errors v2 is consistent with zero. γ-h azimuthal correlations: near side yield ~ 0, hint

of suppression of away side jets in Au+Au, need more statistics.

Multi-purpose Direct Photons