direct photons in 200 gev p+p , d +au, au+au

41
Direct Photons in 200 GeV p+p, d+Au, Au+Au Stefan Bathe UC Riverside for the PHENIX collaboration QM 2005, Budapest, August 4-9

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Direct Photons in 200 GeV p+p , d +Au, Au+Au. Stefan Bathe UC Riverside for the PHENIX collaboration. QM 2005, Budapest, August 4-9. p+p : Test of QCD Reduce uncertainty on pQCD photons in A+A - PowerPoint PPT Presentation

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Page 1: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

Direct Photons in 200 GeV p+p, d+Au, Au+Au

Stefan Bathe UC Riverside

for the PHENIX collaboration

QM 2005, Budapest, August 4-9

Page 2: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 2

Why Direct Photons?

● p+p:

♦ Test of QCD

• Reduce uncertainty on pQCD photons in A+A

● d+Au

♦ Study nuclear effects

● A+A

♦ Photons don’t strongly interact with produced medium

♦ Hard photons

• Allow test of Ncoll scaling for hard

processes• Important for interpretation of high-pT hadron suppression at

RHIC

♦ Thermal photons

• Carry information about early stage of collision

• QGP potentially detectable via thermal photon radiation

Page 3: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 3

Hard Photons

p+p

Page 4: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 4

Direct Photons in p+p● good agreement with NLO

pQCD

● Important baseline for Au+Au

PbSc

at 200 GeVp p s+ =

PbSc

New for QM: PHENIX Preliminary

Poster O. Zaudtke

PbGlnew

Poster A. Hadj Henni

Page 5: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 5

Hard Photons

d+Au

Page 6: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 6

Direct in d+Au

● p+p and d+Au spectra compared to NLO pQCD

● ratio to NLO pQCD

● consistent with 1

● No indication for nuclear effects

2

Poster H. Torii

Poster D. Peressounko

Page 7: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 7

Hard Photons

Au+Au

Page 8: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 8

Direct Photons in Au+Au

PRL 94, 232301

Expectation for Ncoll scaling of

direct photons

Recently published

holds for all centrality classes

0 suppression caused by medium created in Au+Au collisions

Page 9: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 9

Thermal Photons

Au+Au

Page 10: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 10

Schematic Photon Spectrum in Au+Au

Decay photons

nT

1

phard:

/ E Tethermal:

Page 11: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 11

Going to low pT

● No significant excess at low pT

Page 12: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 12

● New data set

● Selection of most stable runs

● Re-evaluation of systematic uncertainties

New from Run4

● Stay tuned for more improvements Poster T. Sakaguchi

Page 13: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 13

Thermal Photons

Au+Au

A New Approach

Page 14: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 14

Opening up the phase space

Minv

pT

direct photon analysis

new dilepton analysis

conventional dilepton analysis

0

Page 15: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 15

phase space factorform factorinvariant mass of virtual photon

invariant mass of Dalitz pair

phase space factorform factorinvariant mass of Dalitz pair

invariant mass of virtual photon

32

222

2

2

2

2

)1()(1

)2

1(4

13

21

M

mmF

mm

m

m

m

dm

dN

Nee

eeeeee

e

ee

e

ee

ee

ee

ee

dm

dN

N

1

The Idea

32

2

)1(M

meeeeee

e

ee

e

mm

m

m

m 1)

21(

41

3

22

2

2

2

22 )( eemF

● Start from Dalitz decay

● Calculate invariant mass distribution of Dalitz pairs

● Now direct photons

● Any source of real produces

virtual with very low mass

● Rate and mass distribution given by same formula

♦ No phase space factor for mee<< pT

photon

0

0

e+

e-

Compton

q

g q

Compton

q

g q

e+

e-

Page 16: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 16

● Calculate ratios of various Minv bins to lowest one: Rdata

● If no direct photons: ratios correspond to Dalitz decays

● If excess: direct photons

Method

÷

÷÷

0-3

0

90-1

40

140-2

00 M

eV

200-3

00

Rdata

● Material conversion pairs removed by analysis cut

● Combinatorics removed by mixed events

Page 17: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 17

Page 18: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 18

Page 19: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 19

S/B=~1

Page 20: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 20

S/B=~1

R

R

Rdirect

0

0

direct

data

incl.

direct

*

*

RR

RR

calculated from Dalitz formula

measuredRdata ÷

Page 21: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 21

S/B=~1

0

0

direct

data

incl.

direct

*

*

RR

RR

calculated from Dalitz formula

measuredRdata ÷

R

R

Rdirect

Page 22: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 22

S/B=~1

0

0

direct

data

incl.

direct

*

*

RR

RR

calculated from Dalitz formula

measuredRdata ÷

R

R

Rdirect

incl.

direct

measured with EMCal

Here we are…

~25 % systematic error :

~20 % from measured 0 ratio

~10 % from inclusive

~5 % acceptance

Page 23: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 23

140-200 MeV0-20 %

Rdata

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

Page 24: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 24

*direct/*inclusive

Significant 10% excess of very-low-mass virtual direct photons

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

0-20 %

Page 25: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 25

Centrality Dependence

Indication for centrality dependence

more peripheral

Page 26: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 26

Comparison to Conventional result

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

( + 1 )

Page 27: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 27

direct

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

Page 28: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 28

The Spectrum

Compare to published Run2 result: PRL94 232301

0

0

direct

data

incl.

direct

*

*

RR

RR

incl.

direct

Page 29: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 29

The SpectrumCompare to NLO pQCD

• excess above pQCD

• L.E.Gordon and W. Vogelsang

• Phys. Rev. D48, 3136 (1993)

Page 30: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 30

The Spectrum

Compare to thermal model

• data above thermal at high pT

2+1 hydro

T0ave=360 MeV(T0

max=570 MeV)

0=0.15 fm/c

• D. d’Enterria, D. Perresounko

• nucl-th/0503054

Compare to NLO pQCD

• excess above pQCD

• L.E.Gordon and W. Vogelsang

• Phys. Rev. D48, 3136 (1993)

Page 31: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 31

The Spectrum

Compare to thermal + pQCD• data consistent with

thermal + pQCD

Compare to thermal model

• data above thermal at high pT

• D. d’Enterria, D. Perresounko

• nucl-th/0503054

Compare to NLO pQCD

• excess above pQCD

• L.E.Gordon and W. Vogelsang

• Phys. Rev. D48, 3136 (1993)

2+1 hydro

T0ave=360 MeV(T0

max=570 MeV)

0=0.15 fm/c

Page 32: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 32

Conclusions

● Hard direct photons pT>4GeV/c

♦ p+p:

• Spectrum consistent with pQCD calculations

♦ d+Au:

• No apparent nuclear effects

♦ Au+Au:

• Confirms Ncoll scaling for hard processes

● Thermal (?) direct photons 1<pT<4GeV/c

♦ New EMCal measurement with reduced systematics

• Stay tuned for further improvements

♦ New measurement through very-low-mass virtual photons

• Significant 10% direct photon excess above decay photons

• Spectrum consistent with thermal model

Page 33: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 33

Page 34: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 34

Backup

Page 35: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 35

Page 36: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 36

WA98 Interpretation: T or kT ?

● QGP + HG rates convoluted with simple fireball model plus pQCD hard photons

● Data described with initial temperature Ti=205 MeV + some nuclear kT broadening (Cronin-effect)

● Data also described without kT broadening but with high initial temperature (Ti=270 MeV)

Turbide, Rapp, Gale, Phys. Rev. C 69 (014902), 2004

Page 37: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 37

WA98 Data: Conclusions

● Data consistent with QGP picture, but also with pure HG picture

● Large variations in extracted initial temperature Ti (however, most models give Ti > Tc)

Data can be described under a variety of different assumptions, e.g.:

Ti = 214 - 255 MeVQGP + HG + pQCD(Non-boost inv. hydro) Huovinen, Ruuskanen, Räsänen

(Nucl. Phys. A 650 (227) 1999)Ti = 213 - 234 MeVPure HG + pQCD

(Non-boost inv. hydro)

Ti = 335 MeV, = 0,2 fm/c

QGP + HG + pQCC(Bjorken hydro)

Svrivastava (nucl-th/0411041)

250 < Ti < 370 MeV,0,5 < < 3 fm/c

QGP + HG + pQCDRenk (Phys.Rev.C67:064901,2003)

Ti = 250 - 270 MeV, = 0,5 fm/c

QGP + HG + pQCD without kT

Ti = 205 MeV, = 1 fm/c

QGP + HG + pQCD with kTTurbide, Rapp, Gale

(Phys.Rev.C69:014903,2004 )

Page 38: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 38

PHENIX 0 RdA--Final

Cronin effect small!

New for QM: to be published

Page 39: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 39

Page 40: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 40

90-140

90-140 MeV, 20-40 %

Page 41: Direct Photons in 200 GeV  p+p ,  d +Au, Au+Au

QM05 Stefan Bathe 41

Only Ncoll scaling?

● What about fragmentation photons?

frag

men

tati

on

con

trib

uti

on

(%

)

● fragmentation contribution substantial in p+p

● parton energy loss in QGP reduces fragmentation contribution in Au+Au

● compensated by induced photon bremsstrahlung in QGP

● Effects cancel?