Review of Electromagnetic Probes O. Drapier LLR-École Polytechnique, France

« Review of electromagnetic probes », OD @ Quark Matter ’05, Budapest, Aug. 08, 2005 1

Review of Electromagnetic

Probes

O. Drapier

LLR-École Polytechnique, France

?


Electromagnetic probes ?

Bp,n

z

partonspartons

plasmaplasma

mixed phase ?mixed phase ?

thermalization

hadronization

kinetic freeze-out

chiral symmetry ?thermal equilib. ?chemical equilib. ?deconfinement ?

,kBt

hadronshadrons

l±

chemical freeze-out

Direct Photons

Single leptons,Dileptons


Photons ! (S.Bathe, 6b)

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

See next talk by C.

Gale


Low mass dileptons

From low energies …

To SPS …

D. Miskowiec, CERES

S.Damjanovic, NA60, 6a

SPS, 158 AGeV

p+Cu, 12 GeV

within acceptance

C+C, 2 AGeV

R.Holtzmann, Hades, 6aR.Muto, Kek-PS-E325,6aSee next talk by C.

Gale


Outline

Charm and Charmonium


Review of Electromagnetic

Probes

O. Drapier

LLR-École Polytechnique, France

Not exactly a


Let’s start with NA50 J/ Precise re-analysis of p-A data

s scaling, kinematical domain, neutron halo, … abs(J/) = 4.18 ± 0.35 mb

abs(’) = 7.6 ± 1.1 mb

Why abs ? Why not A ? L. Ramello, NA50


vsabs

A =

straight line here e – <L> abs

= straight line here

Not equivalent ! Depends on which

nuclei you take < L > or < L >

are only approximations

Calculations by Ruben Shahoyan

C. LourençoStudent’s session

α0Ap Aσσ

LρσexpAσσ abs0Ap

sdσsT1σ

σσ A

absAabs

0Ap


abs e – <L>

abs = intuitive if J/ disappearance in an absorbing medium. May depend on s !! Can be even much more complex

that that ! Combination of energy loss of the

initial parton + J/ « absorption » in nuclear matter

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Energy loss of initial gluon: Depends on Xf

Less important at RHIC

P. Cortese, NA50, 5b

B d() / dycm at ycm

= 0

P. Cortese, NA50, 5b

Doesn’t seem to play a role at NA50 Xf, otherwise would be seen on the


NA60 In+In @ 158 A.GeV

E. Scomparin, R. Arnaldi, 6a

Anomalous suppression ! Even if they fit NA50 data Onset in the range 80 < Npart <

100

Satz, Digal, FortunatoRapp, Grandchamp, BrownCapella, Ferreiro

Not reproduced by models Even if they fit NA50 data

R. Arnaldi, NA60

PLATEAU ???


What is the relevant variable ?

There is NO unique universal variable Depends on what

you want to show e.g. : anomalous

suppression is NOT an absorption by nuclear matter

More tricky if you need to compare different s !!! e.g. allows

comparisons

L or L don’tpure geometry

very preliminary

R. Arnaldi, NA60


What is the relevant variable ?

So, in principle we should: Calculate all the effects that might change with s Subtract them or plot them on top of the data for

comparison Plot the result vs the variable corresponding to the effect

you want to test/rule out

But these variables are model dependent & experiment dependent = nobody else than

the experiment can calulate these quantities

0-5 %

5-10 %10-15 %

15-2

0 %

20-2

5 %

90-95 %

etc…

Number of Participants

NA60

PHENIX

L. Ramello, NA50


SPS -> RHIC

Charm and charmonium cross-sections

Opens the door for cc recombination into J/ N(cc) up to 40 in a central Au+Au collision !

R.L. Thews & R.L. Mangano, nucl-th/0505055

--

J. Dunlop


Open charm measurements @ SPS ?

The « intermediate mass dilepton » puzzle @ SPS: Is there an enhancement of charm, or charm-like contribution

?

The answer is : NO, the excess exists, but it’s PROMPT For now, not enough precision to measure charm

cross-section …

Dimuon weighted offsets in NA60R. Shahoyan, 5b


Open charm @ RHIC Open charm is measured by

Single « non-photonic » electrons in PHENIX and STAR Direct D->k in STAR (see H. Zhang, 5c)

Limited PT domain « binary scaling » = as Ncoll

MORE PRECISION NEEDED !

J. Dunlop

S. Butsyk, 5a

PHENIX, S.S. Adler, et al., PRL 94 082301


Charm @ RHIC : high PT suppression Nuclear modification factor (S. Butsyk, 5a, J. Bielcik,

5c)

For more details, see J. Bielcik this afternoon

High PT suppression does not change charm yields

Djordjevic et al, nucl-th/0507019

J. Dunlop

See talk by X. Dong


Charm @ RHIC : Flow ! Charmed particles have a large V2 at RHIC !

Charm « quenching » and V2 were not expected Higher quark mass -> less gluon radiation (’’dead cone

effect’’) e.g. : Y. L. Dokshitzer & D.E. Kharzeev,

Phys.Lett.B519(2001)199-206 Hard process -> no flow

Influence of light quark flow ?

S. Butsyk, 5a

STAR, F. Laue, 5a

Theory:Greco, Ko, Rapp: PLB 595 (2004) 202See talk by

X. Dong


Heavy flavor = probe for « cold » nuclear effects Parton distribution functions are modified in nuclei

e.g. in d-Au collisions :Pb / p

X

AntiShadowing

Shadowing

X1 X2

J/ Northy > 0

X1X2

J/Southy < 0

X1X2

J/Central y < 0

d

Au

rapidity y

Anti-shadowing ShadowingNothing ?

Cold nuclear effects


Cold nuclear effects PHENIX d+Au @ 200 GeV (nucl-ex/050732, W. Xie, 5c)

(anti)shadowing clearly visible abs seems lower than @ SPS

~1 mb, 3mb overestimated

Dependence with centrality For Au+Au = mirror distribution

X


Now let’s move to PHENIX J/

dAu

200 GeV/c

CuCu

200 GeV/c

AuAu

200 GeV/c

J/ muon arm

1.2 < |y| < 2.2

AuAuee

200 GeV/c

CuCuee

200 GeV/c

J/ eeCentral arm

-0.35 < y < 0.35

CuCu

62 GeV/c

J/ in STAR ! See H. Zhang, 5c this afternoon J/ in PHENIX : H. Büsching, H. Perreira Da Costa, 6b


Tempting to plot NA50 points on top of this, isn’t it ? Well … interesting but …

Meaning of Npart when s * 10 ? NA50 points normalized to p+p

What if abs different ? Shadowing ?

Better : compare to absorption + shadowing

J/ in PHENIX

Suppression = 35 to 40 % wrt to abs = 3mb (overestimated)

~ equivalent to NA50 Need better

reference !!!

H.Pereira Da Costa, 6b


J/ in PHENIX

SatzRapp-GrandchampCapella-Ferreiro

Models: The models « which fit NA50 data

» overestimate the suppression Regeneration needed ???

MAYBE, but These models DO NOT fit NA60 ! Comovers severely underestimate

suppression in In+In Rapp & Grandchamp doesn’t

saturate as seen in the data Only Satz fits the end of the

plateau with Xc suppression only. NO direct J/ suppression ? Would be consistent with recent

lattice QCD calculations

R. Arnaldi, NA60c

J/ ?

See talk by M. Nardi


c-c recombinations ? It seems that these models can reproduce the data,

when they turn on the recombination process

Consequences on the other variables ?

-


Rapidity distributions Rapidity distribution of recombined J/ is supposed

to be peaked at y=0 (e.g. R.L. Thews & al., nucl-th/0505055) True IF charm distribution ~ J/ in p+p !

But Au+Au charm rapidity distributions might be very flat !

pQCD, adjust <kT2>

p+p data

« diagonal »

mainly« off-diagonal »



Rapidity distributions Comparing charm cross-sections in PHENIX central

and muons arms: Au+Au charm rapidity distributions might be very flat in

Au+Au ! Just an indication, because of the limited PT domain

If flat distribution of charm production : Lowers charm density -> less regeneration Rapidity distribution of regenerated less peaked at 0

PHENIX PRELIMINARY

See talk byY. Kwon, 5cthis afternoon !


PT distributions ? PT distribution of recombined J/ is very narrow (R.L.

Thews & al., nucl-th/0505055)

Leads to a drastic reduction of <PT

2> in case of recombination

BUT <PT2> calculated from p+p and d+Au (via

<kT2>)

Large error bars Need for more p (or d) + A data !! (e.g. p+p to d+Au in e±)

« diagonal »

mainly« off-diagonal »


Without

With


NA50 suppression at low PT … Compatible with high PT charm pairs

escaping the hot region before forming the J/

The same mechanism at RHIC would lead to an increase of <PT

2> Very different from regeneration

PT distributions ? Back to SPS

Low PT pairs cannot form a J/ High PT pairs can escape

At RHIC, <PT2> much

higher than at sps, but plasma longer lived. What is the net result for J/ ?F. Karsch & R. Petronzio

M.C. Chu & T. MatsuiJ.P. Blaizot & J.Y. Ollitrault


Is there a J/ flow ? Charm flows recombined

J/ must flow !

Directly produced J/ shouldn’t flow but suppression might be stronger out of reaction plane (as for Jets) … Can simulate some flow for

surviving J/ ?

Comovers should be more active in-plane those J/ which survive

interactions with comovers would have a negative V2 ????

solid: STARopen: PHENIX PRL91(03)

Regenerated J/ should lie on this curveV2/2 vs PT/2 !


Conclusion (1) A LOT OF BEAUTIFUL NEW DATA !

SPS : CERES excess confirmed by NA60 Intermediate mass excess in dimuon spectra confirmed by NA60

IT IS NOT OPEN CHARM, it’s prompt NA50 has re-analyzed p+A reference Anomalous J/ suppression confirmed by NA60 in In+In

RHIC Direct photons at low PT from PHENIX, consistent with thermal emission

Open charm is suppressed at high PT

Significant flow observed for open charm J/ suppression is seen by PHENIX, not stronger than in NA50 Models without recombination of charm quarks are unable to account

for the data


Conclusion (2) WE MUST TAKE SOME TIME, Interpreting

J/ suppression is a tricky thing Reproduce ALL SPS data Extrapolate to RHIC

Shadowing Normal absorption Measured flow Measured Y and PT distributions

THEN ONLY compare to RHIC data

We need GOOD REFERENCES ! p+A @ SPS (NA50, NA60 to be analyzed) p+A or d+A at RHIC

We need good statistics + several systems !!!!


Conclusion (3)

Only a joke !

NA38, QM’91


Thank You !

Special thanks to:F. Fleuret for his help for preparing this talk,

L. Kluberg, C. Lourenço, D. D’Enterria, R. Granier de Cassagnac and many others, for usefull discussions


Backup Slides


Kharzeev, Nardi & Satz

D.Kharzeev, M.Nardi and H.Satz,Phys. Lett. B405 (1997) 14


Heavy flavor production ’’Onia’’ production

Leading order at low x = ’’gluon fusion’’

Sensitive to:

Final stateParton energy loss in the hot & dense medium ?Thermal enhancement ?Flow ?

Initial stateParton distribution functionspT broadeningParton energy loss in the initial state ?Polarization ?

J/or

+ feed-down (e.g. B or c-> J/)


Heavy flavor production Open charm (or beauty)

production Leading order at low x

= ’’gluon fusion’’

Sensitive to:

Final stateParton energy loss in the hot & dense medium ?Thermal enhancement ?Flow ?

Initial stateParton distribution functionspT broadeningParton energy loss in the initial state ?Polarization ?


d-Au (√s = 200 GeV) d-Au: binary scaling also holds for different

centralitiesPHENIX PRELIMINARY PHENIX PRELIMINARY


Au-Au (√s = 62.4 GeV) Open charm in Au-Au @ 62.4 GeV, as compared to ISR p-p

data at the same incident energy Also compatible with <Ncoll> scaling

PHENIX PRELIMINARY


Recent evolutions in µµ B.R.

Year PDG average PDG fit

1998 2.5 - ee->µµ CS is not used in the fit

2000 2.5 3.7 Achasov 99C (3.30) appears

2002 2.5 2.87 Achasov 01G (2.87) appears

2004 2.5 2.85 No new data on this mode

1999: only average of values of photoproduction

2000 BRµµ included in the overall PDG fit

new imprecise measurement of ee->µµ : increase of BRµµ

2002 better ee->µµ measurement, confirming universality principle

1999-2000-2002 : 2.5 – 3.7 – 2.87

2004: BRµµ = (2.85±0.19) 10-4 ; BRee = (2.98±0.04) 10-4


Phi puzzle

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Review of Electromagnetic Probes O. Drapier LLR-École Polytechnique, France