Flow effects on jet profile

N. Armesto

2nd International Conference on Hard and Electromagnetic Probesof High-Energy Nuclear Collisions

Asilomar Conference Grounds, June 9th-16th, 2006

Néstor Armesto

Departamento de Física de Partículasand

Instituto Galego de Física de Altas EnerxíasUniversidade de Santiago de Compostela

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See the talks by M. Djordjevic, R. Fries, R. Hwa, G. Ma, A. Majumder, K. Rajagopal,T. Renk, C. Salgado, E. Shuryak, I. Vitev, U. Wiedemann, and many experimental talks...

Contents

N. Armesto

Flow effects on jet profile

1. Motivation.

2. Radiation in a flowing medium(with C. A. Salgado and U. A. Wiedemann, PRL93 (2004) 242301;PRC72 (2005) 064910)

3. v2, and the determination of qhat.(with C. A. Salgado and U. A. Wiedemann, PRC72 (2005) 064910;T. Renk and J. Ruppert, C72 (2005) 044901; T. Renk, hep-ph/0602045)

4. Conclusions.

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For other proposals, see S. A. Voloshin, nucl-th/0312065.

1. Motivation (I)N. Armesto

Flow effects on jet profile 3

Unsatisfactory aspects in available formalisms for radiative eloss:

Eskola et al '04(Quark Matter 05)

Dainese, talk at PANIC05

s=1/3-1/2

Dainese et al '04

STAR'06

1. Motivation (II)N. Armesto

Flow effects on jet profile 4

Suggestive (preliminary) experimental data:d+Au, 40-100%

Au+Au, 0-5%

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

Magestro at HP04

STAR Preliminary

near: ||<1.1, ||<1.4away: ||<2, ||<1.1

4<pttrig<6 GeV, 0.15<pt

ass<4 GeV

F.Wang at QM04

1. Motivation (III)N. Armesto

Flow effects on jet profile 5

Salgado, Wiedemann, '04● Jet shapes and associatedmultiplicities will be measured atthe LHC by ALICE, ATLAS andCMS (see the talks by the LHC exps.).

● Compromise between energycalibration and fluctuations:

Measurable jet shapes:

1. Motivation (IV)N. Armesto

Flow effects on jet profile 6

Dilution of the medium already taken into account (Baier et al, '98; Gyulassy,Vitev, Wang, '01; Salgado, Wiedemann, '02; '03):

But what if the hard parton is not produced in the frame comovingwith the medium, either longitudinally or transversely?

2. Radiation in a flowing medium (I)

N. Armesto

Flow effects on jet profile 7

Usual assumption:

c~2 (pQCD); c~10 (Eskola et al, '04; Daineseet al '04) from RHIC RAA

light analysis.

The success of ideal hydro:

For =0.5, 1, 1.5, one gets p/p=1,5,18 which may lead to a substantialincrease in radiative eloss.

2. Radiation in a flowing medium (II)

N. Armesto

Flow effects on jet profile 8

Assumption for longitudinal expansion:hard partons are not produced in the mediumcomoving frame, so momentum exchangeswith the radiating partons becomeanisotropic.

At first order in the opacity expansion(Gyulassy, Levai, Vitev, '00; Wiedemann, '00)

In the comoving frame, <kT>~snL; flow contribution q0~.

Our ansatz

2. Radiation in a flowing medium (III)

N. Armesto

Flow effects on jet profile 9

We compute

Energy deposition asymmetric due to:● Random emission.● t- or pT-ordering in emission.● Jacobian:

Vacuum: D0 parametrization(Abbott et al, '97); vacuum (medium)regulated for R<0.04 (0.01).

2. Radiation in a flowing medium (IV)

N. Armesto

Flow effects on jet profile 10

q0=, Emed=23 GeV,Ejet=100 GeV.

Symmetrized

Low shift inthe calorimetriccenter.

Asymmetry clearly visible.

3. v2, and the determination of qhat (I)

N. Armesto

Flow effects on jet profile 11

The defect in v2 triggers the inclusion of floweffects: in terms of the BDMPS parameters

compute

Our proposal:

nT

3. v2, and the determination of qhat (II)

N. Armesto

Flow effects on jet profile 12

Using a blast wave parametrization offlow profile at freeze-out (Lisa, Retiere, '03).

Flow may affect our extraction of qhat.

3. v2, and the determination of qhat (III)

N. Armesto

Flow effects on jet profile 13

Renk, Ruppert, PRC72(2005)044901: dynamical model for expansion, LO,quenching weights.

c=4,s=0.3,vT

i=0.1

s=0.45

● c~10 with no flow effect.● Small longitudinal effect for

●Sensitive to initial flow and toflow profile.

● A 'moderately optimistic scenario'leads to c~2 (pQCD).

3. v2, and the determination of qhat (IV)

N. Armesto

Flow effects on jet profile 14

Renk, hep-ph/0602045: associated particle production from dAu.

pTtrig>8 GeV,4<pTass<6 GeV

● Surface emissionweakened.

● Yields/triggerreproduced.

Dainese et al, '04

Determination of qhat?

N. Armesto

Flow effects on jet profile 15

● Analysis of RAA for light particles with quenching weights, geometry andBjorken expansion give qhat~10 GeV2/fm (4-15; dNg/dy~1000(-3500)).

● RAA for electrons shows uncertainties to be clarified.

● More stringent upper bound to come, hopefully, from less inclusivemeasurements.

● pQCD predicts values ~5 timessmaller; lower bound.

● AdS/CFT correspondence give values~3 GeV2/fm for T~300 MeV:upper bound?

● Consideration of flow may reduceqhat.

STAR‘ 06

4. ConclusionsN. Armesto

Flow effects on jet profile 16

● Flow should modify the pattern of medium-induced radiation if thehard parton is produced in a frame not comoving with the medium.Even the absence of such effect would tell us about its dynamicalexpansion.

● An exploratory study illustrates two examples of such effect:* Longitudinal elongation of the jet shape.* Moderate increase of v2.

● More elaborated implementations show the influence on the determinationof the transport coefficient and on the picture of the medium: flow maymimic the effect of a larger energy density.● More exclusive studies than RAA will be crucial, together withheavy flavors, to set this matter: hadrons at RHIC and the LHC, andcalorimetric measurements at the LHC. This demands new theoreticaltools under development.