flow effects on jet profile n. armesto 2nd international conference on hard and electromagnetic...
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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'06TRANSCRIPT
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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
1
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...
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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.
2
For other proposals, see S. A. Voloshin, nucl-th/0312065.
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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
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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
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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:
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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?
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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.
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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
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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).
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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.
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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
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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.
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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).
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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
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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
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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.