1. Flow effects on jet profile N. Armesto 2nd International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions Asilomar Conference Grounds, June 9th-16th, 2006 Néstor Armesto Departamento de Física de Partículas and Instituto Galego de Física de Altas Enerxías Universidade 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...

2. 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. v 2, 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.

3. 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

4. 1. Motivation (II) N. Armesto Flow effects on jet profile 4 Suggestive (preliminary) experimental data: d+Au, 40-100% Au+Au, 0-5% 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig) Magestro at HP04 STAR Preliminary near: |  |<1.1, |  |<1.4 away: |  |<2, |  |<1.1 4<p t trig <6 GeV, 0.15<p t ass <4 GeV F.Wang at QM04

5. 1. Motivation (III) N. Armesto Flow effects on jet profile 5 Salgado, Wiedemann, '04 ● Jet shapes and associated multiplicities will be measured at the LHC by ALICE, ATLAS and CMS (see the talks by the LHC exps.). ● Compromise between energy calibration and fluctuations: Measurable jet shapes:

6. 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 comoving with the medium, either longitudinally or transversely?

7. 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; Dainese et al '04) from RHIC R AA 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 substantial increase in radiative eloss.

8. 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 medium comoving frame, so momentum exchanges with the radiating partons become anisotropic. At first order in the opacity expansion (Gyulassy, Levai, Vitev, '00; Wiedemann, '00) In the comoving frame, ~  s n    L  ; flow contribution q 0 ~ . Our ansatz

9. 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 p T -ordering in emission. ● Jacobian: Vacuum: D0 parametrization (Abbott et al, '97) ; vacuum (medium) regulated for R<0.04 (0.01).

10. 2. Radiation in a flowing medium (IV) N. Armesto Flow effects on jet profile 10 q 0 = ,  E med =23 GeV, E jet =100 GeV. Symmetrized  Low shift in the calorimetric center. Asymmetry clearly visible.

11. 3. v 2, and the determination of qhat (I) N. Armesto Flow effects on jet profile 11 The defect in v 2 triggers the inclusion of flow effects: in terms of the BDMPS parameters compute Our proposal:  nTnT

12. 3. v 2, and the determination of qhat (II) N. Armesto Flow effects on jet profile 12 Using a blast wave parametrization of flow profile at freeze-out (Lisa, Retiere, '03). Flow may affect our extraction of qhat.

13. 3. v 2, 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, v T i =0.1  s =0.45 ● c~10 with no flow effect. ● Small longitudinal effect for  ● Sensitive to initial flow and to flow profile. ● A 'moderately optimistic scenario' leads to c~2 (pQCD).

14. 3. v 2, and the determination of qhat (IV) N. Armesto Flow effects on jet profile 14 Renk, hep-ph/0602045: associated particle production from dAu. p Ttrig >8 GeV, 4<p Tass <6 GeV ● Surface emission weakened. ● Yields/trigger reproduced. Dainese et al, '04

15. Determination of qhat? N. Armesto Flow effects on jet profile 15 ● Analysis of R AA for light particles with quenching weights, geometry and Bjorken expansion give qhat~10 GeV 2 /fm (4-15; dN g /dy~1000(-3500)). ● R AA for electrons shows uncertainties to be clarified. ● More stringent upper bound to come, hopefully, from less inclusive measurements. ● pQCD predicts values ~5 times smaller; lower bound. ● AdS/CFT correspondence give values ~3 GeV 2 /fm for T~300 MeV: upper bound? ● Consideration of flow may reduce qhat. STAR‘ 06

16. 4. Conclusions N. Armesto Flow effects on jet profile 16 ● Flow should modify the pattern of medium-induced radiation if the hard parton is produced in a frame not comoving with the medium. Even the absence of such effect would tell us about its dynamical expansion. ● An exploratory study illustrates two examples of such effect: * Longitudinal elongation of the jet shape. * Moderate increase of v 2. ● More elaborated implementations show the influence on the determination of the transport coefficient and on the picture of the medium: flow may mimic the effect of a larger energy density. ● More exclusive studies than R AA will be crucial, together with heavy flavors, to set this matter: hadrons at RHIC and the LHC, and calorimetric measurements at the LHC. This demands new theoretical tools under development.