1. Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC N. Armesto Quark Matter 2005: 18th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions Budapest, August 4th-9th 2005 Néstor Armesto Departamento de Física de Partículas and Instituto Galego de Física de Altas Enerxías Universidade de Santiago de Compostela 1

2. Contents N. Armesto Heavy-to-light ratios as... 1. Motivation. 2. Model. 3. Results for RHIC. 4. Results for the LHC. 5. Bottom at RHIC. 6. Conclusions. 2 With Andrea Dainese (Padova), Carlos A. Salgado and Urs A. Wiedemann (CERN), Phys. Rev. D71 (2005) 054027 (hep-ph/0501225). Work in progress with the former plus Matteo Cacciari (Paris VI).

3. 1. Motivation: N. Armesto Heavy-to-light ratios as... 3 BDMPS/GLV/GWZ/ZW: interference of production and scatterings of the radiated gluon Characterization of the medium: Genuine prediction of this approach:  E (g) >  E (q) >  E (Q) colour charge mass effect

4. 2. Model (I): N. Armesto Heavy-to-light ratios as... 4 Standard LO pQCD (PYTHIA): Quenching weights (www.pd.infn.it/~dainesea/qwmassive.html) : probability for medium energy loss. ➔ CTEQ4L pdf's, EKS98. ➔ gg (qqbar) to QQbar, Q(bar)g to Q(bar)g. ➔ g to QQbar (important for the LHC). ➔ Ff into D (B) and semileptonic e-decays. ➔ RHIC: tune to STAR D-meson data. ➔ LHC: tune to NLO pQCD calculation. RHIC, no medium effects

5. 2. Model (II): N. Armesto Heavy-to-light ratios as... 5 (Dainese et al '04; Eskola et al '04; poster by Loizides) Characteristic feature: the mass effect is smaller for smaller lengths. p T parton >5 GeV Detailed modeling of geometry.

6. 3. Results for RHIC: N. Armesto Heavy-to-light ratios as... 6 R D/h =R AA D /R AA h (Dokshitzer-Kharzeev ’01). ➔ q/g difference affects all p T. ➔ Mass effects sizeable for p T <12 GeV. ➔ Look at 7< p T <12 GeV. ➔ v 2 (expected ~ to that for h) and centrality dependence: work in progress.

7. 4. Results for the LHC: N. Armesto Heavy-to-light ratios as... 7 Transport coefficient (density) scaled by multiplicity: factor 2.5 to 7 larger at the LHC than at RHIC (Armesto et al '04, Eskola et al '04). Charm Beauty ➔ Small trigger bias effect (i.e. difference between massless c and b). ➔ 10<p T <20 GeV: charm sensitive to color (g at low x), bottom to mass.

8. 5. Bottom at RHIC (I): N. Armesto Heavy-to-light ratios as... 8 ● RHIC data in AuAu: electron spectra (PHENIX: Butsyk, Kwon; STAR: Bielcik, Laue, Zhang), weak correlation in p T with D/B, and contribution from B decays (Djordjevic et al '05; talks by Djordjevic and Vogt). ● FONLL (Cacciari et al '98; '01; '05) partonic spectra supplemented with radiative Eloss via quenching weights plus FONLL fragmentation: * Uncertainties (mass variation; conservative) upto p T =6 GeV. * R AuAu e can be ~0.4 in the range 5<p T <10 GeV. Data presented here by PHENIX and STAR are consistent with radiative energy loss provided the contribution from b is small. Greene van Leeuwen

9. 5. Bottom at RHIC (II): N. Armesto Heavy-to-light ratios as... 9 If R AuAu e <0.4 in the range 5<p T <10 GeV: ● Strong interaction of heavy quarks with the medium; hadronization inside? (talks by Djordjevic, Rapp, Teaney). ● Larger transport coefficient? (but upper bound to come, hopefully, from correlations (PHENIX: Grau; STAR: Dietel, Magestro) ). Eskola et al '04 ● How well do we control the production of heavy flavours at RHIC? Cacciari et al '05 CDF '03, 1.96 TeV

10. 6. Conclusions: N. Armesto Heavy-to-light ratios as... 10 ● Heavy flavours constitute an experimentally accessible testing ground for our understanding of radiative energy loss. ● Both at RHIC and at the LHC heavy-to-light ratios offer solid possibilities to check the formalism like those presented here: D's for 7<p T <12 GeV at RHIC, and D's and B's for 10<p T <20 GeV at the LHC. ● Problems with single electron spectra in AuAu at RHIC may have several solutions: new effects, hadronization in medium, further constraints on the transport coefficient, contribution from b decays,... ● Data presented here by PHENIX and STAR are consistent with radiative energy loss provided the contribution from b's is small. ● Clarification of this issue will demand (at RHIC and at the LHC): * pp/dAu reference to be controlled (e.g. Kharzeev et al '03) : new possibilities to check our understanding of HF production. * If possible, data for mesons, not only for electrons.

11. Backup I: quenching weights N. Armesto Heavy-to-light ratios as... 11 Mass effect smaller for smaller R=qhat L 3 /2, so small for small lengths.

12. Backup II: bottom in FONLL N. Armesto Heavy-to-light ratios as... 12 Cacciari et al '03; '04 Reasonable description of b production.

13. Backup III: fixed vs. variable L N. Armesto Heavy-to-light ratios as... 13 ● m c =1.5 GeV, m b =4.75 GeV; no fragmentation yet. ● qhat=1.2 GeV 2 /fm with fixed L=6 fm reproduce R AA (0-10%) ~0.2 for pions. ● A large fixed length produces a larger effect of the mass on the Eloss: mass effect small for small L. To try to understand a disagreement with Djordjevic et al ‘05