Heavy-to-light ratios as a testof 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 Partículasand

Instituto Galego de Física de Altas EnerxíasUniversidade de Santiago de Compostela

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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.

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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 formerplus Matteo Cacciari (Paris VI).

1. Motivation:N. Armesto

Heavy-to-light ratios as ... 3

BDMPS/GLV/GWZ/ZW: interference of production and scatteringsof the radiated gluon

Characterizationof the medium:

Genuine prediction of this approach:E (g) > E (q) > E

(Q)

colour charge mass effect

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

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.

pT

parton>5 GeV

Detailed modeling of geometry.

3. Results for RHIC:N. Armesto

Heavy-to-light ratios as ... 6

RD/h=RAAD/RAA

h (Dokshitzer-Kharzeev ’01).

➔ q/g difference affects all pT.

➔ Mass effects sizeable for pT<12 GeV.

➔ Look at 7< pT<12 GeV.

➔ v2 (expected ~ to that for h) and

centrality dependence: work in progress.

4. Results for the LHC:N. Armesto

Heavy-to-light ratios as ... 7

Transport coefficient (density) scaled by multiplicity: factor 2.5 to 7larger at the LHC than at RHIC (Armesto et al '04, Eskola et al '04).

Charm

Beauty➔ Small trigger bias effect (i.e. differencebetween massless c and b).➔10<p

T<20 GeV: charm sensitive to color

(g at low x), bottom to mass.

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 pT 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 withradiative Eloss via quenching weights plus FONLL fragmentation:

* Uncertainties (mass variation; conservative) upto pT=6 GeV.

* RAuAu

e can be ~0.4 in the range 5<pT<10 GeV.

Data presented here by PHENIXand STAR are consistent withradiative energy loss providedthe contribution from b is small.

Greene

van Leeuwen

5. Bottom at RHIC (II):N. Armesto

Heavy-to-light ratios as ... 9

If RAuAu

e<0.4 in the range 5<pT<10 GeV:

● Strong interaction of heavy quarks with the medium; hadronizationinside? (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

6. Conclusions:N. Armesto

Heavy-to-light ratios as ... 10

● Heavy flavours constitute an experimentally accessible testingground for our understanding of radiative energy loss.

● Both at RHIC and at the LHC heavy-to-light ratios offer solidpossibilities to check the formalism like those presented here: D's for7<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 haveseveral solutions: new effects, hadronization in medium, furtherconstraints on the transport coefficient, contribution from b decays,...

● Data presented here by PHENIX and STAR are consistent withradiative 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.

Backup I: quenching weights

N. Armesto

Heavy-to-light ratios as ... 11

Mass effect smaller for smaller R=qhat L3/2, so small for small lengths.

Backup II: bottom in FONLL

N. Armesto

Heavy-to-light ratios as ... 12

Cacciari et al '03; '04

Reasonable description of b production.

Backup III: fixed vs. variable L

N. Armesto

Heavy-to-light ratios as ... 13

● mc=1.5 GeV,

mb=4.75 GeV; no

fragmentation yet.

● qhat=1.2 GeV2/fmwith fixed L=6 fmreproduce R

AA(0-10%)

~0.2 for pions.

● A large fixed lengthproduces a largereffect of the mass onthe Eloss: mass effectsmall for small L.

To try to understand a disagreement with Djordjevic et al ‘05