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