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Heavy-to-light ratios as a test of medium-induced energy loss at RHIC and the LHC

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Heavy-to-light ratios as a testof medium-induced energy loss at RHIC and the LHC

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

Contents

1. Motivation.

2. Model.

3. Results for RHIC.

4. Results for the LHC.

5. Bottom at RHIC.

6. Conclusions.

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).

2

Heavy-to-light ratios as ...

Genuine prediction of this approach:

DE (g) > DE (q) > DE(Q)

mass effect

colour charge

1. Motivation:BDMPS/GLV/GWZ/ZW: interference of production and scatterings

of the radiated gluon

Characterization

of the medium:

3

Heavy-to-light ratios as ...

RHIC, no medium effects

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.

Standard LO pQCD (PYTHIA):

4

Heavy-to-light ratios as ...

2. Model (II):

(Dainese et al \'04; Eskola et al \'04; poster by Loizides)

Detailed modeling of geometry.

pTparton>5 GeV

Characteristic feature: the mass effect is smaller for smaller lengths.

5

Heavy-to-light ratios as ...

RD/h=RAAD/RAAh (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.

3. Results for RHIC:6

Heavy-to-light ratios as ...

- Small trigger bias effect (i.e. difference

between massless c and b).

- 10<pT<20 GeV: charm sensitive to color

(g at low x), bottom to mass.

4. Results for the LHC: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

7

Heavy-to-light ratios as ...

Data presented here by PHENIX

and STAR are consistent with

radiative energy loss provided

the contribution from b is small.

Greene

van Leeuwen

- FONLL(Cacciari et al \'98; \'01; \'05)partonic spectra supplemented with

radiative Eloss via quenching weights plus FONLL fragmentation:

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

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

5. Bottom at RHIC (I):- 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).

8

Heavy-to-light ratios as ...

Eskola et al \'04

- Larger transport coefficient?

(but upper bound to come,

hopefully, from correlations

(PHENIX: Grau; STAR: Dietel, Magestro)).

- How well do we control the production of heavy flavours at RHIC?

Cacciari et al \'05

CDF \'03, 1.96 TeV

5. Bottom at RHIC (II):If RAuAue<0.4 in the range 5<pT<10 GeV:

- Strong interaction of heavy quarks with the medium; hadronization

inside? (talks by Djordjevic, Rapp, Teaney).

9

Heavy-to-light ratios as ...

6. Conclusions:

- 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<pT<12 GeV at RHIC, and D\'s and B\'s for 10<pT<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.

10

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Backup I: quenching weights

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

11

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Backup II: bottom in FONLL

Cacciari et al \'03; \'04

Reasonable description of b production.

12

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Backup III: fixed vs. variable L

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

- mc=1.5 GeV,

mb=4.75 GeV; no

fragmentation yet.

- qhat=1.2 GeV2/fm

with fixed L=6 fm

reproduce RAA(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.

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Heavy-to-light ratios as ...

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