m. djordjevic 1 heavy quark energy loss puzzle at rhic magdalena djordjevic the ohio state...

M. Djordjevic 1

Heavy quark energy loss puzzle at RHIC

Magdalena Djordjevic

The Ohio State University

M. Djordjevic 2

Quark Gluon Plasma

Form, observe and understand Quark-Gluon Plasma (QGP).

Heavy quarks (charm and beauty, M>1 GeV) are widely recognized as the cleanest

probes of QGP.

High Energy Heavy Ion Physics

However, single electron measurements are available.

Heavy mesons not yet measured at RHIC.

N. Brambilla et al., e-Print hep-ph/0412158 (2004).

M. Djordjevic 3

1997 Shuryak argued (Phys.Rev.C 55, 961 (1995)) that heavy quarks will have large energy loss in QGP => large suppression of heavy mesons. (based on the assymption: ΔEcharm= ΔElight=BDPS (1995))

2001 Dokshitzer and Kharzeev proposed “dead cone” effect => heavy quark small energy loss (Phys. Lett. B 519, 199 (2001))

Motivation for studying the heavy quark energy loss

M. Djordjevic 4

Significant reduction at high pT suggests sizeable heavy quark energy loss!

Single electron suppression measurements at RHIC

V. Greene, S. Butsyk, QM2005 talks J. Dunlop, J. Bielcik; QM05 talks

Can this be explained by the energy loss in QGP?

M. Djordjevic 5

1) Initial heavy quark pt distributions

2) Heavy quark energy loss

3) c and b fragmentation functions into D, B mesons

4) Decay of heavy mesons to single e-.

Single electron suppression

D, B

1)

production

2)

medium energy loss

3)

fragmentation

c, b e-

4)

decay

M. Djordjevic 6

D mesons

, ’,

A

B

Initial heavy quark pt distributions

200S GeV=

High quark mass, i.e. M>>ΛQCD

Perturbative calculations of heavy quark production possible.

M. Cacciari, P. Nason and R.Vogt, Phys.Rev.Lett.95:122001,2005;

MNR code (M. L. Mangano, P.Nason and G. Ridolfi,

Nucl.Phys.B373,295(1992)).

R.Vogt, Int.J.Mod.Phys.E 12,211(2003).

M. Djordjevic 7

Radiative heavy quark energy loss

Three important medium effects control the radiative energy loss:

1) Ter-Mikayelian effect (M.L.Ter-Mikayelian (1954); Kampfer-Pavlenko (2000);

Djordjevic-Gyulassy (2003)) 2) Transition radiation (Zakharov (2002); Djordjevic (2006)). 3) Energy loss due to the interaction with the medium

(Djordjevic-Gyulassy (2003); Zhang-Wang-Wang (2004); Armesto-Salgado-Wiedemann (2004))

c

L

c

1) 2) 3)

M. Djordjevic 8

N. Armesto, C. A. Salgado, U. A. Wiedemann, Phys. Rev. D 69, 114003 (2004).

Generalized BDMPS-Z-W (2000) method. Computation based on path integral formalism.

c

Radiative energy loss due to the interaction with the medium

Caused by the multiple interactions of partons in the medium.

M. D. and M. Gyulassy, Phys. Lett. B 560, 37 (2003); Nucl. Phys. A 733, 265 (2004);

Generalized GLV (2000) method to compute heavy quark energy loss to all orders in opacity.

B. W. Zhang, E. Wang and X. N. Wang, Phys. Rev. Lett. 93, 072301 (2004);

Generalized ZW (2003) method. Derivation in terms of Modified FF with pQCD (twist expansion approach).

M. Djordjevic 9Thickness dependence is closer to linear Bethe-Heitler like form. This is different

than the asymptotic energy quadratic form characteristic for light quarks.

M. D. and M. Gyulassy, Nucl. Phys. A 733, 265 (2004);

M. Djordjevic 10M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005).

Pt distributions of charm and bottom before and after quenching at RHIC

Before quenching After quenching

M. Gyulassy, P.Levai and I. Vitev, Phys.Lett.B538:282-288 (2002).

M. Djordjevic 11

Panels show single e- from FONLL M. Cacciari, P. Nason and R. Vogt, Phys.Rev.Lett.95:122001,2005

M. D., M. Gyulassy, R. Vogt and S. Wicks, Phys.Lett.B632:81-86,2006

Single electrons pt distributionsB

efor

e q

uen

chin

g

Aft

er q

uen

chin

g

Bottom dominate the single e- spectrum above 4.5 GeV!

M. Djordjevic 12

Single electron suppression as a function of pt

At pt~5GeV, RAA(e-) 0.7±0.1 at RHIC.

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Comparison with single electron data

Disagreement with PHENIX preliminary data!

1000gdN

dy=

Armesto et al., hep-ph/0510284M. D. et al., Phys.Lett.B632:81-86,2006

M. Djordjevic 14

How can we solve the problem?

Reasonable agreement, but the parameters are not physical!

3500gdN

dy=

Armesto et al., hep-ph/0511257M. D. et al., Phys.Lett.B632:81-86,2006

M. Djordjevic 15

Are there other energy loss mechanisms?

Collisional and radiative energy losses are comparable!

M.G.Mustafa,Phys.Rev.C72:014905,2005

Finite size effects significantly lower collisional energy loss

S. Peigne, P.-B. Gossiaux, T. Gousset, hep-ph/0509185

The paper, however, did not make separation between elastic and part of

radiative energy loss effects.

M. Djordjevic 16

, L=5 fm

, L=5 fm

Collisional energy loss in finite size QCD medium

Collisional and radiative energy losses are comparable!

M.D., nucl-th/0603066

, L=5 fm

M. Djordjevic 17

Single electron suppression with the collisional energy loss

Reasonable agreement with single electron data,

even for dNg/dy=1000.

(S. Wicks, W. Horowitz, M.D. and M. Gyulassy, nucl-th/0512076)

Include collisional energy loss.

BT: E. Braaten and M. H. Thoma, Phys. Rev. D 44, 2625 (1991). TG: M. H. Thoma and M. Gyulassy, Nucl. Phys. B 351, 491 (1991).

M. Djordjevic 18

Conclusions

We applied the theory of heavy quark energy loss to compute the single electron suppression.

We show that bottom quark contribution can not be neglected in the computation of single electron spectra.

The recent single electron data show significant discrepancies with theoretical predictions based only on

radiative energy loss.

However, inclusion of the collisional energy loss may lead to better agreement with experimental results.

M. Djordjevic 19

Acknowledgements:

Miklos Gyulassy

(Columbia University)

Ramona Vogt

(LBNL, Berkeley and University of California, Davis)

Simon Wicks

(Columbia University)

M. Djordjevic 20

backup

M. Djordjevic 24

The uncertainity band obtained by varying the quark mass and scale factors.

Domination of bottom in single electron spectra

M. D., M. Gyulassy, R. Vogt and S. Wicks, Phys.Lett.B632:81-86,2006

R. Vogt, talk given at QM2005

M. Djordjevic 25

Transition & Ter-Mikayelian for charm

Two effects approximately cancel each other for

heavy quarks.

Transition radiation lowers Ter-Mikayelian

effect from 30% to 15%.

M. Djordjevic 26

Heavy quark suppression with the elastic energy loss

The elastic energy loss significantly changes the charm and bottom suppression!

CHARM

BOTTOM

Done by Simon Wicks.

M. Djordjevic 27

Why, according to pQCD, pions have to be at least two times more suppressed than single electrons?

Suppose that pions come from

light quarks only and single e-

from charm only.

Pion and single e- suppression would really be the same.

g

0

b

b+ce-

However,

1) Gluon contribution to pions increases the pion suppression, while

2) Bottom contribution to single e- decreases the single e- suppression

leading to at least factor of 2 difference between pion and single e- RAA.

M. Djordjevic 28RAA(e-) / RAA(0) > 2

M. Djordjevic 29

light

Comparison with pion suppression

M. Djordjevic 30

How to explain this puzzle?

From the current model this would be hard to explain because of:

1) Bottom contribution to single electrons

2) Gluon contribution to pions

PHENIX preliminary data suggest single electron suppression similar to pion suppression!

Therefore, to explain the data, we need a model which would eliminate bottom contribution from single electrons + eliminate

gluon contribution from pions!

M. Djordjevic 31pT [GeV/c]

RA

A

M. Djordjevic et al., hep-ph/0410372

N. Armesto et al. hep-ph/0501225

1000gdN

dy=

3500gdN

dy=

Single electrons from Charm only reproduce Armesto et al. plots

Comparison with results by Armesto et al.