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

28
M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

Post on 19-Dec-2015

222 views

Category:

Documents


1 download

TRANSCRIPT

Page 1: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 1

Heavy quark energy loss puzzle at RHIC

Magdalena Djordjevic

The Ohio State University

Page 2: 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).

Page 3: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 4: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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?

Page 5: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 6: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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).

Page 7: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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)

Page 8: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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).

Page 9: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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);

Page 10: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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).

Page 11: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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!

Page 12: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 12

Single electron suppression as a function of pt

At pt~5GeV, RAA(e-) 0.7±0.1 at RHIC.

Page 13: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 13

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

Page 14: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 15: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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.

Page 16: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 17: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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).

Page 18: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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.

Page 19: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 19

Acknowledgements:

Miklos Gyulassy

(Columbia University)

Ramona Vogt

(LBNL, Berkeley and University of California, Davis)

Simon Wicks

(Columbia University)

Page 20: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 20

backup

Page 21: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 22: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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%.

Page 23: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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.

Page 24: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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.

Page 25: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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

Page 26: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

M. Djordjevic 29

light

Comparison with pion suppression

Page 27: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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!

Page 28: M. Djordjevic 1 Heavy quark energy loss puzzle at RHIC Magdalena Djordjevic The Ohio State University

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.