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