M. Djordjevic 1
Single electron puzzle at RHIC
Magdalena Djordjevic
Columbia University
M. Djordjevic 2
Jet Quenching of light partons strongly suggest that QGP is discovered.
Further tests of jet tomography using heavy quarks could be decisive as a complementary test of the theory.
However, single electron measurements are available.
Is the QGP already discovered at RHIC?
Heavy ion physics has a goal to form and observe a QGP.
Heavy mesons not yet measured at RHIC.
M. Djordjevic 3Significant reduction at high pT suggest sizable energy loss!
Single electron suppression measurements from PHENIX
0
V. Greene, S. Butsyk,
QM2005 talks
M. Djordjevic 4
Charged Hadron RAA
J. Dunlop, J. Bielcik; QM05 talks
0.2
Single electron suppression from STAR
“Suppression is approximately the same as for hadrons.”
Can this be explained by the radiative energy loss in QGP?
M. Djordjevic 5
Outline
To apply the radiative heavy quark energy loss that we developed to compute the heavy quark (c and b) suppression. (M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005); Euro Phys.
J C, in press)
Decay heavy quarks into single electrons and compute single electron suppression.
(M. Djordjevic, M. Gyulassy, R. Vogt and S. Wicks, nucl-th/0507019, submitted to Phys. Lett. B (2005))
Answer: Can pQCD theory explain similar pion and single electron
suppression?
M. Djordjevic 6
To make theoretical predictions for heavy meson and single electron suppression we generalized the GLV method described in PLB538:282-288,2002. To apply this method we need to know:
1) Initial heavy quark pt distribution
2) Radiative heavy quark energy loss
3) c and b fragmentation functions into D, B mesons and how they
decay to single e-.
c, b e-
1)
production
2)
medium energy loss
3)
fragmentation
Single electron suppression
M. Djordjevic 7
To compute the initial charm and beauty pt distributions we applied the MNR code (Mangano et al. Nucl.Phys.B373,295(1992)).
Parameters values from R.Vogt, Int.J.Mod.Phys.E 12,211(2003).
Initial heavy quark pt distributions
200S GeV
M. Djordjevic 8
Radiative heavy quark energy loss
Three important medium effects control the radiative energy loss:
1) Ter-Mikayelian effect (M. D. and M. Gyulassy, Phys. Rev. C 68, 034914 (2003)) 2) Transition radiation (M. D. and M. Gyulassy, in preparation). 3) Energy loss due to the interaction with the medium
(M. D. and M. Gyulassy, Phys. Lett. B 560, 37 (2003); Nucl. Phys. A 733, 265 (2004))
c
L
c
1) 2) 3)
M. Djordjevic 9
The heavy quark radiative energy loss depends on the gluon rapidity density, which we can determine from 0 RAA.
u,d
g
0
1000gdN
dy
u,d
g 0
3500gdN
dy
1000 3500gdN
dy
M. Djordjevic 10
Numerical results for induced radiative energy loss are shown for first order in opacity, with assumed Rx=Ry=6 fm. Mc=1.2 GeV, Mb=4.75 GeV.
Due to its high mass, bottom looses less than half of charm quark energy loss.
M. Djordjevic 11
Aft
er q
uen
chin
g
Before quenching
M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005);
Euro Phys. J C, in press (2005).
M. Djordjevic 12
Panels show single e- from FONLL (M. Djordjevic, M. Gyulassy, R. Vogt and S.
Wicks, nucl-th/0507019, submitted to Phys. Lett. B (2005))
Single electrons at RHIC
Beauty dominate the single e- spectrum after 4.5 GeV!
M. Djordjevic 13
Single electron suppression as a function of pt
red curves: be; blue curves: c e; black curves: b+c e; green curves: Pions
At pt~5GeV, RAA(e-) > 0.5±0.1 at RHIC.
M. Djordjevic 14RAA(e-) / RAA(0) > 2
M. Djordjevic 15
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+c e-
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 16
red curve: B mesons; blue curve: D mesons; green curve: Pions
Heavy quark suppression as a function of pt
(M. D., M. Gyulassy and S. Wicks, Phys. Rev. Lett. 94, 112301 (2005);Euro Phys. J C, press)
Moderate D meson suppression ~ 0.3-0.5 at RHIC.
1000gdN
dy
B
D
g
pT [GeV]
u,d
Pa
rto
n L
ev
el
RA
A(p
T)
B
D
0
3500gdN
dy
g
u,d
Pa
rto
n L
ev
el
RA
A(p
T)
pT [GeV]
M. Djordjevic 17
Conclusions
We here applied the theory of heavy quark radiative energy loss to compute single electron suppression.
We obtained that at pT~5GeV, RAA(e-) > 0.5±0.1 at RHIC.
Theoretically, single electron suppression has to be at least two times smaller than pion suppression.
If STAR RAA(e-) RAA(0) is confirmed, it will be a theoretical challenge to devise novel energy loss mechanisms able to
explain these data.
M. Djordjevic 18
Acknowledgements:
Miklos Gyulassy
Ramona Vogt
Simon Wicks
M. Djordjevic 19
Backup slides
M. Djordjevic 20pT [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.
M. Djordjevic 21
dNg/dy=1000 dNg/dy=3500
be
ce
b+ce
dNg/dy=1000
Sin
gle
Ele
ctr
on
RA
A(p
T)
pT [GeV]
0 ce
be
b+ce
dNg/dy=3500
Sin
gle
Ele
ctr
on
RA
A(p
T)
pT [GeV]
0
M. Djordjevic 22
The ratio of charm to bottom decays to electrons obtained by varying the quark mass and scale factors. The effect of changing the Peterson function parameters from c = 0.06, b = 0.006 (lower band) to c = b = 10−5 (upper band) is also
illustrated.