single electron puzzle at rhic magdalena djordjevic columbia university

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.