Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations

Abelev, B.I.; Aggarwal, M.M.; Ahammed, Z.; Alakhverdyants, A.V.; Anderson, B.D.; Arkhipkin, D.; Averichev, G.S.; Balewski, J.; Barnby, L.S.; Baumgart, S.

doi:10.1103/PhysRevC.82.034909

Studying Parton Energy Loss in Heavy-Ion Collisions via Direct-Photon and Charged-Particle Azimuthal Correlations

STAR

Collaboration

Dec, 2009

6 pages

Published in:

Phys.Rev.C 82 (2010) 034909

e-Print:

0912.1871 [nucl-ex]

DOI:

10.1103/PhysRevC.82.034909

Experiments:

BNL-RHIC-STAR

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Abstract: (arXiv)

Charged-particle spectra associated with direct photon (

\gamma_{dir}

) and

\pi^0

are measured in

p

+

p

and Au+Au collisions at center-of-mass energy

\sqrt{s_{_{NN}}}=200

GeV with the STAR detector at RHIC. A hower-shape analysis is used to partially discriminate between

\gamma_{dir}

and

\pi^0

. Assuming no associated charged particles in the

\gamma_{dir}

direction (near side) and small contribution from fragmentation photons (

\gamma_{frag}

), the associated charged-particle yields opposite to

\gamma_{dir}

(away side) are extracted. At mid-rapidity (

|\eta|<0.9

) in central Au+Au collisions, charged-particle yields associated with

\gamma_{dir}

and

\pi^0

at high transverse momentum (

8< p_{T}^{trig}<16

GeV/

c

) are suppressed by a factor of 3-5 compared with

p

+

p

collisions. The observed suppression of the associated charged particles, in the kinematic range

|\eta|<1

and

3< p_{T}^{assoc} < 16

GeV/

c

, is similar for

\gamma_{dir}

and

\pi^0

, and independent of the

\gamma_{dir}

energy within uncertainties. These measurements indicate that the parton energy loss, in the covered kinematic range, is insensitive to the parton path length.

Note:

submitted to Phys. Rev. Lett, 6 pages, 4 figures

25.75.Bh
hard scattering
relativistic heavy-ion collisions
jets
direct photons
energy loss mechanism
OSG : STAR
p p: interaction
gold
charged particle: yield

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