engleski

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

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.

p p; interaction gold charged particle; yield parton; energy loss photon; direct production pi0; hadroproduction charged particle; associated production angular correlation; (charged particle photon) angular correlation; (charged particle pi0) transverse momentum; dependence heavy ion; scattering Brookhaven RHIC Coll parton; path length STAR 200 GeV-cms/nucleon

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