Large Angle Hadron Correlations from Medium-Induced Gluon Radiation

Abstract

Final state medium-induced gluon radiation in ultradense nuclear matter is examined and shown to favor large angle emission when compared to vacuum bremsstrahlung due to the suppression of collinear gluons. Perturbative expression for the contribution of its hadronic fragments to the back-to-back particle correlations is derived. It is found that in the limit of large jet energy loss gluon radiation determines the yield and angular distribution of | Delta phi | > Pi/2 di-hadrons to transverse momenta pT2 of the associated particles. Clear transition from enhancement to suppression of the away-side hadron correlations is established at moderate pT2 and its experimentally accessible features are predicted versus the trigger particle momentum pT1.

Figures (3)

• Figure 1: The angular distribution of medium-induced bremsstrahlung of $E = 6$ GeV gluon jet for fixed values of the radiative gluon energy $\omega = 0.5, 1, 2, 4$ GeV. Top and bottom panels represent (1+1)D Bjorken expanding medium of transverse size $L=9$ fm and $L=3$ fm, respectively. Inserts show $\langle \theta^* \rangle$ versus $\omega$. Right panels illustrate the gluon spectrum and radiation intensity of $E = 40$ GeV gluon jet.
• Figure 2: Nuclear modification of the back-to-back di-hadron correlations with and without the contribution of medium-induced bremsstrahlung. Top and bottom panels illustrate central and peripheral collisions, respectively. Data is from STAR unknown:2005ph. Right panels predict $R^{(2)}_{AA}$ for low and high $p_{T_1}$ hadron triggers.
• Figure 3: The angular distribution of $|\Delta \varphi|\geq \frac{\pi}{2}$ di-hadrons for central and peripheral A+A collisions. Solid and dashed lines give separately the contribution of the radiative gluons and the attenuated parent parton. The lower right panel compares the the width of the correlation function in p+p to the one of the suppressed parent parton in central A+A reactions.