Extracting the jet transport coefficient from hadron suppressions by confronting current NLO parton fragmentation functions

Nuclear modification factors of single hadrons and dihadrons at large transverse momentum ($p_{\rm T}$) in high-energy heavy-ion collisions are studied in a next-to-leading-order (NLO) perturbative QCD parton model. Parton fragmentation functions (FFs) in $A+A$ collisions are modified due to jet energy loss which is proportional to the jet transport coefficient $\hat{q}$ characterizing the interaction between the parton jet and the produced medium. By confronting 6 current sets of NLO parton FFs for large $p_{\rm T}$ hadron productions, we extract $\hat{q}$ quantitatively via a global fit to data for both single hadron and dihadron suppressions, and obtain $\hat{q}/T^3 = 4.74 - 6.72$ at $T = 370$ MeV in central $Au+Au$ collisions at $\sqrt{s_{\rm NN}}=200$ GeV, and $\hat{q}/T^3 = 3.07 - 3.98$ at $T = 480$ MeV in central $Pb+Pb$ collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV. The numerical results show that the uncertainties for $\hat{q}$ extraction are brought by the different contributions of gluon-to-hadron in the 6 sets of FFs due to gluon energy loss being $9/4$ times of quark energy loss.

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