Speaker
Description
High transverse momentum ($p_T$) jets provide a sensitive probe to the resolving power of the Quark-Gluon plasma (QGP) produced in heavy-ion collisions. In particular, understanding how the medium responds to multi-prong configurations inside jets is essential for a quantitative description of jet quenching and its manifestation in jet substructure sensitive observables.
In this work, we present a next-to-leading order (NLO) study of the nuclear modification effect that incorporates the resolving power of the QGP through a medium resolution scale $Q_{\rm med}$, which controls the transition between coherent and decoherent jet energy loss. Inclusive jet production in $pp$ and $PbPb$ collisions is calculated within an NLO pQCD framework using \texttt{NLOJet++}, supplemented by nuclear parton distribution functions and a realistic hydrodynamic medium evolution. Jet energy loss is modeled in the high-twist formalism, including jet radius dependence, medium induced radiation, and transverse momentum broadening. The jet resolution scale $Q_{\rm jet}$, defined by the invariant mass of intra-jet prong structures from the NLO cross-section, is compared to $Q_{\rm med}$ to determine whether substructures inside a jet lose energy coherently as a single color charge or decoherently as independently resolved emitters.
This subjet merging procedure is formulated at NLO and can be generalized to realistic multi-parton final states from Monte Carlo parton showers.
Our numerical results show that coherent energy loss alone describes inclusive jet suppression at moderate transverse momentum, but leads to a systematic overestimation of the nuclear modification factor $R_{AA}$ at high-$p_T$.
Incorporating decoherent energy loss enhances the suppression of high-$p_T$ jets and results in good agreement with the ATLAS measurements. The same framework also describes reclustered jet observables, where decoherent energy loss is essential for jets containing multiple subjets, and leads to an enhanced jet azimuthal anisotropy $v_2$ at high-$p_T$. A simultaneous description of inclusive jets, reclustered jets, and jet $v_2$ constrains the medium resolution scale to $Q_{\rm med}\simeq14-20$ GeV in $PbPb$ collisions at $\sqrt{s_{NN}}=5.02$ TeV.
| 请选择分会 | 高能重离子物理 |
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