Assessing lattice QCD charm space diffusion coefficient and thermalization time by mean of D meson observables at LHC

A central goal in the study of heavy-flavour production is to determine the interaction strength between Heavy Quarks (HQs) and the Quark-Gluon Plasma (QGP), quantified by the spatial diffusion coefficient Ds ( T ). Recent lattice QCD (lQCD) results with dynamical fermions suggest a remarkably low value of 2 πTDs ≈ 1 at T=Tc for charm quarks - significantly lower than both quenched QCD estimates and most phenomenological models - which typically yield 2πTDs≈3.5−5. This discrepancy raises the question of whether such a small Ds ( T ), corresponding to a thermalization time τth≈1−1.5 fm/c, is compatible with experimental measurements of key observables like the nuclear modification factor RAA , the elliptic and triangular flow coefficients v 2 and v 3 for D mesons. Using an event-by-event Langevin transport framework, we analyze several scenarios and highlight the pivotal role played by the momentum dependence of the drag coefficient A(p)=τth−1(p). Our findings show that a small 2πTDs(p→0)≈1−2 values can align with experimental data only if a significant momentum dependence in τth(p)=1/A(p) is included, as predicted by T-matrix approaches, or by the extended Quasi-Particle Model (QPMp). In contrast, assuming a momentum-independent τth=McDslQCD/T, it fails to reproduce the observed phenomenology. Furthermore, a short thermalization time of τth ≈ 1.5 fm/c implies a loss of sensitivity of the final-state observables to the initial charm-quark momentum distribution up pT ≈ Mc , suggesting a possible universal behavior driven by a dynamical attractor.