Speaker
Description
Colour decoherence in jet quenching has been the subject of intense theoretical activity and is actively searched for at RHIC and the LHC. However, it has so far lacked a systematic foundation from the perspective of open quantum systems, where the notion of decoherence is naturally formulated. In this talk (based on [1]), the open quantum systems framework is used to investigate the real-time propagation of a quark-antiquark pair through a dense QCD plasma, deriving the Lindblad evolution for the pair’s density matrix within the Markovian approximation.
Focusing on the boosted regime with a narrow dipole opening angle, we further explore the limit where the relative transverse momentum of the pair is much larger than both the momentum imbalance and the medium scale $Q_s=\sqrt{\hat qL}$. The resulting Wigner distribution displays quasi-factorisation between a hard factor describing the hard splitting producing the $q\bar q$ pair and the transverse momentum imbalance distribution encoding the broadening induced by the medium. The factorisation is only violated by a "colour decoherence factor" depending on the ratio between the dipole opening angle and the medium critical angle $\theta_c \sim (\hat qL^3)^{-1/2}$.
The open quantum systems formalism clarifies the role of the associated critical time $t_c$ in suppressing off-diagonal density matrix elements and controlling transitions between singlet and octet colour configurations. We further quantify corrections arising from quantum diffusion in $p_\perp$, highlighting the robustness of the quasi-factorised picture to describe the transverse momentum spectrum of colour dipoles and providing a perturbative scheme to systematically go beyond this approximation.
This framework is applied to the phenomenology of processes involving a boosted $q\bar q$ pair in heavy ion collisions, providing a first step towards a quantum-consistent description of such hard probes of the quark-gluon plasma.
[1] F. Arleo, P. Benzoni, P. Caucal, P. B. Gossiaux, Open quantum system approach to the transverse momentum broadening of a colour dipole, arXiv:2606.xxxx