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SUMMARY:Open quantum system approach to the transverse momentum broadening
  of a colour dipole
DTSTART:20260618T080000Z
DTEND:20260618T100000Z
DTSTAMP:20260704T030500Z
UID:indico-event-1696091@indico.cern.ch
DESCRIPTION:Speakers: Pietro Benzoni (Subatech)\n\n\nUsing the open quantu
 m systems formalism\, we study the propagation of a quark-antiquark pair p
 ropagating through a dense QCD plasma of size $L$ and transverse momentum 
 broadening transport coefficient $\\hat q$\, and we derive the Lindblad ev
 olution equation for the density matrix of the system.\nWe focus on the bo
 osted regime where the opening angle $\\theta_{q\\bar q}$ of this effectiv
 e colour dipole satisfies $\\theta_{q\\bar q}\\ll 1$. In the back-to-back 
 limit where the quark-antiquark relative transverse momentum $p_\\perp$ is
  much larger than the imbalance $q_\\perp$ as well as the medium typical t
 ransverse momentum scale $Q_s=\\sqrt{\\hat q L}$\, we demonstrate that the
  resulting Wigner distribution displays quasi factorisation between a hard
  factor describing the hard splitting producing the $q\\bar q$ pair and th
 e transverse momentum imbalance $q_\\perp$-distribution encoding the broad
 ening induced by the medium. The factorisation is violated by a "colour de
 coherence'' factor that controls the $\\theta_{q\\bar q}$ dependence of th
 e $q_\\perp$-distribution through the ratio $\\theta_{q\\bar q}/\\theta_c$
 \, with $\\theta_c \\sim (\\hat q L^3)^{-1/2}$. The open quantum systems a
 pproach enables us to clarify the role of this critical angle $\\theta_c$ 
 and its associated critical time $t_c$ in the genuine quantum decoherence 
 of the density matrix in colour and kinematic space.\nFinally\, we investi
 gate the corrections beyond the quasi-factorised picture due to the quantu
 m diffusion term in $p_\\perp$ of the Lindblad equation and we find that t
 hese corrections are mild.\n \nBased on [F. Arleo\, P. Benzoni\, P. Cauca
 l\, P. B. Gossiaux\, https://arxiv.org/abs/2606.07744].\n\n \n\nhttps://i
 ndico.cern.ch/event/1696091/
LOCATION:4/2-037 - TH meeting room (CERN)
URL:https://indico.cern.ch/event/1696091/
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