Sequential Y(nS) suppression in high-multiplicity pp collisions: the experimental case for an early, globally correlated medium

TL;DR

This paper investigates the suppression of quarkonium states in high-multiplicity proton-proton collisions, providing experimental evidence for an early, globally correlated medium consistent with partonic degrees of freedom.

Contribution

It demonstrates that existing hadronic and string-based models cannot fully explain the observed suppression patterns, supporting the presence of a partonic medium in small collision systems.

Findings

Suppression patterns challenge local hadronic models but align with a globally correlated partonic medium.

Early-time mechanisms are necessary to explain non-prompt suppression flatness.

The results are consistent with phenomena like strangeness enhancement and the long-range ridge.

Abstract

The multiplicity-dependent suppression of $\Upsilon(n\mathrm{S})$ states measured by CMS in $pp$ at $\sqrt s=7\,$TeV \cite{CMS2020}, and of $\psi(2S)\big/J/\psi$ measured by LHCb at $\sqrt s=13\,$TeV \cite{LHCb2024}, is subjected to four multi-differential tests: \emph{cone isolation}, \emph{azimuthal sectors}, \emph{transverse sphericity}, and \emph{prompt vs. non-prompt}. Cone and sphericity close a \emph{scissors constraint}: the local reading of the Comover Interaction Model is in tension with the cone data, its global reading with the sphericity data. The non-prompt flatness forces the mechanism to act at early proper times. None of the considered hadronic or string-based frameworks -- CIM local or global, PYTHIA 8 MPI \cite{Sjostrand2015}, rope hadronisation \cite{Bierlich2015}, CGC \cite{Ma2015}, Trainor TCM \cite{Trainor2008} -- naturally satisfies the four constraints simultaneously in its published form. The surviving class is an early, globally correlated medium consistent with partonic degrees of freedom, co-occurring with the ALICE strangeness enhancement \cite{ALICE_SE}, the long-range ridge \cite{CMS_ridge}, and below the threshold of the partonic baryon-meson $v_2$ \cite{ALICE_v2}, in a density window compatible with the Campanini \& Ferri equation of state \cite{Campanini2011}.