$\phi$ Meson Production in In-In Collisions and the $\phi$ Puzzle

TL;DR

This paper reports on high-statistics measurements of $$ meson production in In-In collisions at 158 AGeV, aiming to clarify the longstanding $$ puzzle by comparing yields and transverse momentum distributions across different centralities.

Contribution

It provides new detailed measurements of $$ meson yields and transverse momentum slopes, highlighting differences with previous experiments and exploring potential effects like radial flow.

Findings

The slope parameter $T$ increases with centrality and saturates.

The $$ yield per participant increases with centrality and exceeds previous measurements.

Variations in $T$ suggest possible radial flow effects.

Abstract

The NA60 experiment measured dimuon production in In-In collisions at 158 AGeV. This paper presents a high statistics measurement of $\phi\to\mu\mu$ with the specific objective to provide insight on the $\phi$ puzzle, i.e. the difference in the inverse $T$ slopes and absolute yields measured by NA49 and NA50 in the kaon and lepton channel, respectively. Transverse momentum distributions were studied as a function of centrality. The slope parameter $T$ shows a rapid increase with centrality, followed by a saturation. Variations of $T$ with the fit range of the order of 15 MeV were observed, possibly as a consequence of radial flow. The $\phi$ meson yield normalized to the number of participants increases with centrality and is consistently higher than the yield measured by the NA49 experiment at any centrality.