Measurements of $\varUpsilon$ States Production in $\textit{p+p}$ Collisions at $\sqrt{s} = 500\:\mathrm{GeV}$ with STAR: Cross Sections, Ratios, and Multiplicity Dependence

TL;DR

This paper presents detailed measurements of $ extUpsilon$ meson production in proton-proton collisions at 500 GeV, including cross sections, ratios, and multiplicity dependence, providing insights into quarkonium production mechanisms.

Contribution

It offers the first comprehensive set of $ extUpsilon$ production data at this energy, comparing results with various theoretical models to evaluate their accuracy.

Findings

CEM model accurately describes $ extUpsilon(1S)$ production.

CGC+NRQCD overestimates the data at low $p_T$.

Multiplicity dependence aligns with saturation and multiple parton interaction models.

Abstract

We report measurements of $\varUpsilon(1S)$, $\varUpsilon(2S)$ and $\varUpsilon(3S)$ production in $\textit{p+p}$ collisions at $\sqrt{s}=500\:\mathrm{GeV}$ by the STAR experiment in year 2011, corresponding to an integrated luminosity $\mathcal{L}_{int}=13\:\mathrm{pb^{-1}}$. The results provide precise cross sections, transverse momentum ($p_{T}$) and rapidity ($y$) spectra, as well as cross section ratios for $p_{\mathrm{T}}<10\:\mathrm{GeV/c}$ and $|y|<1$. The dependence of the $\varUpsilon$ yield on charged particle multiplicity has also been measured, offering new insights into the mechanisms of quarkonium production. The data are compared to various theoretical models: the Color Evaporation Model (CEM) accurately describes the $\varUpsilon(1S)$ production, while the Color Glass Condensate + Non-relativistic Quantum Chromodynamics (CGC+NRQCD) model overestimates the data, particularly at low $p_{T}$. Conversely, the Color Singlet Model (CSM) underestimates the rapidity dependence. These discrepancies highlight the need for further development in understanding the production dynamics of heavy quarkonia in high-energy hadronic collisions. The trend in the multiplicity dependence is consistent with CGC/Saturation and String Percolation models or $\varUpsilon$ production happening in multiple parton interactions modeled by PYTHIA8.