$\Sigma^0$ production in proton nucleus collisions near threshold

TL;DR

This study measures the production cross section of $oldsymbol{ ext{Sigma}}^{0}$ baryons in proton-nucleus collisions near threshold energies using the HADES detector, providing insights into hyperon production mechanisms.

Contribution

It presents the first detailed measurement of $oldsymbol{ ext{Sigma}}^{0}$ production cross sections in proton-nucleus collisions near threshold, including differential and total values, and compares results with transport and statistical models.

Findings

Measured differential $oldsymbol{ ext{Sigma}}^{0}$ cross section: 2.3 mb in the rapidity interval 0.5-1.1.

Total inclusive $oldsymbol{ ext{Sigma}}^{0}$ production cross section: 5.8 mb with uncertainties.

$oldsymbol{ ext{Lambda}}_{all}$/$oldsymbol{ ext{Sigma}}^{0}$ ratio is approximately 2.3 within the acceptance.

Abstract

The production of $\Sigma^{0}$ baryons in the nuclear reaction p (3.5 GeV) + Nb (corresponding to $\sqrt{s_{NN}}=3.18$ GeV) is studied with the detector set-up HADES at GSI, Darmstadt. $\Sigma^{0}$s were identified via the decay $\Sigma^{0} \rightarrow \Lambda \gamma$ with subsequent decays $\Lambda \rightarrow p \pi^{-}$ in coincidence with a $e^{+}e^{-}$ pair from either external ($\gamma \rightarrow e^{+} e^{-}$) or internal (Dalitz decay $\gamma^{*}\rightarrow e^{+} e^{-}$) gamma conversions. The differential $\Sigma^0$ cross section integrated over the detector acceptance, i.e. the rapidity interval $0.5 < y < 1.1$, has been extracted as $\Delta\sigma_{\Sigma^{0}} = 2.3 \pm (0.2)^{stat} \pm \left(^{+0.6}_{-0.6}\right)^{sys} \pm (0.2)^{norm}$ mb, yielding the inclusive production cross section in full phase space $\sigma^{total}_{\Sigma^{0}} = 5.8 \pm (0.5)^{stat} \pm \left(^{+1.4}_{-1.4}\right)^{sys} \pm (0.6)^{norm} \pm (1.7)^{extrapol}$ mb by averaging over different extrapolation methods. The $\Lambda_{all}$/$\Sigma^{0}$ ratio within the HADES acceptance is equal to 2.3 $\pm$ $(0.2)^{stat}$ $\pm$ $(^{+0.6}_{-0.6})^{sys}$. The obtained rapidity and momentum distributions are compared to transport model calculations. The $\Sigma^{0}$ yield agrees with the statistical model of particle production in nuclear reactions.