Σ Hyperons Production in pp and p-Pb Collisions at LHC with ALICE

Abstract

In addition to \(\Lambda \) hyperons, new data on \(\Sigma \) hyperons production are compared to different Monte-Carlo models and contribute to understand hadron production mechanisms. The first measurements of the transverse momentum (\({{p}_{{\text{T}}}}\)) spectra of \({{\Sigma }^{0}}\) and \({{\overline \Sigma }^{0}}\) hyperons in pp collisions at \(\sqrt s = 7\) TeV at the LHC are presented. The \({{\Sigma }^{0}}\)(\({{\overline \Sigma }^{0}}\)) is reconstructed via its electromagnetic decay channel \(\Lambda (\overline \Lambda ) + \gamma \), while the \(\Lambda \)(\(\overline \Lambda \)) baryon is detected via its decay into \(p + {{\pi }^{ - }}\) (\(\bar {p}\) + \({{\pi }^{ + }}\)). The low-energy photon is measured via conversion into \({{e}^{ + }}{{e}^{ - }}\) pairs in the detector material and in PHOS calorimeter by exploiting the unique capability of the ALICE detector. The complementary results on the first detection of \({{\Sigma }^{ + }}\) and \({{\overline \Sigma }^{ - }}\) hyperon at the LHC with ALICE are shown in pp collisions at \(\sqrt s = 13\) TeV. The \({{\Sigma }^{ + }}\)(\({{\overline \Sigma }^{ - }}\)) is reconstructed via its weak decay into p\((\bar {p}) + {{\pi }^{0}}\) with the challenging detection of low-energy photons from \({{\pi }^{0}}\) decay. Also, the first reconstruction of \({{\overline \Sigma }^{ \pm }} \to \bar {n} + {{\pi }^{ \pm }}\) decays and \({{\overline \Sigma }^{ \pm }}\) transverse momenta spectra in pp and p-Pb collisions are presented. Antineutron is identified and reconstructed with PHOS by unique signature of the annihilation process.