부산대학교 도서관

The first measurements of the transverse momentum (pT) spectra and integrated yields of Σ0 and Σ−0 baryons in proton-proton (pp) collisions at √s = 7 TeV are reported. The Σ0(Σ−0) signal is reconstructed via the Λ (Λ−) + γ decay channel by invariant mass analysis. The Λ (Λ−) baryon is reconstructed by its weak decay into p + π−(p− + π+), while the photon is detected exploiting the unique capability of the ALICE detector to measure low energy photons via conversion into e+e− pairs. A significant disagreement between the data and the predictions from the QCD-inspired Monte Carlo event generator PYTHIA is observed for the pT spectrum. The yield ratio of Σ0(Σ−0) to Λ is shown as a function of pT . Finally, the new data point for the integrated yield ratio of Σ0(Σ−0) to Λ from pp collisions at 7 TeV is found to be similar to the results obtained in different elementary collison systems (e+e−, pp) measured at collision energies below 100 GeV.