5 Search Results

Measurements of the sphericity of primary charged particles in minimum bias proton–proton collisions at $$\sqrt{s}$$ = 0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is measured in the plane perpendicular to the beam direction using primary charged tracks with $$p_T$$ > 0.5 GeV/c in |η| < 0.8. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity ($$N_ch$$) is reported for events with different $$p_T$$ scales (“soft” and “hard”) defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity ismore » presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low N ch, whereas the event generators show an opposite tendency. The combined study of the sphericity and the mean p T with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.« less

The production of mesons containing strange quarks ($$K^0_S$$, Φ) and both singly and doubly strange baryons ($$Λ, \overline Λ$$, and $$\Xi^– + \overline {\Xi}^+$$) are measured at mid-rapidity in pp collisions at $$\sqrt{s}$$ = 0.9 TeV with the $$\hbox{ALICE}$$ experiment at the $$\hbox{LHC}$$. The results are obtained from the analysis of about 250 k minimum bias events recorded in 2009. Measurements of yields (d$$N$$ / d$$y$$) and transverse momentum spectra at mid-rapidity for inelastic pp collisions are presented. For mesons, we report yields ($$\langle$$ d$$N$$ / d$$y\rangle$$) of $0.184 ± 0.002(stat.) ± 0.006(syst.)$ for $$K^0_S$$ and $0.021 ± 0.004(stat.) ±more » 0.003(syst.)$ for Φ. For baryons, we find ($$\langle$$ d$$N$$ / d$$y\rangle$$) = $0.048 ± 0.001(stat.)± 0.004(syst.)$ for $$Λ$$, $0.047 ± 0.002(stat.) ± 0.005(syst.)$ for $$\overline Λ$$ and $0.0101 ± 0.0020(stat.) ± 0.0009(syst.)$ for $$\Xi^– + \overline {\Xi}^+$$. The results are also compared with predictions for identified particle spectra from $$\hbox{QCD}$$-inspired models and provide a baseline for comparisons with both future pp measurements at higher energies and heavy-ion collisions.« less