2 Search Results

The first results of K*(892)^± production at midrapidity (|y| < 0.5) in pp collisions at $$\sqrt{s}$$= 13 TeV as a function of the event multiplicity are presented. The K*(892)^± has been reconstructed via its hadronic decay channel K*(892)^± → π^± + K$$^0_{\textrm{S}}$$ using the ALICE detector at the LHC. For each multiplicity class, the differential transverse momentum (p_T) spectrum, the mean transverse momentum ⟨p_T⟩, the p_T-integrated yield (dN/dy), and the ratio of the K*(892)^± to K$$^0_{\textrm{S}}$$ yields are reported. These are consistent with previous K*(892)⁰ resonance results with a higher level of precision. Comparisons with phenomenological models such as PYTHIA6,more » PYTHIA8, EPOS-LHC, and DIPSY are also discussed. For the first time, a significant K*(892)^±/K$$^0_{\textrm{S}}$$ suppression in pp collisions is observed at a 7σ level passing from low to high multiplicity events. The ratios of the p_T-differential yields of K*(892)^± and K$$^0_{\textrm{S}}$$ in high and low multiplicity events are also presented along with their double ratio. For p_T ≲ 2 GeV/c this double ratio persists below unity by more than 3σ suggesting that the suppression affects mainly low p_T resonances. The measured decreasing trend of the K*(892)^±/K$$^0_{\textrm{S}}$$ ratio with increasing multiplicity, which in heavy-ion collisions is typically attributed to the rescattering of decay particles of the short-lived resonances, is reproduced by the EPOS-LHC model without the use of hadronic afterburners.« less

The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. In particular, it allows for the investigations of excited, light-flavour vector mesons. The measurement of coherently photoproduced 𝜋⁺𝜋⁻𝜋⁺𝜋⁻ final states in ultraperipheral Pb–Pb collisions at $$\sqrt{s_{NN}}$$ = 5.02 TeV is presented for the first time. The cross section, d𝜎/d𝑦, times the branching ratio (𝜌 → 𝜋⁺𝜋⁺𝜋⁻𝜋⁻) is found to be 47.8 ± 2.3 (stat.) ± 7.7 (syst.) mb in the rapidity interval |𝑦| < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance without an interference term. Includingmore » in- terference with a non-resonant contribution results in the mass and width values being too far from those reported in PDG, while the production of two interfering resonances, 𝜌(1450) and 𝜌(1700), also provides a good description of the data. The values of the masses (𝑚) and widths (Γ) of the resonances extracted from the fit assuming two interfering resonances are 𝑚₁ = 1385 ± 14 (stat.) ± 3 (syst.) MeV/𝑐², Γ₁ = 431 ± 36 (stat.) ± 82 (syst.) MeV/𝑐², 𝑚₂ = 1663 ± 13 (stat.) ± 22 (syst.) MeV/𝑐² and Γ₂ = 357 ± 31 (stat.) ± 49 (syst.) MeV/𝑐², respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.« less