K*(892)± resonance with the ALICE detector at LHC

K*(892)± resonance with the ALICE detector at LHC Author: Kunal Garg PhD Cycle XXXI, University of Catania It has been established that ultra-relativistic heavy-ion collisions produce a hot and dense QCD system which behaves like a perfect fluid. The study of the Quark Gluon Plasma created in these collisions is important to understand the cosmic evolution of our Universe. The study of strange hadronic resonances in pp collisions contributes to the study of strangeness production in small systems. Usually, measurements in pp collisions constitute a reference for the study in larger colliding systems and provide constraints for tuning QCD-inspired event generators and then to test specific aspects of QCD in the non-perturbative sector. However recent observations at the LHC have shown striking similarities between Pb-Pb collisions and high-multiplicity p-Pb and pp collisions. In the elementary collisions a large variation of the characteristics of the event and of the strange particle production rate has been observed as a function of the charged particle multiplicity density. In particular it has been observed as particle production depends only from the event multiplicity and it is independent of the system size and collision energy. This thesis reports about first measurement of K^{*}(892)^{\pm} in pp collisions at \sqrt{s} = 13 TeV in inelastic pp collisions and in different charged particle multiplicity classes. In particular the transverse momentum (p_{T}) spectrum, the integrated yield, the mean p_{T} and the ratio to stable hadrons as pions and kaons have been measured. Moreover the K^{*}(892)^{0} p_{T} spectrum in inelastic pp collisions at the same energy has been also measured. Similar results have been obtained for charged and neutral K^{*}. The K*(892)± p_{T} spectrum has been compared to the predictions of some event generators as PYTHIA6, PYTHIA8 and EPOS-LHC. Furthermore, the comparison of the p_{T} spectrum with the one obtained at different energies has shown a hardening of the spectra with increasing energy of the collisions. Increase of the K*(892)± yield and mean p_{T} when growing the event multiplicity, confirms the independence of the particle yields from the collision system or energy. From the distribution of the K^{*}/K ratio as a function of the charged particle multiplicity, a hint of suppression of the K* production has been observed in high multiplicity pp collisions. This in an analogy to the K^{*}/K results in heavy-ion collisions, is consistent with the presence of re-scattering effects in an hadronic phase in high multiplicity pp collisions.