Pentaquark Search in the Strange Sector at ALICE at the LHC



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The primary objective of the Large Hadron Collider (LHC) in Geneva, Switzerland is to collide nuclear matter to study its properties under extreme conditions. The LHC has been the leading facility in high energy physics with major discoveries, such as the Higgs boson and assisting with discovering the Quark Gluon Plasma (QGP), which is an extremely hot, dense soup of free quarks and gluons. The transition from the QGP phase to the hadronic phase sees free quarks and gluons transition into bound states of quarks and gluons. The typical hadron formation is to a q q meson state or to a qqq baryon state. Multiquark states with more than three quarks had not been con rmed until 2015, when LHCb announced the discovery of several hidden charm pentaquarks Pc(4312)+;Pc(4440)+; and Pc(4457)+. These hidden-charm pentaquark states were observed as a peak in the J/psi p invariant mass spectrum. This discovery has reopened the question of whether any pentaquarks are able to exist in the strange sector. Past searches for pentaquarks with strangeness have yielded results that have not been replicated or resulted in no new states at all. Strangeness enhancement, measured by ALICE as a function of increasing charged particle multiplicity even in pp collisions, further adds to the likelihood of observing a strange pentaquark state. Following analogous decay channels for the P+c states into the strange sector, results for Ps -> phi p, Ps -> Lambda K, Ps -> Lambda K* , and Ps -> Sigma* K through invariant mass analysis in minimum bias pp collisions at ps = 13 TeV at ALICE are presented. No pentaquark signal is observed for any decay channels in this analysis. Thermal model predictions for the yield of the Ps are obtained and compared to upper limit calculations produced from the ALICE data. Signi cant upper limits are set for the Ps for most of the decay channels that were analyzed.



ALICE, CERN, Pentaquark