Investigation of baryons with strangeness and search for weakly decaying exotics with ALICE at the LHC

Within this work data are analysed which have been taken with the ALICE apparatus (A Large Ion Collider Experiment) at the Large Hadron Collider (LHC). The unique properties and the excellent performance of the LHC made it possible to take data for proton-proton collisions (pp) in the last three years at several center-of-mass energies (0.9 TeV, 2.36 TeV, 2.76 TeV, 7 TeV and 8 TeV). It was further possible to aquire data in two of the three years of lead–lead collisions (Pb–Pb) at sqrt(s_NN) = 2.76TeV and recently a short pilot run of proton–lead collisions (pPb) at sqrt(s_NN) = 5.01TeV was recorded. It will be continued as a full run in January/February this year. The high energies and at the same time low baryo-chemical potential (mu_B around 0) in Pb–Pb collisions at the LHC allow the production of strangeness, charm and bottom quarks in up to now unseen quantities. The particles created, either in the initial hard collision (charm and bottom) or in the quark-gluon plasma, end up in hadrons or light nuclei (up to A=5) in the cool-down phase of the fireball. The production probability of particles decreases while its mass is increasing. But the huge amount of strange quarks produced allows the study of (anti-)hypernuclei, like the (anti-)hypertriton. Since such particles are measured in heavy-ion collisions it should be possible to also measure particles like the H-Dibaryon, predicted in 1977. The H-Dibaryon is a hypothetical bound state of six quarks (uuddss). The search for the H-Dibaryon at the LHC with the ALICE apparatus is the main content of this work. The particle was not observed and an upper limit has been set. Another search for a bound state of a Lambda particle and a neutron was also performed. This particle was also not observed and an upper limit for the production yield was estimated. The thermal model describes the production of all particle species in previously performed experiments, at different energies, quite reasonably. This model and the coalescence model make predictions for the particle production at LHC energies. The comparison between experimental result and these model predictions lead to a factor of around 10 which the upper limit is below the expected yields. This result questions the existence of these particles. Another part of this thesis is dealing with the production of strange baryons, especially the baryonic resonance Lambda(1520) in pp collisions at 7 TeV. Here the focus was to measure mass, width and yield pt dependent. The pt spectrum has to be corrected for the acceptance and efficiency of the detector, to measure the yield per rapidity unit dN/dy of the Lambda(1520). This is compared to the yield of the L hyperon. This shows good agreement with the values measured in the previous experiments NA49 at SPS and STAR at RHIC.