Search for exotic bound states and measurement of the (anti-)alpha production yield in Pb-Pb collisions with ALICE at the LHC (CERN)

The ALICE detector system has excellent particle identification (PID) capabilities employing a variety of techniques. One of these is the specific energy loss dE/dx measurement in the Time Projection Chamber (TPC). The dE/dx is different for each particle species and can be used to identify charged particles including also (anti-)nuclei. The time-of-flight method uses the m${}^2$/z${}^2$ distributions (m = mass of the particle, z charge number of the particle), which are determined from the flight time and the length of the particle trajectory measured with the Time-Of-Flight (TOF) detector, and the momentum extracted through combined tracking in the ALICE setup in the mid-rapidity region. Within this doctoral thesis these techniques are used for the search for two exotic bound states, the $\overline{\Lambda n}$ bound state and the H-dibaryon, as well as for the measurement of the production yield per unit of rapidity dN/dy of alpha and anti-alpha particles. Both, the searches for the exotica and the measurement of the (anti-)alpha, are performed on data from Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV. The searches for the two investigated exotica are carried out in the decay channel $\overline{\Lambda n}$ $\to$ $\overline{d}$ + ${\pi }^{+}$ and H $\to$ $\Lambda$ + p + ${\pi }^{-}$. The different decay products are identified using the specific energy loss measurements in the TPC and their invariant mass is determined. For both investigated bound states no signals are observed in the resulting invariant mass distributions. Therefore, upper limits on the production rates are estimated for eight different assumed lifetimes between 4 cm and 3 m. In addition, the upper limits are determined independent of the branching ratio of the investigated decay channel and are compared to different theory predictions. The alpha particle is the heaviest nucleus produced and detected during ultra-relativistic heavy-ion collisions at LHC energies and the anti-alpha is even the heaviest anti-nucleus observed so far at all. The particles are identified using the dE/dx measurement in the TPC and the m${}^2$/z${}^2$ distributions determined with the measurements of the TOF. The efficiency $\times$ acceptance is determined using a Monte Carlo production. As the observed statistics does not allow for the determination of the transverse momentum p${}_T$-spectrum, a Blast-Wave extrapolation is used, which is based on the measurements of the spectra of deuterons and ${}^3$He. This allows for the p${}_T$-integrated determination of the efficiency. Systematic uncertainties are calculated and the resulting rapidity density dN/dy is comparable with the prediction from a thermal model.