Marek Jezabek

New analyses of baryon spectra in proton-proton and proton-carbon collisions at $$\sqrt{s}_\mathrm {_{NN}}=17.3$$s NN = 17.3 GeV, made in the framework of two phenomenological models are presented. The first model in question is the classic Dual Parton Model by Capella and Tran Thanh Van, the second is the Gluon Exchange Model very recently proposed by the authors. For both studies, the usage of modern experimental data from the CERN SPS eliminates several of the most important limitations inherent to earlier studies of this type. In both studies, the standard mechanism of baryon stopping with preservation of the diquark, proposed by Capella and Tran Thanh Van fails to describe the distribution of non-strange baryons in collisions of the projectile proton with more than one nucleon from the carbon target obtained from experimental data, and the upper limit for the contribution of this mechanism can be established. In both cases, the conclusion is that the projectile diquark must be very often disintegrated. This opens new diagrams not available in proton-proton collisions which lead to the transport of baryon number over long distances in rapidity. The present limitations, and possibility of improvement in both approaches are discussed. The implications of our findings for new measurements are addressed, in particular using antiproton beams.

A search for the flavor-changing neutral-current decay ${\mathrm{\Lambda }}_c^{+}\to p{\mu }^{+}{\mu }^{-}$ is reported using a data set corresponding to an integrated luminosity of $3.0{\mathrm{fb}}^{-1}$ collected by the LHCb Collaboration. No significant signal is observed outside of the dimuon mass regions around the $\varphi$ and $\omega$ resonances, and an upper limit is placed on the branching fraction of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to p{\mu }^{+}{\mu }^{-})<7.7(9.6)\times {10}^{-8}$ at 90%(95%) confidence level. A significant signal is observed in the $\omega$ dimuon mass region for the first time.

The decay $B^0\to \psi (2S)K^{+}{\pi }^{-}$ is analyzed using $3{\mathrm{fb}}^{-1}$ of $pp$ collision data collected with the LHCb detector. A model-independent description of the $\psi (2S)\pi$ mass spectrum is obtained, using as input the $K\pi$ mass spectrum and angular distribution derived directly from data, without requiring a theoretical description of resonance shapes or their interference. The hypothesis that the $\psi (2S)\pi$ mass spectrum can be described in terms of $K\pi$ reflections alone is rejected with more than $8\sigma$ significance. This provides confirmation, in a model-independent way, of the need for an additional resonant component in the mass region of the $Z(4430{)}^{-}$ exotic state.