Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies

We calculate several differential distributions for exclusive double diffractive $\chi_c(0^{++})$ production in proton-antiproton collisions at the Tevatron and in proton-proton collisions at RHIC and LHC in terms of unintegrated gluon distributions (UGDFs) within the $k_t$-factorisation approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed in detail. The $g^* g^* \to \chi_c(0^{++})$ transition vertex is calculated as a function of gluon virtualities applying the standard pNRQCD technique. The off-shell effects are discussed and quantified. They lead to a reduction of the cross section by a factor 2--5, depending on the position in the phase space and UGDFs. Different models of UGDFs are used and the results are shown and discussed. The cross section for diffractive component depends strongly on UGDFs. We calculate also the differential distributions for the $\gamma^* \gamma^* \to \chi_c(0^{++})$ fusion mechanism. The integrated cross section for photon-photon fusion is much smaller than that of diffractive origin. The two components have very different dependence on momentum transfers $t_1, t_2$ in the nucleon lines as well as azimuthal-angle correlations between both outgoing nucleons.Comment: 34 pages, 23 figures, 2 table

Acoustic investigations of relaxation processes in regions of polymorphic transformations of nematics

The temperature-frequency dependences of both velocity and attenuation coefficient anisotropy, as well as their angular dependence coefficients in the nematic phase of nitrophenyl-octyl-oxybenzoate oriented by magnetic field were investigated. The analysis of experimental results was carried out in the framework of generalized hydrodynamic theory with two relaxation processes. It was shown that in the vicinity of the N-A phase transition the experimental results are described by the relaxation theory.Nous analysons l'anisotropie de vitesse et d'absorption ultrasonore en fonction de la température et de la fréquence. Nous déterminons les paramètres caractérisant la dépendance angulaire de la vitesse et de l'absorption ultrasonore dans la phase nématique NPOB orientée au moyen du champ magnétique. L'analyse des résultats a été réalisée dans le cadre d'une théorie hydrodynamique généralisée tenant compte de deux processus relaxationnels. La théorie relaxationnelle rend compte des données expérimentales au voisinage de la transition de phase nématique-smectique A