Exclusive photoproduction of ϕ\phi meson in γp→ϕp\gamma p \to \phi p and pp→pϕpp p \to p \phi p reactions

The amplitude for $\gamma p \to \phi p$ is calculated in a pQCD $k_{T}$ - factorization approach. The total cross section for this process is compared with HERA data. Total cross section, as a function of photon-proton energy and photon virtuality, is calculated. We also discuss the ratio of $\sigma_{L}$ / $\sigma_{T}$ and the dependence on the mass of the strange quark. The amplitude for $\gamma p \to \phi p$ is used to predict the cross section for exclusive photoproduction of $\phi$ meson in proton-proton collisions. Absorption effects are included. The results for RHIC, Tevatron and LHC energies are presented.Comment: 10 pages, 5 figure

Dijet correlations at RHIC, leading-order ktk_t-factorization approach versus next-to-leading order collinear approach

We compare results of $k_t$-factorization approach and next-to-leading order collinear-factorization approach for dijet correlations in proton-proton collisions at RHIC energies. We discuss correlations in azimuthal angle as well as correlations in two-dimensional space of transverse momenta of two jets. Some $k_t$-factorization subprocesses are included for the first time in the literature. Different unintegrated gluon/parton distributions are used in the $k_t$-factorization approach. The results depend on UGDF/UPDF used. For collinear NLO case the situation depends significantly on whether we consider correlations of any two jets or correlations of leading jets only. In the first case the $2 \to 2$ contributions associated with soft radiations summed up in the $k_t$-factorization approach dominate at $\phi \sim \pi$ and at equal moduli of jet transverse momenta. The collinear NLO $2 \to 3$ contributions dominate over $k_t$-factorization cross section at small relative azimuthal angles as well as for asymmetric transverse momentum configurations. In the second case the NLO contributions vanish at small relative azimuthal angles and/or large jet transverse-momentum disbalance due to simple kinematical constraints. There are no such limitations for the $k_t$-factorization approach. All this makes the two approaches rather complementary. The role of several cuts is discussed and quantified.Comment: 26 pages, 17 figure

Exclusive diffractive photoproduction of dileptons by timelike Compton scattering

We derive the forward photoproduction amplitude for the diffractive $\gamma p \to l^+ l^- p$ reaction in the momentum space. within the formalism of $k_\perp$- factorization. Predictions for the $\gamma p \to l^+ l^- p$ reaction are given using unintegrated gluon distribution from the literature. We calculate the total cross section as a function of photon-proton center of mass energy and the invariant mass distribution of the lepton pair. We also discuss whether the production of timelike virtual photons can be approximated by continuing to the spacelike domain $q^2 < 0$. The present calculation provides an input for future predictions for exclusive hadroproduction in the $p p \to p l^+ l^- p$ reaction.Comment: 11 pages, 7 figure

Exclusive double-diffractive production of open charm in proton-proton and proton-antiproton collisions

We calculate differential cross sections for exclusive double diffractive (EDD) production of open charm in proton-proton and proton-antiproton collisions. Sizeable cross sections are found. The EDD contribution constitutes about 1 % of the total inclusive cross section for open charm production. A few differential distributions are shown and discussed. The EDD contribution falls faster both with transverse momentum of the $c$ quark/antiquark and the $c \bar c$ invariant mass than in the inclusive case.Comment: 11 pages, 7 figure

Elastic double diffractive production of axial-vector \chi_c(1^{++}) mesons and the Landau-Yang theorem

We discuss exclusive elastic double diffractive axial-vector \chi_c(1^{+}) meson production in proton-antiproton collisions at the Tevatron. The amplitude for the process is derived within the k_t-factorisation approach with unintegrated gluon distribution functions (UGDFs). We show that the famous Landau-Yang theorem is not applicable in the case of off-shell gluons. Differential cross sections for different UGDFs are calculated. We compare exclusive production of \chi_c(1^+) and \chi_c(0^+). The contribution of \chi_c(1^+) to the J/\Psi + \gamma channel is smaller than that of the \chi_c(0^+) decay, but not negligible and can be measured. The numerical value of the ratio of the both contributions is almost independent of UGDFs modeling.Comment: 14 pages, 5 figures, a numerical error corrected, discussions extended, conclusions unchange