Double parton effects for jets with large rapidity separation

We discuss production of four jets $pp \rightarrow j j j j X$ with at least two jets with large rapidity separation in proton-proton collisions at the LHC through the mechanism of double-parton scattering (DPS). The cross section is calculated in a factorizaed approximation. Each hard subprocess is calculated in LO collinear approximation. The LO pQCD calculations are shown to give a reasonably good descritption of CMS and ATLAS data on inclusive jet production. It is shown that relative contribution of DPS is growing with increasing rapidity distance between the most remote jets, center-of-mass energy and with decreasing (mini)jet transverse momenta. We show also result for angular azimuthal dijet correlations calculated in the framework of $k_t$-factorization approaximation.Comment: Invited talks at Diffraction 2014 (Primosten, Croatia, September 10-15, 2014) and MPI@LHC 2014 (Krak\'ow, Poland, November 3-7 2014

Nonphotonic electrons at RHIC within ktk_t-factorization approach and with experimental semileptonic decay functions

We discuss production of nonphotonic electrons in proton-proton scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the $k_t$-factorization approach. We use different unintegrated gluon distributions from the literature. The hadronization of heavy quarks is done by means of Peterson and Braaten et al. fragmentation functions. The semileptonic decay functions are found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations. We get good description of the data at large transverse momenta of electrons and find a missing strength concentrated at small transverse momenta of electrons. Plausible missing mechanisms are discussed.Comment: 16 pages, 11 figure

Subdominant terms in the production of ccˉc \bar c pairs in proton-proton collisions

At high-energies the gluon-gluon fusion is the dominant mechanism of $c \bar c$ production. This process was calculated in the NLO collinear as well as in the k$_t$-factorization approaches in the past. We show that the present knowledge of gluon distributions does not allow to make a precise predictions for $c \bar c$ production at LHC, in particular at forward rapidities. In this paper we study production of $c \bar c$ pairs including several subleading mechanisms. This includes: $gg \to Q \bar Q$, $\gamma g \to Q \bar Q$, $g \gamma \to Q \bar Q$, $\gamma \gamma \to Q \bar Q$. In this context we use MRST-QED parton distributions which include photon as a parton in the proton as well as elastic photon distributions calculated in the equivalent photon approximation. We present distributions in the $c$ quark ($\bar c$ antiquark) rapidity and transverse momenta and compare them to the dominant gluon-gluon fusion contribution. We discuss also inclusive single and central diffractive processes using diffractive parton distribution found from the analysis of HERA diffractive data. As in the previous case we present distribution in $c$ ($\bar c$) rapidity and transverse momentum. Finally we present results for exclusive central diffractive mechanism discussed recently in the literature. We show corresponding differential distributions and compare them with corresponding distributions for single and central diffractive components.Comment: 20 pages, 19 figure

Production of two ccˉc \bar c pairs in double-parton scattering

We discuss production of two pairs of $c \bar c$ within a simple formalism of double-parton scattering (DPS). Surprisingly very large cross sections, comparable to single-parton scattering (SPS) contribution, are predicted for LHC energies. Both total inclusive cross section as a function of energy and differential distributions for $\sqrt{s}$ are shown. We discuss a perspective how to identify the double scattering contribution.Comment: 8 pages, 6 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

Production asymmetry of open charm mesons within unfavoured ragmentation scenario

We consider unfavoured light quark/antiquark to D meson fragmentation. We discuss nonperturbative effects for small transverse momenta. The asymmetry for D+ and D- production measured by the LHCb collaboration provides natural constraints on the parton (quark/antiquark) fragmentation functions. We find that already a fraction of q/q¯→D$q/\overline q \to D$ fragmentation probability is sufficient to account for the measured asymmetry. Large D-meson production asymmetries are found for large xF which is related to dominance of light quark/antiquark q/q¯→D$q/\overline q \to D$ fragmentation over the standard c → D fragmentation. As a consequence, prompt atmospheric neutrino flux at high neutrino energies can be much larger than for the conventional c → D fragmentation. The latter can constitute a sizeable background for the cosmic neutrinos claimed to be observed recently by the IceCube Observatory