Charm-sea Contribution to High-p_T \psi Production at the Fermilab Tevatron

The direct production of $J/\psi(\psi')$ at large transverse momentum, $p_T \gg M_{J/\psi}$, at the Fermilab Tevatron is revisited. It is found that the sea-quark initiated processes dominate in the high-$p_T$ region within the framework of color-singlet model, which is not widely realized. We think this finding is enlightening for further investigation on the charmonium production mechanism.Comment: Conclusions not changed, to appear in J. of Phys.

The charged-hadron/pion ratio at the Relativistic Heavy Ion Collider

The hadron/pion ratio is calculated in 200 GeV AuAu collisions at midrapidity, applying pQCD and non-universal transverse-momentum broadening. Arguments are presented for such non-universality, and the idea is implemented in a model, which explains the enhancement of the hadron/pion ratio in central AuAu collisions. The model also describes the qualitative difference between the recently-measured dAu nuclear enhancement factors for pions and charged hadrons.Comment: 4 pages, 3 figure

Shower Power: Isolating the Prompt Atmospheric Neutrino Flux Using Electron Neutrinos

At high energies, the very steep decrease of the conventional atmospheric component of the neutrino spectrum should allow the emergence of even small and isotropic components of the total spectrum, indicative of new physics, provided that they are less steeply decreasing, as generically expected. One candidate is the prompt atmospheric neutrino flux, a probe of cosmic ray composition in the region of the knee as well as small-$x$ QCD, below the reach of collider experiments. A second is the diffuse extragalactic background due to distant and unresolved AGNs and GRBs, a key test of the nature of the highest-energy sources in the universe. Separating these new physics components from the conventional atmospheric neutrino flux, as well as from each other, will be very challenging. We show that the charged-current {\it electron} neutrino "shower" channel should be particularly effective for isolating the prompt atmospheric neutrino flux, and that it is more generally an important complement to the usually-considered charged-current {\it muon} neutrino "track" channel. These conclusions remain true even for the low prompt atmospheric neutrino flux predicted in a realistic cosmic ray scenario with heavy and varying composition across the knee (Candia and Roulet, 2003 JCAP {\bf 0309}, 005). We also improve the corresponding calculation of the neutrino flux induced by cosmic ray collisions with the interstellar medium.Comment: 15 pages, 4 figures. Minor modifications, version accepted for publication in JCA

Anomalous production of top quarks at CLIC+LHC based gamma p colliders

The single production of top quark due to flavor changing neutral current (FCNC) interaction and its decay to bW are studied at CLIC+LHC based gamma-p colliders. We consider both t-c-gamma and t-u-gamma anomalous couplings. The anomalous charm (up) quark anomalous coupling parameter kappa_gamma^c (kappa_gamma^u) can be probed down to 9.5x10^-3 (8.0x10^-3) at a gamma-p collider with sqrt{s_ep}=6.48 TeV and L_int=100 fb^-1.Comment: 9 pages, 7 figures, 4 table

Rigidity dependent knee and cosmic ray induced high energy neutrino fluxes

Scenarios in which the knee of the cosmic ray spectrum depends on the particle rigidities usually predict that the cosmic ray composition becomes heavier above the knee and have associated a change in the spectral slope of each individual nuclear component which is steeper than the change ($\Delta\alpha\simeq 0.3$) observed in the total spectrum. We show that this implies that the very high energy ($E_\nu>10^{14}$ eV) diffuse neutrino fluxes produced by cosmic rays hitting the atmosphere or colliding with the interstellar medium in the Galaxy will be significantly suppressed, making their detection harder but also reducing the background for the search of other (more challenging) astrophysical neutrino sources.Comment: 20 pages, 5 figure

Direct Detection of Dark Matter in Supersymmetric Models

We evaluate neutralino-nucleon scattering rates in several well-motivated supersymmetric models, and compare against constraints on the neutralino relic density, BF( b\to s\gamma ) as well as the muon anomalous magnetic moment a_\mu . In the mSUGRA model, the indirect constraints favor the hyperbolic branch/focus point (HB/FP) region of parameter space, and in fact this region is just where neutralino-nucleon scattering rates are high enough to be detected in direct dark matter search experiments! In Yukawa unified SUSY SO(10) models with scalar mass non-universality, the relic density of neutralinos is almost always above experimental bounds, while the corresponding direct detection rates are below experimental levels. Conversely, in five dimensional SO(10) models where gauge symmetry breaking is the result of compactification of the extra dimension, and supersymmetry breaking is communicated via gaugino mediation, the relic density is quite low, while direct detection rates can be substantial.Comment: 25 page latex file including 18 EPS figures; revised version with references added and cross sections rescaled; figures changed. A copy of the paper with better resolution figures can be found at http://www.hep.fsu.edu/~belyaev/projects/directz1

D meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution

When nonlinear effects on the gluon evolution are included with constraints from HERA, the gluon distribution in the free proton is enhanced at low momentum fractions, x < 0.01, and low scales, Q^2 < 10 GeV^2, relative to standard, DGLAP-evolved, gluon distributions. Consequently, such gluon distributions can enhance charm production in pp collisions at center of mass energy 14 TeV by up to a factor of five at midrapidity, y \sim 0, and transverse momentum p_T -> 0 in the most optimistic case. We show that most of this enhancement survives hadronization into D mesons. Assuming the same enhancement at leading and next-to-leading order, we show that the D enhancement may be measured by D^0 reconstruction in the K^-\pi^+ decay channel with the ALICE detector.Comment: 15 pages, 4 figures, final version accepted by J. Phys.