9 research outputs found
Charm-sea Contribution to High-p_T \psi Production at the Fermilab Tevatron
The direct production of at large transverse momentum, , at the Fermilab Tevatron is revisited. It is found that the
sea-quark initiated processes dominate in the high- 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
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
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- 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
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
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
() observed in the total spectrum. We show that this
implies that the very high energy ( 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
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.