4,855 research outputs found
Antiprotons Annihilation in the Galaxy As A Source of Diffuse Gamma Background
The existence of antimatter domains in baryon asymmetrical Universe can
appear as the cosmological consequence of particle theory in inflationary
models with non-homogeneous baryosynthesis. Such a domain can survive in the
early Universe and form globular cluster of antimatter stars in our Galaxy. The
model of antimatter pollution of Galaxy and annihilation with matter gas is
developed. The proton-antiproton annihilation gamma flux is shown to reproduce
the observed galactic gamma background measured by EGRET. From comparison with
observational data the estimation on the maximally allowed amount of antimatter
stars, possibly present in our Galaxy, is found.Comment: LaTeX2e, 18 pages, 3 PostScript figures. Submitted to Yad.Fi
Possible Effects of the Existence of the 4th Generation Neutrino
The 4th generation of fermions predicted by the phenomenology of heterotic
string models can possess new strictly conserved charge, which leads, in
particular, to the hypothesis of the existence of the 4th generation massive
stable neutrino. The compatibility of this hypothesis with the results of
underground experiment DAMA searching for weakly interactive particles of dark
matter and with the EGRET measurements of galactic gamma--background at
energies above 1 GeV fixes the possible mass of the 4th neutrino at the value
about 50 GeV. The possibility to test the hypothesis in accelerator experiments
is considered. Positron signal from the annihilation of relic massive neutrinos
in the galactic halo is calculated and is shown to be accessible for planned
cosmic ray experiments.Comment: 10 pages, 4 PostScript figure, Latex2
The Distribution of Constituent Charm Quarks in the Hadron
Using a statistical approach in the framework of non-covariant perturbation
theory the distributions for light and charmed quarks in the hadron have been
derived, taking into account the mass of the charmed quark. The parameters of
the model have been extracted from the comparison with NA3 data on
hadroproduction of J/psi particles. A reanalysis of the EMC data on charm
production in muon-nucleon scattering has been performed. It has been found in
comparison with the conventional source of charmed quarks from photon-gluon
fusion, that the EMC data indicate the presence of an additional contribution
from deep-inelastic scattering on charmed quarks at large x. The resulting
admixture of the Fock states, containing charmed quarks in the decomposition of
the proton wave function is of the order of 1%. The approach presented for the
excitation of the Fock states with charmed quarks can also be applied to states
with beauty quarks as well as to the hadronic component of the virtual photon
(resolved photon component).Comment: 23 pages, 4 PostScript figures, Latex2e. In revised version in
comparison with the original one all (?) mistypings have been corrected, one
more thank has been added and the comparison of the pion and the proton J/psi
production is described in more detai
Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions
The HERA-B collaboration has studied the production of charmonium and open
charm states in collisions of 920 GeV protons with wire targets of different
materials. The acceptance of the HERA-B spectrometer covers negative values of
xF up to xF=-0.3 and a broad range in transverse momentum from 0.0 to 4.8
GeV/c. The studies presented in this paper include J/psi differential
distributions and the suppression of J/psi production in nuclear media.
Furthermore, production cross sections and cross section ratios for open charm
mesons are discussed.Comment: 5 pages, 9 figures, to be published in the proceedings of the 6th
International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04),
Chicago, IL, June 27 - July 3, 200
Combined QCD and electroweak analysis of HERA data
A simultaneous fit of parton distribution functions (PDFs) and electroweak
parameters to HERA data on deep inelastic scattering is presented. The input
data are the neutral current and charged current inclusive cross sections which
were previously used in the QCD analysis leading to the HERAPDF2.0 PDFs. In
addition, the polarisation of the electron beam was taken into account for the
ZEUS data recorded between 2004 and 2007. Results on the vector and
axial-vector couplings of the Z boson to u- and d-type quarks, on the value of
the electroweak mixing angle and the mass of the W boson are presented. The
values obtained for the electroweak parameters are in agreement with Standard
Model predictions.Comment: 32 pages, 10 figures, accepted by Phys. Rev. D. Small corrections
from proofing process and small change to Fig. 12 and Table
Limits on the effective quark radius from inclusive scattering at HERA
The high-precision HERA data allows searches up to TeV scales for Beyond the
Standard Model contributions to electron-quark scattering. Combined
measurements of the inclusive deep inelastic cross sections in neutral and
charged current scattering corresponding to a luminosity of around 1
fb have been used in this analysis. A new approach to the beyond the
Standard Model analysis of the inclusive data is presented; simultaneous
fits of parton distribution functions together with contributions of "new
physics" processes were performed. Results are presented considering a finite
radius of quarks within the quark form-factor model. The resulting 95% C.L.
upper limit on the effective quark radius is cm.Comment: 10 pages, 4 figures, accepted by Phys. Lett.
Search for a narrow baryonic state decaying to and in deep inelastic scattering at HERA
A search for a narrow baryonic state in the and
system has been performed in collisions at HERA with the ZEUS detector
using an integrated luminosity of 358 pb taken in 2003-2007. The search
was performed with deep inelastic scattering events at an centre-of-mass
energy of 318 GeV for exchanged photon virtuality, , between 20 and 100
. Contrary to evidence presented for such a state around 1.52
GeV in a previous ZEUS analysis using a sample of 121 pb taken in
1996-2000, no resonance peak was found in the invariant-mass
distribution in the range 1.45-1.7 GeV. Upper limits on the production cross
section are set.Comment: 16 pages, 4 figures, accepted by Phys. Lett. B. Minor changes from
journal reviewing process, including a small correction to figure
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