884 research outputs found
Eikonal contributions to ultra high energy neutrino-nucleon cross sections in low scale gravity models
We calculate low scale gravity effects on the cross section for
neutrino-nucleon scattering at center of mass energies up to the
Greisen-Zatsepin-Kuzmin (GZK) scale, in the eikonal approximation. We compare
the cases of an infinitely thin brane embedded in n=5 compactified
extra-dimensions, and of a brane with a physical tension M_{S}=1 TeV and
M_{S}=10 TeV. The extra dimensional Planck scale M_{D} is set at 10^{3} GeV and
2\times10^{3} GeV. We also compare our calculations with neutral current
standard model calculations in the same energy range, and compare the thin
brane eikonal cross section to its saddle point approximation. New physics
effects enhance the cross section by orders of magnitude on average. They are
quite sensitive to M_{S} and M_{D} choices, though much less sensitive to n.Comment: 16 pages, 5 figures; 2 figures were removed and the remaining figures
and the text were modified for clarification; published versio
The small x gluon and b\bar{b} production at the LHC
We study open b\bar{b} production at large rapidity at the LHC in an attempt
to pin down the gluon distribution at very low x. For the LHC energy of 7 TeV,
at next-to-leading order (NLO), there is a large factorization scale
uncertainty. We show that the uncertainty can be greatly reduced if events are
selected in which the transverse momenta of the two B-mesons balance each other
to some accuracy, that is |\vec p_{1T}+\vec p_{2T}| < k_0. This will fix the
scale \mu_F \simeq k_0, and will allow the LHCb experiment, in particular, to
study the x-behaviour of gluon distribution down to x ~ 10^{-5}, at rather low
scales, \mu ~ 2 GeV. We evaluate the expected cross sections using, for
illustrative purposes, various recent sets of Parton Distribution Functions.Comment: 13 pages, 5 figure
A GLOBAL QCD STUDY OF DIRECT PHOTON PRODUCTION
A global QCD analysis of the direct photon production process from both fixed
target and collider experiments is presented. These data sets now completely
cover the parton range from 0.01 to 0.6, thereby providing a stringent test
of perturbative QCD and parton distributions. Previous detailed studies of
direct photons emphasized fixed target data. We find most data sets have a
steeper distribution than the QCD prediction. Neither global fits with
new parton distributions nor improved photon fragmentation functions can
resolve this problem since the deviation occurs at different values for
experiments at different energies. A more likely explanation is the need for
additional broadening of the of the initial state partons. The magnitude
and the possible physical origin of this effect are investigated and discussed.Comment: 8 page Latex file using epsf.sty for figures. 6 eps figures submitted
separately in uuencoded file
Parton Densities in a Nucleon
In this paper we re-analyse the situation with the shadowing corrections (SC)
in QCD for the proton deep inelastic structure functions. We reconsider the
Glauber - Mueller approach for the SC in deep inelastic scattering (DIS) and
suggest a new nonlinear evolution equation. We argue that this equation solves
the problem of the SC in the wide kinematic region where \as \kappa = \as
\frac{3 \pi \as}{2 Q^2R^2} x G(x,Q^2) \leq 1. Using the new equation we
estimate the value of the SC which turn out to be essential in the gluon deep
inelastic structure function but rather small in . We claim that
the SC in is so large that the BFKL Pomeron is hidden under the SC
and cannot be seen even in such "hard" processes that have been proposed to
test it. We found that the gluon density is proportional to in the
region of very small . This result means that the gluon density does not
reach saturation in the region of applicability of the new evolution equation.
It should be confronted with the solution of the GLR equation which leads to
saturation.Comment: latex file 53 pages, 27 figures in eps file
The influence of direct -meson production to the determination on the nucleon strangeness asymmetry via dimuon events in neutrino experiments
Experimentally, the production of oppositely charged dimuon events by
neutrino and anti-neutrino deep inelastic scattering (DIS) is used to determine
the strangeness asymmetry inside a nucleon. Here we point out that the direct
production of -meson in DIS may make substantial influence to the
measurement of nucleon strange distributions. The direct -meson production
is via the heavy quark recombination (HQR) and via the light quark
fragmentation from perturbative QCD (LQF-P). To see the influence precisely, we
compute the direct -meson productions via HQR and LQF-P quantitatively and
estimate their corrections to the analysis of the strangeness asymmetry. The
results show that HQR has stronger effect than LQF-P does, and the former may
influence the experimental determination of the nucleon strangeness asymmetry.Comment: 9 latex pages, 7 figure
The Proton Spin and Flavor Structure in the Chiral Quark Model
After a pedagogical review of the simple constituent quark model and deep
inelastic sum rules, we describe how a quark sea as produced by the emission of
internal Goldstone bosons by the valence quarks can account for the observed
features of proton spin and flavor structures. Some issues concerning the
strange quark content of the nucleon are also discussed.Comment: 59 pages with table of contents, Lecture delivered at the Schladming
Winter School (March 1997), to be published by Springer-Verlag under the
title "Computing Particle Properties" (eds. C. B. Lang and H. Gausterer
Froissart boundary for deep inelastic structure functions
In this letter we derive the Froissart boundary in QCD for the deep inelastic
structure function in low kinematic region. We show that the comparison of
the Froissart boundary with the new HERA experimental data gives rise to a
challenge for QCD to explain the matching between the deep inelastic scattering
and real photoproduction process.Comment: 10 pages,7 figure
The asymmetry of the proton in a Pion Cloud Model approach
We study the asymmetry of the proton in a model approach
in which hadronic fluctuations of the nucleon are generated through gluon
splitting and recombination mechanisms. Within this framework, it is shown that
the
asymmetry of the proton is consistently described by including only
nucleon fluctuations to and bound states. Predictions
of the model closely agree with the recent experimental data of the E866/NuSea
Collaboration.Comment: Final version. To appear in Phys. Rev.
Dilepton mass spectra in p+p collisions at sqrt(s)= 200 GeV and the contribution from open charm
The PHENIX experiement has measured the electron-positron pair mass spectrum
from 0 to 8 GeV/c^2 in p+p collisions at sqrt(s)=200 GeV. The contributions
from light meson decays to e^+e^- pairs have been determined based on
measurements of hadron production cross sections by PHENIX. They account for
nearly all e^+e^- pairs in the mass region below 1 GeV/c^2. The e^+e^- pair
yield remaining after subtracting these contributions is dominated by
semileptonic decays of charmed hadrons correlated through flavor conservation.
Using the spectral shape predicted by PYTHIA, we estimate the charm production
cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) \mu b, which
is consistent with QCD calculations and measurements of single leptons by
PHENIX.Comment: 375 authors from 57 institutions, 18 pages, 4 figures, 2 tables.
Submitted to Physics Letters B. v2 fixes technical errors in matching authors
to institutions. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Total harmonic distortion based method for linearity assessment in electrochemical systems in the context of EIS
Electrochemical Impedance Spectroscopy (EIS) is a widely used electrochemical measurement technique
that has been used in a great spectrum of
fields since it allows deconvolving the individual physic-
chemical processes that take place in a given system. Ohm s generalized law, and thus the impedance
concept, are only valid if 4 conditions are fulfilled: causality,
finiteness, stationarity and linearity. In the
case that any of these conditions is not achieved, the obtained impedance spectra will present distortions
that may lead to biased or even erroneous results and conclusions. For this reason it is crucial to verify if
the 4 conditions are fulfilled, before accepting the results extracted from impedance spectra. In this work,
a linearity assessment quantitative method based in the total harmonic distortion (THD) parameter is
presented and verified experimentally. The experimental validation of the implemented method showed
that the implemented method is able to assess quantitatively the linearity of the system. In addition, it is
also able to determine the threshold frequency above which the system will not present significant
nonlinear effects even for large perturbation amplitudes. It was observed that the THD method is more
sensitive to nonlinear effects than the spectra themselves.The authors are very grateful to the Generalitat Valenciana for its economic support in form of Vali+d grant (Ref: ACIF-2013-268).Giner Sanz, JJ.; Ortega Navarro, EM.; Pérez-Herranz, V. (2015). Total harmonic distortion based method for linearity assessment in electrochemical systems in the context of EIS. Electrochimica Acta. 186:598-612. https://doi.org/10.1016/j.electacta.2015.10.152S59861218
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