399 research outputs found
The QCD corrections to scalar top pair production in photon-photon collisions
The complete QCD corrections to the scalar top quark pair production via
fusion in parent collider are calculated in the
Supersymmetric Model. The various origins of corrections are discussed. We find
that the correction due to gluino exchange is smaller than that due to
conventional gluonic contribution, and the contribution due to squark quartic
interactions is much smaller. Moreover, the dependences of the corrections on
the masses and the mixing angle of the supersymmetric particles are also
investigated.Comment: 25 Pages, LaTex, 10 eps figures
Quark Distributions of Octet Baryons from SU(3) Symmetry
SU(3) symmetry relations between the octet baryons are introduced in order to
connect both the unpolarized and polarized quark distributions of the octet
baryons with those of the nucleon. Two different parametrizations of the
nucleon quark distributions are used. A new scenario of quark flavor and spin
structure of the is found and compared with two other models: a
perturbative QCD based analysis and a quark diquark model. The and
quarks inside the are predicted to be positively polarized at large
Bjorken variable in the new scenario. By using an approximate relation
connecting the quark fragmentation functions with the quark distributions, the
hadron polarizations of the octet baryons in -annihilation, polarized
charged lepton deep inelastic scattering (DIS) processes, and neutrino
(antineutrino) DIS processes are predicted. The predictions for
polarizations in several processes are compatible with the available data at
large fragmentation momentum fraction , and support the prediction of
positively polarized and quarks inside the at large .
Predictions for Drell-Yan processes from and beams on an
isoscalar target are also given and discussed.Comment: 29 latex pages, 16 figures, to appear in PR
Heavy Flavour Production at Tevatron and Parton Shower Effects
We present hadron-level predictions from the Monte Carlo generator Cascade
and numerical calculations of charm and beauty production at the Fermilab
Tevatron within the framework of the -factorization QCD approach. Our
consideration is based on the CCFM-evolved unintegrated gluon densities in a
proton. The performed analysis covers the total and differential cross sections
of open charm and beauty quarks, and mesons (or rather muons from their
semileptonic decays) and the total and differential cross sections of di-jet hadroproduction. We study the theoretical uncertainties of our
calculations and investigate the effects coming from parton showers in initial
and final states. Our predictions are compared with the recent experimental
data taken by the D0 and CDF collaborations. Special attention is put on the
specific angular correlations between the final-state particles. We demonstrate
that the final state parton shower plays a crucial role in the description of
such observables. The decorrelated part of angular separations can be fully
described, if the process is included.Comment: Fig 8,9 10 replaced, small corrections in text A discussion of the
delta phi results is adde
Lambda Polarization in Polarized Proton-Proton Collisions at RHIC
We discuss Lambda polarization in semi-inclusive proton-proton collisions,
with one of the protons longitudinally polarized. The hyperfine interaction
responsible for the - and - mass splittings gives
rise to flavor asymmetric fragmentation functions and to sizable polarized
non-strange fragmentation functions. We predict large positive Lambda
polarization in polarized proton-proton collisions at large rapidities of the
produced Lambda, while other models, based on SU(3) flavor symmetric
fragmentation functions, predict zero or negative Lambda polarization. The
effect of and decays is also discussed. Forthcoming
experiments at RHIC will be able to differentiate between these predictions.Comment: 18 pages, 5 figure
Laparoscopic Sleeve Gastrectomy is a Safe and Effective Bariatric Procedure for the Lower BMI (35.0–43.0 kg/m2) Population
# The Author(s) 2010. This article is published with open access at Springerlink.com Background The laparoscopic vertical sleeve gastrectomy (LSG) is derived from the biliopancreatic diversion with duodenal switch operation (Marceau et al., Obes Surg 3:29
Flavor Asymmetry of the Nucleon Sea and W Boson Production
The advantage and feasibility of using -boson production to extract unique
information on the flavor asymmetry of the and sea-quark
distributions in the proton are examined. The and production cross
section ratios in collisions are shown to be sensitive to the ratios, and they are free from charge-symmetry-breaking and
nuclear-binding effects. The feasibility for measuring these ratios at the RHIC
and LHC proton-proton colliders, as well as the expected sensitivity to the
ratios, are also presented.Comment: 7 pages, 4 figures (updated figures
Direct J/psi and psi' hadroproduction via fragmentation in the collinear parton model and k_T-factorization approach
The p_T-spectra for direct J/psi and psi' in hadroproduction at Tevatron
energy have been calculated based on NRQCD formalism and fragmentation
approximation in the collinear parton model and k_T-factorization approach. We
have described the CDF data and obtained a good agreement between the
predictions obtained in the parton model and k_T-factorization approach. We
performed the calculations using the relevant leading order in alpha_s hard
amplitudes and the equal values of the color-octet long-distance matrix
elements for the both models.Comment: 10 pages, Latex, 4 eps figures, epsfig.sty, graphics.st
Inclusive double-quarkonium production at the Large Hadron Collider
Based on the nonrelativistic QCD (NRQCD) factorization formalism, we
investigate inclusive productions of two spin-triplet S-wave quarkonia
pp->2J/psi+X, 2Upsilon+X, and J/psi+Upsilon+X at the CERN Large Hadron
Collider. The total production rates integrated over the rapidity (y) and
transverse-momentum (p_T) ranges |y|<2.4 and p_T<50 GGeV are predicted to be
sigma[pp->2J/psi+X] = 22 (35) nb, sigma[pp->2Upsilon+X] = 24 (49) pb, and
sigma[pp->J/psi+Upsilon+X] = 7 (13) pb at the center-of-momentum energy sqrt{s}
= 7 (14) TeV. In order to provide predictions that can be useful in both small-
and large-p_T regions, we do not employ the fragmentation approximation and we
include the spin-triplet S-wave color-singlet and color-octet channels for each
quarkonium final state at leading order in the strong coupling. The p_T
distributions of pp->2J/psi+X and 2Upsilon+X in the low-p_T region are
dominated by the color-singlet contributions. At leading order in the strong
coupling, the color-singlet channel is absent for pp->J/psi+Upsilon+X.
Therefore, the process pp->J/psi+Upsilon+X may provide a useful probe to the
color-octet mechanism of NRQCD.Comment: 26 pages, 7 figures, 3 tables, version published in JHE
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