118596758
Uncertainty induced by QCD coupling in the CTEQ global analysis of parton distributions
We examine the dependence of parton distribution functions (PDFs) on the value of the QCD coupling strengths(MZ). We explain a simple method that is rigorously valid in the quadratic approximation normally applied in PDF fitting, and fully reproduces the correlated dependence of theoretical cross sections ons and PDF parameters. This method is based on a statistical relation that allows one to add the uncertainty produced bys, computed with some special PDF sets, in quadrature with the PDF uncertainty obtained for the fixeds value (such as the CTEQ6.6 PDF set). A series of four CTEQ6.6AS PDFs realizing this approach, fors values in the interval 0.116 � �s(MZ) � 0.120, is presented. Using these PDFs, the combineds and PDF uncertainty is assessed for theoretical predictions at the Fermilab Tevatron and Large Hadron Collider.
53532246
Associated production of neutral Higgs boson with squark pair in the minimal supersymmetric standard model with explicit CP violation at the CERN LHC
We investigate the associated production of neutral Higgs boson with squark pair in the minimal supersymmetric standard model with and without explicit $CP$ violation, respectively. We show that the dominant productions in both cases are always ones of the lightest neutral Higgs boson associated with the lightest stop pair, which can reach a few pb, in the ranges of parameters allowed by constraints from the electric dipole moment experiments. In most of the parameter space, the total cross sections in the case with explicit $CP$ violation are significantly enhanced, compared with ones without explicit $CP$ violation. For some special parameters, several orders of magnitude enhancement can be obtained.
15616620
Nonperturbative effect in threshold resummation
We show that the conventional threshold resummation calculation cannot describe well the low energy Drell-Yan (DY) data without including the non-perturbative correction terms which are deduced from analyzing the asymptotic behavior of the resummation formalism. It is demonstrated that the non-perturbative correction is generally small for the large invariant mass DY pairs produced at the Tevatron and the LHC.
118623641
Threshold resummation effects in neutral Higgs boson production by bottom quark fusion at the CERN Large Hadron Collider
We investigate the QCD effects in the production of neutral Higgs bosons via bottom quark fusion in both the standard model and the minimal supersymmetric standard model at the CERN Large Hadron Collider. We include the next-to-leading order (NLO) QCD corrections (including supersymmetric QCD) and the threshold resummation effects. We use the soft-collinear effective theory to resum the large logarithms near threshold from soft gluon emission. Our results show that the resummation effects can enhance the total cross sections by about 5% compared with the NLO results.
28003556
QCD resummation for jet substructures.
We provide a novel development in jet physics by predicting the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large Hadron Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions. The predicted peak positions and heights in jet mass distributions are consistent with CDF data within uncertainties induced by parton distribution functions.
121598302
QCD resummation for jet profiles
We predict the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large-Hadron-Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions.
119185410
Single-particle resonances in a deformed Dirac equation
Single-particle bound and resonant states are obtained by solving the Dirac equation with quadrupole-deformed Woods-Saxon potential in coordinate space with the coupled-channel approach. Taking the m{sup {pi}}=1/2{sup +} resonant states at deformation {beta}=0.1 as examples, the roles of their spherical components have been investigated based on the behaviors of the eigenphases and the corresponding probabilities weighted by the scalar spherical potential. It is shown that the realization of the m{sup {pi}}=1/2{sup +} resonances is supported mainly by the lnot =0 components, and the mixture of the s{sub 1/2} component can lead to the disappearance of some resonances at finite energy. The dominance of the lnot =0 component (d{sub 3/2}) in the small-energy region guarantees the continuation of a certain resonance to the corresponding bound state.
6149638
Connection between the largest Lyapunov exponent, density fluctuation, and multifragmentation in excited nuclear systems
Within a quantum molecular dynamics model we calculate the largest Lyapunov exponent (LLE), the density fluctuation, and the mass distribution of fragments for a series of nuclear systems at different initial temperatures. It is found that the LLE peaks at the temperature ("critical temperature") where the density fluctuation reaches a maximal value and the mass distribution of fragments is best fitted by the Fisher's power law from which the critical exponents for mass and charge distribution are obtained. The time-dependent behavior of the LLE and density fluctuation is studied. We find that the time scale of the density fluctuation is much longer than that of the inverse LLE, which indicates that chaotic motion can be well developed during the process of fragment formation. The finite-size effect on "critical temperature" for nuclear systems ranging from calcium to superheavy nuclei is also studied.
119354648
Density and temperature dependence of nucleon-nucleon elastic cross section
The in-medium neutron-proton, proton-proton (neutron-neutron) elastic scattering cross sections (sigma(np)*,sigma(pp(nn))*) are studied based on the effective Lagrangian of density dependent relativistic hadron theory in which the delta[a(0)(980)] meson is included. Our study shows that at low densities the sigma(np)* is about three to four times larger than sigma(pp(nn))* and at densities higher than the normal density the isospin effect is almost washed out. Because of coupling to delta meson the sigma(nn)* and sigma(pp)* are different in isospin asymmetric medium following the splitting of the proton and neutron masses. The isospin effect on the density dependence of the in-medium nucleon elastic cross section is dominantly contributed by the isovector delta and rho mesons. The temperature effect on the sigma(np)* and sigma(pp(nn))* is studied. It is shown that the temperature effect is weaker compared with the density effect but it becomes obvious as density increases.
124926981
Analysis of Collective Flow in High Energy Heavy-Ion Collisions in the Relativistic VUU Approach
We have calculated the collective flow for collisions of by using the relativistic Vlasov-Uehling-Uhlenbeck (VUU) equation based on the QHD-I model of Walecka. The tensitivity of flow characterized by and to mean field and in-medium NN scattering cross section is studied. It is found that the azimuthal correlation function is reduced dramatically after inserting the collision term and then varies very slowly between NN cross sections from to and reaches the minimum at , while the in-plane mean transverse momentum increases slowly all the way from to . The collective flow is very sensitive to the momentum dependence (indicated by the effective mass ) of the mean field and less sensitive to the compression modulus K and the cross sections from to . The numerical results were compared with the experimental data, and we found that the agreement for both and can be reached with the same set of mean field parameters as well as the appropriate NN cross section in collision terms.
56383623
Systematic study of fusion barriers
A possible method is proposed for extracting fusion barriers from measured fusion excitation functions. The obtained fusion barrier distributions are in good agreement with those determined by the method. The characteristics of the fusion barrier distributions, such as the mean barrier heights, the full widths at half maximum as well as the radii of the barriers, are studied systematically. A systematic comparison between the characteristics of the fusion barrier distributions determined by the proposed method and those of empirical barrier distributions based on the nucleus–nucleus potential calculated with Skyrme energy-density functional together with extended Thomas–Fermi approach has been performed for 120 fusion reactions. A nice agreement between them is found. Simultaneously, the influence of the static deformation and the deformation due to excitation of the reaction partners on the reduction of the fusion barriers was investigated for a series of reactions. From the investigation of the deviation of the calculated fusion excitation functions based on different Skyrme interactions from the experimental data, we find that the nucleus–nucleus potential obtained with SkM* can provide a better description of the fusion cross sections at energies near and above the barrier systematically.