114,112 research outputs found
Partonic State and Single Transverse Spin Asymmetry in Drell-Yan Process
Single transverse-spin asymmetries have been studied intensively both in
experiment and theory. Theoretically, two factorization approaches have been
proposed. One is by using transverse-momentum-dependent factorization and the
asymmetry comes from the so called Sivers function. Another is by using
collinear factorization where the nonperturbative effect is parameterized by a
twist-3 hadronic matrix element. However, the factorized formulas for the
asymmetries in the two approaches are derived at hadron level formally by
diagram expansion, where one works with various parton density matrices of
hadrons. If the two factorizations hold, they should also hold at parton level.
We examine this for Drell-Yan processes by replacing hadrons with partons. By
calculating the asymmetry, Sivers function and the twist-3 matrix element at
nontrivial leading order of , we find that we can reproduce the
result of the transverse-momentum-dependent factorization. But we can only
verify the result of the collinear factorization partly. Two formally derived
relations between Sivers function and the twist-3 matrix element are also
examined with negative results.Comment: 15 pages, 6 figure
Robust variance-constrained filtering for a class of nonlinear stochastic systems with missing measurements
The official published version of the article can be found at the link below.This paper is concerned with the robust filtering problem for a class of nonlinear stochastic systems with missing measurements and parameter uncertainties. The missing measurements are described by a binary switching sequence satisfying a conditional probability distribution, and the nonlinearities are expressed by the statistical means. The purpose of the filtering problem is to design a filter such that, for all admissible uncertainties and possible measurements missing, the dynamics of the filtering error is exponentially mean-square stable, and the individual steady-state error variance is not more than prescribed upper bound. A sufficient condition for the exponential mean-square stability of the filtering error system is first derived and an upper bound of the state estimation error variance is then obtained. In terms of certain linear matrix inequalities (LMIs), the solvability of the addressed problem is discussed and the explicit expression of the desired filters is also parameterized. Finally, a simulation example is provided to demonstrate the effectiveness and applicability of the proposed design approach.This work was supported in part by the Engineering and Physical Sciences Research Council (EPSRC) of the UK under Grant GR/S27658/01, the Royal Society of the UK and the Alexander von Humboldt Foundation of Germany
Elliptic flow of meson and strange quark collectivity at RHIC
Based on A Multi-Phase Transport (AMPT) model, we have studied the elliptic
flow of mesons from reconstructed decay channel at
the top Relativistic Heavy Ion Collider energy at Brookhaven National
Laboratory. The dependences of on transverse momentum and
collision centrality are presented and the rescattering effect of mesons
in the hadronic phase is also investigated. The results show that experimental
measurement of for mesons can retain the early collision
information before decays and that the value obeys the
constituent quark number scaling which has been observed for other mesons and
baryons. Our study indicates that the mostly reflects partonic
level collectivity developed during the early stage of the nucleus-nucleus
collision and the strange and light up/down quarks have developed similar
angular anistropy properties at the hadronization.Comment: 5 pages and 5 figures; accepted by Physical Review
The evolution-dominated hydrodynamic model and the pseudorapidity distributions in high energy physics
By taking into account the effects of leading particles, we discuss the
pseudorapidity distributions of the charged particles produced in high energy
heavy ion collisions in the context of evolution-dominated hydrodynamic model.
The leading particles are supposed to have a Gaussian rapidity distribution
normalized to the number of participants. A comparison is made between the
theoretical results and the experimental measurements performed by BRAHMS and
PHOBOS Collaboration at BNL-RHIC in Au-Au and Cu-Cu collisions at sqrt(s_NN)
=200 GeV and by ALICE Collaboration at CERN-LHC in Pb-Pb collisions at
sqrt(s_NN) =2.76 TeV.Comment: 17 pages,4 figures, 2 table
Gluon GPDs and Exclusive Photoproduction of a Quarkonium in Forward Region
Forward photoproduction of can be used to extract Generalized Parton
Distributions(GPD's) of gluons. We analyze the process at twist-3 level and
study relevant classifications of twist-3 gluon GPD's. At leading power or
twist-2 level the produced is transversely polarized. We find that at
twist-3 the produced is longitudinally polarized. Our study shows that
in high energy limit the twist-3 amplitude is only suppressed by the inverse
power of the heavy quark mass relatively to the twist-2 amplitude. This
indicates that the power correction to the cross-section of unpolarized
can have a sizeable effect. We have also derived the amplitude of the
production of at twist-3, but the result contains end-point
singularities. The production of other quarkonia has been briefly discussed.Comment: Discussions of results are adde
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