32,304 research outputs found
Transverse Momentum Resummation for Dijet Correlation in Hadronic Collisions
We study the transverse momentum resummation for dijet correlation in hadron
collisions based on the Collins-Soper-Sterman formalism. The complete one-loop
calculations are carried out in the collinear factorization framework for the
differential cross sections at low imbalance transverse momentum between the
two jets. Important cross checks are performed to demonstrate that the soft
divergences cancelled out between different diagrams, and in particular, those
associated with final state jets. The leading and sub-leading logarithms are
identified. All order resummation is derived following the transverse momentum
dependent factorization at this order. Its phenomenological applications are
also presented.Comment: 51 pages, 10 figure
TMD Evolution: Matching SIDIS to Drell-Yan and W/Z Boson Production
We examine the QCD evolution for the transverse momentum dependent
observables in hard processes of semi-inclusive hadron production in deep
inelastic scattering and Drell-Yan lepton pair production in collisions,
including the spin-average cross sections and Sivers single transverse spin
asymmetries. We show that the evolution equations derived by a direct integral
of the Collins-Soper-Sterman evolution kernel from low to high Q can describe
well the transverse momentum distribution of the unpolarized cross sections in
the Q^2 range from 2 to 100 GeV^2. In addition, the matching is established
between our evolution and the Collins-Soper-Sterman resummation with
b*-prescription and Konychev-Nodalsky parameterization of the non-perturbative
form factors, which are formulated to describe the Drell-Yan lepton pair and
W/Z boson production in hadronic collisions. With these results, we present the
predictions for the Sivers single transverse spin asymmetries in Drell-Yan
lepton pair production and boson production in polarized pp and collisions for several proposed experiments. We emphasize that these
experiments will not only provide crucial test of the sign change of the Sivers
asymmetry, but also provide important opportunities to study the QCD evolution
effects.Comment: 46 pages, 15 figure
EigenGP: Gaussian Process Models with Adaptive Eigenfunctions
Gaussian processes (GPs) provide a nonparametric representation of functions.
However, classical GP inference suffers from high computational cost for big
data. In this paper, we propose a new Bayesian approach, EigenGP, that learns
both basis dictionary elements--eigenfunctions of a GP prior--and prior
precisions in a sparse finite model. It is well known that, among all
orthogonal basis functions, eigenfunctions can provide the most compact
representation. Unlike other sparse Bayesian finite models where the basis
function has a fixed form, our eigenfunctions live in a reproducing kernel
Hilbert space as a finite linear combination of kernel functions. We learn the
dictionary elements--eigenfunctions--and the prior precisions over these
elements as well as all the other hyperparameters from data by maximizing the
model marginal likelihood. We explore computational linear algebra to simplify
the gradient computation significantly. Our experimental results demonstrate
improved predictive performance of EigenGP over alternative sparse GP methods
as well as relevance vector machine.Comment: Accepted by IJCAI 201
Long Range Correlation in Higgs Boson Plus Two Jets Production at the LHC
We study Higgs boson plus two high energy jets production at the LHC in the
kinematics where the two jets are well separated in rapidity. The partonic
processes are dominated by the t-channel weak boson fusion (WBF) and gluon
fusion (GF) contributions. We derive the associated QCD resummation formalism
for the correlation analysis where the total transverse momentum q_\perp of the
Higgs boson and two jets is small. Because of different color structures, the
resummation results lead to distinguished behaviors: the WBF contribution peaks
at relative low q_\perp while all GF channel contributions are strongly
de-correlated and spread to a much wider q_\perp range. By applying a kinematic
cut on q_\perp, one can effectively increase the WBF signal to the GF
background by a significant factor. This greatly strengthens the ability to
investigate the WBF channel in Higgs boson production and study the couplings
of Higgs to electroweak bosons.Comment: 9 pages, 2 figure
THERMAL LATTICE BOLTZMANN TWO-PHASE FLOW MODEL FOR FLUID DYNAMICS
This dissertation presents a systematic development of a new thermal lattice Boltzmann multiphase model. Unlike conventional CFD methods, the lattice Boltzmann equation (LBE) method is based on microscopic models and mesoscopic kinetic equations in which the collective behavior of the particles in a system is used to simulate the continuum mechanics of the system. Due to this kinetic nature, the LBE method has been found to be particularly useful in applications involving interfacial dynamics and complex boundaries, e.g. multiphase or multicomponent flows. First, the methodology and general concepts of the LBE method are introduced. Following this introduction, an accurate mass conserving wall boundary condition for the LBE method is proposed together with benchmark test results. Next, the widely used Shan and Chen (SC) single component two-phase flow model is presented, as well as improvements to that model. In this model, by incorporating fluid-fluid interaction, phase separation and interfacial dynamics can be properly captured. Sharp interfaces between phases can be easily obtained without any additional numerical treatment. In order to achieve flexibility for the surface tension term, an additional force term which represents the contribution of surface tension is incorporated into the fluid-fluid interaction force term. The validity of this treatment is verified by our simulation results. Different equations of state are also incorporated into this model to compare their behavior. Finally, based on the SC model, a new and generalized lattice Boltzmann model for simulating thermal two-phase flow is described. In this model, the SC model is used to simulate the fluid dynamics. The temperature field is simulated using the passive-scalar approach, i.e. through modeling the density field of an extra component, which evolves according to the advection-diffusion equation. By coupling the fluid dynamics and temperature field through a suitably defined body force term, the thermal two-phase lattice Boltzmann model is obtained. Our simulation results show that different equations of state, variable wettability, gravity and buoyancy effects, and relatively high Rayleigh numbers can be readily simulated by this new model. Lastly, the accomplishments of this study are summarized and future perspectives are provided
Universal Non-perturbative Functions for SIDIS and Drell-Yan Processes
We update the well-known BLNY fit to the low transverse momentum Drell-Yan
lepton pair productions in hadronic collisions, by considering the constraints
from the semi-inclusive hadron production in deep inelastic scattering (SIDIS)
from HERMES and COMPASS experiments. We follow the Collins-Soper-Sterman (CSS)
formalism with the b_*-prescription. A universal non-perturbative form factor
associated with the transverse momentum dependent quark distributions is found
in the analysis with a new functional form different from that of BLNY. This
releases the tension between the BLNY fit to the Drell-Yan data with the SIDIS
data from HERMES/COMPASS in the CSS resummation formalism.Comment: 19 pages, 11 figures; updated the fit with running effects of
\alpha_{s}, \alpha_{em}, N_f; conclusion remains; more discussions on the
result
- …