7,891 research outputs found
Weighted azimuthal asymmetries in a diquark spectator model
We analytically calculate weighted azimuthal asymmetries in semi-inclusive
lepton-nucleon deep-inelastic scattering and Drell-Yan processes, using
transverse-momentum-dependent partonic densities obtained in a diquark
spectator model. We compare the asymmetries with available preliminary
experimental data, in particular for the Collins and the Sivers effect. We make
predictions for other cases of interest in running and planned experiments.Comment: 21 pages, 13 (multiple) figures in eps format, RevTeX
Successful pulmonary thromboendarterectomy in a patient with sickle cell disease and associated resolution of a leg ulcer
© 2017 Indian Chest Society | Published by Wolters Kluwer -Medknow. Pulmonary hypertension (PH) is a relatively frequent and severe complication of sickle cell disease (SCD). PH associated with SCD is classified as Group 5 PH. The exact pathogenesis of PH in SCD in not known. There are also very limited treatment options available at this time for such patients with Group 5 PH. Patients with SCD are predisposed to a hypercoagulable state and thus can also suffer from chronic thromboembolism. These patients can have associated chronic thromboembolic pulmonary hypertension (CTEPH), thus being classified as Group 4 PH. We present such a case of a patient with SCD diagnosed with severe PH who was found to have CTEPH and successfully underwent a thromboendarterectomy with resolution of his symptoms such as reduction of his oxygen requirements and healing of chronic leg ulcer. This case illustrates the importance of screening patients with SCD and elevated pulmonary artery pressures for CTEPH as this would offer possible treatment options such as pulmonary thromboendarterectomy and/or riociguat in this subset of patients
Unpolarized fragmentation function for the pion and kaon via the nonlocal chiral-quark model
In this talk we present our recent studies for the unpolarized fragmentation
functions for the pion and kaon, employing the nonlocal chiral quark model,
which manifests the nonlocal interaction between the quarks and pseudoscalar
mesons, in the light-cone frame. It turns out that the nonlocal interaction
produces considerable differences in comparison to typical local-interaction
models.Comment: 4 pages, 2 figures, Talk given at the international conference The
Fifth Asia-Pacific Conference on Few-Body Systems in Physics 2011 (APFB2011),
Seoul, Republic of Korea, 22-26 August 201
Estimate of the Collins fragmentation function in a chiral invariant approach
We predict the features of the Collins function, which describes the
fragmentation of a transversely polarized quark into an unpolarized hadron, by
modeling the fragmentation process at a low energy scale. We use the chiral
invariant approach of Manohar and Georgi, where constituent quarks and
Goldstone bosons are considered as effective degrees of freedom in the
non-perturbative regime of QCD. To test the approach we calculate the
unpolarized fragmentation function and the transverse momentum distribution of
a produced hadron, both of which are described reasonably well. In the case of
semi-inclusive deep-inelastic scattering, our estimate of the Collins function
in connection with the transversity distribution gives rise to a transverse
single spin asymmetry of the order of 10%, supporting the idea of measuring the
transversity distribution of the nucleon in this way. In the case of e+ e-
annihilation into two hadrons, our model predicts a Collins azimuthal asymmetry
of about 5%.Comment: 12 pages, 15 figures. Figs. 11-14 changed, minor changes in
discussion, few typos fixed and some references added. Final version to
appear in PR
Two-hadron semi-inclusive production including subleading twist
We extend the analysis of two-hadron fragmentation functions to the
subleading twist, discussing also the issue of color gauge invariance. Our
results can be used anywhere two unpolarized hadrons are semi-inclusively
produced in the same fragmentation region, also at moderate values of the hard
scale Q. Here, we consider the example of polarized deep-inelastic production
of two hadrons and we give a complete list of cross sections and spin
asymmetries up to subleading twist. Among the results, we highlight the
possibility of extracting the transversity distribution with longitudinally
polarized targets and also the twist-3 distribution e(x), which is related to
the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae,
added text in Secs. III-V, added reference
Wilson Lines off the Light-cone in TMD PDFs
Transverse Momentum Dependent (TMD) parton distribution functions (PDFs) also
take into account the transverse momentum () of the partons. The
-integrated analogues can be linked directly to quark and gluon matrix
elements using the operator product expansion in QCD, involving operators of
definite twist. TMDs also involve operators of higher twist, which are not
suppressed by powers of the hard scale, however. Taking into account gauge
links that no longer are along the light-cone, one finds that new distribution
functions arise. They appear at leading order in the description of azimuthal
asymmetries in high-energy scattering processes. In analogy to the collinear
operator expansion, we define a universal set of TMDs of definite rank and
point out the importance for phenomenology.Comment: 12 pages, presented by the first author at the Light-Cone Conference
2013, May 20-24, 2013, Skiathos, Greece. To be published in Few Body System
Left-right asymmetry for pion and kaon production in the semi-inclusive deep inelastic scattering process
We analyze the left-right asymmetry in the semi-inclusive deep inelastic
scattering (SIDIS) process without introducing any weighting functions. With
the current theoretical understanding, we find that the Sivers effect plays a
key role in our analysis. We use the latest parametrization of the Sivers and
fragmentation functions to reanalyze the production process and find
that the results are sensitive to the parametrization. We also extend our
calculation on the production, which can help us know more about the
Sivers distribution of the sea quarks and the unfavored fragmentation
processes. HERMES kinematics with a proton target, COMPASS kinematics with a
proton, deuteron, and neutron target (the information on the neutron target can
be effectively extracted from the He target), and JLab kinematics (both 6
GeV and 12 GeV) with a proton and neutron target are considered in our paper.Comment: 7 latex pages, 11 figures, final version for publication, with
references update
Gauge links for transverse momentum dependent correlators at tree-level
In this paper we discuss the incorporation of gauge links in hadronic matrix
elements that describe the soft hadronic physics in high energy scattering
processes. In this description the matrix elements appear in soft correlators
and they contain non-local combinations of quark and gluon fields. In our
description we go beyond the collinear approach in which case also the
dependence on transverse momenta of partons is taken into consideration. The
non-locality in the transverse direction leads to a complex gauge link
structure for the full process, in which color is entangled, even at
tree-level. We show that at tree-level in a 1-parton unintegrated (1PU)
situation, in which only the transverse momentum of one of the initial state
hadrons is relevant, one can get a factorized expression involving transverse
momentum dependent (TMD) distribution functions. We point out problems at the
level of two initial state hadrons, even for relatively simple processes such
as Drell-Yan scattering.Comment: 25 pages, corrected typos and updated reference
Transverse momentum dependence in gluon distribution and fragmentation functions
We investigate the twist two gluon distribution functions for spin 1/2
hadrons, emphasizing intrinsic transverse momentum of the gluons. These
functions are relevant in leading order in the inverse hard scale in scattering
processes such as inclusive leptoproduction or Drell-Yan scattering, or more
general in hard processes in which at least two hadrons are involved. They show
up in azimuthal asymmetries. For future estimates of such observables, we
discuss specific bounds on these functions.Comment: 14 pages, revtex, 7 Postscript figure
A mechanism for the T-odd pion fragmentation function
We consider a simple rescattering mechanism to calculate a leading twist
-odd pion fragmentation function, a favored candidate for filtering the
transversity properties of the nucleon. We evaluate the single spin azimuthal
asymmetry for a transversely polarized target in semi-inclusive deep inelastic
scattering (for HERMES kinematics). Additionally, we calculate the double
-odd asymmetry in this framework.Comment: 6 pages revtex, 7 eps figures, references added and updated in this
published versio
- …