17,708 research outputs found
Single Spin Asymmetry in Lepton Angular Distribution of Drell-Yan Processes
We study the single spin asymmetry in the lepton angular distribution of
Drell-Yan processes in the frame work of collinear factorization. The asymmetry
has been studied in the past and different results have been obtained. In our
study we take an approach different than that used in the existing study. We
explicitly calculate the transverse-spin dependent part of the differential
cross-section with suitable parton states. Because the spin is transverse, one
has to take multi-parton states for the purpose. Our result agrees with one of
the existing results. A possible reason for the disagreement with others is
discussed.Comment: Typos corrected. Conclusions unchange
Local spin fluctuations in iron-based superconductors: 77Se and 87Rb NMR measurements of Tl0.47Rb0.34Fe1.63Se2
We report nuclear magnetic resonance (NMR) studies of the intercalated iron
selenide superconductor (Tl, Rb)FeSe ( K).
Single-crystal measurements up to 480 K on both Se and Rb nuclei
show a superconducting phase with no magnetic order. The Knight shifts and
relaxation rates increase very strongly with temperature above ,
before flattening at 400 K. The quadratic -dependence and perfect
proportionality of both and data demonstrate their origin in
paramagnetic moments. A minimal model for this pseudogap-like response is not a
missing density of states but two additive contributions from the itinerant
electronic and local magnetic components, a framework unifying the and
data in many iron-based superconductors
Next-to-leading order QCD evolution of transversity fragmentation functions
We derive the next-to-leading order splitting kernels for the scale evolution
of fragmentation functions for transversely polarized quarks into transversely
polarized hadrons.Comment: 9 pages, LaTe
Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)
A multi-purpose fixed-target experiment using the proton and lead-ion beams
of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg,
and here we concentrate our study on some issues related to the spin physics
part of this project (referred to as AFTER). We study the nucleon spin
structure through and processes with a fixed-target experiment using
the LHC proton beams, for the kinematical region with 7 TeV proton beams at the
energy in center-of-mass frame of two nucleons GeV. We calculate
and estimate the azimuthal asymmetries of unpolarized and
dilepton production processes in the Drell--Yan continuum region and at the
-pole. We also calculate the , and
azimuthal asymmetries of and dilepton production
processes with the target proton and deuteron longitudinally or transversally
polarized in the Drell--Yan continuum region and around resonances region.
We conclude that it is feasible to measure these azimuthal asymmetries,
consequently the three-dimensional or transverse momentum dependent parton
distribution functions (3dPDFs or TMDs), at this new AFTER facility.Comment: 15 pages, 40 figures. Version accepted for publication in EPJ
Lignin biomarkers as tracers of mercury sources in lakes water column
This study presents the role of specific terrigenous organic compounds as important vectors of mercury (Hg) transported from watersheds to lakes of the Canadian boreal forest. In order to differentiate the autochthonous from the allochthonous organic matter (OM), lignin derived biomarker signatures [Lambda, S/V, C/V, P/(V ? S), 3,5-Bd/V and (Ad/Al)v] were used. Since lignin is exclusively produced by terrigenous plants, this approach can give a non equivocal picture of the watershed inputs to the lakes. Moreover, it allows a characterization of the source of OM and its state of degradation. The water column of six lakes from the Canadian Shield was sampled monthly between June and September 2005. Lake total dissolved Hg concentrations and Lambda were positively correlated, meaning that Hg and ligneous inputs are linked (dissolved OM r2 = 0.62, p\0.0001; particulate OM r2 = 0.76, p\0.0001). Ratios of P/(V ? S) and 3,5-Bd/V from both dissolved OM and particulate OM of the water column suggest an inverse relationship between the progressive state of pedogenesis and maturation of the OM in soil before entering the lake, and the Hg concentrations in the water column. No relation was found between Hg levels in the lakes and the watershed flora composition—angiosperm versus gymnosperm or woody versus non-woody compounds. This study has significant implications for watershed management of ecosystems since limiting fresh terrestrial OM inputs should reduce Hg inputs to the aquatic systems. This is particularly the case for largescale land-use impacts, such as deforestation, agriculture and urbanization, associated to large quantities of soil OM being transferred to aquatic systems
Large corrections to asymptotic and in the light-cone perturbative QCD
The large- behavior of - and -
transition form factors, and
are analyzed in the framework of light-cone perturbative QCD with the heavy
quark ( and ) mass effect, the parton's transverse momentum dependence
and the higher helicity components in the light-cone wave function are
respected. It is pointed out that the quark mass effect brings significant
modifications to the asymptotic predictions of the transition form factors in a
rather broad energy region, and this modification is much severer for
than that for due to the
-quark being heavier than the -quark. The parton's transverse momentum
and the higher helicity components are another two factors which decrease the
perturbative predictions. For the transition form factor
, they bring sizable corrections in the present
experimentally accessible energy region (). For the
transition form factor , the corrections coming from
these two factors are negligible since the -quark mass is much larger than
the parton's average transverse momentum. The coming collider (LEP2)
will provide the opportunity to examine these theoretical predictions.Comment: 8 pages, RevTex, 5 PostScript figure
Orbital Angular Momentum Parton Distributions in Light-Front Dynamics
We study the quark angular momentum distribution in the nucleon within a
light-front covariant quark model. Special emphasis is put into the orbital
angular momentum: a quantity which is very sensitive to the relativistic
treatment of the spin in a light-front dynamical approach. Discrepancies with
the predictions of the low-energy traditional quark models where relativistic
spin effects are neglected, are visible also after perturbative evolution to
higher momentum scales. Orbital angular momentum distributions and their
contribution to the spin sum rule are calculated for different phenomenological
mass operators and compared with the results of the MIT bag model.Comment: 14 pages; latex; 3 ps figure
B_c meson rare decays in the light-cone quark model
We investigate the rare decays
and in the framework of the
light-cone quark model (LCQM). The transition form factors are calculated in
the space-like region and then analytically continued to the time-like region
via exponential parametrization. The branching ratios and longitudinal lepton
polarization asymmetries (LPAs) for the two decays are given and compared with
each other. The results are helpful to investigating the structure of
meson and to testing the unitarity of CKM quark mixing matrix. All these
results can be tested in the future experiments at the LHC.Comment: 9 pages, 11 figures, version accepted for publication in EPJ
Neural-network analysis of Parton Distribution Functions from Ioffe-time pseudodistributions
International audienceWe extract two nonsinglet nucleon Parton Distribution Functions from lattice QCD data for reduced Ioffe-time pseudodistributions. We perform such analysis within the NNPDF framework, considering data coming from different lattice ensembles and dis- cussing in detail the treatment of the different source of systematics involved in the fit. We introduce a recipe for taking care of systematics and use it to perform our extraction of light-cone PDFs
Parton distribution functions and quark orbital motion
Covariant version of the quark-parton model is studied. Dependence of the
structure functions and parton distributions on the 3D quark intrinsic motion
is discussed. The important role of the quark orbital momentum, which is a
particular case of intrinsic motion, appears as a direct consequence of the
covariant description. Effect of orbital motion is substantial especially for
polarized structure functions. At the same time, the procedure for obtaining
the quark momentum distributions of polarized quarks from the combination of
polarized and unpolarized structure functions is suggested.Comment: 17 pages, 2 figures, 1 table. Paper is accepted for publication in
Eur.Phys.J.
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