5,688 research outputs found
Perturbative and non-perturbative QCD corrections to wide-angle Compton scattering
We investigate corrections to the handbag approach for wide-angle Compton
scattering off protons at moderately large momentum transfer: the photon-parton
subprocess is calculated to next-to-leading order QCD and contributions from
the generalized parton distribution E} are taken into account. Photon and
proton helicity flip amplitudes are non-zero due to these corrections which
leads to a wealth of polarization phenomena in Compton scattering. Thus, for
instance, the incoming photon asymmetry or the transverse polarization of the
proton are non-zero although small.Comment: 19 pages, 9 figures (using LATEX with epsfig
The Distance and Age of the SNR Kes 73 and AXP 1E 1841-045
We provide a new distance estimate to the supernova remnant (SNR) Kes 73 and
its associated anomalous X-ray pulsar (AXP) 1E 1841-045. 21 cm HI images and HI
absorption/ emission spectra from new VLA observations, and 13CO emission
spectra of Kes 73 and two adjacent compact HII regions (G27.276+0.148 and
G27.491+0.189) are analyzed. The HI images show prominent absorption features
associated with Kes 73 and the HII regions. The absorption appears up to the
tangent point velocity giving a lower distance limit to Kes 73 of 7.5 kpc,
which has previously been given as the upper limit. Also, G27.276+0.148 and
G27.491+0.189 are at the far kinematic distances of their radio recombination
line velocities. There is prominent HI emission in the range 80--90 km/s for
all three objects. The two HII regions show HI absorption at ~ 84 km/s, but
there is no absorption in the Kes 73 absorption spectrum. This implies an upper
distance limit of ~ 9.8 kpc to Kes 73. This corrected larger distance to Kes
73/ AXP 1E 1841-045 system leads to a refined age of the SNR of 500 to 1000 yr,
and a ~ 50% larger AXP X-ray luminosity.Comment: 10 pages, 2 figures, ApJ, dol:10.1086/"529120
Semileptonic B Decays and Determination of |Vub|
Semileptonic decays of the B mesons provide an excellent probe for the weak
and strong interactions of the bottom quark. The large data samples collected
at the B Factories have pushed the experimental studies of the semileptonic B
decays to a new height and stimulated significant theoretical developments. I
review recent progresses in this fast-evolving field, with an emphasis on the
determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element
|Vub|.Comment: 16 pages, 4 figures, accepted by Mod. Phys. Lett.
Double Spin Asymmetries in P-wave Charmonium Hadroproduction
We discuss the double spin asymmetries in P-wave charmonium hadroproduction
with non-zero transverse momenta at fixed target energies,
GeV, within the framework of the NRQCD factorization approach. The size of the
asymmetries and the projected statistical errors in a future option of HERA
with longitudinally polarized protons scattering off a polarized target
(HERA-) are calculated. Measurements of the and
decays into dilepton plus photon should allow to distinguish between different
parametrizations for the polarized gluon distribution in the proton. At higher
energies ( GeV) the situation appears less favourable with the
presently envisaged integrated luminosities of the polarized RHIC collider.Comment: 10 pages, LaTeX, with 5 eps figs included with epsfig.st
One-Loop Helicity Amplitudes for Parton Level Virtual Compton Scattering
We calculate the one-loop QCD virtual corrections to all helicity amplitudes
for parton level virtual Compton scattering processes. We include the
amplitudes both on quark target process and on gluon
target process . The infrared pole structure of the
amplitudes is in agreement with the prediction of Catani's general formalism
for the singularities of one-loop amplitudes, while expressions for the finite
remainder are given in terms of logarithms and dilogarithms that are real in
the physical region.Comment: 16 pages, 2 figures, detailed comparison with DVCS include
Polarized light-flavor antiquarks from Drell-Yan processes of h+\vec{N}\to\vec{l^{+-}} + l^{-+} + X
We propose a formula to determine the first moment of difference between the
polarized - and -quarks in the nucleon, {\it i.e.} from the Drell-Yan processes in collisions of unpolarized
hadrons with longitudinally polarized nucleons by measuring outgoing lepton
helicities. As coefficients in the differential cross section depend on the
- and -quark numbers in the unpolarized hadron beam, the difference
can be independently tested by changing the hadron
beam. Moreover, a formula for estimating the -factor in Drell-Yan processes
is also suggested.Comment: 10 pages, 1 figur
Color Octet Contribution to J/psi Photoproduction Asymmetries
We investigate photoproduction asymmetries in the framework of the
NRQCD factorization approach. It is shown that the color octet contribution
leads to large uncertainties in the predicted asymmetries which rules out the
possibility to precisely measure the gluon polarization in the nucleon through
this final state. For small values of the color octet parameters being
compatible with photoproduction data it appears possible that a
measurement of asymmetries could provide a new test for the NRQCD
factorization approach, on one hand, or a measurement of the polarized gluon
distribution from low inelasticity events , on the otherComment: 12 pages, LaTeX, with 6 figs. Final version published in Phys.Rev.
Spectroscopy of Heavy Mesons Expanded in 1/m_Q
Operating just once with the naive Foldy-Wouthuysen-Tani transformation on
the relativistic Fermi-Yang equation for bound states described by
the semi-relativistic Hamiltonian which includes Coulomb-like as well as
confining scalar potentials, we have calculated heavy meson mass spectra of D
and B together with higher spin states. Based on the formulation recently
proposed, their masses and wave functions are expanded up to the second order
in with a heavy quark mass and the lowest order equation is
examined carefully to obtain a complete set of eigenfunctions for the
Schr\"odinger equation. Heavy quark effective theory parameters, ,
, and , are also determined at the first and second order
in .Comment: 49 pages, 5 epsf figure
Polarized Parton Distribution Functions in the Nucleon
Polarized parton distribution functions are determined by using world data
from the longitudinally polarized deep inelastic scattering experiments. A new
parametrization of the parton distribution functions is adopted by taking into
account the positivity and the counting rule. From the fit to the asymmetry
data A_1, the polarized distribution functions of u and d valence quarks, sea
quarks, and gluon are obtained. The results indicate that the quark spin
content is \Delta\Sigma=0.20 and 0.05 in the leading order (LO) and the
next-to-leading-order (NLO) MS-bar scheme, respectively. However, if x
dependence of the sea-quark distribution is fixed at small x by "perturbative
QCD" and Regge theory, it becomes \Delta \Sigma=0.24 ~ 0.28 in the NLO. The
small-x behavior cannot be uniquely determined by the existing data, which
indicates the importance of future experiments. From our analysis, we propose
one set of LO distributions and two sets of NLO ones as the
longitudinally-polarized parton distribution functions.Comment: 51 pages, REVTeX, aps.sty, aps12.sty, epsfig.sty, prabib.sty,
revtex.sty, revtex.cls, 17 eps figures. Submitted for publication. Email:
[email protected]
Double-Spin Asymmetry of J/psi Production in Polarized pp Collisions at HERA-
We calculated the color-octet contribution to the double spin asymmetry of
hadroproduction with nonzero transverse momenta at fixed target
energies GeV. It is shown that the color-octet contribution
is dominant in the asymmetries. The expected asymmetries and statistical errors
in a future option of HERA with longitudinally polarized protons at HERA- should allow one to distinguish between different parametrizations for the
polarized gluon distribution in the proton.Comment: 14 pages with 6 figures (epsfig), LaTeX; Some figures are changed and
misprint is correcte
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