721 research outputs found
Scaling properties of direct photon yields in heavy ion collisions
A recent analysis from the PHENIX collaboration of available direct photon
measurement results in collisions of various systems such as Au+Au, Cu+Cu, and
Pb+Pb, at different beam energies ranging from 39 to 2760 GeV, has shown a
universal, within experimental uncertainties, scaling, in which
direct photon -spectra for transverse momenta up to 2 GeV/ are scaled
with charged hadron pseudorapidity density at midrapidity raised to power
. On the other hand, those direct photon -spectra also
exhibit scaling in the similar range. Assuming power-law
dependence of the scaled photon spectra for both scaling laws, we formulate two
independent conditions for the power , which overshoot experimental
data by on average. We discuss possible sources that might improve
this estimate.Comment: 8 pages, 5 figures. The paper has been rewritten, title has been
changed, new material and references added. Version accepted for publication
in EPJ C. In v3 references updated, minor typos correcte
Vanishing cycles and analysis of singularities of Feynman diagrams
In this work, we analyze vanishing cycles of Feynman loop integrals by means
of the Mayer-Vietoris spectral sequence. A complete classification of possible
vanishing geometries are obtained. We employ this result for establishing an
asymptotic expansion for the loop integrals near their singularity locus, then
give explicit formulas for the coefficients of such an expansion. The further
development of this framework may potentially lead to exact calculations of
one- and two-loop Feynman diagrams, as well as other next-to-leading and
higher-order diagrams, in studies of radiative corrections for upcoming
lepton-hadron scattering experiments.Comment: 22 pages and 3 figure
Lowest-order QED radiative corrections in unpolarized elastic electron-deuteron scattering beyond the ultra-relativistic limit for the proposed deuteron charge radius measurement at Jefferson Laboratory
Analogous to the well-known proton charge radius puzzle, a similar puzzle
exists for the deuteron charge radius, . There are discrepancies
observed in the results of , measured from electron-deuteron ()
scattering experiments, as well as from atomic spectroscopy. In order to help
resolve the charge radius puzzle of the deuteron, the PRad collaboration at
Jefferson Lab has proposed an experiment for measuring , named DRad.
This experiment is designed to measure the unpolarized elastic scattering
cross section in a low- region. To extract the cross section with a high
precision, having reliable knowledge of QED radiative corrections is important.
In this paper, we present complete numerical calculations of the lowest-order
radiative corrections in scattering for the DRad kinematics. The
calculations have been performed within a covariant formalism and beyond the
ultra-relativistic approximation (). Besides, we present a
systematic uncertainty on arising from higher-order radiative
corrections, estimated based on our cross-section results.Comment: 16 pages and 6 figure
SIDIS-RC EvGen: a Monte-Carlo event generator of semi-inclusive deep inelastic scattering with the lowest-order QED radiative corrections
SIDIS-RC EvGen is a C++ standalone Monte-Carlo event generator for studies of
semi-inclusive deep inelastic scattering (SIDIS) processes at medium to high
lepton beam energies. In particular, the generator contains binary and library
components for generating SIDS events and calculating cross sections for
unpolarized or longitudinally polarized beam and unpolarized, longitudinally or
transversely polarized target. The structure of the generator incorporates
transverse momentum-dependent parton distribution and fragmentation functions,
whereby we obtain multi-dimensional binned simulation results, which will
facilitate the extraction of important information about the three-dimensional
nucleon structure from SIDIS measurements. In order to build this software, we
have used recent elaborate QED calculations of the lowest-order radiative
effects, applied to the leading order Born cross section in SIDIS. In this
paper, we provide details on the theoretical formalism as well as the
construction and operation of SIDIS-RC EvGen, e.g., how we handle the event
generation process and perform multi-dimensional integration. We also provide
example programs, flowcharts, and numerical results on azimuthal transverse
single-spin asymmetries.Comment: 53 pages, 10 figures, and 3 listing
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