932 research outputs found
Direct Photons in Nuclear Collisions at FAIR Energies
Using the extrapolation of existing data estimations of prompt photon
production at FAIR energies have been made. At the rapidity
density of prompt photons with 1.5 GeV/c per central Au+Au event at 25
AGeV is estimated as . With the planed beam intensity
per second and 1% interaction probability, for 10% of most central events one
can expect the prompt photon rate photons per second.
Direct photons from the hadron scenario of ion collisions generated by the
Hadron-String-Dynamics (HSD) transport approach with implemented meson
scatterings have been analyzed.
Photons from short-living resonances (e.g. )
decaying during the dense phase of the collision should be considered as direct
photons. They contribute significantly in the direct photon spectrum at
GeV/c. At the FAIR energy 25 AGeV in Au+Au central collisions
the HSD generator predicts, as a lower estimate,
0.5% in the region
GeV/c. At GeV/c 2%.
Thermal direct photons have been evaluated with the Bjorken Hydro-Dynamics
(BHD) model. The BHD spectra differ strongly from the HSD predictions. The
direct photon spectrum is very sensitive to the initial temperature parameter
of the model. The 10 MeV increase in the value leads to
2 times higher photon yield.Comment: 9 pages, 5 figures, Talk at the session of Russian Academy of
Sciences, ITEP, Moscow, 26 - 30 November 200
Polarized semi-inclusive electroweak structure functions at next-to-leading-order
We present a next-to-leading order (NLO) computation of the full set of
polarized and unpolarized electroweak semi-inclusive DIS (SIDIS) structure
functions, whose knowledge is crucial for a precise extraction of polarized
parton distributions. We focus on the phenomenology of the polarized structure
functions for the kinematical conditions that could be reached in an
Electron-Ion-Collider.
We show that the NLO corrections are sizeable, particularly in the small-
range. We test the sensitivity of these structure functions on certain quark
distributions and compare it to the situation of inclusive DIS and
electromagnetic SIDIS.Comment: 17 pages, 5 figure
The relationship between renal function and renal urodilatin excretion immediately after cardiac surgery
Single Transverse-Spin Asymmetry in Drell-Yan Production at Large and Moderate Transverse Momentum
We study the single-transverse spin asymmetry for the Drell-Yan process. We
consider production of the lepton pair at large transverse momentum,
, where is the pair's mass. The spin asymmetry is then of
higher twist and may be generated by twist-three quark-gluon correlation
functions. Expanding the result for , we make contact with the
transverse-momentum-dependent QCD factorization involving the so-called Sivers
functions. We find that the two mechanisms, quark-gluon correlations on one
hand and the Sivers effect on the other, contain the same physics in this
region. This ties the two together and imposes an important constraint on
phenomenological studies of single transverse spin asymmetries.Comment: 29 pages, 10 figure
Drell-Yan forward-backward and spin asymmetries for arbitrary vector boson production at next-to-leading order
Longitudinally polarized, unpolarized and forward-backward mass differential
cross sections for Drell-Yan lepton-pair production by arbitrary vector bosons
are calculated in next-to-leading order (NLO) QCD. Analytical results are
presented in a form valid for all consistent -dimensional regularization
schemes, with the mass factorization scheme kept general. NLO predictions for
all Drell-Yan type processes (, and ) at BNL's
relativistic heavy ion collider (RHIC) are made using polarized parton
distributions which fit the recent deep-inelastic scattering data. These are
examined as tools in the determination of the polarized parton distributions
and the unpolarized ratio. NLO predictions for the
forward-backward lepton asymmetry at Fermilab are made and the precision
determination of from future runs is studied. In all the
above, the QCD corrections are found to be significant. An introductory
discussion is given of various theoretical issues, such as allowable
factorization and regularization schemes, and scale dependences.Comment: 34 pages, figures included, revtex. Some discussions and references
added/modified. In more compact form. To appear in Phys. Rev.
Next-to-leading order QCD corrections to spin-dependent hadron-pair photoproduction
We compute the next-to-leading order QCD corrections to the ``direct'' part
of the spin-dependent cross section for hadron-pair photoproduction. The
calculation is performed using largely analytical methods. We present a brief
phenomenological study of our results focussing on the -factors and scale
dependence of the next-to-leading order cross sections. This process is
relevant for the extraction of the gluon polarization in present and future
spin-dependent lepton-nucleon scattering experiments.Comment: 9 pages, 2 eps figure
Spin Structure Function of the Virtual Photon Beyond the Leading Order in QCD
Polarized photon structure can be studied in the future polarized
colliding-beam experiments. We investigate the spin-dependent
structure function of the virtual photon , in
perturbative QCD for , where () is the
mass squared of the probe (target) photon. The analysis is performed to
next-to-leading order in QCD. We particularly emphasize the renormalization
scheme independence of the result.The non-leading corrections significantly
modify the leading log result, in particular, at large as well as at small
. We also discuss the non-vanishing first moment sum rule of ,
where corrections are computed.Comment: 39 pages, LaTeX, 6 Postscript Figures, eqsection.sty file include
Next-to-Leading Order Analysis of Inclusive and Semi-inclusive Polarized Data
We present a combined next-to-leading order QCD analysis to data on both
inclusive and semi-inclusive polarized deep inelastic scattering asymmetries.
Performing NLO QCD global fits with different sets of observables, we evaluate
the impact of the very recent semi-inclusive results presented by SMC in the
extraction of NLO polarized parton distributions.Comment: 22 pages, 4 figures include
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