1,092 research outputs found
A Unified Picture for Single Transverse-Spin Asymmetries in Hard Processes
Using Drell-Yan pair production as an example, we explore the relation
between two well-known mechanisms for single transverse-spin asymmetries in
hard processes: twist-three quark-gluon correlations when the pair's transverse
momentum is large, , and time-reversal-odd and
transverse-momentum-dependent parton distributions when is much less
than the pair's mass. We find that although the two mechanisms have their own
domain of validity, they describe the same physics in the kinematic region
where they overlap. This unifies the two mechanisms and imposes an important
constraint on phenomenological studies of single spin asymmetries.Comment: 4 pages, 3 figure
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
Conatraints on from Prompt Photon plus Jet Production at HERA-
The utility of prompt photon plus associated jet production for constraining
the size and shape of the polarized gluon density of the proton is
examined at GeV, appropriate for the proposed HERA-
polarized collider experiment. The calculation is performed at
next-to-leading order (O()) in QCD. The reliability of the
predictions are examined in some detail.Comment: 16 pages, 3 figure
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
QCD corrections to the longitudinally polarized Drell-Yan process
In this paper we calculate the O() corrections to the - and
-distributions of lepton pairs produced in collisions of longitudinally
polarized hadrons. The numerical importance of these corrections is studied and
consequences for the extraction of the polarized sea quark distributions from a
measurement of the longitudinally polarized Drell-Yan cross section are
discussed.Comment: 21 pages, LaTeX, 8 figures include
Effects of the large gluon polarization on and J/ productions at polarized ep and pp collisions
The recent SMC data of are reproduced with the large polarized
gluons. To study further the polarized gluon distribution in a proton, we
calculate the spin--dependent differential cross section for J/
leptoproductions and the two--spin asymmetry for J/ hadroproductions. Its
experimental implication is discussed.Comment: LaTeX file, 10 pages+6 figures available upon request, KOBE-FHD-93-0
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