11,467 research outputs found
Exclusive diffractive electroproduction of dijets in collinear factorization
Exclusive electroproduction of hard dijets can be described within the
collinear factorization. This process has clear experimental signature and
provides one with an interesting alternative venue to test QCD description of
hard diffractive processes and extract information on generalized nucleon
parton distributions. In this work we present detailed leading-order QCD
calculations of the relevant cross sections, including longitudinal momentum
fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st
On zero-divisors in group rings of groups with torsion
Nontrivial pairs of zero-divisors in group rings are introduced and
discussed. A problem on the existence of nontrivial pairs of zero-divisors in
group rings of free Burnside groups of odd exponent is solved in the
affirmative. Nontrivial pairs of zero-divisors are also found in group rings of
free products of groups with torsion.Comment: 8 pages, to appear in Canadian Math. Bul
Transverse-Mass Effective Temperature in Heavy-Ion Collisions from AGS to SPS
Transverse-mass spectra in Au+Au and Pb+Pb collisions in incident energy
range from 2A to 160A GeV are analyzed within the model of 3-fluid dynamics. It
is shown that dynamical description of freeze-out, accepted in this model,
naturally explains the incident energy behavior of inverse-slope parameters of
these spectra observed in experiment. Simultaneous reproduction of the
inverse-slopes of all considered particles (protons, pions and kaons) suggests
that these particles belong to the same hydrodynamic flow at the instant of
their freeze-out.Comment: 4 pages, 3 figure
Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario
A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions
is introduced. Alongside with two baryon-rich fluids, the new model considers
time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic
charge) fluid of newly produced particles. Its evolution is delayed due to a
formation time, during which the baryon-free fluid neither thermalizes nor
interacts with the baryon-rich fluids. After the formation it starts to
interact with the baryon-rich fluids and quickly gets thermalized. Within this
model with pure hadronic equation of state, a systematic analysis of various
observables at incident energies between few and about 160A GeV has been done
as well as comparison with results of transport models. We have succeeded to
reasonably reproduce a great body of experimental data in the incident energy
range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity
distributions, proton transverse-mass spectra, rapidity distributions of Lambda
and antiLambda hyperons, elliptic flow of protons and pions (with the exception
of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons,
hyperons and antihyperons, including multi-strange particles. This agreement is
achieved on the expense of substantial enhancement of the interflow friction as
compared to that estimated proceeding from hadronic free cross sections.
However, we have also found out certain problems. The calculated yield of K^-
is approximately by a factor of 1.5 higher than that in the experiment. We have
also failed to describe directed transverse flow of protons and pion at E_{lab}
> 40A GeV. This failure apparently indicates that the used EoS is too hard and
thereby leaves room for a phase transition.Comment: 30 pages, 20 figures, 2 tables. Version accepted for publication in
Phys. Rev.
Electroproduction of Soft Pions at Large Momentum Transfers
We consider pion electroproduction on a proton target close to threshold for
Q^2 in the region 1-10 GeV^2. The momentum transfer dependence of the S-wave
multipoles at threshold, E_{0+} and L_{0+}, is calculated using light-cone sum
rules.Comment: 8 pages, 3 figures; Invited talk at the workshop on Exclusive
Reactions at High Momentum Transfer, 21-24 May 2007, Newport News, Virginia,
U.S.A. and International Conference on hadron Physics TROIA'07, 30 Aug. - 3
Sept. 2007, Canakkale, Turke
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