2,649 research outputs found
Nonlocal symmetries of integrable two-field divergent evolutionary systems
Nonlocal symmetries for exactly integrable two-field evolutionary systems of
the third order have been computed. Differentiation of the nonlocal symmetries
with respect to spatial variable gives a few nonevolutionary systems for each
evolutionary system. Zero curvature representations for some new nonevolution
systems are presented
Production of para-- and orthopositronium at relativistic heavy ion colliders
We consider the ortho-- and parapositronium production in the process Ps where A is a nucleus with the charge number Z. The inclusive cross
section and the energy distribution of the relativistic Ps are calculated which
are of primary interest from the experimental point of view. The accuracy of
the corresponding cross sections is given by omitting terms for the para--Ps and for the ortho--Ps production
where and 16 for the RHIC and the LHC. Within this
accuracy the multiphoton (Coulomb) corrections are taken into account. We show
that the RHIC and the LHC will be Ps factories with a productions rate of about
relativistic Ps per day. The fraction of the ortho--Ps is
expected to be of the same order as that of the para--Ps for Au--Au and Pb--Pb
collisions.Comment: 22 pages, 5 figures, RevTeX, misprint correcte
Status of the NICA project at JINR
AbstractThe NICA (Nuclotron-based Ion Collider fAcility) project is now under active realization at the Joint Institute for Nuclear Research (JINR, Dubna). The main goal of the project is a study of hot and dense strongly interacting matter in heavy ion (up to Au) collisions at the centre-of-mass energies up to 11 GeV per nucleon. Two modes of operation are foreseen, collider mode and extracted beams, with two detectors: MPD and BM@N. The both experiments are in preparation stage. An average luminosity in the collider mode is expected as 10E27 cm-2 s-1 for Au (79+). Extracted beams of various nucleus species with maximum momenta of 13 GeV/c (for protons) will be available. A study of spin physics with extracted and colliding beams of polarized deuterons and protons at the energies up to 27 GeV (for protons) is foreseen with the NICA facility. The proposed program allows one to search for possible signs of phase transitions and critical phenomena as well as to shed light on the problem of thenucleon spin structure
Binary collisions of charged particles in a magnetic field
Binary collisions between charged particles in an external magnetic field are
considered in second-order perturbation theory, starting from the unperturbed
helical motion of the particles. The calculations are done with the help of an
improved binary collisions treatment which is valid for any strength of the
magnetic field, where the second-order energy and velocity transfers are
represented in Fourier space for arbitrary interaction potentials. The energy
transfer is explicitly calculated for a regularized and screened potential
which is both of finite range and non-singular at the origin, and which
involves as limiting cases the Debye (i.e., screened) and Coulomb potential.
Two distinct cases are considered in detail. (i) The collision of two identical
(e.g., electron-electron) particles; (ii) and the collision between a
magnetized electron and an uniformly moving heavy ion. The energy transfer
involves all harmonics of the electron cyclotron motion. The validity of the
perturbation treatment is evaluated by comparing with classical trajectory
Monte--Carlo calculations which also allows to investigate the strong
collisions with large energy and velocity transfer at low velocities. For large
initial velocities on the other hand, only small velocity transfers occur.
There the non-perturbative numerical classical trajectory Monte--Carlo results
agree excellently with the predictions of the perturbative treatment.Comment: submitted to Phys. Rev.
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