102 research outputs found
Multiboson effects in multiparticle production
The influence of multiboson effects on pion multiplicities, single-pion
spectra and two-pion correlation functions is discussed in terms of an
analytically solvable model. The applicability of its basic factorization
assumption is clarified. An approximate scaling of the basic observables with
the phase space density is demonstrated in the low density (gas) limit. This
scaling and also its violation at high densities due to the condensate
formation is described by approximate analytical formulae which allow, in
principle, for the identification of the multiboson effects among others. For
moderate densities indicated by the experimental data, a fast saturation of
multiboson effects with the number of contributing cumulants is obtained,
allowing for the account of these effects in realistic transport code
simulations. At high densities, the spectra are mainly determined by the
universal condensate term and the initially narrow Poisson multiplicity
distribution approaches a wide Bose-Einstein one. As a result, the intercepts
of the inclusive and fixed- correlation functions (properly normalized to 1
at large relative momenta) approach 2 and 1, respectively and their widths
logarithmically increase with the increasing phase space density. It is shown
that the neglect of energy-momentum constraints in the model is justified
except near a multipion threshold, where these constraints practically exclude
the possibility of a very cold condensate production. It is argued that
spectacular multiboson effects are likely to be observed only in the rare
events containing sufficiently high density (speckle) fluctuations.Comment: 30 pages including 10 figures, LaTex, a revised version of SUBATECH
99-04 (aps1999_mar21_001) resubmitted to Phys. Rev. C; Chapter II made
shorter, figure description made more clear, a comparison with most recent
works added in Chapter V
Statistics of delay times in mesoscopic systems as a manifestation of eigenfunction fluctuations
We reveal a general explicit relation between the statistics of delay times
in one-channel reflection from a mesoscopic sample of any spatial dimension and
the statistics of the eigenfunction intensities in its closed counterpart. This
opens a possibility to use experimentally measurable delay times as a sensitive
probe of eigenfunction fluctuations. For the particular case of quasi-one
dimensional geometry of the sample we use an alternative technique to derive
the probability density of partial delay times for any number of open channels.Comment: 12 pages; published version with updated reference
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
Reducing nonideal to ideal coupling in random matrix description of chaotic scattering: Application to the time-delay problem
We write explicitly a transformation of the scattering phases reducing the
problem of quantum chaotic scattering for systems with M statistically
equivalent channels at nonideal coupling to that for ideal coupling. Unfolding
the phases by their local density leads to universality of their local
fluctuations for large M. A relation between the partial time delays and
diagonal matrix elements of the Wigner-Smith matrix is revealed for ideal
coupling. This helped us in deriving the joint probability distribution of
partial time delays and the distribution of the Wigner time delay.Comment: 4 pages, revtex, no figures; published versio
Vacuum-field level shifts in a single trapped ion mediated by a single distant mirror
A distant mirror leads to a vacuum-induced level shift in a laser-excited
atom. This effect has been measured with a single mirror 25 cm away from a
single, trapped barium ion. This dispersive action is the counterpart to the
mirror's dissipative effect, which has been shown earlier to effect a change in
the ion's spontaneous decay [J. Eschner et al., Nature 413, 495-498 (2001)].
The experimental data are well described by 8-level optical Bloch equations
which are amended to take into account the presence of the mirror according to
the model in [U. Dorner and P. Zoller, Phys. Rev. A 66, 023816 (2002)].
Observed deviations from simple dispersive behavior are attributed to
multi-level effects.Comment: version accepted by PR
Tensor polarization of deuterons passing through matter
It is shown that the magnitude of tensor polarization of the deuteron beam,
which arises owing to the spin dichroism effect, depends appreciably on the
angular width of the detector that registers the deuterons transmitted through
the target. Even when the angular width of the detector is much smaller than
the mean square angle of multiple Coulomb scattering, the beam's tensor
polarization depends noticeably on rescattering. When the angular width of the
detector is much larger than the mean square angle of multiple Coulomb
scattering (as well as than the characteristic angle of elastic nuclear
scattering), tensor polarization is determined only by the total reaction cross
sections for deuteron-nucleus interaction, and elastic scattering processes
make no contribution to tensor polarization.Comment: 18 pages, 3 figures, to be published in IO
Production of relativistic positronium in collisions of photons and electrons with nuclei and atoms
We consider the production of ultrarelativistic positronium (Ps) in and processes where is an atom or a nucleus
with charge . For the photoproduction of para- and ortho-Ps and the
electroproduction of para-Ps we obtain the most complete description compared
with previous works. It includes high order corrections and
polarization effects. The accuracy of the obtained cross sections is determined
by omitted terms of the order of the inverse Ps Lorentz factor squared. The
studied high order multi-photon electroproduction of ortho-Ps dominates for the
collision of electrons with heavy atoms over the bremsstrahlung production from
the electron via a virtual photon proposed by Holvik and Olsen. Our results
complete and correct the studies of those authors.Comment: 19 pages, 9 figures, RevTex; v2: minor corrections for the accuracy
of the results, a discussion of the literature added in a footnote, one
additional reference; v3: diagram of Fig.2 correcte
Particle Correlations with Heavy Ions at LHC Energies
The ALICE detector will offer very good conditions to study the space-time characteristics of particle production in heavy-ion collisions at LHC from measurements of the correlation function of identical and non-identical particles at small relative velocities. The correlations - induced by Coulomb and nuclear final-state interactions - of non-identical particles appear to be directly sensitive to the space-time asymmetries of particle production allowing, in particular, a measurement of the mean relative delays in particle emission at time scales as small as few fm/c. The problem of Coulomb interaction of the correlated particles is particularly important in the case of the large effective volumes formed in ultra-relativistic heavy-ion reactions
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