981 research outputs found
Non-identical particle correlation analysis as a probe of transverse flow
Non-identical two particle correlation functions probe asymmetries between
the average space-time emission points of different particle species. The
system collective expansion would produce such asymmetry because massive
particles, such as protons, are on average more pushed towards the edge of the
system, than lighter ones, i.e. pions. Measuring pion-kaon, pion-proton and
kaon-proton correlation functions, using the STAR detector, we show that the
data are consistent with the effect of transverse flow in Au-Au collisions at
GeV.Comment: 4 pages, 2 figures, 1 table, Contribution to Quark Matter 2002,
Nantes, France, July 200
Comment on "First Observation of Ground State Dineutron Decay: 16Be"
A recent measurement [Spyrou et al., PRL 108, 102501 (2012)] of the in-flight
decay of 16Be into 14Be+n+n has been interpreted as the first case of dineutron
emission. Here we point out that the inclusion of the n-n interaction neglected
in the description of the direct three-body decay can generate strong
enhancements at low n-n relative energy and angle, as observed, without any
need to invoke dineutron decay.Comment: Final version, published in Physical Review Letter
Finite-size effect on two-particle production in continuous and discrete spectrum
The formalism allowing one to account for the effect of a finite space-time
extent of particle production region is given. Its applications to the lifetime
measurement of hadronic atoms produced by a high-energy beam in a thin target,
as well as to the femtoscopy techniques widely used to measure space-time
characteristics of the production processes, are discussed. Particularly, it is
found that the neglect of the finite-size effect on the pionium lifetime
measurement in the experiment DIRAC at CERN could lead to the lifetime
overestimation comparable with the 10% statistical error. The theoretical
systematic errors arising in the calculation of the finite-size effect due to
the neglect of non-equal emission times in the pair center-of-mass system, the
space-time coherence and the residual charge are shown to be negligible.Comment: LaTeX, 77 pages including 5 tables and 18 figures. Somewhat extended
version to be published in Phys. El. Part. At. Nuc
Imaging Sources with Fast and Slow Emission Components
We investigate two-proton correlation functions for reactions in which fast
dynamical and slow evaporative proton emission are both present. In such cases,
the width of the correlation peak provides the most reliable information about
the source size of the fast dynamical component. The maximum of the correlation
function is sensitive to the relative yields from the slow and fast emission
components. Numerically inverting the correlation function allows one to
accurately disentangle fast dynamical from slow evaporative emission and
extract details of the shape of the two-proton source.Comment: 13 pages, 4 figure
Fast hadron freeze-out generator, part II: noncentral collisions
The fast Monte Carlo procedure of hadron generation developed in our previous
work is extended to describe noncentral collisions of nuclei. We consider
different possibilities to introduce appropriate asymmetry of the freeze-out
hyper-surface and flow velocity profile. For comparison with other models and
experimental data we demonstrate the results based on the standard
parametrizations of the hadron freeze-out hyper-surface and flow velocity
profile assuming either a common chemical and thermal freeze-out or the
chemically frozen evolution from chemical to thermal freeze-out. The C++
generator code is written under the ROOT framework and is available for public
use at http://uhkm.jinr.ru/Comment: 27 pages including 7 figures as EPS-files; prepared using LaTeX
package for publication in Physical Review
Quantum corrections for pion correlations involving resonance decays
A method is presented to include quantum corrections into the calculation of
two-pion correlations for the case where particles originate from resonance
decays. The technique uses classical information regarding the space-time
points at which resonances are created. By evaluating a simple thermal model,
the method is compared to semiclassical techniques that assume exponential
decaying resonances moving along classical trajectories. Significant
improvements are noted when the resonance widths are broad as compared to the
temperature.Comment: 9 pages, 4 figure
Bose-Einstein Correlations of Charged Kaons in Central Pb+Pb Collisions at
Bose-Einstein correlations of charged kaons were measured near mid-rapidity
in central Pb+Pb collisions at 158 AGeV by the NA49 experiment at the
CERN SPS. Source radii were extracted using the Yano-Koonin-Podgoretsky and
Bertsch-Pratt parameterizations. The results are compared to published pion
data. The measured dependence for kaons and pions is consistent with
collective transverse expansion of the source and a freeze-out time of about
9.5 .Comment: 14 pages with 7 figures, submitted to Phys. Lett.
Spin density matrix of the Ï in the reaction pÂŻpâÏÏ0
The spin density matrix of the Ï has been determined for the reaction pÂŻpâÏÏ0 with unpolarized in-flight data measured by the Crystal Barrel LEAR experiment at CERN. The two main decay modes of the Ï into Ï0Îł and Ï+Ï-Ï0 have been separately analyzed for various pÂŻ momenta between 600 and 1940 MeV/c. The results obtained with the usual method by extracting the matrix elements via the Ï decay angular distributions and with the more sophisticated method via a full partial wave analysis are in good agreement. A strong spin alignment of the Ï is clearly visible in this energy regime and all individual spin density matrix elements exhibit an oscillatory dependence on the production angle. In addition, the largest contributing orbital angular momentum of the pÂŻp system has been identified for the different beam momenta. It increases from LpÂŻpmax = 2 at 600 MeV/c to LpÂŻpmax = 5 at 1940 MeV/c
Determination of scattering lengths from measurement of atom lifetime
The DIRAC experiment at CERN has achieved a sizeable production of
atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave scattering length difference
has been attained, providing an important test of Chiral Perturbation Theory.Comment: 6 pages, 6 figure
- âŠ