675 research outputs found
Energy dependence of pion and kaon production in central Pb+Pb collisions
Measurements of charged pion and kaon production in central Pb+Pb collisions at 40, 80 and 158 AGeV are presented. These are compared with data at lower and higher energies as well as with results from p+p interactions. The mean pion multiplicity per wounded nucleon increases approximately linearly with s_NN^1/4 with a change of slope starting in the region 15-40 AGeV. The change from pion suppression with respect to p+p interactions, as observed at low collision energies, to pion enhancement at high energies occurs at about 40 AGeV. A non-monotonic energy dependence of the ratio of K^+ to pi^+ yields is observed, with a maximum close to 40 AGeV and an indication of a nearly constant value at higher energies.The measured dependences may be related to an increase of the entropy production and a decrease of the strangeness to entropy ratio in central Pb+Pb collisions in the low SPS energy range, which is consistent with the hypothesis that a transient state of deconfined matter is created above these energies. Other interpretations of the data are also discussed
Direct Fragmentation of Quarkonia Including Fermi Motion Using Light-cone Wave Function
We investigate the effect of Fermi motion on the direct fragmentation of the
and states employing a light-cone wave function. Consistent
with such a wave function we set up the kinematics of a heavy quark fragmenting
into a quarkonia such that the Fermi motion of the constituents split into
longitudinal as well as transverse direction and thus calculate the
fragmentation functions for these states. In the framework of our
investigation, we estimate that the fragmentation probabilities of and
may increase at least up to 14 percent when including this degree of
freedom.Comment: 7 pages 5 figures Appeared in EPJC; Fig 1 and Appendix revise
High-contrast dark resonance on the D2 - line of 87Rb in a vapor cell with different directions of the pump - probe waves
We propose a novel method enabling to create a high-contrast dark resonance
in the 87Rb vapor D2-line. The method is based on an optical pumping of atoms
into the working states by a two-frequency, linearly-polarized laser radiation
propagating perpendicularly to the probe field. This new scheme is compared to
the traditional scheme involving the circularly-polarized probe beam only, and
significant improvement of the dark resonance parameters is found. Qualitative
considerations are confirmed by numerical calculations.Comment: 7 pages, 4 figure
On tests of local realism by CP-violation parameters of K^0 mesons
Recently various papers have proposed to test local realism (LR) by
considering electroweak CP-violation parameters values in neutral pseudoscalar
meson systems. Considering the large interest for a conclusive test of LR and
the experimental accessibility to these tests, in this paper we critically
consider these results showing how they, albeit very interesting, require
anyway additional assumptions and therefore cannot be considered conclusive
tests of LR
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