1,274 research outputs found
Analysis of Cumulant Moments in High Energy Hadron-Hadron Collisions by Truncated Multiplicity Distributions
Oscillatory behavior of cumulant moments obtained from the experimental data
in collisions and collisions are analyzed by the modified
negative binomial distribution (MNBD) and the negative binomial distribution
(NBD). Both distributions well describe the cumulant moments obtained from the
data. This fact shows sharp contrast to the result in collisions,
which is described by the the MNBD much better than by the NBD.Comment: 7 pages, Latex type, 7 figure
, K and f Production in Au-Au and pp Collisions at = 200 GeV
Preliminary results on , KK and production using the mixed-event
technique are presented. The measurements are performed at mid-rapidity by the
STAR detector in = 200 GeV Au-Au and pp interactions at RHIC.
The results are compared to different measurements at various energies.Comment: 4 pages, 6 figures. Talk presented at Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Photon Production from a Quark--Gluon Plasma
In-medium interactions of a particle in a hot plasma are considered in the
framework of thermal field theory. The formalism to calculate gauge invariant
rates for photon and dilepton production from the medium is given. In the
application to a QED plasma, astrophysical consequences are pointed out. The
photon production rate from strongly interacting quarks in the quark--gluon
plasma, which might be formed in ultrarelativistic heavy ion collisions, is
calculated in the previously unaccessible regime of photon energies of the
order of the plasma temperature. For temperatures below the chiral phase
transition, an effective field theory incorporating dynamical chiral symmetry
breaking is employed, and perturbative QCD at higher temperatures. A smooth
transition between both regions is obtained. The relevance to the soft photon
problem and to high energy heavy ion experiments is discussed.Comment: Paper in ReVTeX. Figures and complete paper available via anonymous
ftp, ftp://tpri6c.gsi.de/pub/phenning/hq95ga
A Transient New Coherent Condition of Matter: The Signal for New Physics in Hadronic Diffractive Scattering
We demonstrate the existence of an anomalous structure in the data on the
diffractive elastic scattering of hadrons at high energies and small momentum
transfer. We analyze five sets of experimental data on
scattering from five different experiments with colliding beams, ranging from
the first-- and second--generation experiments at GeV to the
most recent experiments at 546 GeV and at 1800 GeV. All of the data sets
exhibit a localized anomalous structure in momentum transfer. We represent the
anomalous behavior by a phenomenological formula. This is based upon the idea
that a transient coherent condition of matter occurs in some of the
intermediate inelastic states which give rise, via unitarity, to diffractive
elastic scattering. The Fourier--Bessel transform into momentum--transfer space
of a spatial oscillatory behavior of matter in the impact--parameter plane
results in a small piece of the diffractive amplitude which exhibits a
localized anomalous behavior near a definite value of . In addition, we
emphasize possible signals coming directly from such a new condition of matter
that may be present in current experiments on inelastic processes.Comment: 25 pages, LaTeX (12 figures, not included). A complete postscript
file (except figures 1 and 11, which are available upon request) is available
via anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as
/ttp94-03 /ttp94-03.ps, Local preprint# TTP94-03 (March 1994
Mass Suppression in Octet Baryon Production
There is a striking suppression of the cross section for production of octet
baryons in annihilation, as the mass of the produced hadron
increases. We present a simple parametrization for the fragmentation functions
into octet baryons guided by two input models: the SU(3) flavor symmetry part
is given by a quark-diquark model, and the baryon mass suppression part is
inspired by the string model. We need only eight free parameters to describe
the fragmentation functions for all octet baryons. These free parameters are
determined by a fit to the experimental data of octet baryon production in annihilation. Then we apply the obtained fragmentation functions to
predict the cross section of the octet baryon production in charged lepton DIS
and find consistency with the available experimental data. Furthermore, baryon
production in collisions is suggested to be an ideal domain to check the
predicted mass suppression.Comment: 20 pages, 5 figure
Leading particle effect, inelasticity and the connection between average multiplicities in {\bf } and {\bf } processes
The Regge-Mueller formalism is used to describe the inclusive spectrum of the
proton in collisions. From such a description the energy dependences of
both average inelasticity and leading proton multiplicity are calculated. These
quantities are then used to establish the connection between the average
charged particle multiplicities measured in {\bf } and {\bf } processes. The description obtained for the leading proton cross section
implies that Feynman scaling is strongly violated only at the extreme values of
, that is at the central region () and at the diffraction
region (), while it is approximately observed in the
intermediate region of the spectrum.Comment: 20 pages, 10 figures, to be published in Physical Review
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
First atom lifetime and scattering length measurements
The results of a search for hydrogen-like atoms consisting of
mesons are presented. Evidence for atom production
by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen
in terms of characteristic pairs from their breakup in the same target
() and from Coulomb final state interaction (). Using
these results the analysis yields a first value for the atom lifetime
of fs and a first model-independent measurement of
the S-wave isospin-odd scattering length
( for isospin ).Comment: 14 pages, 8 figure
Evidence for an Excess of Soft Photons in Hadronic Decays of Z^0
Soft photons inside hadronic jets converted in front of the DELPHI main
tracker (TPC) in events of qqbar disintegrations of the Z^0 were studied in the
kinematic range 0.2 < E_gamma < 1 GeV and transverse momentum with respect to
the closest jet direction p_T < 80 MeV/c. A clear excess of photons in the
experimental data as compared to the Monte Carlo predictions is observed. This
excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/-
0.27) x 10^{-3} gamma/jet in the specified kinematic region, while the expected
level of the inner hadronic bremsstrahlung (which is not included in the Monte
Carlo) is (0.340 +/- 0.001 +/- 0.038) x 10^{-3} gamma/jet. The ratio of the
excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8),
which is similar in strength to the anomalous soft photon signal observed in
fixed target experiments with hadronic beams.Comment: 37 pages, 9 figures, Accepted by Eur. Phys. J.
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