3,384 research outputs found
Nucleus-Nucleus Bremsstrahlung from Ultrarelativistic Collisions
The bremsstrahlung produced when heavy nuclei collide is estimated for
central collisions at the Relativistic Heavy Ion Collider. Soft photons can be
used to infer the rapidity distribution of the outgoing charge. An experimental
design is outlined.Comment: 12 pages, 7 figures, uses revte
Strange Particle Production in p+p, p+Pb and Pb+Pb Interactions from NA49
Recent NA49 results on Lambda, Antilambda, Xi- and Antixi+ production in
minimum bias p+p and centrality selected p+Pb collisions at 158 GeV/c, and the
results on Lambda, Antilambda, K+ and K- production in central Pb+Pb collisions
at 40, 80 and 158 A GeV are discussed and compared with other available data.
By comparing the energy dependence of Lambda and Antilambda production at
mid-rapidity a striking similarity is observed between p+p and A+A data. This
is also seen in the energy dependence of the Lambda/pi ratio. K+/pi at
mid-rapidity is affected in a similar way, due to the associated production of
K+ together with Lambda particles. The observed yields increase faster than the
number of wounded nucleons when comparing p+Pb to p+p. As already observed in
A+A collisions, the increase is larger for multistrange than for strange
baryons and for baryons than for anti-baryons.Comment: 8 pages, 10 figures, To appear in proceedings of Strange Quark in
Matter 2001-A Flavourspace Odyssey, Frankfurt am Main, Germany, 24-29. Sept.
200
Hanbury-Brown--Twiss Analysis in a Solvable Model
The analysis of meson correlations by Hanbury-Brown--Twiss interferometry is
tested with a simple model of meson production by resonance decay. We derive
conditions which should be satisfied in order to relate the measured momentum
correlation to the classical source size. The Bose correlation effects are
apparent in both the ratio of meson pairs to singles and in the ratio of like
to unlike pairs. With our parameter values, we find that the single particle
distribution is too distorted by the correlation to allow a straightforward
analysis using pair correlation normalized by the singles rates. An analysis
comparing symmetrized to unsymmetrized pairs is more robust, but nonclassical
off-shell effects are important at realistic temperatures.Comment: 21 pages + 9 figures (tarred etc. using uufiles, submitted
separately), REVTeX 3.0, preprint number: DOE/ER/40561-112/INT93-00-3
Event-by-event fluctuations in collective quantities
We discuss an event-by-event fluctuation analysis of particle production in
heavy ion collisions. We compare different approaches to the evaluation of the
event-by-event dynamical fluctuations in quantities defined on groups of
particles, such quantities as mean transverse momentum, transverse momentum
spectra slope, strength of anisotropic flow, etc.. The direct computation of
the dynamical fluctuations and the sub-event method are discussed in more
detail. We also show how the fluctuation in different variables can be related
to each other.Comment: LaTex, 14 pages and 5 figures. 2 references adde
Time Dependence of Chemical Freeze-out in Relativistic Heavy Ion Collisions
We investigate chemical and thermal freeze-out time dependencies for strange
particle production for CERN SPS heavy ion collisions in the framework of a
dynamical hadronic transport code. We show that the Lambda yield changes
considerably after hadronization in the case of Pb+Pb collisions, whereas for
smaller system sizes (e.g. S+S) the direct particle production dominates over
production from inelastic rescattering. Chemical freeze-out times for strange
baryons in Pb+Pb are smaller than for non-strange baryons, but they are still
sufficiently long for hadronic rescattering to contribute significantly to the
final Lambda yield. Based on inelastic and elastic cross section estimates we
expect the trend of shorter freeze-out times (chemical and kinetic), and thus
less particle production after hadronization, to continue for multi-strange
baryons.Comment: 10 pages, 7 postscript figure
Pentaquarks: review of the experimental evidence
Pentaquarks, namely baryons made by 4 quarks and one antiquark have been
predicted and searched for since several decades without success. Theoretical
and experimental advances in the last 2 years led to the observation of a
number of pentaquark candidates. We review the experimental evidence for
pentaquarks as well as their non-observations by some experiments, and discuss
to which extend these sometimes contradicting informations may lead to a
consistent picture.Comment: Contribution to the International Conference on 'Strangeness in Quark
Matter', 15-21 Sept. 2004, Cape Tawn, South Afric
Energy dependence of kaon production in central Pb+Pb collisions
Recent results from the NA49 experiment on the energy dependence of charged
kaon production in central Pb+Pb collisions are presented. First results from
the new data at 80 AGeV beam energy are compared with those from lower and
higher energies. A difference in the energy dependence of the /
and / ratios is observed. The / ratio shows a
non-monotonic behaviour with a maximum near 40 AGeV.Comment: 8 pages, 7 figures, proceedings of talk at SQM2001, Frankfurt,
Germany, to appear in J. Phys.
Emission times and opacities from interferometry in non-central Relativistic Nuclear Collisions
The nuclear overlap zone in non-central relativistic heavy ion collisions is
azimuthally very asymmetric. By varying the angle between the axes of
deformation and the transverse direction of the pair momenta, the transverse
HBT radii oscillate in a characteristic way. It is shown that these
oscillations allow determination of source sizes, deformations as well as the
opacity and duration of emission of the source created in any non-central high
energy nuclear collisions. The behavior of the physical quantities with
centrality of the collisions is discussed --- in particular changes caused by a
possible phase transition to a quark-gluon plasma.Comment: Revised version, to appear in Phys. Rev. Letter
Interferometry of Direct Photons in Central 280Pb+208Pb Collisions at 158A GeV
Two-particle correlations of direct photons were measured in central
208Pb+208Pb collisions at 158 AGeV. The invariant interferometric radii were
extracted for 100<K_T<300 MeV/c and compared to radii extracted from charged
pion correlations. The yield of soft direct photons, K_T<300 MeV/c, was
extracted from the correlation strength and compared to theoretical
calculations.Comment: 5 pages, 4 figure
Bulk properties and flow
In this report, I summarize the experimental results on {\bf bulk properties
and flow} presented at Quark Matter 2004. It is organized in four sections: 1)
Initial condition and stopping; 2) Particle spectra and freeze-outs; 3)
Anisotropic flow; 4) Outlook for future measurements.Comment: 10 pages, 4 figures, "Rapporteur-Conference Highlights", Quark Matter
2004, Oakland, January 11-1
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