219 research outputs found
SINFONI in the Galactic Center: young stars and IR flares in the central light month
We report 75 milli-arcsec resolution, near-IR imaging spectroscopy within the
central 30 light days of the Galactic Center [...]. To a limiting magnitude of
K~16, 9 of 10 stars in the central 0.4 arcsec, and 13 of 17 stars out to 0.7
arcsec from the central black hole have spectral properties of B0-B9, main
sequence stars. [...] all brighter early type stars have normal rotation
velocities, similar to solar neighborhood stars. We [...] derive improved 3d
stellar orbits for six of these S-stars in the central 0.5 arcsec. Their
orientations in space appear random. Their orbital planes are not co-aligned
with those of the two disks of massive young stars 1-10 arcsec from SgrA*. We
can thus exclude [...] that the S-stars as a group inhabit the inner regions of
these disks. They also cannot have been located/formed in these disks [...].
[...] we conclude that the S-stars were most likely brought into the central
light month by strong individual scattering events. The updated estimate of
distance to the Galactic center from the S2 orbit fit is Ro = 7.62 +/- 0.32
kpc, resulting in a central mass value of 3.61 +/- 0.32 x 10^6 Msun. We
happened to catch two smaller flaring events from SgrA* [...]. The 1.7-2.45 mum
spectral energy distributions of these flares are fit by a featureless, red
power law [...]. The observed spectral slope is in good agreement with
synchrotron models in which the infrared emission comes from [...] radiative
inefficient accretion flow in the central R~10 Rs region.Comment: 50 pages, 10 figures, 2 tables, submitted to ApJ, February 6th, 2005,
abstract abridge
The RHIC zero-degree calorimeters
Abstract The RHIC zero-degree calorimeters provide common event characterization in the four heavy ion experiments which recently completed their first data taking run. Here, we describe simulations which lead to the design of these devices, teastbeam performance and initial experience at RHIC.
Strangeness Enhancement in and Interactions at SPS Energies
The systematics of strangeness enhancement is calculated using the HIJING and
VENUS models and compared to recent data on , and
collisions at CERN/SPS energies (). The HIJING model is used to
perform a {\em linear} extrapolation from to . VENUS is used to
estimate the effects of final state cascading and possible non-conventional
production mechanisms. This comparison shows that the large enhancement of
strangeness observed in collisions, interpreted previously as possible
evidence for quark-gluon plasma formation, has its origins in non-equilibrium
dynamics of few nucleon systems. % Strangeness enhancement %is therefore traced
back to the change in the production dynamics %from to minimum bias
and central collisions. A factor of two enhancement of at
mid-rapidity is indicated by recent data, where on the average {\em one}
projectile nucleon interacts with only {\em two} target nucleons. There appears
to be another factor of two enhancement in the light ion reaction relative
to , when on the average only two projectile nucleons interact with two
target ones.Comment: 29 pages, 8 figures in uuencoded postscript fil
Charged Particle Production in Proton-, Deuteron-, Oxygen- and Sulphur-Nucleus Collisions at 200 GeV per Nucleon
The transverse momentum and rapidity distributions of net protons and
negatively charged hadrons have been measured for minimum bias proton-nucleus
and deuteron-gold interactions, as well as central oxygen-gold and
sulphur-nucleus collisions at 200 GeV per nucleon. The rapidity density of net
protons at midrapidity in central nucleus-nucleus collisions increases both
with target mass for sulphur projectiles and with the projectile mass for a
gold target. The shape of the rapidity distributions of net protons forward of
midrapidity for d+Au and central S+Au collisions is similar. The average
rapidity loss is larger than 2 units of rapidity for reactions with the gold
target. The transverse momentum spectra of net protons for all reactions can be
described by a thermal distribution with `temperatures' between 145 +- 11 MeV
(p+S interactions) and 244 +- 43 MeV (central S+Au collisions). The
multiplicity of negatively charged hadrons increases with the mass of the
colliding system. The shape of the transverse momentum spectra of negatively
charged hadrons changes from minimum bias p+p and p+S interactions to p+Au and
central nucleus-nucleus collisions. The mean transverse momentum is almost
constant in the vicinity of midrapidity and shows little variation with the
target and projectile masses. The average number of produced negatively charged
hadrons per participant baryon increases slightly from p+p, p+A to central
S+S,Ag collisions.Comment: 47 pages, submitted to Z. Phys.
Experimental Study of the Shortest Reset Word of Random Automata
In this paper we describe an approach to finding the shortest reset word of a
finite synchronizing automaton by using a SAT solver. We use this approach to
perform an experimental study of the length of the shortest reset word of a
finite synchronizing automaton. The largest automata we considered had 100
states. The results of the experiments allow us to formulate a hypothesis that
the length of the shortest reset word of a random finite automaton with
states and 2 input letters with high probability is sublinear with respect to
and can be estimated as $1.95 n^{0.55}.
Measurement of event-by-event transverse momentum and multiplicity fluctuations using strongly intensive measures and in nucleus-nucleus collisions at the CERN Super Proton Synchrotron
Results from the NA49 experiment at the CERN SPS are presented on
event-by-event transverse momentum and multiplicity fluctuations of charged
particles, produced at forward rapidities in central Pb+Pb interactions at beam
momenta 20, 30, 40, 80, and 158 GeV/c, as well as in systems of
different size (, C+C, Si+Si, and Pb+Pb) at 158 GeV/c. This publication
extends the previous NA49 measurements of the strongly intensive measure
by a study of the recently proposed strongly intensive measures of
fluctuations and . In the explored kinematic
region transverse momentum and multiplicity fluctuations show no significant
energy dependence in the SPS energy range. However, a remarkable system size
dependence is observed for both and , with the
largest values measured in peripheral Pb+Pb interactions. The results are
compared with NA61/SHINE measurements in collisions, as well as with
predictions of the UrQMD and EPOS models.Comment: 12 pages, 14 figures, to be submitted to PR
Multiplicity fluctuations in nuclear collisions at 158 A GeV
System size dependence of multiplicity fluctuations of charged particles
produced in nuclear collisions at 158 A GeV was studied in the NA49 CERN
experiment. Results indicate a non-monotonic dependence of the scaled variance
of the multiplicity distribution with a maximum for semi-peripheral Pb+Pb
interactions with number of projectile participants of about 35. This effect is
not observed in a string-hadronic model of nuclear collision HIJING.Comment: Presented at "Focus on Multiplicity", 17-19 of June, Bari, Ital
Multiplicity and transverse momentum fluctuations in inelastic proton-proton interactions at the CERN Super Proton Synchrotron
Measurements of multiplicity and transverse momentum fluctuations of charged
particles were performed in inelastic p+p interactions at 20, 31, 40, 80 and
158 GeV/c beam momentum. Results for the scaled variance of the multiplicity
distribution and for three strongly intensive measures of multiplicity and
transverse momentum fluctuations \$\Delta[P_{T},N]\$, \$\Sigma[P_{T},N]\$ and
\$\Phi_{p_T}\$ are presented. For the first time the results on fluctuations
are fully corrected for experimental biases. The results on multiplicity and
transverse momentum fluctuations significantly deviate from expectations for
the independent particle production. They also depend on charges of selected
hadrons. The string-resonance Monte Carlo models EPOS and UrQMD do not describe
the data. The scaled variance of multiplicity fluctuations is significantly
higher in inelastic p+p interactions than in central Pb+Pb collisions measured
by NA49 at the same energy per nucleon. This is in qualitative disagreement
with the predictions of the Wounded Nucleon Model. Within the statistical
framework the enhanced multiplicity fluctuations in inelastic p+p interactions
can be interpreted as due to event-by-event fluctuations of the fireball energy
and/or volume.Comment: 18 pages, 12 figure
Event-by-Event Fluctuations of Particle Ratios in Central Pb+Pb Collisions at 20 to 158 AGeV
In the vicinity of the QCD phase transition, critical fluctuations have been
predicted to lead to non-statistical fluctuations of particle ratios, depending
on the nature of the phase transition. Recent results of the NA49 energy scan
program show a sharp maximum of the ratio of K+ to Pi+ yields in central Pb+Pb
collisions at beam energies of 20-30 AGeV. This observation has been
interpreted as an indication of a phase transition at low SPS energies. We
present first results on event-by-event fluctuations of the kaon to pion and
proton to pion ratios at beam energies close to this maximum.Comment: 4 pages, 4 figures, Quark Matter 2004 proceeding
System size dependence of strange particle yields and spectra at sqrt(s)=17.3 GeV
Yields and spectra of strange hadrons (K+, K-, phi, Lambda and Antilambda) as
well as of charged pions were measured in near central C+C and Si+Si collisions
at 158 AGeV beam energy with the NA49 detector. Together with earlier data for
p+p, S+S and Pb+Pb reactions the system size dependence can be studied.
Relative strangeness production rises fast and saturates at about 60
participating nucleons; the net hyperon spectra show an increasing shift
towards midrapidity for larger colliding nuclei. An interpretation based on the
formation of coherent systems of increasing volume is proposed. The transverse
mass spectra can be described by a blast wave ansatz. Increasing flow velocity
is accompanied by decreasing temperatures for both kinetic and chemical freeze
out. The increasing gap between inelastic and elastic decoupling leaves space
for rescattering.Comment: 8 pages, 6 figures, Proceedings of the Hot Quarks 2004 worksho
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