arXiv
(422.153 recursos)
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Mostrando recursos 1 - 20 de 4.805
1.
Magnetic Moment of the Fragmentation Aligned 61Fe(9/2)+ Isomer - Matea, I.; Georgiev, G.; Daugas, J. M.; Hass, M.; Neyens, G.
We report on the g factor measurement of the isomer in $^{61}Fe$ ($E^{*}=861
keV$). The isomer was produced and spin-aligned via a projectile-fragmentation
reaction at intermediate energy, the Time Dependent Perturbed Angular
Distribution (TDPAD) method being used for the measurement of the g factor. For
the first time, due to significant improvements of the experimental technique,
an appreciable residual alignment of the isomer has been observed, allowing a
precise determination of its g factor: $g=-0.229(2)$. Comparison of the
experimental g factor with shell-model and mean field calculations confirms the
$9/2^+$ spin and parity assignments and suggests the onset of deformation due
to the intrusion of Nilsson orbitals emerging from...
2.
Recent advances in neutrinoless double beta decay search - Miramonti, Lino; Reseghetti, Franco
Even after the discovery of neutrino flavour oscillations, based on data from
atmospheric, solar, reactor, and accelerator experiments, many characteristics
of the neutrino remain unknown. Only the neutrino square-mass differences and
the mixing angle values have been estimated, while the value of each mass
eigenstate still hasn't. Its nature (massive Majorana or Dirac particle) is
still escaping. Neutrinoless double beta decay ($0\nu$-DBD) experimental
discovery could be the ultimate answer to some delicate questions of elementary
particle and nuclear physics. The Majorana description of neutrinos allows the
$0\nu$-DBD process, and consequently either a mass value could be measured or
the existence of physics beyond the standard should be confirmed without...
3.
Highlights of Crystal Ball Physics - Nefkens, B. M. K.; Collaboration, for the Crystal Ball
Differential and total cross sections are presented for pi- - and K- -induced
reactions on a proton target leading to all-neutral final states. Also shown
are rates for rare and upper limits for forbidden eta-meson decays to test
Chiral Perturbation Theory, the pi0-pi0 interactions and C and CP invariance.
4.
The First 3 Years at RHIC- an Overview - Seto, Richard
This is an overview of the results from the first 3 years of RHIC
experiments. RHIC is a collider built to accelerate nuclei to center of mass
energies of 200 GeV per nucleon for the study of QCD in bulk systems. The most
important result so far is the observation of the suppression of high p$_T$
hadrons in central Au-Au collisions followed by the subsequent null experiment
where the same suppression was not seen in deuteron-Au collisions. The observed
suppression is a final state effect in which a large amount of energy is lost
by the fast parton as it penetrates the medium. This observation, together with
measurements...
5.
In-medium properties of nucleon resonances - Krusche, B.
Recent experimental results for the in-medium properties of nucleon
resonances are discussed. The experiments were done with the TAPS detector at
the tagged photon beam of the MAMI accelerator in Mainz. Measured was the
photoproduction of mesons (final states $\pi^o X$, $\eta X$, $2\pi^oX$ and
$\pi^o\pi^{\pm}X$) from the nuclei $^{12}$C, $^{40}$Ca, $^{93}$Nb, and
$^{208}$Pb up to the second resonance region. The results were analyzed in view
of the in-medium properties of the P$_{33}$(1232), the D$_{13}$(1520), and the
S$_{11}$(1535) resonances.
6.
Strangelet search at RHIC - Tang, A. H.; Collaboration, for the STAR
Two position sensitive Shower Maximum Detector (SMDs) for Zero-Degree
Calorimeters (ZDCs) were installed by STAR before run 2004 at both upstream and
downstream from the interaction point along the beam axis where particles with
small rigidity are swept away by strong magnetic field. The ZDC-SMDs provides
information about neutral energy deposition as a function of transverse
position in ZDCs. We report the preliminary results of strangelet search from a
triggered data-set sampling 100 million Au+Au collisions at top RHIC energy.
7.
Volume Effects on Strangeness Production - Caines, Helen
A study of the yields of strange particles produced in heavy-ion and
elementary collisions is presented using preliminary results from the STAR
experiment at RHIC. The strange particle production rates, relative to those of
p+p, have been proposed as a means of determining an enhancement of strangeness
production in heavy-ion collisions. Analysis of results from STAR show that
this enhancement measure is reduced, or comparable, when contrasted to that at
top CERN SPS energies. A smaller suppression in the p+p yields at RHIC energies
due to finite volume effects could be the cause of such a result. By studying
the yields as a function of centrality we hope...
8.
Comments on the question of the discovery of element 112 as early as 1971 - Brandt, R.
There are two independent claims for the discovery of element 112: The claim
by Hofmann et al. from 1996 and the older claim from 1971 by Marinov et al.
This Comment will not challenge the experimental results of Hofmann et al., but
it will discuss one aspect of the claimed discovery of element 112 by Marinov
et al., as their experiment has never been reproduced in exactly the form in
which the original experiment has been carried out. The reasons for this
deficiency may not be found in the field of science, but possibly in
radioprotection restrictions for researchers who want to carry out such an
experiment. However,...
9.
Indications for the onset of deconfinement in nucleus nucleus collisions - Flierl, Dominik
The hadronic final state of central Pb+Pb collisions at 20, 30, 40, 80, and
158 AGeV has been measured by the CERN NA49 collaboration. The mean transverse
mass of pions and kaons at midrapidity stays nearly constant in this energy
range, whereas at lower energies, at the AGS, a steep increase with beam energy
was measured. Compared to p+p collisions as well as to model calculations,
anomalies in the energy dependence of pion and kaon production at lower SPS
energies are observed. These findings can be explained, assuming that the
energy density reached in central A+A collisions at lower SPS energies is
sufficient to force the hot and...
10.
Electroproduction of K* mesons at CLAS - Hleiqawi, Ishaq
The electroproduction of K$^{*0}$ mesons using the CLAS detector is
described. Data for two electron beam energies, 4.056 and 4.247 GeV, were
measured and the normalized yields are compared.
11.
The SAMPLE Experiment and Weak Nucleon Structure - Beise, E. J.; Pitt, M. L.; Spayde, D. T.
One of the key elements to understanding the structure of the nucleon is the
role of its quark-antiquark sea in its ground state properties such as charge,
mass, magnetism and spin. In the last decade, parity-violating electron
scattering has emerged as an important tool in this area, because of its
ability to isolate the contribution of strange quark-antiquark pairs to the
nucleon's charge and magnetism. The SAMPLE experiment at the MIT-Bates
Laboratory, which has been focused on s-sbar contributions to the proton's
magnetic moment, was the first of such experiments and its program has recently
been completed. In this paper we give an overview of some of the...
12.
Method of Monte Carlo grid for data analysis - Filipowicz, M.; Bystritsky, V. M.; Knowles, P. E.; Mulhauser, F.; Wozniak, J.
This paper presents an analysis procedure for experimental data using
theoretical functions generated by Monte Carlo. Applying the classical
chi-square fitting procedure for some multiparameter systems is extremely
difficult due to a lack of an analytical expression for the theoretical
functions describing the system. The proposed algorithm is based on the least
square method using a grid of Monte Carlo generated functions each
corresponding to definite values of the minimization parameters. It is used for
the E742 experiment (TRIUMF, Vancouver, Canada) data analysis with the aim to
extract muonic atom scattering parameters on solid hydrogen.
13.
The search for missing baryon resonances - Thoma, U.
Experiments with electromagnetic probes are promising to search for baryon
resonances that have been predicted by quark models but have not yet been
observed. Data sets from different experiments show interesting resonance
structures possibly due to so far unknow states. This might indicate that at
least some of the missing baryon resonances start to show up.
14.
Experimental Review of Baryons in the Nuclear Medium - Schadmand, S.
Inclusive studies of nuclear photoabsorption have provided clear evidence of
medium modifications but the results have not yet been explained in a model
independent way. A deeper understanding of the situation is anticipated from a
detailed experimental study of meson photoproduction from nuclei in exclusive
reactions. Recent results on meson production in photonuclear experiments
indicate a large difference between quasifree meson production from the nuclear
surface and non-quasifree components.
15.
Structure of collective modes in transitional and deformed nuclei - Caprio, M. A.
The collective structure of atomic nuclei intermediate between spherical and
quadrupole deformed structure presents challenges to theoretical understanding.
However, models have recently been proposed in terms of potentials which are
soft with respect to the quadrupole deformation variable beta. To test these
models, information is needed on low-spin states of transitional nuclei. The
present work involves measurement of electromagnetic decay properties of
low-spin states for nuclei in the A=100 (gamma-soft) and N=90 (axially
symmetric) transition regions. Population in beta-decay and thermal neutron
capture are used, and measurements are carried out using gamma-ray coincidence
spectroscopy, fast electronic scintillation timing, and gamma-ray induced
Doppler broadening techniques, in experiments at Yale, TRIUMF ISAC,...
16.
Resonance production in heavy ion collisions - Markert, Christina
Recent results of resonance production from RHIC at $\sqrt{s_{\rm NN}} = $
200 GeV and SPS at $\sqrt{s_{\rm NN}} = $ 17 GeV are presented and discussed in
terms of the evolution and freeze-out conditions of a hot and dense fireball
medium. Yields and spectra are compared with thermal model predictions at
chemical freeze-out. Deviations in the low transverse momentum region of the
resonance spectrum of the hadronic decay channel, suggest a strongly
interaction hadronic phase between chemical and kinetic freeze-out. Microscopic
models including resonance rescattering and regeneration are able to describe
the trend of the data. The magnitude of the regeneration cross sections for
different inverse decay channels...
17.
What do we learn from Resonance Production in Heavy Ion Collisions? - Markert, Christina
Resonances with their short life time and strong coupling to the dense and
hot medium are suggested as a signature of the early stage of the fireball
created in a heavy ion collision \cite{rap00,lut01,lut02}. The comparison of
resonances with different lifetimes and quark contents may give information
about time evolution and density and temperature of during the expanding of
fireball medium. Resonances in elementary reactions have been measured since
1960. Resonance production in elementary collisions compared with heavy ion
collisions where we expect to create a hot and dense medium may show the direct
of influence of the medium on the resonances. This paper shows a selection of
the...
18.
Low-Energy Deuteron Polarimeter - Bellos, Michael
We built a Low Energy Deuteron Polarimeter which measures the
spin-polarization of deuteron beams in the energy range of 25 to 80 keV. This
polarimeter works by measuring azimuthal asymmetries in the D(\vec d, n)^{3}He
reaction and comparing them to known analyzing powers. We built this
polarimeter to test its performance and to cross-check other existing
polarimeters at KVI. We were able to use this polarimeter as a vector
polarimeter, but not as a tensor polarimeter because of an uncertain 'tensor
analyzing power' calibration.
19.
The width of the rapidity distribution in heavy ion collisions - Netrakanti, Pawan Kumar; Mohanty, Bedangadas
We have studied the widths of the rapidity distributions of particles
produced in nucleus-nucleus collisions at various center of mass energies and
as a function of centrality at SPS energies. We show that the width of the
rapidity distribution is sensitive to longitudinal flow, velocity of sound in
the medium, and rescattering of particles. We explore the possibility of
distinguishing the initial hard scattering regime from final state effects by
studying the variation in the width of the rapidity distribution of the
particles with centrality for various pT values.
20.
On the possible detection of 4n events in the breakup of 14Be - Marques, F. M.; Orr, N. A.; Falou, H. Al; Normand, G.; Clarke, N. M.
In a recent paper --F.M. Marques et al, PRC 65 (2002) 044006-- a new approach
to the production and detection of free neutron clusters was proposed and
applied to data acquired for the breakup of 14Be. Six events that exhibited
characteristics consistent with a bound tetraneutron were observed in
coincidence with 10Be fragments. Here, two issues that were not considered in
the original paper are addressed: namely the signal expected from a low-energy
4n resonance, and the detection of a bound 4n through proccesses other than
elastic scattering by a proton. Searches complementary to the original study
are also briefly noted.
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