4,404 research outputs found
Systematical Approach to the Exact Solution of the Dirac Equation for A Special Form of the Woods-Saxon Potential
Exact solution of the Dirac equation for a special form of the Woods-Saxon
potential is obtained for the s-states. The energy eigenvalues and
two-component spinor wave functions are derived by using a systematical method
which is called as Nikiforov-Uvarov. It is seen that the energy eigenvalues
strongly depend on the potential parameters. In addition, it is also shown that
the non-relativistic limit can be reached easily and directly.Comment: 10 pages, no figures, submitted for Publicatio
Screened alpha decay in dense astrophysical plasmas and magnetars
This paper shows that ultrastrong magnetic fields (such as those of
magnetars) and dense astrophysical plasmas can reduce the half life of alpha
decaying nuclei by many orders of magnitude. In such environments the
conventional Geiger-Nuttall law is modifed so that all half lives are shifted
to dramatically lower values. Those effects, which have never been investigated
before, may have significant implications on the universal abundances of heavy
radioactive elements and the cosmochronological methods that rely on them.Comment: 15 RevTex pages, 3 ps figures (minor revision). This work was
presented during the conference ''Supernova, 10 years of SN1993J'', April
2003, Valencia, Spain. Accepted for publication in Phys.Rev.
Atomic effects in astrophysical nuclear reactions
Two models are presented for the description of the electron screening
effects that appear in laboratory nuclear reactions at astrophysical energies.
The two-electron screening energy of the first model agrees very well with the
recent LUNA experimental result for the break-up reaction , which so far defies all available theoretical models.
Moreover, multi-electron effects that enhance laboratory reactions of the CNO
cycle and other advanced nuclear burning stages, are also studied by means of
the Thomas-Fermi model, deriving analytical formulae that establish a lower and
upper limit for the associated screening energy. The results of the second
model, which show a very satisfactory compatibility with the adiabatic
approximation ones, are expected to be particularly useful in future
experiments for a more accurate determination of the CNO astrophysical factors.Comment: 14 RevTex pages + 2 ps (revised) figures. Phys.Rev.C (in production
Hyperspherical partial wave theory applied to electron hydrogen-atom ionization calculation for equal energy sharing kinematics
Hyperspherical partial wave theory has been applied here in a new way in the
calculation of the triple differential cross sections for the ionization of
hydrogen atoms by electron impact at low energies for various
equal-energy-sharing kinematic conditions. The agreement of the cross section
results with the recent absolute measurements of R\"oder \textit {et al} [51]
and with the latest theoretical results of the ECS and CCC calculations [29]
for different kinematic conditions at 17.6 eV is very encouraging. The other
calculated results, for relatively higher energies, are also generally
satisfactory, particularly for large geometries. In view of the
present results, together with the fact that it is capable of describing
unequal-energy-sharing kinematics [35], it may be said that the hyperspherical
partial wave theory is quite appropriate for the description of ionization
events of electron-hydrogen type systems. It is also clear that the present
approach in the implementation of the hyperspherical partial wave theory is
very appropriate.Comment: 16 pages, 9 figures, LaTeX file and EPS figures. To appear in Phys.
Rev.
Solutions of the Faddeev-Yakubovsky equations for the four nucleons scattering states
The Faddeev-Yakubowsky equations in configuration space have been solved for
the four nucleon system. The results with an S-wave interaction model in the
isospin approximation are presented. They concern the bound and scattering
states below the first three-body threshold. The elastic phase-shifts for the
N+NNN reaction in different () channels are given and the corresponding
low energy expansions are discussed. Particular attention is payed to the n+t
elastic cross section. Its resonant structure is well described in terms of a
simple NN interaction. First results concerning the S-matrix for the coupled
N+NNN-NN+NN channels and the strong deuteron-deuteron scattering length are
obtained.Comment: latex.tar.gz, 36 pages, 10 figures, 11 tables. To be published in
Physical Review
VHMPID: a new detector for the ALICE experiment at LHC
This article presents the basic idea of VHMPID, an upgrade detector for the
ALICE experiment at LHC, CERN. The main goal of this detector is to extend the
particle identification capabilities of ALICE to give more insight into the
evolution of the hot and dense matter created in Pb-Pb collisions. Starting
from the physics motivations and working principles the challenges and current
status of development is detailed.Comment: 4 pages, 6 figures. To be published in EPJ Web of Conference
Studies of the Response of the Prototype CMS Hadron Calorimeter, Including Magnetic Field Effects, to Pion, Electron, and Muon Beams
We report on the response of a prototype CMS hadron calorimeter module to
charged particle beams of pions, muons, and electrons with momenta up to 375
GeV/c. The data were taken at the H2 and H4 beamlines at CERN in 1995 and 1996.
The prototype sampling calorimeter used copper absorber plates and scintillator
tiles with wavelength shifting fibers for readout. The effects of a magnetic
field of up to 3 Tesla on the response of the calorimeter to muons, electrons,
and pions are presented, and the effects of an upstream lead tungstate crystal
electromagnetic calorimeter on the linearity and energy resolution of the
combined calorimetric system to hadrons are evaluated. The results are compared
with Monte Carlo simulations and are used to optimize the choice of total
absorber depth, sampling frequency, and longitudinal readout segmentation.Comment: 89 pages, 41 figures, to be published in NIM, corresponding author: P
de Barbaro, [email protected]
Overview of large area triple-GEM detectors for the CMS forward muon upgrade
In order to cope with the harsh environment expected from the high luminosity LHC, the CMS forward muon system requires an upgrade. The two main challenges expected in this environment are an increase in the trigger rate and increased background radiation leading to a potential degradation of the particle ID performance. Additionally, upgrades to other subdetectors of CMS allow for extended coverage for particle tracking, and adding muon system coverage to this region will further enhance the performance of CMS
A novel application of Fiber Bragg Grating (FBG) sensors in MPGD
We present a novel application of Fiber Bragg Grating (FBG) sensors in the
construction and characterisation of Micro Pattern Gaseous Detector (MPGD),
with particular attention to the realisation of the largest triple (Gas
electron Multiplier) GEM chambers so far operated, the GE1/1 chambers of the
CMS experiment at LHC. The GE1/1 CMS project consists of 144 GEM chambers of
about 0.5 m2 active area each, employing three GEM foils per chamber, to be
installed in the forward region of the CMS endcap during the long shutdown of
LHC in 2108-2019. The large active area of each GE1/1 chamber consists of GEM
foils that are mechanically stretched in order to secure their flatness and the
consequent uniform performance of the GE1/1 chamber across its whole active
surface. So far FBGs have been used in high energy physics mainly as high
precision positioning and re-positioning sensors and as low cost, easy to
mount, low space consuming temperature sensors. FBGs are also commonly used for
very precise strain measurements in material studies. In this work we present a
novel use of FBGs as flatness and mechanical tensioning sensors applied to the
wide GEM foils of the GE1/1 chambers. A network of FBG sensors have been used
to determine the optimal mechanical tension applied and to characterise the
mechanical tension that should be applied to the foils. We discuss the results
of the test done on a full-sized GE1/1 final prototype, the studies done to
fully characterise the GEM material, how this information was used to define a
standard assembly procedure and possible future developments.Comment: 4 pages, 4 figures, presented by Luigi Benussi at MPGD 2015 (Trieste,
Italy). arXiv admin note: text overlap with arXiv:1512.0848
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