243 research outputs found
Contribution of domain wall networks to the CMB power spectrum
We use three domain wall simulations from the radiation era to the late time
dark energy domination era based on the PRS algorithm to calculate the
energy-momentum tensor components of domain wall networks in an expanding
universe. Unequal time correlators in the radiation, matter and cosmological
constant epochs are calculated using the scaling regime of each of the
simulations. The CMB power spectrum of a network of domain walls is determined.
The first ever quantitative constraint for the domain wall surface tension is
obtained using a Markov chain Monte Carlo method; an energy scale of domain
walls of 0.93 MeV, which is close but below the Zel'dovich bound, is
determined.Comment: Submitted to Physics Letters
Systematic study related to the role of initial impurities and irradiation rates in the formation and evolution of complex defects in silicon for detectors in HEP experiments
The influence of oxygen and carbon impurities on the concentrations of
defects in silicon for detector uses, in complex fields of radiation,
characteristic to high energy physics experiments, is investigated in the frame
of the quantitative phenomenological model developed previously by the authors
and extended in the present paper. Continuous irradiation conditions are
considered, simulating realistically the environments for these experiments.
The generation rate of primary defects is calculated starting from the
projectile - silicon interaction and from the recoil energy redistribution in
the lattice. The mechanisms of formation of complex defects are explicitly
analysed. Vacancy-interstitial annihilation, interstitial and vacancy migration
to sinks, divacancy, vacancy- and interstitial-impurity complex formation and
decomposition are considered. Oxygen and carbon impurities present in silicon
could monitor the concentration of all stable defects, due to their interaction
with vacancies and interstitials. Their role in the mechanisms of formation and
decomposition of the following stable defects: V_2, VO, V_2O, C_i, C_iO_i,
C_iC_s and VP, is studied. The model predictions cover a generation primary
rate of defects between 10^2 pairs/cm3/s and 10^{11} pairs/cm3/s, and could be
a useful clue in obtaining harder materials for detectors for space missions,
at the new generation of accelerators, as, e.g. LHC, Super-LHC and Eloisatron,
or for industrial applications.Comment: 15 pages, work in the frame of CERN RD50 Collaboration, submitted to
Physica Script
Scenarios about the long-time damage of silicon as material and detectors operating beyond LHC collider conditions
For the new hadron collider LHC and some of its updates in luminosity and
energy, as SLHC and VLHC, the silicon detectors could represent an important
option, especially for the tracking system and calorimetry. The main goal of
this paper is to analyse the expected long-time degradation in the bulk of the
silicon as material and for silicon detectors, in continuous radiation field,
in these hostile conditions. The behaviour of silicon in relation to various
scenarios for upgrade in energy and luminosity is discussed in the frame a
phenomenological model developed previously by the authors. Different silicon
material parameters resulting from different technologies are considered to
evaluate what materials are harder to radiation and consequently could minimise
the degradation of device parameters in conditions of continuous long time
operation.Comment: submitted to Physica Scripta Work in the frame of CERN RD-50
Collaboratio
Transient thermal effects in solid noble gases as materials for the detection of Dark Matter
The transient phenomena produced in solid noble gases by the stopping of the
recoils resulting from the elastic scattering processes of WIMPs from the
galactic halo were modelled, as dependencies of the temperatures of lattice and
electronic subsystems on the distance to the recoil's trajectory, and time from
its passage. The peculiarities of these thermal transients produced in Ar, Kr
and Xe were analysed for different initial temperatures and WIMP energies, and
were correlated with the characteristics of the targets and with the energy
loss of the recoils. The results were compared with the thermal spikes produced
by the same WIMPs in Si and Ge. In the range of the energy of interest, up to
tens of keV for the self-recoil, local phase transitions solid - liquid and
even liquid - gas were found possible, and the threshold parameters were
established.Comment: Minor corrections and updated references; accepted to JCA
New results on Coulomb interaction effects in relativistic heavy ion collisions
The effects of the Coulomb interaction on charged pion production in Au+Au collisions at RHIC-BES energies are studied. From pT spectra of charged pions measured with STAR experiment, the negative-to-positive pion ratios as a
function of transverse momentum are obtained. Based of these pion ratio the finalstate Coulomb interaction can be investigated. The “Coulomb kick” (a momentum change due to Coulomb interaction) and initial pion ratio for RHIC-BES energies (7.7 GeV, 11.5 GeV, 19.6 GeV, 27 GeV and 39 GeV) and various centrality classes are obtained. The energy and centrality dependence of the Coulomb kick is presented.
These results are connected with the kinetic freeze-out dynamics
Temperature dependence of capture coefficients in trapping phenomena
The temperature dependence of the capture coefficients in trapping phenomena is investigated. It is proved that, besides the dependence induced by the thermal velocity of the carriers, the stress-induced traps at the interfaces of the multi-layered structures present a supplementary temperature dependence. This dependence is found to be of Gaussian type and is in a good agreement with the experimental results. © 2010 IEEE
Stress-induced traps in multilayered structures
The trap parameters of defects in Si/CaF2 multilayered structures were
determined from the analysis of optical charging spectroscopy measurements. Two
kinds of maxima were observed. Some of them were rather broad, corresponding to
"normal" traps, while the others, very sharp, were attributed to stress-induced
traps. A procedure of optimal linear smoothing the noisy experimental data has
been developed and applied. This procedure is based on finding the minimal
value of the relative error with respect to the value of the smoothing window.
In order to obtain a better accuracy for the description of the
trapping-detrapping process, a Gaussian temperature dependence of the capture
crosssections characterizing the stress-induced traps was introduced. Both the
normal and the stress-induced traps have been characterized, including some
previously considered as only noise features.Comment: 37 pages, 9 figure
Stress-induced traps in multilayered structures
The trap parameters of defects in Si/CaF 2 multilayered structures were determined from the analysis of optical charging spectroscopy measurements. Two kinds of maxima were observed. Some of them were rather broad, corresponding to "normal" traps, while the others, very sharp, were attributed to stress-induced traps. A procedure of optimal linear smoothing the noisy experimental data has been developed and applied. This procedure is based on finding the minimal value of the relative error with respect to the value of the smoothing window. In order to obtain a better accuracy for the description of the trapping-detrapping process, a Gaussian temperature dependence of the capture cross-sections characterizing the stress-induced traps was introduced. Both the normal and the stress-induced traps have been characterized, including some previously considered as only noise features. ©2011 American Institute of Physics
The LAGUNA design study- towards giant liquid based underground detectors for neutrino physics and astrophysics and proton decay searches
The feasibility of a next generation neutrino observatory in Europe is being
considered within the LAGUNA design study. To accommodate giant neutrino
detectors and shield them from cosmic rays, a new very large underground
infrastructure is required. Seven potential candidate sites in different parts
of Europe and at several distances from CERN are being studied: Boulby (UK),
Canfranc (Spain), Fr\'ejus (France/Italy), Pyh\"asalmi (Finland),
Polkowice-Sieroszowice (Poland), Slanic (Romania) and Umbria (Italy). The
design study aims at the comprehensive and coordinated technical assessment of
each site, at a coherent cost estimation, and at a prioritization of the sites
within the summer 2010.Comment: 5 pages, contribution to the Workshop "European Strategy for Future
Neutrino Physics", CERN, Oct. 200
The LBNO long-baseline oscillation sensitivities with two conventional neutrino beams at different baselines
The proposed Long Baseline Neutrino Observatory (LBNO) initially consists of
kton liquid double phase TPC complemented by a magnetised iron
calorimeter, to be installed at the Pyh\"asalmi mine, at a distance of 2300 km
from CERN. The conventional neutrino beam is produced by 400 GeV protons
accelerated at the SPS accelerator delivering 700 kW of power. The long
baseline provides a unique opportunity to study neutrino flavour oscillations
over their 1st and 2nd oscillation maxima exploring the behaviour, and
distinguishing effects arising from and matter. In this paper we
show how this comprehensive physics case can be further enhanced and
complemented if a neutrino beam produced at the Protvino IHEP accelerator
complex, at a distance of 1160 km, and with modest power of 450 kW is aimed
towards the same far detectors. We show that the coupling of two independent
sub-MW conventional neutrino and antineutrino beams at different baselines from
CERN and Protvino will allow to measure CP violation in the leptonic sector at
a confidence level of at least for 50\% of the true values of
with a 20 kton detector. With a far detector of 70 kton, the
combination allows a sensitivity for 75\% of the true values of
after 10 years of running. Running two independent neutrino
beams, each at a power below 1 MW, is more within today's state of the art than
the long-term operation of a new single high-energy multi-MW facility, which
has several technical challenges and will likely require a learning curve.Comment: 21 pages, 12 figure
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