1,028 research outputs found
Interplay between collective effects and nonstandard interactions of supernova neutrinos
We consider the effect of non-standard neutrino interactions (NSI, for short) on the propagation of neutrinos through the supernova (SN) envelope within a three-neutrino framework and taking into account the presence of a neutrino background. We find that for given NSI parameters, with strength generically denoted by Δij, neutrino evolution exhibits a significant time dependence. For |ΔÏÏ|âł 10â3 the neutrino survival probability may become sensitive to the Ξ23 octant and the sign of ΔÏÏ. In particular, if ΔÏÏâł10â2 an internal I-resonance may arise independently of the matter density. For typical values found in SN simulations this takes place in the same dense-neutrino region above the neutrinosphere where collective effects occur, in particular during the synchronization regime. This resonance may lead to an exchange of the neutrino fluxes entering the bipolar regime. The main consequences are (i) bipolar conversion taking place for normal neutrino mass hierarchy and (ii) a transformation of the flux of low-energy Îœe, instead of the usual spectral swap
S_3-flavour symmetry as realized in lepton flavour violating processes
A variety of lepton flavour violating effects related to the recent discovery
of neutrino oscillations and mixings is here systematically discussed in terms
of an S_3-flavour permutational symmetry. After a brief review of some relevant
results on lepton masses and mixings, that had been derived in the framework of
a Minimal S_3-Invariant Extension of the Standard Model, we derive explicit
analytical expressions for the matrices of the Yukawa couplings and compute the
branching ratios of some selected flavour changing neutral current (FCNC)
processes, as well as, the contribution of the exchange of neutral flavour
changing scalars to the anomaly of the muon's magnetic moment as functions of
the masses of the charged leptons and the neutral Higgs bosons. We find that
the S_3 x Z_2 flavour symmetry and the strong mass hierarchy of the charged
leptons strongly suppress the FCNC processes in the leptonic sector well below
the present experimental upper bounds by many orders of magnitude. The
contribution of FCNC to the anomaly of the muon's magnetic moment is small but
non-negligible.Comment: 23 pages, one figure. To appear in J. Phys A: Mathematical and
Theoretical (SPE QTS5
New measurement of neutron capture resonances of 209Bi
The neutron capture cross section of Bi209 has been measured at the CERN n
TOF facility by employing the pulse-height-weighting technique. Improvements
over previous measurements are mainly because of an optimized detection system,
which led to a practically negligible neutron sensitivity. Additional
experimental sources of systematic error, such as the electronic threshold in
the detectors, summing of gamma-rays, internal electron conversion, and the
isomeric state in bismuth, have been taken into account. Gamma-ray absorption
effects inside the sample have been corrected by employing a nonpolynomial
weighting function. Because Bi209 is the last stable isotope in the reaction
path of the stellar s-process, the Maxwellian averaged capture cross section is
important for the recycling of the reaction flow by alpha-decays. In the
relevant stellar range of thermal energies between kT=5 and 8 keV our new
capture rate is about 16% higher than the presently accepted value used for
nucleosynthesis calculations. At this low temperature an important part of the
heavy Pb-Bi isotopes are supposed to be synthesized by the s-process in the He
shells of low mass, thermally pulsing asymptotic giant branch stars. With the
improved set of cross sections we obtain an s-process fraction of 19(3)% of the
solar bismuth abundance, resulting in an r-process residual of 81(3)%. The
present (n,gamma) cross-section measurement is also of relevance for the design
of accelerator driven systems based on a liquid metal Pb/Bi spallation target.Comment: 10 pages, 5figures, recently published in Phys. Rev.
Selectivity of Relative Humidity Using a CP Based on S-Block Metal Ions
Herein, we present the syntheses of a novel coordination polymer (CP) based on the perylene-3,4,9,10-tetracarboxylate (pery) linkers and sodium metal ions. We have chosen sodium metal center with the aim of surmising the effect that the modification of the metal ion may have on the relative humidity (RH) experimental measurements of the material. We confirm the role of the ions in the functionalization of the deposited layer by modifying their selectivity towards moisture content, paving the way to the generation of sensitive and selective chemical sensors.This work is part of the I+D+I projects PGC2018-102052-A-C22, PGC2018-102052-B-C21, PID2020-117344R-I00 and CTQ-2015-64049-C3-3R, supported by the MCIN/AEI/10.13039/501100011033/ (FEDER: A way to make Europe), Junta de AndalucĂa (FQM-394, P20_00265 and B-FQM-734-UGR20). It also has been supported by the European Commission through the fellowship H2020-MSCA-IF-2017 794885-SELFSENS.Peer reviewe
Measurement of the neutron capture cross section of the s-only isotope 204Pb from 1 eV to 440 keV
The neutron capture cross section of 204Pb has been measured at the CERN
n_TOF installation with high resolution in the energy range from 1 eV to 440
keV. An R-matrix analysis of the resolved resonance region, between 1 eV and
100 keV, was carried out using the SAMMY code. In the interval between 100 keV
and 440 keV we report the average capture cross section. The background in the
entire neutron energy range could be reliably determined from the measurement
of a 208Pb sample. Other systematic effects in this measurement could be
investigated and precisely corrected by means of detailed Monte Carlo
simulations. We obtain a Maxwellian average capture cross section for 204Pb at
kT=30 keV of 79(3) mb, in agreement with previous experiments. However our
cross section at kT=5 keV is about 35% larger than the values reported so far.
The implications of the new cross section for the s-process abundance
contributions in the Pb/Bi region are discussed.Comment: 8 pages, 3 figures, article submitted to Phys. Rev.
Measurement of the (90,91,92,93,94,96)Zr(n,gamma) and (139)La(n,gamma) cross sections at n_TOF
Open AccessNeutron capture cross sections of Zr and La isotopes have important implications in the field of nuclear astrophysics as well as in the nuclear technology. In particular the Zr isotopes play a key role for the determination of the neutron density in the He burning zone of the Red Giant star, while the (139)La is important to monitor the s-process abundances from Ba up to Ph. Zr is also largely used as structural materials of traditional and advanced nuclear reactors. The nuclear resonance parameters and the cross section of (90,91,92,93,94,96)Zr and (139)La have been measured at the n_TOF facility at CERN. Based on these data the capture resonance strength and the Maxwellian-averaged cross section were calculated
Measurements of high-energy neutron-induced fission of (nat)Pb and (209)Bi
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly citedThe CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure low cross sections as those of neutron-induced fission in subactinides. The cross section ratios of (nat)Pb and (209)Bi relative to (235)U and (238)U were measured using PPAC detectors and a fragment coincidence method that allows us to identify the fission events. The present experiment provides first results for neutron-induced fission up to 1 GeV. Good agreement is found with previous experimental data below 200 MeV. The comparison with proton-induced fission indicates that the limiting regime where neutron-induced and proton-induced fission reach equal cross sections is close to 1 GeV
High-accuracy determination of the U 238 / U 235 fission cross section ratio up to â1 GeV at n-TOF at CERN
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published articleâs title, journal citation, and DOIThe U238 to U235 fission cross section ratio has been determined at n-TOF up to â1 GeV, with two different detection systems, in different geometrical configurations. A total of four datasets has been collected and compared. They are all consistent to each other within the relative systematic uncertainty of 3-4%. The data collected at n-TOF have been suitably combined to yield a unique fission cross section ratio as a function of neutron energy. The result confirms current evaluations up to 200 MeV. Good agreement is also observed with theoretical calculations based on the INCL++/Gemini++ combination up to the highest measured energy. The n-TOF results may help solve a long-standing discrepancy between the two most important experimental datasets available so far above 20 MeV, while extending the neutron energy range for the first time up to â1 GeV.Peer reviewedFinal Published versio
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