188 research outputs found
Quasi-classical versus non-classical spectral asymptotics for magnetic Schroedinger operators with decreasing electric potentials
We consider the Schroedinger operator H on L^2(R^2) or L^2(R^3) with constant
magnetic field and electric potential V which typically decays at infinity
exponentially fast or has a compact support. We investigate the asymptotic
behaviour of the discrete spectrum of H near the boundary points of its
essential spectrum. If the decay of V is Gaussian or faster, this behaviour is
non-classical in the sense that it is not described by the quasi-classical
formulas known for the case where V admits a power-like decay.Comment: Corrected versio
Resonances Width in Crossed Electric and Magnetic Fields
We study the spectral properties of a charged particle confined to a
two-dimensional plane and submitted to homogeneous magnetic and electric fields
and an impurity potential. We use the method of complex translations to prove
that the life-times of resonances induced by the presence of electric field are
at least Gaussian long as the electric field tends to zero.Comment: 3 figure
On the discrete spectrum of spin-orbit Hamiltonians with singular interactions
We give a variational proof of the existence of infinitely many bound states
below the continuous spectrum for spin-orbit Hamiltonians (including the Rashba
and Dresselhaus cases) perturbed by measure potentials thus extending the
results of J.Bruening, V.Geyler, K.Pankrashkin: J. Phys. A 40 (2007)
F113--F117.Comment: 10 pages; to appear in Russian Journal of Mathematical Physics
(memorial volume in honor of Vladimir Geyler). Results improved in this
versio
Borexino's search for low-energy neutrinos associated with gravitational wave events from GWTC-3 database
The search for neutrino events in correlation with gravitational wave (GW)
events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has
been performed using the Borexino data-set of the same period. We have searched
for signals of neutrino-electron scattering with visible energies above 250 keV
within a time window of 1000 s centered at the detection moment of a particular
GW event. The search was done with three visible energy thresholds of 0.25, 0.8
and 3.0 MeV.Two types of incoming neutrino spectra were considered: the
mono-energetic line and the spectrum expected from supernovae. The same spectra
were considered for electron antineutrinos detected through inverse beta-decay
(IBD) reaction. GW candidates originated by merging binaries of black holes
(BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were
analysed separately. Additionally, the subset of most intensive BHBH mergers at
closer distances and with larger radiative mass than the rest was considered.
In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3
catalog were analyzed and no statistically significant excess over the
background was observed. As a result, the strongest upper limits on
GW-associated neutrino and antineutrino fluences for all flavors (\nu_e,
\nu_\mu, \nu_\tau) have been obtained in the (0.5 - 5.0) MeV neutrino energy
range.Comment: 13 pages, 8 figure
Novel techniques for alpha/beta pulse shape discrimination in Borexino
Borexino could efficiently distinguish between alpha and beta radiation in
its liquid scintillator by the characteristic time profile of their
scintillation pulse. This alpha/beta discrimination, first demonstrated at the
tonne scale in the Counting Test Facility prototype, was used throughout the
lifetime of the experiment between 2007 and 2021. With this method, alpha
events are identified and subtracted from the beta-like solar neutrino events.
This is particularly important in liquid scintillator as alpha scintillation is
quenched many-fold. In Borexino, the prominent Po-210 decay peak was a
background in the energy range of electrons scattered from Be-7 solar
neutrinos. Optimal alpha-beta discrimination was achieved with a "multi-layer
perceptron neural network", which its higher ability to leverage the timing
information of the scintillation photons detected by the photomultiplier tubes.
An event-by-event, high efficiency, stable, and uniform pulse shape
discrimination was essential in characterising the spatial distribution of
background in the detector. This benefited most Borexino measurements,
including solar neutrinos in the \pp chain and the first direct observation of
the CNO cycle in the Sun. This paper presents the key milestones in alpha/beta
discrimination in Borexino as a term of comparison for current and future large
liquid scintillator detectorsComment: 13 pages, 14 figure
Experimental Detection of the CNO Cycle
Borexino recently reported the first experimental evidence for a CNO neutrino. Since this process accounts for only about 1% of the Sun’s total energy production, the associated neutrino flux is remarkably low compared to that of the pp chain, the dominant hydrogen-burning process. This experimental evidence for the existence of CNO neutrinos was obtained using a highly radio-pure Borexino liquid scintillator. Improvements in the thermal stabilization of the detector over the last five years have allowed us to exploit a method of constraining the rate of 210Bi background. Since the CNO cycle is dominant in massive stars, this result is the first experimental evidence of a major stellar hydrogen-to-helium conversion mechanism in the Universe
Solar and geoneutrinos
Thanks to the progress of neutrino physics, today we are able of exploiting neutrinos as a tool to study astrophysical objects. The latter in turn serve as unique sources of elusive neutrinos, which fundamental properties are still to be understood. This contribution attempts to summarize the latest results obtained by measuring neutrinos emitted from the Sun and geoneutrinos produced in radioactive decays inside the Earth, with a particular focus on a recent discovery of the CNO-cycle solar neutrinos by Borexino. Comprehensive measurement of the pp-chain solar neutrinos and the first directional detection of sub-MeV solar neutrinos by Borexino, the updated 8B solar neutrino results of Super-Kamiokande, as well as the latest Borexino and KamLAND geoneutrino measurements are also discussed
Identification of the cosmogenic 11C background in large volumes of liquid scintillators with Borexino
Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic 11C decays outnumber solar pep and CNO neutrino events by about ten to one. In order to extract the flux of these two neutrino species, a highly efficient identification of this background is mandatory. We present here the details of the most consolidated strategy, used throughout Borexino solar neutrino measurements. It hinges upon finding the space-time correlations between 11C decays, the preceding parent muons and the accompanying neutrons. This article describes the working principles and evaluates the performance of this Three-Fold Coincidence (TFC) technique in its two current implementations: a hard-cut and a likelihood-based approach. Both show stable performances throughout Borexino Phases II (2012–2016) and III (2016–2020) data sets, with a 11C tagging efficiency of ∼90 % and ∼ 63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically 11C produced in high-multiplicity during major spallation events. Such 11C appear as a burst of events, whose space-time correlation can be exploited. Burst identification can be combined with the TFC to obtain about the same tagging efficiency of ∼90% but with a higher fraction of the exposure surviving, in the range of ∼ 66–68 %
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