67 research outputs found
Measurement of the thorium-228 activity in solutions cavitated by ultrasonic sound
We show that cavitation of a solution of thorium-228 in water does not induce
its transformation at a faster rate than the natural radioactive decay. We
measured the activity of a thorium-228 solution in water before, and after, it
was subjected to a cavitation at 44 kHz and W for 90 minutes in order to
observe any change in the thorium half-life. The results were compared to the
original activity of the sample and we observed no change. Our results and
conclusions conflict with those in a recent paper by F. Cardone et. al. [Phys.
Lett. A 373 (2009) 1956-1958].Comment: 6 pages, 1 figure, 2 tables, v1 submitted to Physics Letters A. v2:
minor corrections, change caption for tables (include comment for counter
efficiency with uncertainty) and symbols for beta-alph
EstrellaNueva: an open-source software to study the interactions and detection of neutrinos emitted by supernovae
Supernovae emit large fluxes of neutrinos which can be detected by detectors
on Earth. Future tonne-scale detectors will be sensitive to several neutrino
interaction channels, with thousands of events expected if a supernova emerges
in the galaxy neighborhood. There is a limited number of tools to study the
interaction rates of supernova neutrinos, although a plethora of available
supernova models exists. EstrellaNueva is an open-source software to calculate
expected rates of supernova neutrinos in detectors using target materials with
typical compositions, and additional compositions can be easily added. This
software considers the flavor transformation of neutrinos in the supernova
through the adiabatic Mikheyev--Smirnov--Wolfenstein effect, and their
interaction in detectors through several channels. Most of the interaction
cross sections have been analytically implemented, such as neutrino-electron
and neutrino-proton elastic scattering, inverse beta decay, and coherent
elastic neutrino-nucleus scattering. This software provides a link between
supernova simulations and the expected events in detectors by calculating
fluences and event rates to ease any comparison between theory and observation.
It provides a simple and standalone tool to explore many physics scenarios
offering an option to add analytical cross sections and define any target
material
New Physics searches in a low threshold scintillating argon bubble chamber measuring coherent elastic neutrino-nucleus scattering in reactors
The sensitivity to New Physics of a low threshold scintillating argon bubble
chamber measuring coherent elastic neutrino-nucleus scattering in reactors is
reported. Namely, light scalar mediators, sterile neutrino oscillations,
unitarity violation, and non-standard interactions are studied. The results
indicate that this detector could be able to set stronger constraints than
current limits set by the recent COHERENT measurements. Considering the best
scenario, a 100 kg detector located 30 m from a 2000 MW reactor, a
sterile neutrino search would cover most of the space parameter allowed from
the reactor anti-neutrino anomaly fit. Unitarity violation studies could set
constraints on more stringent than the current oscillation
experiments fit. A low threshold argon detector with very low backgrounds has
the potential to explore New Physics in different scenarios and set competitive
constraints
Closing the dark photon window to thermal dark matter
The nature of dark matter remains a central question in particle physics,
cosmology, and astrophysics. The prevailing hypothesis postulates that dark
matter consists of particles that interact only weakly with Standard Model
particles. However, the knowledge of dark matter properties beyond these
interactions is limited. This study explores a scenario involving a dark photon
as a mediator between dark matter and the Standard Model, akin to the photon's
role in electromagnetism. Recent cosmological and experimental evidence impose
constraints on this scenario, focusing on results from direct detection
experiments such as PICO-60, XENON-1T, and PANDAX-4T. The results reveal severe
constraints, effectively closing the window for laboratory searches for dark
photons as mediators between the Standard Model and the dark sector (dark
electrons) in the secluded dark matter scenario. The findings underscore the
need for alternative explanations and offer fresh perspectives on the ongoing
quest to understand dark matter and its interactions since they are nearly
independent of the dark electron fraction content for the total dark matter.
This analysis significantly narrows down the parameter space for thermal dark
matter scenarios involving a dark photon portal, reinforcing the urgency of
exploring alternative models and designing new experiments to unravel the
mysteries surrounding the nature of dark matter.Comment: 11 pages, 5 figure
Radon backgrounds in the DEAP-1 liquid-argon-based Dark Matter detector
The DEAP-1 \SI{7}{kg} single phase liquid argon scintillation detector was
operated underground at SNOLAB in order to test the techniques and measure the
backgrounds inherent to single phase detection, in support of the
\mbox{DEAP-3600} Dark Matter detector. Backgrounds in DEAP are controlled
through material selection, construction techniques, pulse shape discrimination
and event reconstruction. This report details the analysis of background events
observed in three iterations of the DEAP-1 detector, and the measures taken to
reduce them.
The Rn decay rate in the liquid argon was measured to be between 16
and \SI{26}{\micro\becquerel\per\kilogram}. We found that the background
spectrum near the region of interest for Dark Matter detection in the DEAP-1
detector can be described considering events from three sources: radon
daughters decaying on the surface of the active volume, the expected rate of
electromagnetic events misidentified as nuclear recoils due to inefficiencies
in the pulse shape discrimination, and leakage of events from outside the
fiducial volume due to imperfect position reconstruction. These backgrounds
statistically account for all observed events, and they will be strongly
reduced in the DEAP-3600 detector due to its higher light yield and simpler
geometry
In-situ characterization of the Hamamatsu R5912-HQE photomultiplier tubes used in the DEAP-3600 experiment
The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum
efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and
is of significant interest for future dark matter and neutrino experiments
where high signal yields are needed.
We report on the methods developed for in-situ characterization and
monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of
typical measured single-photoelectron charge distributions, correlated noise
(afterpulsing), dark noise, double, and late pulsing characteristics. The
characterization is performed during the detector commissioning phase using
laser light injected through a light diffusing sphere and during normal
detector operation using LED light injected through optical fibres
Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
The DEAP-1 low-background liquid argon detector was used to measure
scintillation pulse shapes of electron and nuclear recoil events and to
demonstrate the feasibility of pulse-shape discrimination (PSD) down to an
electron-equivalent energy of 20 keV.
In the surface dataset using a triple-coincidence tag we found the fraction
of beta events that are misidentified as nuclear recoils to be (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil
acceptance of at least 90%, with 4% systematic uncertainty on the absolute
energy scale. The discrimination measurement on surface was limited by nuclear
recoils induced by cosmic-ray generated neutrons. This was improved by moving
the detector to the SNOLAB underground laboratory, where the reduced background
rate allowed the same measurement with only a double-coincidence tag.
The combined data set contains events. One of those, in the
underground data set, is in the nuclear-recoil region of interest. Taking into
account the expected background of 0.48 events coming from random pileup, the
resulting upper limit on the electronic recoil contamination is
(90% C.L.) between 44-89 keVee and for a nuclear recoil
acceptance of at least 90%, with 6% systematic uncertainty on the absolute
energy scale.
We developed a general mathematical framework to describe PSD parameter
distributions and used it to build an analytical model of the distributions
observed in DEAP-1. Using this model, we project a misidentification fraction
of approx. for an electron-equivalent energy threshold of 15 keV for
a detector with 8 PE/keVee light yield. This reduction enables a search for
spin-independent scattering of WIMPs from 1000 kg of liquid argon with a
WIMP-nucleon cross-section sensitivity of cm, assuming
negligible contribution from nuclear recoil backgrounds.Comment: Accepted for publication in Astroparticle Physic
Confirmation of the Double Charm Baryon Xi_cc+ via its Decay to p D+ K-
We observes a signal for the double charm baryon Xi_cc+ in the charged decay
mode Xi_cc+ -> p D+ K- to complement the previously reported decay Xi_cc+ ->
Lambda_c K- pi+ in data from SELEX, the charm hadro-production experiment
(E781) at Fermilab. In this new decay mode we observe an excess of 5.62 events
over an expected background estimated by event mixing to be 1.38+/-0.13 events.
The Poisson probability that a background fluctuation can produce the apparent
signal is less than 6.4E-4. The observed mass of this state is
(3518+/-3)MeV/c^2, consistent with the published result. Averaging the two
results gives a mass of (3518.7+/-1.7)MeV/c^2. The observation of this new weak
decay mode confirms the previous SELEX suggestion that this state is a double
charm baryon. The relative branching ratio Gamma(Xi_cc+ -> pD+K-)/Gamma(Xi_cc+
-> Lambda_c K- pi+) = 0.36+/-0.21.Comment: 11 pages, 6 included eps figures. v2 includes improved statistical
method to determine significance of observation. Submitted to PL
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