132 research outputs found
Resultados finales para el parámetro de asimetría ? de neutrones A 0 del experimento UCNA
The UCNA experiment was designed to measure the neutron ?-asymmetry parameter A0 using polarized ultracold neutrons (UCN). UCN produced via downscattering in solid deuterium were polarized via transport through a 7 T magnetic field, and then directed to a 1 T solenoidal electron spectrometer, where the decay electrons were detected in electron detector packages located on the two ends of the spectrometer. A value for A0 was then extracted from the asymmetry in the numbers of counts in the two detector packages. We summarize all of the results from the UCNA experiment, obtained during run periods in 2007, 2008–2009, 2010, and 2011–2013, which ultimately culminated in a 0.67% precision result for A0
Low-Background gamma counting at the Kimballton Underground Research Facility
The next generation of low-background physics experiments will require the
use of materials with unprecedented radio-purity. A gamma-counting facility at
the Kimballton Underground Research Facility (KURF) has been commissioned to
perform initial screening of materials for radioactivity primarily from
nuclides in the 238U and 232Th decay chains, 40K and cosmic-ray induced
isotopes. The facility consists of two commercial low-background high purity
germanium (HPGe) detectors. A continuum background reduction better than a
factor of 10 was achieved by going underground. This paper describes the
facility, detector systems, analysis techniques and selected assay results.Comment: 7 pages, 7 figures. Submitted to NIM
Causality and statistics on the Groenewold-Moyal plane
Quantum theories constructed on the noncommutative spacetime called the
Groenewold-Moyal plane exhibit many interesting properties such as Lorentz and
CPT noninvariance, causality violation and twisted statistics. We show that
such violations lead to many striking features that may be tested
experimentally. These theories predict Pauli forbidden transitions due to
twisted statistics, anisotropies in the cosmic microwave background radiation
due to correlations of observables in spacelike regions and Lorentz and CPT
violations in scattering amplitudes.Comment: 12 pages, 1 figure. Based on the talk given by APB at the Workshop
"Theoretical and Experimental Aspects of the Spin Statisics Connection and
Related Symmetries", Stazione Marittima Conference Center, Trieste, Italy
from the 21st to the 25th of October 200
Nuclear and nucleon transitions of the H di-baryon
We consider 3 types of processes pertinent to the phenomenology of an H
di-baryon: conversion of two 's in a doubly-strange hypernucleus to an
H, decay of the H to two baryons, and -- if the H is light enough -- conversion
of two nucleons in a nucleus to an H. We compute the spatial wavefunction
overlap using the Isgur-Karl and Bethe-Goldstone wavefunctions, and treat the
weak interactions phenomenologically. The observation of decays from
doubly-strange hypernuclei puts a constraint on the H wavefunction which is
plausibly satisfied. In this case the H is very long-lived as we calculate. An
absolutely stable H is not excluded at present. SuperK can provide valuable
limits
Borexino calibrations: Hardware, Methods, and Results
Borexino was the first experiment to detect solar neutrinos in real-time in
the sub-MeV region. In order to achieve high precision in the determination of
neutrino rates, the detector design includes an internal and an external
calibration system. This paper describes both calibration systems and the
calibration campaigns that were carried out in the period between 2008 and
2011. We discuss some of the results and show that the calibration procedures
preserved the radiopurity of the scintillator. The calibrations provided a
detailed understanding of the detector response and led to a significant
reduction of the systematic uncertainties in the Borexino measurements
Pulse-Shape discrimination with the Counting Test Facility
Pulse shape discrimination (PSD) is one of the most distinctive features of
liquid scintillators. Since the introduction of the scintillation techniques in
the field of particle detection, many studies have been carried out to
characterize intrinsic properties of the most common liquid scintillator
mixtures in this respect. Several application methods and algorithms able to
achieve optimum discrimination performances have been developed. However, the
vast majority of these studies have been performed on samples of small
dimensions. The Counting Test Facility, prototype of the solar neutrino
experiment Borexino, as a 4 ton spherical scintillation detector immersed in
1000 tons of shielding water, represents a unique opportunity to extend the
small-sample PSD studies to a large-volume setup. Specifically, in this work we
consider two different liquid scintillation mixtures employed in CTF,
illustrating for both the PSD characterization results obtained either with the
processing of the scintillation waveform through the optimum Gatti's method, or
via a more conventional approach based on the charge content of the
scintillation tail. The outcomes of this study, while interesting per se, are
also of paramount importance in view of the expected Borexino detector
performances, where PSD will be an essential tool in the framework of the
background rejection strategy needed to achieve the required sensitivity to the
solar neutrino signals.Comment: 39 pages, 17 figures, submitted to Nucl. Instr. Meth.
New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility
The results of background measurements with the second version of the
BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso
Underground Laboratory, were used to obtain limits on the instability of
nucleons, bounded in nuclei, for decays into invisible channels ():
disappearance, decays to neutrinos, etc. The approach consisted of a search for
decays of unstable nuclides resulting from and decays of parents
C, C and O nuclei in the liquid scintillator and the water
shield of the CTF. Due to the extremely low background and the large mass (4.2
ton) of the CTF detector, the most stringent (or competitive) up-to-date
experimental bounds have been established: y, y, y and y, all at 90% C.L.Comment: 22 pages, 3 figures,submitted to Phys.Lett.
Astroparticle Physics with a Customized Low-Background Broad Energy Germanium Detector
The MAJORANA Collaboration is building the MAJORANA DEMONSTRATOR, a 60 kg
array of high purity germanium detectors housed in an ultra-low background
shield at the Sanford Underground Laboratory in Lead, SD. The MAJORANA
DEMONSTRATOR will search for neutrinoless double-beta decay of 76Ge while
demonstrating the feasibility of a tonne-scale experiment. It may also carry
out a dark matter search in the 1-10 GeV/c^2 mass range. We have found that
customized Broad Energy Germanium (BEGe) detectors produced by Canberra have
several desirable features for a neutrinoless double-beta decay experiment,
including low electronic noise, excellent pulse shape analysis capabilities,
and simple fabrication. We have deployed a customized BEGe, the MAJORANA
Low-Background BEGe at Kimballton (MALBEK), in a low-background cryostat and
shield at the Kimballton Underground Research Facility in Virginia. This paper
will focus on the detector characteristics and measurements that can be
performed with such a radiation detector in a low-background environment.Comment: Submitted to NIMA Proceedings, SORMA XII. 9 pages, 4 figure
Study of infrared scintillations in gaseous and liquid argon - Part II: light yield and possible applications
We present here a comprehensive study of the light yield of primary and
secondary scintillations produced in gaseous and liquid Ar in the near infrared
(NIR) and visible region, at cryogenic temperatures. The measurements were
performed using Geiger-mode avalanche photodiodes (GAPDs) and pulsed X-ray
irradiation. The primary scintillation yield of the fast emission component in
gaseous Ar was found to be independent of temperature in the range of 87-160 K;
it amounted to 17000+/-3000 photon/MeV in the NIR in the range of 690-1000 nm.
In liquid Ar at 87 K, the primary scintillation yield of the fast component was
considerably reduced, amounting to 510+/-90 photon/MeV, in the range of
400-1000 nm. Proportional NIR scintillations (electroluminescence) in gaseous
Ar were also observed; their amplification parameter at 160 K was measured to
be 13 photons per drifting electron per kV. No proportional scintillations were
observed in liquid Ar up to the electric fields of 30 kV/cm. The applications
of NIR scintillations in dark matter search and coherent neutrino-nucleus
scattering experiments and in ion beam radiotherapy are considered.Comment: 20 pages, 11 figures. Submitted to JINS
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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