934 research outputs found
Constraining Radon Backgrounds in LZ
The LZ dark matter detector, like many other rare-event searches, will suffer
from backgrounds due to the radioactive decay of radon daughters. In order to
achieve its science goals, the concentration of radon within the xenon should
not exceed Bq/kg, or 20 mBq total within its 10 tonnes. The LZ
collaboration is in the midst of a program to screen all significant components
in contact with the xenon. The four institutions involved in this effort have
begun sharing two cross-calibration sources to ensure consistent measurement
results across multiple distinct devices. We present here five preliminary
screening results, some mitigation strategies that will reduce the amount of
radon produced by the most problematic components, and a summary of the current
estimate of radon emanation throughout the detector. This best estimate totals
mBq, sufficiently low to meet the detector's science goals.Comment: Low Radioactivity Techniques (LRT) 2017 Workshop Proceedings. 6
pages; 3 figure
Results from the Palo Verde neutrino oscillation experiment
The ÎœÌ
e flux and spectrum have been measured at a distance of about 800 m from the reactors of the Palo Verde Nuclear Generating Station using a segmented Gd-loaded liquid scintillator detector. Correlated positron-neutron events from the reaction ÎœÌ
epâe+n were recorded for a period of 200 d including 55 d with one of the three reactors off for refueling. Backgrounds were accounted for by making use of the reactor-on and reactor-off cycles, and also with a novel technique based on the difference between signal and background under reversal of the e+ and n portions of the events. A detailed description of the detector calibration, background subtraction, and data analysis is presented here. Results from the experiment show no evidence for neutrino oscillations. ÎœÌ
eâÎœÌ
x oscillations were excluded at 90% C.L. for Îm2>1.12Ă10-3 eV2 for full mixing and sin22Ξ>0.21 for large Îm2. These results support the conclusion that the observed atmospheric neutrino oscillations do not involve Îœe
Neutron production by cosmic-ray muons at shallow depth
The yield of neutrons produced by cosmic ray muons at a shallow depth of 32
meters of water equivalent has been measured. The Palo Verde neutrino detector,
containing 11.3 tons of Gd loaded liquid scintillator and 3.5 tons of acrylic
served as a target. The rate of one and two neutron captures was determined.
Modeling the neutron capture efficiency allowed us to deduce the total yield of
neutrons neutrons per muon
and g/cm. This yield is consistent with previous measurements at similar
depths.Comment: 12 pages, 3 figure
Systematic Regge theory analysis of omega photoproduction
Systematic analysis of available data for -meson photoproduction is
given in frame of Regge theory. At photon energies above 20 GeV the
reaction is entirely dominated by Pomeron exchange.
However, it was found that Pomeron exchange model can not reproduce the
and data at high energies
simultaneously with the same set of parameters. The comparison between
and data indicates a large room for meson exchange contribution to
-meson photoproduction at low energies. It was found that at low
energies the dominant contribution comes from and -meson exchanges.
There is smooth transition between the meson exchange model at low energies and
Regge theory at high energies.Comment: 7 pages, 8 figures, revtex
Final results from the Palo Verde Neutrino Oscillation Experiment
The analysis and results are presented from the complete data set recorded at
Palo Verde between September 1998 and July 2000. In the experiment, the
\nuebar interaction rate has been measured at a distance of 750 and 890 m
from the reactors of the Palo Verde Nuclear Generating Station for a total of
350 days, including 108 days with one of the three reactors off for refueling.
Backgrounds were determined by (a) the technique based on the difference
between signal and background under reversal of the positron and neutron parts
of the correlated event and (b) making use of the conventional reactor-on and
reactor-off cycles. There is no evidence for neutrino oscillation and the mode
\nuebar\to\bar\nu_x was excluded at 90% CL for \dm>1.1\times10^{-3} eV
at full mixing, and \sinq>0.17 at large \dm.Comment: 11 pages, 8 figure
Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion
We present results of a study of neutrino oscillation based on a 766 ton-year
exposure of KamLAND to reactor anti-neutrinos. We observe 258 \nuebar\
candidate events with energies above 3.4 MeV compared to 365.2 events expected
in the absence of neutrino oscillation. Accounting for 17.8 expected background
events, the statistical significance for reactor \nuebar disappearance is
99.998%. The observed energy spectrum disagrees with the expected spectral
shape in the absence of neutrino oscillation at 99.6% significance and prefers
the distortion expected from \nuebar oscillation effects. A two-neutrino
oscillation analysis of the KamLAND data gives \DeltaMSq =
7.9 eV. A global analysis of data from KamLAND
and solar neutrino experiments yields \DeltaMSq =
7.9 eV and \ThetaParam =
0.40, the most precise determination to date.Comment: 5 pages, 4 figures; submitted to Phys.Rev.Letter
Search for the Invisible Decay of Neutrons with KamLAND
The Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) is used in a
search for single neutron or two neutron intra-nuclear disappearance that would
produce holes in the -shell energy level of C nuclei. Such holes
could be created as a result of nucleon decay into invisible modes (),
e.g. or . The de-excitation of the corresponding
daughter nucleus results in a sequence of space and time correlated events
observable in the liquid scintillator detector. We report on new limits for
one- and two-neutron disappearance: years
and years at 90% CL. These results
represent an improvement of factors of 3 and over previous
experiments.Comment: 5 pages, 3 figure
Measuring CP violation and mass ordering in joint long baseline experiments with superbeams
We propose to measure the CP phase , the magnitude of the
neutrino mixing matrix element and the sign of the atmopheric scale
mass--squared difference with a superbeam by the joint
analysis of two different long baseline neutrino oscillation experiments. One
is a long baseline experiment (LBL) at 300 km and the other is a very long
baseline (VLBL) experiment at 2100 km. We take the neutrino source to be the
approved high intensity proton synchrotron, HIPA. The neutrino beam for the LBL
is the 2-degree off-axis superbeam and for the VLBL, a narrow band superbeam.
Taking into account all possible errors, we evaluate the event rates required
and the sensitivities that can be attained for the determination of
and the sign of . We arrive at a
representative scenario for a reasonably precise probe of this part of the
neutrino physics.Comment: 25 RevTEX pages, 16 PS figures, revised figure captions and
references adde
First Results from KamLAND: Evidence for Reactor Anti-Neutrino Disappearance
KamLAND has been used to measure the flux of 's from distant
nuclear reactors. In an exposure of 162 tonyr (145.1 days) the ratio of
the number of observed inverse -decay events to the expected number of
events without disappearance is for energies 3.4 MeV. The deficit of events is
inconsistent with the expected rate for standard propagation at
the 99.95% confidence level. In the context of two-flavor neutrino oscillations
with CPT invariance, these results exclude all oscillation solutions but the
`Large Mixing Angle' solution to the solar neutrino problem using reactor
sources.Comment: 6 pages, 6 figure
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