11 research outputs found
Experimental Status of Neutrino Physics
After a fascinating phase of discoveries, neutrino physics still has a few
mysteries such as the absolute mass scale, the mass hierarchy, the existence of
CP violation in the lepton sector and the existence of right-handed neutrinos.
It is also entering a phase of precision measurements. This is what motivates
the NUFACT 11 conference which prepares the future of long baseline neutrino
experiments. In this paper, we report the status of experimental neutrino
physics. We focus mainly on absolute mass measurements, oscillation parameters
and future plans for oscillation experiments
Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen
United States. Department of Energy (DE-AC02-05CH11231
Measurement of cosmic-ray muon spallation products in a xenon-loaded liquid scintillator with KamLAND
Cosmic-ray muons produce various radioisotopes when passing through material.
These spallation products can be backgrounds for rare event searches such as in
solar neutrino, double-beta decay, and dark matter search experiments. The
KamLAND-Zen experiment searches for neutrinoless double-beta decay in 745kg of
xenon dissolved in liquid scintillator. The experiment includes dead-time-free
electronics with a high efficiency for detecting muon-induced neutrons. The
production yields of different radioisotopes are measured with a combination of
delayed coincidence techniques, newly developed muon reconstruction and xenon
spallation identification methods. The observed xenon spallation products are
consistent with results from the FLUKA and Geant4 simulation codes
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Publisher's Note: Search for Majorana Neutrinos Near the Inverted Mass Hierarchy Region with KamLAND-Zen [Phys. Rev. Lett. 117, 082503 (2016)].
This corrects the article DOI: 10.1103/PhysRevLett.117.082503
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Measurement of the Double-Beta Decay Half-life of {sup 136}Xe in KamLAND-Zen
We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of {sup 136}Xe. The measured two-neutrino double-beta decay half-life of {sup 136}Xe is T{sup 2{nu}}{sub 1/2} = 2:38 {+-}#6; 0:02(stat)#6;{+-}0.14(syst)#2;x10{sup 21} yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, T{sup 0{nu}}{sub 1/2} > 5.7 x#2; 10{sup 24} yr at 90% C.L
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Precision Analysis of the ^{136}Xe Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements.
We present a precision analysis of the ^{136}Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ_{31}^{2ν}=-0.26_{-0.25}^{+0.31}. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ξ_{31}^{2ν} range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ_{31}^{2ν} values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ξ_{31}^{2ν} provides new insights toward reliable neutrinoless ββ NMEs
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Precision Analysis of the ^{136}Xe Two-Neutrino ββ Spectrum in KamLAND-Zen and Its Impact on the Quenching of Nuclear Matrix Elements.
We present a precision analysis of the ^{136}Xe two-neutrino ββ electron spectrum above 0.8 MeV, based on high-statistics data obtained with the KamLAND-Zen experiment. An improved formalism for the two-neutrino ββ rate allows us to measure the ratio of the leading and subleading 2νββ nuclear matrix elements (NMEs), ξ_{31}^{2ν}=-0.26_{-0.25}^{+0.31}. Theoretical predictions from the nuclear shell model and the majority of the quasiparticle random-phase approximation (QRPA) calculations are consistent with the experimental limit. However, part of the ξ_{31}^{2ν} range allowed by the QRPA is excluded by the present measurement at the 90% confidence level. Our analysis reveals that predicted ξ_{31}^{2ν} values are sensitive to the quenching of NMEs and the competing contributions from low- and high-energy states in the intermediate nucleus. Because these aspects are also at play in neutrinoless ββ decay, ξ_{31}^{2ν} provides new insights toward reliable neutrinoless ββ NMEs
Search for the Majorana Nature of Neutrinos in the Inverted Mass Ordering Region with KamLAND-Zen
The KamLAND-Zen experiment has provided stringent constraints on the
neutrinoless double-beta () decay half-life in Xe using
a xenon-loaded liquid scintillator. We report an improved search using an
upgraded detector with almost double the amount of xenon and an ultralow
radioactivity container, corresponding to an exposure of 970 kg yr of
Xe. These new data provide valuable insight into backgrounds,
especially from cosmic muon spallation of xenon, and have required the use of
novel background rejection techniques. We obtain a lower limit for the
decay half-life of yr at
90% C.L., corresponding to upper limits on the effective Majorana neutrino mass
of 36-156 meV using commonly adopted nuclear matrix element calculations.Comment: 7 pages, 3 figure
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The nylon balloon for xenon loaded liquid scintillator in KamLAND-Zen 800 neutrinoless double-beta decay search experiment
The KamLAND-Zen 800 experiment is searching for the neutrinoless double-beta
decay of Xe by using Xe-loaded liquid scintillator. The liquid
scintillator is enclosed inside a balloon made of thin, transparent,
low-radioactivity film that we call Inner Balloon (IB). The IB, apart from
guaranteeing the liquid containment, also allows to minimize the background
from cosmogenic muon-spallation products and B solar neutrinos. Indeed
these events could contribute to the total counts in the region of interest
around the Q-value of the double-beta decay of Xe. In this paper, we
present an overview of the IB and describe the various steps of its
commissioning minimizing the radioactive contaminations, from the material
selection, to the fabrication of the balloon and its installation inside the
KamLAND detector. Finally, we show the impact of the IB on the KamLAND
background as measured by the KamLAND detector itself