arXiv subjects

Y. Wada

Publications and source records attributed to Y. Wada.

10 recordsLinked to original sources

arXiv2021

Limits on astrophysical antineutrinos with the KamLAND experiment

We report on a search for electron antineutrinos ($\bar{\nu}_e$) from astrophysical sources in the neutrino energy range 8.3 to 30.8 MeV with the KamLAND detector. In an exposure of 6.72 kton-year of the liquid scintillator, we observe 18 candidate events via the inverse beta decay reaction. Although there is a large background uncertainty from neutral current atmospheric neutrino interactions, we find no significant excess over background model predictions. Assuming several supernova relic neutrino spectra, we give upper flux limits of 60--110 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis range and present a model-independent flux. We also set limits on the annihilation rates for light dark matter pairs to neutrino pairs. These data improves on the upper probability limit of $^{8}$B solar neutrinos converting into $\bar{\nu}_e$'s, $P_{\nu_e \rightarrow \bar{\nu}_e} < 3.5\times10^{-5}$ (90% CL) assuming an undistorted $\bar{\nu}_e$ shape. This corresponds to a solar $\bar{\nu}_e$ flux of 60 cm$^{-2}$ s$^{-1}$ (90% CL) in the analysis energy range.

astro-ph.HE↗

arXiv2021

Search for Solar Flare Neutrinos with the KamLAND detector

We report the result of a search for neutrinos in coincidence with solar flares from the GOES flare database. The search was performed on a 10.8 kton-year exposure of KamLAND collected from 2002 to 2019. This large exposure allows us to explore previously unconstrained parameter space for solar flare neutrinos. We found no statistical excess of neutrinos and established 90% confidence level upper limits of $8.4 \times 10^7$ cm$^{-2}$ ($3.0 \times 10^{9}$ cm$^{-2}$) on electron anti-neutrino (electron neutrino) fluence at 20 MeV normalized to the X12 flare, assuming that the neutrino fluence is proportional to the X-ray intensity.

astro-ph.SR↗

arXiv2021

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 $^{136}$Xe by using $^{136}$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 $^{8}$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 $^{136}$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.

physics.ins-det↗

arXiv2021

Proton-$\rm ^3He$ elastic scattering at intermediate energies

We present a precise measurement of the cross section, proton and $\rm ^3He$ analyzing powers, and spin correlation coefficient $C_{y,y}$ for $p$-$\rm ^3He$ elastic scattering near 65 MeV, and a comparison with rigorous four-nucleon scattering calculations based on realistic nuclear potentials and a model with $\Delta$-isobar excitation. Clear discrepancies are seen in some of the measured observables in the regime around the cross section minimum. Theoretical predictions using scaling relations between the calculated cross section and the $\rm ^3 He$ binding energy are not successful in reproducing the data. Large sensitivity to the $NN$ potentials and rather small $\Delta$-isobar effects in the calculated cross section are noticed as different features from those in the deuteron-proton elastic scattering. The results obtained above indicate that $p$-$\rm ^3He$ scattering at intermediate energies is an excellent tool to explore nuclear interactions not accessible by three-nucleon scattering.

nucl-ex↗

arXiv2021

A Search for Charged Excitation of Dark Matter with the KamLAND-Zen Detector

There are many theories where a dark matter particle is part of a multiplet with an electrically charged state. If WIMP dark matter ($χ^{0}$) is accompanied by a charged excited state ($χ^{-}$) separated by a small mass difference, it can form a stable bound state with a nucleus. In supersymmetric models, the $χ^{0}$ and the $χ^{-}$ could be the neutralino and a charged slepton, such as the neutralino-stau degenerate model. The formation binding process is expected to result in an energy deposition of {\it O}(1--10 MeV), making it suitable for detection in large liquid scintillator detectors. We describe new constraints on the bound state formation with a xenon nucleus using the KamLAND-Zen 400 Phase-II dataset. In order to enlarge the searchable parameter space, all xenon isotopes in the detector were used. For a benchmark parameter set of $m_{χ^{0}} = 100$ GeV and $Δm = 10$ MeV, this study sets the most stringent upper limits on the recombination cross section $\langleσv\rangle$ and the decay-width of $χ^{-}$ of $2.0 \times 10^{-31}$ ${\rm cm^3/s}$ and $1.1 \times 10^{-18}$ GeV, respectively (90\% confidence level).

hep-ex↗

arXiv2020

Search for Low-energy Electron Antineutrinos in KamLAND Associated with Gravitational Wave Events

We present the results of a search for MeV-scale electron antineutrino events in KamLAND in coincident with the 60 gravitational wave events/candidates reported by the LIGO/Virgo collaboration during their second and third observing runs. We find no significant coincident signals within a $\pm$ 500 s timing window from each gravitational wave and present 90% C.L. upper limits on the electron antineutrino fluence between $10^{8}$-$10^{13}\,{\mathrm cm^2}$ for neutrino energies in the energy range of 1.8-111 MeV.

astro-ph.HE↗

arXiv2019

Measurement of 3He analyzing power for p-3He scattering using the polarized 3He target

Proton-3He scattering is one of the good probes to study the T=3/2 channel of three--nucleon forces. We have measured 3He analyzing powers for p-3He elastic scattering with the polarized 3He target at 70 and 100 MeV. The data are compared with the theoretical predictions based on the modern nucleon--nucleon potentials. Large discrepancies are found between the data and the calculations at the angles where the 3He analyzing power takes the minimum and maximum values, which are not explained by taking into account Delta-isobar degrees of freedom.

nucl-ex↗

arXiv2019

Conditional stability for an inverse source problem and an application to the estimation of air dose rate radioactive substances by drone data

We consider the density field $f(x)$ generated by a volume source $μ(y)$ in $D$ which is a domain in $\R^3$. For two disjoint segments $γ, Γ_1$ on a straight line in $\R^3 \setminus \ooo{D}$, we establish a conditional stability estimate of Hölder type in determining $f$ on $Γ_1$ by data $f$ on $γ$. This is a theoretical background for real-use solutions for the determination of air dose rates of radioactive substance at the human height level by high-altitude data. The proof of the stability estimate is based on the harmonic extension and the stability for line unique continuation of a harmonic function.

math.AP↗

arXiv2010

Surface Majorana Cone of the Superfluid $^3$He B Phase

The superfluid $^3$He B phase, one of the oldest unconventional fermionic condensates experimentally realized, is recently predicted to support Majorana fermion surface states. Majorana fermion, which is characterized by the equivalence of particle and antiparticle, has a linear dispersion relation referred to as the Majorana cone. We measured the transverse acoustic impedance $Z$ of the superfluid$^3$He B phase changing its boundary condition and found a growth of peak in $Z$ on a higher specularity wall. Our theoretical analysis indicates that the variation of $Z$ is induced by the formation of the cone-like dispersion relation and thus confirms the important feature of the Majorana fermion in the specular limit.

cond-mat.other↗

arXiv2000

Probing the DeltaNN component of 3He

The 3He(gamma,pi^+/- p) reactions were measured simultaneously over a tagged photon energy range of 800<E_gamma<1120 MeV, well above the Delta resonance region. An analysis was performed to kinematically isolate Delta knockout events from conventional Delta photoproduction events, and a statistically significant excess of pi+p events was identified, consistent with Delta++ knockout. Two methods were used to estimate the DeltaNN probability in the 3He ground state, corresponding to the observed knockout cross section. The first gave a lower probability limit of 1.5+/-0.6+/-0.5%; the second yielded an upper limit of about 2.6%.

nucl-ex↗