arXiv subjects

S. Hirota

Publications and source records attributed to S. Hirota.

42 records · Page 3Linked to original sources

arXiv2014

Enhancement of muonium emission rate from silica aerogel with a laser ablated surface

Emission of muonium ($μ^+e^-$) atoms from a laser-processed aerogel surface into vacuum was studied for the first time. Laser ablation was used to create hole-like regions with diameter of about 270$~μ$m in a triangular pattern with hole separation in the range of 300--500$~μ$m. The emission probability for the laser-processed aerogel sample is at least eight times higher than for a uniform one.

physics.ins-det↗

arXiv2014

Measurement of the Inclusive Electron Neutrino Charged Current Cross Section on Carbon with the T2K Near Detector

The T2K off-axis near detector, ND280, is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies ~1 GeV as a function of electron momentum, electron scattering angle and four-momentum transfer of the interaction. The total flux-averaged $ν_e$ charged current cross-section on carbon is measured to be $1.11\pm0.09~(stat)\pm0.18~(syst)\times10^{-38} cm^2/nucleon$. The differential and total cross-section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is $1.23\times10^{-38} cm^2/nucleon$ and the GENIE prediction is $1.08\times10^{-38} cm^2/nucleon$. The total $ν_e$ charged current cross-section result is also in agreement with data from the Gargamelle experiment.

hep-ex↗

arXiv2014

Precise Measurement of the Neutrino Mixing Parameter θ_{23} from Muon Neutrino Disappearance in an Off-axis Beam

New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta_{23}. Using an off-axis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10^{20} protons on target, T2K has fit the energy-dependent nu_mu oscillation probability to determine oscillation parameters. Marginalizing over the values of other oscillation parameters yields sin^2 (theta_{23}) = 0.514 +0.055/-0.056 (0.511 +- 0.055), assuming normal (inverted) mass hierarchy. The best-fit mass-squared splitting for normal hierarchy is Delta m^2_{32} = (2.51 +- 0.10) x 10^{-3} eV^2/c^4 (inverted hierarchy: Delta m^2_{13} = (2.48 +- 0.10) x 10^{-3} eV^2/c^4). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.

hep-ex↗

arXiv2014

First Indication of Terrestrial Matter Effects on Solar Neutrino Oscillation

We report an indication that the elastic scattering rate of solar $^8$B neutrinos with electrons in the Super-Kamiokande detector is larger when the neutrinos pass through the Earth during nighttime. We determine the day/night asymmetry, defined as the difference of the average day rate and average night rate divided by the average of those two rates, to be $(-3.2\pm1.1(\text{stat})\pm0.5(\text{syst}))\%$, which deviates from zero by 2.7 $σ$. Since the elastic scattering process is mostly sensitive to electron-flavored solar neutrinos, a non-zero day/night asymmetry implies that the flavor oscillations of solar neutrinos are affected by the presence of matter within the neutrinos' flight path. Super-Kamiokande's day/night asymmetry is consistent with neutrino oscillations for $4\times10^{-5}$eV$^2\leqΔm^2_{21}\leq7\times10^{-5}$eV$^2$ and large mixing values of $θ_{12}$, at the $68\%$ C.L.

hep-ex↗

arXiv2013

Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-axis Beam

The T2K collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to $3.01 \times 10^{20}$ protons on target. In the absence of neutrino oscillations, $205 \pm 17$ (syst.) events are expected to be detected and only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum assuming three neutrino flavors, normal mass hierarchy and $θ_{23}\leq π/4$ yields a best-fit mixing angle $\sin^2(2θ_{23})=1.000$ and mass splitting $|Δm^2_{32}| =2.44 \times 10^{-3}$ eV$^2$/c$^4$. If $θ_{23}\geq π/4$ is assumed, the best-fit mixing angle changes to $\sin^2(2θ_{23})=0.999$ and the mass splitting remains unchanged.

hep-ex↗

arXiv2013

Measurement of muonium emission from silica aerogel

Emission of muonium ($μ^{+}e^{-}$) atoms from silica aerogel into vacuum was observed. Characteristics of muonium emission were established from silica aerogel samples with densities in the range from 29 mg cm$^{-3}$ to 178 mg cm$^{-3}$. Spectra of muonium decay times correlated with distances from the aerogel surfaces, which are sensitive to the speed distributions, follow general features expected from a diffusion process, while small deviations from a simple room-temperature thermal diffusion model are identified. The parameters of the diffusion process are deduced from the observed yields.

physics.atom-ph↗