Showing papers by "S. Nakayama published in 2013"
TL;DR: In this article, a FLUKA and GEANT3-based simulation was used to model the physical processes involved in neutrino production, from the interaction of primary beam protons in the T2K target, to the decay of hadrons and muons that produce neutrinos.
Abstract: The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations using an off-axis muon neutrino beam with a peak energy of about 0.6 GeV that originates at the Japan Proton Accelerator Research Complex accelerator facility. Interactions of the neutrinos are observed at near detectors placed at 280 m from the production target and at the far detector—Super-Kamiokande—located 295 km away. The flux prediction is an essential part of the successful prediction of neutrino interaction rates at the T2K detectors and is an important input to T2K neutrino oscillation and cross section measurements. A FLUKA and GEANT3-based simulation models the physical processes involved in the neutrino production, from the interaction of primary beam protons in the T2K target, to the decay of hadrons and muons that produce neutrinos. The simulation uses proton beam monitor measurements as inputs. The modeling of hadronic interactions is reweighted using thin target hadron production data, including recent charged pion and kaon measurements from the NA61/SHINE experiment. For the first T2K analyses the uncertainties on the flux prediction are evaluated to be below 15% near the flux peak. The uncertainty on the ratio of the flux predictions at the far and near detectors is less than 2% near the flux peak.
205 citations
TL;DR: The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, and the background-only hypothesis is rejected with a ======p==================
Abstract: The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting,
|
Δ
m
2
32
|
≈
2.4
×
10
−
3
eV
2
. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam’s origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of
3.3
±
0.4
(
syst
)
events is expected. The background-only hypothesis is rejected with a
p
value of 0.0009 (
3.1
σ
), and a fit assuming
ν
μ
→
ν
e
oscillations with
sin
2
2
θ
23
=
1
,
δ
C
P
=
0
and
|
Δ
m
2
32
|
=
2.4
×
10
−
3
eV
2
yields
sin
2
2
θ
13
=
0.088
+
0.049
−
0.039
(
stat
+
syst
)
.
188 citations
TL;DR: The T2K Collaboration reports a precision measurement of muon neutrinos disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV, corresponding to the maximal oscillation disappearance probability.
Abstract: 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 3.01×1020 protons on target. In the absence of neutrino oscillations, 205±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 θ23≤π/4 yields a best-fit mixing angle sin2(2θ23)=1.000 and mass splitting |Δm232|=2.44×10−3 eV2/c4. If θ23≥π/4 is assumed, the best-fit mixing angle changes to sin2(2θ23)=0.999 and the mass splitting remains unchanged.
118 citations