In this document, we present the Technical Design Report of the Upgrade of the T2K Near Detector ND280. The goal of this upgrade is to improve the Near Detector performance to measure the neutrino interaction rate and to constrain the neutrino intera
ction cross-sections so that the uncertainty in the number of predicted events at Super-Kamiokande is reduced to about 4%. This will allow to improve the physics reach of the T2K-II project. This goal is achieved by modifying the upstream part of the detector, adding a new highly granular scintillator detector (Super-FGD), two new TPCs (High-Angle TPC) and six TOF planes. Details about the detector concepts, design and construction methods are presented, as well as a first look at the test-beam data taken in Summer 2018. An update of the physics studies is also presented.
The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle $theta_{13}$ have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation
experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal $sin^22theta_{23}$, the octant of $theta_{23}$, and the mass hierarchy, in addition to the measurements of $delta_{CP}$, $sin^2theta_{23}$, and $Delta m^2_{32}$, for various combinations of $ u$-mode and (bar{ u})-mode data-taking. With an exposure of $7.8times10^{21}$~protons-on-target, T2K can achieve 1-$sigma$ resolution of 0.050(0.054) on $sin^2theta_{23}$ and $0.040(0.045)times10^{-3}~rm{eV}^2$ on $Delta m^2_{32}$ for 100%(50%) neutrino beam mode running assuming $sin^2theta_{23}=0.5$ and $Delta m^2_{32} = 2.4times10^{-3}$ eV$^2$. T2K will have sensitivity to the CP-violating phase $delta_{rm{CP}}$ at 90% C.L. or better over a significant range. For example, if $sin^22theta_{23}$ is maximal (i.e $theta_{23}$=$45^circ$) the range is $-115^circ<delta_{rm{CP}}<-60^circ$ for normal hierarchy and $+50^circ<delta_{rm{CP}}<+130^circ$ for inverted hierarchy. When T2K data is combined with data from the NO$ u$A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero $delta_{CP}$ is substantially increased compared to if each experiment is analyzed alone.
We have searched for proton into muon plus neutral kaon using data from a 91.7 kiloton-year exposure of Super-Kamiokande-I, a 49.2 kiloton-year exposure of Super-Kamiokande-II, and a 31.9 kiloton-year exposure of Super-Kamiokande-III. The number of c
andidate events in the data was consistent with the atmospheric neutrino background expectation and no evidence for proton decay in this mode was found. We set a partial lifetime lower limit of 1.6x10^33 years at the 90% confidence level.
The T2K experiment observes indications of $ u_murightarrow u_e$ appearance in data accumulated with $1.43times10^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario wi
th $|Delta m_{23}^2|=2.4times10^{-3}$ eV$^2$, $sin^2 2theta_{23}=1$ and $sin^2 2theta_{13}=0$, the expected number of such events is 1.5$pm$0.3(syst.). Under this hypothesis, the probability to observe six or more candidate events is 7$times10^{-3}$, equivalent to 2.5$sigma$ significance. At 90% C.L., the data are consistent with 0.03(0.04)$<sin^2 2theta_{13}<$ 0.28(0.34) for $delta_{rm CP}=0$ and a normal (inverted) hierarchy.
In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a
longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7pm1.1(stat)pm1.2 0.6(sys)times10-2 at energies between 4.8 and 7.2 keVee and to 7.7pm2.8(stat)pm2.5 2.8(sys)times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4pm0.2(stat)pm0.3 0.2(sys)times10-1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.
We present a measurement of the branching fraction for the decay B^0->a1+(1260)pi- with a1+->pi+pi+pi- using a data sample containing 535x10^6 BBbar pairs collected with the Belle detector at the KEKB asymmetric-energy e+e- collider operating at the
Upsilon(4S) resonance. We measure the branching fraction Br(B^0->a1+pi-)Br(a1+->pi+pi+pi-) = (14.9 +- 1.6 +- 2.3)x10^-6, where the first and second errors are statistical and systematic, respectively.
