The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle θ13θ13 by observing νeνe appearance in a νμνμ beam. It also aims to make a precision measurement of the known oscillation parameters, View the MathML sourceΔm232 and sin22θ23sin22θ23, via νμνμ disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem

Executive SummaryThis document presents the physics case for bringing SciBar, the fully active, finely segmented tracking detector at KEK, to the FNAL Booster Neutrino Beam (BNB) line. This unique opportunity arose with the termination of K2K beam operations in 2005. At that time, the SciBar detector became available for use in other neutrino beam lines, including the BNB, which has been providing neutrinos to the MiniBooNE experiment since late 2002.The physics that can be done with SciBar/BNB can be put into three categories, each involving several measurements. First are neutrino cross section measurements which are interesting in their own right, including analyses of multi-particle final states, with unprecedented statistics. Second are measurements of processes that represent the signal and primary background channels for the upcoming T2K experiment. Third are measurements which improve existing or planned MiniBooNE analyses and the understanding of the BNB, both in neutrino and antineutrino mode.For each of these proposed measurements, the SciBar/BNB combination presents a unique opportunity or will significantly improve upon current or near-future experiments for several reasons. First, the fine granularity of SciBar allows detailed reconstruction of final states not possible with the MiniBooNE detector. Additionally, the BNB neutrino energy spectrum is a close match to the expected T2K energy spectrum in a region where cross sections are expected to vary dramatically with energy. As a result, the SciBar/BNB combination will provide cross-section measurements in an energy range complementary to MINERνA and complete our knowledge of neutrino cross sections over the entire energy range of interest to the upcoming off-axis experiments.SciBar and BNB have both been built and operated with great success. As a result, the cost of SciBar/BNB is far less than building a detector from scratch and both systems are well understood with existing detailed and calibrated Monte Carlo simulations. The performance expectations assumed in this document are therefore well-grounded in reality and carry little risk of not meeting expectations.This document includes a site optimization study with trade-offs between the excavation costs associated with placing the detector at different angles from the axis of the BNB and the physics which can be performed with the neutrino flux expected at these locations. Table 1 provides a summary of the impact of placing SciBar at these locations on the proposed measurements. The overwhelming conclusion of this study is that an on-axis location presents the best physics case and offsets the additional costs due to excavation. The estimated cost of the detector enclosure at the desired on-axis location is $505K.This proposal requests an extension of the BNB run through the end of FY2007, one year past its currently approved run, regardless of the outcome of the MiniBooNE ν e appearance search. Our schedules show that SciBar would be operational in the BNB within 9 months of initiation of the ...

We study the effect of the MeV-scale asymmetric dark matter annihilation on the effective number of neutrinos $N_{\rm eff}$ at the epoch of the big bang nucleosynthesis. If the asymmetric dark matter $\chi$ couples more strongly to the neutrinos $\nu$ than to the photons $\gamma$ and electrons $e^-$, $\Gamma_{\chi\gamma, \chi e} \ll \Gamma_{\chi\nu}$, or $\Gamma_{\chi\gamma, \chi e} \gg \Gamma_{\chi\nu}$, the lower mass limit on the asymmetric dark matter is about $18$ MeV for $N_{\rm eff}\simeq 3.0$.Comment: 13 pages, 14 figures, version accepted for publication in Physical Review

We study the effect of the MeV-scale asymmetric dark matter annihilation on the effective number of neutrinos N eff at the epoch of the big bang nucleosynthesis. If the asymmetric dark matter χ couples more strongly to the neutrinos ν than to the photons γ and electrons e − , Γχγ,χe ≪ Γχν , or Γχγ,χe ≫ Γχν, the lower mass limit on the asymmetric dark matter is about 18 MeV for N eff ≃ 3.0.