Session MA: Advances in Neutrino/Nuclear Physics

Theoretical Aspects of Coherent Elastic Neutrino Nucleus Scattering

We will discuss the physics potential of coherent elastic neutrino nucleus scattering. This standard model process has never been directly measured, although there are a number of experiments proposed at stopped pion/muon or reactor sites that could make such a first detection. Such a measurement opens up the possibility for a number of interesting physics probes. We will review these from a theoretical point of view, with a particular focus on the nuclear-neutron form factor.   

T2K (Tokai to Kamioka) is a long baseline neutrino oscillation experiment

A high intensity 30 GeV proton beam at J-PARC is directed towards a graphite target. The charged hadrons produced are focussed by magnetic horns to produce a mostly $\nu_{\mu}$ beam. The near detectors are set at 280 m from the target to monitor and measure the neutrino flux and intensity. The far detector is located 2.5 degrees off-axis at a distance of 295 km from the neutrino production point. This exposes the far detector to a narrow-band neutrino beam peaked at 0.6 GeV which is optimised to give the maximum neutrino oscillation probability and the minimum background to the $\nu_e$ appearance measurement. The current data set analized is $6.57 \times 10^{20}$ protons on target. The T2K experiment has observed 120 $\nu_{\mu}$ events at the far detector although $446 \pm 23$ events are expected without neutrino oscillation. This result leads to $\sin^2 \theta_{23}=0.514_{-0.056}^{+0.055} (0.511 \pm 0.055)$ and $|\Delta m^2_{32}| = (2.51 \pm 0.10) \times 10^{-3} ((2.48 \pm 0.10)\times 10^{-3}$) eV$^{2}$ assuming the normal (inverted) mass hierarchy. For the electron neutrino appearance, we have observed 28 $\nu_{e}$ events and measured $\sin^2 2\theta_{13} = 0.140_{-0.032}^{+0.038} (0.170_{-0.037}^{+0.045})$ assuming the normal (inverted) mass hierarchy, $\sin^2 \theta_{23}=0.5, |\Delta m^2_{32}|=2.4 \times 10^{-3}$ eV $^2$, and $\delta_{CP}=0$. This means 7.3 $\sigma$ significance to $\theta_{13}\neq 0$. In addition to the neutrino oscillation analysis, the neutrino interaction cross section measurements of the inclusive Charged Current, Charged Current quasi-elastic, and neutrino-oxygen neutral-current quasi-elastic channels are reported.   

Nuclear Effects in Neutrino Scattering at MINERvA

MINERvA is a neutrino cross section experiment in the NuMI beamline at Fermilab. The MINERvA detector employs fine-grained plastic scintillator (CH) for tracking and calorimetry, and is capable of reconstructing exclusive final states. The detector includes nuclear targets of carbon, iron, lead, liquid helium, and water, with which MINERvA can measure the nuclear dependence of neutrino interactions. Neutrino scattering measurements complement those done with charged leptons, because neutrino scattering directly probes axial structure and is sensitive to the deep inelastic structure function $F_{3}$. In addition, precise neutrino-nucleus measurements will reduce the significant nuclear model uncertainties incurred by using heavy nuclear targets to obtain high statistics in neutrino experiments. Such nuclear effects include both changes to the interaction cross section and alterations to the final state products through their interactions in the target nucleus. These uncertainties have implications for the utilization of neutrino deep inelastic scattering data in fitting parton distribution functions and for the extraction of neutrino oscillation parameters. We present three recent results from MINERvA that address this need for better knowledge of nuclear effects in neutrino scattering. First, measurements of $\nu_{\mu}$ and $\bar{\nu}_{\mu}$ quasielastic cross sections. Then, a measurement of charged pion production from inclusive $\nu_{\mu}$ interactions. Lastly, the first measurements of inclusive $\nu_{\mu}$ cross section ratios of carbon, iron, and lead to scintillator as functions of neutrino energy and Bjorken-x.   

Toward construction of a unified neutrino-nucleus interaction model

A precise knowledge of the neutrino-nucleus interactions is becoming one of the crucial issues for a successful determination of the neutrino parameters from the future neutrino-oscillation experiments. It is therefore urgent to have a reliable neutrino-nucleus interactoin model that enables a quantitative description of neutrino-nucleus reaction cross sections in an accuracy of 10 percent or less. However, the kinematic regions relevant to the neutrino parameter searches extend over the quasi-elastic, resonance, and deep-inelastic-scattering regions, where different theoretical treatments based on hadronic or partonic degrees of freedom are usually employed, and this makes the construction of a unified neutrino-nucleus interaction model covering those kinematic regions challenging. To tackle on such a challenging issue, we have recently developed a collaboration of experimentalists and theorists in different fields at J-PARC Branch of KEK Theory Center (http://www.nuint.kek.jp/index\_e.html). In this talk, I review our efforts toward construction of the unified neutrino-nucleus interaction model at J-PARC Branch of KEK Theory Center.