Dr Kirsty Duffy

Abstract:

As limits improve on the neutrino mixing angles and mass-squared differences, the focus of T2K has shifted towards studying antineutrino oscillation. This will give an insight into CP violation (if P($\bar{\nu}_{\mu} \rightarrow \bar{\nu}_{e}) \neq \mbox{P}(\nu_{\mu} \rightarrow \nu_e)$) and CPT violation (if P($\bar{\nu}_{\mu} \rightarrow \bar{\nu}_{\mu}) \neq \mbox{P}(\nu_{\mu} \rightarrow \nu_{\mu})$) in the lepton sector. This poster summarises the most recent T2K antineutrino oscillation results, from data collected using a $\bar{\nu}_{\mu}$-enhanced neutrino beam corresponding to $4.01 \times 10^{20}$ protons on target (roughly $1/3$ of the total protons on target collected by T2K). We present world-leading measurements of $\Delta \bar{m}^2_{32}$ and $\sin^2\bar{\theta}_{23}$ and the first analysis of $\bar{\nu}_e$ appearance from T2K. Both results use a Bayesian oscillation analysis based on a Markov Chain Monte Carlo method in which data from the near detector and far detector are fit simultaneously.

Abstract:

T2K reports its first measurements of the parameters governing the disappearance of ν¯μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ν¯μ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the ν¯μ survival probability is expected to be minimal. Using a data set corresponding to 4.01×1020 protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin2(θ¯23)=0.45 and |Δm¯232|=2.51×10−3  eV2 with 68% confidence intervals of 0.38–0.64 and 2.26–2.80×10−3  eV2, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the νμ disappearance parameters measured by T2K.

Abstract:

There has been a great deal of theoretical work on sophisticated charged current quasi-elastic (CCQE) neutrino interaction models in recent years, prompted by a number of experimental results that measured unexpectedly large CCQE cross sections on nuclear targets. As the dominant interaction mode at T2K energies, and the signal process in oscillation analyses, it is important for the T2K experiment to include realistic CCQE cross section uncertainties in T2K analyses. To this end, T2K’s Neutrino Interaction Working Group has implemented a number of recent models in NEUT, T2K’s primary neutrino interaction event generator. In this paper, we give an overview of the models implemented and present fits to published νμ and ¯νμ CCQE cross section measurements from the MiniBooNE and MINERνA experiments. The results of the fits are used to select a default cross section model for future T2K analyses and to constrain the cross section uncertainties of the model. We find strong tension between datasets for all models investigated. Among the evaluated models, the combination of a modified relativistic Fermi gas with multinucleon CCQE-like interactions gives the most consistent description of the available data.

Abstract:

We report a measurement of the νμ-nucleus inclusive charged-current cross section (=σcc) on iron using data from the INGRID detector exposed to the J-PARC neutrino beam. The detector consists of 14 modules in total, which are spread over a range of off-axis angles from 0° to 1.1°. The variation in the neutrino energy spectrum as a function of the off-axis angle, combined with event topology information, is used to calculate this cross section as a function of neutrino energy. The cross section is measured to be σcc(1.1 GeV)=1.10±0.15 (10-38 cm2/nucleon), σcc(2.0 GeV)=2.07±0.27 (10-38 cm2/nucleon), and σcc(3.3 GeV)=2.29±0.45 (10-38 cm2/nucleon), at energies of 1.1, 2.0, and 3.3 GeV, respectively. These results are consistent with the cross section calculated by the neutrino interaction generators currently used by T2K. More importantly, the method described here opens up a new way to determine the energy dependence of neutrino-nucleus cross sections.