Dr Kirsty Duffy

Abstract:

We report the measurement of muon neutrino charged-current interactions on carbon without pions in the final state at the T2K beam energy using 5.734×1020 protons on target. For the first time the measurement is reported as a flux-integrated, double-differential cross section in muon kinematic variables (cosθμ, pμ), without correcting for events where a pion is produced and then absorbed by final state interactions. Two analyses are performed with different selections, background evaluations and cross-section extraction methods to demonstrate the robustness of the results against biases due to model-dependent assumptions. The measurements compare favorably with recent models which include nucleon-nucleon correlations but, given the present precision, the measurement does not distinguish among the available models. The data also agree with Monte Carlo simulations which use effective parameters that are tuned to external data to describe the nuclear effects. The total cross section in the full phase space is σ=(0.417±0.047(syst)±0.005(stat))×10-38 cm2 nucleon-1 and the cross section integrated in the region of phase space with largest efficiency and best signal-over-background ratio (cosθμ>0.6 and pμ>200 MeV) is σ=(0.202±0.036(syst)±0.003(stat))×10-38 cm2 nucleon-1.

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.