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## Measurement of neutrino oscillations parameters with the T2K Near Detector Upgrade

Title: Towards the measurement of CP Violation in the leptonic sector with the second phase of T2K and its Near Detector Upgrade

Supervisor: Claudio Giganti

Team: Asymétrie Matière-Antimatière ; group T2K

Description :

The LPNHE neutrino group is heavily involved in the T2K neutrino oscillation experiment.
T2K is a long-baseline accelerator experiment in Japan and was the first experiment to detect neutrino oscillations in appearance mode and is currently searching for CP violation in the lepton sector by comparing electron neutrino appearance probabilities for neutrinos and antineutrinos.
At a given baseline the oscillation probability depends on the energy of the neutrinos and the largest source of uncertainty is due to the modeling of the neutrino cross-sections that needs to be used in order to infer the neutrino energy from reconstructed quantities. In general, each kind of neutrino interaction (quasi-elastic, multinucleon excitations, pion production, …) is described by one or more cross-section models that have to be tuned on data. In T2K this is done by using a multi-purpose magnetized near detector, ND280, able to select samples of neutrinos and anti-neutrino interactions.

T2K recently published first hints of CP violation in the leptonic sector and is finalizing the upgrade of the Near Detector (ND280) towards the second phase of the experiment, T2K-II, in order to improve constraints on the CP violation in the lepton sector. The ND280 Upgrade consists in a new active target (Super-FGD) and two new Time Projection Chambers (HA-TPC) that will be installed in J-PARC by the end of 2022 and will start collecting neutrino data in 2023.
The LPNHE neutrino group is responsible for the overall coordination of the ND280 Upgrade, for the production of the Front-End electronics cards of the HA-TPC and is leading the development of the reconstruction of the HA-TPCs.

The installation of these new detectors will require the development of completely new reconstruction tools to fully exploit the potential of the upgrade.
The ND280 Upgrade is expected to reconstruct with better efficiency muons produced in neutrino interactions (while with the current detector configuration only muons parallel to the beam direction are reconstructed with good efficiency) and the hadronic part of the interaction, largely reducing the threshold for the reconstruction of protons and pions.
The careful description of the hadronic part will help to better reconstruct the energy of the neutrinos and to shed light on the nuclear processes on-going when neutrinos interact with nuclei. This work will be crucial not only to reach the physics goals of the phase II of T2K but also for the next-generation long baseline neutrino oscillation experiment, Hyper-K that has just started construction and is expected to start data taking in 2027. ND280 will be one of the near detectors of Hyper-K and the ND280 Upgrade is expected to provide inputs to oscillation analyses and cross-section modeling also in Hyper-K.

The PhD candidate will contribute to the development of the reconstruction tools and will participate to the commissioning of the detectors in Japan and to the analyses of the first data. Possible analyses topics include exploiting the full reconstruction of the final state of Quasi-Elastic neutrino interactions (muons plus protons or neutrons) to better constraint nuclear effects in neutrino interactions or to select electron neutrino interactions to constraint differences between electron and muon neutrino interactions that constitute one of the main systematics in the search for CPV in T2K-II and in future long-baseline experiments.

Work location: LPNHE, Paris

Possible trips: Tokai (Japon) and CERN, Geneva

Documentation:

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