Characterising the detector response of the SuperFGD as part of the T2K near detector upgrade Tristan Doyle (on behalf of the T2K collaboration) tristan.doyle@stonybrook.edu 1. The T2K Experiment The Tokai-to-Kamioka (T2K) experiment is a long-baseline neutrino experiment based in Japan νµ (¯νµ) beam produced at J-PARC, characterised by near detectors and detected at Super-Kamiokande Measures νµ (¯νµ) disappearance and νe (¯νe) appearance 2. Near Detector (ND280) Upgrade Replace π0 detector with three new sub-detectors: →Super Fine-Grained Detector (SuperFGD): Highly segmented target material with ability to reconstruct neutrons and lower momentum protons →High-Angle Time Projection Chambers (HATPCs): measure momentum, charge and particle ID with better angular acceptance than before See posters by Matteo Feltre and Ulysse Virginet →Time-of-Flight (ToF): Precise timing information to reject backgrounds and improve reconstruction See physics capabilities in posters by Liz Kneale, Katharina Lachner and Weijun Li 3. SuperFGD Concept and Construction 2 million optically isolated 1 cm3 plastic scintillator cubes [1] 56,000 wavelength shifting (WLS) fibers →Each coupled to a multi-pixel photon counter (MPPC) →Three orthogonal fibers per cube Concept proven in charged particle [2] and neutron [3] beam tests Detector assembly at J-PARC October 2022 - April 2023: →Cube layers installed with fishing lines →Vertical alignment using metallic rods →Fishing lines replaced with WLS fibers →MPPCs and LED calibration system installed SuperFGD installed in October 2023 Find description of the electronics in poster by Viet Nguyen 4. Light Yield Measure ADC counts from electronics Can convert ADC counts to photoelectrons (p.e.) See poster on calibration by Daniel Ferlewicz For each hit there is a high gain (HG) ADC and a low gain (LG) ADC Linear relationship between HG and LG provides larger dynamic range Also measure time over threshold (ToT) for each hit Can convert ToT to HG using exponential relationship Provides even larger dynamic range than LG 5. Attenuation Length Having three fibers per cube allows construction of attenuation length plot →More reliable characterisation of response and calibration For a given distance from the MPPCs, plot observed light from hits in cosmic events Fit distribution as a function of distance with an exponential function to extract attenuation length →Measured attenuation length consistent with specification of WLS fibers 6. Time Resolution Select hits > 40 p.e. matched in all three dimensions Compare mean time of hit to mean time for event Gives ∼1.2 ns time resolution →Can be improved by electronics firmware update! 7. Neutrino Interactions in the SuperFGD Some of the first neutrino interaction candidates in the SuperFGD. Possible proton (left) and pion (right) candidates are highlighted. 7. Next Steps Continue tuning Monte Carlo simulation using measurements of light yield and attenuation length Measure dE/dx in the SuperFGD and make selection of proton candidates using Bragg peak Head towards first physics analyses with the SuperFGD! References [1] Y. Abreu et al 2017 JINST 12 P04024 [2] A. Blondel et al 2020 JINST 15 P12003 [3] A. Agarwal et al 2023 Phys. Lett. B 840 137843