Abstract
The T2K experiment studies oscillations of an off-axis muon neutrinobeam between the J-PARC accelerator complex and the Super-Kamiokandedetector. Special emphasis is placed on measuring the mixing angleθ13 by observing νe appearance via the sub-dominant νμ → νeoscillation and searching for CP violationin the lepton sector.The experiment includes a sophisticated, off-axis, near detector, theND280, situated280 m downstream of the neutrino production target in order to measurethe properties of the neutrino beam and to understand better neutrinointeractions at the energy scale below a few GeV. The data collectedwith the ND280 are used to study charged-and neutral-current neutrino interaction rates and kinematics prior tooscillation,in order to reduce uncertainties in the oscillation measurementsby the far detector.A key element of the near detector is the ND280 electromagneticcalorimeter (ECal), consisting ofactive scintillator bars sandwiched between lead sheets and read outwith multi-pixel photon counters (MPPCs). The ECal is vital to thereconstruction of neutral particles, and the identification of chargedparticle species.The ECal surrounds the Pi-0 detector (PØD) and the tracking regionof the ND280, and is enclosed in the former UA1/NOMAD dipole magnet. This paper describes the design, construction and assembly of the ECal, as well as the materials from which it is composed. The electronic and data acquisition (DAQ) systems are discussed, andperformance of the ECal modules, as deduced from measurementswith particle beams, cosmic rays, the calibration system, and T2K data, is described.
Highlights
It consists of three main components: a dedicated beamline from the proton synchrotron main ring of the Japan Proton Accelerator Research Complex (J-PARC) that is used to produce an intense beam of muon neutrinos; a suite of near detectors situated 280 m downstream of the neutrino production target (INGRID and ND280) [1, 2] that characterize the neutrino beam before the neutrinos change flavour; and the far detector, Super-Kamiokande [3], which measures the oscillated neutrino beam
Unlike previous accelerator-based neutrino experiments [4, 5], T2K uses an off-axis configuration in which the detectors sample the neutrino beam at an angle of 2.5◦ to the primary proton beam, providing a narrower neutrino energy spectrum peaked at approximately 600 MeV which is optimized for neutrino oscillation measurements using SuperKamiokande at a distance of 295 km downstream and assuming the current measured value of ∆m232
The ND280 is centred on the same off-axis angle as Super-Kamiokande in order to sample a similar portion of the neutrino flux that will be used to measure the oscillation parameters
Summary
The Tokai-to-Kamioka (T2K) experiment is a long-baseline neutrino oscillation experiment designed to measure several of these parameters. The ND280 must provide a well-measured neutrino energy spectrum, flux, and the beam neutrino composition, as well as measurements of neutrino interaction cross-sections in order to reduce. The ECal forms an important part of the ND280 and is essential to obtain good measurements of neutral particles and electron/positron showers that lead to correct particle identification and improved energy reconstruction. It can be used as target material to determine neutrino interaction cross-sections on lead. This paper describes the design, construction and performance of the ECal
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