ICARUS report to the CXVIII Meeting of SPSC, June 23-24, 2015

The ICARUS-T600 detector, with about 500 ton of sensitive mass, is the largest LAr TPC ever constructed representing the state of the art for this detection technology. ICARUS concluded in June 2013 a very successful, long duration run with the T600 detector at the LNGS underground laboratory taking data both with both the CNGS neutrino beam and cosmic rays. The successful, continuous, long-term operation of the ICARUS T600 detector has conclusively demonstrated that the single phase LAr-TPC [1][2] is the leading technology for the future short and long baseline accelerator driven neutrino physics. This achievement was made possible by the long and continuing efforts of the ICARUS Collaboration and by the support of INFN, which allowed bringing the LAr TPC technology to full maturity. Relevant physics and technical results were achieved during the three years long run at CNGS, demonstrating the excellent detection performance as tracking device with ~1 mm3 spatial resolution and as homogenous calorimeter measuring the total energy with excellent accuracy for contained events. The detector demonstrated remarkable features in e/γ separation and particle identification exploiting the measurement of dE/dx vs. range. The capabilities to reconstruct the neutrino interaction vertex, to identify and measure e.m. showers generated by primary electrons and to accurately measure invariant mass of photon pairs allow to reject to unprecedented level NC background in the study of νμ→νe transitions. Momentum of non- contained muons can be determined via multiple Coulomb scattering with Δp/p ~15% in the 0.4-4 GeV/c range. The solutions adopted for the argon recirculation and purification systems in ICARUS have permitted to reach an extremely low electronegative impurity content in LAr as required to drift the free electrons created by ionizing particles with very small attenuation. A content less than 20 parts per trillion of O2-equivalent contamination corresponding to a free electron lifetime exceeding 16 ms has been measured in the T600 [P2.]. This represents a milestone for –1– any future project involving higher mass scales LAr-TPCs where electron drift paths of several meters are required. ICARUS performed a sensitive search for νe excess related to a LSND-like anomaly on the νμ CNGS beam (~ 1% intrinsic νe contamination, L/Eν ~36.5 m/MeV) providing the limit on the oscillation probability P(νμ→νe) ≤ 3.85x10-3 at 90 % CL with the 7.23x1019 pot analyzed event sample, as presented at Neutrino 2014 and to the CXIV meeting of SPSC [5]. The ICARUS result [3][4] indicates a very narrow region of the parameter space (Δm2 ≈ 0.5 eV2, sin22θ ≈ 0.005) where all experimental results can be accommodated at 90% CL, calling for an ultimate experiment to investigate the neutrino anomalies observed at accelerators, nuclear reactors and with radioactive sources used in the calibration of solar neutrino experiments. The processing and analysis of the collected data at LNGS with CNGS beam and cosmic rays is progressing. Presently about 92% of the total collected CNGS sample has been scanned, filtered and reconstructed and is now available for the further steps in the analysis. Updates of the analyzed statistics of CNGS interactions and of cosmic events are presented as well as the observation of extremely high value of the ionization electrons lifetime, and progress in the validation of the Coulomb multiple scattering algorithm for measuring muon momentum. Data reconstruction improvement The next step will be an experiment [P4.] at the ~ 0.8 GeV FNAL Booster neutrino beam, proposed in the framework of the Short Baseline Neutrino Oscillation Program (SBN) at Fermilab as the definitive answer to the “sterile neutrino puzzle”. Three LAr-TPC detectors, i.e. SBND (82 ton active mass), MicroBooNE (89 ton) and ICARUS-T600 (476 ton) will be installed at 100 m, 470 m and 600 m from target respectively. The neutrino oscillations are searched for comparing the measured neutrino spectra at the far sites with the un-oscillated ones at the near site. The common Conceptual Design Report “A Proposal for a Three Detector Short-Baseline Neutrino Oscillation Program in the Fermilab Booster Neutrino Beam”, submitted to the FNAL-PAC in January 2015, underwent level 1 approval. At the same time ICARUS will also collect a large sample of νe CC events with the NUMI Off-Axis beam peaked at ~ 2 GeV, which will be an asset for the future long base-line LBNF project. INFN and CERN have signed a Memorandum of Understanding for the WA104 project [7] at CERN dedicated to overhauling the T600 detector before its installation in the Booster neutrino beam at FNAL in 2017. The activity at CERN officially started after the arrival of the T600 detectors from LNGS and after the placement of the first T600 unit in the clean room, in December 2014. The overhauling activities on the first T600 unit are now proceeding timely and very efficiently, within the common INFN and CERN effort. Six new US institutions ((Los Alamos National Laboratory, Colorado State University, SLAC, Univ. of Pittsburg, FNAL and Argonne National Laboratory organized as ICAR-US teams) have recently joined the ICARUS Collaboration to participate in the WA104/ICARUS overhauling phase as well as in the subsequent SBN experimental program at FNAL.