M. Y. Pac

Observation of reactor electron antineutrinos disappearance in the RENO experiment.

The RENO experiment has observed the disappearance of reactor electron antineutrinos, consistent with neutrino oscillations, with a significance of 4.9 standard deviations. Antineutrinos from six 2.8  GW(th) reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 and 1383 m, respectively, from the reactor array center. In the 229 d data-taking period between 11 August 2011 and 26 March 2012, the far (near) detector observed 17102 (154088) electron antineutrino candidate events with a background fraction of 5.5% (2.7%). The ratio of observed to expected numbers of antineutrinos in the far detector is 0.920±0.009(stat)±0.014(syst). From this deficit, we determine sin(2)2θ(13)=0.113±0.013(stat)±0.019(syst) based on a rate-only analysis.

Indications of neutrino oscillation in a 250 km long-baseline experiment.

The K2K experiment observes indications of neutrino oscillation: a reduction of nu(mu) flux together with a distortion of the energy spectrum. Fifty-six beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the neutrino production point, with an expectation of 80.1(+6.2)(-5.4). Twenty-nine one ring mu-like events are used to reconstruct the neutrino energy spectrum, which is better matched to the expected spectrum with neutrino oscillation than without. The probability that the observed flux at SK is explained by statistical fluctuation without neutrino oscillation is less than 1%.

Near muon range detector for the K2K experiment: Construction and performance

A muon range detector (MRD) has been constructed as a near detector for the KEK-to-Kamioka long-baseline neutrino experiment (K2K). It monitors the neutrino beam properties at the near site by measuring the energy, angle and production point of muons produced by charged-current neutrino interaction. The detector has been working stably since the start of the K2K experiment.

Temperature and humidity dependence of bulk resistivity of bakelite for resistive plate chambers in CMS

Abstract This paper presents data obtained in a systematic study on the bulk resistivity of Korean bakelite as a function of temperature in the range 20–30°C and relative humidity in the range 35–65%. Strong dependence of resistivity on both temperature and humidity was observed. Measurements were carried out in the framework of R&D work on Resistive Plate Chambers (RPCs) which will be used in the CMS detector.

Beam test results of a large forward Resistive Plate Chamber for the CMS/LHC

Abstract The first real size Resistive Plate Chamber (RPC) prototype of ME2/1 for the forward region of the Compact Muon Solenoid (CMS) detector was constructed at Korea Detector Laboratory (KODEL). The parallel resistive electrodes of the double gap RPC were made of bakelite whose resistivity was 5×10 9 Ω cm . The prototype was tested at the Gamma Irradiation Facility (GIF) of CERN in an environment of the background intensity ranging up to 1 kHz / cm 2 / gap . We report that the full efficiency of 98% has been achieved with time resolution of about 1 ns. These results demonstrate that such a double gap RPC is suitable for the muon trigger in the future experiments.

Study on the operational conditions of a double-gap resistive plate chamber for the CMS

Abstract We present the results from cosmic ray tests on the forward Resistive Plate Chamber (RPC) for the CMS. Double-gap prototype RPC were built and tested in the Korea Detector Laboratory (KODEL). We found that addition of SF 6 and water vapor to the tetrafluorethane-based gas mixture was required for the long-term stable operation of RPC. Efficiency, time resolution as well as cross-talk behavior of the detector were investigated. In addition, we present the temperature and humidity dependence of bulk resistivity of Korean bakelite in detail.

Aspects of operational conditions of a double gap prototype RPC for the CMS/LHC experiment

This paper presents the results from cosmic ray tests performed in the framework of R&D effort on the forward Resistive Plate Chamber (RPC) for CMS. A double gapRPC of dimensions 50 � 50 cm 2 with 2 mm gas gaps was tested. We report data on the use of tetrafluorethane-based gas mixture, with additions of water vapour and SF6. Efficiency, time resolution and cross-talk behaviour of the detector were investigated. # 2001 Elsevier Science B.V. All rights reserved. PACS: 29.40.Cs

Design, construction, and initial performance of SciBar detector in K2K experiment

A new near detector for the K2K long baseline neutrino experiment, the SciBar, was constructed and started data taking to study neutrino interactions. In K2K, neutrino oscillation is studied by comparing the number of neutrino interactions and energy spectrum between near and far detectors. In order to study neutrino oscillations more precisely, it is necessary to improve the measurement of neutrino spectrum and interactions below 1 GeV, where the latest K2K results suggest maximum oscillation. For that purpose, SciBar is designed to be fully active with fine segmentation. We present the design and basic performance. All detector components have been working as expected. Also presented are the measurements of charged current interactions which are used in the latest K2K oscillation analysis