Author/Authors :
Akimov، نويسنده , , D.Yu. and Araْjo، نويسنده , , H.M. and Barnes، نويسنده , , E.J. and Belov، نويسنده , , V.A. and Burenkov، نويسنده , , A.A. and Chepel، نويسنده , , V. and Currie، نويسنده , , A. and Edwards، نويسنده , , and B. A. Francis، نويسنده , , V. and Ghag، نويسنده , , C. and Hollingsworth، نويسنده , , A. G. Horn، نويسنده , , M. and Kalmus، نويسنده , , G.E. and Kobyakin، نويسنده , , A.S. and Kovalenko، نويسنده , , A.G. and Lebedenko، نويسنده , , V.N. and Lindote، نويسنده , , A. and Lopes، نويسنده , , M.I. and Lüscher، نويسنده , , R. and Lyons، نويسنده , , K. and Majewski، نويسنده , , P. and Murphy، نويسنده , , A.St.J. and Neves، نويسنده , , F. and Paling، نويسنده , , S.M. and Pinto da Cunha، نويسنده , , J. and Preece، نويسنده , , R. and Quenby، نويسنده , , J.J. and Reichhart، نويسنده , , L. and Scovell، نويسنده , , P.R. and Solovov، نويسنده , , V.N. and Smith، نويسنده , , N.J.T and Smith، نويسنده , , P.F. and Stekhanov، نويسنده , , V.N. and Sumner، نويسنده , , T.J. and Taylor، نويسنده , , R. Steven Thorne، نويسنده , , C. and Walker، نويسنده , , R.J.، نويسنده ,
Abstract :
The design, optimisation and construction of an anti-coincidence veto detector to complement the ZEPLIN-III direct dark matter search instrument is described. One tonne of plastic scintillator is arranged into 52 bars individually read out by photomultipliers and coupled to a gadolinium-loaded passive polypropylene shield. Particular attention has been paid to radiological content. The overall aim has been to achieve a veto detector of low threshold and high efficiency without the creation of additional background in ZEPLIN-III, all at a reasonable cost. Extensive experimental measurements of the components have been made, including radioactivity levels and performance characteristics. These have been used to inform a complete end-to-end Monte Carlo simulation that has then been used to calculate the expected performance of the new instrument, both operating alone and as an anti-coincidence detector for ZEPLIN-III. The veto device will be capable of rejecting over 65% of coincident nuclear recoil events from neutron background in the energy range of interest in ZEPLIN-III. This will reduce the background in ZEPLIN-III from ≃0.4 to ≃0.14 events per year in the WIMP acceptance region, a significant factor in the event of a non-zero observation. Furthermore, in addition to providing valuable diagnostic capabilities, the veto is capable of tagging over 15% for γ-ray rejection, all whilst contributing no significant additional background. In conjunction with the replacement of the internal ZEPLIN-III photomultiplier array, the new veto is expected to improve significantly the sensitivity of the ZEPLIN-III instrument to dark matter, allowing spin-independent WIMP-nucleon cross sections below 10−8 pb to be probed.
