The ZEPLIN-III Anti-Coincidence Veto Detector - High Energy Physics - ExperimentReport as inadecuate

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Abstract: The design, optimisation and construction of an anti-coincidence vetodetector to complement the ZEPLIN-III direct dark matter search instrument isdescribed. One tonne of plastic scintillator is arranged into 52 barsindividually read out by photomultipliers and coupled to a gadolinium-loadedpassive polypropylene shield. Particular attention has been paid toradiological content. The overall aim has been to achieve a veto detector oflow threshold and high efficiency without the creation of additional backgroundin ZEPLIN-III, all at a reasonable cost. Extensive experimental measurements ofthe components have been made, including radioactivity levels and performancecharacteristics. These have been used to inform a complete end-to-end MonteCarlo simulation that has then been used to calculate the expected performanceof the new instrument, both operating alone and as an anti-coincidence detectorfor ZEPLIN-III. The veto device will be capable of rejecting over 65% ofcoincident nuclear recoil events from neutron background in the energy range ofinterest in ZEPLIN-III. This will reduce the background in ZEPLIN-III from ~0.4to ~0.14 events per year in the WIMP acceptance region, a significant factor inthe event of a non-zero observation. Furthermore, in addition to providingvaluable diagnostic capabilities, the veto is capable of tagging over 15% forgamma-ray rejection, all whilst contributing no significant additionalbackground. In conjunction with the replacement of the internal ZEPLIN-IIIphotomultiplier array, the new veto is expected to improve significantly thesensitivity of the ZEPLIN-III instrument to dark matter, allowing spinindependent WIMP-nucleon cross sections below 1E-8 pb to be probed.

Author: D. Yu. Akimov, H. M. Araujo, E. J. Barnes, V. A. Belov, A. A. Burenkov, V. Chepel, A. Currie, B. Edwards, V. Francis, C. Ghag, A.



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