Please use this identifier to cite or link to this item: http://hdl.handle.net/10125/62684

PERFORMANCE AND FIRST DEPLOYMENT OF NOVEL 3D NUCLEAR RECOIL DETECTORS

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Title:PERFORMANCE AND FIRST DEPLOYMENT OF NOVEL 3D NUCLEAR RECOIL DETECTORS
Authors:Hedges, Michael Thomas
Contributors:Vahsen, Sven E. (advisor)
Physics (department)
Keywords:Particle physics
BEAST II
Belle II
Directional dark matter detection
Directional neutron detection
show 1 moreSuperKEKB
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Date Issued:Dec 2018
Publisher:University of Hawaiʻi at Mānoa
Abstract:We present the performance and first deployment of a system of Time Projection Cham- bers (TPCs) using GEMs and pixel readouts for the purpose of providing 3D charge mea- surements of neutron recoils during the Phase 1 beam commissioning of SuperKEKB.
We find that the high-definition 3D images of ionization clouds provided by the TPCs enable 3D vector tracking of nuclear recoils, nuclear recoil species identification, and excellent electron background rejection for recoil energies down to 50 keVr, i.e. at energies relevant to WIMP dark matter searches. These existing detectors thus represent a stepping stone towards larger detectors fully optimized for directional dark matter searches.
In analyzing the neutron recoils at SuperKEKB, we find that measured rates of detected neutron events created by off-orbit beam particles, due to Touschek and beam-gas scattering, are underestimated in the High Energy Ring (HER) simulations and overestimated in the Low Energy Ring (LER) simulations in the horizontal plane of the beam, whereas the LER beam-background simulations are accurate in the vertical plane of the beam. Furthermore, the vector tracking capability of the detectors allows us to separate the neutron flux into primary neutrons from the beam pipe, and reflected neutrons originating from larger radii. We find that the experimentally measured fractional composition of reflected events is in agreement with the simulated predictions in the horizontal plane at a value of 25% of events. However, we find disagreement in the vertical plane, where we find 50% of the events are reflected, at a significance of 2.44σ, prompting us to recommend further and more detailed future analyses with more experimental and simulated data.
Finally, we present a novel analysis method for decoupling beam-gas and Touschek back- ground processes using full 3D vector information of nuclear recoils by utilizing a fit of fractional composition of background templates to detected recoil rates along the angle of the beam-line axis, θ. Using this method, we find agreement, within errors, with the results from the traditional heuristic method. This heuristic method traditionally requires time- consuming, dedicated experimental runs while varying accelerator parameters. While the results of this novel analysis in this dissertation are limited by significant statistical uncer- tainties, it has the potential to be validated by future experiments. If validated, this method can provide detailed decoupling analyses of beam-backgrounds that can be done symbioti- cally in later phases of Belle II operation, without the need for dedicated experimental runs, and even with a single TPC.
Description:Ph.D. Thesis. University of Hawaiʻi at Mānoa 2018.
Pages/Duration:134 pages
URI:http://hdl.handle.net/10125/62684
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Physics


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