First 3D vector tracking of helium recoils for fast neutron measurements at SuperKEKB

Abstract

We present results from the first deployment of novel, high definition, compact gas Time Projection Chambers (TPCs) with pixel chip readout as part of the BEAST II beam background measurement project at SuperKEKB. The TPCs provide detailed 3D imaging of ionization from neutron-induced nuclear recoils in a helium and carbon dioxide target gas mixture at standard temperature and pressure. We find excellent electron background rejection, leading to background-free nuclear recoil measurements above 50 keVee, despite the extreme high-background environment. We measure an angular resolution better than 20° for recoil tracks longer than 1.7 mm, corresponding to an average ionization energy of ~100 keVee. We also obtain the 3D vector direction of helium recoils by utilizing charge profile measurements along the recoil axis, with a correct head/tail assignment efficiency of approximately 80%. With this performance, we present comparisons between measured and simulated event rates, recoil energy spectra, and directional distributions originating from beam-gas and Touschek beam losses at SuperKEKB. We utilize head/tail recognition to distinguish neutron components travelling with positive radial velocity in the Belle II coordinate system from those with opposite directionality. Finally, we present a novel method of discriminating beam-gas interactions from Touschek beam losses that can eliminate the need for dedicated accelerator runs for background measurements. This method is still statistics-limited. However, future studies should be able to verify this method, which in turn could lead to neutron background analysis runs symbiotic with normal Belle II operation. The capabilities demonstrated here also suggest that high definition recoil imaging in gas TPCs is applicable to low energy, low-background experiments, such as directional dark matter searches.

References in corpus (16)

• A review of the discovery reach of directional Dark Matter detection
• The case for a directional dark matter detector and the status of current experimental efforts
• Readout technologies for directional WIMP Dark Matter detection
• First Measurements of Beam Backgrounds at SuperKEKB
• Directional recoil detection
• CYGNUS: Feasibility of a nuclear recoil observatory with directional sensitivity to dark matter and neutrinos
• Observation of Vertical Betatron Sideband due to Electron Clouds in the KEKB LER
• A compact neutron scatter camera for field deployment
• The Directional Dark Matter Detector
• Measurements of Beam Backgrounds in SuperKEKB Phase 2
• Compact, directional neutron detectors capable of high-resolution nuclear recoil imaging
• Absolute Position Measurement in a Gas Time Projection Chamber via Transverse Diffusion of Drift Charge
• Improved simulation of beam backgrounds and collimation at SuperKEKB
• A time resolved study of injection backgrounds during the first commissioning phase of SuperKEKB
• Application of recoil-imaging time projection chambers to directional neutron background measurements in the SuperKEKB accelerator tunnel
• MIMAC: A micro-tpc matrix project for directional detection of dark matter

Cited by in corpus (4)

• Measurements of Beam Backgrounds in SuperKEKB Phase 2
• Application of recoil-imaging time projection chambers to directional neutron background measurements in the SuperKEKB accelerator tunnel
• Transforming a rare event search into a not-so-rare event search in real-time with deep learning-based object detection
• Primary track recovery in high-definition gas time projection chambers