Have you ever wondered what it is like to build a dark matter experiment two kilometres below the earth’s surface?
After months of meticulous operational efforts, and years of planning and anticipation, the NEWS-G detector has been carefully assembled underground at SNOLAB. The detector was originally scheduled to be installed in the spring of 2020. Due to COVID-related delays, the installation took place during November and December 2020. This was was a huge team effort. We would especially like to thank the TESC Construction Company along with all of the SNOLAB staff who participated in the planning and execution of the installation, especially during these exceptional times.
The installation of the NEWS-G detector has restarted at SNOLAB in September, after a long delay caused by the Covid-19 pandemics. It started with a final cleaning of the copper sphere, dubbed SNOGLOBE.
All the pieces and equipment had been delivered at the beginning of the year, most of them coming from France after the successful test at Laboratoire Souterrain de Modane (LSM) in 2019.
The first step of the installation was the chemical etching of the inner surface of the copper sphere. The inner surface is the only material which is directly exposed to the detecting medium: the gas. It is therefore crucial that it is free of any radioactive impurities, which would create a disrupting background to the detection of the faint dark matter signal.
In 2018, 500µm of extremely pure copper was deposited on the sphere surface through electroplating. After the sphere was fully assembled, the inside was cleaned by chemical etching: a solution of hydrogen peroxide and sulphuric acid is used to remove a very thin layer (a few µm) of copper, and together with it all the impurities that deposited on the surface.
The experiment at LSM in summer 2019 showed that this etching was not sufficient. A second etching was planned at SNOLAB, using the same technique, but with added precautions to reduce potential contaminations. In particular, the procedure was performed under nitrogen atmosphere, to prevent exposure to volatile contaminants present in air.
Below former Queen’s University Undergraduate student and current University of Alberta MSc student Carter Garrah introduces NEWS-G’s latest (non-spherical) detector.
Introducing NEWS-G’s latest (non-spherical) detector: a Micromegas-based muon telescope!
Here is the telescope frame with two panels installed.
At the end of 2019, the NEWS-G team at Queen’s University received four Micromegas (MICRO MEsh Gaseous Structure) muon detectors/trackers from CEA Paris-Saclay to be used for our own custom-designed muon telescope.
Close-up of one of the Mircromegas muon detector/tracker panels.
These square gaseous detectors are capable of detecting cosmic-ray muons over a 50 by 50 centimetre area. When muons ionize the gas molecules within these detectors, an intense electric field over a roughly 100 micrometre thick layer amplifies the corresponding charge signal. This signal can then be mapped to a spatial location on the detector up to a resolution of a few hundred micrometres.
At Saclay, Micromegas were used for the WatTo experiment as part of a muon telescope built for performing muon tomography (aka muography). This imaging technique is performed in the same way as with medicinal CT (computed tomography) scans, but instead of using X-rays, muography uses naturally occurring cosmic-ray muons. By aiming the telescope upwards at a target, a 2-D density image can be reconstructed based upon the number and spatial location of muons which pass through the telescope’s Micromegas detectors. This imaging technique has huge potential in the fields of geology and earth sciences, as well as archeology. Later designs of the WatTo telescope were even used as a part of the fascinating ScanPyramids mission in Cairo, Egypt during 2015 – 2017. Here, muography was used to identify a previously hidden chamber within the Great Pyramid of Giza!
All four panels are now installed and we are nearing the final configuration of the telescope. The SPC will be sandwiched between the Micromegas detector/trackers, with two on either side.
At Queen’s University, it is the goal of NEWS-G to use muography to study the behaviour of muons within our SPC detectors. Over the past half-year, as an undergraduate and summer student I have designed and built the near-complete NEWS-G telescope. This massive 210cm (6.9 feet) tall structure uses a rotatable frame to allow pairs of Micromegas trackers to be placed on either side of the Queen’s lab’s S130 prototype SPC (spherical proportional counter). Once operational, the telescope will be able to record any muons which pass through it and the S130, allowing for new studies into the SPC response to cosmic-ray muons.
Currently, the telescope is going through final structural modifications and testing of its electronics and gas-circulation system before it can be used with the big sphere. Preparations are also being made for a smaller version of the rotatable frame to be used for studies with smaller SPC prototypes at Queen’s. It is also the hope of the team that once the muon-related studies with SPCs are complete that this telescope can be used for future applications beyond fundamental physics, including geological studies.
NEWS-G collaborator and PhD candidate Daniel Durnford (University of Alberta) won first place for best oral presentation by a student within the Particle Physics Division at the (online) 2020 Canadian Association of Physics (CAP) conference. The conference was held by video teleconferencing and was well attended, providing a much-needed moment of connection for a community that looks forward to this annual reunion of physicists.
Daniel’s talk was about the recent dark matter campaign with methane gas at the Laboratoire Souterrain de Modane (LSM) and the ongoing calibration and analysis efforts.
Daniel was also a finalist for the best overall student presentation at the conference.
Congratulations Daniel, and thank you for all your hard work on NEWS-G!
The bulk of NEWS-G activities have been conducted off-site and online since the onset of the pandemic in mid-March and the resultant closure of the Queen’s University laboratory. The installation of the detector at SNOLAB (originally planned for the spring of 2020) has likewise been stalled. Throughout recent months NEWS-G researchers have been diligently working on data analysis and simulations, albeit remotely.
Recently, however, up to two researchers at one time have been permitted back into the laboratory to recommence site-specific projects. Laboratory researchers must follow strict health and safety protocols as they run experiments to improve the understanding of the detector that will be installed at SNOLAB.
The team is also making excellent use of this time by preparing and testing new detectors for future experiments in particle accelerators.
The 8th NEWS-G collaboration meeting was hosted online June 1st to 3rd, 2020. Collaboration members from Canada, the United States and across Europe met to present pertinent results, exchange ideas and gather momentum for NEWS-G’s future endeavours. Originally scheduled for Birmingham, UK, the collaboration leaders quickly recalibrated and organized a virtual meeting when it became clear that international travel was not an option owing to the coronavirus pandemic.
Thank you to everyone who organized, presented and participated, and we look forward to seeing you in person, hopefully soon.