In the search for dark matter particles, a tabletop experiment at the heart of a Canadian mine could do the trick. The SENSEI collaboration uses Skipper Loaded Torque, or CCD, devices which are the most sensitive sensors of their kind, imagined decades ago and only recently made.
The collaboration recently proven that the experiment has a sensitive dark matter detector and that it can reduce background rates in an underground experimental area at the Department of Energy’s Fermilab. Now the collaboration is running a larger, exponentially quieter, and more responsive version of the experience more than a mile underground at SNOLAB in Canada.
With the COVID-19[feminine pandÃ©mie et la fermeture de la frontiÃ¨re canado-amÃ©ricaine, l’expÃ©rience aurait pu facilement prendre du retard en 2020. Au lieu de cela, elle est dans sa phase de mise en service – test avec environ 20% du matÃ©riau cible que l’expÃ©rience utilisera lorsque les couches externes de blindage seront en place. Un travail d’Ã©quipe extraordinaire entre les physiciens des deux cÃ´tÃ©s de la frontiÃ¨re a permis d’avancer dans les dÃ©lais.
Rester en sÃ©curitÃ© tout en faisant progresser la science
Alors que la pandÃ©mie s’installait pour son troisiÃ¨me ou quatriÃ¨me mois, il est apparu Ã Javier Tiffenberg, scientifique associÃ© au Fermilab et collaborateur de SENSEI, que l’installation expÃ©rimentale prÃ©vue par l’Ã©quipe du Fermilab, qui devait commencer en 2020, devait Ãªtre repensÃ©e.
Sans moyen de se rendre sur le site, l’Ã©quipe SENSEI a contactÃ© SNOLAB pour voir si le personnel Ã©tait disposÃ© Ã installer lui-mÃªme l’expÃ©rience hypersensible avec le guidage Ã distance du Fermilab. Le personnel de SNOLAB est dÃ©jÃ familiarisÃ© avec les dÃ©fis uniques de l’installation d’expÃ©riences dans un laboratoire propre situÃ© dans une mine en activitÃ©. Cette fois, ils effectueraient une installation d’une semaine pour une expÃ©rience Ã laquelle ils n’allaient pas participer Ã l’origine.
SNOLAB Ã©tait un jeu.
“Nous serons leurs mains car ils ne peuvent pas Ãªtre ici”, a dÃ©clarÃ© Silvia Scorza, chercheuse au SNOLAB, Ã propos de la perspective adoptÃ©e pour le projet. Elle fait partie des employÃ©s de SNOLAB qui ont aidÃ© Ã installer des projets Ã distance pendant la pandÃ©mie.
“Lorsque les gens de SNOLAB ont dit qu’ils Ã©taient intÃ©ressÃ©s Ã contribuer Ã cela, puis de notre cÃ´tÃ©, les ingÃ©nieurs et les techniciens ont dit:” Oui, nous pouvons le faire “, j’Ã©tais super excitÃ© parce que je pensais vraiment que cela se prÃ©parait”, Tiffenberg mentionnÃ©.
Greg Derylo, engineer in the particle physics division of Fermilab, designed the layout of SENSEI, worked with the drawing group to make drawings of all mechanical parts and sourced parts from workshops on-site and off-site machining. Due to the effects of COVID-19 restrictions on access to the Fermilab campus, he also performed most of the physical assembly of the experiment.
Derylo said dismantling at Fermilab and reassembling at SNOLAB was still part of the plan. But the remote installation presented a new problem.
âThe real stuff comes in terms of who is doing this assembly underground,â he said. The main concern was the handling of the skipper’s fragile (and expensive) CCDs, which are “very sensitive to electrostatic damage”. Less than what a person can feel in their hand after rubbing their feet on a carpet and touching a doorknob could destroy the sensors. Thus, physicists and technicians from SNOLAB followed a special course in electronic manipulation.
Tests, tests and a very pandemic party
Before the experiment could be put into SNOLAB’s hands, it had to be tested and documented.
âWe tested everything at Fermilab. We put everything together the same way they would there, âDerylo said.
The first test was mechanical – assembling the outer shell of the experiment to confirm it would hold a vacuum – and a thermal performance test. SENSEI relies on cryogenics to “cool”. To do this, the Fermilab team has set up additional instrumentation to monitor temperatures and perform diagnostics. Both worked as expected.
In early fall 2020, the Fermilab team installed a set of test modules in the experiment, turned it on, cooled it down, cooled it down and operated the modules. The reading went off without a hitch. The team celebrated – each member from their own location via Zoom – with champagne.
Documentation and hand modeling
Usually, the documentation is more of a series of reminders than step-by-step instructions, and team members may have a hunch of the process or largely rely on their memory.
Creating instructions for a team unfamiliar with the experience required higher level communication. This mainly meant creating documentation with much more detail.
Because the team knew the installation would be remote, they took advantage of their own assembly during testing.
âWe took pictures of everything,â Tiffenberg said. âHaving this documentation was essential. “
But achieving this has not been without challenges. With multiple people documenting at different times due to the pandemic, communication within the group has also become more important than usual. Different technicians had different perspectives, literally.
âIn fact, we actually had opposing definitions of what the front of the setup was,â Derylo said. The cure? SENSEI’s newest and one of its most important components: self-adhesive labels.
The team also incorporated breakpoints into the documentation. Once a SNOLAB pair hit one of these points, they could determine if they had time to take the next step of a shift or if they needed clarification from the team. of Fermilab.
The first draft was ready around the beginning of 2021. Derylo said the documentation was divided into different sections and was around 70 pages long. The document resembles a sketch “heavily spiced with photos”. Drawings of the vacuum system, cooling system and electrical wiring were also provided, but were not part of the booklet.
âThen we took it apart but tried to keep as many parts together as possible and then shipped it to SNOLAB in January,â Tiffenberg said.
An ultra-clean clean room in a working mine
Pandemic issues aside, the process of setting up experiments in the SNOLAB underground facility has always been complex. After all, this is a clean lab located more than a kilometer underground, inside a working mine.
âCareful planning and preparation starts on the surface,â said Scorza.
There, at the start of the day, physicists, engineers and technicians dressed as miners (plus masks and pandemic contact tracing badges) await “the cage”, a mining elevator to take them deep underground. .
The descent takes less than five minutes. But then there’s a nearly mile-long journey through a mining tunnel with a railroad track running alongside it.
âSo watch your steps,â Scorza said.
At the end of this trek, a clean lab. Before entering, the boots are washed in a special station. Clothing and boots are left on one side. People entering the clean lab undress, shower, and dress in new, clean clothes from across the shower to avoid contamination. A âresponsible laboratory coordinatorâ verifies that the laboratory is allowed to work – by checking oxygen levels, among other parameters. It takes about an hour between the surface and the start of the work, and the same – minus the shower – for the return. In a 10 hour day, that leaves about eight hours per team to put the experiment together.
A team of four people, made up of scientists from SNOLAB and a technician, take turns and work in pairs for the installation. (No one can be alone underground, and there are restrictions on the maximum number of people to maintain physical distance.)
âThe packaging is very special,â Tiffenberg said.
Every part received has to go through “the underground car wash,” Scorza said. Each item is triple wrapped and on a double pallet to streamline the complex process of unpacking and wiping materials before they can enter the cleanroom lab. On the other side of the car wash, the clean lab. For SENSEI, the parts included the pipe, cable, tank, copper parts for the interior side, cryogenics, lead and copper shielding layers and the bell.
âWhen these things were designed, of course shipping everything that is assembled was not on the list of requirements,â Tiffenberg said. “For the vast majority of the things we shipped, everything was going perfectly fine.”
Only a few small pieces of plastic – easily replaceable – came loose and broke.
Once everything was opened up and “looked good” Tiffenberg said it was a “big, big relief”.
The installation began on April 19 and was completed at the end of the summer.
Although the SNOLAB cleanroom is equipped with telephones and Wi-Fi, communication outside of documentation is mainly done during weekly meetings. The plan changed from week to week, depending on whether the team was able to go underground due to COVID availability and restrictions.
Some days, that involved extreme care: touching those skipper’s CCDs. In others, it involved using a crane to move lead shielding. Scorza said the mix of work SNOLAB enables scientists to undertake – practical and analytical – gives them a more comprehensive experience in experimental physics. âAnd, it’s a lot of fun. At least for me. “
“I think that the fact that a team, a team of SNOLAB scientists, not very involved in the experiment originally, is able to progress with the underground facility shows that, first of all, physicists are very flexible, âsaid Scorza. “And (it’s) a testament to the robustness of the plan for this experiment.” Hats off to the Fermilab team.
Tiffenberg said he was grateful the installation went without a hitch or surprise.
âIt took a long time to get to this situation where there are no surprises. At first, everything was like, âOkay, we spend a lot of time adjusting, coordinating, reviewing things. And it took a long time. But now that things are moving, this time that we took there, we appreciate, because now everything is no surprises. “
Although now that the experiment is taking data, a surprise in the form of a scientific discovery would be a nice reward.