The Carleton ATLAS Group

This past February, Carleton University sponsored my attendance of the 60^th annual Winter Nuclear Particle Physics Conference (WNPPC) hosted by TRIUMF in Banff Alberta. This is a four-day long conference aimed at early career particle physics graduate students and PhD’s in which students can introduce their work to the particle physics community through presentations or poster sessions. This of course gave me the chance to present my own work, which aims to further our understanding of a rare subset of interactions that involve a process known as “Vector Boson Fusion” (VBF). To order to achieve our goal, Carleton University and I have partnered with the largest particle accelerator in the world, the Large Hadron Collider (LHC). At the LHC, bunches of protons are accelerated to record breaking speeds and steered to collide with one another at energies exceeding 13.6 TeV, the highest ever achieved on earth. The LHC’s largest detector, ATLAS, is able to record the aftermath of these collisions and produce data to be used in analyses just like my own. To study the rare VBF interaction, my research focuses on a decay process occurring within the ATLAS detector known as the electroweak production of a W boson and two particle jets (W+Jets) (Figure 1). Understanding this interaction will implicitly yield information about the VBF process, as the W+Jets final state can only exist if VBF has occurred.

Investigating this interaction is no easy task, as its detection is concealed by many irreducible background processes. To overcome these hurdles, I am developing a novel machine learning based methodology that involves using Boosted Decision Trees (BDT) to efficiently differentiate W+Jets events from background. The BDTs facilitate the work of a fitting algorithm, which can then be used to measure the production rate of W+Jets events with unprecedented precision. This measurement will provide an avenue for testing theories that attempt to push beyond our current model of the universe. Simultaneously, this measurement will pave the way for future measurements of the elusive and recently discovered Higgs Boson, as the Higgs can also be produced via the VBF process. While my work is still in progress, I am optimistic about having results ready for publication in the near future! If you are interested in WNPPC, I highly recommend reaching out to your supervisor and asking if you can attend. Having been able to travel to Banff and present my work on behalf of the Carleton physics team was an incredible experience, and one that I think every early career particle or nuclear physicist should undertake.

This past summer, I spent 3 months working at CERN in Switzerland for the ATLAS experiment. It was an amazing opportunity which allowed me both to work in an incredible environment, surrounded by people working in the same field, and also experience all the history and culture that living in Europe provides.

This summer in particular was an exciting time to be at CERN, since it marked the start of Run 3 of collisions and data-taking for the Large Hadron Collider (LHC)! The LHC shut down in 2018 to give the experiments like ATLAS time to install some exciting new upgrades to the detectors, including the New Small Wheel (NSW); an upgrade to the muon spectrometer which includes detectors that were constructed and tested at Carleton. In addition to the new detector upgrades, the start of Run 3 also marked an increase in the collision energy of the LHC, from 13 TeV to 13.6 TeV. This may seem like a small increase, but it represents the new highest energy achieved by any particle accelerator in the world, and an important step towards the final design energy of 14 TeV.

On top of all the excitement related to the start of Run 3, part of the allure of working at CERN this summer was being able to share a work environment with other physicists, something which had been sorely missed while working from home during the pandemic.

While a lot of my meetings remained online (one of the many features of working for a large international collaboration like ATLAS), there is something so gratifying about being able to ask questions and discuss problems with your peers, face to face. This was, of course, helped by the large community of other Carleton-ATLAS students and post-docs who were also at CERN over the course of the summer. It was definitely exciting to see and work with these people in person for the first time in over 2 years.

Aside from all the work aspects, being stationed at CERN for the summer also means living in Europe for the summer, which in my case meant living in the charming French town of Saint-Genis-Pouilly. Since CERN is located very close to the Swiss-French border (so close in fact that the LHC actually straddles the border and has experiments on both sides), it is often easier (and cheaper) to live on the French side and commute to CERN, by crossing the border into Switzerland. For those of us who aren't used to the European attitude towards borders, this may seem like a daunting task to do every day, but in reality it is as simple as crossing from one Province to another within Canada. Saint-Genis itself is quite small, but mostly that means everything you need is just a a short walk/bike away, and with three French bakeries within walking distance, it's not hard to settle into the French life-style very quickly.

CERN is also very close to Geneva, which means evening and weekend trips to the city are frequent and encouraged; whether getting dinner and drinks by the lake, swimming in the Rhône at Junction, or simply spending the day exploring the old town, having the city so easily accessible can help round out the experience of living in a small town.

Overall, working at CERN has been a fantastic opportunity, one which I highly recommend taking advantage of, if you get the chance.

Over the summer, the Carleton ATLAS group hosted two NSERC USRA students:

William Rettie worked on the reconstruction software for small-strip Thin Gap Chambers in the recently deployed New Small Wheel.  The purpose of the NSW is to provide fast, precise triggering and tracking in the endcap of the ATLAS Muon spectrometer.  One of the ways this is achieves is by measuring charge deposited on a cluster of precision copper strips to specify the position that a muon traversed the sTGC gap.  Multiple layers of sTGCs work together to make a best fit 'track' of the muons passage.  William worked on validating this algorithm and identifying how precise a newly implemented technique called the 'Caruana Method' actually is.  William will be continuing this fall as an incoming MSc. student.

Owen Darragh worked on the search for Emerging Jets which are a hypothesized signal that could be detected in the ATLAS data that would indicate the presence of a 'dark' version of Quantum Chromodynamics and a possible origin for Dark Matter.  Emerging Jets are characterised by a spray of dark particles that are created at the LHC interaction point and travel some macroscopic distance through the ATLAS detector before converting into standard model particles that the detector can measure.  This results in what looks like a jet of particles that 'emerges' into the detector some distance from the IP where normal QCD interactions cause jets that clearly begin at the IP.  Owen worked on implementing machine learning algorithms to discriminate Emerging Jets from standard QCD jets and will continue this work for his Honours Project.

This morning, our own Professor Manuella Vincter and PhD Student Dylan Pizzi were on CBC Radio to talk about the restart of the LHC, the New Small Wheel, and Carleton's involvement in those activities.  Have a listen at: https://www.cbc.ca/listen/live-radio/1-100-ottawa-morning/clip/15924955-rebooted-hadron-collider-key-equipment-built-carleton-lab

Today marks the beginning of Run3 and the Large Hadron Collider.  After 3 years of shutdown for upgrades, there will once again be collisions inside the LHC at a new record centre of mass energy of 13.6 TeV.

Follow along at: https://www.youtube.com/c/CERN

The week of July 4th will be a very exciting time for the Large Hadron Collider and all the physicists around the world who have contributed to it.  The 10th anniversary of the Higgs Boson discovery announcement takes place on Monday with a special symposium that will be webcast around the world from CERN.  This will be followed up by the launch of Run-3 on July 5th at 10am ET.  Make sure to check out the links below for more information!

https://home.cern/news/news/cern/join-cern-historic-week-particle-physics

https://home.cern/news/news/cern/dont-miss-live-stream-launch-run-3

On July 4, 2012 CERN announced one of the most eagerly awaited results from the LHC program to date: the discovery of a new particle consistent with the Higgs boson.  This was one of the major goals of building the LHC and physicists around the world were very excited.  

This summer marks the 10th anniversary of that discovery announcement and CERN is holding a special symposium to celebrate that discovery, the many advances since, and the bright future of Higgs physics.

The symposium will be webcast in English with live captions.  

Mark your calendars!

https://home.cern/events/anniversary-discovery-higgs-boson

Splashes!

The restart of the LHC from its three and a half year shutdown marches on.  Yesterday, ATALS recorded its first data from beam splashes since the shutdown for LS2.  This milestone demonstrates how ATLAS works in concert as a whole detector and provides valuable calibration data for all of its subsystems.  

Of particular excitement is the fact that ATLAS has a completely new subsystem to integrate into its timing and readout: The New Small Wheel!  Carleton was a major force for construction of the NSW over the last few years and we are beyond ecstatic to start seeing real data coming from it.

The LHC expects to begin taking Run-3 physics data later this year.

https://atlas.cern/Updates/News/Run3-beams-splash