McGill physicists contribute to two of Top 10 Breakthroughs for 2012

Posted on Friday, December 14, 2012

Some members of the McGill ATLAS group, gathered recently at CERN: (left to right) Brigitte Vachon, Sue Cheatham (postdoc), Mark Stockton (postdoc), Michael Stoebe (grad student), Steven Robertson." / Photo courtesy of Steven Robertson

By Chris Chipello

McGill researchers contributed to two of the year’s “Top 10 breakthroughs” in physics, announced Dec. 14 by Physics World magazine.

The magazine awarded its 2012 Breakthrough of the Year designation to the ATLAS and CMS collaborations at CERN (the European Organization for Nuclear Research) “for their joint discovery of a Higgs-like particle at the Large Hadron Collider.” The widely heralded announcement was much anticipated because “physicists have had the Higgs boson in their sights for nearly 50 years. Its discovery completes the Standard Model of particle physics – making it the most important physics breakthrough so far in the 21st century,” Physics World declared in announcing the award.

The McGill research group on the ATLAS team includes professors François Corriveau, Steve Robertson, Brigitte Vachon and Andreas Warburton. The McGill group contributed directly to the development and operation of the ATLAS detector trigger system, which is responsible for selecting in real-time the small fraction of interesting collision data to be recorded and further analyzed, as well as to data preparation prior to analysis to ensure satisfactory data quality. The McGill ATLAS group continues its involvement in the measurements of Standard Model parameters and searches for new physics.

In addition, a significant fraction of analysis jobs that led to the preliminary results announced in July were performed at the CLUMEQ-McGill high performance computing centre which acted as a host site for ATLAS data files and provides computing resources to analyze the volumes of ATLAS data. CLUMEQ is the research consortium for high-performance computing that includes McGill, Université Laval, and the Université du Québec network.

Robertson also had a significant role in one of the nine other Top 10 research initiatives cited by Physics World for 2012: the BaBar collaboration, which made the first direct observation of “time-reversal violation.” BaBar is a large international particle physics experimental collaboration based out of the SLAC National Accelerator Laboratory at Stanford University. The McGill team on this project for many years consisted of Robertson and professor Popat Patel, who passed away earlier this year.

In 2010-2011, Robertson was a member of the senior management team of the collaboration, with overall responsibility for the physics program of the experiment during the period in which the analysis was being performed for the recently published paper on time-reversal violation.

“Physicists have been waiting for almost 50 years for a direct observation” of time-reversal violation, Physics World noted. “Now, researchers analysing data obtained at the BaBar detector at the PEP-II facility at the SLAC National Accelerator Laboratory in California have done just that.”

In a news release last month, the SLAC National Accelerator Laboratory explained the findings this way:

“Time marches relentlessly forward for you and me; watch a movie in reverse, and you’ll quickly see something is amiss. But from the point of view of a single, isolated particle, the passage of time looks the same in either direction. For instance, a movie of two particles scattering off of each other would look just as sensible in reverse – a concept known as time reversal symmetry.

Now the BaBar experiment at the Department of Energy’s (DOE) SLAC National Accelerator Laboratory has made the first direct observation of a long-theorized exception to this rule.

Digging through nearly 10 years of data from billions of particle collisions, researchers found that certain particle types change into one another much more often in one way than they do in the other, a violation of time reversal symmetry and confirmation that some subatomic processes have a preferred direction of time.”

The criteria used by Physics World for judging the top 10 breakthroughs included: fundamental importance of research; significant advance in knowledge; strong connection between theory and experiment; and general interest to all physicists.

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