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ATLAS speeds on
Latest on world’s biggest physics experiment
A special scientific seminar to update the search by the ATLAS experiment for the long-sought Higgs boson, is planned for July 4 at the CERN laboratory in Geneva (Tuesday midnight Vancouver time). The seminar precedes the world’s largest annual particle physics conference in Melbourne. SFU scientists are among thousands involved worldwide in the project, which is setting records in the search for new particles resulting from high-energy collisions inside the massive Large Hadron Collider (LHC) at CERN.
ATLAS has already collected more data in 2012 than it did all last year thanks to the remarkable performance of the LHC, says SFU physicist Michel Vetterli, the project leader for the ATLAS Data Centre at TRIUMF in Vancouver. The event will be webcast internationally but given the time difference, Vetterli and colleagues Dugan O’Neil and Bernd Stelzer can be available on Wednesday to offer feedback. Vetterli is at CERN, the project’s headquarters, while O’Neil and Stelzer are at SFU this week. TRIUMF will also host a Higgs Open House from 9-11 a.m. featuring researchers and students from SFU, UBC, UVic and TRIUMF to explain the milestone and next steps.
Scientists say the experiments running at the LHC are also refining their analysis techniques to improve efficiency in picking out Higgs-boson-like events from the millions of collisions occurring every second. This means that their sensitivity to new phenomena has significantly increased for both years’ data sets. The crunching of all this data since the project began in 2009 has been done by the Worldwide LHC Computing Grid, which has exceeded its design specifications to handle the unprecedented volume of data.
If and when a new particle is discovered, says Vetterli, scientists will need time to ascertain whether it is the long sought Higgs boson - the last missing ingredient of the Standard Model of particle physics - or whether it is a more exotic form of the boson that could open the door to new physics.
Backgrounder: SFU's Role in the ATLAS Experiment
Physicists from Simon Fraser University have been members of the ATLAS experiment at CERN in Geneva, Switzerland since 2001.
ATLAS researchers are studying extremely high-energy particle collisions to learn about the fundamental constituents of matter and their interactions. More than 3,000 scientists from 174 institutes in 38 countries are involved.
One of the main goals is the discovery of the Higgs boson, which is central to the current model of the mechanism that generates the mass of subatomic particles. ATLAS is also looking for many new phenomena such as new symmetries of nature, or extra dimensions.
SFU scientists include faculty members Dugan O'Neil, Bernd Stelzer, and Mike Vetterli, postdoctoral fellows Jiri Kvita, Michele Petteni, and Andres Tanasijczuk, and graduate students Michelle Boudreau, Noel Dawe, Jennifer Godfrey, Jamie Horton, David Shinkaruk, Michel Trottier-McDonald, and Koos van Nieuwkoop. The group also regularly employs undergraduate students in the summer and during the school year.
SFU’s main technical contribution is in large-scale computing. The analysis of the enormous data set from ATLAS is done on an international network of high-performance computers, called the Worldwide LHC Computing Grid (WLCG).
These centres are linked together to act in a coordinated way. Vetterli is the project leader for the ATLAS Data Analysis Centre at TRIUMF in Vancouver, one of only ten Tier-1 centres worldwide. He was ATLAS-Canada Computing Coordinator and is a former chair of the WLCG Collaboration Board.
ATLAS also uses substantial computing resources in Canadian universities as part of Compute Canada. SFU hosts one of these centres as part of WestGrid. Vetterli is a founding principle investigator for WestGrid and O'Neil is now the SFU principle investigator, as well as serving on several senior management committees for WestGrid and Compute Canada.
O'Neil is leading the current national proposal to the Canada Foundation for Innovation (CFI) to expand resources and the role of Compute Canada.
Another technical contribution by SFU is in the area of online monitoring of the operation of the ATLAS detector. Stelzer and his group have helped develop computer software that samples the data coming from ATLAS in real time and extracts selected physics results to test the good operation of the systems. This monitoring is crucial to maintaining the high quality of the data for further physics analysis.
Extracting final physics results from ATLAS data is done in several stages. First raw data must be calibrated and reconstruction of the trajectories and energy deposits of subatomic particles emerging from the proton-proton collisions must be done. This process requires an excellent knowledge of the detectors themselves and of the interaction of particles with matter.
O'Neil's group has applied sophisticated statistical techniques to identify tau leptons, which are heavy copies of the electron and which play a very important role in many searches for new physics phenomena such as the Higgs boson.
The technique developed by O'Neil's group is now used by ATLAS as the standard tool to identify tau leptons. O'Neil's group is now applying this knowledge in the search for the Higgs boson through its decay to taus.
Vetterli's group works on understanding jets, which are manifestations of quarks and gluons (fundamental constituents of the proton) coming from the interaction point. Specifically, they are using a particular process to calibrate the energy of jets in-situ to validate the jet energy scale that is based on simulations of the ATLAS detector.
Jets play an important role in most physics analyses at ATLAS, so that the work of Vetterli's group influences most physics results.
SFU is also playing a leading role in the extraction of final physics results from ATLAS. As mentioned, O'Neil's group is spearheading the search for the Higgs boson when it decays to tau leptons.
Stelzer and his group are active in many physics analyses. They are applying sophisticated techniques to the study of the Higgs boson when it decays to a pair of W particles, which are responsible for nuclear beta-decay among other things.
The coupling of the Higgs to Ws is particularly interesting because the Higgs mechanism was invented to explain the mass of the W and its partner the Z. Stelzer's group is also looking for phenomena beyond the standard model of particle physics, such as a new heavy Z particle and extra dimensions.
SFU plays a significant role in the management of the ATLAS experiment in Canada and abroad. O'Neil is the deputy spokesperson and former physics coordinator for ATLAS-Canada. Vetterli is the deputy chair of the ATLAS Publications Committee, which is responsible for organizing and overseeing the review of all scientific publications by the collaboration.
ATLAS produces about 100 journal papers per year, plus at least an equal number of scientific notes. Vetterli will become chair of PubCom in March 2013, when he will spend a sabbatical year at CERN and be a member of the ATLAS Executive Board.
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