(Geneva and Edmonton) University of Alberta physics professors who helped to build the ATLAS detector at CERN are cautious about recent results that may indicate the existence of the Higgs boson.
ATLAS is one of two main detectors at CERN'S Large Hadron Collider (LHC). Like other subatomic particles, the Higgs boson, if it exists, cannot be seen directly. Thus, detectors must look for unusual signals when particles are smashed together and decay in the LHC.
"The LHC experiments have restricted the mass range of the Higgs, but cannot yet provide any statement on its existence," says Doug Gingrich, who leads the University of Alberta's ATLAS effort. Gingrich is currently at CERN, where he participated in the approval of the talk that was the basis of Tuesday's ATLAS presentation. "The mass range has been restricted to about 3% of what it was before the LHC turned on, but in that 3% remaining mass range, we cannot observe it or rule it out."
Also in Geneva, James Pinfold, who was part of ATLAS since its inception and previously led the Alberta team, says the results "could be the 'prequel' to a discovery."
More data needed
A third member of ATLAS Alberta, Roger Moore, cautions that that there is a 0.019% percent chance that the signal is a fluke.
"The data are consistent with a low mass Higgs, so more luminosity, rather than higher energy, is needed to confirm whether there is anything really there," he says. Luminosity is the number of particle collision -- called "events." More events yield more data.
Gingrich agrees. "Two or three times more data would allow the Higgs to be ruled out or discovered by ATLAS."
Pinfold sees the possibility for requiring higher energies. "We know that the Standard Model Higgs must have a mass less than or roughly equal to 1 TeV/c^2. If the Higgs is heavier than the limit we would set next year -- if this current 'discovery' goes away -- we will need to run at full design energy (14 TeV) and luminosity in order to discover -- or rule out -- the Standard Model Higgs."
University of Alberta's long-standing role in ATLAS
Pinfold and Gingrich, who both joined the U of A in the early 1990s, worked on precursors to the ATLAS experiment and were involved in the conceptualization and design of the experiment. Moore joined ATLAS shortly after he arriving at the U of A in 2003.
Parts of the massive, 7,000 tonne ATLAS detector were designed and built at the U of A's Centre for Particle Physics, of which Pinfold, Gingrich and Moore are all members. In the early 1990s, CPP researchers developed a calorimeter designed for use in the low mass region is low mass where the Higgs boson may possibly exist. The calorimeter design eventual became the design used by the ATLAS calorimeter.
Copper plates for the ATLAS hadronic endcaps were milled at CPP's Advanced Machining. The ATLAS trigger was coordinated here, as was the design, construction and installation of the LUCID subdetector that measures luminosity.
Other searches
Currently, U of A physicists are working on physics projects made possible by ATLAS.
Moore works on the ATLAS trigger and his grad student has recently started trying to improve the tau trigger, something which may play an important role in future Higgs searches.
Gingrich has led the international effort to look for black holes using the LHC. "Conventional black holes have been excluded at the LHC," Gingrich states. "Conventional black holes of general relativity could exist at higher energies. However, the LHC experiments have said nothing, of value, yet about quantum black holes, which would exist in more dimensions than our four space-time dimensions."
Pinfold is working with a CERN-based researcher on the physics of the W-boson, which is important in understanding the backgrounds of an important decay mode of the Higgs.
Pinfold also heads MoEDAL, the only Canadian-led experiment at the LHC. With $100,000 in seed money from the University of Alberta's VP Research Office and the Faculty of Science, MoEDAL is being designed to search for subatomic particles that have been theorized, but not yet observed. The collaboration now includes researchers from Campus St-Jean, CERN and King's College London, including John Ellis, former head of CERN's theory division. MoEDAL should be deployed at the LHC in 2013 for a run in 2014.
The future of physics
If the Higgs is found, the Standard Model of physics will be confirmed. However, there are differences over how physics will be affected if the Higgs is not found.
"People often make the statement that if we do not find the Higgs that is exciting because particle physics has to start all over," says Gingrich. "However, theorists have investigated the consequence of not seeing the Higgs for years. To date no ideas come close to the Standard Model that we have, so it is not clear to me how not finding the Higgs will generate ideas. It will only restrict the less favoured ideas and concentrate more of the community, hopeful, in the right direction."
Moore is more bullish on a future without the Higgs. "The range of possibilities would be huge and we don't know what the implications would be and how we might be able to apply that knowledge."
Pinfold sees a future with the Higgs that is anything but boring. "I would say that we are involved in opening up a new window on exclusive physics (where the colliding protons do not break up) at the LHC via our leading involvement with the ATLAS Forward Physics group (AFP)," he says. "One of the aims of this new development is to search for exclusively produced Higgs bosons (i.e., produced by interactions where the protons do not break up). This will give us new insights on the properties of the Higgs boson."