Physicists detect process even rarer than the long-sought Higgs particle
Scientists running the ATLAS experiment at the Large Hadron Collider (LHC), the world's largest and most powerful "atom smasher," report the first evidence of a process that can be used to test the mechanism by which the recently discovered Higgs particle imparts mass to other fundamental particles. More rare than the production of the Higgs itself, this process -- a scattering of two same-charged particles called W bosons off one another -- also provides a new stringent test of the Standard Model of particle physics. The findings, which so far are in agreement with predictions of the Standard Model, are reported in a paper just accepted by Physical Review Letters.
"Only about one in 100 trillion proton-proton collisions would produce one of these events," said Marc-André Pleier, a physicist at the U.S. Department of Energy's Brookhaven National Laboratory who played a leadership role in the analysis of this result for the ATLAS collaboration. Complicating matters further, finding one such rare event is not enough. "You need to observe many to see if the production rate is above or on par with predictions," Pleier said. "We looked through billions of proton-proton collisions produced at the LHC for a signature of these events -- decay products that allow us to infer like Sherlock Holmes what happened in the event."
The analysis efforts started two years ago and were carried out in particular by groups from Brookhaven, Lawrence Berkeley National Laboratory, Michigan State University, and Technische Universität Dresden, Germany. Preliminary results were presented by Pleier at the "Rencontres de Moriond -- QCD and High Energy Interactions" conference in March 2014. Now finalized based on a total of 34 observed events, the measured interaction rate is in good agreement with that predicted by the Standard Model, a theory describing all known fundamental particles and their interactions.
"The Standard Model has so far survived all tests, but we know that it is incomplete because there are observations of dark matter, dark energy, and the antimatter/matter asymmetry in the universe that can't be explained by the Standard Model," Pleier said. So physicists are always looking for new ways to test the theory, to find where and how it might break down.
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http://www.sciencedaily.com/releases/2014/07/140715095517.htm
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