At the “LHC end-of-year jamboree” at CERN on 17 December, the CMS collaboration announced the first results of its search for supersymmetry (SUSY) at the LHC.
SUSY is one of the strong candidates for physics beyond the Standard Model that could be detected in proton–proton collisions at the LHC. If it exists in nature, it could solve many of the outstanding issues in particle physics, such as the gauge hierarchy problem. SUSY can reveal itself through the production of new heavy particles and so could deliver a natural candidate particle to explain the large density of dark matter in the universe.
This first result is based on proton–proton collision events with multiple jets and missing transverse energy. The dataset corresponded to an integrated luminosity of 35 pb–1 collected between March and October 2010 at a centre-of-mass energy of 7 TeV. Large, missing transverse energy is a key characteristic of SUSY event candidates, reflecting the supposition that the lightest SUSY particle is expected to be neutral, stable, and weakly interacting – thereby escaping detection.
After stringent cuts to reduce the background arising from Standard Model processes that can fake missing transverse energy or that may contain escaping neutrinos, 13 events remained. The collision data also allowed estimates of the expected numbers of background events from Standard Model processes and these are consistent with the number of observed events. As a consequence, the present data do not yet show evidence for SUSY; however, they significantly extend previous search results.
The figure illustrates the reach of the CMS analysis with respect to other experiments in the plane of the universal scalar and gaugino masses (m0 and m1/2, respectively) at the grand unified theory scale of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), after just one year of LHC data-taking. The observed limit significantly improves those set previously by other experiments, thus further constraining the masses of SUSY particles.
Physicists are now looking forward to the 2011 physics run at the LHC, which is expected to bring a data sample that could be as much as two orders of magnitude larger than the present one.
For all of the presentations at the LHC end-of-year jamboree, see http://indico.cern.ch/conferenceDisplay.py?confId=113139.
CMS Collaboration 2010 CERN-PH-EP-2010-084, submitted to Phys. Lett. B.