Brumfiel in Nature, “Latest results from the LHC are casting doubt on the theory of supersymmetry”

“Supersymmetry is a theory that solves a host of problems with our understanding of the subatomic world, but there is growing anxiety that the theory, however elegant it might be, is wrong. Data from the Large Hadron Collider (LHC), a 27-kilometre proton smasher that straddles the French–Swiss border near Geneva, Switzerland, have shown no sign of the ‘super particles’ that the theory predicts. If the detectors fail to find any super particles by the end of the year, the theory could be in serious trouble,” reports Geoff Brumfiel in “Beautiful theory collides with smashing particle data,” News, Nature 471: 13-14, 28 February 2011. Brumfiel echoes the following recent papers:

The CMS Collaboration, “Search for Supersymmetry in pp Collisions at 7 TeV in Events with Jets and Missing Transverse Energy,” ArXiv, 8 Jan 2011: “The data corresponding to an integrated luminosity of 35 inverse picobarns collected by the CMS experiment at the LHC are consistent with the standard model backgrounds. Limits are set on the parameters of the constrained minimal supersymmetric extension of the standard model. These limits extend those set previously by experiments at the Tevatron and LEP colliders.”

The ATLAS Collaboration, “Search for supersymmetry using final states with one lepton, jets, and missing transverse momentum with the ATLAS detector in sqrt{s} = 7 TeV pp,” ArXiv, 11 Feb 2011: “The data were recorded by the ATLAS experiment during 2010 show no excess above the standard model background expectation. In the minimal supergravity framework for A_0 = 0 GeV, tan beta = 3, mu > 0 and for equal squark and gluino masses, gluino masses below 700 GeV are excluded at 95% confidence level.”

The ATLAS Collaboration, “Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions,” ArXiv, 25 Feb 2011: “A search for squarks and gluinos in data were recorded by the ATLAS experiment in sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider shows no excess above the Standard Model background expectation. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tan(beta)= 3, A_0=0 and mu>0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date.”

“Researchers have now found every particle predicted by the standard model, save one: the Higgs boson mass is subject to wild fluctuations caused by quantum effects from other fundamental particles. Those fluctuations can increase the Higgs’ expected mass to a point at which other fundamental particles should be much more massive than they actually are, effectively breaking the standard model. Theorists can eliminate the fluctuations from their equations, but only by setting the Higgs mass to a very precise value. Supersymmetry (SUSY) emerged in the 1970s offers an alternative to this ‘fine-tuning’ problem. The theory postulates that each regular particle has a heavier supersymmetrical partner, many of which are unstable and rarely interact with normal matter. The quantum fluctuations of the supersymmetrical particles perfectly cancel out those of the regular particles, returning the Higgs boson to an acceptable mass range.

“The Tevatron at the Fermi National Accelerator Laboratory in Batavia, Illinois, has found no evidence of supersymmetrical quarks (‘squarks’) at masses of up to 379 gigaelectronvolts. The LHC is now rapidly accumulating data at higher energies, ruling out heavier territory for the super particles. As the super particles increase in mass, they no longer perfectly cancel out the troubling quantum fluctuations that they were meant to correct. So far the LHC has doubled the mass limit set by the Tevatron, showing no evidence of squarks at energies up to about 700 gigaelectronvolts. By the end of the year, it will reach 1,000 gigaelectronvolts — potentially ruling out some of the most favoured variations of supersymmetry theory.”

“If we fail to discover SUSY, theoretical physicists will have to go back to the drawing board and find an alternative way to solve the problems with the standard model. That’s not necessarily a bad thing, for particle physics as a whole it will be really exciting.”

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2 Responses to Brumfiel in Nature, “Latest results from the LHC are casting doubt on the theory of supersymmetry”

  1. jerry bylander says:

    I wonder if a negative result ever can be definitive.

    • emulenews says:

      No, Jerry, it can’t be definitive. Note that, f.ex., in string theory, susy is a symmetry at the Planck scale, but is broken at lower energies (only the O(TeV) scale is accesible at the LHC; there is a lot of energy scales for susy outside the reach of the LHC).

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