ATLAS experiment sets strong constraints on supersymmetric dark matter

phys.org | 7/20/2017 | Staff
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Dark matter is an unknown type of matter present in the universe that could be of particle origin. One of the most complete theoretical frameworks that includes a dark matter candidate is supersymmetry. Many supersymmetric models predict the existence of a new stable, invisible particle called the lightest supersymmetric particle (LSP), which has the right properties to be a dark matter particle.

The ATLAS Collaboration at CERN has recently reported two new results on searches for an LSP that exploited the experiment's full Run 2 data sample taken at 13 TeV proton-proton collision energy. The analyses looked for the pair production of two heavy supersymmetric particles, each of which decays to observable Standard Model particles and an LSP in the detector.

Challenge - Searches - Matter - Candidate - Particles

A central challenge of these searches is that dark matter candidate particles would escape the ATLAS detector without leaving a visible signal. Their presence can only be inferred through the magnitude of the collision's missing transverse momentum (ETmiss) – an imbalance in the momenta of detected particles in the plane perpendicular to the colliding protons. In the dense environment of numerous overlapping collisions generated by the Large Hadron Collider (LHC), it can be difficult to separate genuine ETmiss from fake ETmiss originating from mis-measurement of the visible collision debris in the detector.

To resolve this difficulty, ATLAS developed a new ETmiss significance variable that quantifies the likelihood that the observed ETmiss originates from undetectable particles rather than from mis-measured objects. Unlike previous calculations based entirely on the reconstructed event kinematics, the new variable also considers the resolution and misidentification probability of each of the reconstructed particles used in the calculation. This helps discriminate more effectively between events...
(Excerpt) Read more at: phys.org
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