2014: New results for dark matter search in the ATLAS experiment (CERN)

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Physicists of Lomonosov Moscow State University (the group headed by Prof. Lidia Smirnova) in international ATLAS collaboration (CERN) received new results for the dark matter search in the ATLAS experiment.

A search for weakly interacting massive particles (WIMP), denoted by χ, is fulfilled in proton-proton collisions at the center mass energy 8 TeV with all data (20 fb-1) available in the ATLAS experiment. These particles are the most probable candidate for the role of dark matter in the universe. They can be produced in proton collisions by pairs via some unknown intermediate state. These searches have greatest sensitivity at low WIMP masses mχ, where direct detection experiments are less powerful. Similar to neutrinos, WIMPs are invisible in the ATLAS detector, but the events can be registered due to large missing energy if initial-state radiation of a standard model particle exists. The reaction can be written as pp → χχ̄ + X, where X is associated to jet, photon and W or Z bosons. New search is fulfilled for events with associated production of hadronically decaying W or Z bosons with single massive hadron jet in final state.

Events with missing transverse momentum more than 350 and 500 GeV were selected. No excess of events over standard model expectations is observed. As a result, the stronger limits on mass scale M* of the unknown interaction in an effective field theory expressed as a function of mass mχ are set for various operators and couplings of WIMPs with standard model particles. These results can be presented as the limits on the dark matter-nucleon scattering cross section. The essential achievement of ATLAS results is well seen in low mass region of mχ for masses up to few tens of GeV, but as distinct from experiments with direct measurements of dark matter interactions, they are model dependent.

These results have been published by the ATLAS collaboration the group of Prof. Lidia Smirnova is a part of in Phys. Rev. Lett. 112, 041802 (2014).