Department №40

Search for exotic particles: Multi-charged particles

Numerous theories of physics beyond the Standard Model predict long-lived objects producing anomalous ionization. These include slow heavy particles (e.g. stop quarks), Dirac monopoles and particles with electric charges > 1e, often called Q-balls. The latter with charges 2e-6e are of particular interest since they can explain the origin of dark matter.

MEPhI group has set up a hypothesis that the dark matter can consist of “molecules”, generated by heavy stable doubly-charged particles and helium nuclei. These particles are predicted in the Almost Commutative Geometry model, in some realizations of heterotic superstring theories and Walking Technicolor model.

Searches for such kind of particles were performed in several collider experiments at LEP and Tevatron, and are currently conducted in ATLAS and CMS experiments at LHC.

MEPhI group is performing this search with collaboration of University of Victoria (Canada), Universität Bonn (Germany) and CERN (Switzerland).

MEPhI group has developed a search method for these particles in ATLAS experiment. Mass limitations were obtained using 2011 experimental data (centre-of-mass energy 7 TeV) based on this work.

Pic 1. The plane of TRT and MDT dE/dx significances for the search of |q|=2e particles. The distributions of the 2011 data (gray) and the signal sample (here for a mass of 200 GeV in red) are shown. The regions labelled A, B and C are control regions used to estimate the background expected in the signal region D.

Pic 2. Observed 95% CL cross section upper limits and theoretical cross sections as functions of the multi-charged particles mass.


Currently 2012 data (with centre-of-mass energy 8 TeV) analysis is on its way. This analysis exploits higher statistics and particles detection efficiency due to detector aperture.



  1. ATLAS Collaboration; «Search for long-lived, multi-charged particles in pp collisions at √s = 7 TeV using the ATLAS detector», Phys. Lett. B 722 (2013) 305-323

Contact Person:

Smirnov Yuri