Eur. Phys. J. C (2011) 71: 1581
https://doi.org/10.1140/epjc/s10052-011-1581-x

Regular Article - Theoretical Physics

Hunting for CDF multi-muon “ghost” events at collider and fixed-target experiments

Physikalisches Institut and Bethe Center for Theoretical Physics, Universität Bonn, Nussallee 12, 53115, Bonn, Germany

^* e-mail: nicki@th.physik.uni-bonn.de

Received: 5 October 2010
Revised: 23 January 2011
Published online: 1 March 2011

Abstract

In 2008 the CDF collaboration discovered a large excess of events containing two or more muons, at least one of which seemed to have been produced outside the beam pipe. We investigate whether similar “ghost” events could (and should) have been seen in already completed experiments. The CDF di-muon data can be reproduced by a simple model where a relatively light X particle undergoes 4-body decay. This model predicts a large number of ghost events in Fermilab fixed-target experiments E772, E789 and E866, applying the cuts optimized for analyses of Drell–Yan events. A correct description of events with more than two muons requires a more complicated model, where two X particles are produced from a very broad resonance Y. This model can be tested in fixed-target experiments only if the cut on the angles, or rapidities, of the muons can be relaxed. Either way, the UA1 experiment at the CERN collider should have observed ghost events.