Hunting for CDF Multi-Muon "Ghost" Events at Collider and Fixed-Target Experiments

TL;DR

This paper explores the possibility that unexplained multi-muon 'ghost' events observed at CDF could also have been detected in past collider and fixed-target experiments, proposing models involving new particles to explain these phenomena.

Contribution

It introduces models involving a light X particle and a broad resonance Y to explain ghost events, predicting their occurrence in past experiments and suggesting ways to test these models.

Findings

CDF ghost events can be modeled with a light X particle decaying into four muons.

Predicted ghost events in Fermilab fixed-target experiments based on the model.

UA1 collider data should have observed approximately 100 ghost events.

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 four-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 ppbar collider should have observed O(100) ghost events.