Search for new physics in the mu+mu+e/mu+met channel with a low-pT lepton threshold at the Collider Detector at Fermilab

TL;DR

This study searches for new physics signals in low-pT three-lepton events at Fermilab, focusing on supersymmetric processes with improved sensitivity to light particles and tau decays, using innovative background estimation techniques.

Contribution

It introduces a low-pT lepton selection strategy and a novel data-driven background measurement method to enhance sensitivity to new physics in trilepton channels.

Findings

Observed one three-muon event in the signal region.

Expected background in the signal region is 0.4±0.1 events.

Good agreement between data and standard model predictions.

Abstract

A search for new physics using three-lepton (trilepton) data collected with the CDF II detector and corresponding to an integrated luminosity of 976 pb-1 is presented. The standard model predicts a low rate of trilepton events, which makes some supersymmetric processes, such as chargino-neutralino production, measurable in this channel. The mu+mu+l signature is investigated, where l is an electron or a muon, with the additional requirement of large missing transverse energy. In this analysis, the lepton transverse momenta with respect to the beam direction (pT) are as low as 5 GeV/c, a selection that improves the sensitivity to particles which are light as well as to ones which result in leptonically decaying tau leptons. At the same time, this low-p_T selection presents additional challenges due to the non-negligible heavy-quark background at low lepton momenta. This background is measured with an innovative technique using experimental data. Several dimuon and trilepton control regions are investigated, and good agreement between experimental results and standard-model predictions is observed. In the signal region, we observe one three-muon event and expect 0.4+/-0.1 mu+mu+l events