Zero bias and HF-based minimum bias triggering for pp collisions at 14 TeV in CMS

The analysis of the underlying event structure in pp collisions begins with an efficient and minimally biased data sample. This document describes the feasibility of obtaining zero bias data and presents an approach to triggering minimum bias collisions with the CMS detector. Triggering such collisions that often have just a handful of particles is difficult and can lead to severe biases on the data, thus the possibility to obtain zero bias data is evaluated for various beam bunch patterns and luminosity regions. For regions where zero bias triggering is not feasible, the merits of utilising the forward hadronic calorimeter (HF) as a minimum bias trigger is discussed and fully simulated. We find that using HF in a single-side configuration, a hard core (non-diffractive) efficiency of $\sim$$80\%$ can be attained, whilst retaining some sensitivity to diffractive type collisions. Estimated rates and suggested prescale factors are presented for each beam-bunch pattern configuration. The merits of zero-bias and HF-triggered minimum bias are also discussed.