Speaker
Description
The search for long-lived particles is an exciting physics opportunity in the upcoming runs of the Large Hadron Collider. We uniquely study the potential of using the High Granularity Calorimeter (HGCAL), part of the upgrade of the CMS detector, in such searches. In particular, we demonstrate that the precise pointing capability coming with this upgrade can play a crucial roll in identifying the signal and suppressing the background. We study the reach of HGCAL in a simplified model with SM Higgs decay into a pair of long-lived particles $X$. After carefully estimate the Standard Model QCD and the misconnected fake track backgrounds, we give the projected reach both for a more conservative vector boson fusion trigger and a novel displaced-track-based trigger. Our results show that the best reach for vector boson fusion channel is about $\mathcal{O}(10^{-4})$ for SM Higgs decay branching ratio at lifetime of $c\tau \sim 0.1$--$1$ meters, while for the gluon gluon fusion channel it is about $\mathcal{O}(10^{-5}\text{--}10^{-6})$ for similar lifetime. Alternatively, for $c\tau \sim 10^3$ meters, it should be able to probe the branching ratio down to a few $\times 10^{-2}$($10^{-4}$) for the two channels, respectively.