Speaker
Description
In supersymmetric extensions of the Standard Model,higgsino-like charginos and neutralinos are preferred to have masses of the order of the elecktroweak scale by naturalness arguments. Light higgsinos are also well motivated from a top-down perspective. Such light $\tilde{\chi}^{\pm}_{1}$, $\tilde{\chi}^{0}_{1}$ and $\tilde{\chi}^{0}_{2}$ states can be almost mass degenerate. In this talk the analysis of two benchmark points which exhibits mass difference of O [GeV] in the higgsino sector is presented. Due to their mass degeneracy it is very difficult to observe the decay of such higgsinos at hadron colliders. ILC being an $e^+e^-$ collider has the prospect of providing very clean physics environment to observe or exclude such scenarios. However, in addition to the desired $e^+e^- \rightarrow \tilde{\chi}^{+} \tilde{\chi}^{-}$ processes, parasitic collisions of real and virtual photons radiated off the $e^+e^-$ beams occur at the rates depending on the center of mass energy (250 GeV - 1 TeV) and other beam parameters. For instance, at a centre of mass energy 500 GeV the expectation value is about 1.05 $\gamma \gamma$ events per bunch crossing. In the given higgsino scenarios, visible decay products have low transverse momenta due to their small mass differences. This so called $\gamma \gamma$ overlay has a very similar topology to our signal event which makes the removal of overlay very challenging. The standard methods to remove $\gamma \gamma$ background e.g $k_t$ algorithm method remains inadequate. This talk presents a proposed solution namely a newly developed track grouping algorithm which is based on the concept of displaced signal and $\gamma \gamma \rightarrow$ low $p_T$ hadron overlay vertices. By applying the track grouping algorithm to separate $\gamma \gamma \rightarrow$ low $p_T$ hadron tracks from the higgsino decay tracks, an analysis has been performed using the full detector simulation for the International Large Detector (ILD). The results from the analysis and a comparison with the previous study which was performed without the inclusion of $\gamma \gamma \rightarrow$ low $p_T$ hadron events is made to understand the impact of the overlay on the higgsino analysis.
