Integrated Luminosity with 100 ppm Precision, Methods for $\sqrt{s}$ Precision of 1 ppm, and Beyond Standard Model Sensitivity using Photonic Events, at $\mathrm{e^{+}e^{-}}$ Higgs Factories

Abstract

Future electron-positron ($\ee$) colliders, operating as Higgs factories or Z factories, promise unprecedented precision electroweak measurements that are vital to testing the Standard Model (SM) and exploring physics beyond it. Here we present work on the precision of integrated luminosity ($\mathcal{L}$) and center-of-mass energy ($\sqrt{s}$), measurements that are needed to make future precision measurements possible. We also conduct these studies for the International Linear Collider (ILC) from the Z pole ($m_{Z}$) to 1~TeV to provide a comprehensive study of these issues for future $\ee$ colliders. Paths to 100 parts-per-million (ppm) precision on $\mathcal{L}$ are presented, with focus on small-angle Bhabha scattering (SABS) and two-photon production (diphotons, $\gamma\gamma$). Previous studies found that beam deflection of SABS events introduce biases on $\mathcal{L}$ of $10^{-2}$. To address this, we present a novel method that uses M\o{}ller scattering with SABS to measure beam deflection and minimize its effect on $\mathcal{L}$. We present a proposal for a Highly Granular Luminosity Calorimeter, the GLIP LumiCal, and its design considerations. We demonstrate that the GLIP LumiCal can achieve $\approx35$ ppm precision on $\mathcal{L}$ precision with diphotons for all values of $\sqrt{s}$ and that the current LumiCal design is insufficient for reaching 1000 ppm. Multiple methods for precision $\sqrt{s}$ estimation are presented. We introduce the use of Kernel Density Estimation (KDE) to ensure that $\sqrt{s}$ is measured accurately and precisely The utility of photon measurements is extended to photon with invisible ($X^0\gamma$) events where we demonstrate methods to measure left-handed and right-handed neutrino couplings and put constraints on Beyond Standard Model (BSM) physics.