Speaker
Description
For future $e^{+}e^{-}$ Higgs factories two processes have been proposed for precision integrated luminosity measurements, Bhabha scattering and diphoton ($\gamma\gamma$) production. To address some proposals aiming for $10^{-4}$ or even $10^{-5}$ precision on integrated luminosity, two studies were conducted. The first study, summarized in this talk, focused on upgrading the existing luminosity calorimeter to a highly granular design to reduce calorimeter derived uncertainties. This reduced the calorimeter sources of uncertainty from $3\times10^{-4}$ and $35\times10^{-4}$ to $1\times10^{-4}$ and $0.3\times10^{-4}$ for Bhabhas and diphotons respectively. The second study, and this talk's focus, was on the forward tracker performance and investigating possible diphoton backgrounds. It found two key results. First, diphotons can be faked by rare low multiplicity hadronization from $q\bar{q}$ events, which creates a $2\times10^{-4}$ effect if left uncorrected. Second, using the forward tracker alone is insufficient to separate Bhabhas and diphotons, largely due to cross-contamination from Bhabhas which undergo hard bremsstrahlung in the tracker and photons which undergo conversion in the tracker. Steps to minimize these effects are presented.
