Experimental aspects of the Quantum Tomography of tau lepton pairs at a Higgs factory collider

Abstract

Quantum Tomography of tau lepton pairs produced at a Higgs Factory collider will enable measurements of their spin correlations arising from quantum entanglement. Such measurements rely on the ability to measure the components of and correlations between the taus' spins. We present a method to fully reconstruct the kinematics of tau pair events at an electron-positron Higgs factory collider, making use of measured particles' momenta and impact parameters. This procedure results in several consistent solutions per event, which can be assigned weights according to various event properties. Full kinematic reconstruction allows the optimal extraction of the taus' spin orientation via polarimeters. We estimate the precision with which polarimeters can be reconstructed in an ideal detector, and quantify the effects of more realistic detector performance. We conclude that for this analysis, achieving a photon angular resolution of around 1~mrad is the most crucial aspect of detector performance, while photon energy resolution and vertex detector performance are significantly less important.

Figures (11)

• Figure 1: Distribution of pion and photon energies in the considered decay modes (right) at 250 $\mathrm{GeV}$ ILC.
• Figure 2: Simulated distribution of the $\tau^- \tau^+$ invariant mass at 250 $\mathrm{GeV}$ ILC.
• Figure 3: Example events reconstructed assuming perfect detector response and assuming a single unseen ISR photon. Plots in the upper (lower) half show events with small (large) ISR. The extracted tau production position along the $z$ axis, $z_{IP}$, is shown for different assumed momenta $p_Z$ of the ISR photon. There are up to two event solutions per assumed $p_Z$: the first is shown in (red/magenta) and the second in (blue/cyan) for the $\tau^{(-/+)}$. Good solutions occur when the red & magenta or blue & cyan lines are consistent within experimental uncertainties, and $z_{IP}$ is consistent with the luminous region (approximately gaussian with width $\sim 200 \mu m$ at ILC-250).
• Figure 4: Number of solutions selected per event. Perfect detector response is assumed.
• Figure 5: Distribution of events (black), and efficiency to find at least one solution (red) as a function of the true tau-tau invariant mass (left), and the CoM scattering angle for high-- (middle) and close-to-Z--mass (right) events. Perfect detector response is assumed.