Electroweak and CP violation physics at a Linear Collider Z-factory

TL;DR

The paper analyzes the physics potential of running a TESLA-like linear collider at the Z0 resonance with high luminosity and polarized beams. It shows that precision electroweak measurements, especially $A_{\rm LR}$ via the Blondel scheme and $A_{\rm b}$, can reach unprecedented accuracy, largely independent of external polarimetry, and that a massive $Z^0$-decay sample enables competitive CKM-angle studies. It also explores CP-violation measurements in B decays, B_s physics, and related branching-ratio analyses, finding substantial gains in some channels but limited competitiveness for $\gamma$-type measurements compared to hadron colliders. Overall, the Z0-factory option promises significant improvements in electroweak observables and complementary CP-violation probes with reasonable detector requirements, making it a valuable addition to the linear collider program.

Abstract

A future linear collider such as TESLA may be able to run on the Z0 resonance with very high luminosity and polarised electron and positron beams. The possibilities of measuring electroweak quantities with high precision are investigated. Huge improvements with respect to the present precision can be expected, especially for the asymmetries A_LR and A_b where beam polarisation can be exploited. The very large sample of Z to bbbar events also allows studies of various CP-violating b decays. The precision achievable on the CKM unitarity triangle angles is comparable to experiments at b factories and future hadron colliders.

Figures (11)

• Figure 1: The statistical error on $\hbox{$A_{\rm {LR}}$}$ as a function of the luminosity spent on the small cross sections.
• Figure 2: The statistical error on $\hbox{$A_{\rm {LR}}$}$ as a function of the positron polarisation.
• Figure 3: $\Delta \chi^2$ as a function of the Higgs mass for the electroweak precision data now and after the linear collider $\rm Z^0$ factory running.
• Figure 4: Hemisphere correlation for the $A_{\mathrm{FB}}^b$ jet charge analysis as a function of the thrust cut applied, taken from britta.
• Figure 5: $\hbox{$\cal A_{\rm b}$}$ vs $\hbox{$\cal A_{\rm e}$}$ from the current LEP and SLD electroweak data, compared to the expectation for the TESLA $\rm Z^0$ factory running.