Measurement of b quark EW couplings at ILC

TL;DR

This paper presents a precise measurement of b quark electroweak couplings at the ILC using advanced vertex detection and charge identification techniques, aiming to test deviations from previous LEP1 results.

Contribution

It introduces a new method for correcting angular migration due to b charge mis-measurements without external corrections, enhancing measurement accuracy.

Findings

Achieved per mill level precision on b quark couplings

Confirmed potential deviation in ZbRbR coupling observed at LEP1

Set model-independent bounds on tensor couplings F2V and F2A

Abstract

This paper describes an analysis performed at 250 GeV centre of mass energy for the reaction e+e- -> bbbar with the International Linear Collider, ILC, assuming an integrated luminosity of 500 fb-1. This measurement requires determining the b quark charge, which can be optimally performed using the precise micro-vertex detector of the detector ILD and the charged kaon identification provided by the dE/dx information of its TPC. Given that the forward backward asymmetry is maximal for e-L (Left-handed electron polarisation), it has been necessary to develop a new method to correct for unavoidable angular migration due to b charge mis-measurements. This correction is based on the reconstructed events themselves without introducing external corrections which would induce large uncertainties. With polarized beams, one can separate the Z and photon vector and axial couplings to b quarks. The precision reached is at the few per mill level, and should allow to confirm/discard the deviation observed at LEP1 on the ZbRbR coupling. Model independent upper bounds on the tensor couplings, F2V and F2A, are derived using the shape of the angular distribution.