[Moller] Snowmass 2021 White Paper on Upgrading SuperKEKB with a Polarized Electron Beam: Discovery Potential and Proposed Implementation

[Jay Benesch]

A precision electroweak program with better error bars than SoLID or MOLLER per figures on page 7 and 8 of pdf.   
I hope Joe, Marcy and Carlos are aware of the Hiroshima University work on NEA layers on strained GaAs, pages 25-26 of pdf. 
The Compton polarimeter design starts at the bottom of page 59 of pdf
Timing if approved: ready about same time as EIC. 

https://arxiv.org/abs/2205.12847

Snowmass 2021 White Paper on Upgrading SuperKEKB with a Polarized Electron Beam: Discovery Potential and Proposed Implementation
Swagato Banerjee, J. Michael Roney (for the US Belle II Group and Belle II/SuperKEKB e- Polarization Upgrade Working Group)

    Upgrading the SuperKEKB electron-positron collider with polarized electron beams opens a new program of precision physics at a center-of-mass energy of 10.58 GeV. This white paper describes the physics potential of this `Chiral Belle' program. It includes projections for precision measurements of sin2θW that can be obtained from independent left-right asymmetry measurements of e+e− transitions to pairs of electrons, muons, taus, charm and b-quarks. The sin2θW precision obtainable at SuperKEKB will match that of the LEP/SLC world average, but at the centre-of-mass energy of 10.58 GeV. Measurements of the couplings for muons, charm, and b-quarks will be substantially improved and the existing 3σ discrepancy between the SLC ALR and LEP AbFB measurements will be addressed. Precision measurements of neutral current universality will be more than an order of magnitude more precise than currently available. As the energy scale is well away from the Z0-pole, the precision measurements will have sensitivity to the presence of a parity-violating dark sector gauge boson, Zdark. The program also enables the measurement of the anomalous magnetic moment g−2 form factor of the τ to be made at an unprecedented level of precision. A precision of 10−5 level is accessible with 40~ab−1 and with more data it would start to approach the 10−6 level. This technique would provide the most precise information from the third generation about potential new physics explanations of the muon g−2 4σ anomaly. Additional τ and QCD physics programs enabled or enhanced with having polarized electron beams are also discussed in this White Paper. This paper includes a summary of the path forward in R&D and next steps required to implement this upgrade and access its exciting discovery potential. 

Comments: 	74 pages, 56 figures, contribution to Snowmass 2021
Subjects: 	Accelerator Physics (physics.acc-ph); High Energy Physics - Experiment (hep-ex)
Cite as: 	arXiv:2205.12847 [physics.acc-ph]