Speaker
Description
I will describe how at least two large, double-spin Bhabha asymmetries can be used to measure the polarization of the e+ source. Meanwhile, the unique helicity amplitude structure of the parity conserving, singly- or doubly-helicity suppressed, transverse Bhabha asymmetries are sensitive to the introduction of non-QED elements such as scalars, tensors, etc. For e+ beam energies of 5-10 MeV ($E_{cm}$ ~ few MeV), only longitudinal beam polarization will be practical from a LERF e+ source, hence asymmetry measurements using a magnetized Fe target of variable tilt will be limited to $A_{LL}$, $A_{LT}$, and $A_{UT}$ . (Here, the first index is the e+ polarization, and the second index is the e- polarization. Polarization options are L, T, and U for Longitudinal, Transverse, and Unpolarized, respectively.) With fully transverse e+ beam polarization, the additional transverse observables $A_{TT}$, $A_{TU}$, and $A_{TT}’$ become accessible. In the injector, full e+ transverse polarization would require an ambitious 360 degree dipole bend at 110.2 MeV ($E_{cm}$ ~ 10 MeV). By contrast, in the JLab end-stations at GeV-scale energies, delivery of fully transverse e+ polarization would be straightforward with existing infrastructure ($E_{cm}$ ~ 100 MeV).
