Development of a High-Precision Electron Beam Measurement Method in the Several Hundred MeV Range Using Undulator Synchrotron Radiation Interferometry*

We have pioneered the decay pion spectroscopy of electroproduced light Λ hypernuclei at the Mainz Microtron (MAMI), with a particular focus on ³_ΛH (Hypertriton) in latest experiment. In this method, high-precision magnetic spectrometers achieved Δp/p ∼ 10^-4  momentum resolution for 130 MeV/c pion [1]. Despite high precision, large systematic uncertainty has to be addressed. In the spectrometer calibration through elastic electron scattering at several hundred MeV, the absolute calibration error of the electron beam energy is a crucial factor limiting the overall experimental uncertainty.

To resolve this, we developed a novel technique using interference of synchrotron radiations from two undulators along the electron beam [2]. The phase shift of two pulses is caused by electron beam delay with respect to radiation so we can extract energy information from interference. By data-taking with a CMOS camera, we demonstrate the measurement precision Δγ/γ ∼ 10^-5.

In this talk I will report the progress of development and practical aspects of this method.

[1] A. Esser, S.Nagao, F.Schulz et al., (A1 Collaboration) PRL. 114, 232501(2015)

[2] P.Klag et.al., NIM A 910, 147 (2018)