The energy calibration system of the KEDR tagger
The KEDR Tagging System is designed to enhance the detector ability to study the two-photon processes e⁺e⁻ → e⁺e⁻X. The collider magnetic elements (dipoles and lenses) form a magnetic spectrometer for the scattered electrons and positrons. Its energies are measured with 8 coordinate blocks which are placed beside of the vacuum chamber. In the double--tag mode an invariant mass of the system X can be measured with resolution 3-15 MeV for Winv=300÷3000 MeV depending on the mass and the beam energy. The changes of the beam energy cause the small changes in the magnetic structure and the beam orbit. This cause systematic shifts of the e± energy which is measured with the coordinate blocks. These different shifts leads to degradation of the Winv resolution. The complex calibration system was constructed to allow the calibration for all tagger blocks with the necessary accuracy.