XCC: an X-ray FEL-based γγ Compton collider Higgs factory

Abstract

Abstract This report describes the conceptual design of a  γγ Higgs factory in which 62.8 GeV electron beams collide with 1 keV X-ray free electron laser (XFEL) beams to produce colliding beams of 62.5 GeV photons. The Higgs boson production rate is 80,000 Higgs bosons per 107 second year, roughly the same as the ILC Higgs rate at √s = 250 GeV. The electron accelerator is based on cold copper distributed coupling (C3) accelerator technology. Unlike the center-of-mass energy spectra of previous optical wavelength γγ collider designs, the sharply peaked γγ center-of-mass energy spectrum of XCC produces model independent Higgs coupling measurements with precision on par with e + e - colliders. For the triple Higgs coupling measurement, the XCC center-of-mass energy can be upgraded to 380 GeV, where the cross section for  γγ → HH is twice that of  e + e - → ZHH at √s = 500 GeV. Design challenges are discussed, along with the R&D to address them, including demonstrators.