12 Apr/24
16:00 - 17:00 (Europe/Zurich)

Center-of-mass energy calibration, polarization and monochromatization of the electron-positron Future Circular Collider


6/2-024 at CERN


"Although, with the discovery of the Higgs-Boson, the Standard Model of particle physics has been all but completed, numerous important questions of fundamental physics remain yet unanswered, longing for novel high energy physics experiments at higher intensities and energies. With a circumference of about 91 km the Future Circular electron-positron Collider, FCC-ee, is being designed to enable high energy physics experiments from the Z-pole up to above the top-pair-threshold, corresponding to center-of-mass energies from 91.2 to 365 GeV. Combining state-of-the-art accelerator technologies with novel concepts while incorporating the experience from 60 years of lepton storage rings and collider physics, its design is currently being shaped to exceed past and current particle production rates (Z, W, H, t, b,...) by at least one order of magnitude at all operation stages. Therefore, the FCC-ee has unique potential of being the world-leading facility for accelerator science and high energy physics over the next decades.

Center-of-mass energy measurements are envisaged being performed by resonant depolarization of transversely polarized pilot bunches in combination with a polarimeter.  The center-of-mass energy itself depends on the beam energies, the crossing-angle, beamstrahlung, longitudinal impedance, the Earth tides, opposite sign dispersion and possible collision offsets. Thanks to the high collision rate, especially at the Z- and W-pair-energy, a statistical precision of 4 and 100 keV could be achieved. Thus, it is aimed to reduce the systematic uncertainty to the same order of magnitude allowing performing particle physics experiments at an unprecedented precision. At the ZH- and top-pair-mode resonant depolarization is no longer possible and thus it is aimed exploiting information obtained from various di-fermion events. Complementary, applying monochromatization schemes at a certain beam energy regime to reduce the collision energy spread are studied. These challenges are being addressed in the FCC-ee Energy Calibration, Polarization and Monochromatization (EPOL) working group. This seminar reviews the current status, research highlights and open questions of the EPOL working group.