Abstract
The FCC-ee could measure the electron Yukawa coupling in a dedicated run at sim 125 GeV collision energy, provided that the center-of-mass (CM) energy spread can be reduced by means of monochromatization, e.g., through introducing nonzero horizontal dispersion of opposite sign at the interaction point (IP), for the two colliding beams. If the IP dispersion is nonzero, beamstrahlung blows up the horizontal emittance, and self-consistent IP parameters need to be determined. Two configurations are being studied. The first uses crab cavities to establish effective head-on collisions. The second configuration maintains the standard FCC-ee crossing angle, which, together with the IP dispersion, introduces a correlation between the local collision energy and the longitudinal location inside the detector, thereby allowing for an integrated scan of the Higgs resonance curve. We compare both approaches.
Highlights
The FCC-ee can produce the Higgs boson directly in the s-channel, e+e− → H, in a dedicated run at ∼125 GeV center-of-mass (c.m.) energy [1,2]
A measurement of the electron Yukawa coupling is possible by reducing the center-of-mass energy spread, e.g., making it comparable to the width of the standard model Higgs boson itself, H ≈ 4.2 MeV [3]
We introduce the effective monochromatization factor λeff, that compares the true collision energy spread without and with monochromatization λeff ≡ σW,D∗=0/σW,m.c. = (Dx∗2σδ2,SR/(εx βx∗) + 1)1/2
Summary
The FCC-ee can produce the Higgs boson directly in the s-channel, e+e− → H , in a dedicated run at ∼125 GeV center-of-mass (c.m.) energy [1,2]. The energy spread can be reduced, by up to an order of magnitude, by means of monochromatization [4,5,6,7,8,9,10,11,12,13,14,15,16,17], e.g., through introducing nonzero horizontal dispersion of opposite sign at the interaction point (IP), for the two colliding beams Such nonzero IP dispersion leads to a significant increase in the horizontal emittance due to beamstrahlung, i.e., synchrotron radiation emittance in the field of the opposing bunch during the collision. Thanks to the much increased horizontal beam size, the beam energy spread and bunch length return to their natural values attained without collision
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