Machine parameters

 

Update: 16.10.2024.

The latest version for the FCC-ee parameters of the machine at the various centre-of-mass energies (Z peak, WW threshold, HZ cross-section maximum, and above the top-pair threshold) can be obtained from this document. The instantaneous luminosities expected at each centre-of-mass energies in this new baseline (summed over the four interaction points and put in perspective with  luminosities advertised for linear Higgs factories) is shown in the figure below.

We will run

  • 4 years at the Z (with the first two years at half lumi)
  • 2 years at the WW threshold
  • 3 years at the ZH maximum
  • 1 year at the ttbar threshold (at half lumi)
  • 4 years at 365 GeV

Giving

  • 205 ab-1 at and around the Z pole (40 ab-1 at 87.9 GeV, 40 ab-1 at 94.3 GeV, 125 ab-1 at 91.2 GeV, for a total of about 6.10^12 Z)
  • 19.2 ab-1 at the WW threshold (typically 50-50 at 157.5 GeV and 162.5 GeV, maybe also with another lower energy point to measure the continuum background - requires optimisation)
  • 10.8 ab-1 at the ZH maximum (240 GeV, ~2 million ZH events)
  • 0.41 ab-1 for the ttbar threshold scan, and 2.65 ab-1 at 365 GeV (repartition to be optimised, leading to 2 million ttbar events)

Thes numbers may (will) change in the future in an unpredicatble manner. The sequence Z, WW, ZH is very flexible now that we have a single RF system for these three energies. We could, e.g., start with one year at the Z, then go to ZH for the time needed to understand the specific issues encountered during the first Z run, then go back to the Z for three years, and finish with the WW and ZH programmes. We would conclude with the high energy points at and above the ttbar threshold that require a whole new RF system. 

The direct Higgs production at 125 GeV might also become part of the baseline. If it does, this stage would take place just before the ttbar programme (same RF as Z, WW. ZH runs, but must be after the Z run where the monochromatisation will be commissioned, and agter the ZH run, where the Higgs boson mass will be measured with the necessary precision).

Other optional points are not part of the baseline.