First comments on a descoped/staged FCC-ee

TL;DR

This paper compares the physics potential of a descoped FCC-ee collider with the baseline version, highlighting that similar performance can be achieved with longer operation and staged top runs, but further studies are needed.

Contribution

It provides an initial assessment of a descoped FCC-ee option, suggesting feasibility and outlining areas for future detailed analysis.

Findings

Descoped FCC-ee can match baseline performance with longer operation.

Top run remains essential but can be staged later.

Further joint studies are needed for comprehensive evaluation.

Abstract

In response to its remit, the European Strategy Group (ESG) recommended the electron-positron Future Circular Collider (FCC-ee) as the preferred option for the next flagship collider at CERN; and a descoped FCC-ee as the preferred alternative option (with reduced synchrotron radiation (SR) power, without a run at the $\rm t \bar t$ threshold, and with only two interaction regions) in the event that the preferred option turns out not to be feasible. Upon request of the ESG, a basic comparison of the physics potential of the descoped option with that of the baseline version is presented in this short note. Our first observations about the alternative proposal of a descoped FCC-ee are that (i) the same performance as the baseline, apart from $\rm t \bar t$-run related, is achieved with the longer proposed period of operation; and (ii) the top run remains essential, but can be staged at a later date. The full appraisal of the consequences of descoping and a proposal for the best way to integrate possible staging wherever feasible, and possible improvements, will need further joint studies by the physics and accelerator groups.