Higgs factories

TL;DR

This paper reviews proposed future collider projects focused on Higgs boson studies, highlighting shifts in priorities after the 2012 LHC discovery and discussing various designs for precision Higgs measurements.

Contribution

It provides an overview of Higgs factory proposals developed after the 2012 Higgs discovery, based on workshop reports, and discusses the changing landscape of collider R&D.

Findings

Shift in collider R&D priorities post-2012 Higgs discovery

Overview of proposed Higgs factory projects and designs

Discussion of the impact of LHC results on future collider plans

Abstract

Over the past two decades, the high energy physics community has been actively discussing and developing a number of post-LHC collider projects; however, none of them have been approved due to high costs and the uncertainty in post-LHC physics scenarios. There have been great expectations of rich new physics in the 0.1-1 TeV mass region: the Higgs boson (one or several), supersymmetry, or perhaps new particles from the dark-matter family. It has been the general consensus that the best machine for the detailed study of new physics to be discovered at the LHC would be an energy-frontier linear e+e- collider. Physicists held their breath waiting for the results from the LHC. In summer 2012, two LHC detectors, ATLAS and CMS, announced the discovery of a Higgs boson with the mass of 126 GeV and (still) nothing else. The absence of new physics in the region below 1 TeV has changed the post-LHC collider R&D priorities and triggered a zoo of project proposals for the precision study of the 126 GeV Higgs boson, possibly with further upgrades to higher energies. This paper gives an overview of these projects; it is based largely on the reports presented at the first workshop on Higgs factories held at FNAL a few days prior to the present workshop in Protvino.