  On July 4, 2012, the discovery of a new boson, with mass around 125 GeV/c2
and with properties compatible with those of a standard-model Higgs boson, was
announced at CERN. In this context, a high-luminosity electron-positron
collider ring, operating in the LHC tunnel at a centre-of-mass energy of 240
GeV and called LEP3, becomes an attractive opportunity both from financial and
scientific point of views. The performance and the suitability of the CMS
detector are evaluated, with emphasis on an accurate measurement of the Higgs
boson properties. The precision expected for the Higgs boson couplings is found
to be significantly better than that predicted by Linear Collider studies.
