First look at the physics case of TLEP

Abstract

Abstract:The discovery by the ATLAS and CMS experiments of a new boson with mass around 125 GeV and with measured properties compatible with those of a Standard-Model Higgs boson, coupled with the absence of discoveries of phenomena beyond the Standard Model at the TeV scale, has triggered interest in ideas for future Higgs factories. A new circular e + e − collider hosted in a 80 to 100 km tunnel, TLEP, is among the most attractive solutions proposed so far. It has a clean experimental environment, produces high luminosity for top-quark, Higgs boson, W and Z studies, accommodates multiple detectors, and can reach energies up to the tt threshold and beyond. It will enable measurements of the Higgs boson properties and of Electroweak Symmetry-Breaking (EWSB) parameters with unequalled precision, offering exploration of physics beyond the Standard Model in the multi-TeV range. Moreover, being the natural precursor of the VHE-LHC, a 100 TeV hadron machine in the same tunnel, it builds up a long-term vision for particle physics. Altogether, the combination of TLEP and the VHE-LHC offers, for a great cost effectiveness, the best precision and the best search reach of all options presently on the market. This paper presents a first appraisal of the salient features of the TLEP physics potential, to serve as a baseline for a more extensive design study.

Sensitivities of prospective future e + e − colliders to decoupled new physics

“…The estimated errors for each Higgs channel are summarised in table 4 of [40], and we assume the same TGC and Zγ Higgs branching ratio projections as for the ILC.…”

“…We now analyse the prospective sensitivity of the FCC-ee, using the same set of four observables as for the ILC, but with the experimental errors given in [58], that are based on [40],…”

“…Prospective constraints on individual operator coefficients from FCC-ee EWPT measurements. The projected ∆χ 2 for each operator affecting the leptonic subset of EWPT observables when switched on one at a time with the others set to zero, incorporating the prospective FCC-ee measurements [40,58]. The solid (dotted) lines are for dimension-6 contributions computed using the tree-level expressions with s 2 W | SM (s 2 W | tree ), whereas the dashed lines (indistinguishable here from the solid lines) are computed numerically using ZFITTER in the expansion framework of [53].…”

“…In this paper we explore the implications within the SM EFT of the high-precision physics possible with relatively low-energy e + e − colliders, considering in particular the ILC running at 250 GeV with an integrated luminosity of 250 fb −1 [36][37][38], the scenario we call ILC250, and FCC-ee with 10 ab −1 at a centre-of mass energy of 240 GeV [40], both accompanied by lower-energy running at the Z peak and the W + W − threshold. We do not consider the possibilities for producing directly new particles, which are relatively limited at these centre-of-mass energies.…”

“…Together with Verónica Sanz, we have previously published a global analysis of dimension-6 operators in the SM EFT [22,23], providing 95% CL ranges for their coefficients, both when each operator is switched on individually and when marginalising over the possible coefficients of all contributing operators. 3 There is currently growing interest in the physics accessible to possible future e + e − colliders that would continue the studies made with LEP and the SLC to higher energies and or luminosities [34][35][36][37][38][39][40][41][42][43][44]. One of the primary objectives of such machines will be make detailed studies of the Higgs boson and its interactions, with other possible elements of their physics programmes including studies at the Z peak with very high luminosities, studies of W + W − production close to threshold and above, measurements near thett threshold and, of course, searches for possible new particles.…”