First Look at the Physics Case of TLEP

TL;DR

The paper argues that, given the Higgs discovery and absence of new physics signals, a high-precision Higgs/electroweak factory is needed to map Higgs couplings and EWSB parameters to multi-TeV new-physics sensitivity. It proposes TLEP, a circular e+e- collider in an 80–100 km tunnel capable of high luminosity at multiple clean energies (Z pole, WW threshold, HZ maximum, ttbar threshold) and designed to feed into the VHE-LHC hadron collider in the same tunnel as part of a future FCC program. The study provides quantitative estimates of luminosities, integrated luminosities per year, and beamstrahlung effects, and contrasts TLEP's performance with linear collider options while outlining a broader FCC strategy. It concludes that TLEP could achieve unprecedented precision in Higgs and EW measurements, enabling sensitivity to new physics scales up to multi-TeV, and offers a coherent, cost-effective path toward a future 100 TeV frontier.

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 t-tbar 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.

Figures (4)

• Figure 1: The mass dependence of the couplings of the recently discovered Higgs boson to fermions and gauge bosons, from a two-parameter fit (dashed line) to a combination of the CMS and ATLAS data collected at 7 and 8 TeV in 2011 and 2012, taken from Ref. cite:1303.3879. The dotted lines bound the 68% C.L. interval. The value of the coupling of the Higgs boson to the c quark shown in the figure is a prediction of the fit. The solid line corresponds to the Standard Model prediction.
• Figure 2: A possible implementation of the 80 km tunnel (dashed circle) that would host TLEP and the VHE-LHC in the Geneva area, taken from Ref. cite:Osborne. The 100 km version (full line) is currently under study.
• Figure 3: Instantaneous luminosity, in units of $10^{34}~{\rm cm}^{-2}{\rm s}^{-1}$, expected at TLEP (full red line), in a configuration with four interaction points operating simultaneously, as a function of the centre-of-mass energy. For illustration, the luminosities expected at linear colliders, ILC (blue line) and CLIC (green line), are indicated in the same graph. As explained in the text, the TLEP luminosity at each interaction point would increase significantly if fewer interaction points were considered. The possible TLEP energy upgrade up to 500 GeV, represented by a dashed line, is briefly discussed in Section \ref{['sec:VHE-LHC']}.
• Figure 4: The beam-energy spectrum for TLEP (red) for $\sqrt{s} = 240$ GeV. For illustration, the beam-energy spectrum expected in presence of beamstrahlung is shown for the ILC (black) at the same centre-of-mass energy. The $L_{0.01}$ value is the fraction of the integrated luminosity produced within 1% of the nominal centre-of-mass energy. The effect of initial state radiation (common to TLEP and ILC, but physics-process dependent) is not included in this plot.