Abstract
The currently unmeasured triple Higgs coupling is one of the strong motivations for future physics programs at the LHC and beyond. A sufficiently precise measurement can lead to qualitative changes in our understanding of electroweak symmetry breaking and the cosmological history of the Higgs potential. As such, the quantitative measurement of this coupling is now one of the benchmark measurements for any proposed collider. We study the capability of a potential 27 TeV HE-LHC upgrade in measuring the Higgs trilinear coupling via the di-Higgs production process in the boverline{b}upgamma upgamma channel. We emphasize that a key background from single Higgs production via gluon fusion has been underestimated and underappreciated in prior studies. We perform a detailed study taking into account two different potential detector scenarios, and validate against HL-LHC projections from ATLAS. We find that the di-Higgs production process can be observed at ≥ 4.5σ, corresponding to a ∼ 40% measurement of the Higgs self-coupling, with 15 ab−1 of data at the HE-LHC.
Highlights
Measurement of the triple Higgs coupling and beyond
We find that the di-Higgs production process can be observed at ≥ 4.5σ, corresponding to a ∼ 40% measurement of the Higgs self-coupling, with 15 ab−1 of data at the HE-LHC
The strength of a potential EW phase transition (EWPT) depends critically on the value of the effective triple Higgs coupling, and must be measured to the O(10%) level or better to distinguish the order of the phase transition in some cases [12, 13]
Summary
The most direct way to measure the Higgs trilinear coupling, λ3, at a hadron collider is via the Higgs pair production process, which arises primarily from gg → hh. The lowest order diagrams contributing to di-Higgs production for gg → hh in the SM, shown, arise from the “triangle” diagram, as in single-Higgs production with an additional hhh vertex, and from the “box” diagram, which is independent of λ3 To leading order, these amplitudes scale as [19]: M. The leading-order (LO) cross section was known exactly for many years [32,33,34], with a number of approximations to account for higher-order corrections These include next-to-leading order (NLO) [35] and NNLO [36, 37] corrections in QCD, using the infinite top quark mass limit, as well as estimates of threshold resummation effects at NNLL accuracy [38, 39]. A better approximation can be obtained by shifting the NNLO+NNLL values in [43] to account for the finite-mass effects, leading to the values shown in table 1 from [44]
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