Prospects for direct searches for light Higgs bosons at the ILC with 250 GeV
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Regular Article - Theoretical Physics
Prospects for direct searches for light Higgs bosons at the ILC with 250 GeV P. Drechsel1, G. Moortgat-Pick1,2,a , G. Weiglein1,b 1 2
DESY, Notkestraße 85, 22607 Hamburg, Germany II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
Received: 14 May 2020 / Accepted: 6 September 2020 © The Author(s) 2020
Abstract The particle discovered in the Higgs boson searches at the LHC with a mass of about 125 GeV is compatible within the present uncertainties with the Higgs boson predicted in the Standard Model (SM), but it could also be identified with one of the neutral Higgs bosons in a variety of beyond the SM (BSM) theories with an extended Higgs sector. The possibility that an additional Higgs boson (or even more than one) could be lighter than the state that has been detected at 125 GeV occurs generically in many BSM models and has some support from slight excesses that were observed above the background expectations in Higgs searches at LEP and at the LHC. The couplings between additional Higgs fields and the electroweak gauge bosons in BSM theories could be probed by model-independent Higgs searches at lepton colliders. We present a generator-level extrapolation of the limits obtained at LEP to the case of a future e+ e− collider, both for the search where the light Higgs boson decays into a pair of bottom quarks and for the decay-modeindependent search utilising the recoil method. We find that at the ILC with a centre-of-mass energy of 250 GeV, an integrated luminosity of 500 fb−1 and polarised beams, the sensitivity to a light Higgs boson with reduced couplings to gauge bosons is improved by more than an order of magnitude compared to the LEP limits and goes much beyond the projected indirect sensitivity of the HL-LHC with 3000 fb−1 from the rate measurements of the detected state at 125 GeV.
1 Introduction The properties of the Higgs boson that was discovered in 2012 are in agreement with the predictions of the Standard Former address: P. Drechsel. a e-mail:
[email protected] (corresponding author)
b e-mail:
[email protected]
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Model (SM) within the current experimental accuracy, but they are also compatible with a wide variety of extensions of or alternatives to the SM. Extended Higgs sectors predict the existence of additional Higgs bosons, which could be heavier but also lighter than the observed state at 125 GeV. The coupling of the SM Higgs boson to the gauge bosons W and Z is such that terms with a bad high-energy behaviour in longitudinal vector-boson scattering exactly cancel with each other. As a consequence, in an extended Higgs sector comprising the SM-like state at 125 GeV and additional Higgs bosons the couplings of the additional neutral Higgs bosons to W and Z , gφi V V , are expected to be small. This implies that additional heavy neutral Higgs bosons may not be detectable via the search channels φi → Z Z , W + W − and that for an additional light Higgs boson (or mor
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