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Register a new userProbing a Scalar Singlet-Catalyzed Electroweak Phase Transition with Resonant Di-Higgs Production in the $4b$ Channel
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We investigate the prospective reach of the 14 TeV HL-LHC for resonant production of a heavy Higgs boson that decays to two SM-like Higgs bosons in the $4b$ final state in the scalar singlet extended Standard Model. We focus on the reach for choices of parameters yielding a strong first order electroweak phase transition. The event selection follows the $4b$ analysis by the ATLAS Collaboration, enhanced with the use of a boosted decision tree method to optimize the discrimination between signal and background events. The output of the multivariate discriminant is used directly in the statistical analysis. The prospective reach of the $4b$ channel is compatible with previous projections for the $bbgammagamma$ and $4tau$ channels for heavy Higgs boson mass $m_2$ below 500 GeV and superior to these channels for $m_2 > 500$ GeV. With 3 ab$^{-1}$ of integrated luminosity, it is possible to discover the heavy Higgs boson in the $4b$ channel for $m_2< 500$ GeV in regions of parameter space yielding a strong first order electroweak phase transition and satisfying all other phenomenological constraints.
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We analyze the prospects for resonant di-Higgs production searches at the LHC in the $bbar{b} W^+ W^-$ ($W^{+} to ell^{+} u_{ell}$, $W^{-} to ell^{-} bar{ u}_{ell}$) channel, as a probe of the nature of the electroweak phase transition in Higgs portal extensions of the Standard Model. In order to maximize the sensitivity in this final state, we develop a new algorithm for the reconstruction of the $b bar{b} W^+ W^-$ invariant mass in the presence of neutrinos from the $W$ decays, building from a technique developed for the reconstruction of resonances decaying to $tau^{+}tau^{-}$ pairs. We show that resonant di-Higgs production in the $bbar{b} W^+ W^-$ channel could be a competitive probe of the electroweak phase transition already with the datasets to be collected by the CMS and ATLAS experiments in Run-2 of the LHC. The increase in sensitivity with larger amounts of data accumulated during the High Luminosity LHC phase can be sufficient to enable a potential discovery of the resonant di-Higgs production in this channel.
We study the enhancement of the di-Higgs production cross section resulting from the resonant decay of a heavy Higgs boson at hadron colliders in a model with a Higgs singlet. This enhancement of the double Higgs production rate is crucial in understanding the structure of the scalar potential and we determine the maximum allowed enhancement such that the electroweak minimum is a global minimum. The di-Higgs production enhancement can be as large as a factor of ~ 18 (13) for the mass of the heavy Higgs around 270 (420) GeV relative to the Standard Model rate at 14 TeV for parameters corresponding to a global electroweak minimum.
A coupling of a scalar, charged under an unbroken global U(1) symmetry, to the Standard Model via the Higgs portal is one of the simplest gateways to a dark sector. Yet, for masses $m_{S}geq m_{H}/2$ there are few probes of such an interaction. In this note we evaluate the sensitivity to the Higgs portal coupling of di-Higgs boson production at the LHC as well as at a future high energy hadron collider, FCC-hh, taking into account the full momentum dependence of the process. This significantly impacts the sensitivity compared to estimates of changes in the Higgs-coupling based on the effective potential. We also compare our findings to precision single Higgs boson probes such as the cross section for vector boson associated Higgs production at a future lepton collider, e.g. FCC-ee, as well as searches for missing energy based signatures.
We extend the coverage of resonant di-Higgs searches in the $b bar{b} b bar{b}$ final state to the process $p p to H_1 to H_2 H_2 to b bar{b} b bar{b}$, where both $H_{1,2}$ are spin-$0$ states beyond the Standard Model. Such a process constitutes a joint discovery mode for the new states $H_1$ and $H_2$. We present the first sensitivity study of this channel, using public LHC data to validate our analysis. We also provide a first estimate of the sensitivity of the search for the HL-LHC and future facilities like the HE-LHC and FCC-hh. We analyze the discovery potential of this search for several non-minimal scalar sector scenarios: an extension of the SM with two extra singlet scalar fields, the two-Higgs-doublet model and a two-Higgs doublet model plus a singlet, which captures the scalar potential features of the NMSSM. We find that this channel represents a novel, very powerful probe for extended Higgs sectors, offering complementary sensitivity to existing analyses.
We study the correlation between the value of the triple Higgs coupling and the nature of the electroweak phase transition. We use an effective potential approach, including higher order, non-renormalizable terms coming from integrating out new physics. We show that if only the dimension six operators are considered, large positive deviations of the triple Higgs coupling from its Standard Model (SM) value are predicted in the regions of parameter space consistent with a strong first order electroweak phase transition (SFOEPT). We also show that at higher orders sizable and negative deviations of the triple Higgs coupling may be obtained, and the sign of the corrections tends to be correlated with the order of the phase transition. We also consider a singlet extension of the SM, which allows us to establish the connection with the effective field theory (EFT) approach and analyze the limits of its validity. Furthermore, we study how to probe the triple Higgs coupling from the double Higgs production at the LHC. We show that selective cuts in the invariant mass of the two Higgs bosons should be used, to maximize the sensitivity for values of the triple Higgs coupling significantly different from the Standard Model one.
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