Probing the Higgs self-coupling at hadron colliders using rare decays

TL;DR

The paper investigates measuring the Higgs self-coupling λ through Higgs-pair production at hadron colliders for m_H ≤ 140 GeV by exploiting rare decay channels, notably HH → bbγγ. It analyzes LHC, SLHC, and a 200 TeV VLHC, showing that the bbγγ final state provides the best sensitivity, with SLHC and VLHC substantially improving λ bounds while the LHC alone remains limited for lower masses. The bbμμ channel is found to be far less favorable, whereas MSSM scenarios with small tanβ can yield observable hh signals via resonant H → hh, opening a window to the MSSM Higgs sector in otherwise difficult regions. The study emphasizes the need for precise SM background predictions and higher-order corrections to realize robust λ measurements at hadron colliders, and it highlights the complementary role of hadron machines alongside future e+e− colliders.

Abstract

We investigate Higgs boson pair production at hadron colliders for Higgs boson masses m_H\leq 140 GeV and rare decay of one of the two Higgs bosons. While in the Standard Model the number of events is quite low at the LHC, a first, albeit not very precise, measurement of the Higgs self-coupling is possible in the gg -> HH -> b\bar{b}γγchannel. A luminosity-upgraded LHC could improve this measurement considerably. A 200 TeV VLHC could make a measurement of the Higgs self-coupling competitive with a next-generation linear collider. In the MSSM we find a significant region with observable Higgs pair production in the small \tanβregime, where resonant production of two light Higgs bosons might be the only hint at the LHC of an MSSM Higgs sector.

Figures (7)

• Figure 1: SM Higgs branching ratios relevant to our analysis of $HH$ production. For $W^+W^-$ and $ZZ$, one of the gauge bosons is off-shell.
• Figure 2: Distributions of the minimum lego plot (pseudorapidity -- transverse plane) separation between (a) $b$-jets and photons, and (b) the photons, for a SM signal of $m_H=120$ GeV and the QCD $b\bar{b}\gamma\gamma$ background; using the cuts of Eq. (\ref{['eq:cuts1']}) but no minimum $b-\gamma$ separation. We include the NLO K-factor for the signal and a factor 1.3 for the QCD background.
• Figure 3: The visible invariant mass distribution, $m_{\rm vis}$, in $pp\to b\bar{b}\gamma\gamma$, after all kinematic cuts (Eqs. (\ref{['eq:cuts1']}) and (\ref{['eq:cuts2']})), for the conservative (short dashed) and optimistic (long dashed) QCD backgrounds and a SM signal of $m_H=120$ GeV (solid) at the LHC. The dotted and short dash-dotted lines show the signal cross section for $\lambda_{HHH}=\lambda/\lambda_{SM}=0$ and 2, respectively. To illustrate how the reducible backgrounds dominate the analysis, we also show the irreducible QCD $b\bar{b}\gamma\gamma$ background by itself (long dash-dotted). We include the NLO K-factor for the signal and a factor 1.3 for the QCD backgrounds.
• Figure 4: The visible invariant mass distribution, $m_{\rm vis}$, in $pp\to b\bar{b}\gamma\gamma$, after all kinematic cuts (Eqs. (\ref{['eq:cuts1']}) and (\ref{['eq:cuts2']})), for the conservative (short dashed) and optimistic (long dashed) QCD backgrounds and SM signals of $m_H=120$ (upper) and 140 GeV (lower) at the SLHC. The dotted and short dash-dotted lines show the signal cross section for $\lambda_{HHH}=\lambda/\lambda_{SM}=0$ and 2, respectively. To illustrate how the reducible backgrounds dominate the analysis, we also show the irreducible QCD $b\bar{b}\gamma\gamma$ background by itself (long dash-dotted). We include the NLO K-factor for the signal and a factor 1.3 for the QCD backgrounds.
• Figure 5: The visible invariant mass distribution, $m_{\rm vis}$, in $pp\to b\bar{b}\gamma\gamma$, after all kinematic cuts (Eqs. (\ref{['eq:cuts1']}) and (\ref{['eq:cuts2']})), for the conservative (short dashed) and optimistic (long dashed) QCD backgrounds and SM signals of $m_H=120$ (upper) and 140 GeV (lower) at a VLHC. The dotted and short dash-dotted lines show the signal cross section for $\lambda_{HHH}=\lambda/\lambda_{SM}=0$ and 2, respectively. To illustrate how the reducible backgrounds dominate the analysis, we also show the irreducible QCD $b\bar{b}\gamma\gamma$ background by itself (long dash-dotted). We include the NLO K-factor for the signal and a factor 1.3 for the QCD backgrounds.