The total decay width for a light Higgs boson with a mass in the observed range is not expected to be directly observable at the LHC. For the case of the Standard Model the prediction for the total width is about 4 MeV, which is three orders of magnitude smaller than the experimental mass resolution. There is no indication from the results observed so far that the natural width is broadened by new physics effects to such an extent that it could be directly observable. Furthermore, as all LHC Higgs channels rely on the identification of Higgs decay products, the total Higgs width cannot be measured indirectly without additional assumptions. The different dependence of on-peak and off-peak contributions on the total width in Higgs decays to ${{\mathit Z}}{{\mathit Z}^{*}}$ and interference effects between signal and background in Higgs decays to ${{\mathit \gamma}}{{\mathit \gamma}}$ can provide additional information in this context. Constraints on the total width from the combination of on-peak and off-peak contributions in Higgs decays to ${{\mathit Z}}{{\mathit Z}^{*}}$ rely on the assumption of equal on- and off-shell effective couplings. Without an experimental determination of the total width or further theoretical assumptions, only ratios of couplings can be determined at the LHC rather than absolute values of couplings.

VALUE (MeV) CL% DOCUMENT ID TECN  COMMENT $\bf{ 3.7 {}^{+1.9}_{-1.4}}$ OUR AVERAGE $4.5$ ${}^{+3.0}_{-2.5}$ 1 AAD 2023 BR ATLS ${{\mathit p}}{{\mathit p}}$, 13 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $/$ ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$, ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ $3.2$ ${}^{+2.4}_{-1.7}$ 2 TUMASYAN 2022 AM CMS ${{\mathit p}}{{\mathit p}}$, 13 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $/$ ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$, ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ • • We do not use the following data for averages, fits, limits, etc. • • $3.2$ ${}^{+2.8}_{-2.2}$ 3 SIRUNYAN 2019 BL CMS ${{\mathit p}}{{\mathit p}}$, 7, 8, 13 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $/$ ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ $<14.4$ 95 4 AABOUD 2018 BP ATLS ${{\mathit p}}{{\mathit p}}$, 13 TeV, ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$, 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ $<1100$ 95 5 SIRUNYAN 2017 AV CMS ${{\mathit p}}{{\mathit p}}$, 13 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ $<26$ 95 6 KHACHATRYAN 2016 BA CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit W}}{{\mathit W}^{(*)}}$ $<13$ 95 7 KHACHATRYAN 2016 BA CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV,${{\mathit Z}}{{\mathit Z}^{(*)}},{{\mathit W}}{{\mathit W}^{(*)}}$ $<22.7$ 95 8 AAD 2015 BE ATLS ${{\mathit p}}{{\mathit p}}$, 8 TeV, ${{\mathit Z}}{{\mathit Z}^{(*)}}$, ${{\mathit W}}{{\mathit W}^{(*)}}$ $<1700$ 95 9 KHACHATRYAN 2015 AM CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV $ > 3.5 \times 10^{-9}$ 95 10 KHACHATRYAN 2015 BA CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, flight distance $<46$ 95 11 KHACHATRYAN 2015 BA CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{(*)}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ $<5000$ 95 12 AAD 2014 W ATLS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit \gamma}}{{\mathit \gamma}}$ $<2600$ 95 12 AAD 2014 W ATLS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ $<3400$ 95 13 CHATRCHYAN 2014 AA CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ $<22$ 95 14 KHACHATRYAN 2014 D CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit Z}}{{\mathit Z}^{(*)}}$ $<2400$ 95 15 KHACHATRYAN 2014 P CMS ${{\mathit p}}{{\mathit p}}$, 7, 8 TeV, ${{\mathit \gamma}}{{\mathit \gamma}}$ 1  AAD 2023BR use 139 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. The off-shell Higgs boson production in the ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ and ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ decay channels and the on-shell production in the ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ (${{\mathit \ell}}$ = ${{\mathit e}}$ , ${{\mathit \mu}}$, AAD 2020AQ) decay channels are used to measure the total width. The off-shell Higgs signal strength is measured to be $1.1$ ${}^{+0.7}_{-0.6}$ assuming the same on-shell and off-shell coupling modifiers are used individually for gluon-fusion and for gauge-boson modes. The scenario of no off-shell contribution is excluded at 3.3 $\sigma $. Combining with the on-shell signal strength measurement, the total width normalized to its SM expectation $\Gamma _{H}/\Gamma {}^{SM}_{H}$ is measured to be $1.1$ ${}^{+0.7}_{-0.6}$ assuming the same on-shell and off-shell coupling modifiers are used individually for gluon-fusion and for gauge-boson modes. The observed upper limit on the total width is 10.2 MeV at 95$\%$ CL. See their Fig. 7. See corrected width values their erratum AAD 2024P. 2  TUMASYAN 2022AM use up to 140 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. The off-shell Higgs boson production in the ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ and ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ decay channels and the on-shell production in the ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ (${{\mathit \ell}}$ = ${{\mathit e}}$ , ${{\mathit \mu}}$) decay channels are used to measure the total width. The off-shell Higgs signal strength is measured to be $0.62$ ${}^{+0.68}_{-0.45}$ without the constraint on the ratio of the off-shell signal strengths for gluon-fusion and gauge-boson modes. The scenario of no off-shell contribution is excluded at 3.6 $\sigma $. The results are shown in their Table 1 with other constraint scenarios and the decay widths assuming the same coupling modifiers for on- and off-shell couplings (${{\mathit g}_{{{p}}}}$ and ${{\mathit g}_{{{d}}}}$ in their notation). The measurement of anomalous ${{\mathit H}}{{\mathit V}}{{\mathit V}}$ couplings is shown in their Extended Data Table 1 and Fig. 8. 3  SIRUNYAN 2019BL measure the width and anomalous ${{\mathit H}}{{\mathit V}}{{\mathit V}}$ couplings from on-shell and off-shell production in the 4 ${{\mathit \ell}}$ final state. Data of 80.2 fb${}^{-1}$ at 13 TeV, 19.7 fb${}^{-1}$ at 8 TeV, and 5.1 fb${}^{-1}$ at 7 TeV are used. The total width for the SM-like couplings is measured to be also $\lbrack{}$0.08, 9.16] MeV with 95$\%$ CL, assuming SM-like couplings for on- and off-shells (see their Table VIII). Constraints on the total width for anomalous ${{\mathit H}}{{\mathit V}}{{\mathit V}}$ interaction cases are found in their Table IX. See their Table X for the Higgs boson signal strength in the off-shell region. 4  AABOUD 2018BP use 36.1 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV. An observed upper limit on the off-shell Higgs signal strength of 3.8 is obtained at 95$\%$ CL using off-shell Higgs boson production in the ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ and ${{\mathit Z}}$ ${{\mathit Z}}$ $\rightarrow$ 2 ${{\mathit \ell}}$2 ${{\mathit \nu}}$ decay channels (${{\mathit \ell}}$ = ${{\mathit e}}$ , ${{\mathit \mu}}$). Combining with the on-shell signal strength measurements, the quoted upper limit on the Higgs boson total width is obtained, assuming the ratios of the relevant Higgs-boson couplings to the SM predictions are constant with energy from on-shell production to the high-mass range. 5  SIRUNYAN 2017AV obtain an upper limit on the width from the distribution in ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ (${{\mathit \ell}}$ = ${{\mathit e}}$ , ${{\mathit \mu}}$) decays. Data of 35.9 fb${}^{-1}{{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 13 TeV is used. The expected limit is 1.60 GeV. 6  KHACHATRYAN 2016BA derive constraints on the total width from comparing ${{\mathit W}}{{\mathit W}^{(*)}}$ production via on-shell and off-shell ${{\mathit H}}$ using 4.9 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.4 fb${}^{-1}$ at 8 TeV. 7  KHACHATRYAN 2016BA combine the ${{\mathit W}}{{\mathit W}^{(*)}}$ result with ${{\mathit Z}}{{\mathit Z}^{(*)}}$ results of KHACHATRYAN 2015BA and KHACHATRYAN 2014D. 8  AAD 2015BE derive constraints on the total width from comparing ${{\mathit Z}}{{\mathit Z}^{(*)}}$ and ${{\mathit W}}{{\mathit W}^{(*)}}$ production via on-shell and off-shell ${{\mathit H}}$ using 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. The K factor for the background processes is assumed to be equal to that for the signal. 9  KHACHATRYAN 2015AM combine ${{\mathit \gamma}}{{\mathit \gamma}}$ and ${{\mathit Z}}$ ${{\mathit Z}^{*}}$ $\rightarrow$ 4 ${{\mathit \ell}}$ results. The expected limit is 2.3 GeV. 10  KHACHATRYAN 2015BA derive a lower limit on the total width from an upper limit on the decay flight distance $\tau $ $<$ $1.9 \times 10^{-13}$ s. 5.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.7 fb${}^{-1}$ at 8 TeV are used. 11  KHACHATRYAN 2015BA derive constraints on the total width from comparing ${{\mathit Z}}{{\mathit Z}^{(*)}}$ production via on-shell and off-shell ${{\mathit H}}$ with an unconstrained anomalous coupling. 4${{\mathit \ell}}$ final states in 5.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.7 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV are used. 12  AAD 2014W use 4.5 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 20.3 fb${}^{-1}$ at 8 TeV. The expected limit is 6.2 GeV. 13  CHATRCHYAN 2014AA use 5.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.7 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. The expected limit is 2.8 GeV. 14  KHACHATRYAN 2014D derive constraints on the total width from comparing ${{\mathit Z}}{{\mathit Z}^{(*)}}$ production via on-shell and off-shell ${{\mathit H}}$. 4${{\mathit \ell}}$ and ${{\mathit \ell}}{{\mathit \ell}}{{\mathit \nu}}{{\mathit \nu}}$ final states in 5.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.7 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV are used. 15  KHACHATRYAN 2014P use 5.1 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ collisions at $\mathit E_{{\mathrm {cm}}}$ = 7 TeV and 19.7 fb${}^{-1}$ at $\mathit E_{{\mathrm {cm}}}$ = 8 TeV. The expected limit is 3.1 GeV.

References