CMS-PAS-EXO-20-005

CMS-PAS-EXO-20-005
Search for dark photons in VBF Higgs events in proton-proton collisions at $\sqrt{s} =$ 13 TeV
CMS Collaboration
July 2020

Abstract: A search is presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle and an isolated photon. The search is performed by the CMS Collaboration at the Large Hadron Collider, using a data set corresponding to an integrated luminosity of 130 fb$^{-1}$ recorded at a center-of-mass energy of 13 TeV. No significant excess of events above the expectation from the standard model background is found. The results are interpreted in the context of a theoretical model in which the undetected particle is a massless dark photon. An upper limit is set on the product of the cross section for vector boson fusion production and the branching fraction for such a Higgs boson decay, as a function of the Higgs boson mass. For a Higgs boson mass of 125 GeV, assuming the standard model production rates, a combination with previous searches further reduces the observed (expected) 95% confidence level upper limit on the branching fraction to 2.9 (2.1)%. This is the first search for such decays in the vector boson fusion channel. The results improve significantly the constraints on this decay mode.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 03 (2021) 011. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: A Feynman diagram for the production of the $\mathrm{q} \mathrm{q} \mathrm{H} (\to \gamma \gamma _\mathrm {D})$ final state.
png pdf	Figure 2: The $ {m_{{\mathrm {j}} {\mathrm {j}}}} $ distributions from the simultaneous fit with the full data set in the $\gamma$+jets CRs (top left), $ {\mathrm{Z} (\ell \bar{\ell})+\gamma} $ CRs (top right), and $ {\mathrm{W} (\to \ell \nu)+\gamma} $ CRs (bottom). Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 2-a: The $ {m_{{\mathrm {j}} {\mathrm {j}}}} $ distributions from the simultaneous fit with the full data set in the $\gamma$+jets CRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 2-b: The $ {m_{{\mathrm {j}} {\mathrm {j}}}} $ distributions from the simultaneous fit with the full data set in the $ {\mathrm{Z} (\ell \bar{\ell})+\gamma} $ CRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 2-c: The $ {m_{{\mathrm {j}} {\mathrm {j}}}} $ distributions from the simultaneous fit with the full data set in the $ {\mathrm{W} (\to \ell \nu)+\gamma} $ CRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 3: The $ {m_{\mathrm {T}}} $ distributions from the simultaneous fit with the full data set for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} < $ 1500 GeV in the W+jets CRs (top left), for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} \geq $ 1500 GeV in the W+jets CRs (top right), for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} < $ 1500 GeV in the SRs (bottom left), and for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} \geq $ 1500 GeV in the SRs (bottom right). Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 3-a: The $ {m_{\mathrm {T}}} $ distribution from the simultaneous fit with the full data set for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} < $ 1500 GeV in the W+jets CRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 3-b: The $ {m_{\mathrm {T}}} $ distribution from the simultaneous fit with the full data set for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} \geq $ 1500 GeV in the W+jets CRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 3-c: The $ {m_{\mathrm {T}}} $ distribution from the simultaneous fit with the full data set for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} < $ 1500 GeV in the SRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 3-d: The $ {m_{\mathrm {T}}} $ distribution from the simultaneous fit with the full data set for events with $ {m_{{\mathrm {j}} {\mathrm {j}}}} \geq $ 1500 GeV in the SRs. Overflow events are included in the last bin. The gray bands represent the uncertainties in the predicted yields. A hollow green shape indicates the contribution expected from inclusive SM Higgs boson production assuming a semi-visible branching ratio of 5%.
png pdf	Figure 4: Expected and observed upper limits at 95% CL on the product of $ {\sigma _{\text {VBF}}} $ and $ {\mathcal {B}(\mathrm{H} \to \text {invisible}+\gamma)} $ as a function of $m_{\mathrm{H}}$. The dot-dashed line shows the predicted signal corresponding to 0.05$ {\sigma _{\text {VBF}}} $, assuming VBF production only. A linear interpolation is performed between the values obtained for the probed Higgs boson masses.

Tables
png pdf	Table 1: Summary of the selection criteria in the signal region depending on the trigger path and data-taking year. Rows with one value indicates that the same requirement is applied for all data-taking years.
png pdf	Table 2: Summary of the binning choice in the SRs and CRs.
png pdf	Table 3: Data, expected backgrounds, and signal in the different regions. The signal size is chosen to be 0.05$\times {\sigma _{\text {SM}}} $, where $ {\sigma _{\text {SM}}} $ is the SM Higgs boson cross section for $m_{\mathrm{H}} = $ 125 GeV. All data-taking periods and trigger paths are combined together for each region.
png pdf	Table 4: Observed and expected 95% CL limits at $m_{\mathrm{H}} = $ 125 GeV on $ {\mathcal {B}(\mathrm{H} \to \text {invisible}+\gamma)} $ for the VBF category, ZH category, and their combination.

Summary

A search has been presented for a Higgs boson that is produced via vector boson fusion and that decays to an undetected particle together with an isolated photon. This is the first search for this signature. The search has been performed by the CMS Collaboration using a data set corresponding to an integrated luminosity of 130 fb$^{-1}$ recorded at a center-of-mass energy of 13 TeV. No significant excess of events above the expectation from the standard model background is found. The results are used to place limits on the product of the signal cross section for VBF production and the branching fraction for such decays of the Higgs boson, in the context of a theoretical model where the undetected particle is a massless dark photon. Allowing for deviations from standard model VBF production, the product of ${\sigma_{\text{VBF}}} $ and ${\mathcal{B}(\mathrm{H}\to\text{invisible}+\gamma)} $ is excluded above $\sim$150 to $\sim$2 fb, for $m_{\mathrm{H}}$ ranging from 125 to 1000 GeV. By combining with an existing analysis targeting associated $\mathrm{Z}$ boson production, and assuming the standard model rates, the observed (expected) upper limits at 95% confidence level at $m_{\mathrm{H} }= $ 125 GeV on ${\mathcal{B}(\mathrm{H}\to\text{invisible}+\gamma)} $ is 2.9 (2.1)%.

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