Search for Higgs bosons decaying to $aa$ in the $\ensuremath{\mu}\ensuremath{\mu}\ensuremath{\tau}\ensuremath{\tau}$ final state in $pp$ collisions at $\sqrt{s}=8\text{ }\text{ }\mathrm{TeV}$ with the ATLAS experiment

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Search for Higgs bosons decaying to $a a$ in the $μ μ τ τ$ final state in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS experiment

G. Aad et al. (The ATLAS Collaboration)

Phys. Rev. D 92, 052002 – Published 9 September 2015

Abstract

A search for the decay to a pair of new particles of either the 125 GeV Higgs boson ( $h$ ) or a second charge parity ( $C P$ )-even Higgs boson ( $H$ ) is presented. The data set corresponds to an integrated luminosity of $20.3 {fb}^{- 1}$ of $p p$ collisions at $\sqrt{s} = 8 TeV$ recorded by the ATLAS experiment at the LHC in 2012. The search was done in the context of the next-to-minimal supersymmetric standard model, in which the new particles are the lightest neutral pseudoscalar Higgs bosons ( $a$ ). One of the two $a$ bosons is required to decay to two muons while the other is required to decay to two $τ$ leptons. No significant excess is observed above the expected backgrounds in the dimuon invariant mass range from 3.7 to 50 GeV. Upper limits are placed on the production of $h \to a a$ relative to the standard model $g g \to h$ production, assuming no coupling of the $a$ boson to quarks. The most stringent limit is placed at 3.5% for $m_{a} = 3.75 GeV$ . Upper limits are also placed on the production cross section of $H \to a a$ from 2.33 to 0.72 pb, for fixed $m_{a} = 5 GeV$ with $m_{H}$ ranging from 100 to 500 GeV.

Received 8 May 2015

DOI:https://doi.org/10.1103/PhysRevD.92.052002

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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Vol. 92, Iss. 5 — 1 September 2015

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Figure 1
Simulated dimuon invariant mass ( $m_{μ μ}$ ) distribution and the result of the simultaneous fit projected into $SR μ$ for one benchmark mass point with $m_{a} = 5 GeV$ and $m_{H} = m_{h} = 125 GeV$ . The best fit of the $μ μ$ resonance model to the $h \to a a$ signal simulation in $SR μ$ is shown in blue with its uncertainty as a yellow band. Also shown are the forced $\pm 1 σ$ systematic uncertainty variations, defined in Sec. 7, in $α_{CB}$ and $f_{τ τ}$ (dashed magenta). The top plot shows the simulation and fits on a linear scale, the middle on a logarithmic scale, and the % residual of each fit is shown at the bottom. The errors on the signal simulation are statistical only.
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Figure 2
Observed $m_{μ μ}$ distribution in CRj (top) and CRb (bottom) and the SM background model after a simultaneous fit. The $Z / γ^{*}$ component of the fit is the combination of the $Z$ boson resonance and the $γ^{*}$ continuum models. The % residual of the fit is shown below each plot. Simulated SM backgrounds are shown in the stack, with the $Z / γ^{*}$ sample only valid above $m_{μ μ} > 10 GeV$ . The two insets show magnified versions of the $J / ψ$ and $ϒ$ resonances.
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Figure 3
Observed $m_{μ μ}$ distribution in $VR μ$ (top) and $VR e$ (bottom) and the background-only fit. The $Z / γ^{*}$ component of the fit is the combination of the $Z$ boson resonance and the $γ^{*}$ continuum models. The % residuals are shown below each plot. Bins below 4 GeV are 200 MeV wide, between 4 and 15 GeV they are 500 MeV wide, and above 15 GeV they are 2 GeV wide. Simulated SM backgrounds are shown in the stack, with the $Z / γ^{*}$ sample only valid above $m_{μ μ} > 10 GeV$ .
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Figure 4
Observed $m_{μ μ}$ distribution in $SR μ$ (top) and $SR e$ (bottom) and the background-only fit. The $Z / γ^{*}$ component of the fit is the combination of the $Z$ boson resonance and the $γ^{*}$ continuum models. The % residuals are shown below each plot. Bins below 4 GeV are 200 MeV wide, between 4 GeV and 15 GeV they are 500 MeV wide, and above 15 GeV they are 2 GeV wide. The expected distribution from a signal with $BR (h \to a a) = 10 %$ is shown for three different $m_{a}$ hypotheses (5, 10, and 20 GeV). Simulated SM backgrounds are shown in the stack, with the $Z / γ^{*}$ sample only valid above $m_{μ μ} > 10 GeV$ .
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Figure 5
Observed $p$ -value as a function of $m_{μ μ}$ , with downward fluctuations of the data represented by a $p$ -value of 0.5. The $p$ -values are evaluated in 50 MeV intervals below 15 GeV, then 100 MeV intervals up to 30 GeV, and 200 MeV intervals up to $m_{μ μ} = 50 GeV$ . The $p$ -values shown have not been corrected for the look-elsewhere effect.
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Figure 6
Observed (solid red) and expected (dashed black) limits with the expected $\pm 1 σ$ and $\pm 2 σ$ bands shown in green and yellow respectively. The top figure shows the expected and observed limits on the rate $(σ (g g \to h) \times BR (h \to a a))$ relative to the SM Higgs boson gluon-gluon fusion production cross section ( $σ_{SM}$ ) as a function of $m_{a}$ with $m_{H}$ set to 125 GeV. The limits are evaluated in 50 MeV intervals below 15 GeV, then 100 MeV intervals up to 30 GeV, and 200 MeV intervals up to $m_{a} = 50 GeV$ . Shown in the bottom figure is the total rate $(σ (g g \to H) \times BR (H \to a a))$ as a function of $m_{H}$ with $m_{a}$ set to 5 GeV, evaluated at 50 GeV intervals from $m_{H} = 100 GeV$ to 500 GeV and at $m_{H} = m_{h} = 125 GeV$ . The width of the black band in the bottom figure indicates the theoretical uncertainty on the SM $g g \to H$ cross section [56]. In both figures, the observed and expected limits have been scaled by an $O (1)$ parameter, $BR (a \to τ τ)^{2}$ , to account for the branching ratios assumed in this analysis, and facilitate reinterpretation of the results.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for Higgs bosons decaying to $a a$ in the $μ μ τ τ$ final state in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS experiment

G. Aad et al. (The ATLAS Collaboration)

Phys. Rev. D 92, 052002 – Published 9 September 2015

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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for Higgs bosons decaying to aa in the μμττ final state in pp collisions at s=8 TeV with the ATLAS experiment

G. Aad et al. (The ATLAS Collaboration)

Phys. Rev. D 92, 052002 – Published 9 September 2015

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Search for Higgs bosons decaying to $a a$ in the $μ μ τ τ$ final state in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS experiment