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| CMS-EXO-24-012 ; CERN-EP-2026-051 | ||
| Search for low-mass resonances decaying to $ \tau\tau $ and measurement of the $ \Upsilon\to\tau\tau $ decay in proton-proton collisions at $ \sqrt{s} = $ 13.6 TeV | ||
| CMS Collaboration | ||
| 24 May 2026 | ||
| Submitted to Physical Review Letters | ||
| Abstract: An inclusive search is presented for spin-zero bosons decaying to $ \tau\tau $ in a previously unexplored mass range between 20 and 60 GeV using proton-proton collision data at $ \sqrt{s}= $ 13.6 TeV, corresponding to an integrated luminosity of 61.9 fb$ ^{-1} $ recorded by CMS in 2022--2023. A high-rate trigger stream in combination with a novel low-momentum hadronic tau reconstruction algorithm have enabled a measurement of the $ \Upsilon(1S,2S,3S)\to\tau^{+}\tau^{-} $ process in the challenging environment of a hadron collider, with a 5.8 $ \sigma $ significance above background and production cross section of 3.5 $ \pm $ 0.7 (stat) $ \pm $ 0.7 (syst) nb for visible rapidity $ |y_{\text{vis}}| < $ 1.2 and visible transverse momentum $ p_{\mathrm{T}}^\text{vis} > $ 15 GeV. No significant excess above the standard model background is observed. Upper limits on the product of the spin-zero resonance production cross section and branching fraction to $ \tau\tau $ are set at 95% confidence level between 40 and 400 pb. | ||
| Links: e-print arXiv:2605.25103 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
The observed $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ distributions in the $ \Upsilon $ meson (left, middle) and Z boson (right) selection regions are shown with fit results overlaid. The left plot contains prong-only $ \tau_\mathrm{h} $ while the center contains one-prong-plus-strips $ \tau_\mathrm{h} $. The backgrounds for the $ \Upsilon $ are estimated using third order Chebychev polynomials, while the Gaussian shape of the $ \Upsilon $ is inferred from simulation. A fit to the $ \Upsilon $ simulation is overlaid on the background-subtracted data in the bottom panel where the green (1 s.d.) and yellow (2 s.d.) bands show the uncertainty on the background estimate. The Z boson backgrounds are determined by simulation scaled to expected cross section. |
png pdf |
Figure 1-a:
The observed $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ distributions in the $ \Upsilon $ meson (left, middle) and Z boson (right) selection regions are shown with fit results overlaid. The left plot contains prong-only $ \tau_\mathrm{h} $ while the center contains one-prong-plus-strips $ \tau_\mathrm{h} $. The backgrounds for the $ \Upsilon $ are estimated using third order Chebychev polynomials, while the Gaussian shape of the $ \Upsilon $ is inferred from simulation. A fit to the $ \Upsilon $ simulation is overlaid on the background-subtracted data in the bottom panel where the green (1 s.d.) and yellow (2 s.d.) bands show the uncertainty on the background estimate. The Z boson backgrounds are determined by simulation scaled to expected cross section. |
png pdf |
Figure 1-b:
The observed $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ distributions in the $ \Upsilon $ meson (left, middle) and Z boson (right) selection regions are shown with fit results overlaid. The left plot contains prong-only $ \tau_\mathrm{h} $ while the center contains one-prong-plus-strips $ \tau_\mathrm{h} $. The backgrounds for the $ \Upsilon $ are estimated using third order Chebychev polynomials, while the Gaussian shape of the $ \Upsilon $ is inferred from simulation. A fit to the $ \Upsilon $ simulation is overlaid on the background-subtracted data in the bottom panel where the green (1 s.d.) and yellow (2 s.d.) bands show the uncertainty on the background estimate. The Z boson backgrounds are determined by simulation scaled to expected cross section. |
png pdf |
Figure 1-c:
The observed $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ distributions in the $ \Upsilon $ meson (left, middle) and Z boson (right) selection regions are shown with fit results overlaid. The left plot contains prong-only $ \tau_\mathrm{h} $ while the center contains one-prong-plus-strips $ \tau_\mathrm{h} $. The backgrounds for the $ \Upsilon $ are estimated using third order Chebychev polynomials, while the Gaussian shape of the $ \Upsilon $ is inferred from simulation. A fit to the $ \Upsilon $ simulation is overlaid on the background-subtracted data in the bottom panel where the green (1 s.d.) and yellow (2 s.d.) bands show the uncertainty on the background estimate. The Z boson backgrounds are determined by simulation scaled to expected cross section. |
png pdf |
Figure 2:
Distributions of $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ (points with error bars) in the $ \phi $ boson search region, separated by hadronic decay mode with fit results (lines). All plots contain a $ \mathrm{Z}/{\gamma}{\ast} \to\tau\tau $ component determined by simulations overlaid on the continuum fit. The leftmost plot shows the single-prong final-state with contamination due to $ \mathrm{Z}\to\mu\mu $ events (orange) at 91 GeV. The center and right plots show the three-prong and one-prong-plus-one or two-strips respectively. The lower panels of each plot show the differences between the background estimation and the data, divided by the uncertainty in the data points. The $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ range corresponding to $ \phi $ masses from 20 to 60 GeV is 10 to 40 GeV. |
png pdf |
Figure 2-a:
Distributions of $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ (points with error bars) in the $ \phi $ boson search region, separated by hadronic decay mode with fit results (lines). All plots contain a $ \mathrm{Z}/{\gamma}{\ast} \to\tau\tau $ component determined by simulations overlaid on the continuum fit. The leftmost plot shows the single-prong final-state with contamination due to $ \mathrm{Z}\to\mu\mu $ events (orange) at 91 GeV. The center and right plots show the three-prong and one-prong-plus-one or two-strips respectively. The lower panels of each plot show the differences between the background estimation and the data, divided by the uncertainty in the data points. The $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ range corresponding to $ \phi $ masses from 20 to 60 GeV is 10 to 40 GeV. |
png pdf |
Figure 2-b:
Distributions of $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ (points with error bars) in the $ \phi $ boson search region, separated by hadronic decay mode with fit results (lines). All plots contain a $ \mathrm{Z}/{\gamma}{\ast} \to\tau\tau $ component determined by simulations overlaid on the continuum fit. The leftmost plot shows the single-prong final-state with contamination due to $ \mathrm{Z}\to\mu\mu $ events (orange) at 91 GeV. The center and right plots show the three-prong and one-prong-plus-one or two-strips respectively. The lower panels of each plot show the differences between the background estimation and the data, divided by the uncertainty in the data points. The $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ range corresponding to $ \phi $ masses from 20 to 60 GeV is 10 to 40 GeV. |
png pdf |
Figure 2-c:
Distributions of $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ (points with error bars) in the $ \phi $ boson search region, separated by hadronic decay mode with fit results (lines). All plots contain a $ \mathrm{Z}/{\gamma}{\ast} \to\tau\tau $ component determined by simulations overlaid on the continuum fit. The leftmost plot shows the single-prong final-state with contamination due to $ \mathrm{Z}\to\mu\mu $ events (orange) at 91 GeV. The center and right plots show the three-prong and one-prong-plus-one or two-strips respectively. The lower panels of each plot show the differences between the background estimation and the data, divided by the uncertainty in the data points. The $ m_{\text{vis}}(\mu,\tau_\mathrm{h}) $ range corresponding to $ \phi $ masses from 20 to 60 GeV is 10 to 40 GeV. |
png pdf |
Figure 3:
The 95% CL upper limits on the product of the cross section and branching fraction, $ \sigma(\mathrm{p}\mathrm{p}\to\phi)\mathcal{B}(\phi\to\tau\tau) $ in pb. The dotted line represents the median expected limits while the yellow and blue bands indicate the 68 and 95% expected bands, respectively. The solid line shows the observed limits. |
| Tables | |
png pdf |
Table 1:
Summary of selection criteria for the $ \phi $ boson, Z boson, and $ \Upsilon $ meson regions. |
| Summary |
| In summary, an inclusive search for low-mass spin-zero $\phi$ bosons decaying to tau leptons with a hadronic signature has been performed in a previously unexplored mass range using proton-proton collision data at $ \sqrt{s}= $ 13.6 TeV, collected with the CMS detector at the LHC in 2022--2023. The decay $ \Upsilon(1S,2S,3S)\to\tau^{+}\tau^{-} $ has been measured in the challenging environment of a hadron collider with a $5.8\sigma$ significance above background, and a production cross section of $\sigma = 3.5 \pm $ 0.7 (stat) $ \pm $ 0.7 (syst) nb in the fiducial region $ |y_{\text{vis}}| < $ 1.2 and $ p_{\mathrm{T}}^\text{vis} > $ 15 GeV. This measurement demonstrates the efficacy of a novel low-momentum $\tau_\mathrm{h}$ reconstruction algorithm implemented in a high-rate data stream. These innovations allow unprecedented sensitivity to new physics with tau leptons. |
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