CMS-PAS-SMP-22-016

CMS-PAS-SMP-22-016
Search for the Z boson decay to $ \tau^+\tau^-\mu^+\mu^- $ in proton-proton collisions at $ \sqrt{s}= $ 13 TeV
CMS Collaboration
25 March 2023

Abstract: The first search for the Z boson decay to $ \tau^+\tau^-\mu^+\mu^- $ is presented. The data analyzed were collected by the CMS experiment at the CERN LHC in proton-proton collisions at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 138 fb$^{-1}$. Targeting tau lepton decays to muons and neutrinos, events with two pairs of oppositely charged muons are analyzed. The data are found to be compatible with the predicted background. A 95% confidence level upper limit of 6.2 is placed on the ratio of the $ {\mathrm{Z}\to\tau^+\tau^-\mu^+\mu^-} $ to $ {\mathrm{Z}\to\mu^+\mu^-\mu^+\mu^-} $ branching fractions, excluding values above 6.9 times the standard model expectation.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Leading-order Feynman diagram of the Z boson decay into four charged leptons $ \ell $.
png pdf	Figure 2: Distribution of $ m_{\mu\mu\mu\mu} $ after the maximum-likelihood fit of the background-only model (stacked histograms) to the data (black points). The nuisance parameters are set to their post-fit values and the signal (cyan line) is overlaid, scaled to the upper limit on its cross section of 6.9 times the SM expectation. The gray shaded areas in both panels correspond to the total uncertainty in the background prediction.
png pdf	Figure 3: Observed (solid) and expected (black dashed) upper limits on the ratio of the $ {\mathrm{Z}\to\tau^{+}\tau^{-}\mu^{+}\mu^{-}} $ to $ {\mathrm{Z}\to{\mu^{+}\mu^{-}\mu^{+}\mu^{-}}} $ branching fractions for varying CL in the phase space considered. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The horizontal grey dashed line corresponds to the 95% CL.

Summary

In summary, the first search for the Z boson decay to $ \tau^{+}\tau^{-}\mu^{+}\mu^{-} $ has been presented. The sample of proton-proton collision data analyzed was collected at $ \sqrt{s}= $ 13 TeV by the CMS experiment and corresponds to an integrated luminosity of 138 fb$ ^{-1} $. No excess over the SM background prediction was observed. At the 95% confidence level, an upper limit of 6.2 was placed on the ratio of the $ {\mathrm{Z}\to\tau^{+}\tau^{-}\mu^{+}\mu^{-}} $ to $ {\mathrm{Z}\to{\mu^{+}\mu^{-}\mu^{+}\mu^{-}}} $ branching fractions in the phase space considered, which excludes values above 6.9 times the standard model expectation.

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