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| CMS-SMP-18-009 ; CERN-EP-2019-001 | ||
| Search for W boson decays to three charged pions | ||
| CMS Collaboration | ||
| 30 January 2019 | ||
| Phys. Rev. Lett. 122 (2019) 151802 | ||
| Abstract: For the first time, a search for the rare decay of the W boson to three charged pions has been performed. Proton-proton collision data recorded by the CMS experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 77.3 fb$^{-1}$, have been analyzed. No significant excess is observed above the background expectation. An upper limit of 1.01$\times10^{-6}$ is set at 95% confidence level on the branching fraction of the W boson to three charged pions. This provides a strong motivation for theoretical calculations of this branching fraction. | ||
| Links: e-print arXiv:1901.11201 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; | ||
| Figures | |
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Figure 1:
Observed and expected distributions of $ {m_{3 {\pi}}} $, using 77.3 fb$^{-1}$ of data collected in 2016 and 2017. The normalization of the expected backgrounds results from the maximum likelihood fit to the data, which includes all systematic uncertainties. The background contributions are stacked upon each other, and the "Others" background contribution includes events from diboson, triboson, $ {{\mathrm {t}\overline {\mathrm {t}}}} $, single top quark, $ {{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}} $, and $ {{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {W}}$ production. The uncertainty band includes both statistical and systematic sources of uncertainty. The signal is normalized to $\mathcal {B}({\mathrm {W}}\to 3 {\pi})=10^{-6}$, and is shown as an open stacked histogram. |
png pdf |
Figure 2:
Observed and expected upper limits on $\mathcal {B}({\mathrm {W}}\to 3 {\pi})$ at 95%CL. The expected limit corresponds to the assumption $\mathcal {B}({\mathrm {W}}\to 3 {\pi})=$ 0. |
| Summary |
| In summary, the first search for the rare decay of the W boson to three charged pions has been performed. The data correspond to an integrated luminosity of 77.3 fb$^{-1}$ of proton-proton collisions collected in the CMS detector at a center-of-mass energy of 13 TeV. Events with W bosons are selected with a trigger that requires two $\tau$ leptons decaying to hadrons and a neutrino. The data are compatible with the background hypothesis. The upper limit on the branching fraction of the W boson to three charged pions is 1.01$\times10^{-6}$ at 95%CL, which reduces the previous range of values and motivates theoretical calculations of this branching fraction. |
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