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Feynman diagram for the inclusive HNL production from \bquarkbar quarks and its subsequent decay $\N\to\mupm\pimp$. This diagram represents various decay channels depending on the hadronisation of the \bquarkbar quark. The \bquarkbar quark and other quarks (\cquarkbar or \uquarkbar) can either form the initial-state meson or appear in the final state. If the HNL is of a Majorana nature, the two muons in the final state can have the same sign.

Feynman diagram for the inclusive HNL production from \bquarkbar quarks and its subsequent decay $\N\to\mupm\pimp$. This diagram represents various decay channels depending on the hadronisation of the \bquarkbar quark. The \bquarkbar quark and other quarks (\cquarkbar or \uquarkbar) can either form the initial-state meson or appear in the final state. If the HNL is of a Majorana nature, the two muons in the final state can have the same sign.

Branching fractions of various \B-meson channels corresponding to different \B-meson types, \Bz, \Bp, \Bs or \Bc, weighted by the corresponding fragmentation fraction. These values depend on the HNL mass, $m_\N$, and are calculated for a mixing parameter of $|U_{\muon \N}|^2=10^{-4}$. The solid red ``Semileptonic" line is the sum of all semileptonic decay channels, \ie the sum of all the specific decays below the semileptonic line in the legend.

Branching fractions of various \B-meson channels corresponding to different \B-meson types, \Bz, \Bp, \Bs or \Bc, weighted by the corresponding fragmentation fraction. These values depend on the HNL mass, $m_\N$, and are calculated for a mixing parameter of $|U_{\muon \N}|^2=10^{-4}$. The solid red ``Semileptonic" line is the sum of all semileptonic decay channels, \ie the sum of all the specific decays below the semileptonic line in the legend.

Total selection efficiency for HNL events with two same-sign muons, shown for HNL lifetimes of (left) 10\ps and (right) 1\ns. Coloured bands represent the allowed range of values within $\pm1\sigma$ of the combined statistical and systematic uncertainties. For a direct comparison between reconstruction categories, the downstream-track efficiency is multiplied by a factor of five, corresponding to the rescaling factor of the dedicated trigger.

Total selection efficiency for HNL events with two same-sign muons, shown for HNL lifetimes of (left) 10\ps and (right) 1\ns. Coloured bands represent the allowed range of values within $\pm1\sigma$ of the combined statistical and systematic uncertainties. For a direct comparison between reconstruction categories, the downstream-track efficiency is multiplied by a factor of five, corresponding to the rescaling factor of the dedicated trigger.

Total selection efficiency for HNL events with two same-sign muons, shown for HNL lifetimes of (left) 10\ps and (right) 1\ns. Coloured bands represent the allowed range of values within $\pm1\sigma$ of the combined statistical and systematic uncertainties. For a direct comparison between reconstruction categories, the downstream-track efficiency is multiplied by a factor of five, corresponding to the rescaling factor of the dedicated trigger.

Total selection efficiency for HNL events with two same-sign muons, shown for HNL lifetimes of (left) 10\ps and (right) 1\ns. Coloured bands represent the allowed range of values within $\pm1\sigma$ of the combined statistical and systematic uncertainties. For a direct comparison between reconstruction categories, the downstream-track efficiency is multiplied by a factor of five, corresponding to the rescaling factor of the dedicated trigger.

Sensitivity estimate of various reconstruction categories of the analysis for the (left) OS and (right) SS event categories, assuming no background. Lifetimes, shown by the grey contours, and previous limits are for a Majorana-natured HNL. The most stringent limits in this mass range are from the CMS and BEBC collaborations.

Sensitivity estimate of various reconstruction categories of the analysis for the (left) OS and (right) SS event categories, assuming no background. Lifetimes, shown by the grey contours, and previous limits are for a Majorana-natured HNL. The most stringent limits in this mass range are from the CMS and BEBC collaborations.

Sensitivity estimate of various reconstruction categories of the analysis for the (left) OS and (right) SS event categories, assuming no background. Lifetimes, shown by the grey contours, and previous limits are for a Majorana-natured HNL. The most stringent limits in this mass range are from the CMS and BEBC collaborations.

Sensitivity estimate of various reconstruction categories of the analysis for the (left) OS and (right) SS event categories, assuming no background. Lifetimes, shown by the grey contours, and previous limits are for a Majorana-natured HNL. The most stringent limits in this mass range are from the CMS and BEBC collaborations.

Distribution of the \(\muon\pion\) mass in the control region D for the (left) SS and (right) OS \textit{long} categories, showing fits with two Johnson \(S_{\mathrm{U}}\) distributions for peaking backgrounds from charm meson decays and either one (left) or two (right) exponentials for the combinatorial background.

Distribution of the \(\muon\pion\) mass in the control region D for the (left) SS and (right) OS \textit{long} categories, showing fits with two Johnson \(S_{\mathrm{U}}\) distributions for peaking backgrounds from charm meson decays and either one (left) or two (right) exponentials for the combinatorial background.

Distribution of the \(\muon\pion\) mass in the control region D for the (left) SS and (right) OS \textit{long} categories, showing fits with two Johnson \(S_{\mathrm{U}}\) distributions for peaking backgrounds from charm meson decays and either one (left) or two (right) exponentials for the combinatorial background.

Distribution of the \(\muon\pion\) mass in the control region D for the (left) SS and (right) OS \textit{long} categories, showing fits with two Johnson \(S_{\mathrm{U}}\) distributions for peaking backgrounds from charm meson decays and either one (left) or two (right) exponentials for the combinatorial background.

Examples of mass distributions obtained in the signal region for the OS \textit{long} category, with fits for Majorana HNLs. The plots correspond to the inclusive (left) and the leptonic \Bp (right) reconstruction categories.

Examples of mass distributions obtained in the signal region for the OS \textit{long} category, with fits for Majorana HNLs. The plots corresponds to the inclusive (left) and the leptonic \Bp (right) reconstruction categories.

Examples of mass distributions obtained in the signal region for the OS \textit{long} category, with fits for Majorana HNLs. The plots correspond to the inclusive (left) and the leptonic \Bp (right) reconstruction categories.

Examples of mass distributions obtained in the signal region for the OS \textit{long} category, with fits for Majorana HNLs. The plots corresponds to the inclusive (left) and the leptonic \Bp (right) reconstruction categories.

(Left) Combination of all the OS search categories that corresponds to a Dirac-like HNL. (Right) Combination of all the SS and OS search categories that corresponds to a Majorana-like HNL. Lifetime contours are shown in grey.

(Left) Combination of all the OS search categories that corresponds to a Dirac-like HNL. (Right) Combination of all the SS and OS search categories that corresponds to a Majorana-like HNL. Lifetime contours are shown in grey.

(Left) Combination of all the OS search categories that corresponds to a Dirac-like HNL. (Right) Combination of all the SS and OS search categories that corresponds to a Majorana-like HNL. Lifetime contours are shown in grey.

(Left) Combination of all the OS search categories that corresponds to a Dirac-like HNL. (Right) Combination of all the SS and OS search categories that corresponds to a Majorana-like HNL. Lifetime contours are shown in grey.