Upper limits at 90% CL of $B(K^+\to\pi^+a)\times B(a\to\gamma\gamma)$ in the prompt ALP decay assumption.

See caption of Figure 9.

See caption of Figure 9.

See caption of Figure 9.

See caption of Figure 9.

See caption of Figure 9.

See caption of Figure 9.

90% CL upper limit in dark photon coupling vs mass parameter space for the $A^\prime \rightarrow l^+l^-$ analysis.

90% CL upper limit in $BR(B \rightarrow K a, a \rightarrow e^+e^-)$ vs lifetime $\tau$ parameter space.

90% CL upper limit in $BR(B \rightarrow K a, a \rightarrow e^+e^-)$ vs lifetime $\tau$ parameter space.

90% CL upper limit in axion-like particle coupling to SM fermions at UV scale Lambda=1TeV vs mass parameter space for di-lepton final states.

90% CL upper limit in axion-like particle coupling to SM gluons at UV scale Lambda=1TeV vs mass parameter space for hadronic final states.

Number of expected $a \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $C_{bs}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\eta$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $C_{bs}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\gamma$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $C_{bs}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $C_{bs}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $C_{bs}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\eta$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\gamma$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\pi^0$ assuming production coupling $\theta_{\pi^0} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\eta$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\gamma$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta$ assuming production coupling $\theta_{\eta} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\eta$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\gamma$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in mixing with $\eta^\prime$ assuming production coupling $\theta_{\eta^\prime} = 1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\eta$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\gamma$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $a \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Primakoff production assuming production coupling $C_{\gamma\gamma}/\Lambda=1\,\mathrm{GeV}^{-1}$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to K^+K^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to K^+K^-$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to K^+K^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for mixing production assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in light meson decays assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in light meson decays assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in light meson decays assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in light meson decays assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $A^\prime \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for production in light meson decays assuming production coupling $\varepsilon=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to K^+K^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to \pi^+\pi^-$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to \pi^+\pi^-\pi^0\pi^0$ events for BR = 1 in the plane (mass, width) after full selection, for Bremsstrahlung production assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to e^+e^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to \mu^+\mu^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to K^+K^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Number of expected $S \to \pi^+\pi^-$ events for BR = 1 in the plane (mass, width) after full selection, for production in B meson decays assuming production coupling $\mathrm{sin}^2\theta=1$. Acceptance for particles that reach the FV and decay therein and mass resolution.

Pre-fit MC statistical uncertainties per bin. These values are used to quantify the MC statistical uncertainty contributions to the total uncertainty in $m_t$ based on elements from the covariance matrix obtained in the profile likelihood fit. Each MC statistical contribution is estimated by dividing the relevant covariance matrix entry (see Table 2) by the corresponding pre-fit MC statistical uncertainty for that bin.

The contribution of each source of systematic uncertainty to the total uncertainty in $m_t$ is provided. Each source's contribution is taken directly from the relevant element of the covariance matrix for the profile likelihood fit to $\overline{m_J}$, $m_{jj}$, and $m_{tj}$ using data. The sign of the effect of each uncertainty is included.

The fitted $m_t$ is provided for each replica generated using bootstrapping. Each replica is a 3D histogram of $m_{J}$, $m_{jj}$, and $m_{tj}$, where $m_{J}$ has 50 bins between 145.0 GeV and 205.0 GeV. This method uses the BootstrapGenerator class in ROOT to initialise a pseudo-random number generator for each event, which is seeded by the value of the eventNumber and runNumber variables for a given event in the input dataset. The pseudo-random numbers are drawn from a Poisson distribution with rate parameter equal to 1. These are used to fluctuate the amount by which each replica histogram is filled. There are 1000 replicas, numbered from 0 to 999.

The distributions of the variables used in the simultaneous fit for the SR. The black points with error bars represent the data and their statistical uncertainties, whereas the shaded band represents the predicted uncertainties. The bottom panel in each figure shows the ratio of the number of events observed in data to that of the total SM prediction. The last bin of each plot has been extended to include the overflow contribution.

Expected and observed 95% upper limits on the product of the cross section and branching fraction$\sigma(\mathrm{pp} \ ightarrow W\mathrm{a})\mathcal{B}(W ightarrow \ell^{+} v_{\ell})\mathcal{B}(\mathrm{a} \rightarrow Z\gamma)\mathcal{B}(Z \rightarrow \ell^{+} \ell^{-})$ s a function of the ALP mass from 110 to 400 GeV

Expected and observed 95% upper limits on the photophobic ALP model parameter $1/f_{\mathrm{a}}$ as a function of ALP mass reinterpreted from $1/f_{\mathrm{a}}=2~\mathrm{TeV}^{-1}$

Single Event Sensitivity (SES) for the $K^{+}\rightarrow\pi^{+}X$ search as a function of X mass.

Model-independent constraints on the branching ratio of the $K^{+}\rightarrow\pi^{+}X$ decay

Model-independent constraints on the branching ratio of the $K^{+}\rightarrow\pi^{+}X$ decay

Observed model-independent upper limits at 90 % CL of $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)$ as function of $X$ mass, for several $X$ lifetime hypotheses, assuming $X$ decays to visible SM particles.

Observed model-independent upper limits at 90 % CL of $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)$ as function of $X$ mass, for several $X$ lifetime hypotheses, assuming $X$ decays to visible SM particles.

Di-muon mass spectrum of selected $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ events from 2017–2018 data.

Di-muon mass spectrum of selected $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ events from 2017–2018 data.

Expected and observed model-independent upper limits at 90 % CL for $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)\times\mathcal{B}(X\rightarrow\mu^{+}\mu^{-})$ as a function of $m_{X}$ for $\tau_{X}=0$.

Expected and observed model-independent upper limits at 90 % CL for $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)\times\mathcal{B}(X\rightarrow\mu^{+}\mu^{-})$ as a function of $m_{X}$ for $\tau_{X}=0$.

Observed model-independent upper limits at 90 % CL for $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)\times\mathcal{B}(X\rightarrow\mu^{+}\mu^{-})$ for several $\tau_{X}$ values.

Observed model-independent upper limits at 90 % CL for $\mathcal{B}(K^{+}\rightarrow\pi^{+}X)\times\mathcal{B}(X\rightarrow\mu^{+}\mu^{-})$ for several $\tau_{X}$ values.

Branching ratio of the $K^{+}\rightarrow\pi^{+}A^{\prime}$ decay divided by the kinetic mixing coupling squared, $\varepsilon^{2}$, as a function of $m_{A^{\prime}}$ for the BC2 model with dark photon $A^{\prime}$.

Branching ratio of the $K^{+}\rightarrow\pi^{+}A^{\prime}$ decay divided by the kinetic mixing coupling squared, $\varepsilon^{2}$, as a function of $m_{A^{\prime}}$ for the BC2 model with dark photon $A^{\prime}$.

Excluded region, at 90 % CL, of the parameter space $(m_{A^{\prime}},\varepsilon)$ for a dark photon $A^{\prime}$, decaying invisibly, in the BC2 model for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded region, at 90 % CL, of the parameter space $(m_{A^{\prime}},\varepsilon)$ for a dark photon $A^{\prime}$, decaying invisibly, in the BC2 model for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded region, at 90 % CL, of the parameter space $(m_{A^{\prime}},\varepsilon)$ for a dark photon $A^{\prime}$, decaying invisibly, in the BC2 model for the NA62 $\pi^{0}\rightarrow{\rm inv}$ search.

Excluded region, at 90 % CL, of the parameter space $(m_{A^{\prime}},\varepsilon)$ for a dark photon $A^{\prime}$, decaying invisibly, in the BC2 model for the NA62 $\pi^{0}\rightarrow{\rm inv}$ search.

Branching ratio of the $K^{+}\rightarrow\pi^{+}S$ decay divided by $\text{sin}^{2}\theta$, as a function of $m_{S}$.

Branching ratio of the $K^{+}\rightarrow\pi^{+}S$ decay divided by $\text{sin}^{2}\theta$, as a function of $m_{S}$.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta)$ for a dark scalar $S$, in the BC4-inv model for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta)$ for a dark scalar $S$, in the BC4-inv model for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta)$ for a dark scalar $S$, in the BC4-inv model for the NA62 $\pi^{0}\rightarrow{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta)$ for a dark scalar $S$, in the BC4-inv model for the NA62 $\pi^{0}\rightarrow{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta$) for a dar scalar S, in the BC4 model, from the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta$) for a dar scalar S, in the BC4 model, from the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta$) for a dar scalar S, in the BC4 model, from the NA62 $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ study.

Excluded regions, at 90 % CL, of the parameter space $(m_{S},\rm{sin}^{2}\theta$) for a dar scalar S, in the BC4 model, from the NA62 $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ study.

Branching ratio of the $K^{+}\rightarrow\pi^{+}a$ decay divided by $(C_{ff}/\Lambda)^{2}$, as a function of $m_{a}$, assuming Λ = 1 TeV.

Branching ratio of the $K^{+}\rightarrow\pi^{+}a$ decay divided by $(C_{ff}/\Lambda)^{2}$, as a function of $m_{a}$, assuming Λ = 1 TeV.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\Lambda)$ for an ALP $a$, in the BC10-inv model, evaluated assuming $\Lambda = 1$ TeV, for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\Lambda)$ for an ALP $a$, in the BC10-inv model, evaluated assuming $\Lambda = 1$ TeV, for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\Lambda)$ for an ALP $a$, in the BC10-inv model, evaluated assuming $\Lambda = 1$ TeV, for the NA62 $\pi^{0}\rightarrow\rm{inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\Lambda)$ for an ALP $a$, in the BC10-inv model, evaluated assuming $\Lambda = 1$ TeV, for the NA62 $\pi^{0}\rightarrow\rm{inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $K^{+}\rightarrow\pi^{+}X_{\rm inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $\pi^{0}\rightarrow\rm{inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $\pi^{0}\rightarrow\rm{inv}$ search.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ study.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{ff}/\lambda)$ for an ALP $a$, in the BC10 model, evaluated assuming $\Lambda = 1$ TeV for the NA62 $K^{+}\rightarrow\pi^{+}\mu^{+}\mu^{-}$ study.

Branching ratio of the $K^{+}\rightarrow\pi^{+}a$ decay divided by $(C_{GG}/\Lambda)^{2}$, as a function of $m_{a}$, assuming $\Lambda = 1$ TeV.

Branching ratio of the $K^{+}\rightarrow\pi^{+}a$ decay divided by $(C_{GG}/\Lambda)^{2}$, as a function of $m_{a}$, assuming $\Lambda = 1$ TeV.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 search for $K^{+}\rightarrow\pi^{+}X_{\rm inv}$.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 search for $K^{+}\rightarrow\pi^{+}X_{\rm inv}$.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 search for $\pi^{0}\rightarrow\rm{inv}$.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 search for $\pi^{0}\rightarrow\rm{inv}$.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 $K^{+}\rightarrow\pi^{+}\gamma\gamma$ study.

Excluded regions, at 90 % CL, of the parameter space $(m_{a}, C_{GG}/\Lambda)$ for an ALP $a$, of the BC11 model, evaluated assuming $\Lambda = 1$ TeV, from the NA62 $K^{+}\rightarrow\pi^{+}\gamma\gamma$ study.