Recent results from searches for rare kaon decays with the NA62 experiment at CERN are reported, together with the future prospects. A future experiment HIKE, to go beyond NA62, has been proposed to push kaon physics to an unprecedented frontier. The HIKE timescale and expected performance are described. Among the NA62 results, the measurement of the branching ratios of the flavour changing neutral current $K^+\rightarrow\pi^+\mu^+\mu^-$ and the radiative non leptonic $K^+\rightarrow\pi^+\gamma\gamma$ decays are reported, upper limits are given for lepton flavor and lepton number violating decays $K^+\rightarrow\mu^-\nu e^+e^+$ and $K^+\rightarrow\pi^-\pi^0 e^+e^+$. A search for new physics in the branching ratio of the decay $K^+\rightarrow\pi^+ e^+e^-e^+e^-$ is presented

The $K^{+} \to \pi^{+}\pi^{0}\pi^{0}\gamma$ decay is observed by the OKA collaboration. The branching ratio is measured to be $(4.1 \pm 0.9(stat) \pm 0.4(syst))\times 10^{-6}$. The branching ratio and $\gamma$ energy spectrum are consistent with ChPT prediction.

We report the results of a search for dark photon in-flight decays to μ + μ − pairs at NA62. Dark photons could be produced by dumping protons onto a copper-iron absorber, reach the NA62 decay volume more than 80 m downstream of the dump and decay therein. The measurement is based on data collected in 2021 which correspond to 1.4 × 1017 dumped protons.

The NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) studies the onset of deconfinement in hadron matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of π ^± , K^± , p and p̅ produced in the 20

The K+ -> pi(+) nu(nu) over bar decay, with a very precisely predicted branching ratio of less than 10(-10), is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR(K+ -> pi(+) nu(nu) over bar) = (1.06(-0.34)(+0.40)vertical bar(stat) +/- 0.09 vertical bar syst) . 10(-10) at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare K+ -> pi(+)nu(nu) over bar decay, observed with a significance of 3.4 sigma. This measurement is also used to set limits on BR(K+ -> pi(+) X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios.

The production of Ξ (1321)^- and Ξ(1321)^+ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 GeV/c . Double differential distributions in rapidity y and transverse momentum p_T are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both Ξ^- and Ξ^+ . The rapidity and transverse momentum spectra are compared to transport model predictions. The Ξ^- mean multiplicity in inelastic p+p interactions at 158 GeV/c is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.

The production of K^0_S mesons in inelastic p+p collisions at beam momentum 158 GeV /c ( √(s_NN)=17.3 GeV ) was measured with the NA61/SHINE spectrometer at the CERN Super Proton Synchrotron. Double-differential distributions were obtained in transverse momentum and rapidity. The mean multiplicity of K^0_S was determined to be 0.162 ± 0.001 (stat.) ± 0.011 (sys.) . The results on K^0_S production are compared with model predictions ( EPOS 1.99 , SMASH 2.0, PHSD and UrQMD 3.4 models) as well as with published world data.

In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at $$\sqrt{s_\text {NN}}$$ = 2.4 GeV. We show that the low- $$m_t$$ region ( $$m_t < 0.2$$   GeV/ $$c^2$$ ) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a $$A_{\text {part}}^{2/3}$$ scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields.

The production of $$K^{0}_{S}$$ K S 0 mesons in inelastic p+p collisions at beam momentum 158  $$\text{ GeV }/c$$ GeV / c ( $$\sqrt{s_{NN}}=17.3$$ s NN = 17.3   $$\text{ GeV }$$ GeV ) was measured with the NA61/SHINE spectrometer at the CERN Super Proton Synchrotron. Double-differential distributions were obtained in transverse momentum and rapidity. The mean multiplicity of $$K^{0}_{S}$$ K S 0 was determined to be $$0.162 \pm 0.001 (stat.) \pm 0.011 (sys.)$$ 0.162 ± 0.001 ( s t a t . ) ± 0.011 ( s y s . ) . The results on $$K^{0}_{S}$$ K S 0 production are compared with model predictions ( EPOS 1.99 , SMASH 2.0, PHSD and UrQMD 3.4 models) as well as with published world data.

The production of $$\Xi (1321)^{-}$$ and $$\overline{\Xi }(1321)^{+}$$ hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158  $$\hbox {Ge}\hbox {V}\!/\!c$$ . Double differential distributions in rapidity $${y}$$ and transverse momentum $$p_{T}$$ are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both $${\Xi }{^-} $$ and $$\overline{\Xi }{^+} $$ . The rapidity and transverse momentum spectra are compared to transport model predictions. The $${\Xi }{^-} $$ mean multiplicity in inelastic p+p interactions at 158  $$\hbox {Ge}\hbox {V}\!/\!c$$ is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair.

The K+→π+νν¯ decay, with a very precisely predicted branching ratio of less than 10−10, is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR( K+→π+νν¯ ) = 1.06−0.34+0.40|stat ± 0.009| syst ) · 10−10 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare K+→π+νν¯ decay, observed with a significance of 3.4σ. This measurement is also used to set limits on BR(K + → π +X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios.

Double-differential yields of $${\Xi \left( 1530\right) ^{0}} $$ and $${\overline{\Xi }\left( 1530\right) ^{0}} $$ resonances produced in p+p interactions were measured at a laboratory beam momentum of 158  $$\text{ GeV }\!/\!c$$ . This measurement is the first of its kind in p+p interactions below LHC energies. It was performed at the CERN SPS by the NA61/SHINE collaboration. Double-differential distributions in rapidity and transverse momentum were obtained from a sample of $$26\times 10^6$$ inelastic events. The spectra are extrapolated to full phase space resulting in mean multiplicity of $${\Xi \left( 1530\right) ^{0}} $$ ( $$6.73 \pm 0.25\pm 0.67)\times 10^{-4}$$ and $${\overline{\Xi }\left( 1530\right) ^{0}} $$ ( $$2.71 \pm 0.18\pm 0.18)\times 10^{-4}$$ . The rapidity and transverse momentum spectra and mean multiplicities were compared to predictions of string-hadronic and statistical model calculations.

In this erratum, we clarify the details of the comparison of

In this erratum, we clarify the details of the comparison of

In this letter we report the first multi-differential measurement of correlated pion-proton pairs from 2 billion Au+Au collisions at sNN=2.42 GeV collected with HADES. In this energy regime the population of Δ(1232) resonances plays an important role in the way energy is distributed between intrinsic excitation energy and kinetic energy of the hadrons in the fireball. The triple differential d3N/dMπ±pdpTdy distributions of correlated π±p pairs have been determined by subtracting the πp combinatorial background using an iterative method. The invariant-mass distributions in the Δ(1232) mass region show strong deviations from a Breit-Wigner function with vacuum width and mass. The yield of correlated pion-proton pairs exhibits a complex isospin, rapidity and transverse-momentum dependence. In the invariant mass range 1.1

The physics goal of the strong interaction program of the NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) is to study the phase diagram of hadronic matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents differential inclusive spectra of transverse momentum, transverse mass and rapidity of π ^- mesons produced in central ^40 Ar+ ^45 Sc collisions at beam momenta of 13 A , 19 A , 30 A , 40 A , 75 A and 150 A Ge V /c . Energy and system size dependence of parameters of these distributions – mean transverse mass, the inverse slope parameter of transverse mass spectra, width of the rapidity distribution and mean multiplicity – are presented and discussed. Furthermore, the dependence of the ratio of the mean number of produced pions to the mean number of wounded nucleons on the collision energy was derived. The results are compared to predictions of several models.