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A bstract Dark matter is a well-established theoretical addition to the Standard Model supported by many observations in modern astrophysics and cosmology. In this context, the existence of weakly interacting massive particles represents an appealing solution to the observed thermal relic in the Universe. Indeed, a large experimental campaign is ongoing for the detection of such particles in the sub-GeV mass range. Adopting the benchmark scenario for light dark matter particles produced in the decay of a dark photon, with α D = 0 . 1 and m A ′ = 3 m χ , we study the potential of the SHiP experiment to detect such elusive particles through its Scattering and Neutrino detector (SND). In its 5-years run, corresponding to 2 · 10 20 protons on target from the CERN SPS, we find that SHiP will improve the current limits in the mass range for the dark matter from about 1 MeV to 300 MeV. In particular, we show that SHiP will probe the thermal target for Majorana candidates in most of this mass window and even reach the Pseudo-Dirac thermal relic.

A measurement of the transverse polarization of the Lambda and (Lambda) over bar hyperons in pNe fixed-target collisions at root s(NN) = 68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Lambda -> p pi(-) together with its charge conjugated process, the integrated values measured are P-Lambda = 0.029 +/- 0.019 (stat) +/- 0.012 (syst), P-(Lambda) over bar = 0.003 +/- 0.023 (stat) +/- 0.014 (syst). Furthermore, the results are shown as a function of the Feynman x variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.

The NA48/2 experiment at CERN reports the first observation of the $K^± → π^0π^0μ^±$ν decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV2/c4 is measured to be (0.65 ± 0.03) × 10–6. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10–6, in agreement with chiral perturbation theory predictions.

Abstract A measurement of the transverse polarization of the Λ and Λ ¯ $$ \\overline{\\varLambda} $$ hyperons in pNe fixed-target collisions at s NN $$ \\sqrt{{\\textrm{s}}_{\\textrm{NN}}} $$ = 68.4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Λ → pπ − together with its charge conjugated process, the integrated values measured are P Λ = 0.029 ± 0.019 stat ± 0.012 syst , P Λ ¯ = 0.003 ± 0.023 stat ± 0.014 syst . $$ {\\displaystyle \\begin{array}{c}{P}_{\\varLambda }=0.029\\pm 0.019\\left(\\textrm{stat}\\right)\\pm 0.012\\left(\\textrm{syst}\\right),\\\ {}{P}_{\\overline{\\varLambda}}=0.003\\pm 0.023\\left(\\textrm{stat}\\right)\\pm 0.014\\left(\\textrm{syst}\\right).\\end{array}} $$ Furthermore, the results are shown as a function of the Feynman x variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.

A bstract Heavy Neutral Leptons (HNLs) are hypothetical particles predicted by many extensions of the Standard Model. These particles can, among other things, explain the origin of neutrino masses, generate the observed matter-antimatter asymmetry in the Universe and provide a dark matter candidate. The SHiP experiment will be able to search for HNLs produced in decays of heavy mesons and travelling distances ranging between O (50 m) and tens of kilometers before decaying. We present the sensitivity of the SHiP experiment to a number of HNL’s benchmark models and provide a way to calculate the SHiP’s sensitivity to HNLs for arbitrary patterns of flavour mixings. The corresponding tools and data files are also made publicly available.

A bstract A search for the K + → π + X decay, where X is a long-lived feebly interacting particle, is performed through an interpretation of the K + → π + ν ν ¯ analysis of data collected in 2017 by the NA62 experiment at CERN. Two ranges of X masses, 0–110 MeV /c 2 and 154–260 MeV /c 2 , and lifetimes above 100 ps are considered. The limits set on the branching ratio, BR( K + → π + X ), are competitive with previously reported searches in the first mass range, and improve on current limits in the second mass range by more than an order of magnitude.

The first measurement of ϕ (1020) meson production in fixed-target p Ne collisions at √ s NN= 68 . 5 GeV is presented. The ϕ (1020) mesons are reconstructed in their K + K − decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of 21 . 7 ± 1 . 4 nb − 1 , collected by the LHCb detector at CERN. The ϕ (1020) production cross-section in the centre-of-mass rapidity range of − 1 . 8 < y * < 0 and transverse momentum range of 800 < p T < 6500 MeV/ c is found to be σ = 182 . 7 ± 2 . 7 (stat.) ± 14 . 1 (syst) μ b/nucleon. A double-differential measurement of the cross-section is also provided in four regions of rapidity and six regions of transverse momentum of the ϕ (1020) meson and compared with the predictions from Pythia and EPOS4, which are found to underestimate the experimental values.

A bstract The NA62 experiment at CERN, designed to study the ultra-rare decay K + → π + ν ν ¯ , has also collected data in beam-dump mode. In this configuration, dark photons may be produced by protons dumped on an absorber and reach a decay volume beginning 80 m downstream. A search for dark photons decaying in flight to μ + μ − pairs is reported, based on a sample of 1 . 4 × 10 17 protons on dump collected in 2021. No evidence for a dark photon signal is observed. A region of the parameter space is excluded at 90% CL, improving on previous experimental limits for dark photon masses between 215 and 550 MeV /c 2 .

Abstract We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of s NN $$ \\sqrt{s_{\\textrm{NN}}} $$ = 3 GeV with the STAR experiment at RHIC. K S 0 $$ {K}_S^0 $$ meson and Λ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of Λ and K S 0 $$ {K}_S^0 $$ are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4π yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.

A measurement of the transverse polarization of the Λ and $$ \\overline{\\varLambda} $$ Λ ¯ hyperons in p Ne fixed-target collisions at $$ \\sqrt{{\\textrm{s}}_{\\textrm{NN}}} $$ s NN = 68 . 4 GeV is presented using data collected by the LHCb detector. The polarization is studied using the decay Λ → pπ − together with its charge conjugated process, the integrated values measured are $$ {\\displaystyle \\begin{array}{c}{P}_{\\varLambda }=0.029\\pm 0.019\\left(\\textrm{stat}\\right)\\pm 0.012\\left(\\textrm{syst}\\right),\\\ {}{P}_{\\overline{\\varLambda}}=0.003\\pm 0.023\\left(\\textrm{stat}\\right)\\pm 0.014\\left(\\textrm{syst}\\right).\\end{array}} $$ P Λ = 0.029 ± 0.019 stat ± 0.012 syst , P Λ ¯ = 0.003 ± 0.023 stat ± 0.014 syst . Furthermore, the results are shown as a function of the Feynman x variable, transverse momentum, pseudorapidity and rapidity of the hyperons, and are compared with previous measurements.