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Purpose To characterize the rod and cone photoreceptor mosaic at retinal locations spanning the central 60° in vivo using adaptive optics scanning laser ophthalmoscopy (AO-SLO) in healthy human eyes. Methods AO-SLO images (0.7 × 0.9°) were acquired at 680 nm from 14 locations from 30° nasal retina (NR) to 30° temporal retina (TR) in 5 subjects. Registered averaged images were used to measure rod and cone density and spacing within 60 × 60  μ m regions of interest. Voronoi analysis was performed to examine packing geometry at all locations. Results Average peak cone density near the fovea was 164 000±24 000 cones/mm 2 and decreased to 6700±1500 and 5400±700 cones/mm 2 at 30° NR and 30° TR, respectively. Cone-to-cone spacing increased from 2.7±0.2  μ m at the fovea to 14.6±1.4  μ m at 30° NR and 16.3±0.7  μ m at 30° TR. Rod density peaked at 25° NR (124 000±20 000 rods/mm 2 ) and 20° TR (120 000±12 000 rods/mm 2 ) and decreased at higher eccentricities. Center-to-center rod spacing was lowest nasally at 25° (2.1±0.1  μ m). Temporally, rod spacing was lowest at 20° (2.2±0.1  μ m) before increasing to 2.3±0.1  μ m at 30° TR. Conclusions Both rod and cone densities showed good agreement with histology and prior AO-SLO studies. The results demonstrate the ability to image at higher retinal eccentricities than reported previously. This has clinical importance in diseases that initially affect the peripheral retina such as retinitis pigmentosa.

A bstract The NA48/2 experiment at CERN reports the first observation of the K ± → π 0 π 0 μ ± 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 GeV 2 / c 4 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.

AimsIt is well established that glaucoma results in a thinning of the inner retina. To investigate whether the outer retina is also involved, ultrahigh-resolution retinal imaging techniques were utilised.MethodsEyes from 10 glaucoma patients (25–78 years old), were imaged using three research-grade instruments: (1) ultrahigh-resolution Fourier-domain optical coherence tomography (UHR-FD-OCT), (2) adaptive optics (AO) UHR-FD-OCT and (3) AO-flood illuminated fundus camera (AO-FC). UHR-FD-OCT and AO-UHR-FD-OCT B-scans were examined for any abnormalities in the retinal layers. On some patients, cone density measurements were made from the AO-FC en face images. Correlations between retinal structure and visual sensitivity were measured by Humphrey visual-field (VF) testing made at the corresponding retinal locations.ResultsAll three in vivo imaging modalities revealed evidence of outer retinal changes along with the expected thinning of the inner retina in glaucomatous eyes with VF loss. AO-UHR-FD-OCT images identified the exact location of structural changes within the cone photoreceptor layer with the AO-FC en face images showing dark areas in the cone mosaic at the same retinal locations with reduced visual sensitivity.ConclusionLosses in cone density along with expected inner retinal changes were demonstrated in well-characterised glaucoma patients with VF loss.

We report results from a new measurement of the K e4 decay K ± →π + π - e ± ν by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670 000 K e4 decays in both charged modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference (δ=δ s -δ p ) have been measured in ten independent bins of the ππ mass spectrum to investigate their variation. A sizeable acceptance at large ππ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the ππ scattering lengths a 0 0 and a 0 2 . Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane (a 0 0 ,a 0 2 ): a 0 0 =0.233±0.016stat±0.007syst,a 0 2 =-0.0471±0.011stat±0.004syst. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory.

The KLEVER experiment is proposed to run in the CERN ECN3 underground cavern from 2026 onward. The goal of the experiment is to measure BR(KL→π0vv¯), which could yield information about potential new physics, by itself and in combination with the measurement of BR(K+→π+vv¯) of NA62. A full description will be given of the considerations in designing the new K12 beamline for KLEVER, as obtained from a purpose made simulation with FLUKA. The high intensities required by KLEVER, 2 × 1013 protons on target every 16.8 s, with 5 × 1019 protons accumulated over 5 years, place stringent demands on adequate muon sweeping to minimize backgrounds in the detector. The target and primary dump need to be able to survive these demanding conditions, while respecting strict radiation protection criteria. A series of design choices will be shown to lead to a neutral beamline sufficiently capable of suppressing relevant backgrounds, such as photons generated by π0 decays in the target, and Λ → nπ0 decays, which mimic the signal decay.

The NA62 experiment at CERN collected a large sample of charged kaon decays with a highly efficient trigger for decays into electrons in 2007. The kaon beam represents a source of tagged neutral pion decays in vacuum. A measurement of the electromagnetic transition form factor slope of the neutral pion in the time-like region from ∼1 million fully reconstructed π 0 Dalitz decay is presented. The limits on dark photon production in π 0 decays from the earlier kaon experiment at CERN, NA48/2, are also reported.

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.

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 .

A bstract A measurement of the K + → π + ν ν ¯ decay by the NA62 experiment at the CERN SPS is presented, using data collected in 2021 and 2022. This dataset was recorded, after modifications to the beamline and detectors, at a higher instantaneous beam intensity with respect to the 2016–2018 data taking. Combining NA62 data collected in 2016–2022, a measurement of B K + → π + ν ν ¯ = 13.0 − 3.0 + 3.3 × 10 − 11 is reported. With 51 signal candidates observed and an expected background of 18 − 2 + 3 events, B K + → π + ν ν ¯ becomes the smallest branching ratio measured with a signal significance above 5 σ .

A bstract A sample of 2 . 8 × 10 4 K + → π + μ + μ − candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9 . 15 ± 0 . 08) × 10 − 8 , a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at O ( p 6 ).