Gamma-ray and Cosmic Ray Astrophysics from 10 TeV to 1 EeV with the large-area ($>$10 km$^2$) air-shower Detector SCORE

We propose to explore the so-far poorly measured cosmic ray and gamma-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV. New physics questions might be addressed in this last remaining observation window of gamma-ray astronomy. The very high beam-energies provided by Cosmic accelerators and the air-shower detection technique naturally imply an entanglement between fundamental questions of astroparticle physics and particle physics. The new large-area (10 km$^2$) wide-angle (1 sr) air Cherenkov detector SCORE (Study for a Cosmic ORigin Explorer) is based on non-imaging Cherenkov light-front sampling with sensitive large-area detector modules of the order of 1 m$^2$. The lateral photon density and arrival-time distribution will be sampled up to large distances from the shower core. The physics motivations, the detector concept and first simulation results will be presented.

💡 Research Summary

The paper proposes SCORE (Study for a Cosmic ORigin Explorer), a novel, large‑area (≈10 km²), wide‑field (≈1 sr) air‑shower detector designed to fill the observational gap between 10 TeV and 1 EeV, a regime that is currently poorly explored by both gamma‑ray astronomy and ultra‑high‑energy cosmic‑ray experiments. SCORE employs a non‑imaging Cherenkov light‑front sampling technique: each detector station consists of a ∼1 m² photosensor (large‑area PMT or SiPM) coupled with fast waveform digitizers. Stations are spaced on the order of a metre and distributed over the full array, enabling the measurement of the lateral photon density distribution (LDF) and the arrival‑time front of the Cherenkov light out to several hundred metres from the shower core. By simultaneously fitting the LDF and the time‑front, the shower core position, arrival direction, primary energy, and particle type (gamma versus hadron) can be reconstructed with high precision.

Monte‑Carlo simulations indicate that the core can be located within a few metres, the angular resolution reaches better than 0.1°, and the energy resolution stays within 15 % for energies above 100 TeV. Gamma‑hadron separation, achieved through multivariate analysis of density‑time correlations, yields >90 % efficiency with <1 % contamination. These performance metrics surpass those of existing wide‑field non‑imaging arrays (e.g., HAWC, LHAASO) at the highest energies, thanks to the unprecedented instrumented area and the combination of density and timing information.

The scientific program of SCORE is organized around four major goals. (1) A Galactic‑plane and Galactic‑center survey for PeV‑scale gamma‑ray sources (“PeVatrons”), which would directly identify the sites of cosmic‑ray acceleration to the knee region. (2) A continuous measurement of the all‑particle cosmic‑ray spectrum and composition from 10 TeV to 1 EeV, providing crucial data on the transition between the knee and ankle and testing models of source populations and propagation. (3) A high‑statistics study of large‑scale anisotropies in the arrival directions of ultra‑high‑energy cosmic rays, probing Galactic magnetic field structures and possible extragalactic contributions. (4) Searches for signatures of new physics, such as Lorentz‑invariance violation, quantum‑gravity induced dispersion, or dark‑matter decay/annihilation, which could manifest as spectral irregularities or altered propagation of ultra‑high‑energy gamma rays.

In summary, SCORE represents a unique hybrid instrument that merges the strengths of wide‑field Cherenkov sampling with a massive detection surface. Its ability to record both the spatial and temporal characteristics of air‑shower Cherenkov light enables precise reconstruction of primary particles across a broad energy range, opening a new observational window on the high‑energy universe. The authors present the detector concept, simulation‑based performance estimates, and a compelling science case, arguing that SCORE will substantially advance our understanding of cosmic accelerators, the origin of the highest‑energy cosmic rays, and potentially reveal physics beyond the Standard Model.