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| Main Authors: | , , |
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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2602.12167 |
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| _version_ | 1866917270867935232 |
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| author | Conceição, Ruben Costa, Pedro J. Pimenta, Mário |
| author_facet | Conceição, Ruben Costa, Pedro J. Pimenta, Mário |
| contents | Gamma-hadron discrimination based on shower observables is essential for identifying gamma-ray astrophysical sources at the highest energies. In this work, we introduce $P^{α, T}_{\rm tail}$, a new discrimination variable for ultra-high-energy photon searches within the framework of a water-Cherenkov detector (WCD) array. The observable extends signal-integrated methods by incorporating the time structure of WCD traces, using cumulative signal distributions.
Using simulated proton- and gamma-induced air showers at energies around $10^{17}\,\mathrm{eV}$, we evaluate the performance of $P^{α, T}_{\rm tail}$ and compare it with established WCD-based observables such as $S_b$, risetime-based variables, and the SWGO-inspired, $P^α_{\rm tail}$. The new variable attains a background contamination of roughly $2 \times 10^{-2}$ at $50\%$ gamma efficiency, improving upon existing WCD-only methods by nearly a factor of five and approaching the performance of an idealized muon-isolating reference. These results demonstrate the effectiveness of exploiting time-resolved signal tails to enhance ultra-high-energy photon searches in sparse surface arrays. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2602_12167 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Time-Structured Tail Probabilities for Ultra-High-Energy Gamma-Hadron Discrimination in Water-Cherenkov Arrays Conceição, Ruben Costa, Pedro J. Pimenta, Mário High Energy Physics - Phenomenology High Energy Physics - Experiment Gamma-hadron discrimination based on shower observables is essential for identifying gamma-ray astrophysical sources at the highest energies. In this work, we introduce $P^{α, T}_{\rm tail}$, a new discrimination variable for ultra-high-energy photon searches within the framework of a water-Cherenkov detector (WCD) array. The observable extends signal-integrated methods by incorporating the time structure of WCD traces, using cumulative signal distributions. Using simulated proton- and gamma-induced air showers at energies around $10^{17}\,\mathrm{eV}$, we evaluate the performance of $P^{α, T}_{\rm tail}$ and compare it with established WCD-based observables such as $S_b$, risetime-based variables, and the SWGO-inspired, $P^α_{\rm tail}$. The new variable attains a background contamination of roughly $2 \times 10^{-2}$ at $50\%$ gamma efficiency, improving upon existing WCD-only methods by nearly a factor of five and approaching the performance of an idealized muon-isolating reference. These results demonstrate the effectiveness of exploiting time-resolved signal tails to enhance ultra-high-energy photon searches in sparse surface arrays. |
| title | Time-Structured Tail Probabilities for Ultra-High-Energy Gamma-Hadron Discrimination in Water-Cherenkov Arrays |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment |
| url | https://arxiv.org/abs/2602.12167 |