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Diagnosing Hierarchical Retrieval Failure in Long-Document RAG: A LongBook Verifier Ablation Study

Panagiotis Gkilis

Zenodo (CERN European Organization for Nuclear Research), 2026

Abstract

# Zenodo Description ## Title Diagnosing Hierarchical Retrieval Failure in Long-Document RAG: A LongBook Verifier Ablation Study ## Abstract This Zenodo artifact contains Experiment C, a follow-up ablation study for the LongBook Verifier benchmark. The study diagnoses why the original hierarchical book RAG method underperformed chapter-summary chain in a 5-book, 240,767-word long-form narrative corpus with 80 gold questions. Experiment C compares five variants: current hierarchical retrieval, hierarchical retrieval without neighbor expansion, chapter-summary chain, oracle-chapter retrieval, and oracle-chapter retrieval with neighbor expansion. The current hierarchical method achieved context recall 0.3365 and precision 0.3475. Removing neighbor expansion raised recall to 0.4771 and precision to 0.4000, matching chapter-summary chain. Oracle chapter routing raised recall to 0.7844 and precision to 0.6796. The results support the diagnosis that the original hierarchical method underperformed due to both first-stage chapter-selection limits and neighbor-expansion dilution. This is a corpus/protocol-specific diagnostic study, not a universal claim against hierarchical retrieval. ## Keywords - long-document RAG- retrieval-augmented generation- hierarchical retrieval- ablation study- long-book evaluation- evidence grounding- narrative QA- LongBook Verifier- BookProof ## Related Identifier Original LongBook Verifier research package: https://doi.org/10.5281/zenodo.20513116 ##…

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