Rank-R1: Enhancing Reasoning in LLM-based Document Rerankers via Reinforcement Learning

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Main Authors: Zhuang, Shengyao, Ma, Xueguang, Koopman, Bevan, Lin, Jimmy, Zuccon, Guido
Format: Preprint
Published: 2025
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author Zhuang, Shengyao
Ma, Xueguang
Koopman, Bevan
Lin, Jimmy
Zuccon, Guido
author_facet Zhuang, Shengyao
Ma, Xueguang
Koopman, Bevan
Lin, Jimmy
Zuccon, Guido
contents In this paper, we introduce Rank-R1, a novel LLM-based reranker that performs reasoning over both the user query and candidate documents before performing the ranking task. Existing document reranking methods based on large language models (LLMs) typically rely on prompting or fine-tuning LLMs to order or label candidate documents according to their relevance to a query. For Rank-R1, we use a reinforcement learning algorithm along with only a small set of relevance labels (without any reasoning supervision) to enhance the reasoning ability of LLM-based rerankers. Our hypothesis is that adding reasoning capabilities to the rerankers can improve their relevance assessement and ranking capabilities. Our experiments on the TREC DL and BRIGHT datasets show that Rank-R1 is highly effective, especially for complex queries. In particular, we find that Rank-R1 achieves effectiveness on in-domain datasets at par with that of supervised fine-tuning methods, but utilizing only 18\% of the training data used by the fine-tuning methods. We also find that the model largely outperforms zero-shot and supervised fine-tuning when applied to out-of-domain datasets featuring complex queries, especially when a 14B-size model is used. Finally, we qualitatively observe that Rank-R1's reasoning process improves the explainability of the ranking results, opening new opportunities for search engine results presentation and fruition.
format Preprint
id arxiv_https___arxiv_org_abs_2503_06034
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Rank-R1: Enhancing Reasoning in LLM-based Document Rerankers via Reinforcement Learning
Zhuang, Shengyao
Ma, Xueguang
Koopman, Bevan
Lin, Jimmy
Zuccon, Guido
Information Retrieval
Computation and Language
In this paper, we introduce Rank-R1, a novel LLM-based reranker that performs reasoning over both the user query and candidate documents before performing the ranking task. Existing document reranking methods based on large language models (LLMs) typically rely on prompting or fine-tuning LLMs to order or label candidate documents according to their relevance to a query. For Rank-R1, we use a reinforcement learning algorithm along with only a small set of relevance labels (without any reasoning supervision) to enhance the reasoning ability of LLM-based rerankers. Our hypothesis is that adding reasoning capabilities to the rerankers can improve their relevance assessement and ranking capabilities. Our experiments on the TREC DL and BRIGHT datasets show that Rank-R1 is highly effective, especially for complex queries. In particular, we find that Rank-R1 achieves effectiveness on in-domain datasets at par with that of supervised fine-tuning methods, but utilizing only 18\% of the training data used by the fine-tuning methods. We also find that the model largely outperforms zero-shot and supervised fine-tuning when applied to out-of-domain datasets featuring complex queries, especially when a 14B-size model is used. Finally, we qualitatively observe that Rank-R1's reasoning process improves the explainability of the ranking results, opening new opportunities for search engine results presentation and fruition.
title Rank-R1: Enhancing Reasoning in LLM-based Document Rerankers via Reinforcement Learning
topic Information Retrieval
Computation and Language
url https://arxiv.org/abs/2503.06034