Disaggregated memory separates compute and memory resources into independent pools connected by RDMA (Remote Direct Memory Access) networks, which can improve memory utilization, reduce cost, and enable elastic scaling of compute and memory resources. However, existing RDMA-based distributed transactions on disaggregated memory suffer from severe long-tail latency under high-contention workloads. In this article, we propose Scythe, a novel low-latency RDMA-enabled distributed transaction system for disaggregated memory. Scythe optimizes the latency of high-contention transactions in three approaches: (1) Scythe proposes a hot-aware concurrency control policy that uses optimistic concurrency control (OCC) to improve transaction processing efficiency in low-conflict scenarios. Under high conflicts, Scythe designs a timestamp-ordered OCC (TOCC) strategy based on fair locking to reduce the number of retries and cross-node communication overhead. (2) Scythe presents an RDMA-friendly timestamp service for improved timestamp management. And, (3) Scythe designs an RDMA-optimized RPC framework to improve RDMA bandwidth utilization. The evaluation results show that, compared with state-of-the-art distributed transaction systems, Scythe achieves more than 2.5× lower latency with 1.8× higher throughput under high-contention workloads.