Speaker
Description
The Λη threshold region is of particular interest for understanding the excitation spectrum of Λ hyperons. Previous measurements of the K−p → Λη reaction revealed a strongly non-uniform angular distribution near threshold. Since a J/P = 1/2− resonance is expected to produce a nearly isotropic angular distribution in this region, the observed behavior cannot be readily explained by the established Λ(1670) resonance alone. This anomaly has been interpreted as a possible indication of an additional narrow Λ resonance close to the Λη threshold.
The J-PARC E72 experiment was designed to investigate this anomaly through a high-statistics measurement of the K−p → Λη reaction. The experiment employs the Hyperon Spectrometer, consisting of a superconducting dipole magnet and the Hyperon Time Projection Chamber (HypTPC), which provides large-acceptance tracking and precise momentum reconstruction of charged particles. The Λη final state is reconstructed by detecting the charged decay products from Λ → pπ− and identifying the η meson using the missing-mass technique.
The analysis presented here is based on the dataset collected during the November 2025 physics run with a K− beam momentum around 735 MeV/c, corresponding to the center-of-mass energy region near the Λη threshold. The collected dataset exceeds the statistics of previous measurements by approximately two orders of magnitude, enabling precise studies of differential cross sections and polarization observables. In this presentation, we will report the current status of the Λη event reconstruction, including Λ identification and missing-mass analysis, and discuss the expected sensitivity of E72 to a possible narrow Λ resonance near threshold.
