Study of Λ-n Interaction via FSI in γ+d Reaction

Abstract

In this paper we present our motivation for an experiment to measure the scattering length and the effective range of the Λ-n interaction via γ + d reaction using NKS2 spectrometer at Research Center of Electron Photon Science (ELPH), Tohoku University. The effective range approximation is adopted as an approach to estimate the contribution of the enhancement effect in the spectrometer acceptance. For this purpose, we outline and describe the already completed upgrades and further intended improvement in preparation for the new experiment. KEYWORDS:Baryon-Baryon interaction, strangeness, photo-reaction IntroductionThe NKS2 collaboration has been studying the strangeness photoproduction in γ + d reaction near the threshold at ELPH-TOHOKU. A new future focus now includes investigating the Λn interaction via a K + measurement in γ + d reaction. Most of the past efforts involving the ΛN interaction were made through hypernuclei. Results from these studies have highlighted a discrepancy between experimental data and theoretical calculations for the Λ binding energy of 4 Λ H and 4 Λ He. The source of this inconsistency is attributed to the charge symmetry breaking (CSB) in ΛN interaction. Recent reports on precise measurements for 4 Λ H at MAMI [1] and 4 Λ He at J-PARC [2] support the large CSB effect in the ΛN interaction suggested by old emulsion experiments.One of the keys to understand the ΛN CSB is a comparison of Λp with Λn interaction by direct measurement. Presently there are no reported data sets for Λn scattering primarily due to lack of a neutron target and difficulty in experimental setup. In contrast, there have been reported data for Λp interaction from scattering experiments. Consequently, the S-wave Λn scattering length is still not determined. To obtain information about the Λn interaction, we propose a different kind of experiment from hypernuclear studies, which require not only details on the interaction, but also discussions on nuclear structure. The K + measurement in γ+d reaction should yield important information on inelastic scattering and the low energy region of Λn interaction.Theoretical studies show that the cross section of K + production differs in γ + d from γ + p by the final state interaction (FSI) of Λn. The effect appears in the production threshold region and is roughly 10 times larger in forward and backward region in CM system [3][4][5][6]. NKS2 experimentThe NKS2 spectrometer is located downstream of a real photon beam line in the 2nd experimental hall at ELPH. The photon tagging system is located in a synchrotron ring and provides timing and energy information for the generated photons. The photon beam is produced by bremsstrahlung from electrons scattered by a carbon wire inserted into the path of the orbiting electrons and the recoil electrons are measured by the tagger. energy of orbiting electrons with a maximum electron energy of the stretcher booster ring of 1.2 GeV. More detailed information on the photon tagging system can be found elsewhere [7].The booster ring was re...

Light Baryon Spectroscopy

“…This experiment provides a high acceptance for photons, and is well suited for studying neutral mesons. The Neutral Kaon Spectrometer 2 (NKS2) [150] consists of a dipole magnet with a magnetic field strength of 0.42 T at the center. Two drift chambers are used to track charged particles and an inner and outer hodoscopes provide further TOF measurements.…”