Status of the ∆ S = 1

On behalf of JLab the E99-003 collaboration, I would like to resubmit the proposal of E99-003 as is. The physics goals, experimental techniques and requirements have not changed. Since the approval of the JLab experiment E95-002 (later E99-003) a great deal of efforts, both theoretically and experimentally, have been invested in the study of the Strangeness-changing (∆S=1) hadronic weak interaction. On the theoretical side, after years of concerted efforts by a number of groups, the situation has clarified sufficiently that only experimental data with an accuracy of 10-20% can significantly advance the field. However, even though great experimental efforts have been expended in the same time period, the experimental accuracy of some observables is still nowhere this number. Thus, the JLab experiment E99-003 has become an even more important experiment that needs to be executed timely due to its unprecedented precision and unique experimental technique that minimizes ambiguities and systematic errors. Although the proposal of E99-003 (previous E95-002) has sufficient detail of descriptions for the physics goal; experimental technique and beam requirement, I would like to provide a report (see attachment to this letter) that outlines the most recent development in this field. I hope this report can provide PAC members additional information on the development of this field and better view of the importance of this proposed JLab experiment. Please allow me to point out several key features about the status of the field and about our proposed experiment. The ∆S =1 hadronic weak decay, i.e. the ΛN→NN (nonmesonic) and Λ→Nπ (mesonic) decays in the nuclear medium after formation of Λ-hypernuclei, is a unique tool to study hadronic weak interactions. The measurements of the total lifetime τ Λ , the neutron-induced (Λn→nn) nonmesonic decay rate, Γ n , the proton-induced (Λp→pn) nonmesonic decay rate, Γ p , and their A-dependencies into the heavy-mass region provide crucial information on such weak interaction mechanisms. As pointed out in theoretical studies, these observables can provide a direct measure of the level of violation of the empirical ∆I=½ rule observed from free nonleptonic hyperon and kaon decays. The origin of this rule is still not completely understood. Furthermore, precision measurements of the above mentioned observables provide crucial data to test the validity of chiral effective field theories in the SU(3) realm, which has been put into question due to their failure to explain the nonleptonic weak hyperon decay rates. Over the past several …