Description 
=Date and Place=
Mar.28th(Tue.), 13:30~ at RIBF Hall(room 201)
= Lecturer=
Prof.Atsushi Tamii
(Research Center for Nuclear Physics, Osaka University)
=Title=
np spincorrelation in the ground state studied by the sumrules of the spinM1 transition matrix elements and implications to the IS np pairing correlation
=Abstract=
How are nucleons correlated in the ground state of atomic nuclei? It is one of fundamental questions to understand the strongly correlated nuclear system. Amongst many correlations, the correlation between a neutron and a proton, more specifically the isoscalar (IS) np pairing correlation, is thought to play a minor role in meanfield models while the isovector (IV) paring correlations are well descried by the quasiparticle description. However, the IS np paring is obviously stronger in the ground state of light nuclei, e.g. a deuteron or 6Li. How does the IS paring correlation manifest itself in heavier nuclei? We have obtained an evidence of np spincorrelation, that naturally emerges from the np pairing correlation, in sdshell nuclei. The np spincorrelation function (npSCF) is proportional to the difference of the non energyweighted sumrule values of the IS and IV spinM1 squared transition matrix elements. The npSCP takes a value of +1/4(3/4) for the full spinalignment (antialignment) that emerges from the IS (IV) np pairing in swave. The observed npSCFs showed a positive value of +0.1 for all the measured eveneven selfconjugated nuclei in the sdshell [1]. The result shows stronger IS nppairing than the IV nppairing.
How can one understand the result with theoretical models? The shellmodel with the USD interaction does not reproduce the positive npSCFs. Similar result was obtained for a largescale shell model calculation [2]. However the noncore shellmodel predictions hint the positive npSCFs [1] that implies the importance of the corepolarization effect. The positive npSCFs are also predicted for 4He by ab initio calculations employing modern NN interactions [1,3]. Recent phenomenological study using shellmodel wave functions could reproduce the positive npSCFs by introducing an enhanced IS spintriplet pairing interaction and the Deltahole coupling effect [4].
In this seminar, I will discuss in detail the experimental finding and its interpretations as well as possible future extensions to other excited states.
[1] H. Matsubara et al., Phys. Rev. Lett. [2] N. Shimizu, Y. Utsuno, and N. Tsunoda, private communication [3] W. Horiuchi et al., Phys. Rev. C 87, 034001 (2013).[4] H. Sagawa et al., Phys. Rev. C 94, 041303(R).
