Orbital dependent nucleonic pairing in the lightest known isotopes of tin

TL;DR

This paper investigates the unique orbital-dependent nucleonic pairing in the lightest tin isotopes, revealing a reversal in energy level ordering due to a transition from single-particle to collective pairing modes.

Contribution

It provides the first experimental evidence of orbital-dependent pairing effects in light tin isotopes and explains the phenomenon with advanced shell model calculations.

Findings

Reversal of ground and first excited state spins in 101Sn

Transition from single-particle to collective pairing regime

Orbital-dependent pairing correlations dominate in light tin isotopes

Abstract

By studying the 109Xe-->105Te-->101Sn superallowed alpha-decay chain, we observe low-lying states in 101Sn, the one-neutron system outside doubly magic 100Sn. We find that the spins of the ground state (J = 7=2) and first excited state (J = 5=2) in 101Sn are reversed with respect to the traditional level ordering postulated for 103Sn and the heavier tin isotopes. Through simple arguments and state-of-the-art shell model calculations we explain this unexpected switch in terms of a transition from the single-particle regime to the collective mode in which orbital-dependent pairing correlations, dominate.