Chiral interactions and superfluidity in the calcium isotopic chain

We perform calculations of three-point mass differences in the odd- and even-mass <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mmultiscripts> <a:mi>Ca</a:mi> <a:mprescripts/> <a:none/> <a:mrow> <a:mn>39</a:mn> <a:mo>−</a:mo> <a:mn>49</a:mn> </a:mrow> </a:mmultiscripts> </a:math> isotopes to probe nuclear superfluidity via empirical neutron pairing gaps. We also quantify the sensitivity of those gaps to the parameters of the interaction at mean-field level. Recent studies employing accurate chiral nuclear interactions have found these gaps to be too small. We show that experimental values can be reproduced at mean-field level by substantially increasing the attraction of the singlet <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mi>S</b:mi> </b:math> -wave two-nucleon contact interaction, but doing so induces an unphysical bound state of the dineutron. The sensitivity of these predictions to the full calibration of the nuclear interaction is then studied by performing Bayesian posterior sampling in a delta-full chiral effective field theory at third chiral order. We find that pairing gaps remain largely unaffected, leaving the explanation of nuclear superfluidity as a future task for improved many-body modeling and refined interactions at higher chiral orders.