Quantum Monte Carlo calculations of electromagnetic transitions in $^8$Be with meson-exchange currents derived from chiral effective field theory

Journal Article · Fri Aug 01 00:00:00 EDT 2014 · Phys.Rev..C

DOI:https://doi.org/10.1103/PhysRevC.90.024321· OSTI ID:1150625

Pastore, S. ^[1]; Wiringa, Robert B. ^[2]; Pieper, Steven C. ^[2]; Schiavilla, Rocco ^[3]

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1. University of South Carolina
2. ANL
3. Old Dominion U., JLAB

We report quantum Monte Carlo calculations of electromagnetic transitions in $^8$Be. The realistic Argonne $$v_{18}$$ two-nucleon and Illinois-7 three-nucleon potentials are used to generate the ground state and nine excited states, with energies that are in excellent agreement with experiment. A dozen $M1$ and eight $E2$ transition matrix elements between these states are then evaluated. The $E2$ matrix elements are computed only in impulse approximation, with those transitions from broad resonant states requiring special treatment. The $M1$ matrix elements include two-body meson-exchange currents derived from chiral effective field theory, which typically contribute 20--30\% of the total expectation value. Many of the transitions are between isospin-mixed states; the calculations are performed for isospin-pure states and then combined with the empirical mixing coefficients to compare to experiment. In general, we find that transitions between states that have the same dominant spatial symmetry are in decent agreement with experiment, but those transitions between different spatial symmetries are often significantly underpredicted.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177; DE-FG02-09ER41621; AC02- 06CH11357
• OSTI ID: 1150625
• Report Number(s): JLAB-THY-14-1883; DOE/OR/23177-3068; arXiv:1406.2343; NSF Grant PHY-1068305; NUCLEI SciDAC-3 grant
• Journal Information: Phys.Rev..C, Vol. 90, Issue 02; ISSN 0556--2813
• Country of Publication: United States
• Language: English