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Title: Magnetic structure of light nuclei from lattice QCD

Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei with $$A\le4$$, along with the cross-section for the $M1$ transition $$np\rightarrow d\gamma$$, at the flavor SU(3)-symmetric point where the pion mass is $$m_\pi\sim 806$$ MeV. These magnetic properties are extracted from nucleon and nuclear energies in six uniform magnetic fields of varying strengths. The magnetic moments are presented in a recent Letter. For the charged states, the extraction of the polarizability requires careful treatment of Landau levels, which enter non-trivially in the method that is employed. The nucleon polarizabilities are found to be of similar magnitude to their physical values, with $$\beta_p=5.22(+0.66/-0.45)(0.23) \times 10^{-4}$$ fm$^3$ and $$\beta_n=1.253(+0.056/-0.067)(0.055) \times 10^{-4}$$ fm$^3$, exhibiting a significant isovector component. The dineutron is bound at these heavy quark masses and its magnetic polarizability, $$\beta_{nn}=1.872(+0.121/-0.113)(0.082) \times 10^{-4}$$ fm$^3$ differs significantly from twice that of the neutron. A linear combination of deuteron scalar and tensor polarizabilities is determined by the energies of the $$j_z=\pm 1$$ deuteron states, and is found to be $$\beta_{d,\pm 1}=4.4(+1.6/-1.5)(0.2) \times 10^{-4}$$ fm$^3$. The magnetic polarizabilities of the three-nucleon and four-nucleon systems are found to be positive and similar in size to those of the proton, $$\beta_{^{3}\rm He}=5.4(+2.2/-2.1)(0.2) \times 10^{-4}$$ fm$^3$, $$\beta_{^{3}\rm H}=2.6(1.7)(0.1) \times 10^{-4}$$ fm$^3$, $$\beta_{^{4}\rm He}=3.4(+2.0/-1.9)(0.2) \times 10^{-4}$$ fm$^3$. Mixing between the $j_z=0$ deuteron state and the spin-singlet $np$ state induced by the background magnetic field is used to extract the short-distance two-nucleon counterterm, $${\bar L}_1$$, of the pionless effective theory for $NN$ systems (equivalent to the meson-exchange current contribution in nuclear potential models), that dictates the cross-section for the $$np\to d\gamma$$ process near threshold. Thus, combined with previous determinations of NN scattering parameters, this enables an ab initio determination of the threshold cross-section at these unphysical masses.
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [5] ;  [1]
  1. Univ. of Washington, Seattle, WA (United States)
  2. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  3. College of William and Mary, Williamsburg, VA (United States); Jefferson Lab., Newport News, VA (United States)
  4. Univ. of Barcelona, Marti Franques (Spain)
  5. The City College of New York, New York, NY (United States); The CIty Univ. of New York, New York, NY (United States); Brookhaven National Lab. (BNL), Upton, NY (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
JLAB-THY--15-2109; DOE/OR/23177--3492; arXiv:1506.05518
Journal ID: ISSN 1550-7998; PRVDAQ
Grant/Contract Number:
OCI1053575; PHY1206498; PHY1205778; AC02-05CH11231; AC05-00OR22725; FG02-04ER41302; AC05-06OR23177; FG02-00ER41132; SC0010495; FIS2011-24154
Accepted Manuscript
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 92; Journal Issue: 11; Journal ID: ISSN 1550-7998
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Orgs:
NPLQCD Collaboration
Country of Publication:
United States