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Register a new userSpin polarization observables of the deuteron photodisintegration at low energies in pionless effective field theory
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Spin polarization observables of the deuteron photodisintegration at low energies are studied in a pionless effective field theory up to next-to-next-to-leading order (NNLO). The total and differential cross sections, induced neutron polarization $P_{y}$, and tensor analyzing powers $T_{20}$ and $T_{22}$ of the process are calculated at photon energies from the breakup threshold to 20~MeV. We find that the NNLO corrections in the cross sections and $P_{y}$ converge well whereas they turn out to be important contributions in $T_{20}$ and $T_{22}$. We discuss the discrepancy between theory and experiment in $P_{y}$ still persisting as well as an implication of our result to the first measurement of $T_{20}$ at low energies in the HIGS facility.
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With the use of pionless effective field theory including dibaryon fields, we study the $gamma d to vec{n} p$ reaction for the laboratory photon energy $E_gamma^{lab}$ ranging from threshold to 30 MeV. Our main goal is to calculate the neutron polarization $P_{y}$ defined as $P_{y} = (sigma_+ - sigma_-)/(sigma_+ + sigma_-)$, where $sigma_+$ and $sigma_-$ are the differential cross sections for the spin-up and spin-down neutrons, respectively, along the axis perpendicular to the reaction plane. We also calculate the total cross section as well as the differential cross section $sigma(theta)$, where $theta$ is the colatitude angle. Although the results for the total and differential cross sections are found to agree reasonably well with the data, the results for $P_{y}$ show significant discrepancy with the experiment. We comment on this discrepancy.
We study breakup of the deuteron induced by neutrinos in the neutral $ u dto u np$, $bar{ u} dto bar{ u} np$ and the charged $bar{ u} dto e^+ n n$, $ u dto e^- pp$ processes. Pionless effective field theory with dibaryon fields is used to calculate the total cross sections for neutrino energies $E_ u$ from threshold to 20 MeV. Amplitudes are expanded up to next-to-leading order, and the partial wave is truncated at $P$-waves. The Coulomb interaction between two protons is included nonperturbatively in the reaction amplitudes, and an analytic expression of the amplitudes is obtained. The contribution of the next-to-leading order to the total cross section is in the range of 5.2$-$9.9% in magnitude, and that of the $P$-wave is 2.4$-$2.8% at $E_ u = 20$ MeV. Uncertainty arising from an axial isovector low-energy constant is estimated to be on the order of 1%.
High precision measurements of induced and transferred recoil proton polarization in d(polarized gamma, polarized p})n have been performed for photon energies of 277--357 MeV and theta_cm = 20 degrees -- 120 degrees. The measurements were motivated by a longstanding discrepancy between meson-baryon model calculations and data at higher energies. At the low energies of this experiment, theory continues to fail to reproduce the data, indicating that either something is missing in the calculations and/or there is a problem with the accuracy of the nucleon-nucleon potential being used.
We calculate the magnetic form factor of the deuteron up to O(eP^4) in the chiral EFT expansion of the electromagnetic current operator. The two LECs which enter the two-body part of the isoscalar NN three-current operator are fit to experimental data, and the resulting values are of natural size. The O(eP^4) description of G_M agrees with data for momentum transfers Q^2 < 0.35 GeV^2.
We consider the two-nucleon weak interaction with a pionless effective field theory. Dibaryon fields are introduced to facilitate calculations and ensure precision in the initial and final state propagators. Weak interactions are accounted for with the parity-violating dibaryon-nucleon-nucleon vertices, which contain unknown weak dibaryon-nucleon-nucleon coupling constants. We apply the model to the calculation of a parity-violating observable in the neutron-proton capture at threshold. Result is obtained up to the linear order in the unknown dibaryon-nucleon-nucleon coupling constants. We compare our result to the one obtained from a hybrid calculation, and discuss the extension to weak interactions in the few-body systems.
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