9428112
Investigating neutron polarizabilities through Compton scattering on 3He.
We examine manifestations of neutron electromagnetic polarizabilities in coherent Compton scattering from the helium-3 nucleus. We calculate gamma3He elastic scattering observables using chiral perturbation theory to next-to-leading order [O(e2Q)]. We find that the unpolarized differential cross section can be used to measure neutron electric and magnetic polarizabilities, while two double-polarization observables are sensitive to different linear combinations of the four neutron spin polarizabilities.
53550289
Analyzing the effects of neutron polarizabilities in elastic Compton scattering off 3He
Abstract Motivated by the fact that a polarized 3He nucleus is expected to behave approximately as a polarized neutron, we examine manifestations of neutron electromagnetic polarizabilities in elastic Compton scattering from the Helium-3 nucleus. We calculate both unpolarized and double-polarization observables using chiral perturbation theory to next-to-leading order ( O ( e 2 Q ) ) at energies, ω ≲ m π , where m π is the pion mass. Our results show that the unpolarized differential cross-section can be used to measure neutron electric and magnetic polarizabilities, while two double-polarization observables are sensitive to different linear combinations of the four neutron spin polarizabilities.
55918790
Compton Scattering on Light Nuclei
Compton scattering on light nuclei (A = 2, 3) has emerged as an effective avenue to search for signatures of neutron polarizabilities, both spin-independent and spin-dependent ones. In this discussion I will focus on the theoretical aspect of Compton scattering on light nuclei; giving first a brief overview and therafter concentrating on our Compton scattering calculations based on Chiral effective theory at energies of the order of pion mass. These elasticγd andγHe-3 calculations include nucleons, pions as the basic degrees of freedom. I will also discuss γd results where the� -isobar has been included explicitly. Our results on unpolarized and polarization observables suggest that a combination of experiments and further theoretical efforts will provide an extraction of the neutron polarizabilities.
119263975
Nucleon spin-polarisabilities from polarisation observables in low-energy deuteron Compton scattering
Abstract.We investigate the dependence of polarisation observables in elastic deuteron Compton scattering below the pion production threshold on the spin-independent and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The calculation uses Chiral Effective Field Theory ($ \chi$ EFT) with dynamical $ \Delta$(1232) degrees of freedom in the Small Scale Expansion (SSE) at next-to-leading order. Resummation of the NN intermediate rescattering states and including the $ \Delta$ induces sizeable effects. The analysis considers cross-sections and the analysing power of linearly polarised photons on an unpolarised target, and cross-section differences and asymmetries of linearly and circularly polarised beams on a vector-polarised deuteron. An intuitive argument helps one to identify kinematics in which one or several polarisabilities do not contribute. Some double-polarised observables are only sensitive to linear combinations of two of the spin-polarisabilities, simplifying a multipole analysis of the data. Spin-polarisabilities can be extracted at photon energies ≳ 100 MeV, after measurements at lower energies of $ \lesssim$ 70 MeV provide high-accuracy determinations of the spin-independent ones. An interactive Mathematica 7.0 notebook of our findings is available from hgrie@gwu.edu.
118407568
Chiral potentials, perturbation theory and the 1S0 channel of NN scattering
We use nucleon–nucleon phase shifts obtained from experimental data, together with the chiral expansion for the long-distance part of the NN interaction, to obtain information about the short-distance piece of the NN potential that is at work in the 1S0 channel. We find that if the scale R that defines the separation between 'long-' and 'short-' distance is chosen to be 1.8 fm then the energy dependence produced by short-distance dynamics is well approximated by a two-term polynomial for Tlab ≤ 200 MeV. We also find that a quantitative description of NN dynamics is possible, at least in this channel, if one treats the long-distance parts of the chiral NN potential in perturbation theory. However, in order to achieve this we have to choose a separation scale R that is larger than 1.0 fm.
119110936
Universal correlations in pion-less EFT with the resonating group method: Three and four nucleons
Abstract.The Effective Field Theory “without pions” at next-to-leading order is used to analyze universal bound-state and scattering properties of the 3- and 4-nucleon system. Results of a variety of phase shift equivalent nuclear potentials are presented for bound-state properties of 3H and 4He , and for the singlet S -wave 3He -neutron scattering length a0(3He-n) . The calculations are performed with the Refined Resonating Group Method and include a full treatment of the Coulomb interaction and the leading-order 3-nucleon interaction. The results compare favorably with data and values from AV18(+UIX) model calculations. A new correlation between a0(3He-n) and the 3H binding energy is found. Furthermore, we confirm at next-to-leading order the correlations, already found at leading order, between the 3H binding energy and the 3H charge radius, and the Tjon line. With the 3H binding energy as input, we get predictions of the effective field theory “without pions” at next-to-leading order for the root mean square charge radius of 3H of (1.6±0.2) fm, for the 4He binding energy of (28±2.5) MeV, and for Re{a0(3He-n)} of (7.5±0.6) fm. Including the Coulomb interaction, the splitting in binding energy between 3H and 3He is found to be (0.66±0.03) MeV. The discrepancy to data of (0.10±0.03) MeV is model independently attributed to higher-order charge independence breaking interactions. We also demonstrate that different results for the same observable stem from higher-order effects, and carefully assess that numerical uncertainties are negligible. Our results demonstrate the convergence and usefulness of the pion-less theory at next-to-leading order in the 4He channel. We conclude that no 4-nucleon interaction is needed to renormalize the theory at next-to-leading order in the 4-nucleon sector.
118388925
Isgur-Wise function within a QCD quark model with Airy's function as the wave function of heavy-light mesons
We report a somewhat improved wave function for mesons by taking the linear confinement term in standard QCD potential as a parent and the coulombic term as a perturbation while applying quantummechanical perturbation techniques in solving the Schrodinger equation with such a potential. We find that Airy's infinite series appears in the wave function of the mesons. We report our calculations on the Isgur–Wise function and its derivatives for heavy–light mesons within this framework. PACS Nos.: 12.39.–x, 12.39.Jh, 12.39.Pn. Resume : Nous presentons le calcul d'une fonction d'onde amelioree pour les mesons, en prenant comme base le terme de confinement lineaire dans le potentiel standard QCD, et comme perturbation le terme de Coulomb, tout en appliquant la technique des perturbations de lamecanique quantique pour resoudre l'equation de Schrodinger pour ce potentiel. Nous voyons apparaitre les series infinies d'Airy dans la fonction d'onde des mesons. Dans le cadre de ce travail, nous presentons nos calculs sur la fonction de Isgur–Wise et ses derivees pour des mesons de legers jusqu'a lourds. [Traduit par la Redaction]
118486754
Fractal Inspired Models of quark and gluon distributions and longitudinal structure function FL (x, Q2) at small x
In recent years, Fractal Inspired Models of quark and gluon densities at small x have been proposed. In this paper, we investigate longitudinal structure function FL (x, Q2) within this approach. We make predictions using the Quantum Chromodynamics (QCD) based approximate relation between the longitudinal structure function and the gluon density. As the Altarelli-Martinelli equation for the longitudinal structure function cannot be applied to Model I due to the presence of a singularity in the Bjorken x-space we consider Model II only. The qualitative feature of the prediction of Model II is found to be compatible with the QCD expectation.