Search results for " Quantum Mechanics."
showing 10 items of 197 documents
Evaluation of the forward Compton scattering off protons: Spin-independent amplitude
2015
We evaluate the forward Compton scattering off the proton, based on Kramers-Kronig kind of relations which express the Compton amplitudes in terms of integrals of total photoabsorption cross sections. We obtain two distinct fits to the world data on the unpolarized total photoabsorption cross section, and evaluate the various spin-independent sum rules using these fits. For the sum of proton electric and magnetic dipole polarizabilities, governed by the Baldin sum rule, we obtain the following average (between the two fits): $\alpha_{E1}+\beta_{M1}=14.0(2)\times 10^{-4}\,\mathrm{fm}^3$. An analogous sum rule involving the quadrupole polarizabilities of the proton is evaluated too. The spin-…
K -> pi pi Electroweak Penguins in the Chiral Limit
2002
We report on dispersive and finite energy sum rule analyses of the electroweak penguin matrix elements in the chiral limit. We accomplish the correct perturbative matching (scale and scheme dependence) at NLO in alpha_s, and we describe two different strategies for numerical evaluation.
Improved determination of the electroweak penguin contribution to ϵ′/ϵ in the chiral limit
2003
We perform a finite energy sum rule analysis of the flavor ud two-point V-A current correlator, Delta Pi (Q^2). The analysis, which is performed using both the ALEPH and OPAL databases for the V-A spectral function, Delta rho, allows us to extract the dimension six V-A OPE coefficient, a_6, which is related to the matrix element of the electroweak penguin operator, Q_8, by chiral symmetry. The result for a_6 leads directly to the improved (chiral limit) determination epsilon'/epsilon = (- 15.0 +- 2.7) 10^{-4}. Determination of higher dimension OPE contributions also allows us to perform an independent test using a low-scale constrained dispersive analysis, which provides a highly nontrivial…
SU(4) breaking, allowed transitions and total muon capture rates in nuclei
1973
The authors study muon capture rates in light nuclei and show that one can evaluate them in a model-independent way by correcting the Primakoff closure approximation to the first order in the neutrino energy dependence. In this framework the interplay between the existence of allowed transitions and SU(4) breaking is analyzed. In the correction to the first order in the neutrino energy dependence by a sum rule, Majorana and SU(4) breaking potentials are taken into account. The method is also applied to single multipolar transitions, in particular for the dipole transitions. General considerations are illustrated for /sup 6/Li and /sup 12/C by explicit calculations. The stability of the resu…
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
2002
We study spin-dependent sum rules for forward virtual Compton scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at order $O(p^4)$. We show how these sum rules can be evaluated from low energy expansions (in the virtual photon energy) of the forward VVCS amplitudes. We study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher terms in the low energy expansion, which can be related to the generalized forward spin polarizabilities of the nucleon. The dependence of these observables on the photon virtuality $Q^2$ can be accessed, at small and intermediate $Q^2$ values, from existing and forthcoming data at Jefferson Lab.
Meson-baryon components in the states of the baryon decuplet
2014
We apply an extension of the Weinberg compositeness condition on partial waves of L = 1 and resonant states to determine the weight of the meson-baryon component in the Delta(1232) resonance and the other members of the baryon decuplet. We obtain an appreciable weight of pi N in the Delta(1232) wave function, of the order of 60%, which looks more natural when one recalls that experiments on deep inelastic and Drell Yan give a fraction of pi N component of 34% for the nucleon. We also show that, as we go to higher energies in the members of the decuplet, the weights of the meson-baryon component decrease and they already show a dominant part for a genuine, non-meson-baryon, component in the …
The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Nucleon
2004
The Gerasimov-Drell-Hearn sum rule is one of several dispersive sum rules that connect the Compton scattering amplitudes to the inclusive photoproduction cross sections of the target under investigation. Being based on such universal principles as causality, unitarity, and gauge invariance, these sum rules provide a unique testing ground to study the internal degrees of freedom that hold the system together. The present article reviews these sum rules for the spin-dependent cross sections of the nucleon by presenting an overview of recent experiments and theoretical approaches. The generalization from real to virtual photons provides a microscope of variable resolution: At small virtuality …
Study of several double-beta-decaying nuclei using the renormalized proton-neutron quasiparticle random-phase approximation
1997
The renormalized proton-neutron quasiparticle random-phase approximation model (RQRPA) has been used to calculate double-\ensuremath{\beta}-decay matrix elements and associated transition half-lives for two-neutrino double \ensuremath{\beta} decay of parent nuclei ${}^{76}\mathrm{Ge},$ ${}^{78}\mathrm{Kr},$ ${}^{82}\mathrm{Se},$ ${}^{96}\mathrm{Zr},$ ${}^{106}\mathrm{Cd},$ and ${}^{130}\mathrm{Te}$ to the ground state and excited one- and two-phonon states of their daughter nuclei. The results are compared to ordinary proton-neutron QRPA and experiments. In addition, the violation of the Ikeda sum rule in the RQRPA is examined and discussed.
A new measurement of the spin-dependent structure function $g_{1}(x)$ of the deuteron
1995
Abstract We present a new measurement of the spin-dependent structure function g 1 d of the deuteron in deep inelastic scattering of 190 GeV polarised muons on polarised deuterons, in the kinematic range 0.003 x 2 Q 2 2 . This structure function is found to be negative at small x . The first moment Γ 1 d =∫ 0 1 g 1 d d x evaluated at Q 0 2 = 10 GeV 2 is 0.034 ± 0.009 (stat.) ± 0.006 (syst.). This value is below the Ellis-Jaffe sum rule prediction by three standard deviations. Using our earlier determination of Γ 1 p , we obtain Γ 1 p − Γ 1 n = 0.199 ± 0.038 which agrees with the Bjorken sum rule.
Nuclear effects in F_3 structure function of nucleon
2008
We study nuclear effects in the $F^A_3(x)$ structure function in the deep inelastic neutrino reactions on iron by using a relativistic framework to describe the nucleon spectral functions in the nucleus. The results for the ratio $R(x,Q^2)=\frac{F^A_3(x,Q^2)}{AF^N_3(x, Q^2)}$ and the Gross-Llewellyn Smith(GLS) integral $G(x,Q^2)=\int_x^1 dx F^A_3(x,Q^2)$ in nuclei are discussed and compared with the recent results available in literature from theoretical and phenomenological analyses of experimental data.