Form Factor Ratio Research Articles

Proton elastic form factor ratios toQ2=3.5GeV2by polarization transfer

The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic epepreaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV2. In the single-photon exchange approximation, GEp/GMp is directly proportional to Pt/P. The simultaneous measurement of Pt and P in a polarimeter reduces systematic uncertainties. The results for GEp/GMp show a systematic decrease with increasing Q2, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and their systematic uncertainties have become significantly smaller than those reported previously. (Less)

Mitochondrial network complexity and pathological decrease in complex I activity are tightly correlated in isolated human complex I deficiency

Complex I (NADH:ubiquinone oxidoreductase) is the largest multisubunit assembly of the oxidative phosphorylation system, and its malfunction is associated with a wide variety of clinical syndromes ranging from highly progressive, often early lethal, encephalopathies to neurodegenerative disorders in adult life. The changes in mitochondrial structure and function that are at the basis of the clinical symptoms are poorly understood. Video-rate confocal microscopy of cells pulse-loaded with mitochondria-specific rhodamine 123 followed by automated analysis of form factor (combined measure of length and degree of branching), aspect ratio (measure of length), and number of revealed marked differences between primary cultures of skin fibroblasts from 13 patients with an isolated complex I deficiency. These differences were independent of the affected subunit, but plotting of the activity of complex I, normalized to that of complex IV, against the ratio of either form factor or aspect ratio to number revealed a linear relationship. Relatively small reductions in activity appeared to be associated with an increase in form factor and never with a decrease in number, whereas relatively large reductions occurred in association with a decrease in form factor and/or an increase in number. These results demonstrate that complex I activity and mitochondrial structure are tightly coupled in human isolated complex I deficiency. To further prove the relationship between aberrations in mitochondrial morphology and pathological condition, fibroblasts from two patients with a different mutation but a highly fragmented mitochondrial phenotype were fused. Full restoration of the mitochondrial network demonstrated that this change in mitochondrial morphology was indeed associated with human complex I deficiency.

Ratio of the proton electromagnetic form factors from meson dressing

The Dressed K-matrix Model, developed previously for low- and intermediate-energy Compton scattering, is generalized to calculate the photon-nucleon vertex with a virtual photon and an off-shell nucleon. Using this model, the ratio of the proton electromagnetic form factors is computed. The calculated ratio is in excellent agreement with the ratio measured in polarized electron-proton scattering.

Two-photon exchange in elastic electron-proton scattering

Two-photon exchange contributions to unpolarized and polarized elastic electron–proton scattering cross sections are evaluated taking into account nucleon finite size effects using realistic form factors. Contributions from nucleon elastic intermediate states are found to have a strong angular dependence, which partially resolves the discrepancy between Rosenbluth and polarization transfer measurements of the proton electric to magnetic form factor ratio. Two-photon contributions to the longitudinal and transverse polarizations are generally found to be small. A comparison is made of two-photon exchange effects with existing data on the ratio of e+ p to e– p cross sections, which is predicted to be enhanced at backward angles. PACS: 25.30.Bf Elastic electron scattering – 13.40.Gp Electromagnetic form factors

Constraining the Unitarity Triangle with B→Vγ

We discuss the exclusive radiative decays $B\to K^{*}\gamma$, $B \to\rho\gamma$, and $B\to\omega\gamma$ in QCD factorization within the Standard Model. The analysis is based on the heavy-quark limit of QCD. Our results for these decays are complete to next-to-leading order in QCD and to leading order in the heavy-quark limit. Special emphasis is placed on constraining the CKM-unitarity triangle from these observables. We propose a theoretically clean method to determine CKM parameters from the ratio of the $B\to\rho l\nu$ decay spectrum to the branching fraction of $B\to\rho\gamma$. The method is based on the cancellation of soft hadronic form factors in the large energy limit, which occurs in a suitable region of phase space. The ratio of the $B\to\rho\gamma$ and $B\to K^{*}\gamma$ branching fractions determines the side $R_{t}$ of the standard unitarity triangle with reduced hadronic uncertainties. The recent Babar bound on $B(B^0\to\rho^0\gamma)$ implies $R_t < 0.81 (\xi/1.3)$, with the limiting uncertainty coming only from the SU(3) breaking form factor ratio $\xi$. This constraint is already getting competitive with the constraint from $B_{s}$-$\bar B_{s}$ mixing. Phenomenological implications from isospin-breaking effects are briefly discussed.

Backscattering from Isosceles Triangular Metallic Plates

The Geometrical Theory of Diffraction is used to describe backscattering from a triangular plate illuminated with vertical polarization. RCS predictions based upon single diffraction are compared with numerical results from the Method of Moments for conducting plates between 2 and 14 wavelengths in dimension. Results are presented for plates having form factor (ratio of height-to-width) of two or greater. The asymptotic theory provides an excellent match at all aspects except approaching grazing incidence on the rear, where multiple diffraction plays an important role.

Bistatic Scattering from Rectangular Plates

The Geometrical Theory of Diffraction is used to describe bistatic scattering from a rectangular flat plate as a function of incidence and observation angle for vertical polarization. RCS predictions based upon single diffraction are compared with numerical results from the Method of Moments for plates between 2 and 20 wavelengths on a side. Accuracy depends upon the form factor (ratio of height-to-width). When the form factor is greater than unity, the asymptotic theory provides a good match for the smallest plate, and accuracy improves for larger plates. When the form factor is less than unity, accuracy decreases due to grazing phenomena on wide plates viewed near edge-on incidence.

Measurement of the branching ratio of the decay [formula omitted] relative to [formula omitted

We present a new measurement of the branching ratio of the Cabibbo suppressed decay D0→π−μ+ν relative to the Cabibbo favored decay D0→K−μ+ν and an improved measurement of the ratio |f+π(0)/f+K(0)|. Our results are 0.074±0.008±0.007 for the branching ratio and 0.85±0.04±0.04±0.01 for the form factor ratio, respectively.

Analysis of the semileptonic decay [formula omitted

Using data collected by the fixed target Fermilab experiment FOCUS, we present several first measurements for the semileptonic decay D0→K¯0π−μ+ν. Using a model that includes a K¯0π−s-wave component, we measure the form factor ratios to be rv=1.71±0.68±0.34 and r2=0.91±0.37±0.10 and the s-wave amplitude to be A=0.35±0.22±0.05 GeV−1. Finally, we measure the vector semileptonic branching ratio Γ(D0→K*(892)−μ+ν)Γ(D0→K¯0π−π+)=0.337±0.034±0.013.

ElectromagneticN→ΔTransition and Neutron Form Factors

The C2/M1 ratio of the electromagnetic N --> Delta(1232) transition, which is important for determining the geometric shape of the nucleon, is shown to be related to the neutron elastic form factor ratio GnC/GnM. The proposed relation holds with good accuracy for the entire range of momentum transfers where data are available.

Measurement of coherent x-ray scatter form factors for amorphous materials using diffractometers

The feasibility of measuring the coherent x-ray scatter form factors of amorphous materials using powder diffractometers has been assessed. A five-step procedure was developed: (i) Low-angle background, consisting of a portion of the incident x-ray beam that passes directly to the detector, is measured using a specially designed replacement for the sample holder which absorbs most of the photons that otherwise would scatter off the sample holder cavity. (ii) Angle-dependent effects including monochromator efficiency and projected beam area are characterized by extracting the incoherent signal from the diffraction pattern of powdered graphite. The incoherent signal divided by the calculated incoherent cross section gives a correction factor as a function of scattering angle θ. (iii) Diffraction patterns are measured for the samples for θ = 2°–150°. (iv) The scattering data are corrected for background and then for angle-dependent effects. (v) The data are normalized to calculated free atom form factors at high θ, and the coherent form factor extracted. The method was implemented on two diffractometers at different energies (Co Kα and Cu Kα), and the results compared for water and plastics. Over the range 0.117 < x < 5.39 nm−1, where x = λ−1 sin(θ/2), the average form factor ratio for water was 0.93. Systematic errors are difficult to eliminate. While this x-ray powder diffractometer technique suffices for a survey measurement of the form factor of a material, its accuracy is probably insufficient for detailed studies.

Precise Measurement of the Pion Axial Form Factor in theπ+→e+νγDecay

We have studied radiative pion decays pi(+)-->e(+)nugamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 41 601 events we have evaluated absolute pi-->enugamma branching ratios in the three regions. Minimum chi(2) fits to the integral and differential (E(e(+)),E(gamma)) distributions result in the axial-to-vector weak form factor ratio of gamma identical with F(A)/F(V)=0.443(15), or F(A)=0.0115(4) with F(V)=0.0259. However, deviations from standard model predictions in the high-E(gamma)-low-E(e(+)) kinematic region indicate the need for further theoretical and experimental work.

Obtaining CKM Phase Information from B Penguin Decays

We discuss a method for extracting CP phases from pairs of B decays which are related by flavor SU(3). One decay (B0 -> M1 M2) receives a significant bbar -> dbar penguin contribution. The second (B' -> M1' M2') has a significant bbar -> sbar penguin contribution, but is dominated by a single amplitude. CP phase information is obtained using the fact that the B' -> M1' M2' amplitude is related by SU(3) to a piece of the B0 -> M1 M2 amplitude. The leading-order SU(3)-breaking effect (~25%) responsible for the main theoretical error can be removed. For some decay pairs, it can be written in terms of known decay constants. In other cases, it involves a ratio of form factors. However, this form-factor ratio can either be measured experimentally, or eliminated by considering a double ratio of amplitudes. In all cases, one is left only with a second-order effect, ~5%. We find twelve pairs of B decays to which this method can be applied. Depending on the decay pair, we estimate the total theoretical error in relating the B' -> M1' M2' and B0 -> M1 M2 amplitudes to be between 5% and 15%. The most promising decay pairs are Bd -> pi+ pi- and Bu+ -> K0 pi+, and Bd -> D+ D- and Bd -> Ds+ D- or Bu+ -> Ds+ D0bar.

New measurements of the Ds+→φμ+ν form factor ratios

Using a large sample of Ds+→φμ+ν decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of two semileptonic form factor ratios: rv and r2. We find rv=1.549±0.250±0.148 and r2=0.713±0.202±0.284. These values are consistent with rv and r2 form factors measured for the process D+→K̄∗0ℓ+νℓ.

Magnetization screening from gluonic currents and scaling-law violation in the ratio of magnetic form factors for neutron and proton

The ratio ${\mu_p}G_E^p/G_M^p$ exhibits a decrease for four-momentum transfer Q^2 increasing beyond 1 GeV^2 indicating different spatial distributions for charge and for magnetization inside the proton. One-gluon exchange currents can explain this behaviour. The SU(6) breaking induced by gluonic currents predicts furthermore that the ratio of neutron to proton magnetic form factors ${\mu_p}G_M^n/{\mu_n}G_M^p$ falls with increasing Q^2. We find that the experimental data are consistent with our expectations of an almost linear decrease of the ratio ${\mu_p}G_M^n/{\mu_n}G_M^p$ with increasing Q^2, supporting the statement that the spatial distributions of magnetization are different for protons and for neutrons.

Electromagnetic form factors in the hypercentral CQM

We report on the recent results of the hypercentral Constituent Quark Model (hCQM). The model contains a spin independent three-quark interaction which is inspired by Lattice QCD calculations and reproduces the average energy values of the SU(6) multiplets. The splittings are obtained with a SU(6)-breaking interaction, which can include also an isospin dependent term. Concerning Constituent Quark models, we have shown for the first time that the decreasing of the ratio of the elastic form factors of the proton is due to relativistic effects using relativistic corrections to the e.m. current and boosts. Now the elastic nucleon form factors have been recalculated, using a relativistic version of the hCQM and a relativistic quark current showing a very detailed reproduction of all the four form factor existing data over the complete range of 0-4 $GeV^2$. Futhermore, the model has been used for predictions concerning the electromagnetic transverse and longitudinal transition form factors giving a good description of the medium $Q^2$ behaviour. We show that the discrepancies in the reproduction of the helicity amplitudes at low $Q^2$ are due to pion loops. We have calculated the helicity amplitudes for all the 3 and 4 star resonances opening the possibility of application to the evaluation of cross sections.

An overview of the hypercentral constituent quark model

We report on the recent results of the hypercentral Constituent Quark Model (hCQM). The model contains a spin independent three-quark interaction which is inspired by Lattice QCD calculations and reproduces the average energy values of the SU(6) multiplets. The splittings are obtained with a SU(6)-breaking interaction, which can include also an isospin dependent term. The model has been used for predictions concerning the electromagnetic transition form factors giving a good description of the medium Q 2-behaviour. In particular the calculated helicity amplitude A 1 2 for the S 11(1535) resonance agrees very well with the recent CLAS data. Furthermore, we have shown for the first time that the decreasing of the ratio of the elastic form factors of the proton is due to relativistic effects. Finally, the elastic nucleon form factors have been calculated using a relativistic version of the hCQM and a relativistic quark current.

New measurements of the [formula omitted] form factor ratios

Using a large sample of D+→K−π+μ+ν decays collected by the FOCUS photoproduction experiment at Fermilab, we present new measurements of two semileptonic form factor ratios: rv and r2. We find rv=1.504±0.057±0.039 and r2=0.875±0.049±0.064. Our form factor results include the effects of the s-wave interference discussed in Phys. Lett. B 535 (2002) 43.

Semi-leptonic decays of heavy mesons and the Isgur–Wise function in quenched lattice QCD

The form factors for the semi-leptonic B→ D and B→D ∗ decays are evaluated in quenched lattice QCD at two different values of the coupling, β=6.0 and 6.2. The action and the operators are fully O(a) non-perturbatively improved. The slope of the Isgur–Wise function is evaluated, and found to be ρ 2=0.83 +15+24 −11−22 (quoted errors are statistical and systematic, respectively). Ratios of form factors are evaluated and compared to experimental determinations.

Q2independence ofQF2/F1,Poincaré invariance, and the nonconservation of helicity

A relativistic constituent quark model is found to reproduce the recent data regarding the ratio of proton form factors, $F_2(Q^2)/F_1(Q^2)$. We show that imposing Poincare invariance leads to substantial violation of the helicity conservation rule, as well as an analytic result that the ratio $F_2(Q^2)/F_1(Q^2)\sim 1/Q$ for intermediate values of $Q^2$.