Form Factor Model Research Articles

γ*N→N*(1520) form factors in the timelike regime

The covariant spectator quark model, tested before in a variety of electromagnetic baryon excitations, is applied here to the $\gamma^\ast N \to N^\ast(1520)$ reaction in the timelike regime. The transition form factors are first parametrized in the spacelike region in terms of a valence quark core model together with a parametrization of the meson cloud contribution. The form factor behavior in the timelike region is then predicted, as well as the $N^\ast(1520) \to \gamma N$ decay width and the $N^\ast (1520)$ Dalitz decay, $N^\ast (1520) \to e^+ e^- N$. Our results may help in the interpretation of dielectron production from elementary $pp$ collisions and from the new generation of HADES results using a pion beam. In the $q^2=0$--1 GeV$^2$ range we conclude that the {\it QED approximation} (a $q^2$ independent form factor model) underestimates the electromagnetic coupling of the $N^\ast(1520)$ from 1 up to 2 orders of magnitude. We conclude also that the $N^\ast (1520)$ and the $\Delta(1232)$ Dalitz decay widths are comparable.

One-step formulation of nonionic surfactant bicelles (NSBs) by a double-tailed polyglycerol-type nonionic surfactant.

Bicelles are generally formed by phospholipid-based systems and are useful for various applications, such as nanocarriers or membrane protein crystallization. The same disc-like assemblies, nonionic surfactant bicelles (NSBs), can also be formed using nonionic amphiphiles, but this has not been reported extensively. We report a novel NSB system that employs the double-tailed nonionic amphiphile, polyglyceryl dialkyl ether (C12CmGn), which has two alkyl chains and a polyglyceryl group. A symmetric-tail molecule, C12C12G13.8, formed vesicles, whereas an asymmetric-tail molecule, C12C14G15.5, formed NSBs through a simple one-step process using ultrasonication. The 1 wt% aqueous solution of C12C14G15.5 was in a two-phase equilibrium of a lamellar phase and a water phase. Transparent dispersion was obtained through ultrasonication treatment. The size distribution in the dispersion was obtained by dynamic light scattering (DLS), resulting in a narrow distribution of around 20 nm in diameter. A negatively-stained transmission electron microscopy (TEM) image showed oblong and spherical shapes, which are typically observed in bicelle-forming systems. A small angle neutron scattering (SANS) measurement well proved bicelle formation by fitting a core-shell bicelle form factor model. The disc thickness and diameter were in agreement with the values obtained by DLS and TEM, respectively. A larger shell thickness at the rim part than at the flat disc part suggested that NSB aggregates have inhomogeneous molecular distribution. Similar to phospholipid systems, the bicelle-forming C12C14G15.5 system produced a defective lamellar phase formation at high surfactant concentrations, whereas a general lamellar phase was formed in the vesicle-forming C12C12G13.8 system.

Parametrizations of the γ*N→Δ(1232) quadrupole form factors and Siegert’s theorem

The large $N_c$ limit provides relations that can be used to calculate the $\gamma^\ast N \to \Delta(1232)$ quadrupole form factors at low and intermediate $Q^2$ under the assumption of the pion cloud dominance. There are two limitations in those parametrizations. First, the parametrization of the Coulomb quadrupole form factor underestimate the low $Q^2$ data. Second, when extrapolated for the timelike region, the form factors violate Siegert's theorem by terms of the order $1/N_c^2$. We propose here corrections to the parametrization of the electric quadrupole form factor, which violate Siegert's theorem only by terms of the order $1/N_c^4$. Combining the improved large $N_c$ pion cloud parametrizations with the valence quark contributions based on a covariant quark model for the quadrupole transition form factors, we obtain an extrapolation to the timelike region consistent with Siegert's theorem, and accomplish also a very good description of the data.

English

The use of form factors is a practical alternative for estimating tree volume. However, only a few studies in this topic are relevant to Tectona grandis, and only few to those that evaluate the effect of spacing on it. The goal of this study was to generate form factor equations and evaluate spacing influence on it in teak plantations. Samples were taking in 3 × 2 m, 4 × 3 m, 5 × 2 m, and 6 × 2 m plots. The database consisted of rigorous cubage of 120 trees, 30 of which were utilised in spacing for the calculation of the artificial form factor models; these were compared using statistical indicators and graphic analyses. In order to assess possible differences among the equations, the identity test of models at the p < 0.05 significance level was utilised. The results of the identity test of models show that it is possible to utilise a single equation (the reduced model) to estimate the form factor for all spacings, indicating that the factor was not influenced by plantation spacing. It was found that with increasing diameter, teak tree trunks became more cylindrical. Stabilisation occurs starting at a diameter of 27 cm and a height of 25 m, with a form factor of 0.47.     Key words: Teak, volumetric, plantation density.

High-frequency ultrasound detection of cell death: Spectral differentiation of different forms of cell death in vitro.

High frequency quantitative ultrasound techniques were investigated to characterize different forms of cell death in vitro. Suspension-grown acute myeloid leukemia cells were treated to cause apoptosis, oncosis, mitotic arrest, and heat-induced death. Samples were scanned with 20 and 40 MHz ultrasound and assessed histologically in terms of cellular structure. Frequency-domain analysis of 20 MHz ultrasound data demonstrated midband fit changes of 6.0 ± 0.7 dBr, 6.2 ± 1.8 dBr, 4.0 ± 1.0 dBr and −4.6 ± 1.7 dBr after 48-hour cisplatinum-induced apoptosis, 48-hour oncotic decay, 36-hour colchicine-induced mitotic arrest, and heat treatment compared to control, respectively. Trends from 40 MHz ultrasound were similar. Spectral slope changes obtained from 40 MHz ultrasound data were reflective of alterations in cell and nucleus size. Chromatin pyknosis or lysis trends suggested that the density of nuclear material may be responsible for observed changes in ultrasound backscatter. Flow cytometry analysis confirmed the modes of cell death and supported midband fit trends in ultrasound data. Scatterer-size and concentration estimates obtained from a fluid-filled sphere form factor model further corresponded with spectral analysis and histology. Results indicate quantitative ultrasound spectral analysis may be used for probing anti-cancer response and distinguishing various modes of cell death in vitro.

Limits on the effective quark radius from inclusive ep scattering at HERA

The high-precision HERA data allows searches up to TeV scales for Beyond the Standard Model contributions to electron-quark scattering. Combined measurements of the inclusive deep inelastic cross sections in neutral and charged current $ep$ scattering corresponding to a luminosity of around 1 fb$^{-1}$ have been used in this analysis. A new approach to the beyond the Standard Model analysis of the inclusive $ep$ data is presented; simultaneous fits of parton distribution functions together with contributions of "new physics" processes were performed. Results are presented considering a finite radius of quarks within the quark form-factor model. The resulting 95% C.L. upper limit on the effective quark radius is $0.43\cdot 10^{-16}$ cm.

Covariance Constraints for Light Front Wave Functions

Light front wave functions (LFWFs) are often utilized to model parton distributions and form factors where their transverse and longitudinal momenta are tied to each other in some manner that is often guided by convenience. On the other hand, the cross talk of transverse and longitudinal momenta is governed by Poincar\'e symmetry and thus popular LFWF models are often not usable to model more intricate quantities such as generalized parton distributions. In this contribution a closer look to this issue is given and it is shown how to overcome the issue for two--body LFWFs.

Role of the pion electromagnetic form factor in theΔ(1232)→γ*Ntimelike transition

The $\Delta(1232) \to \gamma^\ast N$ magnetic dipole form factor ($G_M^\ast$) is described here within a new covariant model that combines the valence quark core together with the pion cloud contributions. The pion cloud term is parameterized by two terms: one connected to the pion electromagnetic form factor, the other to the photon interaction with intermediate baryon states. The model can be used in studies of pp and heavy ion collisions. In the timelike region this new model improves the results obtained with a constant form factor model fixed at its value at zero momentum transfer. At the same time, and in contrast to the Iachello model, this new model predicts a peak for the transition form factor at the expected position, i.e. at the $\rho$ mass pole. We calculate the decay of the $\Delta \to \gamma N$ transition, the Dalitz decay ($\Delta \to e^+ e^- N$), and the $\Delta$ mass distribution function. The impact of the model on dilepton spectra in pp collisions is also discussed.

Evaluation of the strength of electron-proton scattering data for determining the proton charge radius

Precisely measured electron-proton elastic scattering cross sections [Phys. Rev. Lett. {\bf 105}, 242002 (2010)] are reanalyzed to evaluate their strength for determining the rms charge radius ($R_{\rm E}$) of the proton. More than half of the cross sections at lowest $Q^2$ are fit using two single-parameter form-factor models, with the first based on a dipole parametrization, and the second on a linear fit to a conformal-mapping variable. These low-$Q^2$ fits extrapolate the slope of the form factor to $Q^2$=0 and determine $R_{\rm E}$ values of approximately 0.84 and 0.89~fm, respectively. Fits spanning all $Q^2$, in which the single constants are replaced with cubic splines at larger $Q^2$, lead to similar results for $R_{\rm E}$. We conclude that the scattering data is consistent with $R_{\rm E}$ ranging from at least 0.84 to 0.89~fm, and therefore cannot resolve the discrepancy between determinations of $R_{\rm E}$ made using muonic and electronic hydrogen-atom spectroscopy.

The Parallel Asynchronous Differential Evolution Method as a Tool to Analyze Synchrotron Scattering Experimental Data from Vesicular Systems

In this work we use an Asynchronous Differential Evolution (ADE) method to estimate parameters of the Separated Form Factor (SFF) model which is used to investigate a structure of drug delivery Phospholipid Transport Nano System (PTNS) unilamellar vesicles by experimental small angle synchrotron X-ray scattering spectra (SAXS). We compare the efficiency of different optimizing procedures (OP) for the search for the SFF-model parameters. It is shown that the probability to find the global solution of this problem by ADE-methods is significantly higher than that by either Nelder-Mead method or a Quasi-Newton method with Davidon-Fletcher-Powell formula. The parallel realization of ADE accelerates the calculations significantly. The speed-up obtained by the parallel realization of ADE and results of the model are presented.

Quantification of Ultrasonic Scattering Properties of In Vivo Tumor Cell Death in Mouse Models of Breast Cancer

INTRODUCTION: Quantitative ultrasound parameters based on form factor models were investigated as potential biomarkers of cell death in breast tumor (MDA-231) xenografts treated with chemotherapy. METHODS: Ultrasound backscatter radiofrequency data were acquired from MDA-231 breast cancer tumor–bearing mice (n = 20) before and after the administration of chemotherapy drugs at two ultrasound frequencies: 7 MHz and 20 MHz. Radiofrequency spectral analysis involved estimating the backscatter coefficient from regions of interest in the center of the tumor, to which form factor models were fitted, resulting in estimates of average scatterer diameter and average acoustic concentration (AAC). RESULTS: The ∆AAC parameter extracted from the spherical Gaussian model was found to be the most effective cell death biomarker (at the lower frequency range, r2 = 0.40). At both frequencies, AAC in the treated tumors increased significantly (P = .026 and .035 at low and high frequencies, respectively) 24 hours after treatment compared with control tumors. Furthermore, stepwise multiple linear regression analysis of the low-frequency data revealed that a multiparameter quantitative ultrasound model was strongly correlated to cell death determined histologically posttreatment (r2 = 0.74). CONCLUSION: The Gaussian form factor model–based scattering parameters can potentially be used to track the extent of cell death at clinically relevant frequencies (7 MHz). The 20-MHz results agreed with previous findings in which parameters related to the backscatter intensity (i.e., AAC) increased with cell death. The findings suggested that, in addition to the backscatter coefficient parameter ∆AAC, biological features including tumor heterogeneity and initial tumor volume were important factors in the prediction of cell death response.

Localized direct CP violation in $$B^\pm \rightarrow \rho ^0 (\omega )\pi ^\pm \rightarrow \pi ^+ \pi ^-\pi ^\pm $$ B ± → ρ 0 ( ω ) π ± → π + π - π ±

We study the localized direct CP violation in the hadronic decays $B^\pm\rightarrow \rho^0 (\omega)\pi^\pm\rightarrow\pi^+ \pi^-\pi^\pm$, including the effect caused by an interesting mechanism involving the charge symmetry violating mixing between $\rho^0$ and $\omega$. We calculate the localized integrated direct CP violation when the low invariant mass of $\pi^+\pi^-$ [$m(\pi^+\pi^-)_{low}$] is near $\rho^0(770)$. For five models of form factors investigated, we find that the localized integrated direct CP violation varies from -0.0170 to -0.0860 in the ranges of parameters in our model when $0.750<m(\pi^+\pi^-)_{low}<0.800$\,GeV. This result, especially the sign, agrees with the experimental data and is independent of form factor models. The new experimental data shows that the signs of the localized integrated CP asymmetries in the regions $0.470<m(\pi^+\pi^-)_{low}<0.770$\,GeV and $0.770<m(\pi^+\pi^-)_{low}<0.920$\,GeV are positive and negative, respectively. We find that $\rho$-$\omega$ mixing makes the localized integrated CP asymmetry move towards the negative direction, and therefore contributes to the sign change in those two regions. This behavior is also model independent. We also calculate the localized integrated direct CP violating asymmetries in the regions $0.470<m(\pi^+\pi^-)_{low}<0.770$\,GeV and $0.770<m(\pi^+\pi^-)_{low}<0.920$\,GeV and find that they agree with the experimental data in some models of form factors.

Lepton polarization asymmetries for FCNC decays of the Λb baryon

Branching ratios, lepton forward–backward asymmetries, and lepton polarization asymmetries for the flavor-changing neutral current (FCNC) dileptonic decays of the [Formula: see text] baryon to the ground state and a number of excited state [Formula: see text] baryons are calculated using form factors extracted using wave functions from a constituent quark model. The SM branching ratios for the transition to the ground state calculated using these quark model form factors are consistent with the recent measurement reported by the LHCb collaboration. It is shown that the lepton polarization asymmetries are largely insensitive to the transition form factors and, therefore, may also be insensitive to the effects of QCD in the nonperturbative regime. These observables could therefore provide somewhat model independent ways of extracting various combinations of the Wilson coefficients.

Small angle scattering of 59.54 keV photons by elemental samples in the atomic number region 13 ≤ Z ≤ 82

In the present paper, we report the angle integrated coherent scattering cross sections of some elements at low momentum transfer over four angular ranges for some elements in the atomic number range 13≤Z≤82 for 241Am (59.54 keV) gamma rays. The coherent scattering cross sections were derived from the experimentally measured total (Coherent + incoherent) scattering cross sections for the elements at the energy of interest by subtracting separately the small contribution of the corresponding angle integrated incoherent scattering cross sections. The theoretical angle integrated incoherent scattering cross sections were computed by numerically integrating the values provided in the compilations based on the non-relativistic Hartree-Fock (NRHF) model and the modified form factor (MFF) model for the charge distribution within the atom. The present values of the angle integrated coherent scattering cross sections of the elements Al, Fe, Cu, Zn, Cd, Sn and Pb at 59.54 keV in the angular ranges of (0∘−4∘), (0∘−6∘), (0∘−8∘) and (0°–10°) so obtained are compared with the corresponding theoretical S-matrix data within the range of experimental errors. The root mean square error on the measured cross sections was found to be the lowest for Al at 4.1% and the highest for Pb at 4.9%. For the other elements the error was in between these two values. Possible conclusions are drawn based on the present study.

Evaluation of the Shaping Characteristics of ProTaper Gold, ProTaper NEXT, and ProTaper Universal in Curved Canals

IntroductionThis study evaluated the shaping characteristics of the ProTaper Gold system (PTG; Dentsply Maillefer, Ballaigues, Switzerland) and compared it with that of the ProTaper Next (PTN, Dentsply Maillefer) and ProTaper Universal (PTU, Dentsply Maillefer) systems using micro–computed tomographic imaging. MethodsTwenty-four mandibular first molars with 2 separate mesial canals were matched anatomically using micro–computed tomographic scanning (SkyScan1174v2; Bruker-microCT, Kontich, Belgium) with a voxel size of 19.6 μm. Canals were prepared with PTG, PTU, or PTN rotary systems to F2 or X2 instruments, respectively, and scanned again. Coregistered images were evaluated for 2- and 3-dimensional morphometric measurements of canal transportation, centering ability, untouched canal walls, and remaining dentin thickness. Data were statistically compared using Kruskal-Wallis and 1-way analysis of variance tests (α = 5%). ResultsOverall, PTN showed significantly higher percentage values of static voxels than PTG and PTU systems (P < .05). Surface area, perimeter, and minor diameter were higher in the PTG and PTU groups than in the PTN group (P < .05). No difference was observed in form factor, roundness, major diameter, aspect ratio, or structure model index (P > .05). PTG (0.11 ± 0.05 mm) and PTN (0.09 ± 0.05 mm) produced significantly less transportation than PTU (0.14 ± 0.07 mm) (P < .05), and the percentage decrease in dentin thickness was significantly lower for PTG (22.67 ± 2.96) and PTN (17.71 ± 5.93%) (P ≥ .05) than PTU (29.93 ± 6.24%) (P < .05). ConclusionsPTG and PTN produced less transportation and maintained more dentin than PTU. PTN had less canal wall contact than PTG and PTU, but all file systems were able to instrument moderately curved mesial root canals of mandibular molars without clinically significant errors.

Investigation of the structure of unilamellar dimyristoylphosphatidylcholine vesicles in aqueous sucrose solutions by small-angle neutron and X-ray scattering

The structure of a polydispersed population of unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles in sucrose solutions has been investigated by small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS). Calculations within the model of separated form factors (SFF) show that the structure of the vesicle system depends strongly on the sucrose concentration.

Finite mass corrections forB→(D¯(*),D¯**)ℓνdecays in the Bakamjian-Thomas relativistic quark model

The Bakamjian-Thomas relativistic quark model for hadron current matrix elements, while noncovariant at finite mass, is successful in the heavy quark limit: form factors are covariant and satisfy Isgur-Wise scaling and Bjorken-Uraltsev sum rules. Motivated by the so-called ``$1/2$ vs $3/2$ puzzle'' in $\overline{B}$ decays to positive parity ${D}^{**}$, we examine the implications of the model at finite mass. In the elastic case ${\frac{1}{2}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\frac{1}{2}}^{\ensuremath{-}}$, the heavy quark effective theory (HQET) constraints for the $O(1/{m}_{Q})$ corrections are analytically fulfilled. A number of satisfying regularities is also found for inelastic transitions. We compute the form factors using the wave functions given by the Godfrey-Isgur potential. We find a strong enhancement in the case ${\frac{1}{2}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\frac{1}{2}}^{+}$ for ${0}^{\ensuremath{-}}\ensuremath{\rightarrow}{0}^{+}$. This enhancement is linked to a serious difficulty of the model at finite mass for the inelastic transitions, namely a violation of the HQET constraints at zero recoil formulated by Leibovich et al. These are nevertheless satisfied in the nonrelativistic limit for the light quark. We conclude that these HQET rigorous constraints are crucial in the construction of a sensible relativistic quark model of inelastic form factors.

Comparison between shell model and self-consistent mean field calculations for ground charge density distributions and elastic form factors of 12C and 16O nuclei

The ground charge density distributions, elastic form factors and root mean square radii for 12C and 16O nuclei in 1p-shell nuclei are calculated in shell model using core plus valence and no-core–shell model calculations. The single-particle wave functions of harmonic-oscillators potential are used. For such potential, two harmonic-oscillators size parameters are used: one for neutron and the other for proton. Calculations are compared with the results of self-consistent mean field using SKX Skyrme parameterization and experimental data. The calculated charge density distributions in shell model for 12C and 16O nuclei show good agreement with experimental data. The calculated charge form factors at low q in shell model for 12C and 16O show good agreement with experimental data. At high q, the result for 16O shows no prediction for the position of second diffraction minimum. In general, it is found that enlarging the model space in shell model leads to suppress slightly the behavior of density distribution around central region and also the behavior of form factor at high q, which is good to approach experimental data. On the other side, such increase in model space leads to increase the calculated root mean square radii, which is the same behaviour of the results of Hartree–Fock calculations. The calculated charge form factors in Hartree–Fock calculations show the existence of many diffraction minima, which do not agree with experimental data in contrary to shell model, which predicts less diffraction minima.

Nucleon form factors for elastic electron-deuteron scattering at high momentum transfer

Elastic electron-deuteron scattering at high momentum transfer is investigated within the Bethe-Salpeter approach. The relativistic covariant Graz II separable kernel of nucleon-nucleon interactions is used to analyze the deuteron structure functions, form factors, and tensor of polarization components. The modern data for the electromagnetic structure of nucleons from the double polarization experiments, as well as some other models of the nucleon form factors, are considered.

Transverse charge and magnetization densities in holographic QCD

We present a study of flavor structures of transverse charge and anomalous magnetization densities for both unpolarized and transversely polarized nucleons. We consider two different models for the electromagnetic form factors in holographic QCD. The flavor form factors are obtained by decomposing the Dirac and Pauli form factors for nucleons using the charge and isospin symmetry. The results are compared with two standard phenomenological parametrizations.