Contributions Of Form Factors Research Articles

SAXS Investigation of Core–Shell Microgels with High Scattering Contrast Cores: Access to Structure Factor and Volume Fraction

To explore dense packings of soft colloids, scattering experiments are ideal to access the structure factor. However, for soft microgels determination of the structure factor is difficult because of the low contrast of the polymer network and potential microgel interpenetration and deformation that change the form factor contribution. Here, we employ small-angle X-ray scattering (SAXS) to study soft, thermoresponsive microgels with poly-N-isopropylacrylamide (PNIPAM) shells and gold nanoparticle cores. The scattering of the gold cores dominates the scattering patterns and allows precise determination of the microgel volume fraction over a broad range of concentrations. At high volume fractions we find distinct patterns with sharp Bragg peaks allowing extraction of the structure factor and characterization of the phases combined with UV-Vis spectroscopy. The unique scattering contrast of our core-shell microgels combined with SAXS opens up new ways to investigate dense packings of soft microgels including in situ studies of phase transitions.

Radiative and chiral corrections to elastic lepton-proton scattering in chiral perturbation theory

A unified treatment of both chiral and radiative corrections to the low-energy elastic lepton-proton scattering processes is presented in Heavy Baryon Chiral Perturbations Theory. The proton hadronic chiral corrections include the next-to-next-to leading order corrections whereas the radiative corrections include the next-to-leading order terms in our novel power counting scheme. We find that the net fractional well-defined chiral corrections with respect to the leading order Born cross section can be as large as $10\%$ ($20\%$) for electron (muon) scattering process for MUon proton Scattering Experiment (MUSE) kinematics. We show {\it via} our model-independent treatment of the low-energy lepton-proton kinematics, that the largest theoretical uncertainty is due to the recent different published values of the proton's rms radius while, e.g., the next higher order hadronic chiral terms are expected to give rather nominal errors. For the radiative corrections we demonstrate a systematic order by order cancellation of all infrared singularities and present our finite ultraviolet regularization results. We find that the radiative corrections for muon-proton scattering is of the order of $2\%$, whereas for electron scattering the radiative corrections could be as large as $25\%$. We attribute such a contrasting result partially to the fact that in muon scattering the leading radiative order correction goes through zero in some intermediate low-momentum transfer region, leaving the sub-leading radiative chiral order effects to play a dominant role in this particular kinematic region. For the low-energy MUSE experiment, the often neglected lepton mass as well as the Pauli form factor contributions of the relativistic leptons are incorporated in all our computations.

Light-quark contributions to the magnetic form factor of the Λ(1405)

In a recent study of the Lambda(1405), the suppression of the strange-quark contribution to the magnetic form factor was interpreted as the discovery of a dominant antikaon-nucleon composition for this low-lying state. We confirm this result by calculating the light u- and d-quark contributions to the Lambda(1405) magnetic form factor in lattice QCD in order to determine the extent to which their contributions support this exotic molecular description. Drawing on the recent graded-symmetry approach for the flavor-singlet components of the Lambda(1405), the separation of connected and disconnected contributions is performed in both the flavor-octet and singlet representations. The relationship between light-quark contributions to the Lambda(1405) magnetic form factor and the connected contributions of the nucleon magnetic form factors is established and compared with lattice calculations of the same quantities, confirming the KN molecular structure of the Lambda(1405) in lattice QCD.

Pion Form Factor Contribution in Vacuum Polarization corrections for 1s energy level in different Pionic-Hydrogen Atoms

Pion Form Factor Contribution in Vacuum Polarization corrections for 1s energy level in different Pionic-Hydrogen Atoms

Form factor and boundary contribution of amplitude

The boundary contribution of an amplitude in the BCFW recursion relation can be considered as a form factor involving boundary operator and unshifted particles. At the tree-level, we show that by suitable construction of Lagrangian, one can relate the leading order term of boundary operators to some composite operators of N=4 super-Yang-Mills theory, then the computation of form factors is translated to the computation of amplitudes. We compute the form factors of these composite operators through the computation of corresponding double trace amplitudes.

Structural evolution of colloidal crystal films in the process of melting revealed by Bragg peak analysis.

In situ X-ray diffraction studies of structural evolution of colloidal crystal films formed by polystyrene spherical particles upon incremental heating are reported. The Bragg peak parameters, such as peak position, integrated intensity, and radial and azimuthal widths were analyzed as a function of temperature. A quantitative study of colloidal crystal lattice distortions and mosaic spread as a function of temperature was carried out using Williamson-Hall plots based on mosaic block model. The temperature dependence of the diameter of polystyrene particles was obtained from the analysis of Bragg peaks, and the form factor contribution extracted from the diffraction patterns. Four stages of structural evolution in a colloidal crystal upon heating were identified. Based on this analysis, a model of the heating and melting process in the colloidal crystal film is suggested.

Charge symmetry breaking and parity violating electron-proton scattering

Charge symmetry breaking contributions to the proton's neutral weak form factors must be understood in order for future measurements of parity violating electron-proton scattering to be definitively interpreted as evidence of proton strangeness. We calculate these charge symmetry breaking form factor contributions using chiral perturbation theory with resonance saturation estimates for unknown low-energy constants. The uncertainty of the leading-order resonance prediction is reduced by incorporating nuclear physics constraints. Higher-order contributions are investigated through phenomenological vertex form factors. We predict that charge symmetry breaking form factor contributions are an order of magnitude larger than expected from na\"{\i}ve dimensional analysis but are still an order of magnitude smaller than current experimental bounds on proton strangeness. This is consistent with previous calculations using chiral perturbation theory with resonance saturation.

Scalar and Pseudo-Scalar Form Factors in Electro- and Weak-Production of Pion Near Threshold

We investigated pion production near threshold by the weak current in terms of multipole amplitudes. By exploiting the chiral Ward identity based on the QCD Lagrangian, we derived relevant multipole amplitudes in closed forms and presented their numerical results. In the amplitudes, scalar and pseudo scalar (PS) form factors, which represent the scalar and the PS quark density distributions, manifest by themselves. We applied these amplitudes to the cross sections for the weak- and electro-production near threshold. Both pion and PS form factor contributions are shown to account for the t-channel contribution in the charged pion electro-production near threshold. The asymmetry on the pion production by the neutrino and anti-neutrino is also discussed with their longitudinal and transverse cross sections.

Revisiting the production of charmonium plus a light meson atP¯ANDA

In this work, we calculate the total cross sections and the center-of-mass frame angular distributions of the charmonium production plus a light meson by the low energy $p\bar{p}$ interaction. The results of $p\bar{p}\to \pi^0 \Psi$ with and without form factor (FF) indicate that the FF contribution in the calculation cannot be ignored. The obtained cross section of $p\bar{p}\to \pi^0 J/\psi$ with FF can fit the E760 data well. We also predict the total cross sections and the center-of-mass frame angular distributions of $p\bar{p}\to \omega \Psi$, which show that these physical quantities are dependent on Pauli ($g_\omega$) and Dirac ($\kappa_\omega$) coupling constants of the $pp\omega$ interaction. Thus, $p\bar{p}\to \omega \Psi$ can be as the ideal channel to test the different theoretical values of $g_\omega$ and $\kappa_\omega$. Applying the formulae of $p\bar{p}\to \pi^0 \Psi$ and $p\bar{p}\to \omega \Psi$, we predict the total cross sections of the $p\bar{p}\to \eta \Psi$ and $p\bar{p}\to \rho \Psi$ reactions. Our results show a common behavior of the charmonium production with a light meson by the $p\bar{p}$ interaction, where the total cross section of the $\eta_c$ production is the largest one among all discussed processes. The above observations can be directly tested at the forthcoming $\bar{P}$ANDA experiment.

Higher particle form factors of branch point twist fields in integrable quantum field theories

In this paper we compute higher particle form factors of branch point twist fields. These fields were first described in the context of massive (1+1)-dimensional integrable quantum field theories and their correlation functions are related to the bi-partite entanglement entropy. We find analytic expressions for some form factors and check those expressions for consistency, mainly by evaluating the conformal dimension of the corresponding twist field in the underlying conformal field theory. We find that solutions to the form factor equations are not unique so various techniques need to be used to identify those corresponding to the branch point twist field we are interested in. The models for which we carry out our study are characterized by staircase patterns of various physical quantities as functions of the energy scale. As the latter is varied, the β-function associated with these theories comes close to vanishing at several points between the deep infrared and deep ultraviolet regimes. In other words, renormalization group flows approach the vicinity of various critical points before ultimately reaching the ultraviolet fixed point. This feature provides an optimal way of checking the consistency of higher particle form factor solutions, as the changes on the conformal dimension of the twist field at various energy scales can only be accounted for by considering higher particle form factor contributions to the expansion of certain correlation functions.

Survey of Nucleon Electromagnetic Form Factors

A dressed-quark core contribution to nucleon electromagnetic form factors is calculated. It is defined by the solution of a Poincare' covariant Faddeev equation in which dressed-quarks provide the elementary degree of freedom and correlations between them are expressed via diquarks. The nucleon-photon vertex involves a single parameter; i.e., a diquark charge radius. It is argued to be commensurate with the pion's charge radius. A comprehensive analysis and explanation of the form factors is built upon this foundation. A particular feature of the study is a separation of form factor contributions into those from different diagram types and correlation sectors, and subsequently a flavour separation for each of these. Amongst the extensive body of results that one could highlight are: r_1^{n,u}>r_1^{n,d}, owing to the presence of axial-vector quark-quark correlations; and for both the neutron and proton the ratio of Sachs electric and magnetic form factors possesses a zero.

Bi-partite Entanglement Entropy in Massive QFT with a Boundary: the Ising Model

In this paper we give an exact infinite-series expression for the bi-partite entanglement entropy of the quantum Ising model both with a boundary magnetic field and in infinite volume. This generalizes and extends previous results involving the present authors for the bi-partite entanglement entropy of integrable quantum field theories, which exploited the generalization of the form factor program to branch-point twist fields. In the boundary case, we isolate in a universal way the part of the entanglement entropy which is related to the boundary entropy introduced by Affleck and Ludwig, and explain how this relation should hold in more general QFT models. We provide several consistency checks for the validity of our form factor results, notably, the identification of the leading ultraviolet behaviour both of the entanglement entropy and of the two-point function of twist fields in the bulk theory, to a great degree of precision by including up to 500 form factor contributions.

Chiral corrections to the scalar form factor inBq→Dqtransitions

We consider chiral loop corrections to the scalar form factor in ${B}_{q}\ensuremath{\rightarrow}{D}_{q}l\ensuremath{\nu}$ decays. First we consider chiral corrections to the $1/{m}_{Q}$ suppressed operators and then we propose a procedure for the extraction of the relevant form factor using lattice QCD results. In particular, the extraction of a ${B}^{*}\ensuremath{\rightarrow}{D}^{*}$ matrix element on the lattice can be used to determine all the necessary $1/{m}_{Q}$ suppressed contributions to the scalar form factor in $B\ensuremath{\rightarrow}D$ transitions. In the case of $({B}_{s}\ensuremath{\rightarrow}{D}_{s})/(B\ensuremath{\rightarrow}D)$ decay rate ratios we speculate that effects of kinematics and chiral corrections tend to cancel for the scalar form factor contributions. In particular the $1/{m}_{Q}$ suppression of chiral corrections is compensated by the potentially large $SU(3)$ flavor symmetry breaking corrections. The calculated corrections are relevant for the precise determination of possible new physics effects in ${B}_{q}\ensuremath{\rightarrow}{D}_{q}l\ensuremath{\nu}$ decays.

The weak production of Λ particles in antineutrino–proton scattering and the contributions of the form factors

In support of proposed experiments which might be carried out by the MINER νA Collaboration and eventually elsewhere, we study the strangeness changing charged current reactions ν ¯ L + p → Λ + L + where L stands for an electron, muon, or tau lepton. We calculate the total and differential cross sections for these reactions from near threshold to several GeV. We also obtain the contributions of the various form factors and interference terms to the total and differential cross sections. The calculation is phenomenologically based and makes use of SU(3) relations to obtain the standard vector current form factors and data from Λ beta decay to obtain the axial current form factor. We also make estimates for the contributions of the pseudoscalar form factor and for the F E and F S form factors to the total and differential cross sections. The latter two are second class current form factors for the corresponding p ↔ n transition and forbidden by G-parity but are not forbidden here. We discuss our results and consider under what circumstances we might extract the various form factors. In particular we wish to test the SU(3) obtained form factors and to test the assumptions made in determining the others over a range of q 2 values.

THE STRANGENESS CHANGING ANTINEUTRINO REACTION ${\bar\nu}_L+P\longrightarrow\Lambda+L^+$

We obtain the cross sections for the reactions [Formula: see text] where L is a massive lepton, i.e. a muon or a tau lepton. We do this from near threshold to relativistic energies. We further obtain the contributions of various form factors and interference terms to the cross section with a view to discovering if the contributions from hard to observe form factors such as the weak pseudoscalar form factor, FP, and the weak electric form factor, FE might be obtained via these reactions. The form factor FE is particularly interesting as in the more usually observed p↔n transition it is a second class current and forbidden by G-parity. However in the p↔Λ transition it is not forbidden and it would be desirable to learn if it is present. Finally we discuss our results and prospects for these experiments.

The weak production of Λ hyperons from lepton-proton scattering

We obtain the differential cross sections for the weak, strangeness changing processes, e − + p → Λ + ν e , μ − + p → Λ + ν μ , and τ − + p → Λ + ν τ as well as cross sections for the processes ν ¯ L + p → Λ + L + , where L stands for either a muon or a tau. We do this for electron energies from threshold to 2.0 GeV, for muon energies from near threshold to 5.0 GeV, for a tau energy of 20.0 GeV, and for muon antineutrino energies from threshold to 1.0 GeV and tau antineutrino energies near threshold. We discuss what might be learned from these reactions and obtain the contributions of the various form factors to these cross sections. We pay particular attention to the interference terms which may represent the only possibility of obtaining the weak magnetism form factor, F M , the pseudoscalar form factor, F P , and the form factor, F E . This latter form factor is forbidden by G-parity in the p ↔ n transition but is in principle permitted in the p ↔ Λ transition and its presence would therefore be of interest. Our calculation is a phenomenological one and makes use of SU(3) relations and Λ beta decay data.

Parity-violating electroweak asymmetry ine⃗pscattering

We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from protons. Significant contributions to this asymmetry could arise from the contributions of strange form factors in the nucleon. The measured asymmetry is A=−15.05±0.98(stat)±0.56(syst)ppm at the kinematic point ⟨θlab⟩=12.3° and ⟨Q2⟩=0.477(GeV∕c)2. Based on these data as well as data on electromagnetic form factors, we extract the linear combination of strange form factors GEs+0.392GMs=0.014±0.020±0.010, where the first error arises from this experiment and the second arises from the electromagnetic form factor data. This paper provides a full description of the special experimental techniques employed for precisely measuring the small asymmetry, including the first use of a strained GaAs crystal and a laser-Compton polarimeter in a fixed target parity-violation experiment.23 MoreReceived 16 January 2004DOI:https://doi.org/10.1103/PhysRevC.69.065501©2004 American Physical Society

Probing proton strangeness with time-like virtual Compton scattering

We document that p(γ,e+e−)p measurements will yield new, important information about the off-shell time-like nucleon form factors, especially in the φ meson region (q2=M2φ) governing the φN couplings gV,TφNN. Calculations for p(γ,e+e−)p, utilizing vector meson dominance, predict measurable φ enhancements at high |t| compared to the expected φ background production from π, η and Pomeron exchange. The φ form factor contribution generates a novel experimental signature for OZI violation and the proton strangeness content. The φN couplings are determined independently from a combined analysis of the neutron electric form factor and recent high |t| φ photoproduction. The π, η and Pomeron transition form factors are also predicted and the observed π and η transition moments are reproduced.

Darwin–Foldy term and proton charge radius

In this contribution we study the Dirac equation for a finite size proton in an external electric field with explicit introduction of Dirac-Pauli form factors. Our aim is twofold. On the one hand, we wish to study whether our conclusions regarding the exact cancellation between Dirac form factor and Foldy term contributions occurring for the neutron still hold for the proton. On the other hand, we wish to clearly illustrate some of the specific features of the description of a composite particle like the proton with the Dirac equation.

Craniofacial Form and Obstructive Sleep Apnea in Polynesian and Caucasian Men

This aim of this study was to determine the relative contributions of craniofacial form and anthropometric factors to obstructive sleep apnea (OSA) in two different racial groups, both markedly obese and with a similar mean respiratory disturbance index (RDI). A cross-sectional study of New Zealand Maori (Polynesian) and European (Caucasian) men with RDI> or =15, using lateral and postero-anterior cephalometric radiography. N/A. N/A. Measurements of facial and cranial width, length and height, airway size, stature, weight, body mass index (BMI), neck circumference, RDI, and age were obtained. The Polynesian men had, on average, a greater neck circumference than the Caucasian men. There were no significant differences in age, weight, BMI or RDI between the two groups. The Polynesian men also had broader craniofacial skeletons, larger and more prognathic mandibles, greater neck extension, and some larger airway dimensions than the Caucasian men. In the Polynesian men, the width of the bony nasal aperture was positively associated with RDI, and mandibular prognathism was negatively associated with RDI. In contrast, in the Caucasian men only neck circumference was positively associated with RDI, while the retropalatal airway was negatively associated with RDI. The results indicate that OSA in these two racially distinct groups is due to different etiological factors. Small reductions in mandibular prognathism and a wider bony nasal aperture were major factors associated with OSA in Polynesians. On the other hand, in the Caucasian group OSA was associated with a larger neck circumference and a reduced retropalatal airway size.