Form Factor Parameters Research Articles

Lepton-neutron interaction and S -wave low-energy parameters

A lepton-neutron potential in configuration space is obtained. It is based on the Coulomb plus hyperfine interaction Hamiltonian integrated over the neutron charge and magnetic densities. Different parametrizations of the neutron electromagnetic form factors are compared. It is given in the operator form with central, spin-spin, tensor, and spin-orbit terms. The potentials for lowest partial wave states are presented. We compute the lepton-neutron low-energy parameters for the S waves, estimate the zero-energy cross sections for higher angular momentum states, and point out a possible divergence in the partial wave summation due to the spin-orbit potential. Published by the American Physical Society 2024

Sodium dodecyl sulfate micelles: Accurate analysis of small-angle X-ray scattering data through form factor and atomistic molecular dynamics modelling

The structure of micelles of sodium dodecyl sulfate (SDS) is probed via analysis of small-angle x-ray scattering (SAXS) data with the aim to fit the data over an extended wavenumber q range. This provides detailed information on the micelle shape, which can be described as a polydisperse triaxial ellipsoidal core-shell structure according to model form factor fitting. This model was necessary to fit the data over a wide q range, which is not accurately represented by simpler models such as biaxial ellipsoidal core-shell structures. Data for SDS (at fixed concentration) in a NaCl concentration series revealed increasing structure factor effects with decreasing salt concentration. This reflects decreased charge screening on the headgroups. The structure factor could be modelled using a simple hard sphere structure factor. The analysis of form factor was complemented by atomistic molecular dynamics (MD) simulations, starting from an unbiased initial configuration of a defined number of molecules in a box. The MD configurations were used to calculate the form factor using the software CRYSOL (for small-angle scattering analysis of solution scattering, traditionally for proteins, here for micelles) and accounting for the boundary layer hydration effects. Good agreement with experimental data was found for systems with association numbers close to p = 60. This association number is consistent with that obtained from analysis of the form factor (in the case where structure factor effects could be neglected) and from model-free analysis of the forward scattering intensity. It is also in agreement with prior literature and our findings in regard to form factor parameters are also compared to previous reports.

JLab spectral functions of argon in nuwro and their implications for MicroBooNE

The Short-Baseline Neutrino program in Fermilab aims to resolve the nature of the low-energy excess events observed in LSND and MiniBooNE, and analyze with unprecedented precision neutrino interactions with argon. These studies require a reliable estimate of neutrino cross sections, in particular for charged current quasielastic scattering (CCQE). Here, we report updates of the uro Monte Carlo generator that, most notably, bring the state-of-the-art spectral functions to model the ground state properties of the argon nucleus, and improve the accuracy of the cross sections at low energies by accounting for the effects of the nuclear Coulomb potential. We discuss these developments in the context of electron and neutrino interactions, by comparing updated uro predictions to experimental data from Jefferson Laboratory Hall A and MicroBooNE. The MicroBooNE CCQE-dominated data are described with the χ2 per degree of freedom of 0.7, compared with 1.0 in the local Fermi gas model. The largest improvement is observed for the angular distributions of the produced protons, where the χ2 reduces nearly by half. Being obtained using the axial form factor parametrization from MINERvA, our results indicate a consistency between the CCQE measurements in MINERvA and MicroBooNE. Published by the American Physical Society 2024

Surface integrity after hard turning using specially ground cemented carbides

In order to explore the effects of the tool geometry on the machining process, the aim of this project is to study the surface integrity generated in the 4142 alloy steel after straight turning with customized tungsten carbides cutting tools prepared with customized geometries, verifying their influence on residual stress and roughness behavior. Square cutting inserts were prepared from K10 hardmetal with PVD TiAlN coating varying edge preparation (or form factor) and nose radius. Taguchi methodology was applied for the design of experiments also varying feed rate. Results showed the major influence of feed rate and nose radius, over surface roughness, with the form factor parameter interfering at the components of cutting forces, which could also affect residual stresses and tool-lifetime due to wear.

Structure of Single-Chain Nanoparticles under Crowding Conditions: A Random Phase Approximation Approach.

The conformation of poly(methyl methacrylate) (PMMA)-based single-chain nanoparticles (SCNPs) and their corresponding linear precursors in the presence of deuterated linear PMMA in deuterated dimethylformamide (DMF) solutions has been studied by small-angle neutron scattering (SANS). The SANS profiles were analyzed in terms of a three-component random phase approximation (RPA) model. The RPA approach described well the scattering profiles in dilute and crowded solutions. Considering all the contributions of the RPA leads to an accurate estimation of the single chain form factor parameters and the Flory-Huggins interaction parameter between PMMA and DMF. The value of the latter in the dilute regime indicates that the precursors and the SCNPs are in good solvent conditions, while in crowding conditions, the polymer becomes less soluble.

Wave-packet effects: a solution for isospin anomalies in vector-meson decay

There is a long-standing anomaly in the ratio of the decay width for ψ(3770)→D0D0¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\psi (3770)\\rightarrow D^0\\overline{D^0}$$\\end{document} to that for ψ(3770)→D+D-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\psi (3770)\\rightarrow D^+D^-$$\\end{document} at the level of 9.5σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$9.5\\,\\sigma $$\\end{document}. A similar anomaly exists for the ratio of ϕ(1020)→KL0KS0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi (1020)\\rightarrow K_\ ext {L}^0K_\ ext {S}^0$$\\end{document} to ϕ(1020)→K+K-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi (1020)\\rightarrow K^+K^-$$\\end{document} at 2.1σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.1\\,\\sigma $$\\end{document}. In this study, we reassess the anomaly through the lens of a Gaussian wave-packet formalism. Our comprehensive calculations include the localization of the overlap of the wave packets near the mass thresholds and the composite nature of the initial-state vector mesons. The results align within a ∼1σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 1 \\sigma $$\\end{document} confidence level with the Particle Data Group’s central values for a physically reasonable value of the form-factor parameter, indicating a resolution to these anomalies. We also check the deviation of a wave-packet resonance from the Briet–Wigner shape and find that wide ranges of the wave-packet size are consistent with the experimental data.

Extraction of neutron density distributions from high-statistics coherent elastic neutrino-nucleus scattering data

Forthcoming fixed-target coherent elastic neutrino-nucleus scattering experiments aim at measurements with O(tonne)-scale detectors and substantially reduced systematic and statistical uncertainties. With such high quality data, the extraction of point-neutron distributions mean-square radii requires a better understanding of possible theoretical uncertainties. We quantify the impact of single-nucleon electromagnetic mean-square radii on the weak-charge form factor and compare results from weak-charge form factor parametrizations and weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors, including nucleon form factors Q-dependent terms up to order Q2. We assess as well the differences arising from results derived using weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors and a model-independent approach based solely on the assumption of spherically symmetric nuclear ground state. We demonstrate the impact of the main effects by assuming pseudo-data from a one-tonne LAr detector and find that, among the effects and under the assumptions considered in this paper, weak-charge form factor parametrizations and weak-charge form factor decompositions in terms of elastic vector proton and neutron form factors enable the extraction of the Ar40 point-neutron distribution mean-square radius with a ∼15% accuracy. With a substantial reduction of the beam-related neutron and steady-state backgrounds a ∼1% precision extraction seems feasible, using either of the two approaches.

Light front synchronization and rest frame densities of the proton: Electromagnetic densities

We clarify the physical origin and meaning of the two-dimensional relativistic densities of the light front formalism. The densities are shown to originate entirely from the use of light front time instead of instant form time, which physically corresponds to using an alternative synchronization convention. This is shown by using tilted light front coordinates, which consist of light front time and ordinary spatial coordinates, and which are also used to show that the obtained densities describe a system at rest rather than at infinite momentum. These coordinates allow all four components of the electromagnetic current density to be given clear physical meanings. We explicate the formalism for spin-half targets, obtaining charge and current densities of the proton and neutron using empirical form factor parametrizations, as well as up and down quark densities and currents. Angular modulations in the densities of transversely polarized states are explained as originating from redshifts and blueshifts due to quarks moving in different longitudinal directions.

The Collins Asymmetry in Λ Hyperon Produced SIDIS Process at Electron–Ion Colliders

We investigate Collins asymmetry in the Λ hyperon produced semi-inclusive deep inelastic scattering (SIDIS) process based on the kinematical region of Electron-ion collider in China (EicC) and Electron–ion collider (EIC) within the transverse momentum dependence (TMD) factorization framework at next-to-leading-logarithmic order. The asymmetry is contributed by the convolution of the target proton transversity distribution function and the Collins function of the final-state Λ hyperon. The TMD evolution effect of the corresponding parton distribution functions (PDFs) and fragmentation functions (FFs) is considered with the help of parametrization of the non-perturbative Sudakov form factors for the proton PDFs and Λ fragmentation functions. We apply the parametrization of the collinear proton transversity distribution function and the model results of Λ Collins function from the diquark spectator model as the inputs of the TMD evolution to numerically calculate Collins asymmetry in Λ produced SIDIS process at the kinematical configurations of EIC and EicC. It can be shown that the asymmetry is significant and can be measured at EIC and EicC. The flavor dependence of transversity distribution functions could be further constrained by studying the Λ hyperon produced SIDIS process in the future to improve our understanding of the spin structure within nucleons.

Measurement of the rare decay K + → π + μ + μ − at the NA62 experiment

The NA62 experiment at CERN reports results from the study of the flavour-changing neutral current decay K + → π + μ + μ − using a data sample recorded in 2017–2018 with a dedicated pre-scaled di-muon trigger. The sample comprises about 28k signal events with negligible background contamination, and the presented results include the most precise determination of the corresponding branching fraction and the form factor parameters.

Probing hidden spin-2 mediator of dark matter with NA64e , LDMX, NA64μ , and M3

The connection between Standard Model (SM) particles and dark matter (DM) can be introduced via a hidden spin-2 massive mediator. In the present paper we consider the simplified benchmark link between the charged lepton sector of SM and DM particles, which are considered to be hidden Dirac fermions from the dark sector. The regarding couplings are established through the dimension-five operators involving spin-2 mediator field and the energy-momentum tensors of both SM and DM sectors. We study in detail the implication of this scenario for the lepton fixed-target facilities, such as $\mathrm{NA}64e$, LDMX, $\mathrm{NA}64\ensuremath{\mu}$, and ${\mathrm{M}}^{3}$; in particular, for the specific experiment we discuss in detail, the missing energy signatures of spin-2 boson production followed by its invisible decay into stable DM pairs. Moreover, we derive the expected reaches of these experiments for the projected statistics of the leptons accumulated on the target. We also discuss the implication of both nuclear and atomic form-factor parametrizations for the differential spectra of hidden spin-2 boson emission, the total cross section of its production, and the experimental reach of the fixed-fixed-target facilities for probing hidden spin-2 DM mediator. We briefly discuss the DM relic abundance parameter space that can be probed by these experiments.

Polarization phenomena in the reaction e++e−→N+N¯+π0 in the framework of the nonresonant mechanism

The dependence of the nucleon polarization in the reaction ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}N+\overline{N}+{\ensuremath{\pi}}^{0}$ over different invariant variables is derived for the nonresonant mechanism. The nucleon polarization is expressed in terms of six invariant complex amplitudes, assuming the conservation of the hadron electromagnetic currents and the P invariance of the hadron electromagnetic interaction. An inclusive experimental setup when the proton (or the antiproton) and the pion are detected in coincidence is considered. Numerical estimations are performed for the so-called normal polarization in the energy range from threshold up to $s=16\text{ }\text{ }{\mathrm{GeV}}^{2}$, using selected parametrizations of the nucleon electromagnetic form factors in frame of a formalism derived in a previous work for the calculation of the unpolarized differential cross section.

A measurement of the K+→ π+μ+μ− decay

A sample of 2.8 × 104K+ → π+μ+μ− candidates with negligible background was collected by the NA62 experiment at the CERN SPS in 2017–2018. The model-independent branching fraction is measured to be (9.15 ± 0.08) × 10−8, a factor three more precise than previous measurements. The decay form factor is presented as a function of the squared dimuon mass. A measurement of the form factor parameters and their uncertainties is performed using a description based on Chiral Perturbation Theory at mathcal{O} (p6).

Improved theory predictions and global analysis of exclusive b → sμ+μ− processes

We provide improved Standard Model theory predictions for the exclusive rare semimuonic processes B → K(*)μ+μ− and Bs → ϕμ+μ−. Our results are based on a novel parametrization of the non-local form factors, which manifestly respects a recently developed dispersive bound. We critically compare our predictions to those obtained in the framework of QCD factorization. Our predictions provide, for the first time, parametric estimates of the systematic uncertainties due to non-local contributions. Comparing our predictions within the Standard Model to available experimental data, we find a large tension for B → Kμ+μ−. A simple model-independent analysis of potential effects beyond the Standard Model yields results compatible with other approaches, albeit with larger uncertainties for the B → K*μ+μ− and Bs → ϕμ+μ− decays. Our approach yields systematically improvable predictions, and we look forward to its application in further analyses beyond the Standard Model.

New measurement of the K+ → π+μ+μ− decay

The flavor-changing neutral current decay [Formula: see text] ([Formula: see text]) is well suited to explore the Standard Model structure. A new measurement of this decay branching fraction and form factor has been performed by the NA62 experiment at CERN based on data collected in 2017–2018. From the selected sample of 28011 [Formula: see text] event candidates with a negligible background, the decay form factor parameters [Formula: see text] and [Formula: see text], as well as the branching fraction [Formula: see text] have been measured.

144Ce - 144Pr spectrum measurement with 4π semiconductor β-spectrometer

Precision β-spectra measurement always had a great importance in some fundamental physics problems including neutrino physics. Magnetic and electrostatic spectrometers have high resolution, but at the same time usage of such kinds of equipment involves the size and cost issues. Since electron mean free path at the energy of 3 MeV (which is basically the maximum energy of a β-transition for the long-lived nuclei) does not exceed 2 g/crn2 , electron registration could be effectively performed with the solid state scintillators and semiconductors. A strong probability of backscattering from detector surface is present in case of semiconductor detectors and is dependent upon the detector material. Such problem can be solved with 4π geometry detector development, which fully covers the radioactive source and is able to register the backscattered electrons. In this work we present the newly developed technology of 4π geometry β-spectrometer based on two semiconductor detectors. This spectrometer was used for measurement of the 144Ce - 144Pr spectrum, that is the perspective anti-neutrino source due to endpoint energy at 3 MeV and can be used for the sterile neutrino search experiments. The form-factor parameters that were obtained are: C(W) = 1 + (-0.02877 ± 0.00028)W + (-0.11722 ± 0.00297)W-1. The measurement accuracy was sufficiently enhanced with respect to the previous results.

The overline{B} \u2192 \u03c0 form factors from QCD and their impact on |Vub|

We revisit light-cone sum rules with pion distribution amplitudes to determine the full set of local overline{B} → π form factors. To this end, we determine all duality threshold parameters from a Bayesian fit for the first time. Our results, obtained at small momentum transfer q2, are extrapolated to large q2 where they agree with precise lattice QCD results. We find that a modification to the commonly used BCL parametrization is crucial to interpolate the scalar form factor between the two q2 regions. We provide numerical results for the form factor parameters — including their covariance — based on simultaneous fit of all three form factors to both the sum rule and lattice QCD results. Our predictions for the form factors agree well with measurements of the q2 spectrum of the semileptonic decay {overline{B}}^0to {pi}^{+}{mathrm{ell}}^{-}{overline{nu}}_{mathrm{ell}} . From the world average of the latter we obtain |Vub| = (3.77 ± 0.15) · 10−3, which is in agreement with the most recent inclusive determination at the 1 σ level.

Revisiting fits to B0→D*−ℓ+νℓ to measure |Vcb| with novel methods and preliminary LQCD data at nonzero recoil

We present a study of fits to exclusive ${B}^{0}\ensuremath{\rightarrow}{D}^{*\ensuremath{-}}{\ensuremath{\ell}}^{+}{\ensuremath{\nu}}_{\ensuremath{\ell}}$ measurements for the determination of the Cabibbo-Kobayashi-Maskawa matrix element magnitude $|{V}_{cb}|$, based on the most recent Belle untagged measurement. Results are obtained with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parametrizations, with and without the inclusion of preliminary lattice QCD (LQCD) measurements of form factors at nonzero hadronic recoil from the JLQCD Collaboration. The CLN and BGL fits are also studied in different scenarios with reduced theoretical assumptions and at higher-order expansions, respectively. To avoid bias from high systematic error correlations, we employ a novel technique in the field of $B$-physics phenomenology with a toy Monte Carlo method using a Cholesky decomposition of the covariance matrix. Using additional input from lattice QCD calculations of form factors at nonzero recoil, in collaboration with JLQCD, allows for well-defined fit results with reduced model dependence in CLN and BGL. The results obtained are consistent between different configurations, ultimately providing a method for a more model-independent exclusive measurement of $|{V}_{cb}|$. Using preliminary LQCD inputs and assuming a value of $\mathcal{F}(1)=0.904\ifmmode\pm\else\textpm\fi{}0.012$, we find $|{V}_{cb}|=(38.48\ifmmode\pm\else\textpm\fi{}0.32\ifmmode\pm\else\textpm\fi{}0.97\ifmmode\pm\else\textpm\fi{}0.46)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in BGL(2,2,2) and $(38.42\ifmmode\pm\else\textpm\fi{}0.35\ifmmode\pm\else\textpm\fi{}1.05\ifmmode\pm\else\textpm\fi{}0.46)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ in CLNnoHQS, where the errors are statistical, systematic, and related to $\mathcal{F}(1)$, respectively.

Polarization Effects in the Reaction d+eˉ → d+eˉ

The differential cross section and polarization observables for the elastic reaction induced by deuteron scattering off electrons at rest, are calculated in the one-photon-exchange approximation. The following polarization observables were calculated: 1- the analyzing powers (asymmetries) due to the tensor polarization of the deuteron beam, 2 - the spin correlation coefficients caused by the arbitrarily polarized electron target and the vector polarized deuteron beam, 3 - the coefficients of the polarization transfer from the arbitrarily polarized target electron to the recoil electrons. The differential cross section and polarization observables have been expressed in terms of the deuteron electromagnetic form factors: (charge monopole), (magnetic dipole) and (charge quadrupole). Numerical estimations are given for the analyzing powers (asymmetries) due to the tensor polarization of the deuteron beam. They are calculated as functions of the deuteron beam energy for some values of the scattering angle (the angle between the deuteron beam and the recoil electron momenta). For the numerical calculation we use the existing phenomenological parametrization of the deuteron electromagnetic form factors. It turns out that the analyzing powers (asymmetries) are increasing with the growth of the deuteron beam energy and they have appreciable sensitivity to the value of the scattering angle. The specific interest of this reaction is to investigate the possibility to use this reaction for the measurement of the polarization of the high energy deuteron beams.

Measurement of |Vcb| with Bs0→Ds(*)−μ+νμ decays

The element $|V_{cb}|$ of the Cabibbo-Kobayashi-Maskawa matrix is measured using semileptonic $B_s^0$ decays produced in proton-proton collision data collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. Rates of $B_s^0 \to D_s^{-} \mu^+ \nu_{\mu}$ and $B_s^0 \to D_s^{*-} \mu^+ \nu_{\mu}$ decays are analyzed using hadronic form-factor parametrizations derived either by Caprini, Lellouch and Neubert (CLN) or by Boyd, Grinstein and Lebed (BGL). The measured values of $|V_{cb}|$ are ${(41.4 \pm 0.6 \pm 0.9 \pm 1.2)\times 10^{-3}}$ and ${(42.3 \pm 0.8 \pm 0.9 \pm 1.2)\times 10^{-3}}$ in the CLN and BGL parametrization, respectively. The first uncertainty is statistical, the second systematic, and the third is due to the external inputs used in the measurement. These results are in agreement with those obtained from decays of $B^+$ and $B^0$ mesons. They are the first determinations of $|V_{cb}|$ at a hadron-collider experiment and the first using $B_s^0$ meson decays.