Measurement Of Form Factor Research Articles

Improved measurement of the semileptonic decay Ds+→K0e+νe

Analyzing e+e− collision data corresponding to an integrated luminosity of 7.33 fb−1 collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we measure the branching fraction of the semileptonic decay Ds+→K0e+νe to be (2.98±0.23stat±0.12syst)×10−3. Based on fit to the partial decay rates in various q2 intervals, the product value of Ds+→K0 hadronic form factor and Cabibbo-Kobayashi-Maskawa element is measured to be f+K0(0)|Vcd|=0.143±0.011stat±0.003syst. With |Vcd|=0.22486±0.00067 as an input, the hadronic form factor is evaluated to be f+K0(0)=0.636±0.049stat±0.013syst. The branching fraction and form factor measurements are factors of 1.6 and 1.7 more precise than the previous world averages, respectively. Published by the American Physical Society 2024

Longitudinal kinematic imbalances in neutrino and antineutrino interactions for improved measurements of neutrino energy and the axial vector form factor

Current and future accelerator neutrino oscillation experiments require an improved understanding of nuclear effects in neutrino-nucleus interactions. One important systematic uncertainty is introduced by the collective impact of nuclear effects which bias the reconstruction of the neutrino energy, such as the nuclear removal energy. In this manuscript, we introduce a novel observable for accelerator neutrino oscillation experiments, the visible longitudinal momentum imbalance, reconstructed in charged-current quasielastic interactions from the outgoing charged lepton and nucleon. We demonstrate it to be minimally dependent on the neutrino energy and sensitive to sources of bias in neutrino energy reconstruction. Furthermore, we show how the use of the longitudinal imbalance in antineutrino interactions in a target containing hydrogen allows for an improved, high-purity selection of the interactions on hydrogen. This approach offers the potential for precise measurements of the nuclear axial vector form factor as well as of the antineutrino flux. Published by the American Physical Society 2024

Neutron Skins: Weak Elastic Scattering and Neutron Stars

The recently completed PREX-2 campaign measured the density distribution of neutrons in the lead nucleus as a function of momentum transfer (the form factor), confirmed a relatively large extent of the neutrons beyond the protons in the nucleus (the neutron skin), and provided a precise determination of the density of protons and neutrons at the center of a heavy nucleus. In turn, the measured form factor can be related to various nuclear and neutron star properties. The NICER X-ray telescope has inferred the masses and radii of some X-ray pulsars (neutron stars), although complications arise when determining these quantities independently. Further improvements in NICER have enabled simultaneous mass–radius determinations that had not previously been possible. During the next decade, measurements in astrophysics, gravitational-wave astronomy, and nuclear physics are expected to provide a wealth of more precise data. In this review, we present an overview of the current state of neutron skin measurements and offer insights into prospects for the future.

Novel Measurement of the Neutron Magnetic Form Factor from A=3 Mirror Nuclei.

The electromagnetic form factors of the proton and neutron encode information on the spatial structure of their charge and magnetization distributions. While measurements of the proton are relatively straightforward, the lack of a free neutron target makes measurements of the neutron's electromagnetic structure more challenging and more sensitive to experimental or model-dependent uncertainties. Various experiments have attempted to extract the neutron form factors from scattering from the neutron in deuterium, with different techniques providing different, and sometimes large, systematic uncertainties. We present results from a novel measurement of the neutron magnetic form factor using quasielastic scattering from the mirror nuclei ^{3}H and ^{3}He, where the nuclear effects are larger than for deuterium but expected to largely cancel in the cross-section ratios. We extracted values of the neutron magnetic form factor for low-to-modest momentum transfer, 0.6<Q^{2}<2.9 GeV^{2}, where existing measurements give inconsistent results. The precision and Q^{2} range of these data allow for a better understanding of the current world's data and suggest a path toward further improvement of our overall understanding of the neutron's magnetic form factor.

Recent results of baryon EM form factors at BESIII

Precise experimental measurements of the baryon form factors are a test-bed for understanding the baryon’s properties and dynamical behavior emerge from QCD. With high statistics, the cross section of e+e− → pp and e+e− → nn are both measured with the highest precision in a wide q2 range. The oscillation behavior on the proton and neutron effective form factor is updated with SND result. With the ISR technique, the form factor measurement can reach as low as the mass threshold of pp or nn. Analyticity of nucleon form factors is discussed. Moreover, new results about the hyperon (Λ, Λc, Σ, Ω, ∆) form factors are presented in this talk. Some similar behaviors appear on the hyperon form factors which will help to understand the internal structure or interactions inside of the baryon. The complete determination of EMFFs of Λ and Σ has been carried on and provides a new insight of EMFFs in time-like region.

Studies of Time-like Electromagnetic Structure of Baryons with HADES

We present results of studies of Dalitz decays of baryon resonances (R→Ne+e−) in proton-proton (pp) and pion-proton (πp) collisions performed by the HADES collaboration. They provided the first measurement of electromag netic transition form factors of baryons in the time-like region and contribute to the understanding of the photon-baryon coupling and the role of Vector Dom inance Model in a baryonic sector. We discuss also implications of the results to the understanding of the emissivity of dense and hot QCD matter created in heavy-ion collisions and the role played by the in-medium modification of the ρ meson. Further prospects for future studies with pion beams at GSI with HADES are given in the outlook.

Small Angle Initial State Radiation Analysis of the Pion Form Factor at BESIII

The time-like pion form factor (FF), i.e. the cross section of the process e+e− → π+π−, is presently a matter of intense discussion within the particle physics community. The e+e− → π+π− process is the largest contributor to the hadronic vacuum polarization (HVP) correction in the Standard Model prediction of the muon anomalous magnetic moment (aμ). Recent lattice QCD evaluations of the HVP, as well as a new measurement of the pion FF by the CMD-3 collaboration, have hinted at possible shortcomings in previous measurements, thus preventing an unambiguous interpretation of the latest experimental value of aμ. An intense effort is ongoing to provide new experimental insights into the pion FF, and the BESIII collaboration aims to contribute with a new measurement of world-leading precision. In this work, preliminary studies towards such a measurement are presented.

Calculation of X-ray attenuation coefficients for normal and cancerous breast tissues

The study was carried out by numerical integration based on the diffraction properties and elemental composition. The elemental compositions of breast tissues in the literature were tested. The photon attenuation coefficients calculated using the recent elemental composition were found within 0.2˗16% for adipose tissue and within 0.04˗17% for glandular tissue with the experimental reference data. The attenuation coefficients of cancerous breast tissue calculated according to the elemental content previously measured in breast cancer patients were found within 0˗17% with experimental data in the literature. The attenuation coefficients are of great interest to medical research. To calculate realistic attenuation coefficients, the characteristic coherent scatter, which is most intense at small angles, must be considered. For this reason, experimentally measured form factor data were reviewed, and the most compatible one with the theoretical form factor data produced in this study was used at low momentum transfer x (0 < x ≤ 8 nm−1). The differential linear coherent scattering distributions were calculated for an energy value of 17.44 keV and compared with their experimental counterparts.

Study pion distribution amplitudes from the electromagnetic form factor by data-driven dispersion relation

We study the pion electromagnetic form factor in the modulus squared dispersion relation, and do the model independent extraction of the chiral mass embedded in the sub-leading twist light-cone distribution amplitude. The motivation of this work is the recent measurement of timelike form factor in the resonant regions, which makes up the piece lacking solid QCD-based calculation. With the perturbative QCD calculation up to next-to-leading-order of strong coupling and twist four level of meson distribution amplitudes, we obtain the chiral mass of pion meson as m_0^pi (1 , textrm{GeV}) = 1.31^{+0.27}_{-0.30} , textrm{GeV}. Due to the chiral enhancement contribution from the sub-leading twist distribution amplitudes in the perturbative QCD calculation, we can not extract the lowest Gegenbauer moments of pion from the study of electromagnetic form factor. This problem could be settled down with the foresee Belle-II and BESIII measurement of the transition form factor especially in the large momentum transfers regions.

Measurement of the axial vector form factor from antineutrino–proton scattering

Scattering of high energy particles from nucleons probes their structure, as was done in the experiments that established the non-zero size of the proton using electron beams1. The use of charged leptons as scattering probes enables measuring the distribution of electric charges, which is encoded in the vector form factors of the nucleon2. Scattering weakly interacting neutrinos gives the opportunity to measure both vector and axial vector form factors of the nucleon, providing an additional, complementary probe of their structure. The nucleon transition axial form factor, FA, can be measured from neutrino scattering from free nucleons, νμn → μ−p and {bar{nu }}_{mu }pto {mu }^{+}n, as a function of the negative four-momentum transfer squared (Q2). Up to now, FA(Q2) has been extracted from the bound nucleons in neutrino–deuterium scattering3–9, which requires uncertain nuclear corrections10. Here we report the first high-statistics measurement, to our knowledge, of the {bar{nu }}_{mu },pto {mu }^{+}n cross-section from the hydrogen atom, using the plastic scintillator target of the MINERvA11 experiment, extracting FA from free proton targets and measuring the nucleon axial charge radius, rA, to be 0.73 ± 0.17 fm. The antineutrino–hydrogen scattering presented here can access the axial form factor without the need for nuclear theory corrections, and enables direct comparisons with the increasingly precise lattice quantum chromodynamics computations12–15. Finally, the tools developed for this analysis and the result presented are substantial advancements in our capabilities to understand the nucleon structure in the weak sector, and also help the current and future neutrino oscillation experiments16–20 to better constrain neutrino interaction models.

Hazma meets HERWIG4DM: precision gamma-ray, neutrino, and positron spectra for light dark matter

We present a new open-source package, Hazma 2, that computes accurate spectra relevant for indirect dark matter searches for photon, neutrino, and positron production from vector-mediated dark matter annihilation and for spin-one dark matter decay. The tool bridges across the regimes of validity of two state of the art codes: Hazma 1, which provides an accurate description below hadronic resonances up to center-of-mass energies around 250 MeV, and Herwig4DM, which is based on vector meson dominance and measured form factors, and accurate well into the few GeV range. The applicability of the combined code extends to approximately 1.5 GeV, above which the number of final state hadrons off of which we individually compute the photon, neutrino, and positron yield grows exceedingly rapidly. We provide example branching ratios, particle spectra and conservative observational constraints from existing gamma-ray data for the well-motivated cases of decaying dark photon dark matter and vector-mediated fermionic dark matter annihilation. Finally, we compare our results to other existing codes at the boundaries of their respective ranges of applicability. Hazma 2 is freely available on GitHub at https://github.com/LoganAMorrison/Hazma.

Exclusive lepton pair production at the electron–ion collider

The two-photon exclusive production of lepton pairs at the Electron–Ion Collider will open interesting research directions thanks to a very high luminosity and clean experimental conditions. A survey of the scientific potential of such studies is reported. In particular, we consider unique measurements of the proton elastic electromagnetic form-factors and a possibility of studying the anomalous electromagnetic dipole moments of tau leptons.

Gas electron tracking detector for beta decay experiments

For identification and 3D-tracking of low-energy electrons a new type of gas-based detector was designed that minimizes scattering and energy loss. The current version of the detector is a combination of a plastic scintillator, serving as a trigger source and energy detector, and a hexagonally structured multi-wire drift chamber (MWDC), filled with a mixture of helium and isobutane gas. The drift time information is used to track particles in the plane perpendicular to the wires, while a charge division technique provides spatial information along the wires. The gas tracker was successfully used in the miniBETA project as a beta spectrometer for a measurement of the weak magnetism form factor in nuclear beta decay. The precision of the three-dimensional electron tracking, in combination with low-mass, low-Z materials and identification of backscattering from scintillator, facilitated a reduction of the main systematics effects. The results originate from performance studies with cosmic muons and low-energy electrons (<2 MeV) conducted for several pressures (300–700 mbar) and isobutane content in the gas mixture (10–50%). At certain conditions, a spatial resolution better than 0.5 mm was obtained in the plane perpendicular to the wires, while resolutions of about 6 mm were achieved along wires. Thanks to precise tracking information, it is possible to eliminate electrons and other particles not originating from the desired decay with high efficiency. Additionally, using the coincidence between MWDC and scintillator, background from gamma emission typically accompanying radioactive decays, was highly suppressed. An overview of different event topologies is presented together with the tracker’s ability to correctly recognize them. The analysis is supported by Monte Carlo simulations using Geant4 and Garfield++ packages. Finally, the preliminary results from the 114In spectrum study are presented.

Baryonic form factors of the pion and kaon in a chiral quark model

The baryonic form factor of charged pions is studied in detail in the Nambu--Jona-Lasinio model with constituent quarks, where the spontaneously broken chiral symmetry is the key dynamical ingredient guaranteeing the would-be Goldstone boson nature of the pseudoscalar mesons octet. In general, this form factor arises when the isospin symmetry is broken, which is the case if the $u$ and $d$ quark masses are split, as in the real world, or if the electromagnetic effects were taken into account. We obtain estimates for this basic property of the pion resulting from the quark mass splitting for a range of model parameters, and importantly, for different pion masses, going up to the values used in lattice QCD. We find very stable model results, with the mean square radius of $\pi^+$ in the range $(0.05-0.07~{\rm fm})^2$. From charge conjugation, the baryonic form factor of $\pi^+$ and $\pi^-$ are equal and opposite. We also obtain the transverse-coordinate, relativistically invariant baryonic density of the charged pion. In $\pi^+$, the inner region carries a negative, and the outside -- a positive baryon number density, both cancelling to zero, as obviously the pion carries no net baryon charge. We also carry out an analogous analysis for the kaon, where the effect is much larger due to the sizable $s$ and $u/d$ quark mass splitting. We discuss the prospects of lattice QCD measurements of the baryonic form factors of charged pions and kaons.

Electromagnetic Structure of the Neutron from Annihilation Reactions

The investigation of the fundamental properties of the nucleon is one of the most important topics in the modern hadron physics. Its internal structure and dynamics can be studied through the measurement of electromagnetic form factors which represent the simplest structure observables and serve as a test ground for our understanding of the strong interaction. Since the first attempt to measure the time-like form factors of the neutron, only four experiments published results on its structure from annihilation reactions. Due to the lack of statistics and experimental challenges, no individual determination of the form factors of the neutron has been possible so far. Modern developments of electron-positron colliders and the associated detectors allow to measure the effective FF of the neutron with the process e+e−→nn¯ with unprecedented precision at the BESIII experiment, which is based at the BEPCII collider in Beijing, China. In this report, we review the published results of the form factors on the neutron in the time-like regime, describe the experimental setup, and discuss their impact on our understanding of the strong interaction. Future works at BESIII will help to improve the precision of the neutron FFs and, combined with theoretical progress in this field, help to illuminate the properties of the neutron structure.

Time-like Proton Form Factors with Initial State Radiation Technique

Electromagnetic form factors are fundamental quantities describing the internal structure of hadrons. They can be measured with scattering processes in the space-like region and annihilation processes in the time-like region. The two regions are connected by crossing symmetry. The measurements of the proton electromagnetic form factors in the time-like region using the initial state radiation technique are reviewed. Recent experimental studies have shown that initial state radiation processes at high luminosity electron-positron colliders can be effectively used to probe the electromagnetic structure of hadrons. The BABAR experiment at the B-factory PEP-II in Stanford and the BESIII experiment at BEPCII (an electron positron collider in the τ-charm mass region) in Beijing have measured the time-like form factors of the proton using the initial state radiation process e+e−→pp¯γ. The two kinematical regions where the photon is emitted from the initial state at small and large polar angles have been investigated. In the first case, the photon is in the region not covered by the detector acceptance and is not detected. The Born cross section and the proton effective form factor have been measured over a wide and continuous range of the the momentum transfer squared q2 from the threshold up to 42 (GeV/c)2. The ratio of electric and magnetic form factors of the proton has been also determined. In this report, the theoretical aspect and the experimental studies of the initial state radiation process e+e−→pp¯γ are described. The measurements of the Born cross section and the proton form factors obtained in these analyses near the threshold region and in the relatively large q2 region are examined. The experimental results are compared to the predictions from theory and models. Their impact on our understanding of the nucleon structure is discussed.

Elucidating the ρ-meson’s role as intermediate resonance in the time-like electromagnetic pion form factor

Motivated by the planned measurements of the time-like electromagnetic proton form factors an exploratory study of the time-like electromagnetic pion form factor is presented in a formalism which describes mesons as Poincaré-invariant bound states. In the respective quark interaction kernel, beyond the gluon-intermediated interactions for valence-type quarks, non-valence effects are included by allowing the pions to couple back in a self-consistent manner to the quarks. Consequently, the opening of the dominant ρ decay channel, ρ → ππ, and the presence of a multi-particle branch cut, setting in when the two-pion threshold is crossed, are included consistently, first in the correspondingly calculated quark-photon vertex, and then consequently in the time-like electromagnetic pion form factor. The obtained results are in agreement with the available experimental data and provide further evidence for the effcacy of a vector-meson dominance model. Effects of going beyond the here employed isospin-symmetric limit are discussed. Last but not least, an outlook is provided on how to include in Poincaré-covariant Faddeev approaches the effects of intermediate resonances in the calculation of baryon properties.

The internal structure of the neutron: highlights from BESIII

The BESIII Collaboration has recently published a new precise measurement of the time-like neutron form factor (FF) [1] . In the light of the remarkable accuracy and of the wideness of the explored kinematical range these data represent an unprecedented tool for highlighting and studying specific features of the neutron FF.

K0 and K+ -meson electromagnetic form factors: A nonperturbative relativistic quark model versus experimental, perturbative, and lattice quantum-chromodynamics results

It has been previously shown that a particular nonperturbative constituent-quark model of hadrons describes experimental measurements of electromagnetic form factors of light charged mesons through a small number of common phenomenological parameters, matching at the same time the Quantum-Chromodynamics (QCD) asymptotics for the pi-meson form factor at large momentum transfer. Here we start with the determination of the K0 electromagnetic form factor in this approach. Precise measurement of the K0 charge radius makes it possible to constrain model parameters with high accuracy. Then, with all parameters fixed, we revisit the K+ form factor and find that it matches experimental measurements in the infrared, lattice results at moderate momentum transfer and the perturbative QCD asymptotics in the ultraviolet. In this way we obtain a narrow constraint on the K+ charge radius, <r_K+^2> = 0.403 +0.007 -0.006 fm^2, and extend the successful infrared-ultraviolet connection from pi to K mesons.

Nucleon mass radii and distribution: Holographic QCD, lattice QCD, and GlueX data

We briefly review and expand our recent analysis for all three invariant $A$, $B$, $D$ gravitational form factors of the nucleon in holographic QCD. They compare well to the gluonic gravitational form factors recently measured using lattice QCD simulations. The holographic $A$-term is fixed by the tensor $T={2}^{++}$ (graviton) Regge trajectory, and the $D$-term by the difference between the tensor $T={2}^{++}$ (graviton) and scalar $S={0}^{++}$ (dilaton) Regge trajectories. The $B$-term is null in the absence of a tensor coupling to a Dirac fermion in bulk. A first measurement of the tensor form factor $A$-term is already accessible using the current GlueX data, and therefore the tensor gluonic mass radius, pressure, and shear inside the proton, thanks to holography. The holographic $A$-term and $D$-term can be expressed exactly in terms of harmonic numbers. The tensor mass radius from the holographic threshold is found to be $⟨{r}_{GT}^{2}⟩\ensuremath{\approx}(0.57--0.60\text{ }\text{ }\mathrm{fm}{)}^{2}$, in agreement with $⟨{r}_{GT}^{2}⟩\ensuremath{\approx}(0.62\text{ }\text{ }\mathrm{fm}{)}^{2}$ as extracted from the overall numerical lattice data, and empirical GlueX data. The scalar mass radius is found to be slightly larger $⟨{r}_{GS}^{2}⟩\ensuremath{\approx}(0.7\text{ }\text{ }\mathrm{fm}{)}^{2}$.