Time-like Electromagnetic Form Factors Research Articles

Toy model to understand the oscillatory behavior in timelike nucleon form factors

To understand the oscillatory behavior exhibited in the timelike electromagnetic form factors of nucleons, we propose a toy model based on the Jost function of the $N\bar N$ pair into the timelike form factors with the help of the distorted-wave Born approximation. By constructing a simple square-well potential reflecting the final-state interaction of $N\bar N$, we naturally represent the damped oscillatory phenomenon in the timelike electromagnetic form factors of nucleons. Especially, our study reveals that the ``period" of the oscillation is approximately determined by the Yukawa interaction range $1/m_\pi$. Other possible potentials are also discussed. The threshold enhancements of the cross sections for $e^+e^-\to n\bar n$, $\Lambda\bar\Lambda$, and $\Lambda_c\bar\Lambda_c$ can also be understand within this scenario.

Timelike electromagnetic kaon form factor

We compute the electromagnetic charged kaon form factor in the timelike region by employing a Poincar\'e covariant formalism of the Bethe-Salpeter equation to study quark-antiquark bound states in conjunction with the Schwinger-Dyson equation for the quark propagator. Following a recent kindred calculation of the timelike electromagnetic pion form factor, we include the most relevant intermediate composite particles permitted by their quantum numbers in the interaction kernel to allow for a decay mechanism for the resonances involved. This term augments the usual gluon mediated interaction between quarks. For a sufficiently low energy timelike probing photon, the electromagnetic form factor is saturated by the $\ensuremath{\rho}(770)$ and $\ensuremath{\phi}(1020)$ resonances. We assume $SU(2)$ isospin symmetry throughout. Our results for the absolute value squared of the electromagnetic form factor agree qualitatively rather well and quantitatively moderately so with available experimental data.

The rho meson timelike electromagnetic form factors in kT factorization approach

In this paper, we calculate the [Formula: see text]-meson timelike electromagnetic form factors by employing the [Formula: see text] factorization approach. The theoretical ratio for the moduli of three helicity amplitudes and total cross-section for the annihilation/production process [Formula: see text] are analyzed at [Formula: see text], where the BaBar experiment was done. The results for the moduli of the three helicity amplitudes [Formula: see text] are predicted between [Formula: see text] and [Formula: see text], and the three form factors [Formula: see text] of rho meson are considered.

Predicted [formula omitted] and [formula omitted] decay modes of the charmoniumlike Y(4230)

In this work, we predict the light hadronic decay channels Y(4230)→ΛΛ¯ and Ξ−Ξ¯+ when treating the Y(4230) as a vector charmonium state. By the hadronic loop mechanism, the branching ratios of the Y(4230)→ΛΛ¯ and Ξ−Ξ¯+ processes are calculated. In addition, we discuss the possibility of carrying out the search for the signal of the Y(4230) through ΛΛ¯ and Ξ−Ξ¯+ channels from the e+e− annihilation. Assuming Y(4230) exist in ΛΛ¯ and Ξ−Ξ¯+ channel, we also present the time-like electromagnetic form factors (EMFFs) at s=mY(4230).

Measurement of the Neutron Timelike Electromagnetic form Factors at the VEPP-2000 e+e– Collider with the SND Detector

Measurement of the Neutron Timelike Electromagnetic form Factors at the VEPP-2000 e+e– Collider with the SND Detector

Proton Electromagnetic Form Factors in the Time-like Region through the Scan Technique

For over 100 y, scientists have investigated the properties of the proton, which is one of the most abundant components of visible matter in the universe. Nevertheless, researchers do not fully understand many details about its internal structure and dynamics. Time-like electromagnetic form factors are some of the observable quantities that can help us achieve a deeper understanding. In this review article, we present an overview of the current experimental status in this field, consisting of measurements of the time-like reactions e+e−→pp¯ and pp¯→e+e− and future measurements of pp¯→μ+μ−. The focus is put on recent high-precision results of the reaction e+e−→pp¯ that have been obtained after analyzing 688.5 pb−1 of data taken at the BESIII experiment. They are compared to and put into perspective with results from previous measurements in this channel. We discuss the channels pp¯→e+e− and pp¯→μ+μ− in terms of the few existing, as well as future measurements, which the PANDA experiment will perform. Finally, we review several new theoretical models and phenomenological approaches inspired by the BESIII high-precision results and then discuss their implications for a deeper understanding of the proton’s structure and inner dynamics.

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.

Elucidating the effect of intermediate resonances in the quark interaction kernel on the timelike electromagnetic pion form factor

An exploratory study of the timelike pion electromagnetic form factor in a Poincar\'e-covariant bound state formalism in the isospin symmetric limit is presented. Starting from a quark interaction kernel representing gluon-intermediated interactions for valence-type quarks, nonvalence effects are included by introducing pions as explicit degrees of freedom. The two most important qualitative aspects are, in view of the presented study, the opening of the dominant $\ensuremath{\rho}$-meson decay channel and the presence of a multiparticle branch cut setting in which the two-pion threshold is crossed. Based on a recent respective computation of the quark-photon vertex, the pion electromagnetic form factor for spacelike and timelike kinematics is calculated. The obtained results for its absolute value and its phase compare favorably to the available experimental data, and they are analyzed in detail by comparing them to the expectations based on an isospin-symmetric version of a vector-meson dominance model.

Measurements of Σ+ and Σ− time-like electromagnetic form factors for center-of-mass energies from 2.3864 to 3.0200 GeV

The Born cross sections of the e+e−→Σ+Σ¯− and e+e−→Σ−Σ¯+ processes are determined for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. The cross section lineshapes can be described properly by a pQCD function and the resulting ratio of effective form factors for the Σ+ and Σ− is consistent with 3. In addition, ratios of the Σ+ electric and magnetic form factors, |GE/GM|, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed new features of the Σ± form factors require more theoretical discussions for the hyperons.

Feasibility studies for the measurement of time-like proton electromagnetic form factors from bar{p}p rightarrow mu ^+mu ^- at overline{text {P}}text {ANDA} at FAIR

This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, |G_{E}| and |G_{M}|, using the bar{p} p rightarrow mu ^{+} mu ^{-} reaction at overline{text {P}}text {ANDA} (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at overline{text {P}}text {ANDA}, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is bar{p} p rightarrow pi ^{+} pi ^{-}, due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.

Studying time-like electromagnetic baryonic transitions with HADES in pion induced reactions

A dedicated programme aiming at studying electromagnetic baryonic transitions in the time-like region has started at GSI using the pion beam and the High Acceptance Di-Electron Spectrometer (HADES) set-up. A pioneering experiment has been carried out in the second resonance region, at a center-of-mass energy of 1.49 GeV, using carbon and polyethylene targets, allowing for an analysis of the inclusivee+e-production and of the exclusive quasi-freeπ-p→ne+e-reaction, in complement to hadronic channels. Predictions for the Dalitz decay of N(1520) and N(1535) based on real photon couplings strongly underestimate thee+e-yield at invariant masses larger than 300 MeV/c2, which signals effects of time-like baryon transition form factors, in qualitative agreement with the Vector Dominance Models (VDM). A quantitative description of the observede+e-yield is achieved by taking into account the contribution from off-shellρs. The latter was provided by the preliminary results of a Bonn-Gatchina Partial Wave Analysis of the two-pion production channels, which were measured simultaneously in our experiment. A good agreement is also obtained using a covariant model for the time-like electromagnetic form factors for the N-N(1520) transition. The angular distributions for thee+e-production contain additional selective information on the spin structure of the different transitions. The measurements with the pion beam will be extended in future in the third resonance region. Hyperon Dalitz decay studies in proton induced reactions are also foreseen.

Complete Measurement of the Λ Electromagnetic Form Factors

The exclusive process e^{+}e^{-}→ΛΛ[over ¯], with Λ→pπ^{-} and Λ[over ¯]→p[over ¯]π^{+}, has been studied at sqrt[s]=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, G_{E} and G_{M}. A data sample, corresponding to an integrated luminosity of 66.9 pb^{-1}, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|G_{E}/G_{M}| and, for the first time for any baryon, the relative phase ΔΦ=Φ_{E}-Φ_{M}. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter α_{Λ}=0.750±0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be σ=118.7±5.3(stat)±5.1(syst) pb, which corresponds to an effective form factor of |G|=0.123±0.003(stat)±0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.

Measurement of e+e−→K+K− cross section at s=2.00 – 3.08 GeV

The cross section of the process $e^{+} e^{-} \rightarrow K^{+} K^{-}$ is measured at a number of center-of-mass energies $\sqrt{s}$ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of $M=2239.2 \pm 7.1 \pm 11.3$~and a width of $\Gamma=139.8\pm12.3\pm20.6$ MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.

Baryon Form Factors at BESIII

In this talk I present recent progress on the studies of baryon form factors at BESIII, including the measurements of the time-like proton electromagnetic form factor via e+e−→ pp̅ in the center-mass-system energy region 2.0 −3.08 GeV, as well as the electromagnetic form factors of Λ and Λc, respectively. These results are followed by a short discussion about the prospects of the BESIII program in this area.

Two-photon exchange effects in e+e−→π+π− and timelike pion electromagnetic form factor

The two-photon-exchange (TPE) effects in the process $e^+e^- \rightarrow \pi^+\pi^-$ at large momentum transfer are discussed within the perturbative QCD (pQCD). The contributions from the twist-2 and twist-3 distribution amplitudes (DAs) of pion are considered in the estimation. Different with the results under the one-photon-exchange (OPE) approximation, the TPE effects result in an asymmetry of the differential cross section on the scattering angle. The precise measurement of this asymmetry by the further experiment is an precise test of pQCD at large momentum transfer. The time-like electromagnetic form factor of pion at the leading order of pQCD is re-discussed and the comparison of our results with those in the references are presented.

Fourth dimension of the nucleon structure: Spacetime analysis of the timelike electromagnetic proton form factors

As well known, spacelike proton form factors expressed in the Breit frame may be interpreted as the Fourier transform of static space distributions of electric charge and current. In particular, the electric form factor is simply the Fourier transform of the charge distribution $F(q)=\int e^{i\vec q \cdot \vec r} \rho(r)d^3r$. We don't have an intuitive interpretation of the same level of simplicity for the proton timelike form factor appearing in the reactions $e^+e^-\leftrightarrow \bar{p}p$. However, one may suggest that in the center of mass (CM) frame, where $q_\mu x^\mu =qt$, a timelike electric form factor is the Fourier transform $F(q) =\int e^{iqt} R(t)dt$ of a function $R(t)$ expressing how the electric properties of the forming (or annihilating) proton-antiproton pair evolve in time. Here we analyze in depth this idea, show that the functions $\rho(r)$ and $R(t)$ can be formally written as the time and space integrals of a unique correlation function depending on both time and space coordinates.

Measurement of the proton and kaon time-like electromagnetic form factors at high energy with the BaBar detector

We have used ISR technique to measure the proton magnetic form factor in the energy region from 3.0 to 6.5 GeV and charged kaon form factor in the range from 2.6 to 7.5 GeV. The proton data clearly indicate that the difference between values of time- and space-like magnetic form factors decreases with increase of energy. The kaon form factor decreases with energy faster than 1/E2, approaching the asymptotic pQCD predictions.

ηandη′Physics at MAMI

The Crystal Ball/TAPS setup at MAMI is ideally suited to detect neutral and electromagnetic decays of the η and η′ mesons. In this contribution recent results on η and η′ decays from the Crystal Ball/TAPS experiment at MAMI are presented. These are the accurate measruement of η′ photoproduction cross-sections in the threshold region, the determination of the timelike electromagnetic transition form factors, and a test of low-energy QCD with the η → π 0 γγ decay. Finally, further perspectives are discussed.

RESULTS AND PERSPECTIVES ON NUCLEON FORM FACTORS FROM SND AND CMD-3

During years 2011 and 2012 data taking runs have been carried out at VEPP-2000 e+e- collider to measure the production of the nucleon-antinucleon pairs [Formula: see text] near threshold. In this talk the preliminary results on the nucleon timelike electromagnetic form factors (FF) and the |GE/GM| ratio are presented.

Time-like electromagnetic form factors at PANDA

This proceeding is a summary based on the talk given at the 33rd international school of nuclear physics, Erice, Italy. An introduction following the historical development of a theoretical treatment of nucleon electromagnetic form factors will be given. A feasibility study on the time-like electromagnetic form factor at PANDA is presented based on a Monte Carlo simulation. Some recent progress on electromagnetic processes at PANDA is also given.