Form Factor Model Research Articles

OnD→ππ and $$K\bar K$$ decays

We have analysed the recent data onD→ππ and\(K\bar K\) decays from ARGUS, CLEO and E691. (i) We find that Bauer, Stech and Wirbel (BSW) model does fairly well in explaining all data if we assume that final state interactions simply rotate the amplitudes in the complex plane. However, to get a good fit one needs to raiseD→K transition amplitudes by (5–10)% over the BSW values and lowerD→π amplitudes by a similar amount. (ii) We show that all the data can also be understood in a coupled channel inelastic model. (iii) We also find that the Isgur, Scora, Grinstein and Wise (ISGW) model-form factors, if extrapolated to small momentum transfers (t) by a single pole formula, yield branching ratios too small in comparison to data. We propose an alternate scheme to interpolate between BSW form factors att=0 and ISGW form factors att=tmax.

Calculations for parity violating electron scattering in the 12C to 12C* nuclear transition

The asymmetry for parity violating polarized electron scattering for the 12C to 12C* (15.11 MeV) nuclear transition is calculated using available models for the nuclear form factors involved. The sensitivity of this reaction to the Weinberg angle and to the ratio of the relevant nuclear form factors is discussed in detail.

Small-angle neutron scattering study of sodium hexadecyl sulfate surfactant solutions

The micelle formation in aqueous sodium hexadecyl sulfate solutions is studied by small-angle neutron scattering technique. Measurements are carried out at different concentrations (1.1,2.2,3.2,5.4,10.9 and 32.8mM/dm 3) and at different temperatures (40, 50 and 60°C). The monotonous evolution of the interparticle correlation can be observed on the measured scattering patterns. At high concentrations(10.9 and 32.8 mM/dm 3) scattering patterns are described by interacting ellipsoids. At low concentrations a satisfactory fit can not be obtained by a simple form factor model. The computation of the distance distribution function proved the ellipsoial shape at 10.9 and 32.8 mM/dm 3, but showed an unexpectedly large particle dimension and structurization of the particle at lower concentrations. An assumption is made on the phase transition in the concentration range studied.

QUASIELASTIC ELECTRON SCATTERING AND THE MODIFICATION OF MESONIC MASS PARAMETERS IN NUCLEI

Making use of a vector-dominance model for the nucleon electromagnetic form factors, we investigate the consequences for the calculation of the inclusive electromagnetic response (in the quasielastic domain) of recent suggestions that mesonic mass parameters are modified in a nuclear medium.

Testing the chirality of b to c coupling in B→D ∗ℓν

Two asymmetries in the angular distribution of the lepton ℓ and the D meson in B→D ∗(→Dπ)ℓν are calculated in the standard model. Using four form factor models we find values in the ranges AFB=(19–24)%, AA=(14–18)%. The sign of the two asymmetries was suggested to test the chirality of the b to c coupling. We study the asymmetries in a generic SU(2) L × SU(2) R × U(1) model. We show that, whereas in certain cases the asymmetries can discriminate against a large right-handed component, they cannot always distinguish between left- and right-hand couplings.

Inclusive and exclusive decays of B mesons to final states including charm and charmonium mesons.

We have studied hadronic decays of {ital B} mesons. We report measurements of exclusive branching ratios of several charm decay modes of {ital B} mesons to final states with a {ital D} or {ital D}{sup *} and one to three charged pions or a charged {rho} and to final states with a {psi} or {psi}{prime}, a kaon, and up to two charged pions. We have also measured inclusive branching ratios for {ital B} decays to {ital D} and {ital D}{sup *} and the spectra of these particles in {ital B} decays. The total charm content in {ital B} decay is found to be (101{plus minus}12)%. The branching ratios and spectra are compared to form-factor models. We extract the parameters {ital a}{sub 1} and {ital a}{sub 2} of the model of Bauer, Stech, and Wirbel and the {ital D}{sub {ital S}} decay constant. The masses of the {ital {bar B}} {sup 0} and {ital B}{sup {minus}} mesons are measured. The mass difference between {ital {bar B}} {sup 0} and {ital B}{sup {minus}} is found to be {minus}0.4{plus minus}0.6{plus minus}0.5 MeV/{ital c}{sup 2}.

The hybrid quark-hadron model for three-body systems

Our calculations within the hybrid quark-hadron model of the magnetic form factors of the three-nucleon systems are given. Three-nucleon form factors for 0≤ q 2≤4(GeV/ c) 2 are discussed. Striking six-quark cluster effects are found, with the probability for a nucleon to be in a six-quark cluster about 14%. Needed theoretical improvements in the model are also discussed.

Relativistic constituent-quark model of nucleon form factors.

We explore the electromagnetic properties of relativistic constituent-quark models of the proton and neutron, in particular their dependence on the constituent-quark mass and the confinement scale. Relativistic effects are never negligible in any model which fits the charge radius of the proton. For a fixed charge radius the confinement scale decreases with decreasing quark masses. Nonvanishing Pauli moments of the constituent quarks are needed to fit the magnetic moments for any value of the quark mass and confinement scale. It is possible to describe existing form-factor data at least up to momentum transfers ${Q}^{2}=6$ Ge${\mathrm{V}}^{2}$ with quark masses significantly smaller than the conventional nonrelativistic choice of about one-third of the nucleon mass.

Scattering of alpha-particles from130Te at 40 and 50 MeV

The elastic and inelastic scattering of 40 and 50 MeV unpolarized alpha-particles from130Te has been studied. Angular distributions of the cross-section have been measured for the ground state and the first excited state. Optical-model parameters were obtained by fitting the elastic-scattering data. DWBA calculations with a collective model form factor were performed for the inelastic scattering to the first excited state. Coupled-channel calculations were done with 0+–2+ coupling. Imaginary depth of the optical-model parameters was suitably reduced to obtain simultaneous fit to the elastic and inelastic data when channel coupling was introduced. The value of deformation parameter \pd{in2} has been deduced and compared with those obtained from other studies.

The semileptonic decaysB→Mτν as a probe of hadron dynamics

We show how data on\(\bar B \to M\tau \bar v\) can be used to probe models for the hadronic form-factors which describe the\(\bar B \to M\) transition, whereM isD,D* etc. Extra form-factors contribute to\(\bar B \to M\tau \bar v\), as compared to\(\bar B \to Me\bar v\), and these may be studied by observing the polarisation of the outgoing τ. Model predictions for the decay rate and the τ polarisation are presented.

Constraints on the weak gauge boson composite scale from the muon g−2 factor

We investigate the contribution of the composite weak gauge and Higgs boson to the g−2 factor of a charged lepton, moving in external magnetic fields. The compositeness of the bosons is treated in the form factor model. The constraints on the boson composite scale from the CERN muon g−2 experimental value and the constraints from the future BNL g−2 measurements are discussed.

Microscopic models for hadronic form factors and vertex functions

We review the status of nucleon (N) and few-nucleon form factors (f.f.'s) from the view-point of a gradual unfolding of successively inner degrees of freedom (d.o.f.) with increase inq 2. To this end we focus attention on the problem of a microscopic formulation of hadronic vertex functions (v.f.) from the point of view of their key role in understanding the physics of a large variety of few-hadron reactions on the one hand, and their practical usefulness in articulating the internal dynamics of hadron and few-hadron systems on the other hand. The criterion of an integrated view from low-energy spectroscopy to high-q 2 amplitudes is employed to emphasize the desirability of formulations in terms of relativistic dynamical equations based on Lorentz and gauge invariance in preference to phenomenological models, which often require additional assumptions beyond their original premises to extend their applicability domains. In this respect, the practical possibilities of the Bethe-Salpeter equation (BSE) in articulating the necessary dynamical ingredients are emphasized on a two-tier basis, the basic constant (3) being pre-determined from the mass spectral data (1st stage) in preparation for the construction of the hadron-quark vertex functions (2nd stage). An explicit construction is outlined for meson-quark and baryon-quark vertex functions as well as of meson-nucleon vertex functions in a stepwise fashion. The role of the latter as basic parameter-free ingredients is discussed for possible use in the more serious treatments in the current literature of quark-meson level (α) and meson-isobar (β) d.o.f. in 2-N and 3-N form factor studies. Since most of these studies are characterized by the use of RGM techniques at the six-quark level, a comparative discussion is also given of several contemporary RGM based models. Finally, the concrete prospects for employing such hardon-quark vertex functions for evaluating pp annihilation amplitudes are briefly indicated, keeping in view the LEAR programme for their studies.

Small-angle Compton scattering of gamma rays by atoms

The energy spectra of 344, 779, 964, 1086/1112 and 1408 keV gamma rays scattered through 5, 7, 10 and 15' by targets of Al, Cu, Mo, Sn, Ta and Pb have been measured using a Ge(Li) detector. The Compton peaks are closely fitted by a convolution of an instrumental lineshape and a theoretical lineshape computed using the relativistic impulse model of bound Compton scattering. Integrated energy spectra yield incoherent scattering functions in very close agreement with theoretical values taken from existing tabulations based upon the Waller-Hartree form factor model and with values obtained by direct numerical integration of the relativistic impulse model lineshapes.

TheN-? transition form factor and anomalous?-decays into octet-decuplet baryon-antibaryon Pairs

We develop a Generalized-Vector-Meson Dominance Model (GVDM) for the invariantN-Δ transition form factors which incorporates the correct largeq2 power behaviour of QCD and describes the available lowq2 space-like data. We then use this GVDM transition form factor in the time-like region to calculate theSU (3) singlet and octet contributions to Ψ-decays into octet-decuplet baryon-antibaryon pairs. The results are compared to recent data on Ψ-decays into octet-decuplet baryon-antibaryon pairs.

Inelastic alpha-scattering from the stable even germanium isotopes

Scattering of 31.5 MeV α-particles from the stable even Ge isotopes has been studied with an energy resolution of 15–20 keV FWHM. Angular distributions were measured for excitation energies of up to 5.2 MeV. Most of the levels are well described by collective DWBA calculations with vibrational model form factors. An implicit folding procedure was used to derive isoscalar transition rates. The distribution of the isoscalar multipole strength reveals an increasing fragmentation with increasing neutron number. A detailed comparison with the spectroscopic results of a recent (p, p′) study is made.

Inclusive electron scattering by nuclei and free nucleon form factors

The effect of using different free nucleon electromagnetic form factors in theoretical calculations of (e, e′) longitudinal and transverse responses has been investigated, both in three-nucleon systems and in a complex nucleus. Large discrepancies have been found between the results corresponding to different models of nucleon form factors, mainly due to the uncertainty of the neutron form factors at high momentum transfer.

Thermodynamic oscillator model for elastic nuclear form factors

An elastic form factor of the form F(Q2)=const·K1(z)/z, where z=√a2 + Q2/ ¯Q02 depends on the two parametersa and Q0, is obtained on the basis of an oscillator model with a temperature continuum. An estimate of the parameters of the model is obtained for medium and heavy nuclei regarded as a nucleon gas, and for the nucleon and the deuteron regarded as a quark gas. The model gives a good description of the electromagnetic form factors of the neutron, the proton, and the deuteron in the wide range of momentum transfers 0 <Q2< 6 (GeV/c)2. For heavier nuclei, starting with3He, the quark contribution can be disregarded.

Compatibility of higher rho-resonances with the pion form factor data

A realistic pion form factor model respecting the usual fundamental principles supplemented by reasonable assumptions is constructed by means of conformai mapping having some specific uniformization properties. The model includes the contributions of higher rho-resonances without any conflict with analyticity, provides a certain flexibility for the asymptotic behaviour and depends just on the physical parameters. The best fit of all existing data is achieved withϱ(770),ϱ′'(1600) and the asymptotics∼t−3/2. The predicted values of the pion charge radius, P-wave isovectorππ scattering length, as well as theI=J = 1ππ scattering amplitude at the experimental measurable region coincide with the world averaged data.

Coincident electrofission of 238U at q

We have measured the coincidence cross sections $^{238}\mathrm{U}$(e,e'f) at three values of momentum transfer (q\ensuremath{\approxeq}0.26, 0.40, and 0.55 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$) over the range from 5 to 23 MeV in excitation energy; these values of q correspond approximately to the first maxima of the electric dipole, quadrupole/monopole, and octupole form factors, respectively. The angular distribution of fission fragments is peaked along the direction of q near fission threshold, indicating the dominance of K=0 states, but becomes isotropic above 10 MeV. We have integrated our cross sections over fission angle and compared them to recent calculations of multipole strength derived in the quasiparticle random phase approximation. Using model-dependent form factors generated from the Tassie model and the quasiparticle random phase approximation, we have extracted strength functions for the lowest electric multipoles. The deduced E1 strength agrees well with photofission results for reasonable choices of the model form factors. The E2/E0 distribution displays resonant structures at 10 and 13 MeV which agree in position with the collective E2 and E0 strength, respectively, predicted in the quasiparticle random phase approximation. If we make such an assignment for the multipolarity of these two structures, the observed E0 strength agrees with the theoretical prediction, whereas the E2 strength is low by a factor of 2--3. Higher order multipoles also contribute substantially to the cross section at our highest value of q.

Alpha scattering from 92Zr and 94Zr

Scattering of 35.4 MeV α particles from 92Zr and 94Zr has been studied with an energy resolution of 25–30 keV. Angular distributions were measured from 10 to 45 degrees for an E x range of up to 6.1 MeV and 4.4 MeV for 92Zr and 94Zr, respectively. Several new spin assignments have been made by comparing angular distributions with collective DWBA calculations. An implicit folding procedure was used to derive isoscalar transition rates, which for E x > 2.5 MeV were previously unknown. Most of the levels are well described by a vibrational model form factor.