Search results for "form factor"
showing 10 items of 261 documents
Pseudoscalar transition form factors: (g − 2) of the muon, pseudoscalar decays into lepton pairs, and the η – η′ mixing
2015
We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance …
Rho meson properties in the chiral theory framework
2002
13 páginas, 7 figuras, 1 tabla.-- arXiv:hep-ph/0208199v1
Measurement of theB¯0→D*+ℓ−ν¯ℓdecay rate and|Vcb|
2005
We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ based on a sample of about 53,700 \mbox{$\Bzb \rightarrow D^{*+} \ell^- \bar{\nu}_{\ell}$} decays observed by the \babar\ detector. We obtain the branching fraction averaged over $\ell = e,\mu$, ${\cal B}(\Bzb \rightarrow D^{*+} \ell^- \bar{\nu}_{\ell}) = (4.90 \pm 0.07\mathrm{(stat.)}^{+0.36}_{-0.35}\mathrm{(syst.)})\%$. We measure the differential decay rate as a function of $w$, the relativistic boost $\gamma$ of the $D^{*+}$ in the ${\Bzb}$ rest frame. By extrapolating $d\Gamma/dw$ to the kinematic limit $w \rightarrow 1$, we extract the product of $|V_{cb}|$ and the axial form factor ${\cal A}_1(w=1)$. …
Extraction of form Factors from a Four-Dimensional Angular Analysis of B¯→D*ℓ−ν¯ℓ
2019
An angular analysis of the decay B[over ¯]→D^{*}l^{-}ν[over ¯]_{l}, l∈{e,μ}, is reported using the full e^{+}e^{-} collision data set collected by the BABAR experiment at the ϒ(4S) resonance. One B meson from the ϒ(4S)→BB[over ¯] decay is fully reconstructed in a hadronic decay mode, which constrains the kinematics and provides a determination of the neutrino momentum vector. The kinematics of the semileptonic decay is described by the dilepton mass squared, q^{2}, and three angles. The first unbinned fit to the full four-dimensional decay rate in the standard model is performed in the so-called Boyd-Grinstein-Lebed approach, which employs a generic q^{2} parametrization of the underlying f…
A Comment on form-factor mass singularities in flavor changing neutral currents
1991
Flavor-changing effective verticesq l q h V 0, whereV 0 represents a neutral gauge boson (γ,Z 0,g), involving a heavy external quark, are discussed within the standard model at one-loop level and second-order approximation in external momenta and masses: the logarithmic singular terms in the form factors at vanishing mass of the internal quark in the loop have to be replaced by pieces coming from next order in external momenta. Implications in theb→d+X penguin transitions are commented.
General analysis of weak decay form factors in heavy to heavy and heavy to light baryon transitions
1992
We present a complete analysis of the heavy to heavy and heavy to light baryon semi-leptonic decays in the heavy quark effective theory within the framework of a Bethe-Salpeter (BS) approach and demonstrate the equivalence of this approach to other work in the field. We present in a compact form the baryon BS amplitudes which incorporate the symmetries manifest in the heavy quark limit and which also show clearly the light quark dynamics. A similar form of the BS amplitude is presented for light baryons. Using the BS amplitudes, the heavy to heavy and heavy to light semi-leptonic baryon decays are considered. As expected there is a dramatic reduction in the number of form factors. An advant…
GENERALIZED PARTON DISTRIBUTIONS AND COMPOSITE CONSTITUENT QUARKS
2003
An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario, considering the constituent quarks as complex systems. The GPDs are obtained from the wave functions of the non relativistic CQM of Isgur and Karl, convoluted with the GPDs of the constituent quarks themselves. The latter are modelled by using the structure functions of the constituent quark, the double distribution representation of GPDs, and a recently proposed phenomenological constituent quark form factor. The present approach permits to access a kinematical range corresponding to both the DGLAP and the ERBL regions, for small values of the momentum transfer and of t…
Light-cone quark model with spin force for the nucleon and Δ (1232)
1992
Abstract Electromagnetic structure functions for the nucleon, static observables for the nucleon and N → Δ (1232) transition form factors are calculated in a relativistic constituent quark model on the light cone. The model simulates the main effect of the spin force between quarks in terms of smaller (and lighter) scalar ud diquarks in the nucleon. The polarized proton structure function is found to agree with the EMC data.
Exclusive semi-leptonic decays of bottom mesons in the spectator quark model
1988
We calculate the exclusive semileptonic bottom meson decays\(B \to D(D*) + l^ - + \bar v_l \) in the spectator quark model. The helicity structure of the mesonic current transitionsB→D(D*) is matched to the helicity structure of the free quark current transitionsb→c at minimum momentum transferq2=0. The results are continued toq2≠=0 by pole-dominated form factors. Our results are compared to recent calculations that use quark model dynamics at maximum momentum transferq max 2 = (M1 −M2)2. We find agreement atq max 2 . Atq2=0 there are significant differences between the predictions of the two approaches leading to marked differences in the predictions for the shape of the lepton energy spec…
Rare decay modes of the neutral pion
1984
3 páginas, 2 figuras, 1 tabla.