Search results for "SCALAR"
showing 10 items of 1002 documents
Photo and electroproduction of mesons
1994
The lecture provides an elementary introduction to photo and electroproduction of pseudoscalar mesons in the resonance region. After discussing the general structure of the elementary production amplitude and its symmetry properties the formalism is applied to some interesting physical problems.
Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f[sub 0](980), a[sub 0](980) scalar mesons
1998
We use a nonperturbative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f0 and a0 resonances. The ππ→ππ, ππ→KK phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π0η and KK mass distributions in the T=1 channel. Furthermore, the total and partial decay widths of the f0 and a0 resonances are properly reproduced. The results seem to indicate that chiral symmetry constraint…
Search for exotics at $BABAR$
2014
One of the most intriguing puzzles in hadron spectroscopy are the numerous charmonium-like states observed in the last decade, including charged states that are manifestly exotic. The $BABAR$ experiment has extensively studied those in B meson decays, initial state radiation processes and two photon reactions. The study of the process $B \rightarrow J/\psi \phi K$, with a search for the resonant states X(4140) and X(4270) in their decays to $J/\psi \phi$, will be highlighted. The recent results of the Dalitz analysis of $\eta_c$ to 3 pseudoscalar mesons, via 2-photon interactions, will be presented in this report
Weak Decays of ExcitedBMesons
2015
We investigate the decays of the excited (bq[over ¯]) mesons as probes of the short-distance structure of the weak ΔB=1 transitions. These states are unstable under the electromagnetic or strong interactions, although their widths are typically suppressed by phase space. Compared to the pseudoscalar B meson, the purely leptonic decays of the vector B^{*} are not chirally suppressed and are sensitive to different combinations of the underlying weak effective operators. An interesting example is B_{s}^{*}→ℓ^{+}ℓ^{-}, which has a rate that can be accurately predicted in the standard model. The branching fraction is B∼10^{-11}, irrespective of the lepton flavor and where the main uncertainty st…
Pseudoscalar Transition Form Factors from Rational Approximants
2014
The $\pi^0$, $\eta$, and $\eta^\prime$ transition form factors in the space-like region are analyzed at low and intermediate energies in a model-independent way through the use of rational approximants. Slope and curvature parameters as well as their values at infinity are extracted from experimental data. These results are suited for constraining hadronic models such as the ones used for the hadronic light-by-light scattering piece of the anomalous magnetic moment of the muon, and for the mixing parameters of the $\eta - \eta^\prime$ system.
Search for Dimuon Decays of a Light Scalar Boson in Radiative Transitions Υ→γA0
2009
We search for evidence of a light scalar boson in the radiative decays of the {Upsilon}(2S) and {Upsilon}(3S) resonances: {Upsilon}(2S, 3S) {yields} {gamma}A{sup 0}, A{sup 0} {yields} {mu}{sup +}{mu}{sup -}. Such a particle appears in extensions of the Standaard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. We find no evidence for such processes in the mass range 0.212 {<=} m{sub A{sup 0}} {<=} 9.3 GeV in the samples of 99 x 10{sup 6} {Upsilon}(2S) and 122 x 10{sup 6} {Upsilon}(3S) decays collected by the BABAR detector at the PEP-II B-factory and set stringent upper limits on the effective coupling of the b quark to the A{sup 0}. We also limit the dimuon b…
Measurement of transition form factors in two-photon collisions at BESIII
2019
The two-photon physics program of the BESIII Collaboration is mainly motivated by the need of new measurements of transition form factors as input for the Standard Model calculations of $ \mathop a\nolimits_\mu ^{HLbL} $, the hadronic light-by-light scattering contribution to the anomalous magentic moment of the muon. The large data sets acquired at BESIII allow to study the transition form factors of pseudoscalar mesons in the relevant region of momentum transfer for $ \mathop a\nolimits_\mu ^{HLbL} $. In this presentation the status of the respective measurements for π0,η and η’ mesons are discussed, and prospects for studies of multi-meson systems as well as of doubly-virtual transition …
Recent Results on Meson Decays from A2
2018
Light meson decays are used to investigate topics related to fundamental aspects of particle physics. Precision measurements of meson Dalitz decays give input to theoretical evaluations of the Hadronic Light-by-Light contribution (HLbL) to the anomalous magnetic moment of the muon. The pseudoscalar η' decays allow for studies of topics like ππ scattering lengths, effective field theories and fundamental symmetries. The A2 collaboration, using the Crystal Ball/TAPS setup at MAMI, has recently published several high precision results on transition form factors which are related to HLbL. The value obtained for the slope parameter of the π0 electromagnetic (e/m) transition form factor (TFF) is …
Light-by-light scattering sum rules in light of new data
2016
We evaluate the light-quark meson contributions to three exact light-by-light scattering sum rules in light of new data by the Belle Collaboration, which recently has extracted the transition form factors of the tensor meson $f_2(1270)$ as well as of the scalar meson $f_0(980)$. We confirm a previous finding that the $\eta, \eta^\prime$ and helicity-2 $f_2(1270)$ contributions saturate one of these sum rules up to photon virtualities around 1 GeV$^2$. At larger virtualities, our sum rule analysis shows an important contribution of the $f_2(1565)$ meson and provides a first empirical extraction of its helicity-2 transition form factor. Two further sum rules allow us to predict the helicity-0…
On the precision of a data-driven estimate of the pseudoscalar-pole contribution to hadronic light-by-light scattering in the muon g-2
2016
The evaluation of the numerically dominant pseudoscalar-pole contribution to hadronic light-by-light scattering in the muon g-2 involves the pseudoscalar-photon transition form factor F_{P gamma^* gamma^*}(-Q_1^2, -Q_2^2) with P = pi^0, eta, eta^\prime and, in general, two off-shell photons with spacelike momenta Q_{1,2}^2. We determine which regions of photon momenta give the main contribution for hadronic light-by-light scattering. Furthermore, we analyze how the precision of future measurements of the single- and double-virtual form factor impacts the precision of a data-driven estimate of this contribution to hadronic light-by-light scattering.