Search results for "meson"
showing 10 items of 1548 documents
The Proton Spin in the Chiral Bag Model : Casimir Contribution and Cheshire Cat Principle
1998
The flavor singlet axial charge has been a source of study in the last years due to its relation to the so called {\it Proton Spin Problem}. The relevant flavor singlet axial current is anomalous, i.e., its divergence contains a piece which is the celebrated $U_A(1)$ anomaly. This anomaly is intimately associated with the $\eta^\prime$ meson, which gets its mass from it. When the gauge degrees of freedom of QCD are confined within a volume as is presently understood, the $U_A(1)$ anomaly is known to induce color anomaly leading to "leakage" of the color out of the confined volume (or bag). For consistency of the theory, this anomaly should be canceled by a boundary term. This ``color bounda…
On the Delta-nucleon and rho-pi splittings: A QCD-inspired look in free hadrons versus nuclei
1997
Relationships between mass intervals for free hadrons and in nuclei are studied in two theoretical approaches inspired by QCD: naive quark model and skyrmion model, taking one example each from mesons and baryons, that of pi-rho splitting in mesons, and nucleon-Delta splitting in baryons. Possible deconfinement effects in nuclei are examined.
Nonfactorizable corrections toB→J/ψK
2003
We apply the method of QCD light-cone sum rules to calculate nonfactorizable contributions to the $\stackrel{\ensuremath{\rightarrow}}{B}J/\ensuremath{\psi}K$ decay and estimate soft nonfactorizable corrections to the ${a}_{2}$ parameter. The corrections appear to be positive, favoring the positive sign of ${a}_{2},$ in agreement with recent theoretical considerations and experimental data. Our result also confirms expectations that in the color-suppressed decay nonfactorizable corrections are sizable.
Bottomonium spectroscopy and radiative transitions involving theχbJ(1P,2P)states atBaBar
2014
We use (121±1) million Υ(3S) and (98±1) million Υ(2S) mesons recorded by the BABAR detector at the PEP-II e^+e^− collider at SLAC to perform a study of radiative transitions involving the χ_(bJ)(1P,2P) states in exclusive decays with μ^+μ^−γγ final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timing-based technique to reduce backgrounds, and determine branching-ratio products and fine mass splittings. These results include the best observational significance yet for the χ_(b0)(2P)→γΥ(2S) and χ_(b0)(1P)→γΥ(1S) transitions. In the se…
Improved determination of the mass of the1−+light hybrid meson from QCD sum rules
2003
We calculate the next-to-leading order (NLO) ${\ensuremath{\alpha}}_{s}$ corrections to the contributions of the condensates $〈\ensuremath{\alpha}{G}^{2}〉$ and $〈\overline{q}q{〉}^{2}$ in the current-current correlator of the hybrid current $g\overline{q}(x){\ensuremath{\gamma}}_{\ensuremath{\nu}}{\mathrm{iF}}_{\ensuremath{\mu}\ensuremath{\nu}}^{a}{T}^{a}q(x)$ using the external field method in the Feynman gauge. After incorporating these NLO contributions into the Laplace sum rules, the mass of the ${J}^{\mathrm{PC}}{=1}^{\ensuremath{-}+}$ light hybrid meson is recalculated using the QCD sum rule approach. We find that the sum rules exhibit enhanced stability when the NLO ${\ensuremath{\alp…
The physics of glueballs
2008
Glueballs are particles whose valence degrees of freedom are gluons and therefore in their description the gauge field plays a dominant role. We review recent results in the physics of glueballs with the aim set on phenomenology and discuss the possibility of finding them in conventional hadronic experiments and in the Quark Gluon Plasma. In order to describe their properties we resort to a variety of theoretical treatments which include, lattice QCD, constituent models, AdS/QCD methods, and QCD sum rules. The review is supposed to be an informed guide to the literature. Therefore, we do not discuss in detail technical developments but refer the reader to the appropriate references.
Novel nonperturbative approach for radiativeB¯0(B¯s0)→J/ψγdecays
2016
Radiative ${\overline{B}}^{0}({\overline{B}}_{s}^{0})\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\gamma}$ decays provide an interesting case to test our understanding of (non)perturbative QCD and eventually to probe physics beyond the standard model. Recently, the LHCb Collaboration reported an upper bound, updating the results of the BABAR Collaboration. Previous theoretical predictions based on QCD factorization or perturbative QCD have shown large variations due to different treatment of nonfactorizable contributions and meson-photon transitions. In this paper, we report on a novel approach to estimate the decay rates, which is based on a recently proposed model for $B$ decays…
Bounds on rare decays of η and η′ mesons from the neutron EDM
2019
We provide model-independent bounds on the rates of rare decays $\ensuremath{\eta}({\ensuremath{\eta}}^{\ensuremath{'}})\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$ based on experimental limits on the neutron electric dipole moment (nEDM). Starting from phenomenological $\ensuremath{\eta}({\ensuremath{\eta}}^{\ensuremath{'}})\ensuremath{\pi}\ensuremath{\pi}$ couplings, the nEDM arises at the two-loop level. The leading-order relativistic chiral perturbation theory calculation with the minimal photon coupling to charged pions and a proton inside the loops leads to a finite, counterterm-free result. This is an improvement upon previous estimates which used approximations in evalu…
Diabatic description of charmoniumlike mesons. II. Mass corrections and strong decay widths
2021
From a diabatic bound state approach to $J^{PC}=1^{--}$ and $(0,1,2)^{++}$ charmoniumlike resonances below $4.1$ GeV, formulated in terms of ${c\overline{c}}$ and closed meson-meson channels, we calculate mass shifts and widths due to open meson-meson channels. This calculation does not involve any new free parameter, so comparison of our predictions with existing data provides a direct test of our approach. Further mass corrections are also estimated and good agreement with the measured masses comes out. As for the calculated widths, overall reasonable, they point out to the need of some refinement of our current bound state approximation for an accurate description of data. These results …
Heavy-flavour production in the SACOT-mT scheme
2019
The hadroproduction of heavy-flavoured mesons has recently attracted a growing interest e.g. within the people involved in global analysis of proton and nuclear parton distribution functions, saturation physics, and physics of cosmic rays. In particular, the D- and B-meson measurements of LHCb at forward direction are sensitive to gluon dynamics at small $x$ and are one of the few perturbative small-$x$ probes before the next generation deep-inelastic-scattering experiments. In this talk, we will concentrate on the collinear-factorization approach to inclusive D-meson production and describe a novel implementation --- SACOT-$m_{\rm T}$ --- of the general-mass variable flavour number scheme …