Search results for "meson"
showing 10 items of 1548 documents
Long Range Structure of the Nucleon
2010
The long range structure of the nucleon is discussed starting from the old model of a quark bag with a pion cloud (``cloudy bag'') carrying on to the more recent ideas of the parton model of the nucleon. On the basis of the most recent measurements of the form factors at MAMI, JLab and MIT quantitative results for nucleon charge densities are presented within both non-relativistic and relativistic frameworks.
Charm and bottom baryon decays in the Bethe-Salpeter approach: Heavy to heavy semileptonic transitions
1998
Charm and bottom baryons and mesons are studied within the framework of a relativistically covariant 3D reduction of the Bethe-Salpeter equation. We carry out an analysis of semileptonic decays of heavy hadrons within this framework using explicit oscillator-type wave functions where we calculate Isgur-Wise functions, decay rates and asymmetry parameters. Within this model we also study the effect of interactions between the light quarks inside the heavy baryon and how they affect the values of the computed heavy baryon observables. We also elaborate on the role of relativistic effects in the calculation of the heavy baryon Isgur-Wise function.
A new way to search for right-handed currents in semileptonic B→ρℓν‾ decay
2016
AbstractThere exist a long standing tension among determinations of the CKM matrix element |Vub| from various (semi)leptonic B decay channels with varying significance of up to ∼3σ. An interesting possibility to ease this tension is to allow for a right-handed contribution to the standard model left-handed weak current mediating the b→u quark decay. Current bounds on such a contribution are fairly weak. We propose a new way to search for such a right-handed current in semileptonic B→ρ meson decays. We describe a new variable that we propose, and discuss the theoretical uncertainties. Especially we investigate the uncertainties and their correlations among all contributing form factors with …
Hidden beauty baryon states in the local hidden gauge approach with heavy quark spin symmetry
2013
Using a coupled-channel unitary approach, combining the heavy quark spin symmetry and the dynamics of the local hidden gauge, we investigate the meson-baryon interaction with hidden beauty and obtain several new states of N around 11 GeV. We consider the basis of states eta (b) N, I'N, BI > (b) , BI pound (b) , B (*) I > (b) , B (*) I pound (b) , B (*) I pound (b) (*) and find four basic bound states which correspond to BI pound (b) , BI pound (b) (*) , B (*) I pound (b) and B (*) I pound (b) (*) , decaying mostly into eta (b) N and I'N and with a binding energy about 50-130 MeV with respect to the thresholds of the corresponding channel. All of them have isospin I = 1/2 , and we find no bo…
Resonant structure and flavour tagging in the Bπ±system using fully reconstructed B decays
1998
Abstract Starting from a sample of four million hadronic Z decays collected with the ALEPH detector at LEP, 404 charged and neutral B mesons are fully reconstructed and used to look for resonant structure in the Bπ system. An excess of events is observed above the expected background in the Bπ mass spectrum at a mass ≈5.7 GeV/c 2 , consistent with the production and decay to B (∗) π of the B ∗∗ states predicted by Heavy Quark Symmetry (HQS). In the framework of HQS, it is found that the mass of the B 2 ∗ state is (5739 + 8 −11 ( stat ) +6 −4 ( syst )) MeV/c 2 and the relative production rate of the B ∗∗ system is BR(b→B ∗∗ →B (∗) π)/BR(b→B u,d )=(31±9 (stat) +6 −5 (syst)) % . In the same sa…
Spectator Effects in the Heavy Quark Effective Theory
1996
We present a complete analysis of the Heavy Quark Effective Theory Lagrangian at order $1/m^2$ in the leading logarithmic approximation, including effects induced by spectator quarks. At this order new correction terms appear in the effective Lagrangian, as four-quark operators containing both heavy and light quark fields. We compute the coefficients of these operators to one-loop order and in the leading-logarithmic approximation. Two of them break the heavy quark spin symmetry and we estimate their contribution to the hyperfine splitting of the heavy mesons in the factorization approximation. We find that they make a positive contribution to the hyperfine splitting of about 10% of the mea…
Quark effects, meson-exchange currents and background in the d(e,e'p)delta reaction
1994
[EN] We have studied in detail the cross section for the d(e, e'p)Delta reaction leading to the emission of a fast nucleon and a Delta at rest, which has been advocated as a tool to investigate quark effects in nuclei. We find that ordinary meson-exchange currents mechanisms dominate the quark-exchange effects in the region of excitation of the Delta and could be competitive at higher energies. Furthermore, at these higher energies, the small cross sections for the quark signal, together with the presence of a background about one order of magnitude bigger than the quark signal, make in any case the extraction of information about quark-exchange currents effects extraordinarily difficult.
Four-quark spectroscopy within the hyperspherical formalism
2006
We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ …
Generalized screened potential model
2014
A new non relativistic quark model to calculate the spectrum of heavy quark mesons is developed. The model is based on an interquark potential interaction that implicitly incorporates screening effects from meson-meson configurations. An analysis of the bottomonium spectrum shows the appearance of extra states as compared to conventional non screened potential models.
One-photon decay of the tetraquark stateX(3872)→γ+J/ψin a relativistic constituent quark model with infrared confinement
2011
We further explore the consequences of treating the $X(3872)$ meson as a tetraquark bound state by analyzing its one-photon decay $X\ensuremath{\rightarrow}\ensuremath{\gamma}+J/\ensuremath{\psi}$ in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the $X(3872)$ meson with its four constituent quarks by using the $P$-exponential path-independent formalism. We calculate the matrix element of the transition $X\ensuremath{\rightarrow}\ensuremath{\gamma}+J/\ensuremath{\psi}$ and prove its gauge invariance. We evaluate the $X\ens…