588 research outputs found
XYZ: four-quark states?
The observation of many unexpected states decaying into heavy quarkonia has
challenged the usual Q-Qbar interpretation. We will discuss the nature of some
of the charmonium-like resonances recently observed by BES III and LHCb, and
their identication according to the compact tetraquark model. We also commment
the production of light nuclei in hadron collisions and the relevance for the
physics of the X(3872).Comment: 5 pages, 2 figures, 1 table. Contribution to the proceedings of "IFAE
2015 Incontri di Fisica delle Alte Energie", Roma 8-10 April 201
A Mechanism for Hadron Molecule Production in p pbar(p) Collisions
We propose a mechanism allowing the formation of loosely bound molecules of
charmed mesons in high energy proton-(anti)proton collisions.Comment: 4 pages, 3 figure
Hybridized tetraquarks
We propose a new interpretation of the neutral and charged X,Z
exotic hadron resonances. Hybridized-tetraquarks are neither purely compact tetraquark states nor bound or loosely bound molecules but rather a manifestation of the interplay between the two. While meson molecules need a negative or zero binding energy, its counterpart for h -tetraquarks is required to be positive. The formation mechanism of this new class of hadrons is inspired by that of Feshbach metastable states in atomic physics. The recent claim of an exotic resonance in the View the MathML source
channel by the D0 Collaboration and the negative result presented subsequently by the LHCb Collaboration are understood in this scheme, together with a considerable portion of available data on X,Z
particles. Considerations on a state with the same quantum numbers as the X(5568)
are also made
Consensus-based control for a network of diffusion PDEs with boundary local interaction
In this paper the problem of driving the state of a network of identical
agents, modeled by boundary-controlled heat equations, towards a common
steady-state profile is addressed. Decentralized consensus protocols are
proposed to address two distinct problems. The first problem is that of
steering the states of all agents towards the same constant steady-state
profile which corresponds to the spatial average of the agents initial
condition. A linear local interaction rule addressing this requirement is
given. The second problem deals with the case where the controlled boundaries
of the agents dynamics are corrupted by additive persistent disturbances. To
achieve synchronization between agents, while completely rejecting the effect
of the boundary disturbances, a nonlinear sliding-mode based consensus protocol
is proposed. Performance of the proposed local interaction rules are analyzed
by applying a Lyapunov-based approach. Simulation results are presented to
support the effectiveness of the proposed algorithms
On the Spin of the X(3872)
Whether the much studied X(3872) is an axial or tensor resonance makes an
important difference to its interpretation. A recent paper by the BaBar
collaboration raised the viable hypothesis that it might be a 2-+ state based
on the 3 pions spectrum in the X -> J/psi omega decays. Furthermore, the Belle
collaboration published the 2 pions invariant mass and spin-sensitive angular
distributions in X -> J/psi rho decays. Starting from a general parametrization
of the decay amplitudes for the axial and tensor quantum numbers of the X, we
re-analyze the whole set of available data. The level of agreement of the two
spin hypotheses with data is interpreted with a rigorous statistical approach
based on Monte Carlo simulations in order to be able to combine all the
distributions regardless of their different levels of sensitivity to the spin
of the X. Our analysis returns a probability of 5.5% and 0.1% for the agreement
with data of the 1++ and 2-+ hypotheses, respectively, once we combine the
whole information (angular and mass distributions) from both channels. On the
other hand, the separate analysis of J/psi rho (angular and mass distributions)
and J/psi omega (mass distribution) indicates that the 2-+ assignment is
excluded at the 99.9% C.L. by the former case, while the latter excludes at the
same level the 1++ hypothesis. There are therefore indications that the two
decay modes behave in a different way.Comment: 12 pages, 9 figures, 2 tables. Added angular distributions, which
lead to different conclusion
Doubly Charmed Tetraquarks in B_c and Xi_bc Decays
The phenomenology of the so-called X, Y and Z hadronic resonances is hard to
reconcile with standard charmonium or bottomonium interpretations. It has been
suggested that some of these new hadrons can possibly be described as tightly
bound tetraquark states and/or as loosely bound two-meson molecules. In the
present paper we focus on the hypothetical existence of flavored, doubly
charmed, tetraquarks. Such states might also carry double electric charge, and
in this case, if discovered, they could univocally be interpreted in terms of
compact tetraquarks. Flavored tetraquarks are also amenable to lattice studies
as their interpolating operators do not overlap with ordinary meson ones. We
show that doubly charmed tetraquarks could significantly be produced at LHC
from B_c or Xi_bc heavy baryons.Comment: 12 pages, 8 figures. Comments and references added. Version to appear
in Phys.Rev.
A Tentative Description of Z_c,b States in Terms of Metastable Feshbach Resonances
We attempt a description of the recently discovered Z_{c,b} states in terms
of Feshbach resonances arising from the interaction between the `closed'
subspace of hadrocharmonium levels and the `open' one of open-charm/beauty
thresholds. We show how the neutrality of the X(3872) might be understood in
this scheme and provide a preliminary explanation of the pattern of the
measured total widths of X,Z_{c,b}.Comment: To appear in the proceedings of The 6th International Workshop on
Charm Physics (CHARM 2013
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