2,646 research outputs found
H -> gamma gamma: a Comment on the Indeterminacy of Non-Gauge-Invariant Integrals
We reanalyze the recent computation of the amplitude of the Higgs boson decay
into two photons presented by Gastmans et al.. The reasons for which this
result cannot be the correct one have been discussed in some recent papers. We
address here the general issue of the indeterminacy of integrals with
four-dimensional gauge-breaking regulators and to which extent it might
eventually be solved by imposing physical constraints. Imposing gauge
invariance as the last step upon R_xi gauge calculations with four-dimensional
gauge-breaking regulators, allows indeed to recover the well known H -> gamma
gamma result. However we show that in the particular case of the unitary gauge,
the indeterminacy cannot be tackled in this same way. The combination of
unitary gauge with a cutoff regularization scheme turns out to be
non-predictive.Comment: 17 pages, 6 figure
The Z(4430) and a New Paradigm for Spin Interactions in Tetraquarks
Following the recent confirmation of the Z+(4430) resonance with
J^{PG}=1^{++}, we have re-examined the model of S- and P-wave tetraquarks. We
propose a `type-II' diquark-antidiquark model which shows to be very effective
at producing a simple and comprehensive picture of the J^{PG}=1^{++} and 1^{--}
sectors of the recently discovered charged tetraquarks and of the observed Y
resonances. The model is still faced with the unresolved difficulty of
explaining why some states seem to have incomplete isospin multiplets.Comment: 17 pages, 1 figure, comments added, typos corrected, to appear in
Phys Rev
Four-Quark Mesons
The features of a model interpreting the light scalar mesons as
diquark-antidiquark bound states and the consequences of its natural extension
to include heavy quarks are briefly reviewed.Comment: Talk given at the 6th Conference on Quark Confinement and the Hadron
Spectrum, Villasimius, Sardinia, Italy, 21-25 Sep 200
Four Quark Interpretation of Y(4260)
We propose that the Y(4260) particle recently announced by BaBar is the first
orbital excitation of a diquark-antidiquark state ([cs][cbar sbar]). Using
parameters recently determined to describe the X(3872) and X(3940) we show that
the Y mass is compatible with the orbital excitation picture. A crucial
prediction is that Y(4260) should decay predominantly in D_s D_sbar. The
Y(4260) should also be seen in B non-leptonic decays in association with one
kaon. We consider the full nonet of related four-quark states and their
predicted properties. Finally, we comment on a possible narrow resonance in the
same channel.Comment: 3 pages, 2 figures, RevTex, Revised discussion of the Y mas
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
Diquark-antidiquark states with hidden or open charm
Some features and predictions of a recently proposed model based on
diquark-antidiquark bound states are illustrated. Its ability in accomodating
newly discovered charmed resonances around 4 GeV is discussed.Comment: To appear in the proceedings of the HEP2005 International Europhysics
Conference on High Energy Physics, July 21st-27th 2005, Lisboa, Portuga
The 2^-+ assignment for the X(3872)
Very recently the BaBar collaboration has put forward a claim that the
X(3872) is not a 1^++ resonance, as most of the phenomenological work on the
subject was relying on, but rather a 2^-+ one. We examine the consequences of
this quantum number assignment for the solution of the X(3872) puzzle. The
molecular interpretation appears less likely, and the conventional charmonium
interpretation should be reconsidered. There are several well-known
difficulties with this interpretation, to which we add a new one: the
production cross section at CDF is predicted to be much smaller than that
observed. We also confirm, using a relativistic string model, the conclusion
from potential models that the mass of the state is not consistent with
expectations. In the tetraquark interpretation the 2^-+ assignment implies a
rich spectrum of partner states, although the X(3872) may be among the few
which are narrow enough to be observable.Comment: 18 pages, 6 figures, 4 tables; minor style corrections. Version to
appear in PR
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