631 research outputs found
The double life of the X meson
The molecule and the tetraquark model are the two competing interpretations
of the X(3872). I will briefly comment on how far these two pictures are really
resolvable by the experiment, and I will give a concise account on a new method
for defining the quark content of hadrons at heavy-ion colliders.Comment: 6 pages, to appear in the Proceedings of IFAE2006, Pavia, Ital
How can one understand the lightest scalars, especially the sigma
We discuss how the a_0(980), f_0(980), K^*_0(1430) and particularly the broad
sigma resonance can be understood within a coupled channel framework, which
includes all light two-pseudoscalar thresholds together with constraints from
Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable
analyticity. All (qbar q) scalars are, when unitarized, strongly distorted by
hadronic mass shifts, and the nonstrange isoscalar state becomes a very broad
resonance, with its pole at 470-i250 MeV. We believe this is the sigma meson
required by models for spontaneous breaking of chiral symmetry. Recently this
light resonance has clearly been observed in D-> sigma pi-> 3pi by the E791
experiment at Fermilab, and we discuss how this decay channel can be predicted
in a Constituent Quark Meson Model (CQM), which incorporates heavy quark and
chiral symmetries. We also discuss the less well known phenomenon that with a
large coupling there can appear two physical resonance poles on the second
sheet although only one bare quark-antiquark state is put in. The f_0(980) and
f_0(1370) resonance poles can thus be two manifestations of the same (sbar s)
quark state. Both of these states are seen clearly in D_s-> 3pi by the E791
experiment, where (sbar s) intermediate states are expected to be dominant.Comment: 9 pages; Invited plenary talk by N.A. Tornqvist at the ''Biennial
Conference on Low Energy Antiproton Physics'' (LEAP2000), Venice, Italy,
August 20-26, 2000. To appear in Nucl. Phys. A (proc. suppl.
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
On the mass of the Ds(0+,1+) system
In this note we discuss a determination for the mass of the Ds(0+,1+) system
recently discovered by the BaBar, CLEO II and Belle Collaborations. The value
of the mass is derived by making explicit the prediction obtained in a
quark-meson model prior to the discovery of these states.Comment: 3 pages, revte
Jet Shapes in Opaque Media
We present general arguments, based on medium-induced radiative energy loss,
which reproduce the non-gaussian shapes of away-side di-jet azimuthal
correlations found in nucleus-nucleus collisions at RHIC. A rather simple
generalization of the Sudakov form factors to opaque media allowing an
effective description of the experimental data is proposed.Comment: 4 pages, 2 ps figure
Heavier Higgs Particles: Indications from Minimal Supersymmetry
We use the most recent data on the Higgs-like resonance h observed at 125 GeV
to derive information about the mass of the heavier Higgs particles predicted
by Minimal Supersymmetry. We treat as independent parameters the couplings of h
to top quark, beauty and massive vector bosons and, in this three dimensional
space, we locate the point realizing the best fit to data and compare it to the
position of the Standard Model point and to the region of coupling values
accommodating heavier Higgs particles in Minimal Supersymmetry. We conclude
that mass values 320< M_H< 360 GeV are compatible at 2sigma with the best fit
of couplings to present data, larger values being compatible at the 1sigma
level. Values of 1< tan(beta)< 6 are compatible with data.Comment: 5 pages, 5 figures. Clarifications and new references adde
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
Indications of a Four-Quark Structure for the X(3872) and X(3876) Particles from Recent Belle and BABAR Data
Recent results by BELLE and BaBar point to the existence of a second X
particle decaying in D^0 D^0bar pi^0, a few MeV above the X(3872). We identify
the two X states with the neutral particles predicted by the 4-quark model and
show that production and decays are consistent with this assignement. We
consider the yet-to-be-observed charged partners and give new hints on how to
look for them.Comment: 5 pages, some revision of the text, results unchanged. To appear in
Phys. Rev. Let
Neutron Production Rates by Inverse-Beta Decay in Fully Ionized Plasmas
Recently we showed that the nuclear transmutation rates are largely
overestimated in the Widom-Larsen theory of the so called `Low Energy Nuclear
Reactions'. Here we show that unbound plasma electrons are even less likely to
initiate nuclear transmutations.Comment: 9 pages, 1 Figure, minor revisions and clarifications, results
unchanged. To appear in EPJ
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