42 research outputs found
Baryon Spectroscopy and the Origin of Mass
The proton mass arises from spontaneous breaking of chiral symmetry and the
formation of constituent quarks. Their dynamics cannot be tested by proton
tomography but only by studying excited baryons. However, the number of excited
baryons is much smaller than expected within quark models; even worse, the
existence of many known states has been challenged in a recent analysis which
includes - compared to older analyses - high-precision data from meson
factories. Hence elastic scattering data do not provide a well-founded
starting point of any phenomenological analysis of the baryon excitation
spectrum. Photoproduction experiments now start to fill in this hole. Often,
they confirm the old findings and even suggest a few new states. These results
encourage attempts to compare the pattern of observed baryon resonances with
predictions from quark models, from models generating baryons dynamically from
meson-nucleon scattering amplitudes, from models based on gravitational
theories, and with the conjecture that chiral symmetry may be restored at high
excitation energies. Best agreement is found with a simple mass formula derived
within AdS/QCD. Consequences for our understanding of QCD are discussed as well
as experiments which may help to decide on the validity of models.Comment: Hadron 2009 invited talk, 8 pages, 6 figures, 4 table
Glueballs in Radiative Decays
The scalar glueball is observed in a coupled-channel analysis of the -wave
amplitude from BESIII data on radiative decays and further data. Ten
scalar isoscalar resonances were required to fit the data. Five of them were
interpreted as mainly-singlet, five as mainly-octet resonances in SU(3). The
yield of resonances showed a striking peak with properties expected from a
scalar glueball. The wave amplitude in the BESIII data on radiative
decays reveales a high-mass structure which can be described by a
single Breit-Wigner or by the sum of three resonances interpreted as
tensor glueballs a long time ago. The structure - and further tensor resonances
observed in radiative decays - are tentatively interpreted as tensor
glueball. In decays into several resonances
are reported. The possibility is discussed that the pseudoscalar glueball might
be hidden in these data.Comment: Contribution to XVth Quark confinement and the Hadron spectrum
conference, August 1st - 6th, 2022, University of Stavanger, Norwa
The Glueball Candidate \eta(1440) as \eta Radial Excitation
The Particle Data Group decided to split the into two states,
called and . The and the are supposed to
be the radial excitations of the and , respectively. The
state cannot be accomodated in a quark model; it cannot be a state,
however, it might be a glueball. In this contribution it is shown that that the
does not have the properties which must be expected for a radially
excited state. The splitting of the is traced to a node in the
wave function of a radial excitation. Hence the two peaks, and
, originate from one resonance which is interpreted here as first
radial excitation of the .Comment: 8 pages, 3 figures, contribution to ICHEP04, Beijing, 200
Glueballs, a fulfilled promise of QCD?
This is a contribution to the review "50 Years of Quantum Chromdynamics"
edited by F. Gross and E. Klempt [arXiv:2212.11107], to be published in EPJC.
The contribution remembers the early searches and explains how to find a
glueball, based on its properties. The results of a coupled-channel analysis
are presented that provides evidence for the scalar glueball and first hints
for the tensor glueball. Data on radiative decays of and
show scalar intensity that is likely due to glueball production.Comment: 9 pages, 12 figure
Are the XYZ states unconventional states or conventional states with unconventional properties?
We discuss three possible scenarios for the interpretation of mesons
containing a heavy quark and its antiquark near and above the first threshold
for a decay into a pair of heavy mesons in a relative --wave. View I assumes
that these thresholds force the quark potential to flatten which implies that
while in these energy ranges molecular states may be formed there should not be
any quark--anti-quark states above these thresholds. View II assumes that the
main part of the interaction between two mesons is due to the poles which
originate from the interaction. The properties of the
mesons are strongly influenced by opening thresholds but the number of states
is given by the quark model. In View III, both types of mesons are admitted
also near and above the open flavor thresholds: mesons and
dynamically generated mesons. Experimental consequences of these different
views are discussed.Comment: 15 pages, 5 figure
Heavy-flavor baryons
This is a contribution to the review "50 Years of Quantum Chromdynamics"
edited by F. Gross and E. Klempt [arXiv:2212.11107], to be published in EPJC.
The contribution reviews the properties of baryons with one heavy flavor: the
lifetimes of ground states and the spectrum of excited states. The importance
of symmetries to understand the excitation spectrum is underlined. An overview
of searches for pentaquarks is given.Comment: 10 pages, 8 tables, 7 figure
Baryon spectroscopy
About 120 baryons and baryon resonances are known, from the abundant nucleon
with and light-quark constituents up to the recently discovered
, and the which contains one quark of each
generation. In spite of this impressively large number of states, the
underlying mechanisms leading to the excitation spectrum are not yet
understood. Heavy-quark baryons suffer from a lack of known spin-parities. In
the light-quark sector, quark-model calculations have met with considerable
success in explaining the low-mass excitations spectrum but some important
aspects like the mass degeneracy of positive-parity and negative-parity baryon
excitations are not yet satisfactorily understood. At high masses, above 1.8
GeV, quark models predict a very high density of resonances per mass interval
which is not observed. In this review, issues are identified discriminating
between different views of the resonance spectrum; prospects are discussed how
open questions in baryon spectroscopy may find answers from photo- and
electro-production experiments which are presently carried out in various
laboratories.Comment: Review article, 53 pages, 40 figures, 23 Tables. Review of Modern
Physics (accepted for publication