1,863 research outputs found
Baryon resonances and strong QCD
Light-baryon resonances (with u,d, and s quarks in the SU(3) classification)
fall on Regge trajectories. When their squared masses are plotted against the
intrinsic orbital angular momenta {\rm L}, 's with even and odd
parity can be described by the same Regge trajectory. For a given {\rm L},
nucleon resonances with spin {\rm S}=3/2 are approximately degenerate in mass
with resonances. To which total angular momentum {\rm L} and {\rm S}
couple has no significant impact on the baryon mass. Nucleons with spin 1/2 are
shifted in mass; the shift is - in units of squared masses - proportional to
the component in the wave function which is antisymmetric in spin and flavor.
Based on these observations, a new baryon mass formula is proposed which
reproduces nearly all known baryon masses. It is shown that the masses are
compatible with a quark-diquark picture while the richness of the
experimentally known states require three particles to participate in the
dynamics. This conflict is resolved by proposing that quarks polarize the QCD
condensates and are surrounded by a polarization cloud shielding the color. A
new interpretation of constituent quarks as colored quark clusters emerges;
their interaction is responsible for the mass spectrum. Fast flavor exchange
between the colored quark clusters exhausts the dynamical richness of the
three-particle dynamics. The colored-quark-cluster model provides a mechanism
in which the linear confinement potential can be traced to the increase of the
volume in which the condensates are polarized. The quark-spin magnetic moment
induces currents in the polarized condensates which absorb the quark-spin
angular momentum: the proton spin is not carried by quark spins. The model
provides a new picture of hybrids and glueballs.Comment: 33 pages, 8 Figure
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
Committing to Incentives: Should the Decision to Sanction be Revealed or Hidden?
Sanctions are widely used to promote compliance in principal-agent-relationships. While there is ample evidence confirming the predicted positive incentive effect of sanctions, it has also been shown that imposing sanctions may in fact reduce compliance by crowding-out intrinsic motivation. We add to the literature on the hidden costs of control by showing that these costs are restricted to situations where principals ex ante reveal their decision to sanction low compliance. If this decision is not revealed and agents do not know whether they will be sanctioned or not in case of low compliance, we do not find evidence of crowding-out - not even in those cases where agents firmly believe that they will be sanctioned in case of low performance.Intrinsic Motivation, Monetary Incentives, Job Performance
Classification of -Wave and Systems
An exotic meson, the with , has been seen to
decay into a p-wave system. If this decay conserves flavor SU(3),
then it can be shown that this exotic meson must be a four-quark state () belonging to a flavor representation
of SU(3). In contrast, the with a substantial decay mode into
is likely to be a member of a flavor octet.Comment: 8 page
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
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