1,182 research outputs found
Highlights from COMPASS in hadron spectroscopy
Since Quantum Choromdynamics allows for gluon self-coupling, quarks and
gluons cannot be observed as free particles, but only their bound states, the
hadrons. This so-called confinement phenomenon is responsible for of the
mass in the visible universe. The measurement of the hadron excitation spectra
therefore gives valuable input for theory and phenomenology to quantitatively
understand this phenomenon. One simple model to describe hadrons is the
Constituent Quark Model (CQM), which knows two types of hadrons: mesons,
consisting of a quark and an antiquark, and baryons, which are made out of
three quarks. More advanced models, which are inspired by QCD as well as
calculations within Lattice QCD predict the existence of other types of
hadrons, which may be e.g. described solely by gluonic excitations (glueballs)
or mixed quark and gluon excitations (hybrids). In order to search for such
states, the COMPASS experiment at the Super Proton Synchrotron at CERN has
collected large data sets, which allow to study the light-quark meson and
baryon spectra in unmatched precision. The overview shown here focuses on the
light meson sector, presenting a detailed Partial-Wave Analysis of the
processes: and . A
new state, the with is observed. Its Breit-Wigner
parameters are found to be in the ranges: and
. In the same analysis, a signal in a wave
with is observed. A resonant origin of this signal would not be
explicable within the CQM. In addition to this possibility of an exotic state,
a possible non resonant origin of this signal is discussed.Comment: Proceedings of the International Conference Dark Matter, Hadron
Physics and Fusion Physics Messina (Italy) - September 24-26, 2014, 8 pages,
16 figure
Recent progress in the partial-wave analysis of the diffractively produced final state at COMPASS
The COMPASS spectrometer at CERN has collected a large data set for
diffractive three-pion production of exclusive events. Based on
previous conventional Partial-Wave Analyses (PWA), we performed a `freed-isobar
PWA' on the same data, removing model assumptions on the dynamic isobar
amplitudes for dominating waves. In this analysis, we encountered continuous
mathematical ambiguities, which we were able to identify and resolve. This
analysis gives an unprecedented insight in the interplay of and
dynamics in the process. As an example we show results for a spin-exotic wave
wave.Comment: Proceedings for the 15th International Workshop on Meson Physics
(MESON 2018) from June 7th to 12th 2018 in Krak\'ow, Poland. Five pages, four
figure
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