First results from an extended freed-isobar analysis at COMPASS

Abstract

One of the goals of the COMPASS experiment is the precision study of light-meson spectroscopy with data for various final states. With 46 × 10 6 exclusive events, the process π − p → π − π + π − p constitutes the flagship channel. Based on this data set, the results of an extensive partial-wave analysis (PWA), using a total of 88 partial waves in the model, were published. Along with it, results of a first study of the so-called freed-isobar method were shown. Here, the fixed amplitudes for appearing π + π − intermediate states used in the conventional analysis were replaced by sets of piecewise constant functions to extract the amplitudes of the π + π − subsystems directly from the data. In this first study, this was done for three π partial waves with J PC = 0 ++ intermediate π + π − states. The promising results inspired further extension of this method, by also freeing intermediate π + π − states with J PC = 1 −− and 2 ++ . With this extension of the set of freed waves, mathematical ambiguities in the model arise due to the much higher flexibility of the model. We will present first results of these extended studies on COMPASS data along with methods to resolve the arising ambiguities.

$ω\to 3π$ and $ωπ^{0}$ transition form factor revisited

“…7 constitutes a prediction for it. 4 Finally, we note that the "low φ ωπ 0 (0)" solution is rather close to φ ωπ 0 (0) = 0, and the "high φ ωπ 0 (0)" is close (but less than the previous one) to φ ωπ 0 (0) = π. If the amplitudes were computed from a Lagrangian approach with a stable ω, the couplings in the Lagrangians would be real.…”

“…A precise description of the amplitudes involving three particles in the final state is one of the open challenges in hadron physics. It becomes even more important in view of the high precision data from the GlueX, CLAS12, COMPASS, BESIII, and LHCb experiments, where various exotic states decaying to three particles have been or will be measured [1][2][3][4][5][6][7]. A proper description of three-particle amplitudes is also required for extraction of resonance parameters from lattice QCD computations [8][9][10][11][12].…”

$$\omega \rightarrow 3\pi $$ and $$\omega \pi ^{0}$$ transition form factor revisited

“…8 constitutes a prediction for it. 4 Finally, we note that the "low φ ωπ 0 (0)" solution is rather close to φ ωπ 0 (0) = 0, and the "high φ ωπ 0 (0)" is close (but less than the previous one) to φ ωπ 0 (0) = π . If the amplitudes were computed from a Lagrangian approach with a stable ω, the couplings in the Lagrangians would be real.…”

“…A precise description of the amplitudes involving three particles in the final state is one of the open challenges in hadron physics. It becomes even more important in view of the high precision data from the GlueX, CLAS12, COMPASS, BESIII, and LHCb experiments, where various exotic states decaying to three particles have been or will be measured [1][2][3][4][5][6][7]. A proper description of three-particle amplitudes is also required for extraction of resonance parameters from lattice QCD computations [8][9][10][11][12].…”

Three-body scattering: ladders and resonances

“…Furthermore, a better understanding of three-hadron dynamics is necessary to take full advantage of the large data sets from COMPASS, LHCb, CLAS, GlueX, BESIII, and BelleII where genuine three-body effects have already been observed (e.g. see the a 1 (1420) phenomenon [6,[14][15][16]).…”