arXiv subjects

S. Wallner

Publications and source records attributed to S. Wallner.

5 recordsLinked to original sources

arXiv2026

An analysis of four stellar rings

About 50 years ago, one thousand ring-like structures (called stellar-rings) were discovered by Isserstedt (1968). They were believed to be groups of young stars formed by shell-like triggered star formation, which would make them excellent tracers of spiral arms, for example. Neglected for 40 years, we used highly accurate kinematic, astrometric, and photometric data to investigate the four most prominent stellar rings. The aim is to investigate if those structures are indeed physically related groups of stars. We used proper motions and parallaxes from the Gaia DR2 to calculate distances and to search for common properties. Color-magnitude diagrams using BVJHKs measurements were investigated and isochrones fitted. None of the four stellar rings consists of a physically related group of young stars. The location of stars in the line-of-sight mimics a ring-like structure on the sky. The color-magnitude diagrams are typical for an integrated field population and not for a young star cluster, for example. The currently available data are sufficient to analyze ring-like structures with a high statistical significance. This allows a new search for such structures in the Milky Way.

astro-ph.SR↗

arXiv2025

Studies of hadron spectroscopy at Belle and Belle II

The Belle and Belle II experiments have collected a $1.6\,\mathrm{ab}^{-1}$ sample of $e^+e^-$ collision data at center-of-mass energies near the $\Upsilon(nS)$ resonances. We conduct searches for transitions from the spin-singlet $h_b(1P,2P)$ states to the spin-triplet $\Upsilon(1S)$ and $\chi_{bJ}(1P)$ states. We do not find evidence for the $h_b(1P,2P)\to \Upsilon(1S) \pi^0$ and $h_b(2P) \to \chi_{bJ}(1P)\gamma$ transitions. We find the first evidence for the $h_b(2P)\to \Upsilon(1S)\eta$ transition. However, the measured branching fraction is lower than expected from related decays. Furthermore, we find evidence for $P_{c\bar c s}(4459)^0 \to J/\psi \Lambda$ decays in inclusive $\Upsilon(1S,2S)$ decays. This is the first evidence for an exotic state produced in $\Upsilon(1S,2S)$ decays.

hep-ex↗

arXiv2023

Strange-Meson Spectroscopy with COMPASS

While the spectrum of non-strange light mesons is well known, many predicted strange mesons have not yet been observed, and many potentially observed states require further confirmation. Using the $K^-$ component of the hadron beam at the M2 beamline at CERN, we study the strange-meson spectrum with the COMPASS experiment. The flagship channel is the $K^-\pi^-\pi^+$ final state, for which COMPASS has obtained the world's largest sample. Based on this sample, we have performed the most detailed and comprehensive partial-wave analysis of this final state to date. For example, we observe a clear signal from the well-known $K_2^*(1430)$, and for the first time we study the $K_2(1770)$, $K_2(1820)$, and $K_2(2250)$ in a single analysis. We also find evidence for a supernumerary signal called $K(1630)$, suggesting that this signal is a pseudoscalar exotic strange meson.

hep-ex↗

arXiv2022

Strange-Meson Spectroscopy -- from COMPASS to AMBER

COMPASS is a multi-purpose fixed-target experiment at CERN's M2 beam line aimed at studying the structure and spectrum of hadrons. It has collected the so far world's largest data set on diffractive production of the $K^-\pi^-\pi^+$ final state, which in principle gives access to all strange mesons. Based on this data set, we performed an elaborate partial-wave analysis. It reveals signals in the mass region of well-known states, such as the $K_2^*(1430)$. In addition, we found indications for a resonance-like signal in the mass region of the $K(1630)$. This state would be a supernumerary state and hence could be a candidate for an exotic strange meson. The partial-wave analysis is limited in some areas by the limited kinematic coverage of the final-state particle identification of the COMPASS setup. To overcome this limitation, we propose a new high-precision strange-meson spectroscopy measurement at the AMBER experiment, which will be located at CERN's M2 beam line.

hep-ex↗

arXiv2019

Strange-Meson Spectroscopy at COMPASS

COMPASS is a multi-purpose fixed-target experiment at CERN aimed at studying the structure and spectrum of hadrons. It has collected the so far world's largest data set on diffractive production of the $K^-\pi^-\pi^+$ decay, which in principle gives access to all kaon states. We performed an elaborate partial-wave analysis, using model-selection techniques to select the wave set based on a large systematically constructed pool of allowed partial waves. The partial-wave decomposition reveals signals in the mass region of well-known states, such as $K_1(1270)$ and $K_1(1400)$. In addition, we observe potential signals from excited states, such as $K_1(1650)$.

hep-ex↗