arXiv subjects

R. Knoebel

Publications and source records attributed to R. Knoebel.

5 recordsLinked to original sources

arXiv2026

Current Results on Light Hypernuclei in the WASA-FRS HypHI Experiment

The current understanding of light hypernuclei, subatomic nuclei exhibiting strangeness, is being actively investigated by several collaborations. Recent studies employing high-energy heavy-ion beams have revealed unexpected results for the three-body bound state $^3_Λ$H, known as the hypertriton. Experimental measurements of its lifetime and binding energy across multiple experiments have produced a puzzling situation referred to as the ``hypertriton puzzle''. This puzzle is the central focus of the data analysis from the WASA-FRS HypHI experiment at GSI-FAIR within the SuperFRS Experiment collaboration. Light hypernuclei are being investigated using 1.96 GeV/u $^6$Li beams impinging on a fixed carbon target, in conjunction with the WASA detector system and the Fragment Separator (FRS) at GSI-FAIR. The WASA-FRS experimental campaign was carried out during the first quarter of 2022. The primary objective of the experiment is to measure the lifetimes of $^3_Λ$H and $^4_Λ$H. The possible observation of the nn$Λ$ state constitutes the second component of the WASA-FRS research program. This contribution provides an overview of our investigation of hypernuclei. Focusing on the WASA-FRS HypHI experiment, details of the current analysis status are presented.

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arXiv2018

Missing-mass spectroscopy of the ${}^{12}{\rm C}(p,d)$ reaction near the $η^\prime$-meson production threshold

Excitation-energy spectra of $^{11}$C nuclei near the $η^\prime$-meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$C($p$,$d$) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $η^\prime$ meson bound states in $^{11}$C nuclei. Deuterons emitted at $0^\circ$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $η^\prime$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $η^\prime$-mesic states are determined, and thereby a constraint imposed on the $η^\prime$-nucleus interaction is discussed.

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arXiv2016

Observation of Large Enhancement of Charge Exchange Cross Sections with Neutron-Rich Carbon Isotopes

Production cross sections of nitrogen isotopes from high-energy carbon isotopes on hydrogen and carbon targets have been measured for the first time for a wide range of isotopes. The fragment separator FRS at GSI was used to deliver C isotope beams. The cross sections of the production of N isotopes were determined by charge measurements of forward going fragments. The cross sections show a rapid increase with the number of neutrons in the projectile. Since the production of nitrogen is mostly due to charge exchange reactions below the proton separation energies, the present data suggests a concentration of Gamow-Teller and Fermi transition strength at low excitation energies for neutron-rich isotopes. It was also observed that the cross sections were enhanced much more strongly for neutron rich isotopes in the C-target data.

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arXiv2015

Spectroscopy of $η'$-nucleus bound states at GSI and FAIR --- very preliminary results and future prospects ---

The possible existence of η'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the η' mass at finite density, which is expected to be reduced because of the interplay between the $U_A(1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed.

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arXiv2015

Search for η'(958)-nucleus bound states by (p,d) reaction at GSI and FAIR

The mass of the η' meson is theoretically expected to be reduced at finite density, which indicates the existence of η'-nucleus bound states. To investigate these states, we perform missing-mass spectroscopy for the (p, d) reaction near the η' production threshold. The overview of the experimental situation is given and the current status is discussed.

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