Experimental activities in few-body physics

Understanding the few-nucleon system remains one of the challenges in modern nuclear and hadron physics. Observables in few-nucleon scattering processes are sensitive probes to study the two and many-body interactions between nucleons in nuclei. In the past decades, several facilities provided a large data base to study in detail the three-nucleon interactions below the pion-production threshold by exploiting polarized proton and deuteron beams and large-acceptance detectors. Only since recently, the four-nucleon scattering process at intermediate energies has been explored. In addition, there is a focus to collect data in the hyperon-nucleon sector, thereby providing access to understand the more general baryon-baryon interaction. In this contribution, some recent results in the few-nucleon sector are discussed together with some of the preliminary results from a pioneering and exclusive study of the four-nucleon scattering process. Furthermore, this paper discusses the experimental activities in the hyperon sector, in particular, the perspectives of the hyperon program of PANDA.Comment: 9 pages, 4 figures, proceedings of the 21st European Conference on Few Body Problems in Physics, Salamanca, Spain, 30 August - 3 September 201

Studying the ω\omega-mass in-medium in γ+A→π0γ+X\gamma + A\to \pi^0\gamma +X reactions

Simulations based on a coupled-channel transport model have been performed to analyze the feasibility to study the in-medium $\omega$ mass exploiting the process $\gamma+A\to\pi^0\gamma+X$ for C, Ca and Nb nuclei. The distortions due to final-state interactions of the $\pi^0$ and background contributions from the reaction $\gamma+A\to\pi^0\pi^0+X$ are found to be small in the mass range of interest ($0.6<M_{\pi^0\gamma}<0.8$ GeV). Furthermore, the effect of the detector resolution on the $\pi^0\gamma$-mass determination is discussed

Observation of a Vector Charmoniumlike State at 4.7 GeV/c2 and Search for Zcs in e+e- →k+K-J/ψ

Using data samples with an integrated luminosity of 5.85 fb-1 collected at center-of-mass energies from 4.61 to 4.95 GeV with the BESIII detector operating at the BEPCII storage ring, we measure the cross section for the process e+e-→K+K-J/ψ. A new resonance with a mass of M=4708-15+17±21 MeV/c2 and a width of Γ=126-23+27±30 MeV is observed in the energy-dependent line shape of the e+e-→K+K-J/ψ cross section with a significance over 5σ. The K+J/ψ system is also investigated to search for charged charmoniumlike states, but no significant Zcs+ states are observed. Upper limits on the Born cross sections for e+e-→K-Zcs(3985)+/K-Zcs(4000)++c.c. with Zcs(3985)±/Zcs(4000)±→K±J/ψ are reported at 90% confidence levels. The ratio of branching fractions {[B(Zcs(3985)+→K+J/ψ)]/B[Zcs(3985)+→(D¯0Ds∗++D¯∗0Ds+)]} is measured to be less than 0.03 at 90% confidence level. © 2023 authors. Published by the American Physical Society

Observation of a Vector Charmoniumlike State at 4.7 GeV/c2 and Search for Zcs in e+e- →k+K-J/ψ

Using data samples with an integrated luminosity of 5.85 fb-1 collected at center-of-mass energies from 4.61 to 4.95 GeV with the BESIII detector operating at the BEPCII storage ring, we measure the cross section for the process e+e-→K+K-J/ψ. A new resonance with a mass of M=4708-15+17±21 MeV/c2 and a width of Γ=126-23+27±30 MeV is observed in the energy-dependent line shape of the e+e-→K+K-J/ψ cross section with a significance over 5σ. The K+J/ψ system is also investigated to search for charged charmoniumlike states, but no significant Zcs+ states are observed. Upper limits on the Born cross sections for e+e-→K-Zcs(3985)+/K-Zcs(4000)++c.c. with Zcs(3985)±/Zcs(4000)±→K±J/ψ are reported at 90% confidence levels. The ratio of branching fractions {[B(Zcs(3985)+→K+J/ψ)]/B[Zcs(3985)+→(D¯0Ds∗++D¯∗0Ds+)]} is measured to be less than 0.03 at 90% confidence level. © 2023 authors. Published by the American Physical Society

Measurements of the absolute branching fractions of ω- Decays and test of the Δi=1/2 rule

Based on a dataset of (27.12±0.10)×108 ψ(3686) events collected at the BESIII experiment, the absolute branching fractions of the three dominant ω- decays are measured to be Bω-→Ξ0π-=(25.03±0.44±0.53)%, Bω-→Ξ-π0=(8.43±0.52±0.28)%, and Bω-→ΛK-=(66.3±0.8±2.0)%, where the first and second uncertainties are statistical and systematic, respectively. The ratio between Bω-→Ξ0π- and Bω-→Ξ-π0 is determined to be 2.97±0.19±0.11, which is in good agreement with the PDG value of 2.74±0.15, but greater by more than four standard deviations than the theoretical prediction of 2 obtained from the ΔI=1/2 rule. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.<br/

Observation of a Vector Charmoniumlike State at 4.7 GeV/c2 and Search for Zcs in e+e- →k+K-J/ψ

Using data samples with an integrated luminosity of 5.85 fb-1 collected at center-of-mass energies from 4.61 to 4.95 GeV with the BESIII detector operating at the BEPCII storage ring, we measure the cross section for the process e+e-→K+K-J/ψ. A new resonance with a mass of M=4708-15+17±21 MeV/c2 and a width of Γ=126-23+27±30 MeV is observed in the energy-dependent line shape of the e+e-→K+K-J/ψ cross section with a significance over 5σ. The K+J/ψ system is also investigated to search for charged charmoniumlike states, but no significant Zcs+ states are observed. Upper limits on the Born cross sections for e+e-→K-Zcs(3985)+/K-Zcs(4000)++c.c. with Zcs(3985)±/Zcs(4000)±→K±J/ψ are reported at 90% confidence levels. The ratio of branching fractions {[B(Zcs(3985)+→K+J/ψ)]/B[Zcs(3985)+→(D¯0Ds∗++D¯∗0Ds+)]} is measured to be less than 0.03 at 90% confidence level. © 2023 authors. Published by the American Physical Society

Observation of the ψ (3686) decays into ς+ ς ¯ -ω and ς+ ς ¯ -φ

Based on (2712.4±14.3)×106 events recorded at the ψ(3686) nominal mass collected with the BESIII detector operating at the BEPCII collider, the ψ(3686)→ς+ς¯-ω and ς+ς¯-φ decays are observed for the first time with statistical significances of 13.8σ and 7.6σ, respectively. The corresponding branching fractions are measured to be B(ψ(3686)→ς+ς¯-ω)=(1.89±0.18±0.21)×10-5 and B(ψ(3686)→ς+ς¯-φ)=(2.96±0.54±0.41)×10-6, where the first uncertainties are statistical and the second systematic.<br/

Improved measurement of the branching fractions for J/ψ →γπ0, γη, and γη′

Using a data sample of (1.0087±0.0044)×1010 J/ψ events collected with the BESIII detector, the decays of J/ψ→γπ0(η,η′)→γγγ are studied. Newly measured branching fractions are B(J/ψ→γπ0)=(3.34±0.02±0.09)×10-5, B(J/ψ→γη)=(1.096±0.001±0.019)×10-3, and B(J/ψ→γη′)=(5.40±0.01±0.11)×10-3, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world average values within two standard deviations. The ratio of partial widths Γ(J/ψ→γη′)/Γ(J/ψ→γη) is measured to be 4.93±0.13. The singlet-octet pseudoscalar mixing angle θP is determined to be θP=-(22.11±0.26)° or -(19.34±0.34)° with two different phenomenological models. © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.<br/