The three-nucleon system as a laboratory for nuclear physics: the need for 3N forces

Recent experimental results in three-body systems have unambiguously shown that calculations based on nucleon-nucleon forces fail to accurately describe many experimental observables and one needs to include effects which are beyond the realm of the two-body potentials. This conclusion owes its significance to the fact that experiments and calculations can both be performed with a high accuracy. In this short review, a sample of recent experimental results along with the results of the state-of-the-art calculations will be presented and discussed.Comment: Commissioned article for Nuclear Physics News, 8 pages, 6 figure

The Use of Storage Rings in the Study of Reactions at Low-momentum Transfers

A few aspects of the nucleus manifest themselves in direct reactions where the transferred momentum to the nucleus is very small. In the study of radioactive isotopes, one has to use inverse kinematics in which the radioactive ion impinges on a stable target. When the momentum transfer is low, one has to do these reactions with either an active target or in a storage-ring environment. In this contribution, the latter method will be discussed in some detail as the active targets are discussed in other contributions. The pilot studies performed by the EXL Collaboration in 2012 lead to the first ever measurements of reactions employing radioactive isotopes in the ring. In this contribution, the first results will be presented. The outlook will indicate in which directions the future of this field will be headed.</p

A new Time-of-flight detector for the R ³ B setup

We present the design, prototype developments and test results of the new time-of-flight detector (ToFD) which is part of the R3B experimental setup at GSI and FAIR, Darmstadt, Germany. The ToFD detector is able to detect heavy-ion residues of all charges at relativistic energies with a relative energy precision σΔE/ ΔE of up to 1% and a time precision of up to 14 ps (sigma). Together with an elaborate particle-tracking system, the full identification of relativistic ions from hydrogen up to uranium in mass and nuclear charge is possible.</p

Measurement of the branching fraction of the singly Cabibbo-suppressed decay Λc+ → Λk+

We report a branching fraction measurement of the singly Cabibbo-suppressed decay Λc+→ΛK+ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of 6.44 fb-1. The branching fraction of Λc+→ΛK+ relative to that of the Cabibbo-favored decay Λc+→Λπ+ is measured to be R=B(Λc+→ΛK+)B(Λc+→Λπ+)=(4.78±0.34±0.20)%. Combining with the world-average value of B(Λc+→Λπ+), we obtain B(Λc+→ΛK+)=(6.21±0.44±0.26±0.34)×10-4. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the Λc+→Λπ+ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that nonfactorizable contributions have been underestimated in current models

WASA-FRS EXPERIMENTS IN FAIR PHASE-0 AT GSI

We have developed a new and unique experimental setup integrating the central part of the Wide Angle Shower Apparatus (WASA) into the Fragment Separator (FRS) at GSI. This combination opens up possibilities of new experiments with high-resolution spectroscopy at forward 0◦ and measurements of light decay particles with nearly full solid-angle acceptance in coincidence. The first series of the WASA-FRS experiments have been successfully carried out in 2022. The developed experimental setup and two physics experiments performed in 2022 including the status of the preliminary data analysis are introduced.</p

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

Measurement of the cross section of e + e − → ηπ + π − at center-of-mass energies from 3.872 GeV to 4.700 GeV

Using data samples with an integrated luminosity of 19 fb−1 at twenty-eight center-of-mass energies from 3.872 GeV to 4.700 GeV collected with the BESIII detector at the BEPCII electron-positron collider, the process e+e− → ηπ+π− and the intermediate process e+e− → ηρ0 are studied for the first time. The Born cross sections are measured. No significant resonance structure is observed in the cross section lineshape. [Figure not available: see fulltext.]