Shape of Dipole Radiative Strength Function for Asymmetric Nuclei

The semiclassical method for description of the radiative strength function is used for asymmetric nuclei with $N \ne Z$. The theory is based on the linearized Vlasov-Landau equations in two-component finite Fermi liquid. The dependence of the shape $E1$ strength on the coupling constant between proton and neutron subsystems was studied.Comment: Latex, 4 pages; 2 *.ps files with figures. Poster Report of Eleventh Inter. Symp. on Capture Gamma-Ray Spectroscopy and Rel. Topics, Prague, 2-6 September, 2002 (to be published in proceedings

Studies of three-and four-body hypernuclei with heavy-ion beams, nuclear emulsions and machine learning

Interests on few-body hypernuclei have been increased by recent results of experiments employing relativistic heavy ion beams. Some of the experiments have revealed that the lifetime of the lightest hypernucleus, hypertriton, is significantly shorter than 263 ps which is expected by considering the hypertriton to be a weakly-bound system. The STAR collaboration has also measured the hypertriton binding energy, and the deduced value is contradicting to its formerly known small binding energy. These measurements have indicated that the fundamental physics quantities of the hypertriton such as its lifetime and binding energy have not been understood, therefore, they have to be measured very precisely. Furthermore, an unprecedented Λnn bound state observed by the HypHI collaboration has to be studied in order to draw a conclusion whether or not such a bound state exists. These three-body hypernuclear states are studied by the heavy-ion beam data in the WASA-FRS experiment and by analysing J-PARC E07 nuclear emulsion data with machine learning.</p

Observation of the doubly Cabibbo-suppressed decays D + → K + π 0 π 0 and D + → K + π 0 η

By analyzing e+e− annihilation data corresponding to an integrated luminosity of 2.93 fb−1 collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first observations of the doubly Cabibbo-suppressed decays D+→ K+π0π0 and D+→ K+π0η. The branching fractions of D+→ K+π0π0 and D+→ K+π0η are measured to be (2.1 ± 0.4stat ± 0.1syst) × 10−4 and (2.1 ± 0.5stat ± 0.1syst) × 10−4 with statistical significances of 8.8σ and 5.5σ, respectively. In addition, we search for the subprocesses D+→ K*(892)+π0 and D+→ K*(892)+η with K*(892)+→ K+π0. The branching fraction of D+→ K*(892)+η is determined to be (4.4−1.5stat+1.8± 0.2syst) × 10−4, with a statistical significance of 3.2σ. No significant signal for D+→ K*(892)+π0 is found and we set an upper limit on the branching fraction of this decay at the 90% confidence level to be 5.4 × 10−4. [Figure not available: see fulltext.

Observation of the hindered electromagnetic Dalitz decay ψ (3686) →e+e-ηc

Using a data sample of (448.1±2.9)×106 ψ(3686) decays collected at an e+e- center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay ψ(3686)→e+e-ηc with a significance of 7.9σ. The branching fraction is determined to be B(ψ(3686)→e+e-ηc)=(3.77±0.40stat±0.18syst)×10-5, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the ψ(3686) and the ηc, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ηc decays

Observation of the decay ψ(3686) → Σ −Σ ¯ + and measurement of its angular distribution

Using (448.1 ± 2.9) × 106ψ(3686) events collected with the BESIII detector at the BEPCII collider, the decay ψ(3686) →Σ −Σ ¯ + is observed for the first time with a branching fraction of (2.82 ± 0.04stat.± 0.08syst.) × 10−4, and the angular parameter αΣ− is measured to be 0.96 ± 0.09stat.± 0.03syst.. [Figure not available: see fulltext.

Improved measurement of the strong-phase difference δDKπ in quantum-correlated DD¯ decays

The decay D→ K-π+ is studied in a sample of quantum-correlated DD¯ pairs, based on a data set corresponding to an integrated luminosity of 2.93 fb- 1 collected at the ψ(3770) resonance by the BESIII experiment. The asymmetry between CP-odd and CP-even eigenstate decays into K-π+ is determined to be AKπ= 0.132 ± 0.011 ± 0.007 , where the first uncertainty is statistical and the second is systematic. This measurement is an update of an earlier study exploiting additional tagging modes, including several decay modes involving a KL0 meson. The branching fractions of the KL0 modes are determined as input to the analysis in a manner that is independent of any strong phase uncertainty. Using the predominantly CP-even tag D→ π+π-π and the ensemble of CP-odd eigenstate tags, the observable AKππππ0 is measured to be 0.130 ± 0.012 ± 0.008. The two asymmetries are sensitive to rDKπcosδDKπ, where rDKπ and δDKπ are the ratio of amplitudes and phase difference, respectively, between the doubly Cabibbo-suppressed and Cabibbo-favoured decays. In addition, events containing D→ K-π+ tagged by D→KS,L0π+π- are studied in bins of phase space of the three-body decays. This analysis has sensitivity to both rDKπcosδDKπ and rDKπsinδDKπ. A fit to AKπ, AKππππ0 and the phase-space distribution of the D→KS,L0π+π- tags yields δDKπ=(187.6-9.7+8.9-6.4+5.4)∘, where external constraints are applied for rDKπ and other relevant parameters. This is the most precise measurement of δDKπ in quantum-correlated DD¯ decays

Study of e+e- → ω- ω ¯ + at center-of-mass energies from 3.49 to 3.67 GeV

Using data samples of e+e- collisions collected with the BESIII detector at eight center-of-mass energy points between 3.49 and 3.67 GeV, corresponding to an integrated luminosity of 670 pb-1, we present the upper limits of Born cross sections and the effective form factor for the process e+e-→ω-ω¯+. A fit to the cross sections using a perturbative QCD-derived energy-dependent function shows no significant threshold effect. The upper limit on the measured effective form factor is consistent with a theoretical prediction within the uncertainty of 1σ. These results provide new experimental information on the production mechanism of ω

Measurement of Proton Electromagnetic Form Factors in e(+) e(-) -&gt; p(p)over-bar in the Energy Region 2.00-3.08 GeV

The process of e+e-→pp̄ is studied at 22 center-of-mass energy points (s) from 2.00 to 3.08 GeV, exploiting 688.5 pb-1 of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section (σpp̄) of e+e-→pp̄ is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio (|GE/GM|) and the value of the effective (|Geff|), electric (|GE|), and magnetic (|GM|) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. |GE/GM| and |GM| are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and |GE| is measured for the first time. We reach unprecedented accuracy, and precision results in the timelike region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on nonperturbative quantum chromodynamics

Search for hyperon Δs= Δq violating decay Ξ0 → ς-e+νe

Using a data sample of (1.0087±0.0044)×1010 J/ψ decay events collected with the BESIII detector at the center-of-mass energy of s=3.097 GeV, we present a search for the hyperon semileptonic decay Ξ0→ς-e+νe which violates the ΔS=ΔQ rule. No significant signal is observed, and the upper limit on the branching fraction B(Ξ0→ς-e+νe) is determined to be 1.6×10-4 at the 90% confidence level. This result improves the previous upper limit result by about one order of magnitude