S. Marcello

Observation of Spin-Dependent Charge Symmetry Breaking in

The energy spacing between the spin-doublet bound state of _{Λ}^{4}He(1^{+},0^{+}) was determined to be 1406±2±2  keV, by measuring γ rays for the 1^{+}→0^{+} transition with a high efficiency germanium detector array in coincidence with the ^{4}He(K^{-},π^{-})_{Λ}^{4}He reaction at J-PARC. In comparison to the corresponding energy spacing in the mirror hypernucleus _{Λ}^{4}H, the present result clearly indicates the existence of charge symmetry breaking (CSB) in ΛN interaction. By combining the energy spacings with the known ground-state binding energies, it is also found that the CSB effect is large in the 0^{+} ground state but is vanishingly small in the 1^{+} excited state, demonstrating that the ΛN CSB interaction has spin dependence.

\Lambda N

Abstract First results on meson spectroscopy using antineutrons as projectiles are reported. Three-body (π + π + π − ) and five-body (π + π + π + π − π − ) final states following the annihilation of 100 to 290 MeV/ c antineutrons on hydrogen were analyzed. The (π + π − ) invariant mass spectrum in the three-body reaction is accounted for by the ϱ 0 anf f 2 (1270) resonances, together with an enhancement around 1540 MeV, in the region of the AX (1565) and the f 2 (1515) resonances, whereas the best fit for the (π + π + π − π − ) invariant mass in five-body events shows the already reported structure ζ(1480) and suggests the presence of a second structure around 1650 MeV.

Interaction: Gamma-Ray Spectroscopy of

Abstract The FINUDA experiment performed a systematic study of the charged mesonic weak decay channel of p -shell Λ -hypernuclei. Negatively charged pion spectra from mesonic decay were measured with magnetic analysis for the first time for 7 Λ Li, 9 Λ Be, 11 Λ B and 15 Λ N. The shape of the π − spectra was interpreted through a comparison with pion distorted wave calculations that take into account the structure of both hypernucleus and daughter nucleus. Branching ratios Γ π − / Γ tot were derived from the measured spectra and converted to π − decay rates Γ π − by means of known or extrapolated total decay widths Γ tot of p -shell Λ -hypernuclei. Based on these measurements, the spin-parity assignment 1 / 2 + for 7 Λ Li and 5 / 2 + for 11 Λ B ground-state are confirmed and a spin-parity 3 / 2 + for 15 Λ N ground-state is assigned for the first time.

^4_{\Lambda }

Abstract Hyperon production in the threshold region was studied in the reaction pp → K + Λ p using the time-of-flight spectrometer COSY-TOF. Exclusive data, covering the full phase-space, were taken at the three different beam momenta of p beam = 2.95 , 3.20 and 3.30 GeV/ c , corresponding to excess energies of e = 204 , 285 and 316 MeV, respectively. Total cross-sections were deduced for the three beam momenta to be 23.9 ± 0.8 ± 2.0 μb , 28.4 ± 1.3 ± 2.2 μb and 35.0 ± 1.3 ± 3.0 μb . Differential observables including Dalitz plots were obtained. The analysis of the Dalitz plots reveals a strong influence of the N ( 1650 ) -resonance at p beam = 2.95 GeV / c , whereas for the higher momenta an increasing relative contribution of the N ( 1710 ) - and/or of the N ( 1720 ) -resonance was observed. In addition, the pΛ -final-state interaction turned out to have a significant influence on the Dalitz plot distribution.

He

Abstract Three candidate events of the neutron-rich hypernucleus H Λ 6 were uniquely identified in the FINUDA experiment at DAΦNE, Frascati, by observing π + mesons from the ( K stop − , π + ) production reaction on 6 Li targets, in coincidence with π − mesons from H Λ 6 → He 6 + π − weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of ( 2.9 ± 2.0 ) ⋅ 10 − 6 / K stop − for the H Λ 6 production rate times the two-body π − weak decay branching ratio. The H Λ 6 binding energy with respect to H 5 + Λ was determined jointly from production and decay to be B Λ = ( 4.0 ± 1.1 ) MeV , assuming that 5 H is unbound with respect to H 3 + 2 n by 1.7 MeV. The binding energy determined from production is higher, in each one of the three events, than that determined from decay, with a difference of ( 0.98 ± 0.74 ) MeV here assigned to the 0 g.s. + → 1 + excitation. The consequences of this assignment to Λ hypernuclear dynamics are briefly discussed.

Meson spectroscopy with antineutrons

The two-pion production reaction pp → ppπ+π− was measured with a polarized proton beam at Tp ≈ 750 and 800MeV using the short version of the COSY-TOF spectrometer. The implementation of a delayed-pulse technique for Quirl and central calorimeter provided positive π+ identification in addition to the standard particle identification, energy determination as well as time-of-flight and angle measurements. Thus all four-momenta of the emerging particles could be determined with 1–4 overconstraints. Total and differential cross-sections as well as angular distributions of the vector analyzing power have been obtained. They are compared to previous data and theoretical calculations. In contrast to predictions we find significant analyzing-power values up to Ay = 0.3. The data taken in the energy region of the excitation of the Roper resonance confirm that its dominant ππ decay channel is N* → Nσ.

New results on mesonic weak decay of p-shell Lambda-hypernuclei

Abstract The reaction p p → p p ω was investigated with the TOF spectrometer, which is an external experiment at the accelerator COSY (Forschungszentrum Julich, Germany). Total as well as differential cross sections were determined at an excess energy of 93 MeV ( p beam = 2950 MeV / c ). Using the total cross section of ( 9.0 ± 0.7 ± 1.1 ) μb for the reaction p p → p p ω determined here and existing data for the reaction p p → p p ϕ , the ratio R ϕ / ω = σ ϕ / σ ω turns out to be significantly larger than expected by the Okubo–Zweig–Iizuka (OZI) rule. The uncertainty of this ratio is considerably smaller than in previous determinations. The differential distributions show that the ω production is still dominated by S-wave production at this excess energy, however higher partial waves clearly contribute. A comparison of the measured angular distributions for ω production to published distributions for ϕ production at 83 MeV shows that the data are consistent with an identical production mechanism for both vector mesons.

Influence of N*-resonances on hyperon production in the channel pp->K+ Lambda p at 2.95, 3.20 and 3.30 GeV/c beam momentum

Abstract A confirming evidence for two pseudoscalar states with masses M 1 =1405±5, Γ 1 =50±4 MeV/ c 2 and M 2 =1500±10, Γ 2 =100±20 MeV/ c 2 is reported. The second pseudoscalar fills the nonet and leaves the first as an outsider supporting the hypothesis for its exotic nature.

First observation of the hyper superheavy hydrogen HΛ6

Abstract The study of the I =1, J PC =0 ++ states with the OBELIX detector in the channel p p→K ± K 0 S π ∓ at three different target densities is reported. The data show the evidence for an extra scalar state with mass 1.29±0.01 GeV/ c 2 and width 0.080±0.005 GeV/ c 2 .

Two-pion production in proton-proton collisions with a polarized beam

Abstract Data of antiproton annihilation at rest in a hydrogen gas target at NTP have been collected with the Obelix spectrometer exposed to the beam extracted from the LEAR accelerator of CERN. The reactions p p → φπ 0 and p p → φη have been studied. The analysis of the angular distribution of the kaons emitted by the φ decay has shown that the reaction p p → φπ 0 occurs essentially from 3 S 1 states with a production rate R NTP = (2.46 ± 0.23 ± 0.07) × 10 −4 , while the rate from 1 P 1 states is compatible with zero. Because of acceptance limitations, 3 S 1 and 1 P 1 contributions to the reaction p p → φη could not be resolved and lower and upper limits for the production rate have been measured with the middle value R NTP = (0.87 ± 0.21) × 10 −4 . Also, for the phase-space K + K − η events the production rate R NTP = (4.67 ± 0.35) × 10 −4 has been measured. The φπ 0 and φη branching ratios in S- and P-waves (defined in the text) have been estimated in a model dependent way. For the evaluation of the φη rate, a combination of our production rate and of data obtained with a liquid target has been used. The φπ 0 production rate, compared to our preliminary value for the ωπ 0 production, confirms the strong violation of the OZI rule observed in other experiments. No violation is apparent in the φη production.