A. Feliciello

First results on 12ΛC production at DAΦNE

Lambda-hypernuclei are produced and studied, with the FINUDA spectrometer, for the first time at an e+e- collider: DAPHNE, the Frascati phi-factory. The slow negative kaons from phi(1020) decay are stopped in thin (0.2 g/cm^2) nuclear targets, and Lambda-hypernuclei formation is detected by measuring the momentum of the outgoing pi^-. A preliminary analysis on 12Lambda-C shows an energy resolution of 1.29 MeV FWHM on the hypernuclear levels, the best obtained so far with magnetic spectrometers at hadron facilities. Capture rates for the ground state and the excited ones are reported, and compared with previous experiments.

Evidence for heavy hyperhydrogen (Lambda)H-6

Evidence for the neutron-rich hypernucleus H-6(Lambda) is presented from the FINUDA experiment at DA Phi NE, Frascati, studying (pi(+), pi(-)) pairs in coincidence from the (K) over bar (-)(stop) + Li-6 -> H-6(Lambda) + pi(+) production reaction followed by H-6(Lambda) -> He-6 + pi(-) weak decay. The production rate of H-6(Lambda) undergoing this two-body pi(-) decay is determined to be (2.9 +/- 2.0) x 10(-6)/K-stop(-). Its binding energy, evaluated jointly from production and decay, is B-Lambda(H-6(Lambda)) = (4.0 +/- 1.1) MeV with respect to 5H + Lambda. A systematic difference of (0.98 +/- 0.74) MeV between B-Lambda values derived separately from decay and from production is tentatively assigned to the H-6(Lambda) 0(g.s)(+) excitationEvidence for the neutron-rich hypernucleus 6{\Lambda}H is presented from the FINUDA experiment at DA{\Phi}NE, Frascati, studying ({\pi}+, {\pi}-) pairs in coincidence from the K- +6Li \rightarrow 6 H+{\pi}+ production reaction followed by 6{\Lambda}H \rightarrow 6He + {\pi}- weak decay. The production rate of 6{\Lambda}H undergoing this two-body {\pi}- decay is determined to be (2.9\pm2.0)\cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{\Lambda}(6{\Lambda}H) = (4.0\pm1.1) MeV with respect to 5H+{\Lambda}. A systematic difference of (0.98 \pm 0.74) MeV between B{\Lambda} values derived separately from decay and from production is tentatively assigned to the 6{\Lambda}H 0+g.s. \rightarrow 1+ excitation.

Evidence for 6{\Lambda}H

Evidence for the neutron-rich hypernucleus H-6(Lambda) is presented from the FINUDA experiment at DA Phi NE, Frascati, studying (pi(+), pi(-)) pairs in coincidence from the (K) over bar (-)(stop) + Li-6 -> H-6(Lambda) + pi(+) production reaction followed by H-6(Lambda) -> He-6 + pi(-) weak decay. The production rate of H-6(Lambda) undergoing this two-body pi(-) decay is determined to be (2.9 +/- 2.0) x 10(-6)/K-stop(-). Its binding energy, evaluated jointly from production and decay, is B-Lambda(H-6(Lambda)) = (4.0 +/- 1.1) MeV with respect to 5H + Lambda. A systematic difference of (0.98 +/- 0.74) MeV between B-Lambda values derived separately from decay and from production is tentatively assigned to the H-6(Lambda) 0(g.s)(+) excitationEvidence for the neutron-rich hypernucleus 6{\Lambda}H is presented from the FINUDA experiment at DA{\Phi}NE, Frascati, studying ({\pi}+, {\pi}-) pairs in coincidence from the K- +6Li \rightarrow 6 H+{\pi}+ production reaction followed by 6{\Lambda}H \rightarrow 6He + {\pi}- weak decay. The production rate of 6{\Lambda}H undergoing this two-body {\pi}- decay is determined to be (2.9\pm2.0)\cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{\Lambda}(6{\Lambda}H) = (4.0\pm1.1) MeV with respect to 5H+{\Lambda}. A systematic difference of (0.98 \pm 0.74) MeV between B{\Lambda} values derived separately from decay and from production is tentatively assigned to the 6{\Lambda}H 0+g.s. \rightarrow 1+ excitation.

Measurement of the electromagnetic form factor of the proton in the time-like region

Abstract The cross section for the process e + e − → p p has been measured in the s range 3.6–5.9 GeV2 by the FENICE experiment at the e+e− Adone storage ring and the proton electromagnetic form factor has been extracted.

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

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.

First observation of the hyper superheavy hydrogen HΛ6

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.

Proton spectra from Non-Mesonic Weak Decay of p-shell Λ-hypernuclei and evidence for the two-nucleon induced process

Abstract New spectra from the FINUDA experiment of the Non-Mesonic Weak Decay (NMWD) proton kinetic energy for Be Λ 9 , B Λ 11 , C Λ 12 , C Λ 13 , N Λ 15 and O Λ 16 are presented and discussed along with the published data on He Λ 5 and Li Λ 7 . Exploiting the large mass number range and the low energy threshold (15 MeV) for the proton detection of FINUDA, an evaluation of both Final State Interactions (FSI) and the two-nucleon induced NMWD contributions to the decay process has been done. Based on this evaluation, a linear dependence of FSI on the hypernuclear mass number A is found and for the two-nucleon stimulated decay rate the experimental value of Γ 2 / Γ p = 0.43 ± 0.25 is determined for the first time. A value for the two-nucleon stimulated decay rate to the total decay rate Γ 2 / Γ NMWD = 0.24 ± 0.10 is also extracted.

Hypernuclear spectroscopy with K− at rest on 7Li, 9Be, 13C and 16O

Abstract The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction K stop − + Z A → Z Λ A + π − . From the analysis of the momentum of the emerging π − , binding energies and formation probabilities of Li Λ 7 , Be Λ 9 , C Λ 13 and O Λ 16 have been measured and are here presented. The behavior of the formation probability as a function of the atomic mass number A is also discussed.

Measurement of the proton spectra from non-mesonic weak decay of 5ΛHe, 7ΛLi and 12ΛC

Abstract The results of a measurement of the proton spectra following the non-mesonic weak decay of 5ΛHe, 7ΛLi and 12ΛC are presented and discussed. The experiment was performed at the ( e + e − ) collider DAΦNE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for 7ΛLi, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free Λ p → n p weak reaction, with a low energy rise that should be due to final state interactions and/or two-nucleon induced weak processes. The decay spectrum of 5ΛHe is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the 12ΛC one.

First measurement of the neutron electromagnetic form factor in the time-like region

Abstract The first measurement of the neutron form factor in the time-like region has been performed by the FENICE experiment at the ADONE e + e − storage ring. Results at q 2 = 4.0 and 4.4 (GeV/ c ) 2 , together with a new measurement of the proton form factor are presented here.