arXiv subjects

A. Feliciello

Publications and source records attributed to A. Feliciello.

28 records · Page 2Linked to original sources

arXiv2011

The $A(K^-_{stop},π^\pmΣ^\mp)A'$ reaction on p-shell nuclei

This letter is concerned with the study of the $K^-_{stop}A\rightarrow π^\pmΣ^\mp A'$ reaction in p-shell nuclei, i.e., $^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$. The $π^\pmΣ^\mp / K^-_{stop}$ emission rates are reported as a function of $A$. These rates are discussed in comparison with previous findings. The ratio $π^-Σ^+/π^+Σ^-$ in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold $Λ(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the $π^\pmΣ^\mp$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$Φ$NE $ϕ$-factory (LNF-INFN, Italy).

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arXiv2011

Study of some two-body non-mesonic decays of $^4_Λ$He and $^5_Λ$He

The Non-Mesonic (NM) decay of $^4_Λ{\mathrm{He}}$ and $^5_Λ{\mathrm{He}}$ in two-body channels has been studied by the FINUDA Collaboration. Two-body NM decays of hypernuclei are rare and the existing observations and theoretical calculations are scarce. The $^4_Λ{\mathrm{He}}\rightarrow d+d,\; p+t$ decay channels simultaneously observed by FINUDA on several nuclei are compared: the $pt$ channel is the dominant one. The decay yields for the two decay channels are assessed for the first time: they are $(1.37\pm 0.37)\times 10^{-5}/K^-_{stop}$ and $(8.3\pm 1.0)\times 10^{-5}/K^-_{stop}$, respectively. Due to the capability of FINUDA of identifying $^5_Λ{\mathrm{He}}$ hypernuclei, a few $^5_Λ{\mathrm{He}}\rightarrow d+t$ decay events have also been observed. The branching ratio for this decay channel has been measured for the first time: $(3.0\pm 2.3)\times 10^{-3}$.

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arXiv2011

Hypernuclear spectroscopy with K$^-$ at rest on $^7$Li, $^9$Be, $^{13}$C and $^{16}$O

The FINUDA experiment collected data to study the production of hypernuclei on different nuclear targets. The hypernucleus formation occurred through the strangeness-exchange reaction $K^-_{stop} + \; ^AZ \rightarrow \; ^A_ΛZ + π^-$. From the analysis of the momentum of the emerging $π^-$, binding energies and formation probabilities of $^7_Λ$Li, $^9_Λ$Be, $^{13}_Λ$C and $^{16}_Λ$O 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.

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arXiv2011

An improved determination of the two--nucleon induced non mesonic weak decay of $Λ$-hypernuclei

The decay of $Λ$-hypernuclei without pion emission, known as Non Mesonic Weak Decay (NMWD), gives an effective tool to investigate $Δ$S=1 four-baryon interactions. It was theoretically suggested that the two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of $Γ_{2N}$/$Γ_{NMWD}$=0.24$\pm$${0.03_{stat}}^{+0.03_{sys}}_{-{0.02_{sys}}}$ has been deduced, with an error reduced by a factor more than two compared with the previous assessment.

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arXiv2010

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

New spectra from the FINUDA experiment of the Non Mesonic Weak Decay (NMWD) proton kinetic energy for 9(Lambda)Be, 11(Lambda)B, 12(Lambda)C, 13(Lambda)C, 15 (Lambda)N and 16(Lambda)O are presented and discussed along with the published data on 5(Lambda)He and 7(Lambda)Li. 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 Gamma2/Gammap=0.43+-0.25 is determined for the first time. A value for the two nucleon stimulated decay rate to the total decay rate Gamma2/GammaNMWD=0.24+-0.10 is also extracted.

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arXiv2009

New results on Mesonic Weak Decay of $p$-shell $Λ$-Hypernuclei

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 ${^{7}_ΛLi}$, ${^{9}_ΛBe}$, ${^{11}_ΛB}$ and ${^{15}_ΛN}$. 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 ${^{7}_ΛLi}$ and $5/2^+$ for ${^{11}_ΛB}$ ground-state are confirmed and a spin-parity $3/2^+$ for ${^{15}_ΛN}$ ground-state is assigned for the first time.

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arXiv2006

Performance of HPGe Detectors in High Magnetic Fields

A new generation of high-resolution hypernuclear gamma$-spectroscopy experiments with high-purity germanium detectors (HPGe) are presently designed at the FINUDA spectrometer at DAPhiNE, the Frascati phi-factory, and at PANDA, the antiproton proton hadron spectrometer at the future FAIR facility. Both, the FINUDA and PANDA spectrometers are built around the target region covering a large solid angle. To maximise the detection efficiency the HPGe detectors have to be located near the target, and therefore they have to be operated in strong magnetic fields B ~ 1 T. The performance of HPGe detectors in such an environment has not been well investigated so far. In the present work VEGA and EUROBALL Cluster HPGe detectors were tested in the field provided by the ALADiN magnet at GSI. No significant degradation of the energy resolution was found, and a change in the rise time distribution of the pulses from preamplifiers was observed. A correlation between rise time and pulse height was observed and is used to correct the measured energy, recovering the energy resolution almost completely. Moreover, no problems in the electronics due to the magnetic field were observed.

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arXiv2006

Production of $^{6}_Λ$H and $^{7}_Λ$H with the (K$^{-}_{stop}$,$π^+$) reaction

The production of neutron rich $Λ$-hypernuclei via the ($K^-_stop$,$π^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$Φ$NE $ϕ$-factory (LNF). The analysis of the inclusive $π^+$ momentum spectra is presented and an upper limit for the production of $^6_Λ$H and $^7_Λ$H from $^6$Li and $^7$Li, is assessed for the first time.

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arXiv2006

A study of the proton spectra following the capture of $K^-$ in $^6$Li and $^{12}$C with FINUDA

Momenta spectra of protons emitted following the capture of $K^-$ in $^6$Li and $^{12}$C have been measured with 1% resolution. The $^{12}$C spectrum is smooth whereas for $^6$Li a well defined peak appears at about 500 MeV/$c$. The first observation of a structure in this region was identified as a strange tribaryon or, possibly, a $\bar K$-nuclear state. The peak is correlated with a $π^-$ coming from $Σ^-$ decay in flight, selected by setting momenta larger than 275 MeV/$c$. The $Σ^-$ could be produced, together with a 500 MeV/$c$ proton, by the capture of a $K^-$ in a deuteron-cluster substructure of the $^6$Li nucleus. The capture rate for such a reaction is $(1.62\pm 0.23_{stat} ^{+0.71}_{-0.44}(sys))%/K^-_{stop}$, in agreement with the existing observations on $^4$He targets and with the hypothesis that the $^6$Li nucleus can be interpreted as a $(d+α)$ cluster.

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arXiv2006

New detectors for the kaon and hypernuclear experiments with KaoS at MAMI and with PANDA at GSI

The KaoS spectrometer at the Mainz Microtron MAMI, Germany, is perceived as the ideal candidate for a dedicated spectrometer in kaon and hypernuclei electroproduction. KaoS will be equipped with new read-out electronics, a completely new focal plane detector package consisting of scintillating fibres, and a new trigger system. First prototypes of the fibre detectors and the associated new front-end electronics are shown in this contribution. The Mainz hypernuclei research program will complement the hypernuclear experiments at the planned FAIR facility at GSI, Germany. At the proposed antiproton storage ring the spectroscopy of double Lambda hypernuclei is one of the four main topics which will be addressed by the PANDA Collaboration. The experiments require the operation of high purity germanium (HPGe) detectors in high magnetic fields (B= 1T) in the presence of a large hadronic background. The performance of high resolution Ge detectors in such an environment has been investigated.

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