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H. Fujioka

Publications and source records attributed to H. Fujioka.

At least 55 records · Page 3Linked to original sources
arXiv2014

Search for $^6_Λ$H hypernucleus by the $^6$Li$(π^-,K^+)$ reaction at $p_{π^-}$ = 1.2 GeV/$c$

We have carried out an experiment to search for a neutron-rich hypernucleus, $^6_Λ$H, by the $^6$Li($π^-,K^+$) reaction at $p_{π^-}$ =1.2 GeV/$c$. The obtained missing mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the $^6_Λ$H hypernucleus neither below nor above the $^4_Λ$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound $^6_Λ$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.

nucl-ex↗
arXiv2012

Formation of eta-prime(958)-mesic nuclei by (p,d) reaction

We calculate theoretically the formation spectra of eta'(958)-nucleus systems in the (p,d) reaction for the investigation of the in-medium modification of the eta' mass. We show the comprehensive numerical calculations based on a simple form of the eta' optical potential in nuclei with various potential depths. We conclude that one finds an evidence of possible attractive interaction between eta' and nucleus as peak structure appearing around the eta' threshold in light nuclei such as 11C when the attractive potential is stronger than 100 MeV and the absorption width is of order of 40 MeV or less. Spectroscopy of the (p,d) reaction is expected to be performed experimentally at existing facilities, such as GSI. We also estimate the contributions from the omega and phi mesons, which have masses close to the eta' meson, concluding that the observation of the peak structure of the eta'-mesic nuclei is not disturbed although their contributions may not be small.

nucl-th↗
arXiv2012

Search for the neutron-rich hypernucleus 9ΛHe

Search for the neutron-rich hypernucleus 9LHe is reported by the FINUDA experiment at DAFNE, INFN-LNF, studying (pi+, pi-) pairs in coincidence from the K-stop + 9Be --> 9LHe + pi+ production reaction followed by 9LHe --> 9Li + pi- weak decay. An upper limit of the production rate of 9LHe undergoing this two-body pi- decay is determined to be (2.3 +/- 1.9) 10-6/K-stop at 90% confidence level.

nucl-ex↗
arXiv2012

Neutron imaging detector based on the muPIC micro-pixel chamber

We have developed a prototype time-resolved neutron imaging detector employing the micro-pixel chamber (muPIC), a micro-pattern gaseous detector, coupled with a field programmable gate array-based data acquisition system for applications in neutron radiography at high-intensity neutron sources. The prototype system, with an active area of 10cm x 10cm and operated at a gas pressure of 2 atm, measures both the energy deposition (via time-over-threshold) and 3-dimensional track of each neutron-induced event, allowing the reconstruction of the neutron interaction point with improved accuracy. Using a simple position reconstruction algorithm, a spatial resolution of 349 +/- 36 microns was achieved, with further improvement expected. The detailed tracking allows strong rejection of background gamma-rays, resulting in an effective gamma sensitivity of 10^-12 or less, coupled with stable, robust neutron identification. The detector also features a time resolution of 0.6 microseconds.

physics.ins-det↗
arXiv2012

First observation of the hyper superheavy hydrogen 6ΛH

Three candidate events of the neutron-rich hypernucleus 6ΛH were uniquely identified in the FINUDA experiment at DAΦNE, Frascati, by observing π+ mesons from the (K-stop,π+) production reaction on 6Li targets, in coincidence with π-mesons from 6ΛH \rightarrow 6He+π- weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of (2.9\pm2.0)\cdot10-6/K- stop for the 6ΛH production rate times the two-body π- weak decay branching ratio. The 6ΛH binding energy with respect to 5H + Λ was determined jointly from production and decay to be BΛ = (4.0 \pm 1.1) MeV, assuming that 5H is unbound with respect to 3H + 2n 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 \pm 0.74) MeV here assigned to the 0+g.s. \rightarrow 1+ excitation. The consequences of this assignment to Λ hypernuclear dynamics are briefly discussed.

nucl-ex↗
arXiv2012

Search for the $Θ^{+}$ pentaquark via the $π^-p\to K^-X$ reaction at 1.92 GeV/$c$

The $Θ^+$ pentaquark baryon was searched for via the $π^-p\to K^-X$ reaction in a missing-mass resolution of 1.4 MeV/$c^2$(FWHM) at J-PARC. $π^-$ meson beams were incident on the liquid hydrogen target with the beam momentum of 1.92 GeV/$c$. No peak structure corresponding to the $Θ^+$ mass was observed. The upper limit of the production cross section averaged over the scattering angle of 2$^{\circ}$ to 15$^{\circ}$ in the laboratory frame was obtained to be 0.26 $μ$b/sr in the mass region of 1.51$-$1.55 GeV/$c^2$.The upper limit of the $Θ^+$ decay width using the effective Lagrangian approach was obtained to be 0.72 MeV/$c^2$ and 3.1 MeV/$c^2$ for $J^P_Θ=1/2^+$ and $J^P_Θ=1/2^-$, respectively.

nucl-ex↗
arXiv2011

Evidence for 6ΛH

Evidence for the neutron-rich hypernucleus 6ΛH is presented from the FINUDA experiment at DAΦNE, Frascati, studying (π+, π-) pairs in coincidence from the K- +6Li \rightarrow 6 H+π+ production reaction followed by 6ΛH \rightarrow 6He + π- weak decay. The production rate of 6ΛH undergoing this two-body π- decay is determined to be (2.9\pm2.0)\cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is BΛ(6ΛH) = (4.0\pm1.1) MeV with respect to 5H+Λ. A systematic difference of (0.98 \pm 0.74) MeV between BΛ values derived separately from decay and from production is tentatively assigned to the 6ΛH 0+g.s. \rightarrow 1+ excitation.

nucl-ex↗
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).

nucl-ex↗
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: $(3.0\pm 2.3)\times 10^{-3}$.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-ex↗
arXiv2010

Search for η-Mesic Nuclei at J-PARC

The merits of searching for η-mesic nuclei by use of the (π, N) reaction at J-PARC is discussed, by comparison with an old experiment with the same reaction at BNL in 1980's. The importance of a pilot experiment using deuterium target is also stressed for a better understanding of the background which should exist even after the coincidence of the decay particles of η-mesic nuclei.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-ex↗
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.

nucl-ex↗