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Register a new userProduction of $^{6}_{Lambda}$H and $^{7}_{Lambda}$H with the (K$^{-}_{stop}$,$pi^+$) reaction
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The production of neutron rich $Lambda$-hypernuclei via the ($K^-_stop$,$pi^+$) reaction has been studied using data collected with the FINUDA spectrometer at the DA$Phi$NE $phi$-factory (LNF). The analysis of the inclusive $pi^+$ momentum spectra is presented and an upper limit for the production of $^6_Lambda$H and $^7_Lambda$H from $^6$Li and $^7$Li, is assessed for the first time.
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We searched for the bound state of the neutron-rich $Lambda$-hypernucleus ${}^{6}_{Lambda}$H, using the ${}^{6}$Li($pi^{-}, K^{+}$)X double charge-exchange reaction at a $pi^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4 times 10^{12}$ $pi^{-}$ was driven onto a ${}^{6}$Li target of 3.5-g/$rm cm^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}^{4}_{Lambda}$H + 2n, in the missing-mass spectrum of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction in the $2^{circ}$ < $theta_{pi K}$ < $20^{circ}$ angular range. Furthermore, no event was found up to 2.8 MeV/$c^2$ above the bound threshold. We obtained the the double-differential cross section spectra of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction in the angular range of $2^{circ}$ < $theta_{pi K}$ < $14^{circ}$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}^{6}_{Lambda}$H hypernucleus bound state. In addition, not only the bound state region, but also the $Lambda$ continuum region and part of the $Sigma^{-}$ quasi-free production region of the ${}^{6}$Li($pi^{-}, K^{+}$)X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $Sigma^{-}$-nucleus optical potential for $Sigma^{-}$-${}^{5}$He through spectrum shape analysis.
Evidence 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 (2.9pm2.0)cdot10-6/K-. Its binding energy, evaluated jointly from production and decay, is B{Lambda}(6{Lambda}H) = (4.0pm1.1) 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.
Correlated $Lambda d$ pairs emitted after the absorption of negative kaons at rest $K^{-}_{stop}Ato Lambda d A$ in light nuclei $^6Li$ and $^{12}C$ are studied. $Lambda$-hyperons and deuterons are found to be preferentially emitted in opposite directions. The $Lambda d$ invariant mass spectrum of $^6Li$ shows a bump whose mass is 3251$pm$6 MeV/c$^2$. The bump mass (binding energy), width and yield are reported. The appearance of a bump is discussed in the realm of the [$bar{K}3N$] clustering process in nuclei. The experiment was performed with the FINUDA spectrometer at DA$Phi$NE (LNF).
Three candidate events of the neutron-rich hypernucleus 6{Lambda}H were uniquely identified in the FINUDA experiment at DA{Phi}NE, Frascati, by observing {pi}+ mesons from the (K-stop,{pi}+) production reaction on 6Li targets, in coincidence with {pi}-mesons from 6{Lambda}H rightarrow 6He+{pi}- weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of (2.9pm2.0)cdot10-6/K- stop for the 6{Lambda}H production rate times the two-body {pi}- weak decay branching ratio. The 6{Lambda}H binding energy with respect to 5H + {Lambda} was determined jointly from production and decay to be B{Lambda} = (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 {Lambda} hypernuclear dynamics are briefly discussed.
A study of the $^2$H$({gamma},{Lambda})$X reaction was performed using a tagged photon beam at the Research Center for Electron Photon Science (ELPH), Tohoku University. The photoproduced $Lambda$ was measured in the $p{pi^{-}}$ decay channel by the upgraded Neutral Kaon Spectrometer (NKS2+). The momentum integrated differential cross section was determined as a function of the scatting angle of ${Lambda}$ in the laboratory frame for five energy bins. Our results indicated a peak in the cross section at angles smaller than cos$theta^{LAB}_{Lambda}$ = $0.96$. The experimentally obtained angular distributions were compared to isobar models, Kaon-Maid (KM) and Saclay-Lyon A (SLA), in addition to the composite Regge-plus-resonance (RPR) model. Both SLA(r$K_{1}K_{gamma}$ = $-1.4$) and RPR describe the data quite well in contrast to the KM model, which substantially under predicted the cross section at the most forward angles. With the anticipated finalized data on ${Lambda}$ integrated and momentum dependent differential cross sections of $^2$H$({gamma},{Lambda})$X~cite{Kaneta_Beckford}, we present our findings on the angular distributions in this report.
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