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Register a new user$Lambda d$ correlations from the $^4$He(stopped-$K^-$,$d$) reaction
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We have observed an intense high-energy component in an inclusive $^4$He(stopped $K^-$, $d$) spectrum. For back-to-back $Lambda d$ pairs a prominent event cluster has been found just below the $m_{^4textrm{He}}+m_{K^-}-m_{n}$ mass threshold in the $Lambda d$ invariant mass spectrum of $Lambda dn$ events, which is evidence for a three-nucleon absorption process of $K^-$ in $^4$He. In addition, an appreciable strength is revealed below $sim$3220 MeV/$c^2$. Well separated $Sigma^0 dn$ events show a peak similar to the case of $Lambda dn$.
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We have investigated correlations of coincident $Lambda N$ pairs from the stopped $K^-$ reaction on ${}^4$He, and clearly observed $Lambda p$ and $Lambda n$ branches of the two-nucleon absorption process in the $Lambda N$ invariant mass spectra. In addition, non-mesonic reaction channels, which indicate possible exotic signals for the formation of strange multibaryon states, have been identified.
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).
We measured the neutron time-of-flight spectrum in the ^4He(stopped K^-, n) reaction by stopping negative kaons in a superfluid helium target. A clear enhancement was observed in the neutron spectrum, which indicates the formation of a strange tribaryon of charge +1 with a mass and width of M = 3141 +/- 3 (stat.) +4/-1 (sys.) MeV/c^2 and G < 23 MeV/c^2. This state, denoted as S^+(3140), is about 25 MeV/c^2 higher than the previously observed S^0(3115) T=1.
The gamma d to K^+K^-pn reaction has been studied to search for the evidence of the Theta^+ by detecting K^+K^- pairs at forward angles. The Fermi-motion corrected nK^+ invariant mass distribution shows a narrow peak at 1.524 +- 0.002 + 0.003 GeV/c^2. The statistical significance of the peak calculated from a shape analysis is 5.1 sigma, and the differential cross-section for the gamma n to K^- Theta^+ reaction is estimated to be 12 +- 2 nb/sr in the photon energy range from 2.0 GeV to 2.4 GeV in the LEPS angular range by assuming the isotropic production of the Theta^+ in the gamma n center-of-mass system. The obtained results support the existence of the Theta^+.
The real and imaginary parts of the bar K^0 d scattering length are extracted from the bar K^0 d mass spectrum obtained from the reaction pp to d bar K^0 K^+ measured recently at the Cooler Synchrotron COSY at Julich. We extract a new limit on the K^- d scattering length, namely Im a le 1.3 fm and |Re a| le 1.3 fm. The limit for the imaginary part of the K^- d scattering length is supported by data on the total K^- d cross sections.
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