Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user$Lambda N$ correlations from the stopped $K^-$ reaction on ${}^4$He
113
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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 $Lambda dn$.
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.
To search for an S= -1 di-baryonic state which decays to $Lambda p$, the $ {rm{}^3He}(K^-,Lambda p)n_{missing}$ reaction was studied at 1.0 GeV/$c$. Unobserved neutrons were kinematically identified from the missing mass $M_X$ of the $ {rm{}^3He}(K^-,Lambda p)X$ reaction in order to have a large acceptance for the $Lambda pn$ final state. The observed $Lambda p n$ events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the $Lambda p$. To account for the observed peak structure, the simplest S-wave pole was assumed to exist in the reaction channel, having Breit-Wigner form in energy and with a Gaussian form-factor. A minimum $chi^2$ method was applied to deduce its mass $M_X =$ 2355 $ ^{+ 6}_{ - 8}$ (stat.) $ pm 12$ (syst.) MeV/c$^2$, and decay-width $Gamma_X = $ 110 $ ^{+ 19}_{ - 17}$ (stat.) $ pm 27$ (syst.) MeV/c$^2$, respectively. The form factor parameter $Q_X sim$ 400 MeV/$c$ implies that the range of interaction is about 0.5
We have performed an exclusive measurement of the $K^{-}+! ~^{3}{rm He} to Lambda pn$ reaction at an incident kaon momentum of $1 {rm GeV}/c$.In the $Lambda p$ invariant mass spectrum, a clear peak was observed below the mass threshold of $bar{K}!+!N!+!N$, as a signal of the kaonic nuclear bound state, $bar{K}NN$.The binding energy, decay width, and $S$-wave Gaussian reaction form-factor of this state were observed to be $B_{K} = 42pm3({rm stat.})^{+3}_{-4}({rm syst.}) {rm MeV}$, $Gamma_{K} = 100pm7({rm stat.})^{+19}_{-9}({rm syst.}) {rm MeV}$, and $Q_{K} = 383pm11({rm stat.})^{+4}_{-1}({rm syst.}) {rm MeV}/c$, respectively. The total production cross-section of $bar{K}NN$, determined by its $Lambda p$ decay mode, was $sigma^{tot}_{K} cdot BR_{Lambda p} = 9.3pm0.8({rm stat.})^{+1.4}_{-1.0}({rm syst.}) mu{rm b}$.We estimated the branching ratio of the $bar{K}NN$ state to the $Lambda p$ and $Sigma^{0}p$ decay modes as $BR_{Lambda p}/BR_{Sigma^{0}p} sim 1.7$, by assuming that the physical processes leading to the $Sigma N!N$ final states are analogous to those of $Lambda pn$.
Very recently, we have performed a couple of experiments, {it{KEK PS-E549/E570}}, for the detailed study of the strange tribaryon $S^0(3115)$ obtained in {it{KEK PS-E471}}. These experiments were performed to accumulate much higher statistics with improved experimental apparatusespecially for the better proton spectroscopy of the $^4$He({it{stopped K}}$^-$, {it{N}}) reaction. In contrast to the previous proton spectrum, no narrow ($sim$ 20 MeV) peak structure was found either in the inclusive $^4$He({it{stopped K}}$^-$, {it{p}}) or in the semi-inclusive $^4$He({it{stopped K}}$^-$, {it{p}}$X^pm$) reaction channel, which is equivalent to the previous $E471$ event trigger condition. Detailed analysis of the present data and simulation shows that the peak, corresponding to $S^0(3115)$, has been an experimental artifact. Present analysis does not exclude the possible existence of a much wider structure. To be sensitive to such structure and for better understanding of the non-mesonic $K^-$ absorption reaction channel, detailed analysis of the data is in progress.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
