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Register a new userHyperon-nucleon interactions in the $p p to K^+ Lambda p$ reaction
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We present calculations of the invariant mass spectra of the $Lambda$p system for the exclusive $p p to K^+ Lambda p$ reaction with the aim of studying the final state interaction between the $Lambda$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Lambda p$ interaction is incorporated through an off-shell t-matrix for the $Lambda p to Lambda p$ scattering, constructed using the available hyperon-nucleon (YN) potentials. The cross sections are found to be sensitive to the type of YN potential used especially at the $Lambda$ and $Sigma$ production thresholds. Hence, data on this exclusive reaction, which can be used to constrain the YN potentials are desirable.
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The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. Narrow S = -1 resonances predicted by bag model calculations are not visible in the missing mass spectrum. Small structures observed in a previous experiment are not confirmed. Upper limits for the production cross section of a narrow resonance are deduced for missing masses between 2058 and 2105 MeV/c^2.
The reaction pp -> K+ + (Lambda p) was measured at Tp=1.953 GeV and Theta = 0 deg with a high missing mass resolution in order to study the Lambda p final state interaction. The large final state enhancement near the Lambda p threshold can be described using the standard Jost-function approach. The singlet and triplet scattering lengths and effective ranges are deduced by fitting simultaneously the Lambda p invariant mass spectrum and the total cross section data of the free Lambda p scattering.
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
The most recent high-precision data on spin observables $Sigma$, $T$, $P$, $E$, $F$ and $H$ reported by the CLAS Collaboration together with the previous data on differential cross sections and spin-density-matrix elements reported by the CLAS, A2, GRAAL, SAPHIR and CBELSA/TAPS Collaborations for the reaction $gamma p to omega p$ are analyzed within an effective Lagrangian approach. The reaction amplitude is constructed by considering the $t$-channel $pi$ and $eta$ exchanges, the $s$-channel nucleon and nucleon resonances exchanges, the $u$-channel nucleon exchange and the generalized contact current. The latter accounts effectively for the interaction current and ensures that the full photoproduction amplitude is gauge invariant. It is shown that all the available CLAS data can be satisfactorily described by considering the $N(1520)3/2^-$, $N(1700)3/2^-$, $N(1720)3/2^+$, $N(1860)5/2^+$, $N(1875)3/2^-$, $N(1895)1/2^-$ and $N(2060)5/2^-$ resonances in the $s$-channel. The parameters of these resonances are extracted and compared with those quoted by PDG.
Polarization properties of strange baryons produced in pp reactions, p + p -> p + Lambda^0 + K^+ and p + p -> p + Sigma^0 + K^$, near thresholds of the final states (p Lambda^0 K^+) and (p Sigma^0 K^+) are analysed relative to polarizations of colliding protons. The cross sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)).
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