The $\bar{K} + N \to K + Ξ$ reaction is studied for center-of-momentum energies ranging from threshold to 3 GeV in an effective Lagrangian approach that includes the hyperon $s$- and $u$-channel contributions as well as a phenomenological contact amplitude. The latter accounts for the rescattering term in the scattering equation and possible short-range dynamics not included explicitly in the model. Existing data are well reproduced and three above-the-threshold resonances were found to be required to describe the data, namely, the $Λ(1890)$, $Σ(2030)$, and $Σ(2250)$. For the latter resonance we have assumed the spin-parity of $J^P=5/2^-$ and a mass of 2265 MeV. The $Σ(2030)$ resonance is crucial in achieving a good reproduction of not only the measured total and differential cross sections, but also the recoil polarization asymmetry. More precise data are required before a more definitive statement can be made about the other two resonances, in particular, about the $Σ(2250)$ resonance that is introduced to describe a small bump structure observed in the total cross section of $K^- + p \to K^+ + Ξ^-$. The present analysis also reveals a peculiar behavior of the total cross section data in the threshold energy region in $K^- + p \to K^+ + Ξ^-$, where the $P$- and $D$-waves dominate instead of the usual $S$-wave. Predictions for the target-recoil asymmetries of the $\bar{K} + N \to K + Ξ$ reaction are also presented.
The neutrino induced hyperon production processes $\barν_{e/μ} + p \to e^+/μ^+ + π+ Λ/Σ$ may provide a unique clean place for studying low energy $πΛ/Σ$ interaction and hyperon resonances below $KN$ threshold. The production rates for some neutrino induced hyperon production processes are estimated with theoretical models. Suggestions are made for the study of hyperon production from neutrino-nucleon reaction at present and future neutrino facilities.
The cross sections for producing K$^-$ mesons in nucleon-hyperon elementary processes are estimated assuming one-pion exchange and using the experimentally known pion-hyperon cross sections. The results are implemented in a transport model which is applied to calculation of proton-nucleus collisions. In significant difference to earlier estimates for heavy-ion collisions the inclusion of the nucleon-hyperon cross section roughly doubles the K$^-$ production in near-threshold proton-nucleus collisions.
The near-threshold $e^+e^- \to Λ\barΛ$ reaction is studied with the assumption that the production mechanism is due to a near-$Λ\barΛ$-threshold bound state. The cross section of $e^+e^- \to Λ\barΛ$ reaction is parametrized in terms of the electromagnetic form factors of $Λ$ hyperon, which are obtained with the vector meson dominance model. It is shown that the contribution to the $e^+e^- \to Λ\barΛ$ reaction from a new narrow state with quantum numbers $J^{PC}=1^{--}$ is dominant for energies very close to threshold. The mass of this new state is around 2231 MeV, which is very close to the ma…
The recent data taken by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility for the reaction of $γp \to K^+ K^+ Ξ^-$ are reanalyzed within a relativistic meson-exchange model of hadronic interactions. The present model is an extension of the one developed in an earlier work by Nakayama, Oh, and Haberzettl [Phys. Rev. C 74, 035205 (2006)]. In particular, the role of the spin-5/2 and -7/2 hyperon resonances, which were not included in the previous model, is investigated in the present study. It is shown that the contribution of the $Σ(2030)$ hyperon having spin-7/2 and …
In this review, we have studied the quasielastic production cross sections and polarization components of $Λ$, $Σ^0$ and $Σ^-$ hyperons induced by the weak charged currents in the antineutrino reactions on the nucleon and the nuclear targets like $^{12}$C, $^{16}$O, $^{40}$Ar and $^{208}$Pb. It is shown that the energy and the $Q^2$ dependence of the cross sections and the various polarization components can be effectively used to determine the axial vector transition form factors in the strangeness sector and test the validity of various symmetry properties of the weak hadronic currents like …
We have studied quasielastic charged current hyperon production induced by $\barν_μ$ on free nucleon and the nucleons bound inside the nucleus. The calculations are performed for several nuclear targets like $^{12}C$, $^{40}Ar$, $^{56}Fe$ and $^{208}Pb$ which are presently being used in various oscillation experiments using accelerator neutrinos. The inputs are the hyperon-nucleon transition form factors determined from neutrino-nucleon scattering as well as from semileptonic decays of neutron and hyperons using SU(3) symmetry. The calculations for the nuclear targets are done in local density…
We study the strangeness production in antiproton-nucleus collisions at the beam momenta from 200 MeV/c to 15 GeV/c within the Giessen Botzmann-Uehling-Uhlenbeck (GiBUU) transport model. The GiBUU model contains a very detailed description of the underlying antinucleon-nucleon cross sections, in-particular, of the strangeness production channels. We compare our calculations with the bubble chamber data on Λ- and K^0_S-production in antiproton-nucleus collisions and with the earlier intranuclear cascade calculations. The contributions of the various partial channels to the hyperon production ar…
We present calculations of the invariant mass spectra of the $Λ$p system for the exclusive $p p \to K^+ Λp$ reaction with the aim of studying the final state interaction between the $Λ$-hyperon and the proton. The reaction is described within a meson exchange framework and the final state $Λp$ interaction is incorporated through an off-shell t-matrix for the $Λp \to Λp$ 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 $Λ$ and $Σ$ production thresholds. Hence, data on this…
Within the framework of quantum molecular dynamics transport model, the isospin and in-medium effects on the hyperon production in the reaction of $^{197}$Au + $^{197}$Au are investigated thoroughly. A repulsive hyperon-nucleon potential from the chiral effective field theory is implemented into the model, which is related to the hyperon momentum and baryon density. The correction on threshold energy of the elementary hyperon cross section is taken into account. It is found that the $Σ$ yields are suppressed in the domain of midrapidity and kinetic energy spectra with the potential. The hypero…
The $K^- d \to πYN$reaction is theoretically studied so as to investigate the $K^{-}$-induced production of the hyperon resonances $Σ(1385)$ and $Λ(1405)$. For this purpose we take into account the p-wave amplitudes for the meson-baryon two-body scatterings as well as the s-wave amplitudes. Due to the fact that the hyperon resonances are selectively produced from the $\bar{K} N$ channel in this reaction, the $Λ(1405)$ peak appears at 1420 MeV, which implies that $Λ(1405)$ and $Σ(1385)$ could be separately seen in the missing mass spectrum of the emitted nucleon in the $K^{-} d \to n X$ reactio…
We report our recent effort for the extraction of resonance parameters (complex pole mass and residues etc.) associated with Lambda* and Sigma* hyperons. This was accomplished via a comprehensive partial-wave analysis of the data for K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi reactions from the thresholds up to W=2.1 GeV within a dynamical coupled-channels approach. The results suggest a possible existence of new narrow J^P=3/2^+ Λresonance with pole mass 1671^{+2}_{-8} -i(5^{+11}_{-2}) MeV, located close to the eta Lambda threshold. This resonance is found to be responsible for r…
In this work we extend our formalism to study meson-baryon interactions by including $s$- and $u$-channel diagrams for pseudoscalar-baryon systems. We study the coupled systems with strangeness $-1$ and focus on studying the isospin-1 resonance(s), especially in the energy region around 1400 MeV. By constraining the model parameters to fit the cross section data available on several processes involving relevant channels, we find resonances in the isoscalar as well as the isovector sector in the energy region around 1400 MeV.
We present results on deep sub threshold hyperon production in nuclear collisions, with the UrQMD transport model. Introducing anti-kaon+baryon and hyperon+hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in Ar+KCl reactions at $E_{lab}=1.76$ A GeV. We find that the hyperon strangeness exchange is the dominant process contributing to the $Ξ^-$ yield, however remains short of explaining the $Ξ^-/Λ$ ratio measured with the HADES experiment. We also discuss possible reasons for the discrepancy with previous studies and th…
Electromagnetic form factors of hyperons ($Λ$, $Σ$, $Ξ$) in the timelike region, accessible in the reaction $e^+e^- \to \bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $\bar YY$ system. This interaction is taken into account in the calculation, utilizing $\bar YY$ potential models that have been constructed by the Jülich group for the analysis of data from the reaction $\bar pp \to \bar YY$ in the past. The enhancement of the effective form factor for energi…
We investigate the production of a cascade hyperon ($Ξ$) and bound $Ξ^-$ hypernuclei in the $(K^-,K^+)$ reaction on proton and nuclear targets, respectively, within a covariant effective Lagrangian model. The $K^+Ξ^-$ production vertex is described by excitation, propagation and decay of $Λ$ and $Σ$ resonance states in the initial collision of a $K^-$ meson with a free or bound proton in the incident channel. The parameters of the resonance vertices are taken from previous studies and SU(3) symmetry considerations. The model is able to provide a good description of the available data on total …
Cross-section, vector-polarization, and tensor-polarization distributions are calculated for the reactions $e^+ e^- \rightarrow \bar{p}p$ and $e^+ e^- \rightarrow \barΛ Λ$. Each reaction requires six characteristic functions that are bilinear in the, possibly complex, electromagnetic form factors, denoted $G_E(P^2)$ and $G_M(P^2)$, of $p$ and $Λ$. For the hyperon reaction also the joint-decay distributions of $Λ$ and $\barΛ$ are calculated. Their knowledge allow a complete determination of the hyperon electromagnetic form factors, without measuring hyperon spins. We explain how this is done in…
In the framework of the nuclear spectral function approach for incoherent primary proton-nucleon and secondary pion-nucleon production processes we study the inclusive Lambda(1520) hyperon production in the interaction of 2.83 GeV protons with nuclei. In particular, the A and momentum dependences of the absolute and relative Lambda(1520) hyperon yields are investigated in two scenarios for its in-medium width. Our model calculations show that the pion-nucleon production channel contributes distinctly to the "low-momentum" Lambda(1520) creation both in light and heavy nuclei in the chosen kinem…
We investigate the production of a cascade hyperon (Xi) through the K^- + p --> K^+ (K^0) + Xi^- (Xi^0) reactions, within an effective Lagrangian model where these reactions proceed via excitations of Lambda and Sigma resonance intermediate states in s- and u-channels. The coupling constants at the various vertices are taken from previous studies and SU(3) symmetry considerations. The calculated total cross sections of these reactions, which are in good agreement with the available data, are dominated by the contributions from the Lambda(1520) intermediate resonant state. However, the K^+ meso…
We discuss in detail the formation and propagation of multi-strangeness particles in reactions induced by hadron beams relevant for the forthcoming experiments at FAIR. We focus the discussion on the production of the decuplet-particle $Ω$ and study for the first time the production and propagation mechanism of this heavy hyperon inside hadronic environments. The transport calculations show the possibility of $Ω$-production in the forthcoming \panda-experiment, which can be achieved with measurable probabilities using high-energy secondary $Ξ$-beams. We predict cross sections for $Ω$-productio…
Motivated by the successes of covariant baryon chiral perturbation theory in one-baryon systems and in heavy-light systems, we study relevance of relativistic effects in hyperon-nucleon interactions with strangeness $S=-1$. In this exploratory work, we follow the covariant framework developed by Epelbaum and Gegelia to calculate the $YN$ scattering amplitude at leading order. By fitting the five low-energy constants to the experimental data, we find that the cutoff dependence is mitigated, compared with the heavy-baryon approach. Nevertheless, the description of the experimental data remains q…
The measured electromagnetic form factors of $Λ$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $ϕ$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $p\bar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.
Resonance parameters (pole masses and residues) associated with the excited states of hyperons, Lambda^* and Sigma^*, are extracted within a dynamical coupled-channels model developed recently by us [Phys. Rev. C 90, 065204 (2014)] through a comprehensive partial-wave analysis of the K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi data up to invariant mass W = 2.1 GeV. We confirm the existence of resonances corresponding to most, if not all, of the four-star resonances rated by the Particle Data Group. We also find several new resonances, and in particular propose a possible existence …
A combined study of the reactions $K^-p\rightarrow Σ^0π^0$, $Λπ^0$ and $\bar{K}^0n$ at low energies is carried out with a chiral quark-model approach. Good descriptions of the experimental observations are obtained. The roles of the low-lying strangeness $S=-1$ hyperon resonances in these processes are carefully analyzed. We find that: (i) In the $K^-p\rightarrow Σ^0π^0$ process, both $Λ(1405)S_{01}$ and $Λ(1520)D_{03}$ play dominant roles. Significant contributions of $Λ(1670)S_{01}$ and $Λ(1690)D_{03}$ could be seen around their threshold; (ii) In the $K^-p\rightarrow Λπ^0$ process, some obv…
We study the mechanism of the associated Lambda-kaon and Sigma-kaon production in nucleon-nucleon collisions over an extended range of near threshold beam energies within an effective Lagrangian model, to understand of the new data on pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions published recently by the COSY-11 collaboration. In this theory, the hyperon production proceeds via the excitation of N*(1650), N*(1710), and N*(1720) baryonic resonances. Interplay of the relative contributions of various resonances to the cross sections, is discussed as a function of the beam energy over a la…
Based on reflection symmetry in the reaction plane, it is shown that measuring the transverse spin-transfer coefficient $K_{yy}$ in the $\bar{K}N \to KΞ$ reaction directly determines the parity of the produced cascade hyperon in a model-independent way as $π_Ξ=K_{yy}$, where $π_Ξ=\pm 1$ is the parity. This result based on Bohr's theorem provides a completely general, universal relationship that applies to the entire hyperon spectrum. A similar expression is obtained for the photoreaction $γN \to K K Ξ$ by measuring both the double-polarization observable $K_{yy}$ and the photon-beam asymmetry …
A model for the $\bar K d \to πY N$ reactions with $Y=Λ, Σ$ is developed, aiming at establishing the low-lying $Λ$ and $Σ$ hyperon resonances through analyzing the forthcoming data from the J-PARC E31 experiment. The off-shell amplitudes generated from the dynamical coupled-channels (DCC) model, which was developed in Kamano et al. [Phys. Rev. C 90, 065204 (2014)], are used as input to the calculations of the elementary $\bar K N \to \bar K N$ and $\bar K N \to πY$ subprocesses in the $\bar K d \to πY N$ reactions. It is shown that the cross sections for the J-PARC E31 experiment with a rather…
Strange particles and hyperfragments in collisions of antiprotons and protons on nuclei have been investigated systematically within a microscopic transport model. The hyperons are produced from the annihilation in antibaryon-baryon collisions and strangeness exchange process in antiproton induced reactions. A coalescence approach is used for constructing the primary hyperfragments in phase space and the statistical model is modified for describing the decay of hyperfragments via evaporating hyperon, neutron, charged particles etc, in which the shell effect, binding energy and root-mean-square…
Investigations of thermal evolution of neutron stars with hyperon cores require neutrino emissivities for many neutrino reactions involving strongly degenerate particles (nucleons, hyperons, electrons, muons). We calculate the angular integrals $I_n$ (over orientations of momenta of $n$ degenerate particles) for major neutrino reactions with $n$ =3, 4, 5 at all possible combinations of particle Fermi momenta. The integrals $I_n$ are necessary ingredients for constructing a uniform database of neutrino emissivities in dense nucleon-hyperon matter. The results can also be used in many problems o…
Formation mechanism of hyperfragments with strangeness s=-1 and s=-2 in collisions of antikaons on nuclei has been investigated within a microscopic transport model. Dynamics of pseudoscalar mesons and hyperons is modeled within the transport model, in which all possible reaction channels for creating hyperons such as the elastic scattering, resonance production and decay, strangeness exchange reaction and direct strangeness production in meson-baryon and baryon-baryon collisions have been included. A coalescence approach is developed for constructing hyperfragments in phase space and the deca…
The quantum molecular dynamics model has been improved to investigate the reaction dynamics induced by antiprotons. The reaction channels of elastic scattering, annihilation, charge exchange and inelastic collisions have been included in the model. Dynamics on particle production, in particular pions, kaons, antikaons and hyperons, is investigated in collisions of $\overline{p}$ on $^{12}$C, $^{20}$Ne, $^{40}$Ca, $^{112}$Sn, $^{181}$Ta, $^{197}$Au and $^{238}$U from a low to high incident momentum. The rapidity and momentum distributions of $π^{+}$ and protons from the LEAR measurements can be…
The theoretical results for the total cross sections and polarization components of the $τ^{+}$ lepton produced in the charged current induced $|ΔS| = 1$ quasielastic $\barν_τ- N$ scattering leading to hyperons ($Λ, Σ$) have been presented assuming T invariance. The theoretical uncertainties arising due to the use of different vector, axial vector and pseudoscalar form factors as well as the effect of SU(3) symmetry breaking have been studied. We have also presented, for the first time, a comparison of the total cross sections for the production of $e,μ,τ$ leptons to facilitate the implication…
We explore the strangeness-changing decays of the lightest hyperons into another baryon plus missing energy within and beyond the standard model (SM). In the SM these processes arise from the loop-induced quark transition $s\to dν\barν$ and their branching fractions are estimated to be less than $10^{-11}$. In the presence of new physics (NP) the rates of these hyperon decays with missing energy could increase significantly with respect to the SM expectations because of modifications to the SM process or contributions from additional modes with new invisible particles. Adopting a model-indepen…
We study the pp -> p Lambda K+ and pp -> p Sigma0 K+ reactions near threshold by using a chiral unitary approach. We consider the single-pion and single-kaon exchange as well as the final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems. Our results on the total cross section of the pp -> p Lambda K+ reaction is consistent with the experimental data, and the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same excess energy can also be explained in our model.
A method to extract the polarization of $Ω$ hyperons produced via the strong interaction is presented. Assuming they are spin 3/2 particles, the corresponding spin density matrix can be written in terms of seven non-zero polarization parameters, all retrievable from the angular distribution of the decay products. Moreover by considering the full decay chain $Ω\rightarrow ΛK\rightarrow pπK$ the magnitude of the asymmetry parameters $β_Ω$ and $γ_Ω$ can be obtained. This method, applied here to the specific $Ω$ case, can be generalized to any weakly decaying hyperon and is perfectly suited for th…
Using a gauged flavor SU(3)-invariant hadronic Lagrangian, we calculate the cross sections for the strangeness-exchange reactions YY to NΞ(Y=Λ, Σ) in the Born approximation. These cross sections are then used in the Relativistic Vlasov-Uehling-Uhlenbeck (RVUU) transport model to study Ξproduction in Ar+KCl collisions at incident energy of 1.76A GeV and impact parameter b=3.5 fm. We find that including the contributions of hyperon-hyperon scattering channels strongly enhances the yield of Ξ, leading to the abundance ratio Ξ^{-}/(Λ+Σ^{0})=3.38E-3, which is essentially consistent with the recentl…
This paper presents the Extended-Soft-Core (ESC) potentials ESC08c for baryon-baryon channels with total strangeness S=-2. The potential models for S=-2 are based on SU(3) extensions of ESC potential models for the S=0 and S=-1 sectors, which are fitted to experimental data. Flavor SU(3)-symmetry is broken only kinematically by the masses of the baryons and the mesons. For the S=-2 channels no experimental scattering data exist, and also the information from hypernuclei is rather limited. Nevertheless, in the fit to the S=0 and S=-1 sectors information from the so called NAGARA event and the $…
We analyze the reaction gamma + d --> K^+ + Lambda (Sigma) + N using the Nijmegen soft core hyperon-nucleon interactions NSC97f and NSC89 and a recently updated production operator for the gamma + N --> K^+ + Lambda(Sigma) processes. Significant effects of the YN final state interaction are found near both the K^+ Lambda N and K^+ Sigma N thresholds.
We report on a theoretical study of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions near threshold using a chiral dynamical approach. The production process is described by single-pion and single-kaon exchange. The final state interactions of nucleon-hyperon, K-hyperon and K-nucleon systems are also taken into account. We show that our model leads to a fair description of the experimental data on the total cross section of the pp->p Lambda K+ and pp->p Sigma0 K+ reactions. We find that the experimental observed strong suppression of Sigma0 production compared to Lambda production at the same…
The YN results are presented from a new version of the Extended-soft-core (ESC) potential model for Baryon-baryon (BB) scattering. The potentials consist of local- and non-local-potentials due to (i) One-boson-exchange (OBE), (ii) Pomeron and Odderon exchanges, (iii) Two pseudoscalar-exchange (PS-PS), and (iv) Meson-Pair-exchange (MPE). The OBE- and MPE-vertices are regulated by gaussian form factors, producing moderate size potentials in the origin. In addition to the mentioned ingredients of the ESC-model, also the possible short range repulsion due to the quark Pauli-principle in the BB-cha…
