Hyperon Production Research Articles

Deep sub-thresholdΞandΛproduction in nuclear collisions with the UrQMD transport model

We present results on deep sub-threshold hyperon production in nuclear collisions, with the UrQMD transport model. Introducing anti-$\text{kaon}+\text{baryon}$ and hyperon + hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in $\text{Ar}+\text{KCl}$ reactions at ${E}_{\mathrm{lab}}=1.76A$ GeV. We find that the hyperon strangeness exchange is the dominant process contributing to the ${\ensuremath{\Xi}}^{\ensuremath{-}}$ yield; however, our study remains short of explaining the ${\ensuremath{\Xi}}^{\ensuremath{-}}/\ensuremath{\Lambda}$ ratio measured with the HADES experiment. We also discuss possible reasons for the discrepancy with previous studies and the experimental results, finding that many details of the transport simulation may have significant effects on the final ${\ensuremath{\Xi}}^{\ensuremath{-}}$ yield.

Dynamical coupled-channels model ofK−preactions: Determination of partial-wave amplitudes

The authors develop a dynamical coupled-channels model for kaon-nucleon reactions that satisfies unitarity. The model overcomes limitations of previous approaches to study baryon resonances with strangeness below 2 GeV and their decay. The resultant amplitudes can play an important role in predicting hyperon production in kaon-nucleus reactions.

Lambda hyperon production and polarization in collisions of p(3.5 GeV)+Nb

Results on $ \Lambda$ hyperon production are reported for collisions of p(3.5 GeV) + Nb , studied with the High-Acceptance Di-Electron Spectrometer (HADES) at SIS18 at GSI Helmholtzzentrum for Heavy-Ion Research, Darmstadt. The transverse mass distributions in rapidity bins are well described by Boltzmann shapes with a maximum inverse slope parameter of about 90 MeV at a rapidity of y = 1.0, i.e. slightly below the center-of-mass rapidity for nucleon-nucleon collisions, $ y_{cm}=1.12$ . The rapidity density decreases monotonically with increasing rapidity within a rapidity window ranging from 0.3 to 1.3. The $ \Lambda$ phase-space distribution is compared with results of other experiments and with predictions of two transport approaches which are available publicly. None of the present versions of the employed models is able to fully reproduce the experimental distributions, i.e. in absolute yield and in shape. Presumably, this finding results from an insufficient modelling in the transport models of the elementary processes being relevant for $ \Lambda$ production, rescattering and absorption. The present high-statistics data allow for a genuine two-dimensional investigation as a function of phase space of the self-analyzing $ \Lambda$ polarization in the weak decay $ \Lambda\rightarrow p\pi^{-}$ . Finite negative values of the polarization in the order of 5-20% are observed over the entire phase space studied. The absolute value of the polarization increases almost linearly with increasing transverse momentum for p t > 300 MeV/c and increases with decreasing rapidity for y < 0.8 .

Proton and Λ hyperon production in nucleus-nucleus collisions

The experimental data on net proton and net Lambda-hyperon spectra obtained by the NA35 Collaboration, as well as the inclusive densities of Lambda and bar-Lambda obtained by NA49, NA57, and STAR collaborations, are compared with the predictions of the Quark-Gluon String Model. The contributions of String Junction diffusion, interactions with nuclear clusters, and the inelastic screening corrections are accounted for. The level of numerical agreement of the calculations with the experimental data is of about 20-30%. The predictions for LHC are also presented.

Particle production in antiproton-induced nuclear reactions

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 $\pi^{+}$ and protons from the LEAR measurements can be well reproduced. The impacts of system size and incident momentum on particle emissions are investigated from the inclusive spectra, transverse momentum and rapidity distributions. It is found that the annihilations of $\overline{p}$ on nucleons are of importance on the particle production. Hyperons are mainly produced via meson induced reactions on nucleons and strangeness exchange collisions when the incident momentum is below the threshold value of annihilation reaction. A higher nuclear temperature is obtained from the kaon emission, but it has a lower value for hyperon production.

Antihyperon-hyperon production in antiproton-proton annihilations with PANDA

Hyperon production is an excellent probe of the strong interaction in the confinement domain. The spin observables provide a powerful tool in understanding the underlying physical processes. Expressions of the seven non-zero polarisation parameters of the Ω baryon from decay angular distributions have recently been derived by the Uppsala group. Simulation studies show that all strange and single charmed hyperon production channels have great prospects with the PANDA detector.

Study of heavy hyperons production in DIS at COMPASS

Samples of Λ and \(\bar \Lambda\) hyperons produced in deep-inelastic muon scattering off 6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of Σ-(1385), \(\bar \Sigma ^ - (1385)\), \(\bar \Sigma ^ + (1385)\), Ξ−(1321), and \(\bar \Xi ^ + (1321)\) hyperons decaying into the \(\Lambda \left( {\bar \Lambda } \right)\pi\) were measured. The yield ratios of heavy hyperons to Λ were found to be in the range 3.8%–5.6% with a precision of about 10%. The experimental values are used to tune the parameters of the LEPTO Monte-Carlo generator relevant for strange particle production.

Physics with antiprotons at [formula omitted]ANDA

The P¯ANDA collaboration (anti-Proton ANnihilations at DArmstadt) is a next generation hadron physics experiment to be operated at the future Facility for Antiproton and Ion Research (FAIR) at Darmstadt, Germany. It will use intensive cooled antiproton beams with a momentum between 1.5 GeV/c and 15 GeV/c. The P¯ANDA detector is a state-of-the-art internal target detector allowing the detection and identification of neutral and charged particles almost in the whole solid angle.One of the major goal of the experiment is the comprehensive study of charmonium and candidates to the hybrids, molecules and other exotics. Charmonium states with different quantum numbers can be reached via the decay of these resonances. The P¯ANDA will scan the parameters of the resonances in formation mode with the use of the excellent momentum resolution Δp/p=104 – 105 of the HESR beam. The precision measurements of light mesons mass and width will be fulfilled as well as glueball search.Study of double hyperon production including their spin properties is another important item of the P¯ANDA experiment.

ν¯linduced pion production from nuclei at∼1 GeV

We have studied charged current ${\overline{\ensuremath{\nu}}}_{l}$ induced one pion production from $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ nuclear targets at MiniBooNE and atmospheric antineutrino energies. The calculations have been done for the incoherent pion production process as well as for the pions coming from the hyperons in the quasielastic production of $\ensuremath{\Lambda}$ and $\ensuremath{\Sigma}$. The calculations are done in the local density approximation. For the inelastic processes the calculations have been done in the $\ensuremath{\Delta}$ dominance model, and we take into account the effect of Pauli blocking, Fermi motion of the nucleon, and renormalization of $\ensuremath{\Delta}$ properties in the nuclear medium. The effect of final state interaction (FSI) of pions is also taken into account. For the hyperon production, the nuclear medium effects due to Fermi motion and FSI effects due to hyperon-nucleon scattering have been taken into account. These results may be quite useful in the analysis of SciBooNE, MicroBooNE, $\mathrm{MINER}\ensuremath{\nu}\mathrm{A}$, and ArgoNeuT experiments when the pion analysis is done by using antineutrino beams.

Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering

Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+, \Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and \bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.

Σ− production in pn interactions at ANKE at COSY

Study of light hyperon production in nucleon-nucleon interactions is a large part of scientific program at the ANKE-spectrometer which is an internal-beam experiment at the Cooler Synchrotron (COSY-Juelich). The Σ− production in pn collisions was studied at two proton beam momenta of 2915 MeV/c and 3015 MeV/c. The deuterium target was exploited as an effective neutron target due to measurement of "spectator" proton momentum to determine the energy of reaction. The Fermi motion allowed to cover a wide range of excess energy Q = 30 – 130 MeV where data was absent. The Σ− production was identified by the missing mass technique. Preliminary result for the energy dependence of the pn → pK+Σ− total cross section is presented.

Production of theHdibaryon via the (K−,K+) reaction on a12C target

We study the production of the stable six-quark $H$ dibaryon via the $(K^-,K^+)$ reaction on a $^{12}$C target within a covariant effective Lagrangian model. The calculations are performed within a factorization approximation, in which the full production amplitude is written as a product of the amplitudes for the $K^- + p \to K^+ + \Xi^-$ and $\Xi^- + p \to H$ processes. The $K^+\Xi^-$ production vertex is described by excitation, propagation and decay of $\Lambda$ and $\Sigma$ resonance states in the initial collision of a $K^-$ meson with a target proton in the incident channel. The parameters of the resonance vertices are taken to be the same as those determined previously by describing the available data on total and differential cross sections for the $p(K^-, K^+)\Xi^-$ reaction within a similar model. The $\Xi^- + p \to H$ fusion process is treated within a quark model where the $H$ dibaryon is considered as a stable particle. For the $K^+$ meson angle fixed at 0$^o$, the $H$ production cross-section is found to be about 2.9 $\mu b/sr$ for $H$ mass just below the $\Lambda \Lambda$ threshold at a $K^-$ beam momentum of 1.67 GeV/c. This is an order of magnitude larger than the value for this quantity reported earlier in calculations performed on a $^3$He target using a different model for the cascade hyperon production. We have also calculated the beam momentum dependence of the $H$ production cross section and the energy spectrum of the emitted $K^+$ meson.

QCD analysis of Lambda hyperon production in DIS target-fragmentation region

We consider Lambda-hyperon production in the target-fragmentation region of semi-inclusive deep-inelastic scattering within the framework of fracture functions. We present a first attempt to determine the flavour and energy dependences of these non-perturbative distributions through a simultaneous QCD-based fit to available neutral- and charged-current semi-inclusive-DIS cross sections. Predictions based on the resulting nucleon-to-Lambda fracture functions are in good agreement with data and observables not included in the regression. The successful prediction of the $Q^2$ dependence of the Lambda multiplicity notably represents the first validation of the perturbative framework implied by fracture functions.

Transverse polarization ofΣ+(1189)in photoproduction on a hydrogen target in CLAS

Experimental results on the $\Sigma^+(1189)$ hyperon transverse polarization in photoproduction on a hydrogen target using the CLAS detector at Jefferson laboratory are presented. The $\Sigma^+(1189)$ was reconstructed in the exclusive reaction $\gamma+p\rightarrow K^{0}_{S} + \Sigma^+(1189)$ via the $\Sigma^{+} \to p \pi^{0}$ decay mode. The $K^{0}_S$ was reconstructed in the invariant mass of two oppositely charged pions with the $\pi^0$ identified in the missing mass of the detected $p\pi^+\pi^-$ final state. Experimental data were collected in the photon energy range $E_{\gamma}$ = 1.0-3.5 GeV ($\sqrt{s}$ range 1.66-2.73 GeV). We observe a large negative polarization of up to 95%. As the mechanism of transverse polarization of hyperons produced in unpolarized photoproduction experiments is still not well understood, these results will help to distinguish between different theoretical models on hyperon production and provide valuable information for the searches of missing baryon resonances.

Constraints the properties of neutron star matter from the mass of neutron star PSR J1614-2230

The constraints on the properties of neutron star matter from the mass of neutron star PSR J1614-2230 are examined in the framework of the relativistic mean field theory. We find that there are little differences between the σ potentials of large mass neutron star and those of canonnical mass neutron star. For potentials of ω, ρ, neutrons and electrons, the values corresponding to the large mass neutron star are larger than those to the canonnical mass neutron star as the baryon number density is more than a certain value. We also find that for the relative particle number density of electrons, muons, neutrons and protons and the pressure of the neutron star, the values corresponding to the large mass neutron star are far larger than those to the canonnical mass neutron star. For the relative particle number density of hyperons Λ, Σ−, Σ0, Σ+ and Ξ−, the values corresponding to the large mass neutron star are far smaller than those to the canonnical mass neutron star. These mean that the larger mass of neutron star is more advantageous to the production of protons but is not advantageous to the production of hyperons.

J-PARC E27 Experiment to Search for a Nuclear Kaon Bound State K − pp

In the J-PARC E27 experiment, we search for a K − pp bound state via the d(π +, K +) reaction at 1.7 GeV/c at the K1.8 beam line. The binding energy and decay width of the K − pp bound state can be obtained in the missing mass measurement with a good energy resolution of 2 MeV/c 2. A range counter array (RCA) was constructed to detect the two high-momentum protons from the K − pp decay and to reduce the background such as quasi-free hyperon production. Recently, we have carried out a pilot run in June, 2012. The d(π +, K +) missing-mass spectrum has been obtained for the first time. In this report, an overview of the E27 experiment and a preliminary result on this pilot run are presented.

Ξ− hyperon and hypernuclear production in the (K−,K+) reaction on nucleon and nuclei in a field theoretical model

We investigate the production of a cascade hyperon ($\Xi$) and bound $\Xi^-$ hypernuclei in the $(K^-,K^+)$ reaction on proton and nuclear targets, respectively, within a covariant effective Lagrangian model. The $K^+\Xi^-$ production vertex is described by excitation, propagation and decay of $\Lambda$ and $\Sigma$ 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 and differential cross sections for the $p(K^-, K^+)\Xi^-$ reaction. The same mechanism was used to describe the hypernuclear production reactions $^{12}$C$(K^-,K^+)^{12}{/!/!/!_{/Xi^-}}$Be and $^{28}$Si$(K^-,K^+)^{28}{/!/!/!_{\Xi^-}}$Mg, where $\Xi$ bound state spinors calculated within a phenomenological model have been employed. Both the elementary and hypernuclear production cross sections are dominated by the contributions from the $\Lambda$(1520) intermediate resonant state. The beam momentum dependence of the $0^\circ$ differential cross sections for the formation of the $\Xi$ hypernuclei is found to be remarkably different from what has been observed previously in the impulse approximation model calculations

Hyperon photoproduction from polarized H and D towards a complete N⁎ experiment

Abstract New complete experiments in pseudoscalar meson photo-production are being pursued at several laboratories. Here the designation of complete refers to measurements of most if not all of the possible reaction observables, of which there are 16 involving spins of the beam, target and recoil baryon. Hyperon production to Λ or Σ + final states affords attractive opportunities, since their weak decays provide an efficient self-analysis of their polarization. When the beam and target are also polarized, the resulting triple polarization measurements determine the full suite of observables with a single target orientation. This has been a focus at Jefferson Lab in the recently completed g9/FROST and g14/HDice experiments now under analysis. Multipole analyses of γ p → K + Λ have been carried out with a large though incomplete set of recently published polarization data, and the uniqueness of the extracted amplitudes has been studied. Experiments with realistically achievable uncertainties require a significantly greater number of spin asymmetries than the in-principle minimum needed for a mathematical solution of the amplitude.

Theory of the electromagnetic production of hyperons

Some basic properties of isobar models are discussed using the Saclay-Lyon, Kaon-MAID, and H2 models and a comparison of their predictions with experimental data is given for photo- and electroproduction of $K^+$ on the proton and for photoproduction of $K^0$ on the deuteron in specific kinematical regions. Results of the isobar models are also compared with the Regge-isobar hybrid model, Regge-plus-resonance.

Final State Interactions and Polarization Observables in the Reaction [formula omitted

Hyperon-Nucleon (YN) interactions are ideally suited to study the role of strangeness in hadron physics. The breaking of the SU(3) flavor symmetry beyond the mass splitting can also be tested. Due to the lack of high quality hyperon beams, final state interactions in hyperon production reactions are a compelling tool for these studies. Recent measurements of the reaction pp→pKΛ with a polarized beam using the COSY-TOF detector allow for the determination of the spin triplet pΛ scattering length, which is a fundamental parameter of the pΛ interaction. Furthermore, the polarized beam together with the self analyzing decay of the polarized Λ give access to a plethora of observables for studies of the hyperon production mechanism close to threshold. Recent experimental results on the scattering length and the Λ depolarization are presented.