Structure Of Hyperons Research Articles

Extracting the femtometer structure of strange baryons using the vacuum polarization effect

One of the fundamental goals of particle physics is to gain a microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons are still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tool to investigate their inner structure. We present a method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the effect of vacuum polarization at the J/ψ resonance. Using the 10 billion J/ψ events collected with the BESIII detector, this allows a precise determination of the hyperon structure function. The result is essentially a precise snapshot of the Λ¯Σ0(ΛΣ¯0)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{\\Lambda }{\\Sigma }^{0}\\,(\\Lambda {\\bar{\\Sigma }}^{0})$$\\end{document} transition process, encoded in the transition form factor ratio and phase. Their values are measured to be R = 0.860 ± 0.029(stat.) ± 0.015(syst.), ΔΦΛ¯Σ0=(1.011±0.094(stat.)±0.010(syst.))rad\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta {\\Phi }_{\\bar{\\Lambda }{\\Sigma }^{0}}=(1.011\\pm 0.094({{\\rm{stat.}}})\\pm 0.010({{\\rm{syst.}}}))\\,{{\\rm{r}}}ad$$\\end{document} and ΔΦΛΣ¯0=(2.128±0.094(stat.)±0.010(syst.))rad\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta {\\Phi }_{\\Lambda {\\bar{\\Sigma }}^{0}}=(2.128\\pm 0.094({{\\rm{stat.}}})\\pm 0.010({{\\rm{syst.}}}))\\,{{\\rm{r}}}ad$$\\end{document}. Furthermore, charge-parity (CP) breaking is investigated in this reaction and found to be consistent with CP symmetry.

Hyperons in neutron stars: studies of hyperon spectroscopy and the hyperon-nucleon interaction with the K-long Facility.

Elucidating the role of strange baryons (hyperons) in neutron stars requires detailed knowledge of hyperon-nucleon interactions in the light (u,d,s) quark sector. The structure of the hyperons and their excitation spectra also directly impact, and are an input to, models of big-bang nucleosynthesis. The upcoming K-long Facility will provide a much-needed intense and clean neutral strange meson beam, from which hyperons can be produced at rates where hyperon structure, hyperon-nucleon interactions and higher-order interactions can be studied with a new level of accuracy and for hitherto unreachable measurements. The new facility has the potential to address long-standing questions surrounding the strange sector of the strong force and its relevance to the structure of atomic nuclei, neutron stars and the cosmos at large. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'.

Hyperon production and interaction studies in protonproton scattering with HADES

Hyperons and their interactions with baryonic matter may play a key role in our understanding of the core of neutron stars. Moreover, the internal structure of hyperons and their excitations are of great interest. Their structure can be probed by exploiting their couplings to radiative probes such as by measuring electromagnetic transition form factors. HADES (High-Acceptance Di-Electron Spectrometer) at GSI collected high-statistics proton-proton scattering data in 2022 at √s = 3.48 GeV. The Λ - Λ interaction is currently being studied in this data along with production of Σ states where the Dalitz decay of hyperons might be observed for the first time. In addition, the reaction pp → pK+K+Ξ−[π−Λ[pπ−]] has been studied to probe the production mechanism of double strangeness near its production threshold. This proceeding addresses the hyperon physics case and discusses the ongoing Ξ− analysis. A preliminary upper limit for the cross section at √s = 3.48 GeV is presented taking into account only statistical uncertainties.

Production and decay of polarized hyperon-antihyperon pairs* *The authors are grateful to the Knut and Alice Wallenberg Foundation (2016.0157, 2021.0299) (Sweden), the Swedish Research Council (2019-04594, 2021-04567) (Sweden), The Swedish Foundation for International Cooperation in Research and Higher Education (CH2018-7756), the Olle Engkvist Foundation (200-0605) (Sweden), Lundström-Åman Foundation (Sweden), the National Natural Science Foundation of China (11935018, 12122509), the CAS

Polarized hyperon-antihyperon pairs shed light on various unresolved puzzles in contemporary physics: How the strong interaction confines quarks into hadrons, how accurately the Standard Model describes microcosmos and even why our universe consists of so much more matter than antimatter. Thanks to their weak, parity violating decays, hyperons reveal their spin properties. This can be exploited e.g. the decomposition of the electromagnetic structure of hyperons, precision tests of flavour symmetry and searches for CP violation. At the BESIII experiment at BEPC-II, Beijing, China, hyperon-antihyperon pairs can be produced in abundance. Recently collected large data samples have triggered the development of new methods that provide unprecedented precision and a plethora of new results have emerged. When applied at future high-intensity facilities like PANDA and STCF, precision physics will be taken to a new level which can contribute to the solution to the aforementioned puzzles.

Hyperon pair production at BESIII

Hyperons provide a unique avenue to study the strong interaction. Due to their limited lifetime, the hyperon production in e +e − collisions is a new viable way to obtain information to understand the hyperon structure and internal dynamics, and even insight into the nature of the charmonium(-like) states. With the unique data sets obtained by the BESIII experiment, the recent results for the hyperon pair production in e +e − collisions are presented, such as observation of ψ(3686) → Ξ(1530)−Ξ(1530) ¯ +, determination of the Ω − spin, observation of the Ξ hyperon polarization, study of threshold effect in the sector of Ξ hyperon, search for Y (4230/4260) → Ξ −Ξ¯+ and so on.

Electromagnetic transition form factors and Dalitz decays of hyperons

Dalitz decays of a hyperon resonance to a ground-state hyperon and an electron-positron pair can give access to some information about the composite structure of hyperons. We present expressions for the multi-differential decay rates in terms of general transition form factors for spin-parity combinations J^P = frac{1}{2}^pm , frac{3}{2}^pm of the hyperon resonance. Even if the spin of the initial hyperon resonance is not measured, the self-analyzing weak decay of the “final” ground-state hyperon contains information about the relative phase between combinations of transition form factors. This relative phase is non-vanishing because of the unstable nature of the hyperon resonance. If all form factor combinations in the differential decay formulae are replaced by their respective values at the photon point, one obtains a QED type approximation, which might be interpreted as characterizing hypothetical hyperons with point-like structure. We compare the QED type approximation to a more realistic form factor scenario for the lowest-lying singly-strange hyperon resonances. In this way we explore which accuracy in the measurements of the differential Dalitz decay rates is required in order to distinguish the composite-structure case from the pointlike case. Based on the QED type approximation we obtain as a by-product a rough prediction for the ratio between the Dalitz decay width and the corresponding photon decay width.

Hyperon Structure and CP tests at BESIII

Hyperons are a powerful diagnostic tool that can shed light on some of the most intriguing questions in contemporary physics. Electromagnetic form factors (EMFFs) are currently the best way to study hyperon structure. In the time-like region the EMFFs can be complex with a relative phase. A non-zero phase polarizes the final state even when the initial state is unpolarized. A dedicated data sample collected by the BESIII experiment allowed for a first complete reconstruction of Λ in the time-like region. The ratio, R and relative phase between the electric and magnetic form factor, ΔΦ are measured to be 0.96±0.14(stat)±0.002(syst) and 37°±12°(stat)±6°(syst), respectively. In addition, the BESIII experiment has collected the world’s largest J/ψ data sample. Due to symmetric excellent detector conditions and low hadronic background, the experiment offers a clean environment for CP-violation tests using . That hyperons can be polarized allows for a simultaneous measurement of angular distributions of hyperons and antihyperons and to test CP symmetry directly. This has been done for the process recently measured by the BESIII experiment. The experimental results showed that the asymmetry decay parameter α(Λ → ππ−) = +0.750±0.009±0.004, is nearly twenty percent larger compared to the old PDG tabulated value. The test on CP symmetry, is the most sensitive test for Λ CP-violation. Preliminary results are presented for the process . The asymmetry decay parameter and −0.015 ± 0.037 ± 0.008 are both measured for the first time.

Two Recent Developments in QCD Spectroscopy

The presentation has two parts, the first, and main part, is devoted to the presentation of results fromthe first measurements of the production of Λ, Σ Ξ and Ω hyperons at large timelike momentutransfers of 13.6, 14.2 and 17.4 GeV/c2 made using e+e− annihilation data taken at the CESER election-positron collider at Cornell using the CLEOc detector. The measurements reveal interesting features of hyperon production systematics and timelike form factors, and provide evidence for diquark correlations in hyperon structure. The second part of the presentation is devoted to measurements of photoproduction of J/ψ near threshold energies, EG = 8 − 12 GeV, at the new photon physics facility, GlueX, at the Jefferson Laboratory. The first preliminary results are presented. These are expected to shed light on the gluon structure of protons, gluons which mediate the production of J/ψ in the reaction,γp → J/ψ → e+e−.

Electromagnetic decay ofΛ(1520)

The electromagnetic decay processes of excited hyperon states are a very sensitive probe of the structure of hyperons. We will argue that the recent measurements of electromagnetic decay rates indicate that the wave functions of the hyperon ground states should contain sizable components of excited quark states (configuration mixing). Flavor-$\mathit{SU}(3)$ is a broken symmetry and it appears that the hyperon wave functions should preferably be written in a $\mathit{uds}$-basis, where only the light $u$ and $d$-quarks are symmetrized, and not in the usual $\mathit{SU}(6)$-basis.

Study of Decays in Quark Model**The project supported in part by National Natural Science Foundation of China under Grant Nos. 10225525 and 10055003, and by the CAS Knowledge Innovation Project No. KJCX2-SW-NO2

Exclusive decays are studied in the quark model by combining the structure of hyperons in the transition. The branching ratios are evaluated contrastively by adopting different hyperon wavefunctions, SU(6) basis, and uds basis, which account for SU(3)f breaking, and the results show that the different description of quark mass breaking plays an important role in the evaluation of the decay width for processes .

Flavor and spin structure of hyperons from quark fragmentation

We systematically study the hadron longitudinal polarizations of the octet baryons at large $z$ from quark fragmentations in $e^+e^-$-annihilation, polarized charged lepton deep inelastic scattering (DIS) process, and neutrino (antineutrino) DIS process, based on predictions of quark distributions for the octet baryons in the SU(6) quark-spectator-diquark model and a perturbative QCD based counting rule analysis. We show that the $e^+e^-$-annihilation and polarized charged lepton DIS process are able to distinguish between the two different predictions of the hyperon polarizations. We also find that the neutrino/antineutrino DIS process is ideal in order to study both the valence content of the hyperons and the antiquark to hyperon (quark to anti-hyperon) fragmentations, which might be related to the sea content of hyperons.

Extended vector meson dominance model for the baryon octet electromagnetic form factors.

An unresolved issue in the present understanding of nucleon structure is the effect of hidden strangeness on electromagnetic observables such as ${\mathit{G}}_{\mathit{E}}^{\mathit{n}}$(${\mathit{q}}^{2}$). Previously, we have shown that ${\mathit{G}}_{\mathit{E}}^{\mathit{n}}$(${\mathit{q}}^{2}$) is sensitive to small \ensuremath{\varphi}NN couplings. A complementary approach for understanding effects due to strangeness content and the Okubo-Zweig-Iizuka (OZI) rule is to investigate the electromagnetic structure of hyperons. We apply Sakurai's universality limit of the SU(3${)}_{\mathit{F}}$ symmetry relations and a prescription based on the OZI rule to calculate the electromagnetic form factors of the baryon octet states (p,n,\ensuremath{\Lambda},${\mathrm{\ensuremath{\Sigma}}}^{+}$,${\mathrm{\ensuremath{\Sigma}}}^{0}$,${\mathrm{\ensuremath{\Sigma}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\Xi}}}^{0}$,${\mathrm{\ensuremath{\Xi}}}^{\mathrm{\ensuremath{-}}}$) within the framework of an extended vector meson dominance model. To provide additional motivation for experimental investigation, we discuss the possibility of extracting the ratio ${\mathit{G}}_{\mathit{M}}^{\mathrm{\ensuremath{\Lambda}}}$(${\mathit{q}}^{2}$)/${\mathit{G}}_{\mathit{M}}^{\mathrm{\ensuremath{\Sigma}}\mathrm{\ensuremath{\Lambda}}}$(${\mathit{q}}^{2}$) from the \ensuremath{\Lambda}/\ensuremath{\Sigma} polarization ratio in kaon electroproduction experiments. \textcopyright{} 1996 The American Physical Society.

Hyperon structure and strangeness content of the proton

The hamiltonian of the bound kaon-soliton approach to strangeness is diagonalized exactly by a canonical transformation. By reformalating the model as an approximation to some underlying quark theory, we then estimate microscopic (or quark) properties of the “ground state”, namely the proton, with a Skyrme model that provides a good description of the hyperon spectra. We find that the proton has a very small component of s̄s and yet a large sigma term Σ πN ≈ 50 MeV, in disagreement with some current algebra estimates. Relevance on kaon condensation is also mentioned.

The ΔS=1 Weak Radiative Decays of Hyperons

We calculate the rates and asymmetry parameters of radiative hyperon decays based on the hybrid structure of hyperons. We exploit an effective Hamiltonian derived from a penguin-Like Feynman diagram. We also consider a model of a static mean gluon field. A plausible recoil effect is taken into account in the final results. The resultant asymmetry parameters are reasonably consistent with data.

Erratum to: Nucleon and hyperon structure

Erratum to: Nucleon and hyperon structure

Nucleon and hyperon structure

Nucleon and hyperon structure

An Approach to the Non-Leptonic Decays of Hyperons

The interrelation between the effective weak interaction and the hyperon structure is discussed with the aim of explaining non-leptonic decays of hyperons. A consistent model is found by assuming that Σ- and Λ-hyperons are bound states of [KN] with I=1 and 0, respectively, and that the effective Hamiltonian is given solely by the phenomenological kaon interactions, K→π, 2π, with |ΔI|=1/2. This model leads naturally to the consequences: αΣ0≃-αΛ- and αΣ+≃αΣ-≃0, which are consistent with the experiments. Derivation of this model from the field theory of composite particles is given by the covariant new Tamm-Dancoff approach. Extending our theory to the Ξ decay, it is suggested that the Ξ-hyperon is a superposed state of the configurations [KΣ] and [KΛ]. Finally, comparing the p-wave transition rates of Σ-decay with that of Λ, the co-existence of D- and F-type strong interactions defined by SU3-symmetric theory is shown to be necessary.

Complete symmetry and isotopic spin conservation in the nonleptonic decay of hyperons

The possibility is considered that there exists a universal V-A interaction and complete symmetry in the nonleptonic decay of hyperons. The departure from the expected symmetry that is observed in actual decays Is explained by effects caused by the mesonic structure of hyperons. In close connection with the idea of complete symmetry, a new isotopic spin is defined, which is equal to 1/2 for all baryons and to 0 or 1 for K mesons. The law of conservation of this isotopic spin holds in nonleptonic decays.

Global Symmetry and Isotopic Spin Conservation in Non-Leptonic Hyperon Decays

Possible existence of the universal V ∓ A coupling and the global symmetry in the non-leptonic hyperon decays is discussed. The observed deviations from the expected symmetries in actual decays are explained as effects due to the mesonic structure of hyperons. In a close relation with the idea of the global symmetry a new isotopic spin is defined, which is 1/2 for all the baryons and integer for K. The conservation law of this isotopic spin is satisfied in the non-leptonic decays.