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The spectrum of Λ and Σ excitations is reviewed taking into account (nearly) all hyperon resonances which were seen in early analyses or in one of the recent partial-wave analyses. The spectrum is compared with the old Isgur–Karl model and the Bonn model. These models allows us to discuss the SU(3) structure of the observed resonances. The SU(3) decomposition is compared with SU(6) relations between the different decay modes. Seven Λ states are proposed to be classified as SU(3) singlet states. The hyperon spectrum is compared with the spectrum of N and Δ resonances. [ABSTRACT FROM AUTHOR]

Low-energy data on the three charge states in γ p → K + (Σ π) from CLAS at JLab, on K - p → π 0 π 0 Λ and π 0 π 0 Σ from the Crystal Ball at BNL, bubble chamber data on K - p → π - π + π ± Σ ∓ , low-energy total cross sections on K - induced reactions, and data on the K - p atom are fitted with the BnGa partial-wave-analysis program. We find that the data can be fitted well with just one isoscalar spin-1/2 negative-parity pole, the Λ (1405) , and background contributions. In a fit with one isocsalar state, the Λ (1405) structure can be determined as a dominantly SU(3) singlet state. A fit with two isoscalar singlet states, with imposed properties of the low-mass state, is, however, also not incompatible with data. [ABSTRACT FROM AUTHOR]

The two reactions $\gamma p\rightarrow K^{+}\Lambda$ and $\pi^{-} p\rightarrow K^{0}\Lambda$ are analyzed to determine the leading photoproduction multipoles and the pion-induced partial wave amplitudes in slices of the invariant mass. The multipoles and the partial-wave amplitudes are simultaneously fitted in a multichannel Laurent+Pietarinen model (L+P model), which determines the poles in the complex energy plane on the second Riemann sheet close to the physical axes. The results from the L+P fit are compared with the results of an energy-dependent fit based on the Bonn-Gatchina (BnGa) approach. The study confirms the existence of several poles due to nucleon resonances in the region at about 1.9 GeV with quantum numbers $J^{P} = 1/2^{+}, 3/2^{+}, 1/2^{-}, 3/2^{-}, 5/2^{-}$ . [ABSTRACT FROM AUTHOR]

Amplitudes for the reaction π p → ΛK are reconstructed from data on the differential cross section d σ/d Ω, the recoil polarization P, and on the spin rotation parameter β. At low energies, no data on β exist, resulting in ambiguities. An approximation using S and P waves leads only to a fair description of the data on d σ/d Ω and P; in this case, there are two sets of amplitudes. Including D waves, the data on d σ/d Ω and P are well reproduced by the fit but, now, there is a multitude of distinct solutions which describe the data with identical precision. In the range where the spin rotation parameter β was measured, a full and unambiguous reconstruction of the partial wave amplitudes is possible. The energy-independent (single-energy) amplitudes are compared to the energy-dependent amplitudes which resulted from a coupled-channel fit (BnGa2011-02) to a large data set including both pion- and photo-induced reactions. Significant deviations are observed. Consistency between energy-dependent and energy-independent solutions is obtained by choosing the energy-independent solution which is the closest to the energy-dependent solution. In a second step, the known energy-dependent solution for low (or high) partial waves is imposed and only the high (or low) partial waves are fitted leading to smaller uncertainties. [ABSTRACT FROM AUTHOR]

The helicity amplitudes $A^{1/2}_{n}$ and $A^{3/2}_{n}$ for the photoexcitation of nucleon resonances off neutrons are determined in a multichannel partial wave analysis. [ABSTRACT FROM AUTHOR]

Masses, widths and photocouplings of baryon resonances are determined in a coupled-channel partial-wave analysis of a large variety of data. The Bonn-Gatchina partial-wave formalism is extended to include a decomposition of t and u exchange amplitudes into individual partial waves. The multipole transition amplitudes for $ \gamma$ p $ \rightarrow$ p $ \pi^{0}_{}$ and $ \gamma$ p $ \rightarrow$ n $ \pi^{+}_{}$ are given and compared to results from other analyses. [ABSTRACT FROM AUTHOR]

A formalism is developed for the partial-wave analysis of data on meson photoproduction off deuterons and applied to photoproduction of $ \eta$ and $ \pi^{0}_{}$ mesons. Different interpretations of a dip-bump structure of the $ \eta$ photoproduction cross-section in the 1670MeV region are presented and discussed. Helicity amplitudes for two low-mass S11 states are determined. [ABSTRACT FROM AUTHOR]

The mass spectrum of Δ -resonances is compared to predictions based on three quark-model variants, to predictions assuming that chiral symmetry is restored in high-mass baryon resonances, and to predictions derived from AdS/QCD. The latter approach yields a nearly perfect agreement when the confinement property of QCD is modeled by a soft wall in AdS. [ABSTRACT FROM AUTHOR]

A Dalitz plot analysis of the OZI rule violating decay D+ s into π-π+π+ is presented using different partial wave approaches. Scalar and vector waves are described by K-matrices; their production is parameterized in a P-vector approach. Alternatively, Breit–Wigner amplitudes and Flatté parametrization are used. Special emphasis is devoted to scalar mesons. The f0(980) resonance provides the most significant contribution. Adding f0(1500) to the scalar wave leads to an acceptable fit while introduction of f0(1370) and/or f0(1710) does not lead to significant improvements. A scan of the scalar wave optimizes for M=1452 ± 22 MeV/ c 2. When f0(1710) is added, the mass uncertainty increases, and the fit yields M=1470 ± 60 MeV/ c 2 which is fully compatible with the nominal f0(1500) mass. The scalar wave seems to exhibit a phase motion of 270° units in the mass range from 1200 to 1650 MeV/ c 2. [ABSTRACT FROM AUTHOR]

A Dalitz plot analysis of the OZI rule violating decay D+ s into π-π+π+ is presented using different partial wave approaches. Scalar and vector waves are described by K-matrices; their production is parameterized in a P-vector approach. Alternatively, Breit–Wigner amplitudes and Flatté parametrization are used. Special emphasis is devoted to scalar mesons. The f0(980) resonance provides the most significant contribution. Adding f0(1500) to the scalar wave leads to an acceptable fit while introduction of f0(1370) and/or f0(1710) does not lead to significant improvements. A scan of the scalar wave optimizes for M=1452 ± 22 MeV/ c 2. When f0(1710) is added, the mass uncertainty increases, and the fit yields M=1470 ± 60 MeV/ c 2 which is fully compatible with the nominal f0(1500) mass. The scalar wave seems to exhibit a phase motion of 270° units in the mass range from 1200 to 1650 MeV/ c 2. [ABSTRACT FROM AUTHOR]

A partial-wave analysis of data on photoproduction of hyperons including single and double polarization observables is presented. The large spin transfer probability reported by the CLAS Collaboration can be successfully described within an isobar partial-wave analysis. [ABSTRACT FROM AUTHOR]

Partial-wave scattering amplitudes in baryon-baryon and baryon-antibaryon collisions and amplitudes for the production and decay of baryon resonances are constructed in the framework of the spin-momentum operator expansion method. The approach is relativistically invariant and it allows us to perform combined analyses of different reactions imposing analyticity and unitarity directly. The role of final-state interactions (triangle and box diagrams) is discussed. [ABSTRACT FROM AUTHOR]

A novel technique to probe the resonant structure of a partial-wave amplitude is proposed and applied to data on photoproduction of baryon resonances. [ABSTRACT FROM AUTHOR]

A combined analysis of photoproduction data on γ p↦ π N, η N was performed including the data on KΛ and KΣ. The data are interpreted in an isobar model with s-channel baryon resonances and π, ρ (ω), K, and K* exchange in the t-channel. Three baryon resonances have a substantial coupling to η N, the well-known N(1535) S11, N(1720) P13, and N(2070) D15. The inclusion of data with open strangeness reveals evidence for further new resonances, N(1840) P11, N(1875) D13 and, with weaker evidence, for N(2170) D13. [ABSTRACT FROM AUTHOR]

Cross-sections, beam asymmetries, and recoil polarisations for the reactions γ p → K+Λ;γ p → K+Σ0, and γ p → K0Σ+ have been measured by the SAPHIR, CLAS, and LEPS Collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P11 state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D13 states at 1875 and, optimistically, at 2170 MeV. [ABSTRACT FROM AUTHOR]

The reaction ?p?K0S+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the S+ as a function of the kaon production angle in the centre-of-mass system, cosTc.m.K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of ?p?K+S0. The S+ is polarized predominantly at cosTc.m.K ˜ 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations. [ABSTRACT FROM AUTHOR]

Partial-wave amplitudes for production and decay of baryon resonances are constructed in the framework of the operator expansion method. The approach is fully relativistically invariant and allows us to perform combined analyses of different reactions imposing directly analyticity and unitarity constraints. All formulas are given explicitly in the form used by the Crystal Barrel Collaboration in the (partly forthcoming) analyses of the electro-, photo- and pion-induced meson production data. [ABSTRACT FROM AUTHOR]

The photoproduction of ?0-mesons and ?-baryons at photon energies up to 2.6 GeV has been studied with the SAPHIR detector at the electron stretcher ELSA. Total and differential cross-sections were obtained. The decay angular distributions of ?0-mesons show thats-channel helicity conservation, which is valid at high photon energies, is broken near threshold. The energy dependencies of the decay angular distributions in the helicity system as well as in the Gottfried-Jackson system hint at smalls- oru-channel resonance contributions. For the reactions ?p? ?{++}p- and ?p? ?0p+ new data on cross-sections are presented. [ABSTRACT FROM AUTHOR]

The reactions γp ↠K+ A and γp ↠K+ E0 were measured in the energy range from threshold up to a photon energy of 2.6 GeV. The data were taken with the SAPFHR detector at the electron stretcher facility, ELSA. Results on cross-sections and hyperon polarizations are presented as a function of the kaon production angle and the photon energy. The total cross-section for A production rises steeply with energy close to threshold, whereas the E0 cross-section rises slowly to a maximum at about Eγ = 1.45 GeV. Cross-sections together with their angular decompositions into Legendre polynomials suggest contributions from resonance production for both reactions. In general, the induced polarization of A has negative values in the kaon forward direction and positive values in the backward direction. The magnitude varies with energy. The polarization of E0 follows a similar angular and energy dependence as that of A, but with opposite sign. [ABSTRACT FROM AUTHOR]

The photoproduction of the vector meson w has been studied between threshold and W =2.4 GeV with the SAPFIIR detector at the Bonn electron stretcher ring ELSA. Besides, the total cross- sections angular distributions in the CMS and decay angular distributions in the helicity and Gottfried- Jackson systems have been measured. [ABSTRACT FROM AUTHOR]

: Photoproduction of Φ-vector-mesons has been studied from reaction threshold up to W = 2.4 GeV with the SAPHIR spectrometer at the Bonn electron stretcher ring ELSA. Total cross-sections, differential cross-sections and decay angular distributions were measured. We find evidence for strong non-diffractive contributions to Φ photoproduction. [ABSTRACT FROM AUTHOR]

An exotic meson, the π1(1400) with JPC = 1- +, has been seen to decay into a p-wave ηπ system. If this decay conserves flavor SU(3), then it can be shown that this exotic meson must be a four-quark state ( q¯q + q¯q) belonging to a flavor ¯10 representation of SU(3). In contrast, the π1(1600) with a substantial decay mode into π is likely to be a member of a flavor octet. [ABSTRACT FROM AUTHOR]

$$N\bar N$$ annihilation at rest into five pions was studied in the ASTERIX spectrometer by stopping antiprotrons from LEAR in a H or D gas target. In $$\bar pp$$ annihilations in H leading to the πππππ final state, the invariant mass spectra of two, three, and four pions show no evidence for any new narrow states. In $$\bar pn \to \pi ^ + \pi ^ - \pi ^ + \pi ^ - \pi ^ - $$ the difference of the four pion mass spectra recoiling against a π and those recoiling against a π shows a resonance-like structure ('ζ (1480)'), confirming a previous analysis with a smaller event sample. The ζ (1480) mass is shown to depend strongly on the momentum of the spectator proton. In H, we searched for the ζ (1480) in the reaction $$\bar pp \to \pi ^0 \zeta $$ (1480), ζ (1480) →ππππ to clarify whether the ζ (1480) is identical to the 4π-mode of the f (1520). No evidence for this decay mode was found. A prominent resonance in $$\bar pp$$ innihilation into five pions is the ω meson. We find two quasi-two-body intermediate states: $$\bar pp \to \rho \omega $$ and $$\bar pp \to \pi ^ \pm b_1^ \mp $$ (1235). The mass and width of the b (1235) are determined to be: [ABSTRACT FROM AUTHOR]

We have measured the branching ratios for $$\bar pp$$ annihilation at rest into π π η and π π η′ in hydrogen gas in two data samples that have different fractions of S-wave and P-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for $$\bar pp$$ annihilations into four charged pions of (49±4)% and the branching ratio into π π π π π of (18.7±1.6)%. We find a significant reduction of the branching ratios from P-states for $$\bar pp \to \pi ^ + \pi ^ - \eta $$ and π π η′ in comparison to S-state annihilation. In a partial wave analysis of the π π η Dalitz plot we find the following contributions: Phase space, $$a_2^ + (1320)\pi ^ \mp $$ , ηρ and f(1270)η: We find a 2 σ effect for the reaction $$\bar pp \to a_0^ \pm (980)\pi ^ \mp $$ , $$a_0^ \pm \to \eta \pi ^ \pm $$ , with a branching ratio of (0.13±0.07)·10. For η' production we give a branching ratio of $$\bar pp \to \rho \eta '$$ of (1.81±0.44)·10 from S. We estmate a contribution of about 0.3·10 for ρη' from P-states. The ratio of ρη and ρη' rpoduction is used to test the validity of the quark line rule. In the π π π π γ final state we do not observe the reaction $$\bar pp \to \pi ^ + \pi ^ - \omega $$ , ω→ π π λ and derive an upper limit of 3·10 for decay mode ω→ π π λ. [ABSTRACT FROM AUTHOR]

Annihilation of antiprotonic hydrogen atoms into π π π is studied by stopping antiprotons from LEAR in hydrogen gas. Two data samples were taken. In the first data sample events were collected independently of the cascade of the $$\bar pp$$ atom; in the second sample only those events are selected for which a low-energy X-ray is observed in coincidence with the final state. The latter data sample contains a large fraction of events in which a radiative transition to the 2 P level of the $$\bar pp$$ atom was followed by annihilation. The former data contain comparable fractions of annihilation from S and P states. By subtraction of the P wave contribution annihilation from S states can be studied. The spin-parity analysis of the π π π Dalitz plot shows that $$\bar pp$$ annihilation from S waves proceeds dominantly via production of ϱ mesons from the spin-triplet isospin-singlet state of the $$\bar pp$$ atom. Strong interference with a background amplitude or an amplitude for ϱ(1600) production is needed to obtain a satisfactory description of the data. The production of f mesons is weak. [ABSTRACT FROM AUTHOR]

Antiproton-proton annihilation at rest in a gaseous H target at NTP into the final state π π K π ( K) with an undetected K or $$\bar K^0 $$ has been investigated. We observe the E(1420) resonance in the invariant mass spectrum ( K) K π with mass M=1413±8 MeV/c and width Г=62 ± 16MeV/c and find evidence for the production of the f(1285). The absolute branching ratio of $$\bar p$$ p → π π E, E → K K π at (61±6)% P wave annihilation is (3.0±0.9)·10 of all annihilations. The observed suppression of the E production from P wave with respect to the S wave together with some simple selection rules suggest that the quantum numbers of the E(1420) are J=0 and not I. [ABSTRACT FROM AUTHOR]

We use SU(3)- and charge conjugation-invariance to analyse the annihilation of a $$\bar pp$$ bound state of definite C-parity into two mesons. We introduce four sets of SU(3) invariant couplings and write down the transformations among them. They allow for a direct interpretation in terms of different physical assumptions. The couplings permit an easy incorporation of the quark line- (or OZI-) rule. The four sets of invariant couplings - even though mathematically equivalent - correspond to different pictures of the annihilation mechanism. One coupling scheme refers to a description of $$\bar pp$$ annihilation in terms of baryon exchange. A second scheme specifies the octet decomposition of the s-channel intermediate states. The third scheme traces the flow of quarks from the initial $$\bar pp$$ system to the outgoing mesons. And finally, we use the octet coupling scheme. The latter has no obvious interpretation in form of a simple physical picture but is needed to relate the different coupling schemes by transformation matrices. [ABSTRACT FROM AUTHOR]

Recent experiments at LEAR have found surprisingly large branching ratios for reactions $$\bar NN \to \phi \pi $$ from S-wave initial states while no φπ production is observed from P states of the $$\bar pp$$ system. Also, no φπ is seen in radiative J/ ψ decays even though the rate for ωπ is substantial. We calculate the φπ production rates for these three cases via KK* intermediate states and $$K\bar K$$ rescattering using the dispersion relation technique; we find that the large φπ rate in $$\bar pp$$ annihilations from S states can be reproduced with a reasonable cut-off for the dispersion integral; for J/ ψ decays the calculated φπ rate is compatible with the observed upper limit. We would, however, expect φπ to be seen from $$\bar pp$$ P-states, in contrast to experimental findings. Yet the branching ratio for $$\bar pp \to K*\bar K$$ via isospin I = 1 of $$\bar pp$$ , P state is not known; and therefore no definite conclusion can be drawn. We also compare the Dalitz plots we obtain for direct φ production and for φ production via rescattering. Clear differences between the two theoretical distributions are observed; yet very high precision data would be required to establish the origin - direct production or rescattering - of the φ mesons. This observation supports the use of the isobar model in data analyses. [ABSTRACT FROM AUTHOR]

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The importance of approximate isospin selection rules observed in N¯ N annihilation at rest into two strange mesons is emphasized. The selection rules are traced back to a symmetry between amplitudes describing annihilation by the flux of quarks. Presumably the symmetry reflects the symmetry of ¯ qq annihilation vertices. The relation of the symmetry to a quark - diquark substructure of the nucleon is discussed. [ABSTRACT FROM AUTHOR]

Proton-antiproton annihilation at rest into two mesons is analysed in a model describing annihilation by quark lines. The model allows to fit existing data with two parameters. The parameters describe the amplitudes for diagrams with and without rearrangement of quark lines. [ABSTRACT FROM AUTHOR]

The cyclotron resonance of protons and electrons in a magnetic field of 5.7 Tesla produced by a superconducting solenoid has been measured. Protons and electrons were alternately confined in an electrostatic quadrupole trap. The quotient of the cyclotron frequencies provides a first direct determination of the proton-electron mass ratio. The result of M/ M=1836.1502(53) agrees with other more precise but indirect determinations of this quantity. [ABSTRACT FROM AUTHOR]

It is shown that a previously described method for measuring the spin resonance of free electrons in a trap can also be used to measure their ( g-2) anomaly. The electrons are trapped in an electrostatic quadrupole field with a superimposed homogeneous axial magnetic field, and are polarized by spin exchange. The spin and ( g-2) resonance are monitored through the spin dependence of the excitation process e+Na (3 S)→ e+Na(3 P). Calculations are made of the energy levels and transition probabilities of the trapped electrons. [ABSTRACT FROM AUTHOR]

We report properties of Λ and Σ hyperon resonances formed in K - induced reactions. Special emphasis is laid on the analysis of the three-body final states 2 π 0 Λ and 2 π 0 Σ and of the quasi-two-body final states π Λ (1520) , K ¯ Δ (1232) , π Σ (1385) , K ¯ * N , and ω Λ . We give pole positions of Λ and Σ hyperon resonances and transition residues from the K - p initial to various final states as well as Breit-Wigner masses and widths and decay branching ratios. Twenty resonances and "bumps" reported in the Review of Particle Physics are not required in our fits, evidence for five new resonances is reported. The observed mass spectrum is compared to the spectrum calculated in the Bonn quark model. Three spin doublets, six Λ hyperons, are tentatively assigned to the SU(3) singlet system. [ABSTRACT FROM AUTHOR]

Early data on K - induced reactions off protons are collected and used in a coupled-channel partial-wave analysis (PWA). Data that had been published in the form of Legendre coefficients are included in the PWA. In a primary fit using 3 * and 4 * resonances only, we observe some significant discrepancies with the data. In a systematic search for new Λ and Σ hyperon resonances, additional candidates are found. The significance of the known and of the additional resonances is evaluated. Seventeen resonances listed with 1 * or 2 * and one resonance listed with 3 * in the Review of Particle Physics cannot be confirmed, five new hyperons are suggested. The partial-wave amplitudes deduced in this analysis are compared to those from other analyses. [ABSTRACT FROM AUTHOR]

Cross-sections, beam asymmetries, and recoil polarisations for the reactions γ p → K+Λ;γ p → K+Σ0, and γ p → K0Σ+ have been measured by the SAPHIR, CLAS, and LEPS Collaborations with high statistics and good angular coverage for centre-of-mass energies between 1.6 and 2.3 GeV. The combined analysis of these data with data from π and η photoproduction reveals evidence for new baryon resonances in this energy region. A new P11 state with mass 1840 MeV and width 140 MeV was observed contributing to most of the fitted reactions. The data demand the presence of two D13 states at 1875 and, optimistically, at 2170 MeV. [ABSTRACT FROM AUTHOR]

The reaction ?p?K0S+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross-section and the polarization of the S+ as a function of the kaon production angle in the centre-of-mass system, cosTc.m.K, and the photon energy. The cross-section is lower and varies less with photon energy and kaon production angle than that of ?p?K+S0. The S+ is polarized predominantly at cosTc.m.K ˜ 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations. [ABSTRACT FROM AUTHOR]