Beam–target helicity asymmetry E in K+Σ− photoproduction on the neutron
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Engineering topics
Nikonov, V. A.
Publications and source records attributed to Nikonov, V. A..
Hyperon III: $$K^{-}p - \pi \varSigma $$ coupled-channel dynamics in the $$\varLambda (1405)$$ mass region
Abstract Low-energy data on the three charge states in $$\gamma p \rightarrow K^+(\varSigma \pi )$$ γ p → K + ( Σ π ) from CLAS at JLab, on $$K^-p\rightarrow \pi ^0\pi ^0\varLambda $$ K - p → π 0 π 0 Λ and $$\pi ^0\pi ^0\varSigma $$ π 0 π 0 Σ from the Crystal Ball at BNL, bubble chamber data on $$K^-p\rightarrow \pi ^-\pi ^+\pi ^{\pm }\varSigma ^{\mp }$$ K - p → π - π + π ± Σ ∓ , low-energy total cross sections on $$K^-$$ K - induced reactions, and data on the $$K^-p$$ 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 $$\varLambda (1405)$$ Λ ( 1405 ) , and background contributions. In a fit with one isocsalar state, the $$\varLambda (1405)$$ 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.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
First Measurements of the Double-Polarization Observables F , P , and H in ω Photoproduction off Transversely Polarized Protons in the N * Resonance Region
First measurements of double-polarization observables in ${\omega}$ photoproduction off the proton are presented here using transverse target polarization and data from the CEBAF Large Acceptance Spectrometer (CLAS) FROST experiment at Jefferson Lab. The beam-target asymmetry $F$ has been measured using circularly polarized, tagged photons in the energy range 1200–2700 MeV, and the beam-target asymmetries $H$ and $P$ have been measured using linearly polarized, tagged photons in the energy range 1200–2000 MeV. These measurements significantly increase the database on polarization observables. The results are included in two partial-wave analyses and reveal significant contributions from several nucleon (${N}^{*}$) resonances. In particular, contributions from new ${N}^{*}$ resonances listed in the Review of Particle Properties are observed, which aid in reaching the goal of mapping out the nucleon resonance spectrum.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Beam-target helicity asymmetry E in K 0 Λ and K 0 Σ 0 photoproduction on the neutron
Here, we report the first measurements of the $E$ beam-target helicity asymmetry for the $\vec{\gamma} \vec{n} \to K^{0}\Lambda$, and $K^{0}\Sigma^{0}$ channels in the energy range of 1.70$\leq W\leq$2.34 GeV. The CLAS system at Jefferson Lab used a circularly polarized photon beam and a target consisting of longitudinally polarized solid molecular hydrogen deuteride (HD) with low background contamination for the measurements. Comparisons with predictions from the KaonMAID, SAID, and Bonn-Gatchina models are presented. These results will help separate the isospin $I=0$ and $I=1$ photo-coupling transition amplitudes in pseudoscalar meson photoproduction.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Measurement of the beam asymmetry Σ and the target asymmetry T in the photoproduction of ω mesons off the proton using CLAS at Jefferson Laboratory
Here, the photoproduction of $\omega$ mesons off the proton has been studied in the reaction $\gamma p\to p\,\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) and the frozen-spin target (FROST) in Hall B at the Thomas Jefferson National Accelerator Facility. For the first time, the target asymmetry, $T$, has been measured in photoproduction from the decay $\omega\to\pi^+\pi^-\pi^0$, using a transversely-polarized target with energies ranging from just above the reaction threshold up to 2.8 GeV. Significant non-zero values are observed for these asymmetries, reaching about 30-40% in the third-resonance region. New measurements for the photon-beam asymmetry, $\Sigma$, are also presented, which agree well with previous CLAS results and extend the world database up to 2.1 GeV. These data and additional $\omega$-photoproduction observables from CLAS were included in a partial-wave analysis within the Bonn-Gatchina framework. Significant contributions from $s$-channel resonance production were found in addition to $t$-channel exchange processes.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the helicity asymmetry E in ω → π + π - π 0 photoproduction
The double-polarization observable $E$ was studied for the reaction $\gamma p\to p\omega$ using the CEBAF Large Acceptance Spectrometer (CLAS) in Hall B at the Thomas Jefferson National Accelerator Facility and the longitudinally-polarized frozen-spin target (FROST). The observable was measured from the charged decay mode of the meson, $\omega\to\pi^+\pi^-\pi^0$, using a circularly-polarized tagged-photon beam with energies ranging from the $\omega$ threshold at 1.1 to 2.3 GeV. A partial-wave analysis within the Bonn-Gatchina framework found dominant contributions from the $3/2^+$ partial wave near threshold, which is identified with the sub-threshold $N(1720)\,3/2^+$ nucleon resonance. To describe the entire data set, which consisted of $\omega$ differential cross sections and a large variety of polarization observables, further contributions from other nucleon resonances were found to be necessary. Here, with respect to non-resonant mechanisms, $\pi$ exchange in the $t$-channel was found to remain small across the analyzed energy range, while pomeron $t$-channel exchange gradually grew from the reaction threshold to dominate all other contributions above $W \approx 2$ GeV.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
N* resonances from K $\Lambda$ Λ amplitudes in sliced bins in energy
The two reactions $\gamma p\to K^+\Lambda$ and $\pi^-p\to K^0\Lambda$ 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 $J^P = 1/2^+$, $3/2^+, 1/2^-, 3/2^-, 5/2^-$.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Measurement of the differential and total cross sections of the γ d → K 0 Λ ( p ) reaction within the resonance region
Here, we report the first measurement of differential and total cross sections for the ${\gamma}d \to K^0{\Lambda}(p)$ reaction, using data from the CLAS detector at the Thomas Jefferson National Accelerator Facility. Data collected during two separate experimental runs were studied with photon-energy coverage 0.8 - 3.6 GeV and 0.5 - 2.6 GeV, respectively. The two measurements are consistent giving confidence in the method and determination of systematic uncertainties. The cross sections are compared with predictions from the KAON-MAID theoretical model (without kaon exchange), which deviate from the data at higher W and at forward kaon angles. These data, along with previously published cross sections for $K^+ {\Lambda}$ photoproduction, provide essential constraints on the nucleon resonance spectrum. A first partial wave analysis has been performed that describes the data without the introduction of new resonances.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Neutron helicity amplitudes
Here we determine the helicity amplitudes for the photoproduction of nucleon resonances excited from neutrons in the Bonn-Gatchina coupled-channel partial wave analysis. The upper limits for the decay fraction of the pentaquark candidate N(1685) → K 0 Λ are given. The electric and magnetic couplings at the pole positions are also tabulated, and these are used to suggest candidates for possible multiplets with quark-spin-1/2 and -3/2 content.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Photon beam asymmetry Σ in the reaction γ → p → p ω for E= 1.152 to 1.876 GeV
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
N⁎→Nη′ decays from photoproduction of η′-mesons off protons
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Strong Evidence for Nucleon Resonances near 1900 MeV
Data on the reaction yp→K + A from the CLAS experiments are used to derive the leading multipoles, E 0+ , M 1- , E 1+ , and M 1+ , from the production threshold to 2180 MeV in 24 slices of the invariant mass. The four multipoles are determined without any constraints. The multipoles are fitted using a multichannel L+P model that allows us to search for singularities and to extract the positions of poles on the complex energy plane in an almost model-independent method. The multipoles are also used as additional constraints in an energy-dependent analysis of a large body of pion and photoinduced reactions within the Bonn-Gatchina partial wave analysis. The study confirms the existence of poles due to nucleon resonances with spin parity J P =1/2 - , 1/2 + , and 3/2 + in the region at about 1.9 GeV.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Differential cross sections and polarization observables from CLAS K ⁎ photoproduction and the search for new N ⁎ states
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71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Beam-target helicity asymmetry for γ → n → → π - p in the N * resonance region
In this paper, we report the first beam-target double-polarization asymmetries in the $\gamma + n(p) \rightarrow \pi^- + p(p)$ reaction spanning the nucleon resonance region from invariant mass $W$= $1500$ to $2300$ MeV. Circularly polarized photons and longitudinally polarized deuterons in $HD$ have been used with the CLAS detector at Jefferson Lab. The exclusive final state has been extracted using three very different analysis techniques that show excellent agreement, and these have been used to deduce the $E$ polarization observable for an effective neutron target. These results have been incorporated into new partial wave analyses, and have led to revised values for several $\gamma nN^*$ resonance photo-couplings.
43 PARTICLE ACCELERATORS↗
Photon beam asymmetry Σ for η and η ' photoproduction from the proton
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Scrutinizing the evidence for N ( 1685 )
The helicity-dependent observable E for the reaction γd → ηn(p) with a spectator proton was recently measured in this paper by the A2 Collaboration at MAMI in Mainz. The data were interpreted as further evidence for a narrow resonance with spin and parity J P = 1/2 + (P 11 wave). However, a full partial-wave analysis without any narrow resonance leads to an excellent description of the data. Finally, imposing a narrow resonance with the properties suggested by the A2 Collaboration leads to a significant deterioration of the fit quality: there is no need for a narrow resonance.
74 ATOMIC AND MOLECULAR PHYSICS↗