Measurements Of Polarization Observables Research Articles

Measurement of polarization observables in multi-meson photoproduction off the proton with the CBELSA/TAPS experiment

The reaction γp → pπ 0π 0 was analyzed using data of the CBELSA/TAPS experiment where linearly polarized photons impinged on a transversely polarized butanol target. Single and double polarization observables were extracted. Within the BnGa-PWA resonance parameters were determined. N∗ and ∆∗ resonances demonstrated systematic differences in their decay branching ratios via excited hadrons which hint at the internal structure of these states.

The strangeness program at GlueX

The GlueX experiment located at Jefferson Lab studies the spectrum of hadrons using photoproduction on a LH2 target in a wide variety of final states. With its detector system capable of measuring neutral and charged final state particles over almost the full solid angle, and very good particle identification capabilities, GlueX can measure many different hadrons containing strangeness. A linearly polarized photon beam allows the measurement of polarization observables, which contain information about the production mechanisms involved in generating strange particles in photoproduction. In addition, GlueX can perform precise cross-section measurements, which help to study the spectrum of strange hadrons. In this presentation, the GlueX experiment is introduced, and recent progress of its strangeness program is discussed. We present recent results on Σ0 beam asymmetries, Λ(1520) spin-density matrix elements and ongoing studies of the Λ(1405) lineshape. We also present our recent progress on measurements of ΛΛ̅ and Ξ(∗) photoproduction. Also, future prospects for strangeness measurements at GlueX are discussed.

Measurement of polarization observables in neutral double pion photoproduction off the proton with the CBELSA/TAPS experiment

Data on the reaction γp → pπ0π0 were taken with the CBELSA/TAPS experiment at ELSA where linearly polarized photons impinged on a transversely polarized butanol target. Target asymmetries and double polarization observables were extracted and entered the BnGa-PWA. Systematic differences in the branching ratios of N* and Δ* resonances hint at the internal structure of these states

Determining dominant partial waves in photoproduction via moment analysis

Important insights into the excitation spectra of baryons are provided by measurements of polarization observables in reactions that involve particles with spin. The photoproduction of a single pseudoscalar meson constitutes an example-reaction that has been under intense investigation recently. We present the basic method of moment-analysis for pseudoscalar meson photoproduction, in which just the angular distributions are analyzed. Using this method, the total angular momentum quantum number of the dominant partial waves contributing in the data can be extracted quickly. Furthermore, the Legendre-coeffcients extracted from the angular distributions show interesting composition-patterns in terms of multipoles and allow for instructive comparisons to models. In this contribution, recent results for moment analyses of polarization data for the photoproduction of pions and eta-mesons are shown.

Vector meson photoproduction studied in its radiative decay channel

We provide an analysis of vector meson photoproduction in the channel of the vector meson decaying into a pseudoscalar meson plus a photon, i.e. $V\to P\gamma$. It is shown that non-trivial kinematic correlations arise from the measurement of the $P\gamma$ angular distributions in the overall c.m. system in comparison with those in the vector-meson-rest frame. In terms of the vector meson density matrix elements, the implication of such kinematic correlations in the measurement of polarization observables is discussed. For the $\omega$ meson production, due to its relatively large branching ratios for $\omega\to\pi^0\gamma$, additional events from this channel may enrich the information about the reaction mechanism and improve the statistics of the recent measurement of polarized beam asymmetries by the GRAAL Collaboration. For $\phi\to \eta\gamma$, $\rho\to \pi\gamma$, and $K^*\to K\gamma$, we expect that additional information about the spin structure of the vector meson production vertex can be derived.

Possible methods for the determination of the P-parity of the Θ+-pentaquark in NN-collisions

We present two possibilities to determine the P-parity of the pentaquark Θ+, in a model independent way, via the measurement of polarization observables in p+p→Σ++Θ+, or n+p→Λ0+Θ+, in the near threshold region. Besides the measurement of the spin correlation coefficient, Axx=Ayy, (in collisions of transversally polarized nucleons), the coefficient Dxx=Dyy of polarization transfer from the initial proton to the final Σ+(Λ0) hyperon is also unambiguously related to the Θ+ parity.

Possible methods for the determination of the P-parity of the $Theta;+-pentaquark in NN-collisions

We present two possibilities to determine the P -parity of the pentaquark Θ + , in a model independent way, via the measurement of polarization observables in p + p → Σ + + Θ + , or n + p → Λ 0 + Θ + , in the near threshold region. Besides the measurement of the spin correlation coefficient, A xx = A yy , (in collisions of transversally polarized nucleons), the coefficient D xx = D yy of polarization transfer from the initial proton to the final Σ + ( Λ 0 ) hyperon is also unambiguously related to the Θ + parity.

Measurement of polarization observables in elastic and inelastic electron–deuteron scattering at the VEPP-3 storage ring

Measurement of polarization observables in elastic and inelastic electron–deuteron scattering at the VEPP-3 storage ring

Measurement of polarization observables in the d→+p→p→+p+n reaction at Td = 2.0 GeV

We have studied the deuteron breakup in the $p(d,2p)n$ reaction at ${T}_{d}$=2.0 GeV. In this experiment, the vector analyzing power ${A}_{Y},$ the tensor analyzing power ${A}_{\mathrm{YY}},$ and the polarization of the forward scattered proton are measured close to the quasifree $\mathrm{pp}$ scattering kinematics. These observables are presented as a function of the neutron momentum ranging from 0.04 to 0.45 GeV/$c$ in the rest frame of the deuteron. Marked deviations from the impulse approximation using conventional deuteron wave functions are observed. Corrections due to the multiple scattering, the final state interaction, and the $\ensuremath{\Delta}$ excitation are calculated in a model where the spin-isospin structure of the elementary amplitudes is treated rigorously. With this model, a reasonable account of the measured polarization observables is obtained. The global agreement with all observables is, however, not good enough that we can reliably discriminate between conventional wave functions.

Spin-Isospin excitations studied by polarized beams

The spin-parity J π of the spin dipole resonances (SDR) in 12N and 12B are investigated via the measurements of polarization observables, the transverse polarization transfer conefficient D NN for the ( p , n ) reaction at 197 and 295 MeV and the tensor analyzing power A xx for the ( d, 2 He ) reaction at 270 MeV. The polarization observables, D NN and A xx for the peak at 4.5 MeV are consistent with the DWIA prediction with 2 − but those for the peak at 7.5 MeV contradict the predictions with an expected J π = 1 −. Neither polarization observables could detect any concentration of 0 − strength. The usefulness of these spin observables in identifying J π is shown.

Experiments on four-nucleon reactions

The status of experimental evidence on four-nucleon reactions in the range from very low to medium energies (∼50 MeV) is reviewed. The recent progress of microscopic theories as well as computer capabilities, the renewed interest in astrophysical and the new fusion-energy aspects of the four-nucleon reactions, the emphasis on improved measurements of polarization observables especially at very low energies and on new types of studies such as break-up reactions with polarized projectiles prompt such a survey. The aim is to stimulate interest in the four-nucleon system. It is expected that the four-nucleon system will undergo a development similar to the three-nucleon system as a special testing ground for nuclear forces.