Pion Angles Research Articles

Tensor analyzing power component [formula omitted] of the [formula omitted] process in the photon energy range from 200 to 400 MeV

The tensor analyzing power component, T20, of the γd→→π0d process in the photon energy range from 200 to 400 MeV is investigated. This work is motivated by the most recent and unique measurements from the VEPP-3 electron storage ring at the Budker Institute of Nuclear Physics in Novosibirsk, Russia. We point out a special sensitivity of T20 to the elementary γN→πN amplitude and to the realistic NN potential model adopted for the deuteron wave function at backward pion angles, especially in the region 90°<θ<150°. The estimated results for T20 are compared with the experimental data from VEPP-3 and a satisfactory agreement is obtained at incident photon energies below 375 MeV. At higher photon energies and extreme backward pion angles, the estimated results of T20 considerably underestimate the data.

Coherent π0-Photoproduction on the Deuteron near Threshold and the Role of D-Wave Component of the Deuteron Wave Function

Near-threshold coherent photoproduction of π0-meson on the deuteron is investigated. Numerical results for the unpolarized differential and total cross sections, the linear photon Σ-asymmetry, the vector T11 and tensor T2M (M = 0, 1, 2) deuteron spin asymmetries, and the spin asymmetry $$\tilde{T}_{20}$$ of the total cross section are presented. The role of D-wave component of the deuteron wave function on these physical observables is studied. The calculations are based on the impulse approximation in which we use the realistic and high-precision Bonn NN potential (full model) for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary γN → πN amplitude that describes well the threshold region. We have found that the D-wave component has a negligible effect on the unpolarized cross sections and the vector deuteron T11-asymmetry at photon lab-energies close to threshold. On the contrary, we have obtained a significant role of the D-wave part of the deuteron wave function on the Σ, T2M, and $$\tilde{T}_{20}$$ spin asymmetries. The results for the unpolarized differential cross section are compared to the experimental data from TAPS and a satisfactory agreement within the uncertainties has been obtained at forward pion angles. At backward pion angles, our results underestimate the experimental data and a disagreement has been found.

First measurement of the cross section for νμ and ν¯μ induced single charged pion production on argon using ArgoNeuT

We report on the first cross section measurement of charged-current single charged pion production by neutrinos and antineutrinos on argon. This analysis was performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The measurements are presented as functions of muon momentum, muon angle, pion angle, and angle between muon and pion. The flux-averaged cross sections are measured to be $2.7\pm0.5(stat)\pm0.5(syst) \times 10^{-37} \textrm{cm}^{2}/\textrm{Ar}$ for neutrinos at a mean energy of 9.6 GeV and $8.4\pm0.9(stat)^{+1.0}_{-0.8}(syst) \times 10^{-38} \textrm{cm}^{2}/\textrm{Ar}$ for antineutrinos at a mean energy of 3.6 GeV with the charged pion momentum above 100 MeV/$c$. The results are compared with several model predictions.

Tensor Target Spin Asymmetries in Coherent π0-Photoproduction on the Deuteron Including Intermediate ηNN Interaction Within a Three-Body Approach

Motivated by the recent measurements from the VEPP-3 electron storage ring, we investigate the tensor target polarization asymmetries T2M (M = 0, 1, 2) in the reaction γd → π0d with a particular interest in the effect of the intermediate ηNN three-body approach. This approach is based on realistic separable representations of the driving two-body interaction in the πN, ηN, and NN subsystems. It is shown that the influence of rescattering effects in the intermediate state on the tensor target spin asymmetries is sizable at extreme backward pion angles. At forward angles, the contribution from the pure impulse approximation is dominated and the spin asymmetries show very little influence of rescattering effects. The sensitivity of results to the elementary pion photoproduction operator and to the NN potential model adopted for the deuteron wave function is investigated, and considerable dependences are found. The predicted spin asymmetries are also compared with available experimental data, and a satisfactory agreement with the recent data from VEPP-3 is obtained at photon energies below 400 MeV. At higher energies, the calculated spin asymmetries slightly underestimate the data.

Tensor target spin asymmetries in incoherent π−-photoproduction off the deuteron including rescattering effects

Tensor target spin asymmetries [Formula: see text] ([Formula: see text]=0,1,2) in the reaction [Formula: see text] are studied for photon energies from [Formula: see text]-threshold up to 1.5[Formula: see text]GeV with inclusion of rescattering effects. It is shown that the influence of rescattering effects on the tensor target spin asymmetries is sizable in the energy region near [Formula: see text]-threshold. At higher energies, much smaller influence of rescattering effects is seen. The sensitivity of the obtained results to the elementary pion photoproduction operator is investigated and a considerable dependence is found, in particular at forward pion angles. In addition, a comparison with results of other theoretical models is also given. The extracted spin asymmetries are compared with available experimental data and a qualitative agreement is obtained. The predictions presented here may be useful to interpret the recent measurements from the VEPP-3 electron storage ring.

Influence of the Choice of NN Potential Model on γd → π0d Observables near η-Threshold

Influence of the choice of the NN potential model governing the deuteron wave function on the observables for coherent π0-photoproduction on the deuteron near η-threshold is investigated by using a three-body model for the intermediate ηNN system with separable two-body interactions. Results for unpolarized differential cross section and polarization observables are predicted. It is revealed that the choice of the NN potential model has a visible effect on the differential cross section and most of the polarization observables, especially in the photon energy range of 600–800 MeV and extreme backward pion angles. We find that the deviation among results obtained by using different deuteron wave functions is quite large. The use of the CD-Bonn NN potential for deuteron wave function doubles the differential cross section in this kinematic region. Compared with the experimental data from CLAS collaboration for differential cross section, sizeable discrepancies are found.

Sensitivity of γd → π0d Observables Near η-Threshold to the Intermediate ηNN Interaction and the Choice of Elementary Pion Production Amplitude

The role of intermediate ηNN interaction is studied in coherent π0-photoproduction on the deuteron near η-threshold using a three-body model with separable two-body interactions. This work is motivated by the measurements of the CLAS Collaboration at Jefferson laboratory, where a cusp-like structure in the energy dependence of the differential cross section has been observed at extremely backward pion angles. Results for differential and total cross sections are predicted and compared with available data. We found that the results for differential cross section differ significantly from those predicted by a simple model in which only the impulse approximation and two-body process contributions are considered. In addition, the sensitivity of the results for unpolarized cross sections and polarization observables to the elementary amplitude is investigated and considerable dependences are obtained. The results revealed that the intermediate ηNN three-body calculation and the choice of the elementary amplitu...

Helicity-dependent reaction γd → π0d near the η-threshold and its contribution to the E-asymmetry and the GDH sum rule for the deuteron

The helicity-dependent coherent π0-photoproduction in the reaction γd → π0d near the η-threshold is investigated. The calculations are performed within an approach which includes the reaction amplitudes of the impulse approximation (IA), two-step process with intermediate πN- and ηN-rescattering, and the higher order terms in the multiple scattering series for the intermediate ηNN interaction. The contribution of γd → π0d to the deuteron spin asymmetry is calculated and its contribution to the Gerasimov–Drell–Hearn (GDH) integral is explicitly evaluated by integration up to a photon energy of 900 MeV. In addition, the helicity E-asymmetry is calculated. The results revealed that the doubly polarized differential cross-sections and the helicity E-asymmetry are sensitive to the interference of rescattering effects, specially at photon energies 600–800 MeV and extreme backward pion angles. The sensitivity of the obtained results for the GDH integral to the choice of NN potential model governing the deuteron wave function is discussed. We find that the deviation among results obtained for the deuteron GDH integral using different deuteron wave functions is quite large.

Influence of intermediate [formula omitted] interaction on spin asymmetries for [formula omitted] reaction near the [formula omitted]-threshold within a three-body approach

The influence of intermediate ηNN interaction on spin asymmetries for coherent π0-photoproduction on the deuteron in the energy region around the η-threshold is studied using a three-body model with separable two-body interactions. We calculate all possible spin asymmetries with polarized photons and/or oriented deuterons and compare our results with available data. The calculations are based on a theoretical approach which includes the amplitudes of the impulse approximation, two-body process with πN- and ηN-rescattering, and the higher order terms in the multiple scattering series for the intermediate ηNN interaction. We found that the results for spin asymmetries of the differential cross section differ significantly from those calculated by a simple model in which only the impulse approximation and first-order rescattering contributions are considered. The effect of intermediate ηNN interaction is significant in certain spin asymmetries, specially at extreme backward pion angles. It turns out that the inclusion of a full ηNN three-body contribution is quite essential. The spin asymmetries of the total cross section are much less affected by rescattering contributions. Compared to the experimental data from YerPhi Collaboration for the linear photon asymmetry, sizeable discrepancies are found.

Coherent [formula omitted]-photoproduction on the deuteron near the [formula omitted]-production threshold including polarization observables

Coherent π0-photoproduction on the deuteron including polarization observables is studied in the energy region near the η-production threshold at backward center-of-mass angles of the outgoing pion. This work is motivated by the measurements of the CLAS Collaboration at Jefferson Lab, where a cusp-like structure in the energy dependence of the differential cross section has been observed at extremely backward pion angles. The present approach is based on the impulse approximation and first-order rescattering diagrams with intermediate production of both π- and η-mesons. Numerical results for unpolarized cross sections, the linear photon asymmetry (Σ), the vector (T11) and tensor (T2M, M=0, 1, 2) deuteron target asymmetries, and the double polarization E-asymmetry are predicted and compared with available experimental data and other theoretical models. The effect of first-order rescattering is found to be much larger in spin asymmetries than in the unpolarized cross sections. It reaches on average about 40% in the tensor target and E asymmetries. Compared to the experimental data from CLAS Collaboration, sizable discrepancies are found. This is not the case for the linear photon asymmetry, for which a better comparison with the data from YerPhI Collaboration is obtained.

Helicity Dependence and Contribution to the Spin Asymmetry and the GDH Sum Rule of the \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) Reaction Near the η-Threshold

The helicity dependence of the \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) reaction is studied for incident photon lab-energies near the η-threshold at backward center-of-mass pion angles. The influence of first-order rescattering with intermediate production of both π- and η-mesons on the doubly polarized differential and total cross sections for parallel and antiparallel helicity states is investigated. Then the contribution of \(\vec{\gamma }\vec{d} \to \pi ^{0}d\) to the deuteron spin asymmetry of the total cross section is calculated and its contribution to the Gerasimov–Drell–Hearn (GDH) integral for the deuteron is explicitly evaluated by integration up to a photon lab-energy of 900 MeV. Moreover, the double polarization E-asymmetry is predicted. Although the first-order rescattering effect is found to be negligible in the doubly polarized total photo-absorption cross sections and the deuteron GDH integral, it reached on average about 40% in the doubly polarized differential cross sections and the helic...

Semi-exclusive structure functions and inclusive form factors for [formula omitted] in the energy region from threshold up to 500 MeV

The separated structure functions R L , R T , R LT , and R TT governing the semi-exclusive differential cross section for the d ( e , e ′ π ) NN reaction are evaluated in the energy region from threshold up to 500 MeV. We present results for both the neutral and the charged pion production channels in a variety of kinematic settings. For the elementary pion electroproduction operator, the realistic unitary isobar MAID-2003 model is used which gives a good description of the process on the free nucleon. The completely inclusive form factors, which determine the inclusive differential cross section when only the scattered electron is detected, are also computed. It has been found that the structure functions and form factors reveal clear differences between the production dynamics for the π 0 and π ± pions. Considerable dependencies of the structure functions and form factors on the pion angle and virtual photon lab-energy are found. The predicted results are found to be insensitive to the potential model used for the deuteron wave function.

Signature of the ηNN configurations in coherent πphotoproduction on the deuteron

The photoproduction of a neutral pion on the deuteron is considered in the energy region around the eta threshold, where a bump-like structure was observed at very backward pion angles. Different dynamical aspects which may be responsible for this phenomenon are analysed within a theoretical frame which includes intermediate eta-NN configurations. The results show in particular, that a three-body treatment of the eta-NN interaction is of special importance.

Analysing power for the reaction $\mathrm{np} \rightarrow \mathrm{pp} \pi^{-}$ and for np elastic scattering from 270 to 570 MeV

The analysing power of the reaction ${\rm n}{\rm p} \to {\rm p}{\rm p} \pi^{-}$ for neutron energies between threshold and 570 MeV has been determined using a transversely polarised neutron beam at PSI. The reaction has been studied in a kinematically complete measurement using a time-of-flight spectrometer with large acceptance. Analysing powers have been determined as a function of the c.m. pion angle in different regions of the proton-proton invariant mass. They are compared to other data from the reactions ${\rm n}{\rm p} \to {\rm p}{\rm p} \pi^{-}$ and ${{\rm p}{\rm p} \to {\rm p}{\rm p} \pi^{0}}$. The np elastic scattering analysing power was determined as a by-product of the measurements.

Precision pion-proton elastic differential cross sections at energies spanning the Δ resonance

A precision measurement of absolute pi+p and pi-p elastic differential cross sections at incident pion laboratory kinetic energies from T_pi= 141.15 to 267.3 MeV is described. Data were obtained detecting the scattered pion and recoil proton in coincidence at 12 laboratory pion angles from 55 to 155 degrees for pi+p, and six angles from 60 to 155 degrees for pi-p. Single arm measurements were also obtained for pi+p energies up to 218.1 MeV, with the scattered pi+ detected at six angles from 20 to 70 degrees. A flat-walled, super-cooled liquid hydrogen target as well as solid CH2 targets were used. The data are characterized by small uncertainties, ~1-2% statistical and ~1-1.5% normalization. The reliability of the cross section results was ensured by carrying out the measurements under a variety of experimental conditions to identify and quantify the sources of instrumental uncertainty. Our lowest and highest energy data are consistent with overlapping results from TRIUMF and LAMPF. In general, the Virginia Polytechnic Institute SM95 partial wave analysis solution describes our data well, but the older Karlsruhe-Helsinki PWA solution KH80 does not.

Cross sections of the [formula omitted] reaction between 310 and 425 MeV

Extensive kinematically complete measurements of the pp→ ppπ 0 reaction have been made at six beam energies: 310, 320, 340, 360, 400, and 425 MeV. Angles and energies of both final-state protons are extracted from the forward detector system of the WASA-CELSIUS apparatus. Projected one-parameter distributions of the centre-of-momentum pion angle and the angle of the two-proton relative momentum show significant deviations from isotropy. The slope in the pion angular distribution changes from being negative at 310 MeV to positive at 425 MeV. These distributions, and that of the two-proton relative momentum, are described in terms of partial waves corresponding to the Ss,Ps,Pp,Sd and Ds final states. Commonly used amplitudes, derived from their simple threshold behaviour, fail to reproduce the data at the higher energies. However, in a DWBA treatment, assuming interaction ranges related either to π or ρ exchange, we find acceptable agreement, though the longer range of pion exchange provides significantly better description of the Ps and Pp waves.

Cross section and analyzing power ofp→p→pnπ+near threshold

The cross section and analyzing power of the (p)-over-right-arrow-p-->pn pi(+) reaction near threshold are estimated in terms of data obtained from the (p)-over-right-arrow-p-->d pi(+) and pp-->pp pi(0) reactions. A simple final state interaction theory is developed which depends weakly upon the form of the pion-production operator and includes some Coulomb corrections. Within the uncertainties of the model and the input data, the approach reproduces well the measured energy dependence of the total cross section and the proton analyzing power at a fixed pion center-of-mass angle of 90 degrees, from threshold to T-p=330 MeV. The variation of the differential cross section with pion angle is also very encouraging.

Coherent, semicoherent and incoherent pion production in heavy-ion reactions

Two types of coherent pion production in heavy-ion collisions are studied and calculations are performed for 12C against 12C collisions. The first one, doubly coherent production, produces a pion in one nucleus leaving it in its ground state, while the second nucleus is excited to the 1 +, T = 1 state. The second process, semicoherent production, also leaves in its ground state the nucleus where the pion is produced while the second one is broken. The cross sections for forward pions are compared to the standard incoherent production process. We observe that at energies below 130 MeV/ A the semicoherent process dominates the cross section for forward pion angles while at large energies around 800 MeV/ A it represents a fraction of around 30% of the incoherent cross section. The doubly coherent process leads to smaller cross sections, still in the measurable range for energies above 200 MeV/ A.

πo photoproduction on quasi-free neutrons in the reaction γd → πo np in the Δ region

The possibility of obtaining information about the reaction γn → πon in the Δ resonance region from the reaction γd → πonp is analyzed. To this aim, the differential cross sections d3σ/dEndΩπdΩn both for unpolarized particles and in case of polarized photons and deuterons as well as the asymmetry Σ for linearly-polarized photons are calculated at photon energies from 250 to 400 MeV in the diagrammatic approach. The contributions from the pole diagrams as well as one-loop diagrams both with n-p and π-N-rescattering are taken into account. The main contribution to the differential cross sections of πo photoproduction on the neutron in the quasi-free kinematics arises from the neutron pole diagram. The correction due to n-p rescattering decreases with increasing pion angle and becomes to be less than 8% at Θπ ≥ 90°. The contributions of the proton pole diagram and the one of π-N rescattering were found to be negligible. Background effects are more pronounced in the case of the asymmetry Σ. However, they are also strongly suppressed in the neutron quasi-free kinematics at photon energies above 300 MeV.

The 13C(γ,π−)13N reaction at Eγ≈ 184 MeV (Tπ ≈ 41 MeV)

Abstract Differential cross sections for the 13 C( γ , π − ) 13 N reaction at E γ ≈ 184 MeV ( T π ≈ 41 MeV) were measured with the Saskatoon tagged-photon facility and two range-telescope detectors. Data were obtained at pion angles of 45°, 60°, 80° and 100°, with emphasis on the forward angles, where the cross section shows a strong rise. The present data, together with existing ones at larger angles, are compared to several theoretical calculations.