Charge-exchange Differential Cross Sections Research Articles

Quasi-elastic and elastic charge-exchange differential cross sections (critical review)

More than 50 years ago the charge-exchange of one nucleon in the quasi-elastic nucleon deuteron scattering was proposed to determine the spin independent, or the spin dependent parts of the elastic backward neutron proton differential cross section. For this purpose two measurements are to be performed using unpolarized particles only. Such a suggestion was very attractive for experimentalists, since at that time polarized beams were rare and polarized targets were nonexistent. One experiment consists in the inclusive measurement of the charge-exchange quasi-elastic nucleon deuteron differential cross section. The energy of the fast outgoing nucleon is to be approximately the same as that of the incident nucleon. The intrinsic momenta of the remaining two identical nucleons should be small. The impulse approximation has been assumed, i.e. in the final state of the two nucleons their interaction can be neglected. The quasi-elastic result is to be compared with the elastic np differential cross section in the backward direction at the same energy. The theory related the ratio RQE(π) of the quasi-elastic to the elastic np charge-exchange differential cross sections to the spin dependent part of the np backward elastic scattering amplitude. Several experiments in the nucleon kinetic energy interval below 1 GeV were carried out, where the RQE(π) values were determined. Recently the energy interval was extended up to 2 GeV by successful experiments at the JINR VBLHE Nuclotron. The quasi-elastic results can be compared with the values of the analogous quantity Rnp(π) for the np elastic scattering, calculated from the phase shift analyses below 1.3 GeV. The present paper is a critical review checking expressions for Rnp(π) in different amplitude representations, listing numerical values of elastic np quantities and results of existing quasi-elastic experiments. Conclusions and statements of some authors and the validity of the relevant theory is discussed.

Measurement ofπ−p→π0nin the vicinity of the η threshold

We report a new measurement of the differential cross section for {pi}{sup -}p{yields}{pi}{sup 0}n from p{sub {pi}}=649 to 752 MeV/c, which is around the opening of the {eta} channel (685 MeV/c). Our data support the main features of the {pi}{sup -}p charge-exchange differential cross sections generated by the SAID {pi}N partial-wave analysis. The opening of the {eta} channel has a clear effect on the shape of the excitation function for d{sigma}({pi}{sup -}p{yields}{pi}{sup 0}n), which is most noticeable in the backward direction.

MEASUREMENT OF PION CHARGE EXCHANGE IN THE REGION OF THE S11(1535) RESONANCE

Pion charge-exchange (π-p→π0n) differential cross sections are one of the basic sources of information on neutral pion-nucleon resonances. We present new, high statistics, high quality charge-exchange differential cross-section data obtained in the incident π- momentum range 650–750 MeV/c. The total uncertainty of the measurements is 6% or less. 648 new data points were obtained using the Crystal Ball multiphoton spectrometer covering 94% of the full solid angle. Our data show deviations from the results of the partial–wave analysis for some momenta, in particular at very backward angles. We also report on a search for the cusp effect in π-p→π0n at the opening of the π-p→ηn channel.

Differential cross sections for pion charge exchange on the proton at 27.5 MeV

We have measured pion single charge exchange differential cross sections on the proton at 27.5 MeV incident {pi}{sup {minus}} kinetic energy in the center of momentum angular range between 0{degree} and 55{degree}. The extracted cross sections are compared with predictions of the standard pion-nucleon partial wave analysis and found to be in excellent agreement. {copyright} {ital 1998} {ital The American Physical Society}

A new measurement of the [formula omitted]p → [formula omitted]n charge-exchange differential cross-section at LEAR

We have measured the p p → n n charge-exchange differential cross-section at two incoming p momenta (601.5 and 1202 MeV/ c) at the CERN Low Energy Antiproton Ring. After reviewing the experimental method, the data analysis is fully detailed, and the results on the whole statistics available in the centre of mass forward hemisphere are given. A precision in the absolute normalisation of 2% and 4% at 601.5 and 1202 MeV/ c respectively is achieved, while over most of the angular range the point-to-point error is lower than 1%. The forward peak associated with the nearby pion pole and a dip-bump structure are accurately measured. The “Chew” extrapolation to the pion-pole suggests a “low” value for the πNN coupling constant g c 2.

High precision measurement of the p → n charge-exchange differential cross-section [Phys. Lett. B 339 (1994) 325

High precision measurement of the p → n charge-exchange differential cross-section [Phys. Lett. B 339 (1994) 325

High-precision measurement of the [formula omitted] charge-exchange differential cross-section

The differential p p → n n charge-exchange cross section has been measured at the CERN Low Energy Antiproton Ring (LEAR), at two incident p momenta, 601 and 1202 MeV/c. features of the differential cross-section near the forward direction, i.e. a sharp peak at 0° scattering angle followed by an energy dependent dip-bump structure, are confirmed and measured with good precision and high statistical accuracy. The data show very clearly that the shape of the cross-section is a manifestation of the pion-exchange amplitude, and a simple extrapolation to the pion pole already indicates that the pion-nucleon coupling constant f c 2 can be determined with good precision.

Second Born approximation differential cross sections for p+H and p+He charge-exchange collisions.

Charge-exchange differential cross sections are calculated by the second Born approximations without a recourse to any further approximation. The exact second Born approximation cross sections show satisfactory agreement with the experimental data for proton-helium collisions at all the energies of 2.82, 5.42, and 7.4 MeV while they are considerably smaller than the existing experimental cross sections in the Thomas peak region for proton-hydrogen collisions at 2.8 MeV. Discussions are given on how to choose the interactions for two-electron systems in order to satisfy the boundary condition of neutral-atom collisions.

Elastic, inelastic and charge exchange differential cross sections in He++H collisions

Elastic, inelastic and charge exchange differential cross sections are calculated for He+(1s)+H(1s) collisions, in the energy range 1.5 keV<or=E<or=25 keV, using a 15-state molecular treatment, modified with an optimized translation factor. The authors compare their results with previous theoretical and experimental data. Agreement with the latter is, in general, quite good, with the important exception of elastic cross sections.

Bonn nucleon-nucleon meson exchange model with a relativistic quark-gluon annihilation potential.

The full Bonn potential, combined with a relativistic quark-gluon annihilation potential, is compared with recent NN\ifmmode\bar\else\textasciimacron\fi{} polarization data from LEAR and with measured differential cross sections (elastic and charge exchange) below ${\mathit{p}}_{\mathrm{lab}}$=800 MeV/c. It is demonstrated within this approach that a careful analysis of pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}pp\ifmmode\bar\else\textasciimacron\fi{}(EL) and pp\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\rightarrow}nn\ifmmode\bar\else\textasciimacron\fi{}(CEX), at the same energy, in terms of the five independent helicity amplitudes can be used to selectively test specific boson exchange contributions to NN\ifmmode\bar\else\textasciimacron\fi{} scattering. The charge-exchange differential cross section in forward direction is particularly sensitive to the one-pion-exchange potential in this model. This feature could be used to see if recent attempts to fit NN data with a much softer \ensuremath{\pi}NN form factor can be made compatible with NN\ifmmode\bar\else\textasciimacron\fi{} data.

Total and differential charge transfer cross sections in H++Na(3s) or Na*(3p) collisions

Proton-sodium charge transfer is studied, using 9- and 19-state adiabatic molecular bases and the impact parameter method, in the energy range 0.5-5 keV. The dynamical radial and rotational coupling terms and a common translation factor (CTF) are included. The effect of the choice of the coordinate centre on the total charge exchange cross sections to H(n=2) is clearly demonstrated when no CTF is included. The alignment dependence of the capture to H(n=2) is obtained and is satisfactorily compared with the atomic expansion calculations. State-to-state charge exchange differential cross sections are calculated; the alignment and orientation effects are expected to be observable at the collision energy 0.5 keV where they are spread out at scattering angles theta >0.1'.

Coupled-channels study of antiproton-proton reactions.

Low energy antiproton-proton elastic, charge exchange, charged pion, and charged kaon production reactions are studied in a coupled-channels model. The need for a coupled-channels approach to antiproton-proton reactions is first demonstrated. Meson exchange potentials describe the long-range N\ifmmode\bar\else\textasciimacron\fi{}N interaction; smooth phenomenological forms are used for the N\ifmmode\bar\else\textasciimacron\fi{}N interaction at short distances. Effective channels are introduced to simulate strong absorptive effects, such as multimeson production processes. Transition potentials for kaon and pion production are derived in coordinate space and shown to include an important spin-times-derivative coupling form. These transition potentials, along with a one-boson-exchange model with effective absorptive channels, are used to determine the role of multistep processes of the type \ensuremath{\pi}\ifmmode\bar\else\textasciimacron\fi{}\ensuremath{\pi}\ensuremath{\leftrightarrows}p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\leftrightarrows}n\ifmmode\bar\else\textasciimacron\fi{}n\ensuremath{\leftrightarrows}K\ifmmode\bar\else\textasciimacron\fi{}K. Control over such coupled-channels effects is sought as a step toward unfolding short-distance quark effects in a reliable way. The p\ifmmode\bar\else\textasciimacron\fi{}p elastic and charge exchange differential cross sections at three p\ifmmode\bar\else\textasciimacron\fi{}p laboratory momenta (780, 690, and 590 MeV/c) are examined first, since ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$ and ${K}^{\mathrm{\ensuremath{-}}}$${K}^{+}$ data also exist at these energies. Results are then presented that manifest strong coupling effects, especially between the pion and kaon production channels. Based on that result, a full coupled-channels fit to the p\ifmmode\bar\else\textasciimacron\fi{}p, n\ifmmode\bar\else\textasciimacron\fi{}n, ${K}^{\mathrm{\ensuremath{-}}}$${K}^{+}$, and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$${\ensuremath{\pi}}^{+}$ data is presented and analyzed.

Réaction antiproton–proton aux basses énergies (Expérience PS173 au LEAR)

The antiproton–proton interaction has been studied by measuring the elastic scattering, charge exchange, and annihilation cross sections simultaneously, for beam momenta between 180 and 600 MeV/c. Here we describe the experimental setup and present partial results of the experiment. We have not found any evidence of the existence of the X (1935) resonance. It is possible to reproduce the elastic scattering and charge exchange differential cross sections with potential models. The Re f(0)/Im f(0) ratio shows an anomaly at low energy.[Journal Translation]

Effective range analysis of low-energy nucleon-antinucleon interaction

An effective range expansion is developed for the N N system incorporating annihilation, charge-exchange and Coulomb interaction. By fitting the LEAR data on elastic scattering and charge-exchange differential cross sections the N N scattering lengths and effective ranges are obtained. These solutions reproduce also the data on antiprotonic hydrogen, antineutron-proton total and annihilation cross sections and the behavior of the forward amplitude real-to-imaginary ratio.

Polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c for the 4-momentum transfer range 0&lt;|t|&lt;2 (GeV/c)2

The results on measuring polarization in charge exchange reaction π−+p→π0+n at 40 GeV/c are presented for the 4-momentum transfer range from 0 up to 2 (GeV/c)2. At |t|≦0.4 (GeV/c)2 the polarization has a positive sign. In the “crossover” region of π± elastic scattering a possible minimum in the polarization behaviour has been seen for the first time. the polarization is zero within the statistical accuracy near this point. In the “deep” region of the charge-exchange differential cross-section the polarization has a negative sign. The presented data are not in agreement with the modern theoretical models.

Differential cross sections for one electron two center symmetric systems

We use the two-state atomic expansion with variable nuclear charge to study charge-exchange differential cross sections for symmetrical one-electron systems at intermediate energy. The nonclassical small angle diffraction scattering is discussed. Our results are compared with data for H +-H collisions.

Amplitude analysis of forward nucleon-nucleon scattering

Our previous proton-proton amplitude analysis based on dispersion relations is repeated, using new experimental information from SIN, TRIUMF, LAMPF and SACLAY. Exploiting Argonne Δσ L(pd) data and forward pn charge-exchange differential cross sections, the analysis now provides, for the first time, the full set of forward pp and pn amplitudes. These are compared in detail with recent phase-shift analyses. Implications for dibaryon resonances and for polarization experiments in the near forward region are discussed.

Small-momentum-transfer K−p charge exchange scattering at 30 GeV/c

The\(K^ - p \to \bar K^0 n\) charge exchange differential cross-section has been measured at 30 GeV/c with high statistical accuracy and high angular resolution. The experiment was made at the IHEP 70 GeV accelerator, by using a hodoscope hadron calorimeter to detect KL0. The cross-section shows a dip at small |t|, which indicates a dominance of spin-flip amplitudes in ρ and A2 exchanges in thet-channel.

Low-energy πN partial wave analysis

An energy-independent partial-wave analysis has been performed on pion-nucleon elastic and charge-exchange differential cross sections and elastic polarizations, for lab. momenta below 500 MeV/ c. The amplitudes were constrained by a simultaneous fixed momentum transfer analysis, which leads to a unique and smooth solution. The masses and widths of Δ ++ and Δ 0 have been redetermined from total cross sections as m Δ ++ = 1230.9 ± 0.3 MeV, m Δ 0 = 1233.6 ± 0.5 MeV, Γ Δ ++ = 111 ± 1 MeV and Γ Δ 0 = 113 ± 1.5 MeV. For the pion-nucleon coupling constant the value | 2 = 0.079 ± 0.001 was obtained.

Measurements of the π−p → π0n forward scattering cross section in the energy region 400–600 MeV

The forward charge-exchange differential cross section has been measured using two Čerenkov spectrometers at five energies of incident pions. The resulting cross-section values are 4.02 ± 0.22, 3.61 ± 0.13, 4.19 ± 0.13, 3.91 ± 0.12, 3.02 ± 0.14 mb/sr at incident pion energies 400, 450, 500, 550 and 600 MeV, respectively. These values are in a good agreement with dispersion-relation predictions.