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The polarization parameter for the reaction π−p→π0n has been measured at five incident been momenta between 1.03 and GeV/c. The results are compared with predictions of recent phase-shift analyses.
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A high statistics measurement of the reaction π − p → π 0 n has been performed at the Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/ c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. More than 3 million charge-exchange events have been recorded in total. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small | t |, as exponentials with the same slopes to within a few percent. Also the behaviour of the differential cross section for small and medium | t | agrees with the prediction of a geometrical s -channel model which describes binary reactions in terms of a complex pole b 0 ( s ). The imaginary part of this universal pole, Im b 0 ( s ), has been determined and found to be growing logarithmically with s .
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We report a new measurement of the differential cross section for π−p→π0n from pπ=649 to 752 MeV/c, which is around the opening of the η channel (685 MeV/c). Our data support the main features of the π−p charge-exchange differential cross sections generated by the SAID πN partial-wave analysis. The opening of the η channel has a clear effect on the shape of the excitation function for dσ(π−p→π0n), which is most noticeable in the backward direction.
Differential cross section for incident pion momentum 649, 654 and 657 MeV.
Differential cross section for incident pion momentum 661, 666 and 669 MeV.
Differential cross section for incident pion momentum 673, 678 and 681 MeV.
Measured values of the differential cross section for pion-nucleon charge exchange are presented at momenta 148, 174, 188, 212, 238, 271, 298, and 323 MeV/c, a region dominated by the Delta resonance. Complete angular distributions were obtained using the Crystal Ball detector at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). Statistical uncertainties of the differential cross sections are typically 2-6%, exceptions being the results at the lowest momentum and at the most forward measurements of the five lowest momenta. We estimate the systematic uncertainties to be 3-6%.
The errors shown are statistical only.
The errors shown are statistical only.
The total charge-exchange reaction cross section as a function of pion momentum obtained by integrating the differential cross sections. The errors shown are the total and statistical errors.
This paper presents the results of a study of the dominant neutral final states from π−p interactions. The data were obtained in an experiment performed at the Brookhaven National Laboratory Alternating Gradient Synchrotron, using a set of steel-plate optical spark chambers surrounding a liquid-hydrogen target. We present differential and total cross sections for the reactions (1) π−p→n+π0 and (2) π−p→n+η0(η0→2γ) and total cross sections for the reactions (3) π−p→n+kπ0 (k=2, 3, 4, and 5) and (4) π−p→all neutrals for eighteen values of beam momentum in the interval 1.3 to 4.0 GeV/c. The angular distributions for (1) and (2) have been analyzed in terms of expansions in Legendre polynomials, the coefficients for which are also given.
No description provided.
SIG = 4*PI*LEG(L=0).
FORWARD DIFFERENTIAL CROSS SECTION CALCULATED FROM LEGENDRE POLYNOMIAL COEFFICIENTS AND ERROR MATRICES.
A high-statistics measurement of the reaction π − p→ η n; η →2 γ has been performed at the 70 GeV Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/ c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small | t |, as exponentials with the same slopes to within a few percent. For | t | ≳ 1 (GeV/ c ) 2 there is a break in the differential cross section. In addition, the A 2 effective trajectory deviates markedly for | t | ≳ 1 GeV/ c ) 2 from the linear behaviour valid for smaller | t |.
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The polarization parameter P(t) for the reaction π−p→π0n has been measured at 3.5 and 5.0 GeV/c over the range 0.2<~−t<~1.8 (GeV/c)2. The two γ rays from the π0 decay were detected in a large lead-glass hodoscope. The results agree with the positive polarization values found in earlier Argonne National Laboratory data at −t<0.35 (GeV/c)2. P(t) drops to a small value near t=−0.6 (GeV/c)2 and remains the same out to t=−1.8 (GeV/c)2.
DATA POINTS MEASURED FROM SMALL GRAPH.
Differential cross sections for the reaction π−p→π0n were measured at nine incident-pion kinetic energies in the interval from 500 to 1300 MeV. The negative pion beam from the bevatron was focused on a liquidhydrogen target completely surrounded by a cubic array of six steel-plate spark chambers. The spark chambers were triggered on events with neutral final states. Charge-exchange events were identified from the one-shower and two-shower events in the spark-chamber pictures. By the Monte Carlo technique, the π0 distributions were calculated from the bisector distributions of the two-shower π0 events together with the observed γ-ray distributions of the one-shower π0 events. These π0 distributions were fitted with both Legendre-polynomial expansions and power-series expansions by the method of least squares. The extrapolated forward differential cross sections are in good agreement with the dispersion calculations. The Legendre coefficients for the differential cross sections in isospin state T=12 were obtained by combining our results with available data on π±p elastic scattering. In the light of existing phase-shift solutions, the behavior of these coefficients is discussed. The D5F5 interference term that peaks near 900 MeV is verified to be in isospin state T=12 only. We report here also the total neutral cross sections and the cross sections for the production of neutral multipion final states 2π0n and 3π0n. The 4π solid angle and the calibrated energy response of the spark chambers contribute to the accuracy of the results.
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We have studied neutral final states produced in π−p collisions at momenta of 1.71, 1.89, 2.07, 2.27, and 2.46 GeVc, by observing the γ rays emitted. In particular, measurements are presented of (i) π−p→π0n, for which the Regge-pole fit at momenta ≥5.9 GeVc also agrees rather well here; (ii) π−p→η0n, for which the Regge model which fits at higher energies does not agree here; (iii) π−p→π0γn, in which there is some evidence for a diffraction dissociation process as well as ω0-meson production; (iv) π−p→π0π0n, which is dominated by production of N*0(1236)π0 and by peripheral production of pion pairs. In (iv), the former process is found to fit with the same Reggeized ρ-meson exchange model as charge-exchange scattering, while the latter gives indication of the s-wave ππ interaction. An account is given of new techniques, particularly in the data analysis, which were developed in the course of this work.
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A bubble chamber study of π-p charge-exchange scattering at 930 MeV is reported. The forward differential cross-section is derived and compared with the result obtained on the basis of dispersion relations and the charge-independence hypothesis. Satisfactory agreement is obtained.
No description provided.
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