We present differential cross-section data for the reaction π+p→π+p near 180° in the center-of-mass system at beam momenta between 3.25 GeVc and 10 GeVc.
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The polarization in π + p → π + p and K + p → K + p has been measured at 6 and 12 GeV/ c in the four-momentum transfer interval 0.1 ⩽ | t | ⩽ 2.0 (GeV/ c ) 2 by scattering on protons of a polarized deuteron target. Comparison with existing results obtained with polarized proton targets shows good general agreement and no evidence for asymmetry effects due to the presence of the spectator neutron. For K + p elastic scattering polarization the experiment yields improved statistics, especially at 6 GeV/ c
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Data on 6.2 GeV/ c π − p and K − p elastic scattering cross sections are presented in the range 0.3 < − t < 10.7 (GeV/ c ) 2 .
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The polarization parameter has been measured for π − p elastic scattering in the backward region at 3.5 GeV/ c incident momentum. The experimental set-up consisted of a polarized target in a spectrometer magnet, hodoscopes and wire spark chambers. Data are presented for the range −0.95< u ⩽−0.19 GeV 2 . An isospin analysis has been carried out to separate the I u = 1 2 and I u = 3 2 contributions.
BACKWARD SCATTERING.
Data on polarization in backward elastic π + p scattering at 2.0, 3.5 and 4.0 GeV/ c are presented. The data at 2.0 GeV/ c are compared with the result of a recent phase-shift analysis. Our data at 3.5 and 4.0 GeV/ c , and existing data above 3 GeV/ c , show no significant energy dependence of the polarization over the measured u -range. A comparison with Regge models and with results from amplitude analysis is made.
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The polarization parameter in π±p elastic scattering has been measured at several momenta in the range 2.50-5.15 GeV/c pion laboratory momentum and covering the range in t approximately from -0.2 to -2.0(GeV/c)2. The data show positive polarization for π±p scattering, having a dip near t=−0.6 (GeV/c)2 and becoming relatively large at greater values of −t. The results for π+ and π− scattering are approximately equal in magnitude but of opposite sign. The data have been analyzed to separate the components, which are symmetric and antisymmetric with respect to pion charge, and to show both the t and s dependence of each part.
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Polarization in π−p elastic scattering, with emphasis in the region around the secondary dip and also θc.m.=90°, has been measured at 2.93 and 3.25 GeV/c. We observe an interesting sign change in this angular region.
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Measurements of polarization in π+p elastic scattering have been made at 1.60, 1.80, 2.11, and 2.31 GeVc. The data cover the entire angular range, with emphasis on the backward region. Comparisons have been made with both u-channel and t-channel models, as well as with predictions of phase-shift analyses. While the agreement is generally poor in all cases, the best agreement is with some t-channel predictions.
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We have made measurements of polarization in π−p elastic scattering, with emphasis over the backward region, at 1.60 to 2.28 GeVc. The results indicate the absence of u-channel dominance in the backward region, as was observed in the case of π+p scattering. Comparisons have been made with predictions of various phase-shift analyses which show that the agreement is generally very poor in the backward region.
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We have measured the polarization for elastic scattering in the reaction π−p→π−p at 2.93 and 3.25 GeV/c using a polarized proton target and multiwire proportional chambers (MWPC's) with emphasis on large-angle scattering. Events were selected by fast scintillation-counter logic. Beam trajectories were measured with four MWPC's and the scattered-particle angles were measured with one or two MWPC's; elastic events were determined by coplanarity and angle-angle correlations. The polarization is in agreement with previous measurements below |t|=2.0 (GeV/c)2, and crosses from negative to positive near the secondary dip in the differential cross section dσdt. In the backward region, an energy dependence appears with the polarization being large and negative at 2.93 GeV/c and consistent with zero at 3.25 GeV/c.
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Results on polarization in π − p and π + p forward elastic scattering at 10, 14 and 17.5 GeV/ c are presented.
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The polarization parameter in π − p elastic scattering has been measured in the backward angular region at an incident momentum of 6 GeV/ c . The measurements cover the range of four momentum transfer u = 0 to −1 (GeV/ c ) 2 , and were obtained with a high intensity pion beam, a butanol polarized proton target, and arrays of scintillation counter hodoscopes. The polarization is different from zero, in contradiction to the prediction of the naive one trajectory Regge-exchange model. It increases positively with the four-momentum transfer u, reaching a maximum of about 0.4 at u ≈ −0.3 (GeV/c)2. It then decreases and becomes slightly negative beyond u ≈ −0.5 (GeV/c)2. A variety of baryon exchange models are briefly reviewed and none are found to be in complete agreement with all the experimental data.
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The polarization parameter in π + p backward elastic scattering at 6 GeV/ c incident pion momentum has been measured using a butanol polarized proton target, a high intensity pion beam, and a scintillation hodoscope detection system. Details of the apparatus and data analysis are presented here, together with the final results.
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We present results of measurements of the differential cross sections for the following elastic-scattering reactions: (i) π + p at 5.2 and 7.0 GeV/ c in the range −1 < u < 0.02 (GeV/ c ) 2 , (ii) π − p at 7.0 GeV/ c in the range −0.7 < u < 0.05 (GeV/ c ) 2 , (iii) K + p at 5.2 and 7.0 GeV/ c in the ranges −1 < t < −0.01 (GeV/ c ) 2 and −1 < u < 0 (GeV/ c ) 2 , and K − p at 7.0 GeV/ c in the range −1 < u < 0 (GeV/ c ) 2 .
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SIDE GEOMETRY.
We present the final results of a measurement of the polarization parameter P 0 in high-energy n~-p and p-p elastic scattering, performed using a target which contained polarized protons. Data were taken at beam momenta of 6.0, 8.0, 10.0 and 12.0 GeV/c for n-, and of 6.0, 10.0 and 12.0 GeV/c for n+ and p, in the interval of invariant four-momentum transfer squared-t from 0.1 to 0.75 (GeV/c)2.
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Angular distributions of π + and K + p elastic scattering have been measured for an incident beam momentum of 10.0 GeV/ c . For π + p elastic scattering almost the complete angular distribution was measured. The angular distribution of proton-proton elastic scattering was measured for an incident momentum of 9.0 GeV/ c in the interval of the four-momentum transfer squared from 0.7 (GeV/ c ) 2 to 5.0 (GeV/ v ) 2 . For π + p elastic scattering the structures at − t = 2.8 (GeV/ c ) 2 and − t = 4.8 (GeV/ c ) 2 are less pronounced than at lower momenta. The cross section for scattering at 90° in the c.m. system is of the order of 1 nb/GeV/ c ) 2 . For K + p elastic scattering is a break in the angular distribution around − t = 3 (GeV/ c ) 2 . The differential cross sections for proton-proton elastic scattering decrease smoothly with increasing momentum transfers.
S=19.667 GEV**2, U=-T-17.867 GEV**2.
S=19.91 GEV**2, U=-T-17.704 GEV**2.
S=18.74 GEV**2.
Elastic differential cross sections were measured at 6 energies between 2.3 and 6 BeVc for π++p and π−+p. The behavior of the secondary peak as a function of energy and charge is shown. Evidence for considerable resonance structure is seen in the angular distributions.
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The elastic scattering of 3.55 GeV/ c π + and π − mesons by protons was measured at centre-of-mass angles between 165° and 177°. The angular distributions for 864 events show a steeply rising backward peak for π + p, while the shape is less clear for π − p.
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Extrapolations.
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Total and differential cross sections for π−p elastic scattering are presented at 35 energies between 1400 and 2000 MeV.
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We have measured dσ du for π − p elastic scattering at 3 and 4 GeV c in the ranges −0.119⩽ u ⩽0.113 and −0.233⩽ u ⩽0.088, respectively. A fit of the form d σ /d u = A exp ( Bu + Cu 2 ) gives B = 4.34±0.42 and C = 7.0±3.5 at 4 GeV c with χ 2 = 5.7 for 9 degrees of freedom; the simpler form d σ /d u = A exp( Bu ) gives B = 3.7 ± 0.3 with χ 2 = 9.6. At 3 GeV c we confirm with high statistics the structures already observed.
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We have measured the differential cross section for π − p elastic scattering at eight incident momenta, 2.06, 2.26, 2.45, 2.65, 2.86, 3.05, 3.26 and 3.48 GeV/ c , in a wide range of c.m. scattering angle between 15° and 160°. A pronounced dip-bump structure has been found at large angles. Details of the structure are quantitatively described as functions of the incident momentum.
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Backward elastic scattering has been measured for π + p at 2.85 and 3.30 GeV/ c and for π − p at 3.30 GeV/ c . The π + p angular distributions show steep backward peaks, whereas the π − p distribution is flatter. At 2.85 GeV/ c the π + p differential cross section close to 180° is more than twice that at 3.30 GeV/ c , supporting the assignment J P = 11 2 + for Δ δ (2420) resonance. The π + p data at 2.85 GeV/ c indicate the onset of a dip at cos θ c.m. ≈ −0.97.
The data for cos(theta) = 1 is the extrapolation.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
The data for cos(theta) = 1 and U = 0 are the extrapolations.
Elastic π−+p differential cross-section data are presented at the incident-pion momenta 1.72, 1.89, 2.07, 2.27 and 2.46 GeV/c. Resonant behaviour in the coefficients of a Legendre polynomial expansion indicates G- or H-wave resonance. Further analysis using an energy-dependent parametrization of G- and H-waves shows the results to be compatible with the 7−/2 assignment for the , but equally acceptable solutions are obtained with the inclusion of an additional 9+/2 resonance contribution.
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We present results of measurements of K ± p and p p elastic scattering and of the annihilation reactions p p →π + π − and p p → K + K − at an incident laboratory momentum of 5 GeV/ c . Nearly complete angular distributions were obtained. Results are also presented for π -meson proton elastic scattering in the momentum transfer ranges 2 < − t < 8 (GeV/ c ) 2 (for π + ) and 0.16 < − t < 7 (GeV/ c ) 2 (for π − ). All measurements were done in one experimental geometry. The measured differential cross sections range from 10 to 10 −5 mb/(GeV/ c ) 2 .
-U = T + 8.486 GEV**2.
THE DATA FOR -T = 7.31 TO 8.45 GEV**2 WERE NORMALIZED TO OTHER EXPERIMENTS.
-U = T + 8.304 GEV**2.
New high-statistics measurements of π + p elastic scattering differential cross sections are presented at 30 momentum points between 1.282 and 2.472 GeV/ c , covering most of the angular distribution outside the forward diffractive peak. These data show significant disagreements at some momenta with previous high-statistics experiments and with current partial wave analyses.
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The polarization and the differential cross section in π−p elastic scattering have been measured at incident pion laboratory momenta of 1.70, 1.88, 2.07, 2.27, and 2.50 GeV/c. The experiment was carried out at the Argonne zero-gradient synchrotron with a polarized proton target. Details of the apparatus and data analysis are presented here together with the final results. A partial-wave analysis of the data has verified the JP=72+ assignment for the Δ(1950) and established a JP=72− assignment for the N(2190). It does not support a JP=112+ assignment for the Δ(2460), nor does it give support for some of the possible resonances found in the CERN phase-shift analysis. Apart from the resonance behavior, the partial-wave analysis reveals several new features. We find a striking correlation among the various partial-wave amplitudes at the highest energy, which is different for J=l+12 and J=l−12. In addition, several fixed-(−t) features of high-energy scattering emerge in the energy region of this analysis.
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The spin rotation parameter R has been measured at CERN, for π ± p at 6 GeV c and for π − p at 16 GeV c , with t ranging from −0.19 to −0.51 ( GeV c ) 2 . The parameter A was measured for π − p at 6 GeV c in the interval between t =−0.19 and minus;0.41 ( GeV c ) 2 . The averaged values are the following; R (+6) =−0.08±0.04, R (−6) =−0.23±0.05 and R (−16) =−0.23±0.05. The values obtained for A are close to +1.
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Results are presented concerning topological cross-sections and multiplicity distribution for a π−p experiment at 11.2 GeV/c. The statistics used are one-half of the total ones (106 bubble chamber pictures). Comparison with data at different energies and theoretical predictions are made, and satisfactory agreement is obtained.
TABLE ALSO QUOTES PRONG CROSS SECTIONS FOR PRODUCTION OF VEE(S).
We have measured the reactions π±p→π±p and π+p→K+Σ+ at 5.0 GeV/c in the region 2.2<−t<3.5 (GeV/c)2. We find the minimum cross section of the dip at −t=2.8 (GeV/c)2 in π+p elastic scattering to be 0.16 ± 0.05 μb/GeV2. The π−p differential cross section exhibits similar structure, while the π+p→K+Σ+ channel shows a steady decline in cross section as |t| increases. The polarization of the Σ+ remains large and positive to at least −t=2.8 (GeV/c)2.
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Measurements of π±p, K±p, pp, and p¯p elastic scattering are presented for incident momenta of 3, 3.65, 5, and 6 GeVc and momentum transfers typically 0.03 to 1.8 GeV2. The angle and momentum of the scattered particle were measured with the Argonne Effective Mass Spectrometer for 300 000 events, yielding 930 cross-section values with an uncertainty in absolute normalization of ±4%. Only the K+ and proton data show any significant change in slope of the forward diffraction peak with incident momentum. The particle-antiparticle crossover positions are consistent with no energy dependence, average values being 0.14 ± 0.03, 0.190 ± 0.006, and 0.162 ± 0.004 GeV2 for π' s, K' s, and protons, respectively; these errors reflect both statistics and the ±1.5% uncertainty in particle-antiparticle relative normalization. Differences between particle and antiparticle cross sections isolate interference terms between amplitudes of opposite C parity in the t channel; these differences indicate that the imaginary part of the odd-C nonflip-helicity amplitude has a J0(r(−t)12) structure for −t<0.8 GeV2, as predicted by strong absorption models. The cross-section differences for K± and proton-antiproton are in qualitative agreement with the predictions of ω universality, the agreement improving with increasing energy. The corresponding quark-model predictions relating the π± and K± differences failed by more than a factor of 2. We have combined our π± cross sections with other data to better determine the πN amplitudes in a model-independent way; results of this analysis are presented.
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Total and differential elastic cross-section data are presented at eight incident π+ momenta: 1.28, 1.34, 1.40, 1.43, 1.55, 1.68, 1.77, and 1.84 GeVc. These data were obtained from a hydrogen-bubble-chamber exposure at the Bevatron, and contain more than 65 000 events. This represents more than 1½ times the world's data hitherto available in this energy region.
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A sample of 43000 two-prong events obtained at a momomentum of 11.7 GeV/c is used to determine the cross-sections of the fitted channels, and to study the reaction π+p→π+pπ0. We investigate in particular the quasi-two-body channels π0Δ++ and ρ+p.
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The energy dependence of the differential cross section for $\pi^+ p$ elastic scattering at a c.m. angle near 174 ° has been measured. The momentum range of incident $\pi^+$ was 2.06-4.70 GeV/c. On this energy dependence one can see a structure, i.e. maxima corresponding to the baryon resonances $\Delta(2420)$ and $\Delta(2840)$. The structure is used for determination of the parities of these resonances.
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The reactions π − p → p π − and π − p → p ϱ − ( ϱ − → π − π 0 ) at 10 GeV/ c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π − p → p π − π 0 . The total backward cross sections are 0.52±0.10 and 1.52±0.28 μ b, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ δ Regge trajectory exchange. The ϱ − decay angular distributions are studied in the u -channel helicity frame and the spin density matrix elements are presented as functions of u .
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DATA FROM PRIV COMM WITH B. GHIDINI.
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From an experiment done with the CERN Omega spectrometer, triggered by a fast forward proton device, we present results on the differential cross section d σ d u for π − p backward elastic scattering. The d σ d u distribution agrees with an A e Bu law. The compilation of existing results shows a discrepancy between results but the ( d σ d u ) u=0 data fit perfectly an s 2 α 0 −2 dependence, as predicted by a single Δδ Regge trajectory exchange. A search for the reaction π − p → d p , with a fast forward deuteron, which can be produced by a double-baryon exchange mechanism, gives cross-section upper limits of ∼1% of the backward elastic cross section.
UMIN IS 0.0446 GEV**2.
UMIN IS 0.0333 GEV**2.
D(SIG)/DU FITTED FOR 0 < -U < 0.75 GEV**2 TO GIVE SLOPE/INTERCEPT.
Results of a high-statistics study of elastic scattering and meson resonances produced by π−p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ0,−, f0, g0,−, Δ±, Δ0, and N* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ0 and f0 resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ0 and f0 production mechanisms are similar. The similarity of the g0 t distribution to that of the ρ0 and f0 suggests a common production mechanism for all three resonances.
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SLOPE REFERS TO EXPONENTIAL FIT IN U.
Differential cross sections for the elastic scattering of positive pi mesons by protons were measured at the Berkeley Bevatron at pion laboratory kinetic energies between 500 and 1600 MeV. Fifty scintillation counters and a matrix coincidence system were used to identify incoming pions and detect the recoil proton and pion companions. Results were fitted with a power series in the cosine of the center-of-mass scattering angle, and total elastic cross sections were obtained by integrating under the fitted curves. The coefficients of the cosine series are displayed, plotted versus the laboratory kinetic energy of the pion. The most striking features of these curves are the large positive value of the coefficient of cos6θ*, and the large negative value of the coefficient of cos4θ*, both of which maximize in the vicinity of the 1350-MeV peak in the total cross section. These results indicate that the most predominant state contributing to the scattering at the 1350-MeV peak has total angular momentum J=72, since the coefficients for terms above cos6θ* are negligible at this energy. One possible explanation is that the 1350-MeV peak is the result of an F72 resonance lying on the same Regge-pole trajectory as the (32, 32) resonance near 195 MeV.
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