Search

A polarized proton beam extracted from SATURNE II and the Saclay polarized proton target were used to measure the rescattering observables $K_{onno}$ and $D_{onon}$ at 26 energies from 1.94 to 2.80 GeV and at 0.80 GeV. The beam and target polarizations were oriented vertically and left-right as well as up-down asymmetries in the second scattering on carbon were measured. The present data, obtained in small energy steps, are practically constant as a function of energy at 90°CM, where $K_{onno} = D_{onon}$ . These data will bring about important modification to phase shifts and stabilize the solutions.

The direct reconstruction of the isospin I = 0 amplitudes is discussed under the assumption that the I = 1 amplitudes are known and that a sufficient number of independent np observables have been measured at a centre-of-mass angle θ. We show that at least one observable measured at angle π — θ is necessary in order to determine the I = 0 amplitudes, including the phase relative to the I = 1 amplitudes. Special cases at θ = 0, π/2 and π are also discussed.

A polarized proton beam extracted from SATURNE II was scattered on an unpolarized CH2 target. The angular distribution of the beam analyzing power Aoono was measured at large angles from 1.98 to 2.8 GeV and at 0.80 GeV nominal beam kinetic energy. The same observable was determined at the fixed mean laboratory angle of 13.9° in the same energy range. Both measurements are by-products of an experiment measuring the spin correlation parameter Aoon.

The direct reconstruction of the neutron-proton elastic-scattering amplitudes was carried out at six energies from 0.80 to 1.1 GeV. At the five highest energies the complete sets of spin-dependent observables used were measured in the nucleon-nucleon experimental program at SATURNE II. At 0.80 GeV, LAMPF data were also used. The invariant amplitudesa,b,c,d, ande were fit to the experimental data using a least-squares method. A search for solutions starting from random initial values was performed to determine different possible sets of amplitudes. The real and imaginary parts at several angles are listed in tables and compared with the predictions of two phase shift analyses.

Neutron-proton total cross section differences with the beam and target polarizations orientated either transversally or longitudinally with respect to the beam direction, as well as 11 spin dependent elastic scattering observables measured at SATURNE II as a function of energy and angle are presented. A major part of results was measured using the quasimonoenergetic polarized neutron beam and/or the polarized proton target. A small part of data was obtained using a polarized deuteron beam considered as a beam of quasifree neutrons and protons. The present paper represents a review of measured observables. Several sets of present data are compared with results obtained in other laboratories below 0.8 GeV. Imaginary parts of spin dependent forward amplitudes for np scattering and for the isospin stateI=0 were determined. First direct reconstruction of the np scattering matrix at 0.84 GeV is shown.

We present data of several rescattering observables measured inn p elastic scattering between 0.80 and 1.10 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the Saclay polarized frozen-spin proton target. Three different configurations of beam and target polarization directions were used: the observablesDonon andKonno were measured with the normal-normal spin configuration at eight energies;Nonkk,Dos″ok andKos″ko were determined with the longitudinal-longitudinal configuration at six energies;Nonsk,Dos″ok andKos″so with the sideway-longitudinal configuration at six energies. Part of the data was obtained with an unpolarized CH2 target where only the two spin-index polarization transfer parametersKos″ko andKos″so were determined. Data are compared with phase shift analyses predictions and with the LAMPF results at 0.788 GeV. Present results are the first measurements of rescattering observables above 0.80 GeV. They provide an important contribution to any future theoretical or phenomenological analysis.

We present a total of 191 and 203 data points of the elastic neutron-protonspin correlation parameters A ookk and A oosk , respectively. Both observables were measured in a large angular interval. The observable A ookk was measured from 0.312 to 1.10 GeV and A oosk from 0.80 to 1.10 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. The beam polarization was oriented either along the beam direction or sideways, the target polarization was oriented longitudinally. Data are compared with phase-shift analyses predictions and with the PSI, LAMPF and SATURNE II results. Present results provide an important contribution to any future theoretical or phenomenological analysis.

The angular dependece of the pp elastic scattering spin correlation parameter was measured in the angular range from 60° to 97° CM at 14 energies between 1.96 and 2.23 GeV. A rapid decrease of the energy dependence of this observable at 90° CM is observed around 2.11 GeV kinetic energy. This agrees with the behavior of Aoonn predicted on the basis of an exotic six-quark structure. The Aoonn (90° CM), together with the known differential cross section, allows the determination of the absolute value of the pure spin-singlet amplitude. The energy dependence of this amplitude shows a shoulder centered at 2.11 GeV, corresponding to a total mass of 2.735 GeV and an estimated width of 17 MeV.

A muon beam polarimeter was built for the SMC experiment at the CERN SPS, for beam energies of 100 and 190 GeV. The beam polarisation is determined from the asymmetry in the elastic scattering off the polarised electrons of a ferromagnetic target whose magnetisation is periodically reversed. At muon energies of 100 and 190 GeV the measured polarisation is P-mu = -0.80 +/- 0.03 (stat.) +/- 0.02 (syst.) and P-mu = - 0.797 +/- 0.011 (stat.) +/- 0.012 (syst.), respectively. These results agree with measurements of the beam polarisation using a shape analysis of the decay positron energy spectrum. (C) 2000 Elsevier Science B.V. All rights reserved.

The analyzing power [ital A][sub [ital N]] of proton-proton elastic scattering in the Coulomb-nuclear interference region has been measured using the 200-GeV/[ital c] Fermilab polarized proton beam. A theoretically predicted interference between the hadronic non-spin-flip amplitude and the electromagnetic spin-flip amplitude is shown for the first time to be present at high energies in the region of 1.5[times]10[sup [minus]3] to 5.0[times]10[sup [minus]2] (GeV/[ital c])[sup 2] four-momentum transfer squared, and our results are analyzed in connection with theoretical calculations. In addition, the role of possible contributions of the hadronic spin-flip amplitude is discussed.

We present a total of 273 independent data points of the analyzing powers A oono (nP) and A ooon (nP) in a large angular interval at four energies between 0.477 and 0.940 GeV. The SATURNE II polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the polarized Saclay frozen-spin proton target. Part of the data was obtained with a CH 2 target. A comparison of the two measured observables allows one to determine the polarization of the neutron beam. The present results provide an important contribution to any future theoretical or phenomenological analysis.

We present a total of 427 np analyzing power data points in a large angular interval at 12 energies between 0.312 and 1.10 GeV. The SATURNE II polarized beam of free monochromatic neutrons was scattered either on the Saclay frozen-spin polarized proton target or on CH2 and C targets. Present results are compared with existing elastic and quasieleastic data.

Measurements of 20 vector and tensor spin observables in {ital d}-{ital p} elastic scattering at a deuteron bombarding energy of 1.6 GeV (800 MeV equivalent proton beam energy) are reported. Of these 10 are two-spin observables and the remaining ten are three-spin observables. The two-spin observables, six of which have been measured for the first time, were measured in the four-momentum-transfer range 0.12 to 0.85 (GeV/{ital c}){sup 2}. The three-spin observables, of which eight were measured for the first time, were measured in the momentum-transfer range 0.2 to 0.85 (GeV/{ital c}){sup 2}. The magnitude of the average vector polarization of the deuteron beam was 0.3, and of the average tensor alignment was 0.85. A frozen spin-polarized proton target was utilized for these measurements. These results are compared with previous measurements when possible, and show a general agreement. They are also compared with the predictions of the relativistic-impulse approximation, and its modified version, which takes into account a nontrivial off-mass-shell behavior of nucleon-nucleon scattering amplitudes.

The direct reconstruction of the elastic scattering amplitudes at eleven energies between 0.83 and 2.7 GeV is described. Complete sets of spin dependent observables used for this reconstruction were measured in the nucleon-nucleon experimental program at Saturne II. The invariant amplitudes a, b, c, d and e were deduced using the least square method fit to the experimental data. A search for solutions starting from random initial values was performed to determine different possible sets of amplitudes. The absolute values show a similar angular dependence at all energies and for all solutions. The dependence of phases show discrete ambiguities especially at the higher energies. One of the solutions at 2.1 GeV suggests a behaviour which could be related to a dibaryon resonance of mass 2.73 GeV with the half-width at the half-maximum less than 50 MeV.

Measurements at 18 beam kinetic energies between 1975 and 2795 MeV and at 795 MeV are reported for the pp elastic scattering spin correlation parameter A{sub 00nn}=(N,N;0,0)=C{sub NN}=A{sub NN}. The c.m. angular range is typically 60{sup o}-100{sup o}. These results are compared to previous data from Saturne II and other accelerators. A search for energy-dependent structure at fixed c.m. angles is performed. Comparisons are made to phase shift analysis and theoretical model predictions of this spin observable.

We describe a new polarized-proton and -antiproton beam with 185-GeV/c momentum in the Fermilab MP beam line which is currently operational. The design uses the parity-conserving decay of lambda and antilambda hyperons to produce polarized protons and antiprotons, respectively. A beam-transport system minimizes depolarization effects and uses a set of 12 dipole magnets that rotate the beam-particle spin direction. A beam-tagging system determines the momentum and polarization of individual beam particles, allowing a selection of particles in definite intervals at momentum and polarization. We measured polarization of the beam by using two types of polarimeters, which verified the determination of polarization by a beam-particle tagging system. Two of these processes are the inverse-Primakoff effect and the Coulomb-nuclear interference (CNI) in elastic proton-proton scattering. Another experiment measured the {pi}{sup 0} production asymmetry of large-x{sub F} values; this process may now be used as an on-line beam polarimeter. 9 refs., 9 figs.

Measurements at 19 beam kinetic energies between 1795 and 2235 MeV are reported for the $\mathrm{pp}$ elastic scattering spin correlation parameter ${A}_{00nn}{=A}_{\mathrm{NN}}{=C}_{\mathrm{NN}}.$ The c.m. angular range is typically 60--100\ifmmode^\circ\else\textdegree\fi{}. The measurements were performed at Saturne II with a vertically polarized beam and target (transverse to the beam direction and scattering plane), a magnetic spectrometer and a recoil detector, both instrumented with multiwire proportional chambers, and beam polarimeters. These results are compared to previous data from Saturne II and elsewhere.

Measurements at 18 beam kinetic energies between 1975 and 2795 MeV and at 795 MeV are reported for the pp elastic-scattering single spin parameter A{sub ooon}=A{sub oono}=A{sub N}=P. The c.m. angular range is typically 60{endash}100{degree}. These results are compared to previous data from Saturne II and other accelerators. A search for energy-dependent structure at fixed c.m. angles is performed, but no rapid changes are observed. {copyright} {ital 1999} {ital The American Physical Society}

Experimental results are presented for the $\mathrm{pp}$ elastic-scattering single spin observable ${A}_{\mathrm{oono}}{=A}_{\mathrm{ooon}}{=A}_{N}=P,$ or the analyzing power, at 19 beam kinetic energies between 1795 and 2235 MeV. The typical c.m. angular range is $60--100\ifmmode^\circ\else\textdegree\fi{}.$ The measurements were performed at Saturne II with a vertically polarized beam and target (transverse to the beam direction and scattering plane), a magnetic spectrometer and a recoil detector, both instrumented with multiwire proportional chambers, and beam polarimeters.

A polarized proton beam from SATURNE II, the Saclay polarized targets with $^6$ Li compounds, and an unpolarized $\mathrm{CH}_2$ target were used to measure spin-dependent observables for protons scattered on bound nucleons. The beam and target polarizations were oriented vertically. The analyzing power $A_{\mathrm{oono}}$ and the depolarization $D_{\mathrm{nono}}$ were determined at seven energies between 1.1 and 2.4 GeV. The spin correlation parameter $A_{\mathrm{oonn}}$ was measured at only 1.1 and 1.6 GeV. Measurements with the $\mathrm{CH}_2$ target at 1.1 GeV provided $A_{\mathrm{oono}}$ data for scattering of polarized protons on neutrons in carbon. The quasi-elastic observables are compared with previous elastic scattering measurements and at 1.1 GeV with predictions of phase shift analyses.

The pp elastic scattering analyzing power was measured in small energy steps in the vicinity of the accelerator depolarizing resonance \(\gamma G= 6 \) at 2.202 GeV. A vertically polarized proton beam was extracted from SATURNE II at energies above the resonance and passed through different copper degraders. The beam was focused on the beam line polarimeter CH\(_2\) target. Its halo was removed by four powerful magnets. Measurements at degraded energies were complemented by data obtained with the directly extracted polarized beam outside the resonance region. Analyzing power results at fixed laboratory angles are compared with existing data in the region under discussion, with polynomial fits from 1.6 to 3.5 GeV, and with phase shift analysis predictions.

The angular dependence of the pp elastic scattering analyzing power was measured at SATURNE II with an unpolarized proton beam and the Saclay polarized proton target. The energy region in the vicinity of the accelerator depolarizing resonance Gγ = 6 at Tkin = 2.202 GeV was studied. Measurements were carried out at seven energies between 2.16 and 2.28 GeV from 17° to 55°CM. No significant anomaly was observed in the angular and energy dependence of the results presented, whereas the existing data sets differ in this energy range.

The spin correlation parameters A00kk and A00sk were measured at 0.874, 0.934, 1.095, 1.295, 1.596, 1.796, 2.096, and 2.396 GeV, using the SATURNE II polarized proton beam and tha Saclay frozen spin polarized target. The present results for beam-target spin correlations obtained during measurements of three-spin index observables confirm, in particular, relatively large positive values of A00sk at certain energies and angles, as was shown in previously published data from a dedicated experiment.

The present paper describes an apparatus used for the measurement of spin dependent observables in pp elastic scattering at SATURNE II. Fast electronics, on-line data acquisition, event selection and off-line analysis are also presented.

We present the measurements of the spin correlation parameterAookk(np). A longitudinally polarized beam of free neutrons obtained from the break-up of polarized deuterons was scattered on the longitudinally polarized Saclay frozen-spin proton target. Measurements were carried out at SATURNE II, at neutron beam kinetic energies of 0.63, 0.88, 0.98 and 1.08 GeV. The data points cover the angular region from about 40° to 110° CM. The observed angular dependence ofAookk(np) at 0.63 GeV agree with the phase shift analysis predictions except at small angles.

Both the np and the pp analyzing powers were measured simultaneously using the SATURNE II polarized deuteron beam at 0.550, 0.725, 0.900 and 1.15 GeV/nucleon. The results for the pp analyzing power coincide with the free pp elastic scattering data. We thus can assume that also the np analyzing power is equal to the one for scattering of free polarized neutrons. The np data cover the angular region 90° ≤ θCM ≤ 125°. Our results for the np analyzing power clarify a discrepancy between earlier data at 0.5 GeV and allow conclusions about the energy dependence of the minimum of polarization at θCM ⋍ 100° in the region from 0.5 to 0.9 GeV.

The spin-dependent observables D0n0n and K0nn0 in pp elastic scattering were measured at 11 energies between 0.84 and 2.7 GeV using the SATURNE II polarized proton beam and the Saclay frozen-spin polarized target. The beam and target polarizations were oriented along the normal to the scattering plane. Below 1 GeV the present data agree with previously existing measurements. Below 1.3 GeV they are compared with the predictions of the Saclay-Geneva phase-shift analysis. The results will improve the phase-shift analysis solutions and will contribute to their extension towards higher energies.

The ratio of the analyzing powers was measured from T = 0.52 to 2.8 GeV by scattering of the SATURNE II polarized proton beam on carbon and CH2.

The spin correlation parameter Aoosk was measured using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The measurements at 0.88 and 1.1 GeV were carried out in the angular region θCM from 28° to ⋍ 50°. At 0.88 GeV they complete our previous measurements from 45° to 90°. Above 1.1 GeV the measurements presented here cover both regions, extending from gqCM = 28° (at lower energies) or θCM = 18° (at higher energies) to θCM > 90°. The shape of the angular distribution Aoosk (pp) = ƒ(θCM) changes considerably between 1.8 and 2.4 GeV.

The spin correlation parameter A ookk in pp elastic scattering was measured using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The measurements at 0.88 and 1.1 GeV were carried out in the angular region θ CM from 28° to ⋍ 50° and complete our previous measurements from 45° to 90°. Above 1.1 GeV the measurements presented here cover both regions, extending from θ CM = 28° (at the lower energies) or θ CM = 18° (at the higher energies) to θ CM > 90°. The shape of the angular distribution A ookk (pp) = f ( θ CM ) changes considerably between in our energy region.

A magnetic spectrometer TELAS was constructed for experiments with a polarized target to measure various spin dependent variables. The system was first used for the measurement of polarization parameters on K + n elastic and charge exchange reaction and pn elastic scattering in the momentum range between 1 GeV/ c and 2 GeV/ c .

The spin correlation parameter A00kk (pp) has been measured in the angular region 45°

The spin rotation parameter R has been measured for elastic π − p scattering at 40 GeV/ c , at four momentum transfers t ranging from −0.19 to −0.52 (GeV/ c ) 2 . The average value within this interval is R π − p = -0.200± 0.023. The resulting constraints on the πN scattering amplitudes are discussed. The experiments also yields an average value for K − p scattering, R K − p scattering, R K − p = -0.16±0.16.

The np and the pp analyzing powers Aoonod and spin correlations Aoonnd and Aooskd were measured simultaneously using the SATURNE II polarized deuteron beam at 0.744 and 0.794 GeV/nucleon. The results for the pp observables coincide with the free pp elastic scattering data. We thus can assume that also the np analyzing power Aoonod and spin correlations Aoonnd and Aooskd are equal to those for scattering of free polarized neutrons. The np data cover the angular region 95°⩽θCM⩽122°. Our results for Aoonod (np) confirm the phase-shift analysis predictions but spin correlations Aoonnd (np) and Aooskd (np) have never been measured in this energy region and will considerably affect the PSA solution. Present results allow conclusions about the angular dependence near the minimum of Aoono (np) and Aoonn (np) in the vicinity of 0.8 GeV.

The polarization parameters of the pn elastic scattering were measured at beam momenta between 1.30 and 1.82 GeV/c. The results are discussed in comparison with the partial-wave analysis of Hashimoto and Hoshizaki.

The spin-dependent observables N 0 s ″ kn , D 0 n 0 n and K 0 s ″ k 0 in pp elastic scattering were measured at nine energies between 0.84 and 2.1 GeV using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The beam polarization was oriented longitudinally and the target polarization was oriented vertically. Precession of the recoil particle spin in the target holding field introduces a small contribution from other parameters. The present results for K 0 s ″ k 0 and D 0 n 0 n agree with our previous measurements of the same observables carried out in different beam and target spin configurations as well as with previously existing measurements. The observable N 0 s ″ kn had not been measured previously above 0.58 GeV. Below 1.3 GeV our data are compared with the predictions of the Saclay-Geneva phase shift analysis. The new results will considerably affect the phase shift analysis solutions and will contribute to their extension towards higher energies.

The polarization parameter P has been measured for elastic π + p, K + p and pp scattering at 45 GeV/c. Four-momentum transfer ranges from −0.08 to −1.1 (GeV/) 2 for pp, and from −0.08 to −0.9 (GeV/) 2 for π + p and K + p. The energy dependence of the polarization P ( t ) in π + p and in K + p above 6 GeV/c incident momentum is compatible with interference between pomeron and Regge poles. On the other hand, the polarization in p p elastic scattering decreases faster than ordinary Regge model predictions. This result can be explained by interference between non flip and flip amplitudes of the pomeron, leading to negative values for the polarization.

The spin rotation parameterR in pp and π+ p elastic scattering at 45 GeV/c has been measured at the Serpukhov accelerator, for ¦t¦ ranging from 0·2 to 0·5 (GeV/c)2. The results are presented, together with previousR measurements at lower energies, and are compared with the predictions of Regge pole models. The equality of the values forR in proton-proton and pion-proton scattering, within the experimental errors, is a test of factorization of the residues.

The spin correlation parameters Aoosk and Aookk were measured at 0.834 and 0.995 GeV using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The measurements were carried out in the angular region φCM from 50° to ≃ 90°. The shape of the angular distribution Aoosk (pp) = f(θCM) changes rapidly from 0.8 to 1.0 GeV. The Aookk data points specify our previous measurements.

The polarization parameterP has been measured for elastic scattering on polarized protons, of π−, K− and ¯p at 40 GeV/c and of π+, K+ and p at 45 GeV/c. Four-momentum transfer ranges from −0·08 to −1·8 (GeV/c)2 for π−p, and from −0·08 to about −1sd0(GeV/c)2 for p, π+, K± and ¯p. The angular distribution of the polarization in π−p exhibits the well known non sense double zero att=−0·6 (GeV/c)2. The K−p and ¯pp results are compatible with exchange degeneracy for ¦t¦r

We report final results on the polarization parameter P in elastic scattering of π − , K − and antiprotons at 40 GeV/ c incident momentum. The energy dependence of P (t) in π − p above 10 GeV/ c is well fitted by P (t) α s αR(t)-α P (t) where α R (t) are the effective Regge and Pomeron trajectories respectively. The data in K − p are compatible with exchange degeneracy. The results inp¯p show an important structure for |t|> 0.3 (GeV/c) 2 demonstrating the existence of a large helicity flip amplitude.

The emission of charged particles in proton-carbon interactions results from several different reactions: elastic or inelastic coherent scattering off the nucleus and elastic or inelastic scattering on quasi-free protons or neutrons. The polarized-beam asymmetry for the reaction p↑C ⇒- p′X involving all of these channels was measured at several laboratory angles between 11.6° and 73° at 20 energies from 0.52 to 2.8 GeV.

The differential cross sections for elastic π − p, K − p , p p and π + p, pp scattering at 39 and 44.5 GeV/c, respectively, have been measured in the interval of momentum transfer squared 0.15 ≤ ovbt| ≤ 2 (GeV/c)2.

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

The spin correlation parameter A oonn and the analyzing powers A oono and A ooon were measured simultaneously, in the energy range 0.5–0.8 GeV and in the angular region 40°–80° CM. The experiment used the polarized proton beam of SATURNE II and the Saclay frozen spin polarized target.

The main parts of an apparatus for simultaneous measurements of the polarization and spin-rotation parameters in high-energy elastic scattering on polarized protons are described, including the beam design, the polarized target, detectors, fast electronics, and the data acquisition. Measurements have been performed in 1972 to 1974 at the Serpukhov accelerator with π − , K − and p of 40 GeV/ c , and with p, π + and K + of 45 Ge V / c incident momentum. In addition to the results for P and R , the experiment also yields information on the unpolarized differential cross section.

The spin dependent observables N 0s n ″ k , K 0s″s0 and D 0s″0k in pp elastic scattering were measured at 11 energies between 0.84 and 2.7 GeV using the SATURNE II polarized proton beam and the Saclay frozen spin polarized target. The beam polarization was oriented in the vertical plane, the target polarization was oriented along the incident beam direction. Below 1 GeV the present data agree with previously existing measurements. Below 1.3 GeV they are compared with the predictions of the Saclay-Geneva phase shift analysis. The results will improve the phase shift analysis solutions and will contribute to their extensions towards higher energies. Together with our previous results the data allow a direct reconstruction of the pp elastic matrix over the energy region from 0.84 too 2.7 GeV.

The ratio of the analysing powers for quasi-elastic pp scattering in carbon and for elastic scattering on free protons was measured fromT = 0.52 to 2.8 GeV by scattering of the SATURNE II polarized proton beam on carbon and CH2. It was found to have a maximum at about 0.8 GeV. The energy dependence for quasielastic scattering on carbon had not been measured before above 1 GeV. The observed effect was not expected from simple models.

The polarization P in proton-proton elastic scattering has been measured at 3.83 GeV/c for 0.35 ⩽ |t| ⩽ 3.0 (GeV/c)2, i.e. 29° ⩽ θc.m. ⩽ 93°. The polarization shows a minimum at − ⋍ 1.0 ( GeV /c) 2 followed by a maximum at −⋍1.5 ( GeV /c) 2 . At the same energy the spin rotation parameter R has been measured in the interval 0.18 ⩽ |t| ⩽ 0.57 (GeV/c)2. Comparison with the results at 6.0 and 15.75 GeV/c shows a similar t-dependence and the same average value at all three energies.