Search

In an experiment carried out at the CERN Proton Synchrotron and using the CERN polarized deuteron target, the reaction K/sup +/n/sub up-arrow/..-->..K/sup +/..pi../sup -/p was measured in the region -t = 0.1--1.0 (GeV/c)/sup 2/ and m(K/sup +/..pi../sup -/) = 0.812--0.972 GeV at incident momenta of 5.98 and 11.8 GeV/c. The experiment yields the m and t dependence of 14 linearly independent spin-density-matrix elements describing the coherent production of K/sup +/..pi../sup -/ states with dimeson spins J = 0 and J = 1. This first measurement of the KN..-->..K..pi..N reaction on a polarized target enables us to study experimentally pion production on the level of production amplitudes. Although the mass dependence of partial cross sections averaged over nucleon spins is smooth, we observe large and systematic structures in the moduli squared of individual nucleon transversity amplitudes which reveal an unexpected but essential role of nucleon spin in the pion production process. Our polarization data suggest the possibility of a new state I = (1/2 0/sup ++/(860) with a width of 20--40 MeV. At present we consider this conclusion as only tentative. The predictions of the additive quark model relating K/sup +/n/sub up-arrow/..-->..K/sup *//sup 0/p and p/sub up-arrow/p..--> delta../sup ++/n are wellmore » satisfied at 6 GeV/c. Our results emphasize the need for a systematic study of single-pion production in a new generation of dedicated experiments with spin at the recently proposed high-intensity hadron facilities.« less

In an experiment carried out at the CERN Proton Synchrotron and using the CERN polarized deuteron target, the reaction ..pi../sup +/n/sub arrow-up/..--> pi../sup +/..pi../sup -/p has been measured in the region -t = 0.1--1.0 (GeV/c)/sup 2/ and m(..pi../sup +/..pi../sup -/) = 0.36--1.04 GeV at incident momenta of 5.98 and 11.85 GeV/c. We present the m and t dependence of the measured 14 linearly independent spin-density-matrix elements and of the bounds on the moduli squared of the S- and P-wave recoil transversity amplitudes. The results show the presence of ''A/sub 1/'' exchange in the unnatural nucleon-helicity-nonflip amplitudes. The natural ''A/sub 2/''-exchange amplitudes dominate at large t. In the range 0.2< or =-t< or =0.4 (GeV/c)/sup 2/ the mass dependence shows that the unnatural exchange amplitudes with transversity ''down'' are generally larger than those with transversity ''up.'' The opposite is true for the natural exchange. In this range of t and at the rho/sup 0/ mass, the P-wave unnatural amplitudes with both transversities contribute in equal amounts while the production by natural exchange proceeds entirely with transversity up. We observe rapid changes of the moduli within the rho/sup 0/ mass range and variations of the width and the position of the rho/supmore » 0/ peak in spin-averaged partial-wave cross sections. These structures have not been seen in previous polarization experiments and reveal spin dependence of rho/sup 0/ production. Our bounds cannot exclude an S-wave resonance in the range 700--800 MeV.« less

The polarization in pion-nucleon charge exchange was measured at 6 GeV/c incident momentum for 0.1 (GeV/c)2 < |t| < 1.6 (GeV/c)2. Using the channel π+ n ↑ → π0p allowed precise measurement of the recoil proton for good rejection of inelastic events. The results are compared with previous experiments using channel π−p ↑ with or without detection of the recoil neutron.

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 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 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 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 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 rotation sf R in pp and π + p elastic scattering at 45 GeV/c has been measured at the Seppukhov accelarator, for z . sfnc ; t |; ranging from 0.2 to 0.5 (GeV/) 2 . The results are presented, together with previous R measurements at lower energies. The equality of the values for R in proton-proton and pion-proton scattering, within the experimental errors, is a test of factorization of the residues in the pomeron exchange.

The polarization in K+n↑ → K0p has been measured at 6 and 12 GeV/c in the interval 0.1 < |t| < 1.0 using a polarized deuteron target. The results are compared to predictions from SU(3), exchange degeneracy (EXD) and line reserval, and from various phenomenological models.

The reaction K+n → K+π-p has been measured at CERN-PS using the CERN transversely polarized deuteron target at 5.98 and 11.85 GeV/c incident momentum. The data are analysed in the dimeson mass region 0.812 ≤ m(K+π-) ≤ 0.972 GeV and momentum transfer 0.1 ≤ |t| ≤ 1.0 (GeV/c)2 with the assumption that only S- and P- waves contribute. We present the first measurement of the 9 target polarization dependent observables. The 5 polarization independent observables are in agreement with existing data. The improved statistics permits verification of additive quark model predictions with better precision.

The experiment studies the pion production reactions K+n →K+π∓p and π+ n →π+π∓p on neutrons polarized transversely to the beam direction. The events are described by the variables (s, m, t, ψ,θ,φ where s is the center of mass energy squared, t is the four-momentum transfer squared and m is the invariant mass of the (Kπ) or (ππ) system in the final state. The angle ψ defines the normal to the production plane with respect to the direction of the target polarization. The angles (θ, φ) describe the direction of the positive particle in the (K+π−) or (π+π−) rest frame. The analysis is carried out in both the s- and t-channel frames of the dimeson. Information on the amplitudes, at given values of (s, t, m), is contained in the cross sections d2σ/(dtdm) and in the angular distributions d3σ/(dψdθdφ). At dimeson invariant masses of m ≲ l GeV all partial waves with angular momentum J ≥ 2 are small. The eight complex nucleon trans- versity amplitudes describing S- arid P-wave interaction can be determined - except for the absolute phase and one of the relative phases - from the distribution in (ψ, θ, φ) on a transversely polarized target. The missing relative phase can be obtained only by measuring also the recoil nucleon polarization.

In an experiment carried out at the CERN-PS the reaction π+n ↑ → π+π-p has been studied using the CERN polarized deuteron target. Assuming that only S- and P-waves contribute to the angular distribution for dipion masses ≲ 1 GeV, the experiment yields 14 linearly independent observables which allow model independent amplitude analysis. The experiment contributes new information on the energy dependence and also on the mass-dependence of dipion production at |t| ≳ 0.3 where natural exchange is found to dominate.