L. van Rossum

The pion-nucleon scattering amplitudes at 6 GeVc and 16 GeVc

Abstract The helicity amplitudes are determined at 6 GeV c , for both isospin I =0 and I =1 states in the crossed channel. The analysis is extended to the interval from t =0 to t =−1.0 (GeV/ c ) 2 . At 16 GeV c , the number of independent experiments is still insufficient. Only the amplitudes for I =0 exchange are calculated, in the interval from t =0 to t=−0.5 ( GeV c 2 .

A proton and neutron beam polarimeter at SATURNE II

Abstract A beam polarimeter using CH 2 and carbon targets has been used to measure proton and neutron beam polarization in the energy range 0.4–2.8 GeV in one of the beam lines at the SATURNE II accelerator. The analyzing power for np-scattering is calibrated against the known analyzing power for pp-scattering by using the polarized deuteron beam to measure simultaneously the asymmetries for scattering of quasifree protons and neutrons in the deuterons. A low level of systematic errors is achieved by pulse to pulse polarization reversal at the ion source of the accelerator, and by measuring left and right scattering simultaneously. The detailed operation procedure and the beam polarizations measured during all experiments from 1981 to 1984 are presented.

Measurements of spin rotation parameters in pion-nucleon elastic scattering at 6 GeVc and at 16 GeVc

Abstract 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.

Measurement of the total cross section difference ΔσT(pp) in the energy range from 0.43 to 2.4 GeV

Abstract The SATURNE II polarized proton beam and the Saclay frozen spin polarized proton target were used to measure the total cross section difference Δσ T = −2 σ 1 tot at 26 energies between 0.43 and 2.4 GeV. Here Δσ T is the total cross section difference for transverse beam and target spins parallel and antiparallel, respectively, and σ 1tot is one of spin-dependent terms in the total cross section σ tot . The energy dependence of Δσ T below 1 GeV shows similar structures as for Δσ L . An additional minimum appears at about 1.3 GeV, which involves a structure in singlet spin partial waves.

Measurement of the spin correlation parameter A00kk for pp elastic scattering in the energy range 0.72–1.1 GeV

The spin correlation parameter A00kk (pp) has been measured in the angular region 45°<θCM<90° at 0.719, 0.834, 0.874, 0.934, 0.995 and 1.095 GeV using the SATURNE II polarized proton beam incident on a polarized target. The parameters A00nn(pp and A00sk(pp) were measured at 0.874 in the same angular region.

Measurement of the total cross section difference ΔαL(pp) in the energy range from 0.52 to 2.8 GeV

Abstract The total cross section difference ΔαL(pp) for proton-proton scattering with beam and target polarized longitudinally parallel and antiparallel, respectively, has been measured using the polarized proton beam from SATURNE II and a frozen spin polarized proton target. The beam polarization was reversed from pulse to pulse, and at each energy ΔαL was measured for both signs of target polarization. The data below 800 MeV confirm the previously observed structures. The cross section difference is found to change by 8.0 ± 0.5 mb between 520 MeV and 760 MeV. At the higher energies the results show no indication for similar structures or for a change of the sign of ΔαL.

First results for the two-spin parameter ALL in π0 production by 200 GeV polarized protons and antiprotons

Abstract The two-spin parameter A LL in inclusive π 0 productionby longitudinally-polarized protons and antiprotons on a longitudinally-polarized proton target has been measured at the 200 GeV Fermilab spin physics facility, for π 0 s at x F =0 with 1⩽ p t ⩽3 GeV/ c . The results exclude, at the 95% confidence level, values of A LL (pp) > 0.1 and 0 s produced by protons, and values of A LL ( p p) > 0.1 and for incident antiprotons. The relevance of A LL (pp) for the gluon spin density is discussed. The data are in good agreement with “conventional”, small or zero, gluon polarization.

Measurement of Deep Inelastic Compton Scattering of High-energy Photons

Abstract We present the first results on inclusive photo-production of prompt photons at high transverse momenta. The data were taken in an open spectrometer at CERN using a high intensity photon beam energy between 50 and 150 GeV. After subtracting the yield of photons from indirect sources, a clear excess is observed for transverse momenta above 2.5 GeV c Deep inelastic Compton scattering with appropriate QCD corrections account for this excess. The data disfavour the gauge integer charge quark models so far proposed.

Polarization measurements in π+p, K+p and pp elastic scattering at 45 GeV/c and comparison with Regge phenomenology

Abstract 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.

Measurement ofJ/ψ and ψ′ real photoproduction on lithium-6 at a mean energy of 90 GeV

Inelastic and elasticJ/ψ (3097) photoproduction on Li6 are measured at a mean γ energy of 90 GeV in an open spectrometer. TheJ/ψ are identified by their decays intoμ+μ− ore+e−. A signal of ψ′(3685) intoμ+μ− andJ/ψπ+π− is also seen. The inelastic cross-section withZ=Eψ/Eγ<0.9 is compared in shape and magnitude with the colour singlet model of photon-gluon fusion.