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The reaction pp → pπ+ X was studied at different incident energies around T p = 2 GeV. Narrow baryonic structures were observed in the missing mass M X and in the invariant mass M pπ{+}. The masses of these structures are 1004, 1044, 1094, 1136, 1173, 1249, 1277, and 1384 MeV (and possibly 1339 MeV). Some of them were also observed at the same masses in the missing-mass spectra of the dp → ppX reaction although with a weaker signature. Many checks were performed to make sure that these structures were not produced by experimental artifacts. Several narrow small-amplitude peaks, were also extracted using already published photonucleon cross-sections. The small widths of all these results, and the stability of the observed structures, regardless of the experiment, were used to conclude that they are genuine baryons and not merely the consequence of dynamical rescatterings. These baryons cannot be associated with classical q3 quark configurations. We associate them with two colored-quark cluster configurations.

The total cross section of the pd→pdη reaction has been measured at two energies near threshold by detecting the final proton and deuteron in a magnetic spectrometer. The values are somewhat larger than expected on the basis of two simple theoretical estimates.

The total cross section for $\ensuremath{\omega}$ production in the $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pp}\ensuremath{\omega}$ reaction has been measured at 5 c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold $\ensuremath{\varphi}$ and $\ensuremath{\omega}$ production is, to within relatively large uncertainties, consistent with the predictions of a simple one-pion-exchange model. The degree of violation of the Okubo-Zweig-Iizuka rule is similar to that found in the ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}n\ensuremath{\omega}/\ensuremath{\varphi}$ reactions.

The polarized d d -> alpha X reaction at beam energies close to the eta threshold shows very strong structure in the missing mass corresponding to the ABC enhancement. The deuteron tensor analysing power A_yy, and the slope of the vector analysing power A_y with respect to angle, have been measured for this reaction around the forward direction. Both signals are small, and their variations with the alpha-particle momentum are in broad agreement with a theoretical model in which each pair of nucleons in the projectile and target deuterons undergoes pion production through the NN -> d pi reaction.

The total cross section of the pp -> pp eta' reaction has been measured at two energies near threshold by detecting the final protons in a magnetic spectrometer. The values obtained are about a factor of 70 less than for the corresponding eta production, in good agreement with the predictions of a one-pion-exchange model.

The reaction pp → pπ+X was studied at three energies (Tp = 1520, 1805 and 2100 MeV). The analyzing powers of pp → ΔΔ, pp → Δn and pp → pπ+X reactions (0.94 < MX < 1.5 GeV) were extracted between 0° and 17° in the lab, which corresponds to an angular range between 0° and 100° (c.m.). A theoretical analysis was performed based on s-channel contributions in 2+ and 1− intermediate states. The resulting formulas allow us to obtain good fits with experimental data.

The reaction pp{r_arrow}p{pi}{sup +}N has been studied at three energies (T{sub p}=1520 , 1805, and 2100MeV) and six angles from 0{degree} up to 17{degree} (laboratory). Several narrow states have been observed in missing mass spectra at 1004, 1044, and 1094MeV. Their widths are typically 1 order of magnitude smaller than the widths of N{sup {asterisk}} or {Delta} . Possible biases are discussed. These masses are in good agreement with those calculated within a simple phenomenological mass formula based on color magnetic interaction between two colored quark clusters. {copyright} {ital 1997} {ital The American Physical Society}

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He., LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters B

The tensor polarization ${\ensuremath{\rho}}_{20}$ of deuterons emitted in the ${}^{1}\mathrm{H}{(}^{3}\mathrm{He},\stackrel{\ensuremath{\leftrightarrow}}{d})X$ reaction at ${0}^{\ensuremath{\circ}}$ in the laboratory system was measured at the Saturne National Laboratory in Saclay using the SPES-4 spectrometer with the HYPOM polarimeter located downstream from its focal plane. The momentum of the detected deuterons was kept fixed at 3.77 GeV$/c$, while the momentum of the ${}^{3}\mathrm{He}$ beam was varied from 4.60 to 5.66 GeV$/c$, thus providing a range of internal momenta $k$ of the deuteron in ${}^{3}\mathrm{He}$ from 0 up to 0.4 GeV$/c$. The data obtained are compared with theoretical predictions.

The [ital pp][r arrow][ital pp][eta] reaction is studied at energies near the [eta] production threshold. The total cross sections at nominal machine energies of 1260, 1265, and 1300 MeV are 90[plus minus]15, 790[plus minus]120, and 3460[plus minus]690 nb, respectively. None of the existing perturbative model calculations reproduces the energy dependence, which deviates strongly from phase space. This suggests that the cross section is enhanced in the near vicinity of the production threshold by a large [eta]-[ital pp] scattering length.

The analyzing power excitation function has been measured with high accuracy between 510 and 725 MeV. The 182 measured points show no structure of an amplitude 4×10 −3 or more.

Two reactions, pp{yields}ppX and pp{yields}p{pi}{sup +}X, are used to study the 1.47{

EI SEP PHASE ACC; The paper describes the spectrometric system “SPES4–$\pi$” used at the National Laboratory Saturne (CE Saclay, France) for the exclusive study of the baryon resonance excitation in inelastic α and d scattering on the proton, as well as coherent pion production in charge exchange reactions. The system consists of the magnetic spectrometer SPES4 and two wide-aperture position-sensitive detector arrays, equipped with wire chambers and scintillator hodoscopes, installed around a large-gap C-shape dipole magnet.

The conventional methods for measuring the polarization of electron beams are either time consuming, invasive or accurate only to a few percent. We developped a method to measure electron beam polarization by observing the light emitted by argon atoms following their excitation by the impact of polarized electrons. The degree of circular polarization of the emitted fluorescence is directly related to the electron polarization. We tested the polarimeter on a test GaAs source available at the MAMI electron accelerator in Mainz, Germany. The polarimeter determines the polarization of a 50 keV electron beam decelerated to a few eV and interacting with an effusive argon gas jet. The resulting decay of the excited states produces the emission of a circularly polarized radiation line at 811.5 nm which is observed and analyzed.

Signals of two narrow structures at M=1747 MeV and 1772 MeV were observed in the invariant masses M_{pX} and M_{��^{+}X} of the pp->ppX and pp->p��^{+}X reactions respectively. Many tests were made to see if these structures could have been produced by experimental artefacts. Their small widths and the stability of the extracted masses lead us to conclude that these structures are genuine and may correspond to new exotic baryons. Several attempts to identify them, including the possible "missing baryons" approach, are discussed., 17 pages including 8 figures and 3 tables. ReVtex

The analyzing powers of the {sup 1}H({ital {rvec d}},{ital pp}){ital X} reaction have been measured using polarized deuteron beams at {ital T}{sub {ital d}}=2.1 GeV, {theta}=17{degree} and {ital T}{sub {ital d}}=1.722 GeV, {theta}=0{degree}. In both cases a small oscillatory pattern has been observed in the tensor analyzing power at the same two-proton invariant mass and width {ital M}{sub {ital p}{ital p}}=1.945 GeV, {Gamma}{sub 1/2}{approx}8 MeV. The number of standard deviations are equal to 2.5 and 3.9, respectively.

The reaction $\stackrel{\ensuremath{\rightarrow}}{p}\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{ppX}$ was studied at two energies ${(T}_{p}=1520$ and 1805 MeV) and at several angles between $0\ifmmode^\circ\else\textdegree\fi{}$ and $17\ifmmode^\circ\else\textdegree\fi{}$ in the laboratory. The analyzing powers and cross sections of the $\mathrm{ABC}$ enhancement production were measured in the missing mass ${(M}_{{\ensuremath{\pi}}^{0}}l~{M}_{X}l~{M}_{\ensuremath{\eta}}).$ Several substructures were observed at different angles and both energies. Substructures at ${M}_{X}\ensuremath{\approx}310$ and 350 MeV were systematically extracted. Substructures in the higher mass range $400l~{M}_{X}l~500 \mathrm{MeV}$ were observed but their masses were less stable. These substructure masses have been associated with ${q}^{2}\ensuremath{-}{q}^{2}$ (and ${q}^{3}\ensuremath{-}{q}^{3})$ configurations, allowing a new assumption for the $\mathrm{ABC}$ effect description, as being colored multiquark clusters.

The characteristics of a polarimeter to measure the tensor polarization of deuterons with energy of a few GeV have been studied by Monte Carlo simulations. The analyzing reaction is forward elastic dp scattering. The results of the simulation have been verified with a prototype hydrogen cell and a recoil proton detector using drift tubes inserted in the polarimeter POMME. The test used a vector and tensor polarized deuteron beam of 1.6 GeV kinetic energy at the accelerator Saturne. The feasability of a vector and tensor deuteron high-energy polarimeter based on deuteron–proton elastic scattering reaction has been studied. We present here the prediction of a Monte Carlo simulation and the first results of a test made with a prototype, at the Saturne National Laboratory.

A source of polarized electrons based on a helium flowing afterglow has been developed at Orsay. This source, SELPO-M, has been placed on a 100 kV platform and set up in such a way as to allow its connection to the MAMI accelerator. Its performances in terms of current, polarization and optical properties are given. Its figure of merit (IP 2 ≃75 μA) appears highly competitive as compared to strained GaAs sources.

The reaction pp→pπ+X has been studied at three energies (Tp=1520, 1805 and 2100 MeV), using the Saturne polarized proton beam and the SPES3 experimental facility. The analyzing powers of pp→Δ++Δ0, pp→Δ++n and pp→pπ+X reactions have been studied between 0° and 17° in the lab., which corresponds to an angular range between 0° and 100° (c.m.).

Double differential cross sections d 2 σ/dpdΩ have been measured for π + and K + emitted around midrapidity in d + A and α + A collisions at a beam kinetic energy of 1.15 GeV/nucleon. The total π + yield increases by a factor of about 2 when using an alpha projectile instead of a deuteron whereas the K + yield increases by a factor of about 4. According to transport calculations, the K + enhancement depends both on the number of hadron-hadron collisions and on the energy available in those collisions: their center-of-mass energy increases with increasing number of projectile nucleons.

Double differential K$^+$ cross sections have been measured in p+C collisions at 1.2, 1.5 and 2.5 GeV beam energy and in p+Pb collisions at 1.2 and 1.5 GeV. The K$^+$ spectrum taken at 2.5 GeV can be reproduced quantitatively by a model calculation which takes into account first chance proton-nucleon collisions and internal momentum with energy distribution of nucleons according to the spectral function. At 1.2 and 1.5 GeV beam energy the K$^+$ data excess significantly the model predictions for first chance collisions. When taking secondary processes into account the results of the calculations are in much better agreement with the data.

The tensor polarization (?20) of deuterons emitted in the p(3He,d)X reaction at 0? in the lab. system was measured at the Saturne National Laboratory in Saclay, using the SPES-4 spectrometer with the HYPOM polarimeter in the area of its focal plane. The momentum of the detected deuterons was kept fixed at 3.77 GeV/c, while the momentum of the 3He beam was varied from 4.60 to 5.66 GeV/c, thus providing a range of internal momenta k of the deuteron inside the 3He from 0 up to 0.4 GeV/c. The obtained data are compared with the theoretical predictions.