The p ̄ Ne annihilation cross section is measured for the first time in the momentum interval (53÷63) MeV/c. About 9000 pictures collected by the Streamer Chamber Collaboration (PS179) at LEAR-CERN have been scanned. Four events are found, corresponding to σ ann =2210±1105 mb. The result is compared to the set of measurements presently available in the region of low p̄ momentum.
No description provided.
Neutral and charged two-pion production in p+d→ 3 He+2 π reactions has been studied at CELSIUS at a proton beam energy of 477 MeV. The total cross section for double pion production is 0.22±0.03 μ b. The ratio of the cross sections for the production of charged pion pairs with isospin T =1 and T =0 was determined to be σ ( π + π − ; T =1)/ σ ( π + π − ; T =0)=1.4±0.4.
(I=1, I=0) stands for isospin of PI+ PI- system.
The d( α , 6 Li ∗ 3.56 ) π 0 reaction has been studied at E c.m. =1.2 and 1.9 MeV above threshold with an alpha-particle beam incident on a deuterium cluster-jet target in CELSIUS. Complete differential cross sections were measured at both energies, integrated to σ =228±6+70 nb and 141±12+42 nb respectively. Observed large anisotropies are discussed in relation to the cluster structure of the 6 Li ∗ halo.
The excited LI6* level has E=3.56 mev (at the highest beam energy the second T=1 state in LI6 at 5.37 mev is possible to populate).
A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .
Upper limit is given.
The production of the H-dibaryon could occur via the (K-, K+) reaction on two protons in a nucleus: K- (PP) --> K+ H-dibaryon. Upper limit is given.
Total cross sections for the pp --> pp eta' reaction have been measured in the excess energy range from Q = 1.53 MeV to Q = 23.64 MeV. The experiment has been performed at the internal installation COSY-11 using a stochastically cooled proton beam of the COoler SYnchrotron COSY and a hydrogen cluster target. The determined energy dependence of the total cross section weakens the hypothesis of the S-wave repulsive interaction between the eta' meson and the proton. New data agree well with predictions based on the phase-space distribution modified by the proton-proton final-state-interaction (FSI) only.
Total cross sections w.r.t the excess energy in the CM system. Statistical errors only are given. As well as the 15 PCT overall systematic uncertainty there is an uncertainty on the energy of 0.44 MeV.
The antineutron–proton total cross section has been measured in the low momentum range 50–400 MeV/ c (below 100 MeV/ c for the first time). The measurement was performed at LEAR (CERN) by the OBELIX experiment, thanks to its unique antineutron beam facility. A thick target transmission technique has been used. The measured total cross section shows an anomalous behaviour below 100 MeV/ c . A dominance of the isospin I =0 channel over the I =1 one at low energy is clearly deduced.
Measured values of the total cross section.
Measurements at 19 beam kinetic energies between 1795 and 2235 MeV are reported for the pp elastic scattering spin correlation parameter A00nn=ANN=CNN. The c.m. angular range is typically 60–100°. 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.
Measured values of CNN at EKIN 1795 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.110.
Measured values of CNN at EKIN 1845 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.073.
Measured values of CNN at EKIN 1935 Mev.. Fractional systematic uncertainty in the absolute beam and target polarization is +-0.095.
Yields and phase space distributions of φ -mesons emitted from p+p (minimum bias trigger), p+Pb (at various centralities) and central Pb+Pb collisions are reported ( E beam =158 A GeV). The decay φ →K + K − was used for identification. The φ / π ratio is found to increase by a factor of 3.0±0.7 from inelastic p+p to central Pb+Pb. Significant enhancement in this ratio is also observed in subclasses of p+p events (characterized by high charged-particle multiplicity) as well as in the forward hemisphere of central p+Pb collisions. In Pb+Pb no shift or significant broadening of the φ -peak is seen.
Transverse mass distribution for PHI mesons produced in PB PB collisions averaged over the rapidity region 3.0 to 3.8.
Transverse mass distribution for PHI mesons produced in P P collisions averaged over the rapidity region 2.9 to 4.5.
Rapidity distributions for PHI mesons produced in PB PB collisions.
The experimental results for the (π+,π−) reaction on nuclei obtained in recent years reveal clear systematic features of this reaction. New data on 7Li, 12C, 16O, and 56Fe supplementing the existing data base are presented. The data on 12C are partly at variance with previous results. The dependence of the cross sections on incident energy, scattering angle, and on the target mass is discussed for transitions leading to the ground state of the final nucleus or to the double isobaric analog state.
GST means nonanalog ground state.
GST means nonanalog ground state.
GST means nonanalog ground state.
Kinematically complete events have been studied for the reactions dp→dpπ0 and dp→dnπ+ at projectile energies between 437 and 559 MeV. The measurement covers a range of pion momenta η=pπ,c.m.max/mπc from near the production threshold (η=0.32) to η=0.86 close to the NN→NNπ threshold. The measurements were performed at the CELSIUS storage ring with the PROMICE/WASA setup. Angular and spectral distributions of the charged ejectiles as well as total cross sections are decomposed into the fractions that can be attributed to a quasifree NN→dπ process with a spectator nucleon, and to a process involving all three nucleons. The quasifree contribution increases with energy and dominates from the NN→NNπ threshold on. The results are compared to calculations with a spectator model with and without dp final state interactions.
Two first points on energy correspond to different luminosities.
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