We measured the in flight annihilation frequencies and cross sections of reactions n p → π + π 0 ,π + η and K + K S in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the n p annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.
No description provided.
Charged particle production in central S-S collisions at 200 GeV/ c per nucleon has been studied by the WA94 experiment at the CERN-SPS. Particle identification has been provided by the Omega RICH, while a silicon telescope in the Omega spectrometer and an array of MultiWire Proportional Chambers have been used to trace particles through the RICH detector. Production ratios and transverse mass spectra for π ± , K ± and p( p ) at central rapidity and p T > 1.3 GeV/ c are presented.
Distributions are fitted with (1/MT**1.5)*DSIG/DMT = CONST*EXP(-MT/SLOPE).
1.54 GeV ratio is calculated from the fit to the MT distribution.
1.54 GeV ratio is calculated from the fit to the MT distribution.
The Drell-Yan and J ψ cross-sections measured in PbPb collisions are compared with the values extrapolated from the results obtained in proton and light ion induced reactions. While the Drell-Yan production exhibits the normal expected behaviour, the yield of J ψ in PbPb interactions is abnormally low, as it lies 9 standard deviations below the expected value. Moreover, the departure from the expected behaviour increases significantly from peripheral to central collisions.
The results from other experiments are also presented.
Different data are rescaled at 200 GeV.
Production of charged particles identified by a multi cell threshold Čerenkov counter in proton-tungsten and central sulphur-tungsten collisions at 200 GeV/ c per nucleon is discussed. The π ± , p and p production ratios and transverse mass spectra at central rapidity and p T > 0.6 GeV/ c are presented and compared with results from other experiments at the same beam energy.
No description provided.
No description provided.
The slope evaluated from the D(N)/D(MT)/(MT**1.5) distribution (denoted as D(N)/D(MT)).
A partial wave analysis of p̄p → π 0 π 0 η ′ has been performed using the η′ → π 0 π 0 η and η ′ → γγ decay modes. The data are dominated by an η ′ recoiling against the ( ππ ) S-wave. In addition, α 2 (1320) → η′π 0 is needed. There is evidence for contributions from α 0 (1450) → η′π 0 . The branching ratio of α 0 (1450) → η′π 0 with respect to ηπ 0 is consistent with the prediction of SU(3).
No description provided.
The reactions p p → ∑ + ∑ + and p p → ∑ − ∑ − have been investigated at GeV/c beam momentum by the PS185 Collaboration at LEAR, CERN. Of both reaction types together 170 events could be identified. The cross section of the reaction p p → ∑ + ∑ + was determined to be σ tot = 3.68 ± 0.43 μ b at an excess energy of 23 MeV. Its angular distribution exhibits a pronounced forward peaking. The ratio of the cross sections σ( p p → ∑ + ∑ + ) σ( p p → ∑ − ∑ − ) = 2.4 −1.3 +3.0 was extracted with a confidence limit of 90%. It is the first time that experimental data of these reaction channels are available close to the threshold. We compare our results with those of earlier experiments and with theoretical predictions.
No description provided.
The n̄-Fe absorption cross section σ abs n Fe has been measured at LEAR (the Low Energy Antiproton Ring at CERN) using tagged n̄'s produced in the p̄p → n̄n charge-exchange reaction. With incident p̄ momenta of 875 and 545 MeV/ c σ abs n Fe has been measured in the momentum interval between 125 and 780 MeV/ c , in a region where only a few measurements presently exist. The overall statistical and systematic errors range from 20 to 5%; the normalisation error is less than 3%. The measured cross sections are well reproduced by a parametrisation a + b p n , with a = 0.680 ± 0.051 barn and b = 0.228 ± 0.024 barn·GeV/ c .
The errors are the sum in quadrature of the statistical and systematical errors.
The double strangeness exchange reaction ( K − , K + ) is investigated with respect to the sub-threshold production of scalar and vector mesons ( f 0 / a 0 / φ ) decaying into K + K − and the two-step processes induced by intermediate mesons and Ξ − hyperons at p k − = 1.66 GeV/ c using a scintillating fiber active target. The differential cross section ( 〈 dσ dΩ L 〉) averaged over the angular interval (2.3° ⩽ θ K + L ⩽ 14.7°) for the sub-threshold f 0 / a 0 / φ meson production with the K + K − decay is 11 ± 6 μ b/sr at 0.6 ⩽ p K 1 < 0.95 GeV/ c . The present result differs significantly from the theoretical calculation which predicts the contribution of the f 0 / a 0 / φ meson production to be predominant in the ( K − , K + ) reaction below p K + = 0.95 GeV/ c . We found a sizable contribution from two-step ( K − , K + processes, characterized by production of two S = −1 hyperons, consistent with the result of the intra-nuclear cascade (INC) model calculation with respect to the meson-induced hyperon (or hyperon resonance) pair production in the momentum region 0.6 ⩽ p K + < 0.95 GeV/ c . The observed enhancement of the cross section for the two-step ΛΛ production beyond the prediction of the INC model at p K + ⋍ 1.1 GeV /c could be due to the Ξ − p → ΛΛ reaction in 12 C.
No description provided.
No description provided.
No description provided.
Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θ cms = 75° and θ cms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M 1+ 3 2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M 1+ 3 2 - photoproduction amplitude at the resonance energy of 320 MeV is: |M 1+ 3 2 | = (39.6 ± 0.4) × 10 −3 m π + −1 .
No description provided.
No description provided.
The reaction pp→pπ+N has been studied at three energies ( Tp=1520, 1805, and 2100 MeV) and six angles from 0° up to 17° (laboratory). Several narrow states have been observed in missing mass spectra at 1004, 1044, and 1094 MeV. Their widths are typically 1 order of magnitude smaller than the widths of N* or Δ. 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.
No description provided.
No description provided.
No description provided.
Forum