The transverse momentum distributions for\(\rho ^0 (770),f_2 (1270),K*^0 (892),\bar K*^0 (892)\) and ϕ (1020) have been studied in thept region between 2 and 4 GeV/c and central rapidity. The data analysed come from the WA77 experiment at CERN with a 300 GeV/c π− beam incident on a Be target. These distributions are well described by the functionpt−n withn∼8. A sample of simulated events from the Lund Monte Carlo in the same experimental conditions reproduces well the data.
No description provided.
Acceptance corrected tranverse momentum distribution.
Acceptance corrected tranverse momentum distribution.
The production dynamics of baryon-antibaryon pairs are investigated using hadronic Z 0 decays, recorded with the OPAL detector, which contain at least two identified Λ baryons. The rapidly difference for Λ Λ pairs shows the correlations expected from models with a chain-like production of baryon-antibaryon pairs. If the baryon number of a Λ is compensated by a Λ , the Λ is found with a probability of 53% in an interval of ±0.6 around the Λ rapidity. This correlation strength is weaker than predicted by the Herwig Monte Carlo and the Jetset Monte Carlo with a production chain of baryon-antibaryon, and stronger than predicted by the UCLA model. The observed rapidity correlations can be described by the Jetset Monte Carlo with a dominant production chain of baryon-meson-antibaryon, the popcorn mechanism. In addition to the short range correlations, one finds an indication of a correlation of Λ Λ pairs in opposite hemispheres if both the Λ and the Λ have large rapidities. Such long range correlations are expected if the primary quark flavours are compensated in opposite hemispheres and if these quarks are found in energetic baryons. Rates for simultaneous baryon and strangeness number compensation for Λ Λ , Ξ − Ξ + and Ξ − Λ ( Λ + Λ ) are measured and compared with different Monte Carlo models.
No description provided.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified LAMBDA(LAMBDABAR). CT.= Data read from plot.
Opposite and same baryon number invariant PI P mass distribuition for additional LAMBDA(LAMBDABAR) candidates in events with one identified XI-(XIBAR+). CT.= Data read from plot.
New measurements of the hadronic and leptonic cross sections and of the leptonic forward-backward asymmetries ine+e− collisions are presented. The analysis includes data recorded up to the end of 1991 by the OPAL experiment at LEP, with centre-of-mass energies within ±3 GeV of the Z0 mass. The results are based on a recorded total of 454 000 hadronic and 58 000 leptonic events. A model independent analysis of Z0 parameters based on an extension of the improved Born approximation is presented leading to test of lepton universality and an interpretation of the results within the Standard Model framework. The determination of the mass and width of the Z0 benefit from an improved understanding of the LEP energy calibration.
Statistical and systematic point-to-point errors included. There is an additional 0.2 pct overall systematic uncertainty.
Systematic error of 0.45 pct not included.
Systematic error of 0.25 pct not included.
Antinucleon-nucleus annihilations into two-body final states containing only one or no meson are unusual annihilations (Pontecorvo reactions), practically unexplored experimentally, with the exception of the channel p d → π − p , for which only two low-statistics measurements exist. Their physical interest lies in the possibility of exploring small-distance nuclear dynamics, in which an important role can be played by non-nucleonic degrees of freedom. A new measurement of the p d → π − p reaction rate at rest, performed with the OBELIX spectrometer at LEAR, with the best statistics up to now and a careful evaluation of systematic effects is reported, together with a critical analysis of the existing theoretical models. The measured branching ratio, which confirms the previous results, can represent a reference point for the studies in the field.
No description provided.
The results of intranuclear cascade calculations (ideal gas with two-body collisions and no mean field), complemented by a simple percolation procedure, are compared with experimental data on protons and light nuclear fragments (d, t, He3, and He4) measured in 400 and 800 MeV/nucleon Ne+Nb collisions using a large solid angle detector. The model reproduces quite well global experimental observables like nuclear fragment multiplicity distributions or production cross sections, and nuclear fragment to proton ratios. For rapidity distributions the best agreement occurs for peripheral reactions. Transverse momentum analysis confirms once again that the cascade, although being a microscopic approach, gives too small a collective flow, the best agreement being reached for Z=2 nuclear fragments. Nevertheless these comparisons are encouraging for further improvements of the model. Moreover, such an approach is easy to extend to any other models that could calculate the nucleon phase space distribution after the compression stage of the reaction, when light nuclear fragments emitted at large angles are constructed from percolation.
No description provided.
No description provided.
The H2(e,e’n)1H quasielastic cross section was measured at Q2 values of 0.109, 0.176, and 0.255 (GeV/c)2. The neutron detection efficiency was determined by the associated particle technique with the H2(γ,pn) reaction for each of the three neutron kinetic energies. These H2(e,e’n) measurements of the coincidence cross sections are the first at low Q2. The cross sections are sensitive primarily to the neutron magnetic form factor GMn at these kinematics. The extracted GMn values have smaller uncertainties than previous data and are consistent with the dipole parametrization at the two higher momentum transfers; at the lowest momentum transfer, the value of GMn is ∼10% higher than the dipole value.
No description provided.
Production of Λ, Λ , and K s 0 has been measured for a wide range of event multiplicity in S+Pb reactions at 200 GeV/c per nucleon. The production of Λ is shown to increase with multiplicity faster than expected from a superposition of p+p collisions. The effect is seen for low multiplicity (below 100 negative particles).
No description provided.
No description provided.
No description provided.
The study of the K + total cross sections on a wide range of nuclei has revealed important modifications of the free-space K + -nucleon interaction when the nucleon is embedded in a nucleus. Data indicating such an effect were first obtained in a comparison of the total cross sections on carbon and deuterium. In this letter we report new measurements on 6 Li, silicon, and calcium, and demonstrate that the previously reported modifications occur quite generally.
No description provided.
No description provided.
No description provided.
The depolarization parameter D 0 n 0 n in the charge-exchange reaction p p ↑→ n n ↑ has been measured for the first time at the CERN Low Energy Antiproton Ring (LEAR) at 875 MeV/ c antiproton beam momentum, in the forward hemisphere. The measured values of D 0 n 0 n are always smaller than ±0.3, indicating that the two-spin amplitudes dominate the scattering matrix as suggested by the meson exchange potential models.
No description provided.
The differential cross section for the reaction H2(γ,p)n has been measured at several center-of-mass angles ranging from 50° to 143° for photon energies between 0.8 and 1.8 GeV. The experiment was performed at the SLAC-NPAS facility with the use of the 1.6 GeV/c spectrometer to detect the high energy protons produced by a bremsstrahlung beam directed at a liquid deuterium target. Contributions from concurrent disintegration by the residual electron beam were determined by measuring the proton yield without the Cu photon radiator. At angles not very far from 90°, the energy dependence of the cross sections is consistent with predictions of scaling using counting rules for constituent quarks. At least one theoretical calculation based on a meson-baryon picture of the reaction is able to reproduce the magnitude and energy dependence of the 90° cross section. The angular distribution exhibits a large enhancement at backward angles at the higher energies.
THE QUOTED ERRORS ARE STATISTICAL ONLY.
Forum