The production of neutral pions has been studied in the reactions 40 Ar + nat Ca , 86 Kr + nat Zr and 197 Au + 197 Au at 1 A GeV. For high energy pions emitted from the heavier systems a steeper than linear rise of the pion multiplicity with the centrality of the reaction is observed, indicating a pion production process other than binary nucleon-nucleon collisions. At low transverse momenta an enhancement of the π 0 -multiplicity increasing with the mass of the collision system is found. Systematic discrepancies between the experimental results and recent BUU, QMD and Cascade calculations are discussed.
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RESULTS OF AN EXTRAPOLATION TO THE FULL SOLID ANGLE TAKING THE EXPERIMENTALTEMPERATURES INTO ACCOUNT.
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A liquid hydrogen target was used to study the nuclear fragmentation of beams of relativistic heavy ions, Ne22 to Ni58, over an energy range 400 to 900 MeV/nucleon. The experiments were carried out at the Lawrence Berkeley Laboratory Bevalac HISS facility, using the charge-velocity-rigidity method to identify the charged fragments. Here we describe the general concept of the experiment and present total charge-changing cross sections obtained from 17 separate runs. These new measured cross sections display an energy dependence which follows semiempirical model predictions. The mass dependence of the cross sections behaves as predicted by optical models, but within the experimental energy range, the optical model parameters display a clear energy dependence. The isospin of the projectile nuclei also appears to be an important factor in the interaction process.
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Inclusive double differential multiplicities d2N/dy dpt and related quantities have been measured for protons and deuterons produced in 14.6A GeV/c Si+Al and Si+Pb collisions using the E814 forward spectrometer at the AGS at BNL. Collision ‘‘centrality’’ is determined by measuring Nc, the total charged particle multiplicity in the pseudorapidity range 0.85<η<3.8. For both systems Si + Al and Si + Pb, an increase in the proton rapidity distribution dN/dy at midrapidity and a corresponding decrease at higher rapidities are observed with increasing Nc. For Si+Pb, Boltzmann slope parameters TB increase significantly in the most central collisions. The measured distributions exhibit a centrality dependence even when σ/σgeo≲10%, where full overlap between the Si and Pb nuclei occurs in a simple geometric picture. The proton rapidity distribution dN/dy is presented for the symmetric system Si+Al over the entire rapididty interval. The total number of protons, which is the integral of this quantity over rapidity, varies with Nc. Results are compared with various model calculations, mostly using the hadronic cascade codes ARC and RQMD. No significant nuclear transparency is observed, indicating that large baryon and energy densities are produced in these collisions.
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Negative pion spectra emitted in the reactions of 775 MeV/nucleon La139+12C and La139+139La reactions have been measured in coincidence with the projectile fragments using the HISS spectrometer at the Bevalac. Prominent peaks near the beam velocity were observed in the pion spectra. Position and widths of the peaks were studied as a function of the ‘‘sum charge’’ of projectile fragments which is a good measure of impact parameter; the smaller the ‘‘sum charge,’’ the smaller the impact parameter. The peak position down shifts with the smaller ‘‘sum charge.’’ The pion peak is wider in the transverse than in the longitudinal direction, possibly mirroring the velocity dispersions of projectile fragments in the early stage of reactions.
THE CHARGE IN THE TABLE IS THE SUM CHARGE OF OBSERVED FRAGB. A TWO-DIMENSIONAL SPECTRUM WAS FITTED BY A SINGLE TWO-DIMENSIONAL GAUSSIAN FUNCTION ON A FLAT BACKGROUND.
THE CHARGE IN THE TABLE IS THE SUM CHARGE OF OBSERVED FRAGB. A TWO-DIMENSIONAL SPECTRUM WAS FITTED BY A SINGLE TWO-DIMENSIONAL GAUSSIAN FUNCTION ON A FLAT BACKGROUND.
Annihilation cross-sections σann for antineutrons on some nuclei (C, Al, Cu, Sn and Pb) at three antineutron momenta (180, 240 and 280 MeV/c) were measured at LEAR (CERN) with the OBELIX spectrometer. A behaviour σann=σ0Aν has been found withν≈2/3. The data are discussed following some models for antineutron-nucleus interaction.
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In this paper the main experimental results on some significant physical quantities obtained in He−Li collisions at 4.5A GeV/c are presented. The experiments have been performed at the Syncrophasotron from JINR Dubna, in the frame of the SKM 200 Collaboration.
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A new method to study the nuclear periphery using antiproton annihilation was applied to nine isotopes with mass numbers between 58 and 238. The method makes use of the detection of the radioactive annihilation products one unit lower in mass number than the target. A clear neutron halo effect, strongly correlated with the neutron binding energy, was observed in some nuclei. The experimental results are in qualitative agreement with calculations of proton and neutron densities at the nuclear periphery based on either a simple asymptotic density model or a more complex Hartree-Fock approach.
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A(FRAGT)=A(TARGET)-1.
Experimental results on some characteristics of high multiplicity (≧45) proton-AgBr interactions at 800 GeV are presented. The results are compared with those in lower multiplicity regions as well as for CNO target. The various parameters investigated here are pseudorapidity distribution, mean normalised multiplicity, mean number of intranuclear collisions and normalised pseudorapidity.
NUCLEUS IS AgBr (NUMBER(HTRACK) >= 9).
NUCLEUS IS CNO (2 <= NUMBER(HTRACK) <= 5).
The mean free path for inelastic interactions of 6Li in emulsion is measured and found not to be in systematic agreement with the different known theoretical parameterizations. This may be attributed to the loosely bound structure of 6Li nuclei. Possible internal structures of 6Li nuclei are investigated via the analysis of the shower particles multiplicity distributions for inclusive and central 6Li-Em interactions. In this analysis the experimental P-Em, d-Em and α-Em data are used as inputs for folding the corresponding distributions for 6Li-Em interactions. The results from central collisions favour the (α + d) cluster structure for the incident 6Li nuclei.
INTERACTION WITH EMULSION NUCLEUS WAS MEASURED.
INTERACTION WITH average AgBr NUCLEUS WAS MEASURED.
INTERACTION WITH average AgBr NUCLEUS WAS MEASURED.
We report on a measurement of the forward-backward charge asymmetry in e+e−→qq¯ at KEK TRISTAN, where the asymmetry is near maximum. We sum over all flavors and measure the asymmetry by determining the charge of the quark jets. In addition we exploit flavor dependencies in the jet charge determination to enhance the contributions of certain flavors. This provides a check on the asymmetries of individual flavors. The measurement agrees with the standard model expectations.
Forward--backward asymmetry summed over all flavours of quarks.
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