We report on the production ofe ± μ∓ pairs in 450 GeV/c pBe collisions at the CERN SPS. Theeμ signal, which has average missing energy of 21 GeV, is shown to be consistent with expectations from charm decay, and implies a σ ×B for\(c\bar c\) production in p-nucleon collisions of 0.63 ± 0.35μb. Alternatively, using an estimate of charm production from other experiments, the data imply a 95% confidence level upper limit of 1.16μb on any new physics process which producese ± μ ∓.

We report on the production of low-mass electron pairs and muon pairs in p-Be collisions at 450 GeV/c at the CERN SPS. For both electron and muon pairs the low-mass spectrum can be explained satisfactorily by lepton pairs from hadronic decays, and there is no need to invoke any “unconventional” source. The normalisation of the major hadronic sources is set by the data. The upper limit, at 90% confidence level, on any new source of lepton pairs is ∼20% of the hadronic decay contribution for muons, and ∼40% for electrons.

The results of two sets of transverse energy measurements, performed with incident proton beams of 200 and 450 GeV/c momentum on several nuclear targets, are presented. The transverse energy cross sections dσ/dE T are measured in a pseudorapidity range including the target fragmentation region (−0.1<η<2.9) for both data sets and also in a nearly complete pseudorapidity coverage (−0.1<η<5.5) for the data taken at 200 GeV/c incident momentum. A comparison is made of the transverse energy distributions in the target fragmentation region and in the full η region. We find that the mean value of pseudorapidity of the dE T /dη distributions shifts towards the target fragmentation region as the atomic mass number of the target increases or a selection of high transverse energy events is made. A parametrization based on a simple geometrical nucleonnucleon scattering approach was found to be inadequate to describe all features of the transverse energy distributions. Finally, the VENUS model is compared with the experimental data.

We present measurements of the rapidity and transverse-momentum distributions of the protons emitted in S+W, O+W, andp+W reactions at 200 GeV/A around the target rapidity (y=1). The rapidity density rises linearly with the transverse energy for all three systems, but the slope forp+W is much steeper than for O+W and S+W. The rapidity density forp+W is much higher than predicted by summing single nucleonnucleon collisions without any nuclear effects, indicating substantial rescattering of the produced particles. The predictions of the VENUS 3 model, including rescattering, show reasonable agreement with the data for all three systems. We do not have evidence for a strong collective flow of the outgoing particles.

Results from the HELIOS External Spectrometer on kaon production in 200 GeV/A S + W and p + W collisions are presented. The Kπ ratios are compared with results from a lower beam energy and are found to be remarkably similar. Evidence for secondary production of K+ by meson-baryon rescattering is reviewed. Our results at y = 1.0–1.5 are compared with neutral strange particle results at midrapidity.

Diffractive dissociation of nuclei (Be, Al, W) in collisions with 450 GeV/c protons,pA→pX, has been measured with the HELIOS spectrometer at the CERN Super Proton synchrotron. The dependence of the single-diffraction cross-section on the nuclear massA can be parametrized as σSD mb×A0.35±0.02, showing the peripheral nature of the process. The differential cross-section dσSD=(3.8±0.3)mb ×A0.35±0.02, is exponential with the slope parameter, increasing from 6.2±0.4 (GeV/c)−2 for beryllium to 7.9±0.5 (GeV/c)−2 for tungsten. The slope parameter also increases with increasing massM X of the diffractively produced state. The rapidity, multiplicity, and transverse-momentum distributions of the particles of the diffractively produced stateX show a longitudinal phase-space population and are remarkably insensitive to the nuclear mass. This, together with theA1/3 dependence of σSD, suggests that the dominant process of nuclear diffractive excitation is the dissociation of single nucleons.

Interactions of 16O and 32S at 200 GeV per nucleon in emulsion and in emulsion-tungsten chamber targets were tagged by transverse energy and multiplicity triggers in the HELIOS apparatus at CERN. As a first sample, 375 events, covering a wide range of transverse energies, were located and studied in emulsion. Results are reported in this paper. The angular distribution has been measured, event by event, with a wide pseudorapidity coverage, both in emulsion and in the HELIOS calorimeters. The total charged multiplicity and the transverse energy per charged particle have been obtained as a function of the transverse energy and of the pseudorapidity. The measured distributions are compared with the predictions of the Dual Parton Model, as coded in the IRIS generator. Assuming that 59% of the ET is transported by charged particles, and estimating the energy density by a full transparency picture, a comparison with cosmic-ray data has also been attempted.

The HELIOS experiment has measured inclusivep⊥ spectra of negative particles in the rapidity region 1.0 is found to be approximately constant up to the highest accessible values ofE⊥.

Multiplicity distributions of charged particles produced in the pseudorapidity range 0.9 < ηlab < 5.5 were measured in oxygen-nucleus collisions for Al, Ag, and W target nuclei at incident energies of 60 and 200 GeV per nucleon. The multiplicity differential cross sections and the pseudorapidity distributions as a function of transverse energy are presented for the various target nuclei. The correlation between charged multiplicity and transverse energy is studied as a function of transverse energy. Data are compared with predictions of the IRIS and FRITIOF generators.

Inclusive photonp ⊥ spectra were measured with 200 GeV/u proton,16O and32S beams on W and Pt targets, using a conversion method. The measurement of charged pions in the same apparatus allows a comparison of the γ data with the expected γ's from hadronic decays π0, η, η', ω). In all data sets, no deviation from the expected shape is observed in the range of 0.1 0.1 GeV/c andp ⊥>0.6 GeV/c.

Transverse-energy distributions have been measured for the collisions of the 32S nucleus with Al, Ag, W, Pt, Pb, and U target nuclei, at an incident energy of 200 GeV per nucleon. The shapes of these distribution reflect the geometry of the collisions, including the deformation effects. For central collisions, the transverse-energy production in the region −0.1<ηlab<2.9 increases approximately as A0.5, where A is the atomic mass number of the target. This increase is accompanied by a relative depletion in the forward region ηlab > 2.9. These results are compared with those obtained under similar conditions with incident 16O nuclei. A comparison is also made with the predictions of a Monte Carlo generator based on the dual parton model. Finally, we give estimates of the energy density reached and its dependence on the atomic mass number of the projectile.

Transverse-energy distributions have been measured in the pseudorapidity region −0.1<ηlab<2.9 for oxygen-nucleus collisions at incident energies of 60 and 200 GeV per nucleon for Al, Ag, and W target nuclei. The cross-section for the heaviest target nuclei at the highest incident energy is measured over 5 orders of magnitude and out to a maximumE T of 200 GeV. Measurements of the differential densitydET/dηlab as a function ofηlab are presented. In the pseudorapidity region −0.1<ηlab<2.9 the transverse energy for an average central collision is proportional to ≈A0.5, while the fraction of the total transverse energy measured in an extended region ofηlab>2.9 decreases with increasingA. The distributions are compared with the predictions of a dual parton model. Finally the question of the energy density is addressed.

Using data on coherent production of π+π+π- systems in π+ collisions with nuclei we exclude the existence ofJPC=1−+,I=1, exotic hybrid mesons with masses below 1.5 GeV and widths greater than 20 MeV, provided that their primary coupling is to πρ systems. Hybrid states with just such properties have recently been predicted from arguments based on QCD sum rules. Our experimental limit is based on Primakoff production of these states, and on an argument using vector dominance to relate their radiative widths to πρ channels. There has been increasing interest of late in the existence of hybrid states, which, in the case of mesons, contain a valence gluon in addition to aq\(\bar q\) pair in a color-octet state [1–5]. The pursuit of spectroscopic gluon degrees of freedom has been strongly motivated by the general QCD picture of hadrons, as well as by many specific calculations based on QCD sum rules, lattice simulations, and more phenomenological approaches such as QCD-bag models. Although much effort, both thoretical and experimental, has been devoted to the spectroscopy of glueballs, for which several candidates exist [6], it has also been realized that hybrid states may be as amenable to discovery, and perhaps less ambiguous to interpretation.

We present the results of new precision measurements of the radiative decay width, total width, and mass of the ${\ensuremath{\rho}}^{+}$ meson. These parameters are, respectively, 59.8\ifmmode\pm\else\textpm\fi{}4.0 keV, 0.150\ifmmode\pm\else\textpm\fi{}0.005 GeV, and 0.771\ifmmode\pm\else\textpm\fi{}0.004 GeV, and were extracted from data obtained on the coherent production of ${\ensuremath{\rho}}^{+}$ in 200-GeV/c ${\ensuremath{\pi}}^{+}$ interactions with nuclear targets.

We have measured the coherent nuclear production of low-mass ${K}^{+}\ensuremath{\omega}$ systems in ${K}^{+}A$ collisions at 202.5 GeV. Results for carbon, copper, and lead targets are similar to those found for ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ production in ${\ensuremath{\pi}}^{+}A$ reactions at the same energy.

We have carried out a partial-wave analysis (PWA) of three-pion systems produced in the coherent dissociation of ${\ensuremath{\pi}}^{+}$ mesons on nuclear targets. The data have been analyzed for copper and lead targets at an incident ${\ensuremath{\pi}}^{+}$ energy of 202.5 GeV. This PWA provides further evidence for resonant contributions to ${J}^{P}={1}^{+} \mathrm{and} {0}^{\ensuremath{-}}$ waves at $3\ensuremath{\pi}$ masses below 1.5 GeV, which can be plausibly identified with ${A}_{1}$ and ${\ensuremath{\pi}}^{\ensuremath{'}}$ mesons. The contribution from electromagnetic production of the ${A}_{2}$ has also been extracted, and an estimate for Coulomb production and radiative width of the ${A}_{1}$ has been obtained.

The problem of nuclear stopping power and its importance to the study of nucleus-nucleus collisions at very high energies was brought to general attention one year ago at Quark Matter 83 by Busza and Goldhaber. In this context, nuclear stopping power can be thought of as the rate of energy (or rapidity) loss of a proton traversing nuclear matter. It does not directly address the important question of energy deposition. Busza and Goldhaber showed that knowledge of nuclear stopping power is needed to estimate the minimum center-of-mass energy required in nucleus-nucleus collisions to ensure the production of very high temperatures at low baryon density. At cm energies of about 1 to 10 GeV/A, the stopping power is important in the estimation of the maximum baryon densities attainable in nucleus-nucleus collisions. The data presented are more relevant to this latter point.

Based on theoretical comparison of ${\ensuremath{\pi}}^{+}$ elastic Compton scattering with data on production of ${\ensuremath{\pi}}^{+}\ensuremath{\gamma}$ systems in ${\ensuremath{\pi}}^{+}Z\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\gamma}Z$ reactions, we present additional evidence of the veracity of the Primakoff formalism at the \ensuremath{\lesssim} 10% level of uncertainty.

Using data on the coherent production of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ systems in ${\ensuremath{\pi}}^{+}$ collisions with nuclei, we have extracted an estimate for the radiative partial width of the ${A}_{1}$. The rate for ${{A}_{1}}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}\ensuremath{\gamma}$ is 640\ifmmode\pm\else\textpm\fi{}246 keV, which is a factor of about 2-3 below the value expected on the basis of predictions from quark models and from vector dominance ideas.