Search

The diffractive dissociation of pions into 3π and 5π final states has been studied using π−d interactions at 15 GeV/c. Peripherally produced low-mass enhancements are observed in both channels. the 3π enhancements consist predominantly of two-body final states, ϱπ, andfπ; evidence for agπ enhancement is inconclusive. The 5π channel shows no strong two-body structure. A multiperipheral Deck model and the statistical dissociation model are studied as possible mechanisms for these enhandements. The multiperipheral model describes the 3π channel well, whereas the less structured statistical model gives a better description of the 5π data.

Results on inclusive particle production in π−n interactions at 21, 205 and 360 GeV/c are presented. The invariant cross sections in both neutron fragmentation and central regions are found to be equal within errors to the corresponding cross sections for π−p collisions and exhibit the same energy dependence. A strong energy dependence of the invariant cross section ratios of negative and positive pions is observed. There is also an indication of transverse momentum dependence of these ratios. The η− correlations in the neutron fragmentation region show little variation with energy and are in agreement with the predictions of the naive quark recombination scheme.

Diffractively produced five-pion final states are studied in the reaction π−d → 3π−2π+d at 15 GeV/c and compared with predictions of the statistical dissociation model and multiperipheral models.

Evidence for a bound ${\ensuremath{\Delta}}_{33}(1236)\ensuremath{-}{\ensuremath{\Delta}}_{33}(1236)$ component of the deuteron is sought by using ${\ensuremath{\pi}}^{+}$, ${\ensuremath{\pi}}^{\ensuremath{-}}$, and ${K}^{+}$ mesons as probes of nuclear structure. Events are observed which might contain $\ensuremath{\Delta}(1236)$ "spectators" in the breakup of a deuteron in a $\ensuremath{\Delta}\ensuremath{\Delta}$ state. However, other mechanisms may contribute to the signal, and we cannot unambiguously ascribe our events to a $\ensuremath{\Delta}\ensuremath{\Delta}$ contribution in the deuteron. With certain assumptions we obtain an upper limit of \ensuremath{\sim}0.7% for the $\ensuremath{\Delta}\ensuremath{\Delta}$ component of the deuteron.

The orbital angular momentum of the ${A}_{1}$ meson produced from ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}p$ at 16 GeV/c was studied by analyzing the decay angular distributions in the ${\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{\ensuremath{-}}$ state. A completely Bose-symmetrized formalism was used to measure the ratio $\frac{{g}_{1}}{{g}_{0}}$ of the helicity states of the $\ensuremath{\rho}$ from the ${A}_{1}$ decay. The value obtained, $|\frac{{g}_{1}}{{g}_{0}}|=0.48\ifmmode\pm\else\textpm\fi{}0.13$, indicates a substantial $d$-wave contribution in the ${A}_{1}$ decay.

Coherent production of π+2π− occurs in ∼1% of 15 and 16 GeV/c π− C2F5Cl interactions (studied in the Ecole Polytechnique HLBC exposed at CERN P.S.). For nearly every coherent event, one or both π+π− combinations lies in the ϱ0 or f0. The ratio of π−f0 to π−ϱ0 coherent production is 0.05±0.02. NoN* peaks are seen in the coherent events. The π−ϱ0 mass distribution is dominated by a peak in the A1 region but nearly 250 MeV wide.S-wave π−ϱ0 (J p=1+) dominates up to at least 1.2 GeV inM π − ϱ 0 but small admixture of waves of opposite parity is necessary to explain some angular distribution asymmetries. The A1 peak is too narrow to be explained by the momentum transfer limitation imposed by the nuclear form factor. The Dalitz plot excludes dominances of triangle singularity effects. The calculated OPE (Deck model) and ρ exchangeM πρ distributions are also too broad to fit our data, but uncertainties in the model preclude its firm rejection. In the case of dominance of resonances in our data, it would be necessary to assume two other resonances in addition to A2 to preserve an A1 of width ≾150 MeV.

Coherent production of 2π+3π occurs with cross section (0.1 ± 0.03) mb/nucleus in 16 GeV π- C2F5Cl collisions, compared with (4.0 ± 0.6) mb/nucleus for π+2π- coherent production. Comparison of 2π+3π- and π+2π− yields 90% confidence upper limits (γ0→2π+2π-)< 0.2% (γ0→π+π-) and (A1→2π+3π−)<

Data on the inclusive production of hadrons in νμNe and ?μNe interactions are presented and compared with the corresponding quantities obtained in π±Ne interactions. With 224 νNe and 219 ?Ne events, no differences are seen which would distinguish the hadronic states created by pions and neutrinos.