P. Schübelin

Evidence for a two-peak structure in the A2 meson

Abstract The missing-mass spectrum of the A 2 meson [ M = 1297 ± 16 MeV, Γ = 95 ± 15 MeV] obtained in the reaction π − p → pX − in three independent runs at 6 and 7 GeV/ c shows a narrow dip of 6 standard deviations in the centre of the A 2 peak at 1297 MeV, thus suggesting a two-peak structure.

Confirmation of the A2 splitting near threshold

Abstract The shape of the A 2 resonance has been measured in π p → pA 2 at 2.6 GeV/ c , i.e. near threshold, with A 2 produced at minimum momentum transfer. The results confirm, with a new method and instrument, the A 2 splitting found previously with the Jacobian-peak method.

Structure within the R(1675) boson and possible structure within the A2(1290)

Abstract Three narrow peaks with masses 1632 ± 15, 1700 ± 15 and 1748 ± 15, reffered to as R1, R2 and R3, have been observed in missing-mass spectrometer runs at incident pion momenta of 7 and 12 GeV/c and a mass-resolution of ± 15 MeV. One-peak hypothesis gives a confidence level P(χ2)=0.8%; the three-peak one gives P(χ2)=60%. Statistical significance for R1, R2 and R3 is, respectively, 3.8, 6.6 and 6.1 standard deviations from the highest background line. R1 and R2 decay into one and three, while the R3 decays mainly into three charged particles. Their physical widths are compatible with zero, with upper limits of the order of Γ ⩽30 MeV. An apparent two-peak structure is observed within the A2(1286) peak, with the mass-values 1260 and 1312 MeV, at incident pion momenta of 6 and 7 GeV/c. The one-peak and two-peak hypotheses give the same confidence level P(χ2) = 5%.

A2 splitting in the decay channel A2− → K10K− produced in the reaction π−p → pA2− at 7 GeV/c

Abstract A K10K− mass spectrum in the A2 region has been obtained in the reaction π−p → p K10K− at 7 GeV/c. The double peak structure of the A2 meson, observed in the earlier missing mass spectra, is found to be present also in the decay channel A2− → K10K−.

Spectrum of charged non-strange bosons in the mass region 2.5–3.0 GeV

Abstract The CERN boson spectrometer shows significant enhancements in the spectrum of charged non-strange bosons near 2.6 GeV and 2.8 GeV mass values.

SPECTRUM OF CHARGED NON-STRANGE BOSONS IN THE MASS REGION FROM 3.0 TO 3.8 GeV.

Abstract With the CERN Boson Spectrometer five new resonances have been found in the spectrum of charged non-strange bosons with masses between 3.0 and 3.8 GeV.

Experimental confirmation of R-meson structure

Abstract Experimental confirmation of the structure in the region of the R(1700) meson, in the reaction π − + p → p + R − reported earlier at incident pion momenta of 7 and 12 GeV/ c , has been obtained at 11.5 GeV/ c with the missing-mass spectrometer. The peaks R 1 (1630), R 2 (1700) and R 3 (1748) have been observed; in addition a peak at 1830 ± 15 MeV, reported by the CERN-Liverpool bubble chamber group, is indicated. Speculative comparison of our peaks and bubble chamber data with the L -excitation quark-antiquark model predictions gives a suggestive agreement in both mass separations and G -parities; however, we cannot exclude this as being coincidence.

Spin-parity analysis of A2L and A2H in the decay channel A2− → ϱ0π−

Abstract A Dalitz plot of the ϱ 0 π − system, obtained in the reaction π − p → pA 2 − at 7 GeV/ c has been analyzed separately for the two peaks of the split A 2 meson. For both peakes J P = 2 + is strongly preferred over other hypotheses.

Spin-parity analysis of 3π decays in the A2 meson region

Abstract A dalitz plot with 600 events in the A 2 mass region has been obtained at 7 GeV/ c in the reaction π − p→ →pA 2 s − , where A 2 − → π + π − π − , using a system of wire spark chambers in connection with the CERN -Missing-Mass Spectrometer. A spin parity analysis shows that for the overall A 2 region (1260 M J P =2 + is favoured P ( Ξ 2 )=40% over 1 − , 1 + , 2 − p (all with P ( Ξ 2 ) 2 region is divided into A 2 high and A 2 low as suggested by the missing mass spectrum, the distributions still favour 2 + over 1 − , particularly for A 2 low .

Slope of differential cross section for inelastic processes at 12 GeV/c π−p interaction

The dependence on t of dσ/dt is studied for the processes π−p→ pMM− at 12 GeV/c and 0.26 < |t| < 0.37 (GeV/c)2.