B.J. Stacey

A02 production by charge exchange in π+n interactions at 4 GeV/c

Abstract A partial wave analysis of the reaction π + n → π + π − π 0 p yields an A 0 2 production cross section of 225 ± 30μb for momentum transfer squared c ) 2 ; the differential cross-section and density matrix are presented and compared with ω 0 production in the light of theoretical models.

A search for spectator isobars in deuteron collisions

Abstract A search has been made for spectator delta resonances from the breakup of deuterons by a 4 GeV/c incident π+ beam. It is shown that the narrow pπ enhancement produced backwards in the laboratory system is mostly not Δ, and an upper limit of 0.8% is estimated for the Δ Δ component of the deuteron.

A study of ϱ0 and f0 production in 4 GEV/c π+d interactions

Abstract The production of ϱ 0 and f 0 mesons has been studied using a sample of 15485 fits to the reaction π + d → p s p π + π − at 4 GeV/ c . Results are presented on the spin structure and production mechanisms of these resonances. An Estabrooks and Martin analysis has been carried out in the ϱ 0 region, giving results similar to those obtained in their analysis of 17.2 GeV/ c data. Natural parity exchange is less important at our momentum, however. In the case of f 0 production, we find evidence for the presence of s-, p- and d-waves in the π π system. Averaging all events in the f 0 peak, the s- and d-waves are found to be close in phase. The f 0 production mechanism has been investigated using a positivity analysis of the complete J = 0, 1, 2 density matrix, and the same general features are observed as are seen in ϱ 0 production. However, the unnatural parity exchange component is found to be even more dominant in f 0 production than in ϱ 0 production. Our results are compared with the predictions of various models.

Backward production of meson resonances in 4 GeV/c π+ d interactions

Abstract We have studied the backward production of ϱ 0 , f 0 and ω 0 mesons at 4 GeV/ c . Results are presented on total and differential cross-sections, and on the spin density matrix elements. Our results suggest (i) that the three reactions studied are mediated by similar exchanges; (ii) that they resemble backward photoproduction data rather than backward elastic scattering data; and (iii) that substantial s-wave contributions could be present in the ϱ 0 and f 0 regions.

Branching ratios of the f0 meson

Branching ratios have been determined for the f0 meson produced in 4 GeV/c π+d interactions. The decay rates to 2π+2π− and KK are 2.4 ± 0.6% and 2.5 ± 1.5% respectively, both relative to the ππ mode. Upper limits are given for the decays to ηπ+π−, ηη and K±π±K0.

A partial wave analysis of the (3π)0 system from the charge exchange reaction π+n→π+π−πop AT 4 GeV/c

Abstract From a partial wave analysis of the (3 π ) o state in the charge exchange reaction π + n→ π + π − π o p, we observe strong unnatural parity as well as natural parity production. The observed strong unnatural parity states are identified with well-established resonances. The unnatural parity production is consistent with Reggeized Deck model predictions, with the exception of the I = 1, JP = 1 + state. Here there is no evidence for A 1 production at ∼1.1 GeV, but the data could support resonance production at higher masses.

Test of the vector dominance model by forward and backward ϱo and ωo production

We compare new data on π+n → ϱop and π+n → ωop at 4 GeV/c with single-pion photoproduction data. Good agreement is obtained with the predictions of the vector dominance model from unpolarized photoproduction data. However, in the forward direction, the proportion of natural parity exchange observed in vector meson production is much smaller than that predicted by the VDM from polarized photoproduction data.

Cross sections for strange particle production in π+d interactions at 4 GeV/c

Abstract The production of strange particles in π + d interactions has been examined at 4 GeV/ c where no previous data exist. Careful attention has been given to the resolution of ambiguities and to corrections for losses in a total sample of about 22 000 events which have been used to determine channel cross sections. Where they can be checked, the cross sections fit well into the observed variation of existing cross sections at higher and at lower energies.

The production of the ω0 meson in the reaction π+d → pSpω0 at 4 GeV/c

Abstract The reaction π+n → ω0 p has been studied at 4 GeV/c giving a total cross section of 313 ± 26 μb. The sample of about 3500 ω0 events produced in the forward direction has been used to determine the differential cross section and the spin density matrix elements. The effective trajectory for unnatural parity exchange has been determined by a comparison of ϱ00 dσ/dt at different energies. A comparison of ϱ00 dσ/dt has been made with the similar data for ϱ0 production in this experiment allowing π-B exchange degeneracy and ϱ-ω interference to be investigated. These methods result in an unnatural trajectory consistent with that expected for the B-meson. A further study of ϱ-ω interference has been made by comparing the reactions π+n → ω0p and π−p → ω0n at similar energies. Our results on ω and ϱ production are combined with data on K∗0 and K ∗0 production at 4 GeV/c and an SU(3) sum rule relating the production of these four mesons is shown to be satisfied.

A spin-parity analysis of the 3π system produced in the reaction π+d→π−π+π+d AT 4 GeV/c

Abstract A spin-parity analysis of the low-mass 3 π system produced in the reaction π + d → π − π + π + d has been performed using data from an exposure of the CERN 2m bubble chamber to a π + beam of 4 GeV/ c momentum. Unnatural parity states predominate, 1 + being much more significant than 0 − and 2 − . The J P = 2 + contribution in the A 2 region was found to be (5±2)%.