T. Jacobsen

Some features of particle multiplicities and momentum spectra in inelastic proton-proton collisions at 19 GeV/c

Abstract Various general features of inelastic proton-proton collisions at 19 GeV/ c , as they appear in a 2 m hydrogen bubble chamber, have been studied, and results concerning particle multiplicities in the final states and single-particle momentum spectra are presented. It is found that the average numbers of produced pions are 〈 n π − 〉 = 1.0, 〈 n π O 〉 = 1.4 ± 0.1, 〈 n π + 〉 = 1.6. The variation of the average c.m. momentum of π − with the number of produced pions is studied, and the fraction of the c.m. energy available for particle production, which is carried away by the pions, is estimated to be 52%.

Exchange mechanisms and energy dependence of isospin amplitudes for the reaction pN → NNπ in the energy range 5–1480 GeV☆

Data on the reactions pp → ppπ0, pp → pnπ+ and new data on pn → ppπ− at 19 GeV/c are used to study the reaction N1N2 → N3(N4π) in terms of the three isospin amplitudes MIIx, where Ix and I are the isospins of the exchanged particle and the N4π combination respectively. The result is that the amplitude with isospin zero exchange is dominating at 19 GeV/c. Analysis of available data from 5 to 1480 GeV yields that the isoscalar amplitude M120 is interpreted to be dominated by pomeron exchange and the isovector amplitude M321 by π exchange. The isovector amplitude M121 seems to be a mixture of A2(ϱ) and π exchanges. The only interference term which is definitely non-zero, is the one between M120 and M121 which is large in magnitude and negative.

Annihilation of Antiprotons at Rest in 3He and 4He

Abstract At LEAR of CERN the annihilation of antiprotons, stopping in 3 He and 4 He filling a self-shunted streamer chamber in a magnetic field, has been studied. The charged-particle multiplicities have been measured and the relative probabilities of π − production in p 3 He and p 4 He annihilation events have been obtained. The ratio between the p annihilation probability on the neutron and the proton for 3 He and 4 He has been deduced to be about half the value obtained for 2 H in bubble chamber experiments. The analysis of the results shows that this difference cannot be due only to the pion final-state interaction or to the shadow effect of the nucleons of the nuclei. The probability of p annihilation at rest on a proton bound in the nucleus results to be twice as high as that on a bound neutron, showing the dominance of annihilation in the I = 0 isospin states.

Study of the 1500 and 1700 MeV enhancements in the pπ+π− mass in the reaction pp→ppπ+π− at 19 GeV/c

The 1500 MeV and 1700 MeV enhancements observed in the pππ system are analyzed. It is found that the 1500 MeV effect is not a pure angular momentum state. Neither t- nor s-channel helicity is conserved. The 1700 MeV effect gives good fits to J=32 and 52 decaying to pππ. In the decay mode Δ++π−J=52 is preferred over 32. Moment analysis shows consistency with t- rather than s-channel helicity conservation.

Observation of a Δ++(≈1900) resonance decaying into Δ++(1236)π−π+

Abstract Production of Δ ++ (≈1900) has been observed in the reaction pp → Δ ++ (≈1900)n. The observed decay mode is Δ ++ (≈1900) → Δ ++ (1236) π − π + . The cross section for the process multiplied by the branching ratio of the observed decay mode is 29 ± 7 μ b. There is no indication of the decay mode Δ ++ (≈1900) → Δ ++ (1236) ϱ o (765).

Study of the reaction pp→ϱΔ N at 19 GeV/c

Abstract Production of ϱ-mesons in several charge states has been observed in 19 GeV/c pp collisions leading to five-body final states, pp→npπ+π+π− and pp→ppπ+π−πo. A strong association with simultaneous production of Δ(1236) is found. Our estimate of the total cross section, summed over all five possible charge configurations is σ(pp→ϱΔN)= 0.57 ± 0.07 mb. These reactions seem to account for most of the ϱ-production. The partial reaction channel pp→ϱoΔ++n with a cross section of 194 ± 35 μb has been studied in some detail. The data do not support the existence of the decay of a Δ(≈1900) resonance via ϱo(765). The fractions of the total cross section going into each partial channel with specified charges of ϱΔN are compared with the predictions of various isospin coupling models.

A Study of the Angular Distribution of the Secondary Particles of bar pAg/Br Reactions at 1.4 GeV/c Incident Momentum Observed in Photographic Emulsion

Some features of Ag/Br reactions at 1.4 GeV/c incident momentum are studied by means of the emulsion technique. The distributions of the number of charged particles/event are present. The angular distributions indicate some anisotropic process in the nuclear matter, possibly shock-waves, and some back-to-back emission.

On the nature of the exchanges in the reactions pp → baryon + baryon + pion at 19 GeV/c by analysis of differential cross sections

Abstract A study of some four-momentum and angular distributions in reactions of the type pp → baryon + baryon + pion , at 19 GeV/ c is presented. The reaction pp → NN π is divided into two parts: pp → N ( N π ) I 3 2 , pp → N ( N π ) I 1 2 and these two parts show some significant differences. While (i) shows features, which remind one of pion-nucleon scattering and therefore suggest that this channel contains an important contribution of pion-exchange, (ii) has a different structure suggesting that this channel is dominated by some other type of exchange. Similar features are seen in the reaction pp → Δ ++ p π − .

Isospin analysis of single ϱ and f0 production in pN collisions in the energy range 7–24 GeV

New data on the reactions pp → ppϱ0, pn → pnϱ0, pn → ppϱ−, pp → ppf0, and pn → pnf0 at 7, 11.6 and 19 GeV/c are used to study the reactions pN → NNϱ and pN → NNf0 in terms of isospin amplitudes. In the ϱ case there are three such amplitudes MI1I2 where I1 and I2 are the isospins of the exchanges in a double peripheral diagram. The result is that the amplitude with I1 = 1 and I2 = 0 is dominating. The properties of this amplitude are such that it is likely to be dominated by the pair of exchanges ϱ + η. In the f0 case there are only two amplitudes. It is found that the I1 = I2 = 0 amplitude is larger than the I1 = I2 = 1 amplitude and that it has an energy dependence such that it could be dominated by the pair of exchanges η + η.

Note on F1(1540) production in the reaction pp → pnπ+π+π− at 19 GeV/c

Evidence is presented for production of the F1(1540) resonance decaying to 3π in the reaction pp → pnπ+π+π− at 19 GeV/c beam momentum, thereby establishing the assignment IG JPC = 1−2−+.