H. Fesefeldt

Multiplicities, topological cross sections, and single particle inclusive distributions from pp interactions at 12 and 24 GeV/c

Results on multiplicities, topological cross sections, total particle production cross sections, and correlations between charged particle and π0 production are presented for pp interactions at 12 and 24 GeV/c incident laboratory momentum. Inclusive production of π±, Ks0, p, Λ, Σ± andΛ is studied; particle spectra are shown in single and double differential form and are compared, in different kinematic regions, with data obtained at other incident momenta and with other beam particles.

Observation of vector meson production in inclusive pp reactions

Abstract We have measured cross sections, rapidity and transverse momentum distributions, and vector meson polarization for the reactions pp→ ϱ o +anything, pp→ ω +charged particles, and pp → K ∗± + anything at incident laboratory momenta of 12 and 24 GeV/ c . We discuss various consequences of our results as well as possible connections with lepton pair production.

Rapidity-gap separation and study of single-diffraction dissociation in pp collisions at 12 and 24 GeV/c☆

Abstract An event-by-event separation of the single-diffractive component in the inclusive reaction p + p → p + X is attempted with our 12 and 24 GeV/ c bubble-chamber data, using a method involving largest rapidity gaps. The method yields a (non-strange) single-diffraction cross section of about 7 mb at both energes, dominated by two and four prongs. For the diffractive component the recoil mass distribution d σ /d M X 2 shows a sharp peak near M X 2 = 2 GeV 2 at both energies, with a long tail that broadens significantly with increasing energy. This shape is reasonably well described by the diffractive terms of a triple-Regge fit to the full pp data. The slope parameter of the diffractive t distribution shows a precipitous drop with increasing M X 2 , levelling off abruptly at M X 2 ≈ 3 GeV 2 . The mean charged multiplicity of the diffractive system appears to be linear in log M X 2 and independent of s .

A study of charge distributions in inelastic proton-proton collisions

Abstract Charge distributions for the secondaries from inelastic proton-proton collisions are studied by means of new data from an experiment at 12 and 24 GeV/ c (2 m HBC at CERN). By comparison with π ± p data at 16 GeV/ c , the inclusive charge distributions for the fragments of an incident proton and pion, respectively, are analysed. In addition, the cross sections for charge exchange between cms hemispheres are presented for the various charged-particle multiplicities. For events with no more than one neutral particle, charge and baryon exchange between cms hemispheres are compared to those between clusters. For the inelastic two-prong reactions, the two-dimensional distributions in longitudinal phase space are presented.

Pionization in pp interactions at 12 and 24 GeV/c

Abstract Inclusive π − and π + distributions in the region of small longitudinal c.m. momenta, from pp interactions at 12 and 24 GeV /c , are presented and compared with CERN-ISR data. Interesting scaling and factorization properties are found. The extent to which the observed behavior can be interpreted as evidence for pionization is discussed.

Investigation of the reactions pp→pp+meson resonance at 12 and 24 GeV/c

Abstract The reactions pp→pp+meson, where meson= η , ϱ 0 , ω , and f, have been investigated at P inc = 12 and 24 GeV/ c . Cross section, rapidity distributions, momentum transfer and decay angular distributions are presented. Upper limits on the cross sections for S ∗ (1000) and Φ production are given. An attempt is made to determine the dominating pairs of exchanges in the production of these resonances.

Partial-wave analysis of the low-mass (π+π−p) system produced in the reaction pp→p(π+π−p) at 12 and 24 GeV/c

Abstract A partial-wave analysis of the (π+π−p) system produced in the reaction pp→p(π+π−p) at 12 and 24 GeV/c has been performed for (π+π−p) masses below 2 GeV, using the Illinois program. It is found that this system can be adequately described by the spin-parity states J P = 1 2 + , 3 2 − and 5 2 + . The two enhancements observed in the total (π+π−p) mass distribution at ≈ 1450 MeV and ≈ 1700 MeV have predominantly J P = 3 2 − . The diffractive production of the low-mass (π+π−p) system is consistent with t-channel helicity conservation.

Exchange model analysis of the reactions pp → pnπ+ and pp → ppπ+π− at 12 GeV/c

New data are presented for the reactions pp → pnπ+ and pp → ppπ+π− at 12 GeV/c. An attempt is made to understand various features of the data in terms of three one-pion-exchange models, namely the elementary one-pion-exchange (OPE) model in the version of Wolf, a Reggeized pion-exchange (RPE) model and the double-Regge-pole (DRP) model in the version of Berger. The predictions from these models are compared with several distributions of invariant masses, mometum-transfers, Treiman-Yang and Gottfried-Jackson angles. The Regge models are able to describe the gross features of these distributions better than the OPE model, although they are not capable of reproducing all details.

Isospin analysis of the reactions pp→N(Nπ) at 12 and 24 GeV/c

The reaction pp → nucleon + nucleon + pion at 12 and 24 GeV/c is analyzed in terms of the isospin amplitudes for the production of the (Nπ) system. The energy dependence of the I(Nπ) = 12 amplitude is weak, while the I(Nπ) = 32 contribution shows the strong energy dependence known from meson exchange reactions. The slope parameter B of the dσ/dt′ distributions of the I(Nπ)=12 contribution is a strong function of the (Nπ) mass, decreasing sharply from about 12 GeV−2 at threshold to about 4 GeV−2 above 1700 MeV. Comparing our results for the I(Nπ) = 12 cross section with those of similar investigations in πp and Kp reactions, we find that factorisation is valid within experimental errors. The results support the conclusion that the I(Nπ) = 12 contribution is dominated by diffraction dissociation of the proton.

Analysis of the reaction pp → p(ππ)0 p, and the question of double pomeron exchange in high-energy production processes

Abstract A low-mass S-wave ( ππ ) 0 enhancement is observed in the reaction pp → p ( ππ ) 0 p at 12 and 24 GeV/ c incident momentum. The mechanism for producing these low-mass pion pairs is investigated, and it is shown that double pomeron exchange can contribute at most 5% to their production cross section at 24 GeV/ c .