P. G. Innocenti

Observation of jet structure in high pT events at the ISR and the importance of parton transverse momentum

Abstract Events with a charged particle of high transverse momentum were studied in pp collisions at √s = 52.5 GeV with the Split Field magnet (SFM) at the CERN-ISR, triggering on a charged particle of pT > 2 GeV/c, in the c.m. angular region θ ≅ 20° and θ ≅ 45°. The results provide further evidence for jet-like structure in high pT reactions. One of two produced jets is associated with the triggering hadron whereas the other is produced at an azimuthal angle that differs from that of the trigger by roughly 180°. The main features of the data are found to agree with the predictions of a simple parton-parton hard scattering model with vector gluon exchange, provided that one allows for partons in the proton to have transverse momentum. The ingredients of the model are all derived from data on deep inelastic lepton-proton scattering and from hadron production in e+e− annihilation. The model retains a simple pT−4 dependence for the parton-parton scattering. However, for pT ≲ 4GeV/c, the transverse movement of partons yields an approximate pT−8 scaling for the inclusive hadron distribution in agreement with observations. For the understanding of our data, it is found to be essential to take into account the soft component arising from the fragmentation of the spectator partons into hadrons.

A measurement of p̄p and pp elastic scattering at ISR energies

We have measured the differential cross section for pp and pp elastic scattering at √s = 31, 53 and 62 GeV in the interval 0.05 < |t| < 0.85 GeV2 at the CERN ISR using the Split Field Magnet detector. At 53 and 62 GeV, for 0.17 < |t| < 0.85 GeV2 both pp and pp data show simple exponential behaviour in t; at √s = 31 GeV the data for 0.05 < |t| < 0.85 GeV2 are consistent with a change in slope near |t| = 0.15 GeV2.

Charmed baryon production at the CERN Intersecting Storage Rings

Abstract The production of a Λ+c charmed baryon has been observed in pp collisions at the CERN ISR. A sharp peak at 2.26 GeV/c2 was found in the decay mode Λ+c → K ∗0 p in events triggered with a forward K− meson. Also the decay mode Λ+c → K− Δ++ seems to be present. The estimation of the total cross section for Λ+c production is given. However, the resulting value depends on the assumed form of the differential cross section. In addition, Λ+c production in events triggered by the presence of a direct electron is discussed.

Observation of charmed D meson production in pp collisions

Abstract Evidence for the forward production of D + mesons has been found in pp collisions at a c.m. energy of 52.5 GeV. A signal of 92 ± 18 events above background has been observed in the decay channel D + → K ∗ o π + → K − π + π + . The cross section in the phase space region of our experiment is given and implications for the total cross section for charmed D meson production are discussed.

Density, charge and transverse momentum correlations of particles in non-diffractive proton-proton collissions at √s = 52.5 GeV

Abstract Inelastic events with an observed charged multiplicity n obs ⩾ 7 have been studied at the CERN ISR using the split field magnet detector. Correlations of particle densities, charges and transverse momenta have been determined and a phenomenological analysis in the framework of cluster models has been performed. A good description of all results is obtained if one allows for charged clusters, produced in a mechanism with limited charge exchange. The mean transverse momentum of clusters is 0.65 ± 0.10 GeV/ c . Short-range correlations of particles of like charge due to the Bose-Einstein effect can be described as a second-order interferrence phenomenon with a radius R = 1.34 ± 0.31 fm and a lifetime of cτ = 1.38 ± 0.60 fm for the pion source.

A measurement of the inclusive cross section of charged pions at very high transverse momenta

Abstract The inclusive cross sections for the production of high transverse momentum π + and π − mesons in proton-proton interactions have been measured at the highest ISR energy √ s = 63 GeV and at a c.m. production angle of 50°. The cross sections for π + and π − mesons are compared as a function of transverse momentum. It is shown that the inclusive cross section of π − mesons decreases faster than the π + cross section. particle σ ( π ± )/ σ (charged particles) are presented as a function of transverse momentum.

High pT K±π± production in p-p collisions at the ISR; strangeness suppression and gluon effects

Abstract The ratios of high p T charged kaon to pion production cross sections at √ s = 45 and 62 GeV are presented. The values of the K ± π ± ratios are essentially independent of both √ s and x T = 2p T √s and are compatible with a strangeness suppression factor λ = 0.55. By contrast, the K − π − values fall with x T suggesting a gluonic origin of K − . QCD calculations agrees with the measurements.

Production of vector and tensor mesons in proton-proton collisions at\(\sqrt s = 52.5\) GeV

AbstractInclusive production of ϱ0,f, andg0 mesons and ofKs0,K*0 (892), ϕ andK*0(1430)mesons has been measured at ∼2.6 and ∼1.1 GeV/c in proton-proton interactions at

Multiplicity dependence of transverse momentum spectra at ISR energies

\sqrt s = 52.5