H. Frehse

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.

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 leading particles in pp interactions with large transverse momentum secondaries at the CERN-ISR

Abstract Events with a positive particle of large transverse momentum emitted at medium angles have been studied using the split field magnet spectrometer at the CERN-ISR at a c.m. energy of √s = 52.5 GeV. Positive particles with large longitudinal momentum, |x| > 0.5, i.e., leading particles, associated to large pT events, are analysed.

High

Abstract The composition of high pT particles is determined for pp collisions at a CMS energy s = 62 GeV at three CMS polar angles θ ≈ 10°, 20°, and 45°. The fractions of protons and antiprotons are given as functions of transverse momentum pT. The fractional yield of high pT protons depends strongly on θ, whereas the one for anti-protons is constant.

p_T

Abstract The split field magnet facility of the CERN ISR has been used to measure events with a secondary particle of large transverse momentum. The selection was done by triggering on positive particles of p T > 1.5 GeV/ c emitted near the forward direction. Inclusive distributions of the other charged secondaries have been studied over almost the full kinematical range as a function of their y , p T , o and charge. The particle density shows a broad increase in the o hemisphere opposite to the selected large p T particle. This increase occurs in a wide rapidity interval centered at y = 0, although the trigger is at y = 2.

Baryons Emitted at

Abstract The relative yields of pions of both charges have been measured in the c.m angular 5.5° ⩽θ ∗ ⩽21° in collisions at s=52.5 GeV . The transverse momentum and x -dependence of these relative yields are presented and discussed.

\theta=10

Abstract The relative yields of pions of both charges have been measured in the c.m angular 5.5° ⩽θ ∗ ⩽21° in collisions at s=52.5 GeV . The transverse momentum and x -dependence of these relative yields are presented and discussed.