A structure has been observed at 2220 MeV in the mass spectrum of ηη ′ systems produced by 38GeV/ c and 100 GeV/ c ′ negative pions on protons. The angular distribution of the decay products shows that this structure is presumably a spin J ⩾ 2 meson.
Cross sections for inclusive π0 production at large transverse momentum pT were measured in π−p, π+p, and pp collisions at 300 GeV/c. The cross-section ratio σ(π−p→π0X)/σ(π+p→π0X) was found to be consistent with unity in the pT region of 1 to 5 GeV/c. The cross-section ratio σ(π+p→π0X)/σ(pp→π0X) however is growing with increasing pT and increasing π0 c.m.-system rapidity in agreement with parton-model expectations, where the partons in the pions have on average higher momenta than in the proton.
Cross sections for inclusive direct photon production in π−p, π+p, and pp collisions at 300 GeV/c are measured at transverse momenta pT up to 7 GeV/c (xT=0.6). For π−p→γX also the rapidity distribution is presented. The cross-section ratio σ(π−p→γX)/σ(π+p→γX) is found to be 1 at pT=4 GeV/c and rises with increasing pT. This observation signals the occurrence of valence-quark–antiquark annihilation. The results are in good agreement with QCD predictions.
Large transverse energy cross sections of 300 GeV/ c pions and protons on hydrogen have been measured with a segmented calorimeter covering the central rapidity region −0.88 < y < 0.67 and 2 π in azimuth. The selected events show large multiplicities and no jet-like event structure. Processes more complicated than the scattering of two constituents appear to dominate these inelastic collisions.
The reactions π − p → p π − and π − p → p ϱ − ( ϱ − → π − π 0 ) at 10 GeV/ c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π − p → p π − π 0 . The total backward cross sections are 0.52±0.10 and 1.52±0.28 μ b, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ δ Regge trajectory exchange. The ϱ − decay angular distributions are studied in the u -channel helicity frame and the spin density matrix elements are presented as functions of u .
Data on inclusive jet production in the transverse-momentum (p⊥) range 0-8 GeV/c for 200-GeV/c p, π−, π+, K−, K+, and p¯ incident on a hydrogen target are presented. The jet cross section is fully corrected for losses and biases, and compared with the predictions of a model based on quantum chromodynamics. Both the absolute cross section and the inclusive charged-particle distributions inside and outside the jet are in qualitative agreement with the model.
We present single inclusive π±, π0 andK± spectra in the forward fragmentation region (x>0.2,pT<1.5 GeV/c) as well as correlations between two charged particles. The data were recorded in an unseparated negative hadron beam at the CERN SPS using a large acceptance forward spectrometer. Our maasurements are compared in detail with several models which emphasise the role of the beam valence quarks in this production process. The connection to measurements at largepT is also investigated.
Measurements are reported of inclusive production of π0-mesons in the beam fragmentation region in γp, πp andKp collisions. Results include the ratio of π0 production inKp and πp collisions, showing reduced production from fragmentation of theK-meson, and the ratio of π0 production in photon and hadron collisions which shows agreement with modified Vector Meson Dominance at lowPT, and departures at higherPT signalling the onset of direct photon reactions. The pattern of departure from Feynman scaling at highPT points to a contribution of hard parton-parton collisions in both γp and πp collisions.
Measurements are reported of inclusive production of η-mesons in the beam fragmentation region in γp, πp andKp collisions. Results include a small but significant departure from VMD, and a pronounced rise in theη/π0 ratio with increasingpT.
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