Events with a large transverse energy in a calorimeter with full azimuthal coverage and | y | < 0.9 have been investigated in pp collisions at √ s = 30, 45, and 63 GeV. A striking change in the event structure, corresponding to a clear emergence of high- p T jets, is observed at √ s = 63 and 45 GeV in the region between 25 and 35 GeV in transverse energy. At √ s = 30 GeV, the data extend to E T ∼ 20 GeV, but no such change in the event structure is observed.
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Proton-antiproton elastic scattering was measured at a centre of mass energy s = 540 GeV . In the four-momentum transfer range 0.21 < − t < 0.50 GeV 2 the t -distribution of about 7000 events is well represented by the exponential shape exp ( bt ) with slope parameter b = 13.7 ± 0.3 GeV −2 . A new measurement of the slope for − t < 0.19 GeV 2 confirms our earlier result, giving evidence for a change of slope of about 4 GeV −2 around − l ̷ ≈ 0.15 GeV 2 .
NUMERICAL VALUES OF LOW T DATA GIVEN IN BOZZO 84. STATISTICAL ERRORS ONLY.
NUMERICAL VALUES OF MEDIUM T DATA TAKEN FROM BOZZO 84. THESE ARE THE EARLIER (BATTISTON 83) VALUES RENORMALISED TO THE NEW LOW T DATA IN THE OVERLAP REGION. ERRORS ARE STATISTICAL ONLY.
SLOPE VALUES FROM BATTISTON 83.
A measurement of the proton-proton elastic differential cross section at 50 GeV/ c incident momentum in the momentum transfer range 0.8<| t |<4.0 (GeV/ c ) 2 is presented. The data are compared to pp data at lower and higher energies, and to some model predictions.
NUMERICAL VALUES OF DATA SUPPLIED BY D. IMRIE. ERROR CONTAINS BOTH STATISTICAL AND SYSTEMATICS EXCEPT THE OVERALL NORMALIZATION ERROR.
The reactions γ p→K + K − π 0 (p) and γ p→ K s 0 K ± π ± (p) have been measured using tagged photons in the energy range 20 to 70 GeV. No resonance structure is observed in either of the K K π invariant mass distributions, which range from threshold up to ∼ 3 GeV. The photoproduction cross sections for φπ 0 and K ∗ (892)K are presented and are compared with theoretical predictions. No evidence has been found for the photoproduction of φ′ (1680).
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NO EVIDENCE FOR RESONANT STRUCTURE AT PHIPRIME(1680).
Results on photoproduction of π + π − π 0 in the photon energy range 20–70 GeV are presented. For the ω meson, the production cross-section is found to be 1010±15 (statistical)±290 (systematic) nb and is constant over the incident photon energy range. Spin-density matrix elements are evaluated for ω meson production. The φ meson is observed with a total photoproduction cross section (corrected for branching ratio to π + π − π 0 ) of 610±35±170 nb. A third resonance, at 1.67 GeV, is seen in the mass spectrum and its interpretation is discussed. The production of a broad π + π − π 0 continuum, mainly via ϱπ, and peaking at 1.2 GeV, contributes with a cross section of about 2.5 ωb. The spin-parity content is analysed by the moments of the π + π − π 0 decay angular distribution in the helicity frame and by maximum likelihood fits to the π + π − π 0 Dalitz plot. It is found that production of J P = 1 − states accounts for less than half of the total mass spectrum above 900 MeV. There is a broad enhancement in the 1 + wave around 1.15 GeV indicating photoproduction of the H(1190) meson.
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EXPONENTIAL FITS TO D(SIG)/DT IN OMEGA MASS REGION.
EXPONENTIAL FITS TO D(SIG)/DT OVER FULL ENERGY FOR THREE MASS REGIONS CORRESPONDING TO OMEGA, PHI AND OMEGA*.
Hard hadronic scattering was studied by selecting 150 GeV and 300 GeV π − p and pp events with large energy in a 240 cell calorimeter covering 45† to 135† in the c.m.s. polar angle and the full 2 π azimuth. A downstream calorimeter measured the remaining energy flow at smaller angles. For large energy deposited in the segmented calorimeter the proton induced cross section drops below the pion induced cross section, as expected in a constituent scattering picture. However, neither a simple energy scaling of the cross section nor a dominant jet structure of the events is observed. No evidence was found for recently proposed higher-twist mechanisms leading to events
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An experiment has been performed to search for associated hadronic production of charmed mesons, using a large-aperture forward magnetic spectrometer setup in a π − beam at the CERN SPS. A prompt electron trigger was used to select events containing a pair by charmed particles. D mesons have been identified by reconstruction of hadronic decay modes such as Kπ, Kππ. Data have been taken at 120, 175, and 200 GeV, The D D cross section measured at 175 200 GeV is σ( D D ) = (48 ± 15) μ b with a systematic uncertainty of ±50%. The energy dependence of the cross section is measured to be σ( D D ) [120 GeV )/σ( D D [175/200 GeV ] = 0.62 ± 0.34 .
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Results on moments of the azimuthal angle ϕ of final state hadrons from 120 GeV and 280 GeV μp scattering are presented. A ϕ asymmetry is observed and its W 2 , Q 2 , z and p T dependences compared with model calculations which include intrinsic transverse momentum and first order QCD corrections. These studies indicate that the observed asymmetry is mainly due to intrinsic transverse momentum k T .
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Typical phi distribution.
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Bose-Einstein correlations between pions produced in the central region of rapidity in αα, pp and p p interactions have been studied at the ISR. The parameters r and τ c -often interpreted as the radius and depth of the π-emitting region - are found to be independent of incident particle type but to depend on the mean charged multiplicity. In high multiplicity events, the pions appear to originate from a larger space-time region.
FOR DEFINITION OF R++ SEE PAPER.
FOR DEFINITION OF R++ SEE PAPER.
FOR DEFINITIONS OF R++ AND TAU*C SEE PAPER.
We have studied the inclusive production of the hadrons π ± , K ± , p, p , Λ, Λ , ρ and ⋉ in the central region at the ISR s = 53 GeV , in both pp and p p collisions. Differences are observed only for K ± , p, and p production. We then study also correlations between low- p T pp and p p pairs in the two types of collisions, separating the contribution from baryon pair production and from the incident particles (stopping protons). We observe a positive correlation between two stopping protons; between the production of two pairs, and between a stopping proton and a pair production, there are negative correlations.
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Forum