A.L.S. Angelis

Determination of the angular and energy dependence of hard constituent scattering from π0 pair events at the CERN intersecting storage rings

We present data on proton-proton collisions, obtained at the CERN Intersecting Storage Rings, in which two roughly back-to-back ..pi../sup 0/s of high transverse momentum (p/sub T/) were produced. The angular distribution of the dipion axis relative to the collision axis is found to be independent of both the effective mass m of the dipion system and the centre-of-mass energy ..sqrt..s of the proton-proton collision. The cross-sections dsigma/dm at the two values of ..sqrt..s satisfy a scaling law of the form dsigma/dm = G(x)/m/sup n/, where x = m(..pi../sup 0/,..pi../sup 0/)/..sqrt..s and n = 6.5 +- 0.5. We show from our data that the leading ..pi../sup 0/ carries most of the momentum of the scattered parton. Given this fact, the axis of the dipion system follows closely the direction of the scattered constituents, and we exploit this to determine the angular dependence of the hard-scattering subprocess. We also compare our data with the lowest order QCD predictions using structure functions as determined in deep-inelastic scattering and fragmentation functions from electron-positron annihilation.

Observation of jet structure in high transverse energy events at the CERN intersecting storage rings

Abstract The spectrum d N d E T 0 ( E T 0 = neutral transverse energy) has been measured with an electromagnetic calorimeter covering 90% of 2 π in azimuth. The measurement, performed in pp collisions at s = 62 GeV , covered the E T 0 range from 10 to 30 GeV. Evidence is presented that a large fraction of these events are jet-like, the fraction increasing with E T 0 .

Observation of KNO scaling in the neutral energy spectra from αα and pp collisions at ISR energies

Abstract Neutral transverse energy spectra in pp and αα interactions are analyzed in terms of the wounded nucleon model. Analysis of the αα spectrum by application of a multiple nucleon-nucleon collision mechanism is conveniently performed when a gamma distribution is used to represent the pp spectral shape. The wounded nucleon model provides a reasonable description of the αα spectrum for the first three orders of magnitude, but completly fails to account for the slope of the high energy tail of the distribution. However, the pp and αα spectra can both be fitted to the same gamma distribution when scaled by their respective mean values and thus exhibit KNO scaling.

Jets in high transverse energy events at the CERN intersecting storage rings

Abstract Most events with high neutral transverse energy, ET0, produced in pp colisions at √s = 62.3 GeV, are jet-like. The evidence for this is presented, based on data collected using an electromagnetic calorimeter covering 90% of 2π in azimuth. The spectrum dN/dET0 has been measured over the ET0 range from 10 to 35 GeV. Properties of the observed jets are discussed.

High pT π0 production from αα and αp collisions at the CERN ISR

Abstract The invariant cross sections for π0 meson production in alpha—alpha and alpha—proton collisions at the ISR were meas- ured up to transverse momenta of 7 GeV c and 8 GeV c , respectively. These measurements are compared with π0 production in pp collisions at the same values of s / nucleon, and the variation of the nuclear A-dependence with pT is determined.

A study of e+e− pairs in the mass range 11 to 25 GeV/c2 at the CERN intersecting storage rings

Abstract A sample of 58e + e − events with an invariant mass greater than 11 GeV/c 2 produced in pp collisions at a centre-of-mass energy of 62.3 GeV is discussed. The cross sections are presented as a function of the mass and transverse momentum. The electron pairs produced with a mean transverse momentum of 2.50 ± 0.25 GeV/ c .

Three-jet events at the CERN intersecting storage rings

Three-jet events have been observed in pp collisions at s = 62.3 GeV. The data were collected using a total neutral energy trigger with a threshold at 25 GeV. These events appear predominantly as two jets, with some appearing as three jets. A novel analysis for the extraction of 2-jet and 3-jet events is described, and some of the event properties are discussed. The relative numbers of two- and three-jet events are studied within the framework of leading-order QCD, and yield a value of αs(K3/K2) = 0.19 ± 0.02 (stat.) ± 0.04 (syst.).

High transverse energy and high transverse momentum events in pp and pp interactions at the CERN intersecting storage rings

Abstract A comparison between p p and pp interactions at √s = 52.7 GeV is presented for a total neutral transverse energy (ETo) trigger and for a high transverse momentum (pT) neutral cluster trigger. The rate of production of events in the range 6 p p collisions than in pp collisions. A study of the structure of the events shows this excess to be due to more isotropic events being produced in p p collisions. The ratio of the production cross section for single neutral clusters in p p and pp interactions in the range 1.25

A study of associated particles and second-order processes in electron-pair production at the CERN intersecting storage rings

Abstract The multiplicity of particles associated with electron pairs with mass greater than 11 GeV/c 2 is found to increase with the transverse momentum p T of the electron pair. The associated particles are observed to recoil against the electron pair and compensate locally its transverse momentum. The data are compared with lower √ s dimuon data using the scaling form: s 2 p T 2 (d 3 σ /d y d p T 2 d m 2 ) = H ( x T , y , τ ).

A study of massive electron pairs and associated particles produced at the CERN ISR

Abstract A sample of 105 e + e − events with an invariant mass greater than 11 GeV/ c 2 produced in pp collisions at a center-of-mass energy of 62.3 GeV is discussed. Cross sections are presented as a function of mass and transverse momentum. The multiplicity, transverse momentum, and azimuthal dependence of associated particles are also studied.