Andpp Collisions Research Articles

Similarity of hadron production inpp and heavy-ion collisions

The characteristic features of pseudorapidity distributions of hadron production are investigated in terms of a geometrical parameterh≡(dn/dη)0/Φ, Φ being the phase space covered by the η distribution. It is found thath is about the same for the heavy-ion (HI) andpp collisions at the same energy, the same for π andK production and behaves ash∼Ecm−1/3. This similarity property yieldsK−/π−=0.041±0.004 andK+/K−=4.5±0.6 for HI collisions at 14.6 GeV/A in agreement with BNL experiments.

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ+,K+p andpp collisions at 250 GeV/c (\(\sqrt s \)=22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp\(\bar p\)-Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe+e− data in terms of impact parameters is tested.

The structure of events triggered by direct photons in ?? p, ?+ p andpp collisions at 280 GeV/c

The structure of events associated with the production of direct photons in π−p, π+p andpp reactions of 280 GeV/c has been studied using data from the WA 70 experiment at the CERN SPS. Results are presented on the distributions of the fractional momenta of the colliding partons and on the fragmentation of the recoil jet and a comparison is made with predictions using the structure functions of Duke and Owens in the Lund Monte Carlo with string fragmentation.

Charged particle production inK + p, π p andpp interactions at 250 GeV/c

New results are reported on inclusive charged particle production inK + p,π + p andpp collisions at 250 GeV/c. Inclusive longitudinal and transverse momentum spectra of positively and negatively charged particles are presented. Scaling in the fragmentation regions and scaling violation in the central c.m. region is investigated in detail. The topological pseudo-rapidity densities are shown to scale in the c.m. energy range from 22 to 900 GeV.

Phase space dependence of the multiplicity distribution in π+ andpp collisions at 250 GeV/c

The charged particle multiplicity distribution has been studied for non-single-diffractive π+ p andpp collisions at\(\sqrt s = 22\) GeV, for full phase space as well as for intervals in rapidity, azimuthal angle and transverse momentum. In general, the multiplicity distribution is well described by a negative binomial. From comparison of the distribution for negative or positive particles to that of all charged particles, cascading is favoured as an interpretation over stimulated emission. Interesting consequences follow from a comparison of our results to those at collider energies and toe + e − data at comparable energy. Furthermore, evidence is given that the multiplicity distribution is not exactly of negative binomial type in every (connected or disconnected) phase space region.

Charged particle spectra in αα and αp collisions at the CERN ISR

Momenta of charged particles produced in inelastic αα, αp, andpp collisions were measured using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. Inclusive and semi-in-clusive spectra are presented as a function of rapidityy, Feynman-x, and transverse momentump T . The inclusivey distributions agree well with predictions of the dual parton model; the highest particle densities are reached aty≃0 and the momenta of leading protons decrease significantly for increasing total multiplicity. ‘Temperatures’ are equal in αα, αp, andpp interactions. Thep T distributions depend weakly on the multiplicity.

$$Q^2 \to A\sqrt s $$ Scaling law fore + e ??hadrons andpp collisions at high energy

It has been conjectured recently that multiparticle production in low momentum transfer hadronic collisions is due to gluon bremsstrahlung off highly virtual (mass\(\mu ^2 \sim \sqrt s \)) quarks. The model gives a new scaling law:\(Q^2 \to A\sqrt s \), for comparinge+e−→hadrons andpp non-diffractive inelastic data. The scaling law is tested for average multiplicities, plateau height and 〈p 2 ⊥ 〉. Fore+e− annihilation a parametrization of data based on perturbative QCD approach is used.

Hadron production inπ +,K + p andpp collisions at 147 GeV/c and properties of jet-like multiparticle systems

The gross features of the data are reviewed and the momentum tensor components, 〈S〉, and 〈T〉 are studied. Evidence for coplanarity effects is observed. A probabilistic method to search for jets is proposed. The jets found by this method are seen to be similar to highpT jets frompp interactionse+e− annihilations andvp interactions. The effect of subtracting the leading particles and the effect of lowpT diffractive and non diffractive components are investigated.

Approach to scaling in inclusive π+/π− ratios at 147 GeV/c

The ratio of hadronic π+/π− production has been studied in the target fragmentation region of π+p, π−p,K+p andp p collisions at 147 GeV/c beam momentum. The difference between this ratio in the π+p and π−p data is less than at lower energies but still present. No difference exists anymore for the π+/π− ratio at this energy betweenK+p andpp collisions. Exclusion of diffraction dissociation and resonance production does not change the main conclusions. The energy dependence of the ratio for π+p and π−p collisions gives evidence for a universal asymptotic ratio for all beams. Thep t -dependence at low-p t is in agreement with the expectation from geometrical correlation of the valence quarks.

Gluons in the hadronicS matrix

We derive a theoretical explanation of the similarities which have been experimentally observed between final state distributions in soft processes (K−p interactions andpp collisions at ISR) and hard processes (e+e− annihilations and deep inelastic scattering). The theoretical framework is the correspondence between QCD and dual topological unitarization (DTU), which expresses confinement as the equivalence of the hadron and parton bases to account for unitarity. Starting from the interpretation of the zero handle topology in DTU in terms of the naive quark parton model, we show how to characterize gluons in the hadron basis: primordial gluons are associated with the one handle topology, and the cascading of hard gluons is related to the sum of all higher topologies in DTU. We get this way a QCD interpretation of the reggeon calculus which is the theoretical framework of soft hadronic processes at asymptotic energies.

Charge-charge correlations and the detection of weak vector bosons by hadronic jets in $$\bar pp$$ andpp collisions at collider energies

We study the charge properties of quark jets within a chain decay model for quark jet fragmentation. Using the charge properties of quark jets, we define charge-charge two-jet cross sections and correlations. In\(\bar pp\) collisions these correlations show significant structure due to the weak vector bosonsW± andZ0.

Regularity of particle production in hadron collisions and the structure of the nucleon

The multiplicity distribution for charged secondaries emitted from pp, π±p, pn, π±n, nn, K+p andp-p collisions was found to define a single set of curves which can be expressed by a universal set of «multiplicity distribution functions» constructed from Poisson terms when conservation laws are suitably incorporated. The ΛK0 accompanying the pions produced in π-p collision, and the neutrals (mostly π0) produced in π-p inelastic charge-exchange reactions were also found to follow the same distribution. The distribution functions so obtained contain no adjustable parameter and fit well theNN cosmic-ray jet data. The Poissonian characteristic of the multiplicity regularity found points immediately to the existence of a number of nearly independent production regions or «cells» inside the nucleon (and other hadrons), and the fireball.