Analysis of two particle rapidity correlations at ISR energies

The short range two particle rapidity correlations at ISR energies are interpreted in terms of clustering effects in the central rapidity region. It is shown that the experimental data give an indication that large clusters are produced, and as a consequence one should observe short range correlation between π^?′s. The energy dependence of the data is also simply explained.     

Semiinclusive two-particle correlations and independent cluster emission at ISR energies

Semiinclusive two-particle correlations are calculated in the independent cluster emission model. The resulting semi-inclusive correlation functions ?₂ⁿ(y₁ = y₂ = 0) agree rather than well experimental data, esp. with respect to the multiplicity dependence. The average number of charged particles per cluster found from comparison with semiinclusive data is 2.5 charged particles per cluster, a value found earlier also from analysis of inclusive correlations.     

Di-hadron correlations at ISR and RHIC energies

The structure of hadron–hadron correlations is investigated in proton–proton (pp)$(pp)$ collisions. We focus on the transmission of the initial transverse momenta of partons (“intrinsic kT$k_T$”) to the hadron–hadron correlations. Values of the intrinsic transverse-momentum obtained from experimental correlations are compared to the results of a model with partially randomized parton transverse momenta at ISR and RHIC energies. Procedures for extracting the correlations from data are discussed.     

Inclusive production at LHC energies

We consider the first LHC data for pp collisions in the framework of Regge theory. The integral cross sections and inclusive densities of secondaries are determined by the Pomeron exchange, and we present the corresponding predictions for them. The first measurements of inclusive densities in the midrapidity region are in agreement with these predictions. The contribution of the baryon-number transfer due to String Junction diffusion in the rapidity space is at the origin of the differences in the inclusive spectra of particle and antiparticle in the central region, and this effect could be significant at LHC energies. We discuss the first data of ALICE and LHCb collaborations on the baryon/antibaryon asymmetry at LHC.     

Fractal behaviour and correlations in rapidity particle distributions at high energies

Recent arguments of Sarcevic and Satz for multifractal behaviour in rapidity particle distributions are shown to have a simple explanation in terms of multisource production in hadron collisions as it happens in the negative binomial approximation. The arguments for strict fractal behaviour may, however, still be justified if use is made of the correlation Mueller moments instead of the factorial moments.     

Effect of Bose-Einstein statistics on two-particle azimuthal and rapidity correlations

The short-range effect in azimuthal and rapidity correlations can be explained within the independent cluster model taking into account the cluster transverse momentum and the Bose-effect (identical particle effect) in the single as well as the two-cluster term. Good agreement with data from Dubna, NAL and ISR is obtained. From the data we determine parameters related to the longitudinal and transverse dimensions of the clusters.     

Inclusive cross section ratios in highp T proton-proton scattering at ISR energies

Ratios of inclusive cross sections σ(π⁺)/σ(π⁺+K ⁺+p) and \(\sigma (\pi ^ - )/\sigma (\pi ^ - + K^ - + \bar p)\) were measured for proton-proton interactions with a highp _T hadron in the final state around c.m.s. scattering angles θ?20°, 20° and 45° at two ISR energies \(\sqrt s = 31\) Gev and 62 GeV. Results are shown as functions of transverse and longitudinal momentum and are compared with parton model predictions. The different dependences of positive and negative pion fractions atp _T ?2–3 GeV/c on longitudinal momenta is similar to that observed in soft hadronic interactions at low values ofp _T where the leading proton effect (diquark fragmentation) is known to contribute. The quantitative agreement of the data with diquark model predictions indicates the presence of diquark fragmentation also in highp _T jets.     

Inclusive two-and three-particle rapidity correlations in high-energy hadron-nucleus collisions

Three-particle pseudorapidity correlations are investigated for relativistic secondaries from proton-nucleus interactions at 50, 67, 200 and 400 GeV/c and from pion-nucleus interactions at 50 and 200 GeV/c. The experimental data on two- and three-particle correlations are compared with quantitative predictions of current multiple scattering models of nuclear production. Within these models the influence of various factors on the magnitude of correlations is discussed and it is shown, in particular, that energy-momentum conservation plays an essential role at present accelerator energies.     

Pionization at ISR energies

It is shown that the same formula that describes pionization in multiple-particle production at accelerator energies, up to 30 GeV, can also describe inclusive single-particle production spectra obtained at the CERN Intersecting Storage Rings, corresponding to an energy of 1000 GeV. By determining the parameters of the pionization formula at ISR energies we can draw some conclusions about the pionization process at high energies and about some gross features of multiple particle production.     

A comparison of two-particle rapidity correlations in antiproton-proton and proton-proton interactions at 31 GeV centre-of-mass energy

We investigated correlations between pairs of charged secondaries produced in antiproton-proton and proton-proton interactions at a centre-of-mass energy of 31 GeV using the pseudorapidity variable η=?ln (tanθ/2). Positive, short-range correlations were observed in both reactions. In the antiproton-proton case, however, there is a stronger correlation at very short range when both particles are produced in the central region and when the charged multiplicity of the event is about 30% higher than the mean. A simple Monte Carlo calculation indicates that quark-antiquark annihilation into two hadronic jets could account for the observed effect.     

Two particle rapidity correlations among produced particles in proton-nucleus interactions at high energies

Significant dynamical correlations increasing with incident beam momentum and short-ranged in nature are observed in proton-nucleus interactions.     

Inclusive η production at high pT at the ISR

The inclusive η production cross section at the CERN ISR has been measured for p_T values of up to 11 GeV/c. We find that the $\text{η}\text{π}{}^0$ cross-section ratio has an average value of 0.55 ± 0.07 and varies little with p_T.     

Inclusive Pomeron-Pomeron interactions at the CERN ISR

Data are presented for the first time on inclusive Pomeron-Pomeron interactions which produce a central systemX (composed mainly of multimeson states) in proton-proton collisions at \(\sqrt s \) at the CERN ISR. The systemX has a Feynman-x distribution which is sharply peaked atx _f=0, is inconsistent with any significant contributions from Reggeon exchange processes, and has an invariant mass dependence in good agreement with the predicted formM _x ^?2 . Kaon production is about 15% of pion production, nearly independent ofM _x, while proton-antiproton production averages about 5% of pion production and increases withM _x. The structure of the central systemX develops into a jetlike shape, asM _x increases, as would be expected from a model of Pomeron fragmentation. The shape of thex _f(π) distribution in the center of mass of theX system (although not proving existence) is consistent with asoft partonic substructure of the Pomeron.     

Inclusive charged particle cross sections in full phase space from proton proton interactions at ISR energies

Measurements are presented of inclusive charged particle production in proton-proton collisions at √s=31, 44 and 62 GeV at the CERN ISR. The large acceptance of the Split Field Magnet detector allows a single experimental setup to cover almost the full longitudinal phase space up to a transverse momentum of 3 GeV/c.     

Modeling of exclusive parton distributions and long-range rapidity correlations in proton-proton collisions at the LHC energies

The soft part of proton-proton interaction is considered within a phenomenological model that involves the formation of color strings. Under the assumption that an elementary collision is associated with the interaction of two color dipoles, the total inelastic cross section and the multiplicity of charged particles are estimated in order to fix model parameters. Particular attention is given to modeling of exclusive parton distributions with allowance for the energy-conservation law and for fixing the center of mass, which are necessary for describing correlations. An algorithm that describes the fusion of strings in the transverse plane and which takes into account their finite rapidity width is developed. The influence of string-fusion effects on long-range correlations is found within this mechanism.     

Inclusive particle production in π− n interactions at high energies

Results on inclusive particle production in π^? n interactions at 21, 205 and 360 GeV/c are presented. The invariant cross sections in both neutron fragmentation and central regions are found to be equal within errors to the corresponding cross sections for π^? p collisions and exhibit the same energy dependence. A strong energy dependence of the invariant cross section ratios of negative and positive pions is observed. There is also an indication of transverse momentum dependence of these ratios. The η^? correlations in the neutron fragmentation region show little variation with energy and are in agreement with the predictions of the naive quark recombination scheme.     

An investigation of unitarity at ISR energies

We analyse the unitarity equation in impact-parameter space using recent ISR data (at s=930 GeV²) on σ_T, dσ/dt (elastic) and d²σ/dtdM² (diffractive) as input. The assumption of s-channel helicity conservation for the diffractive process leads to a diffractive overlap function which is central. Unitarity then restricts single diffraction to satisfy 2σ_d?5.8 mb. The assumption of t-channel helicity conservation, on the other hand, gives the interesting result that diffractive processes are peripheral in b-space if the diffractively produced state has high spin. Unitarity in this case gives no significant bound on 2σ_d. For both cases, non-diffractive processes are peripheral.     

Diffusion and two-particle correlations

Fluctuation signals of the QCD phase transition in nuclear collisions can be dissipated due to diffusion. Diffusive modes in the standard formulation of relativistic hydrodynamics propagate with infinite speed, violating causality. We develop a causal diffusion equation study the dissipation of net-charge fluctuations. We find that causality restricts the extent to which diffusion can dissipate these fluctuations.     

Additive quark model of multiparticle production and α-α interactions at ISR energies

Using a specific version of the additive quark model we compute the relative (to proton-proton) single particle rapidity distributions for particles produced in α-α interactions at CERN ISR energies.