Multiplicity fluctuations in one- and two-dimensional angular intervals compared with analytic QCD calculations

Multiplicity fluctuations in rings around the jet axis and in off-axis cones have been measured by the DELPHI collaboration in e⁺e⁻ annihilations into hadrons at LEP energies. The measurements are compared with analytical perturbative QCD calculations for the corresponding multiparton system, using the concept of Local Parton Hadron Duality. Some qualitative features are confirmed by the data but substantial quantitative deviations are observed.     

Asymmetry in charmed-particle production in a Σ− beam

We present a calculation of the inclusive x _F distributions of charmed hadrons produced in a high-energy Σ^? beam. The calculation is based on the modified mechanism of charmed-quark fragmentation, as well as on the mechanism of c-quark recombination with the valence quarks from initial hadrons. We predict additional asymmetry in the production of charmed hadrons due to different distributions of the valence s and d quarks in a Σ^? beam.     

Analyzing power fluctuations in nuclear reactions

The joint analysis of differential analyzing power (AP) and differential cross section in the nuclear reactions of +J ₁→J ₂ +J ₃ type in the region of strongly overlapping resonances are presented. Consideration is valid in the absence of the channel-channel compound nuclear correlations. The fluctuations of AP and cross section are proved to be statistically correlated, the greater the direct contribution to the reaction cross section the stronger this correlation. For the purely statistical reactions the correlation is absent. It is shown that the joint investigation of the AP and cross section fluctuations gives possibility to extract the direct reaction AP and the separate the direct and compound nucleus contributions into the reaction cross section. In particular it can be done by means of the statistical correlation (SC) analysis. Furthermore, the SC analysis may serve as a test for revealing the intermediate structure involved in the reaction. Finally, the joint study of differential AP and differential cross section may be used to determine the spins of nuclear levels and polarization of incident beam. The results are employed to separate the compound and direct contributions in the inelastic scattering of polarized protons on²⁸Si. Comparison with experiment quantitatively supports the existence of the SC between the fluctuations of AP and cross section. Possible extension of the SC analysis to the case of the presence of channel-channel compound nuclear correlations are discussed.     

Azimuthal correlation and fractal study of compound hadrons (pions and protons) at Dubna and SPS energy

This paper presents an investigation of compound hadrons (pions and protons) distribution emitted from ²⁴Mg-AgBr and ¹²C-AgBr interactions both at 4.5 AGeV and ³²S-AgBr interactions at 200 AGeV. The study includes azimuthal correlations (two particle and three particle), azimuthal asymmetry and fractal behaviour. This paper reveals some interesting results.     

Charge fluctuations in Au+Au collisions at RHIC energy

A hadron and string cascade model, JPCIAE, together with the corresponding Monte Carlo event generator, has been employed in this paper to investigate further the charge fluctuations in Au+Au collisions at Snn = 130 GeV. The default JPCIAE calculations are in good agreement with PHENIX and STAR data. We found that the thermal predictions for the π gas, the resonance π gas and quark matter deviate, respectively, from the corresponding dynamical simulations from the JPCIAE model. The discrepancies were also found between the π charge fluctuations and the charge fluctuations of all species of hadrons. However the charge fluctuations for "π from ρ and ω decay" and for all the hadrons from resonance decay are close to each other, indicating the correlation between positively and negatively charged hadrons is not sensitive to the species of hadrons. This work shows further that it is questionable to use the charge fluctuations as a signature of QGP.     

Multiplicity distributions in a thermodynamical model of hadron production ine + e − collisions

Predictions of a thermodynamical model of hadron production for multiplicity distribution ine ⁺ e ^? annihilations at LEP and PEP-PETRA centre of mass energies are shown. The production process is described as a two-step process in which primary hadrons emitted from the thermal source decay into final observable particles. The final charged tracks multiplicity distributions turn out to be of Negative Binomial type and are in quite good agreement with experimental observations. The average number of clans calculated from fitted Negative Binomial coincides with the average number of primary hadrons predicted by the thermodynamical model, suggesting that clans should be identified with primary hadrons.     

On the scale dependence of the dimension of hadronic matter

We advance the notion of a dynamical, scale-dependent Hausdorff dimension for hadronic matter. The physical motivations behind such a concept are explained. For very small scales, we relate this dimension to the anomalous dimension of the product of two momentum densities. For hadrons, we rely on the precocious onset of Bjorken scaling in e-p inelastic scattering and a heuristic parton model to obtain the Hausdorff dimensional profile for the proton d(q²) as a function of the probing photon momentum q². We find that d reaches a maximum around d = 1 for a range of low q² values. This feature is indicative of a string-like structure of the hadrons at low momentum transfers.     

Dilepton and strange particles production by neutrinos in gargamelle

New results are presented of an analysis of pictures taken during an exposure of Gargamelle to the CERN ν beam in 1975. In addition to three ν_μ+N→μ^?+e⁺+V⁰+ hadrons events previously reported, an excess is found of events of the type ν_μ+N→μ^?+e⁺+ hadrons without V⁰. An analysis of strange particle production in charged current events suggests a possible violation of the ΔS=ΔQ rule. Interpreted in terms of charm production, the data permit an estimate of branching ratios and production rate of charmed particles. A limit is also placed on charmed particle production by neutral currents.     

Transverse momentum of hadrons produced in ν and ν interactions on an isoscalar target in BEBC

The average transverse momentum squared, 〈p_⊥²〉, of hadrons is studied as a function of W² and of Q² for ν and $\text{ν}$ interactions on an isoscalar target. An increase of 〈p_⊥²〉 with W² is observed for the hadrons emitted forward in the hadronic c.m.s. The p_⊥ dependence of the fragmentation function is found to factorise from the structure function at fixed W, but does not factorise at fixed Q². Unlike the case of forward-going particles, the 〈p_⊥²〉 of hadrons going backward in the c.m.s. shows no strong dependence on W².     

Measurement of the hadron structure function in hadron-hadron interactions

Previously published data on low-p _T π⁺/K ⁺/p?p interactions at 250 GeV/c are used to analyze the rapidity charge distribution and hadron structure function for the projectile hadrons. It is shown that the rapidity charge distribution for projectile hadrons can be approximated by a Gauss distribution, and their structure functions are found.     

A model for multiplicity distributions in high energy collisions

A phenomenological model is presented which regards the system after collision as a single entity that emits hadrons directly. The evolution of this entity gives a new two parameter distribution which fits the high energypp, \(\bar pp\) ,e ⁺ e ^?, π⁺ p andK ⁺ p data reasonably well. The entity emits hadrons along the rapidity axis and exhibits intermittency behaviour under certain conditions.     

Jets in pp collisions: Radiation zeroes and the electric charges of colored quarks

Measurements involving more than one photon (e.g., γγ → hadrons, e⁺e^- → q$\text{q}$γ) can determine the electric charge of colored quarks rather than the color-averaged value measured, for example, by the R-value in e⁺e^- → hadrons. We draw attention to the fact that this measurement of the absolute quark charges can be performed in hadron collisions via the process qq → qqγ. The charge signature is dramatic due to the appearance of radiation zeroes whose position depends on the values of the electric charges. This can be exploited to perform such measurements with a detector lacking γ/π⁰ separation capability. Such experiments also study the interface of color and electromagnetic amplitudes and can further elucidate the QCD origin of jets.     

Heavy quark correlations ine + e − annihilations

In heavy quark jets the quark mass acts as a regulator of collinear singularities, making the quark momentum an infra-red safe variable in perturbative QCD. This allows a direct comparison of measured heavy hadron momentum spectra with perturbative calculations. We exploit the factorisation of heavy quark fragmentation to derive QCD predictions for momentum correlations between heavy hadrons produced ine ⁺ e ^? annihilations. We study the practical feasibility and model sensitivity of our approach using Monte Carlo simulations. Higher order perturbative corrections and contributions from non-perturbative effects are found to be at the level of 10%.     

Chiral and UA(1) phase transitions in QCD: an analysis of the I=0 pseudoscalars

We study chiral and U_A(1) phase transition in the dilute gas approximation. A comprehensive analysis of the mass and mixing angel of η and η^′ reveals that in the transition of the quark-gluon-plasma droplets to the hadrons, besides the chiral phase transition, the U_A(1) phase transition also plays a significant and non-trivial role.     

Quark model for multiparticle and inclusive reactions

The relative multiplicity of different hadrons produced in high-energy collisions is found in the framework of the quark model. Appart from the usual hypothesis about the quark structure of hadrons, two extra assumptions are made. Firstly, produced particles are supposed to be mainly the members of the meson 36-plet and baryon (antibaryon) 56-plet. Secondly, production of strange quarks is assumed to be suppressed relative to non-strange quarks roughly by a factor of three, as taken from experiment. In the small-x region the agreement with experimental data is satisfactory. In the fragmentation region it is necessary to take into account the kinematics of the resonant state's decay. The influence of such decay on the x and p_T² distributions of hadrons is discussed.     

Investigation of the inclusive spectra of secondary protons and pions of low kinetic energies and of their wide pair correlations in π − A interactions at 43 GeV/c

The inclusive invariant cross sections for protons produced at angles of θ=90° and 60° and for positively and negatively charged pions produced at an angle of θ=90° are presented for π ^?Be, π ^?Al, and π ^?Cu interactions induced by 43-GeV/c incident π ^? mesons. The shape of the inclusive spectra of secondary hadrons, the A dependence of their cross sections, and the correlation functions for pairs of likely charged secondary hadrons at large angles of their divergence are studied. The kinematical region explored in the present article corresponded to kinetic energies of T≈0.16–0.70 GeV and T≈0.20–0.76 GeV for secondary protons and secondary pions, respectively. The angles of divergence of hadrons forming a pair, ψ, satisfied the condition cos ψ相似文献   

Observation of planar three-jet events in e+e− annihilation and evidence for gluon bremsstrahlung

Topological distributions of charged and neutral hadrons from the reaction e⁺e^? → multihadrons are studied at √s of about 30 GeV. An excess of planar events is observed at a rate which cannot be explained by statistical fluctuations in the standard two-jet process. The planar events, mostly consisting of a slim jet on one side and a broader jet on the other, are shown actually to possess three-jet structure by demonstrating that the broader jet itself consists of two collinear jets in its own rest system. Detailed agreement between data and predictions is obtained if the process $\text{e}{}^{\mathrm{+}}\text{e}{}^{\mathrm{?}}\text{→q}\text{q}\text{?}\text{g}$ is taken into account. This strongly suggests gluon bremsstrahlung as the origin of the planar three-jet events. By comparison of the data with the qq?g-model we obtain a value for the strong coupling constant of α_S(q² = 0.17 ± 0.04.     

Weak asymmetries in e+e− -annihilation at high energies

We study the effects of neutral weak currents in high energy e⁺e^? -annihilation into hadrons with polarized incident beams. It is shown that in current gauge models considerable weak asymmetries arise from q ≈ 28 GeV.