Multiplicity distributions of charged hadrons invp and charged current interactions

Using data onvp and charged current interactions from a bubble chamber experiment with BEBC at CERN, the multiplicity distributions of charged hadrons are investigated. The analysis is based on 20000 events with incidentv and 10000 events with incident . The invariant massW of the total hadronic system ranges from 3 GeV to 14 GeV. The experimental multiplicity distributions are fitted by the binomial function (for different intervals ofW and in different intervals of the rapidityy), by the Levy function and the lognormal function. All three parametrizations give acceptable values forX ². For fixedW, forward and backward multiplicities are found to be uncorrelated. The normalized moments of the charged multiplicity distributions are measured as a function ofW. They show a violation of KNO scaling.     

Production of charmed hadrons in neutrino proton and antineutrino proton charged current interactions

Usind data from avp and \(\bar v\) p experiment with BEBC at CERN, the rates for inclusive production ofD ^*+,Λ _c ⁺ andD ⁰ invp scattering and ofD ^*? in \(\bar v\) p scattering are measured. Some examples of the exclusive production ofD ^*+,Λ _c ⁺ and∑ _c ⁺⁺ are given. The cross section for the reactionvp→μ ^? _c ⁺⁺ is estimated.     

Reactions with leading hadrons in meson-proton interactions at 250 GeV/c

Inelastic final states with one or two leading hadrons are studied in π⁺p and K⁺p interactions at 250 GeV/c. In reactions with two leading hadrons, the dependence of the average charge multiplicity of associated pions on their effective mass is essentially consistent with that observed in p?p and γγ-collisions, but differs from that obtained in e⁺e^? -annihilation. The multiplicity and (semi)inclusive characteristics of the π⁺-induced non-diffractive reactions are compared to predictions of current versions of the FRITIOF fragmentation model. We show that the hard-like sub-processes, essentially responsible for the production of leading hadrons with relatively large transverse momentum as well as for the relatively large multiplicity of associated pions, are not properly treated in the model.     

Central exclusive diffractive production as a spin-parity analyser: from hadrons to Higgs

We present the general rules for double-Reggeon production of objects with different spins and parities. The existing experimental information on resonance production in these central exclusive diffractive processes is discussed. The absorptive corrections are calculated and found to depend strongly on the quantum numbers of the produced states. The central exclusive diffractive production of 0 ⁺ and 0^- Higgs bosons is studied as an illustrative topical example of the use of the general rules. The signal for diffractive 0 ⁺ and 0^- Higgs production at the LHC is evaluated using, as an example, the minimal supersymmetric model, with large .Received: 7 July 2003, Revised: 8 August 2003, Published online: 24 October 2003     

Rumsfeld hadrons

A missing link in the Standard Model is understanding hadrons, particles that respond to the strong interactions. In this article I summarise our knowledge in three classes, which are reminiscent of Donald Rumsfeld's (in)famous: ‘things that we know we know; things that we know we don't know; and things that we don't know that we don't know'. Recent discoveries in particle physics concerning strongly interacting hadrons fall into those categories. It is of course the third category that is the most tantalising, but lessons from the first two may help resolve the third.     

Observation of scaling deviations in the energy distribution of secondary hadrons in inelastic neutrino-proton interactions

An analysis is presented of the z distributions of secondary hadrons produced in 5600 charged current events from a BEBC neutrino-hydrogen experiment. Evidence is presented for scaling deviations in the z distributions and a breakdown of factorization in the single particle inclusive cross sections. The results are consistent with the leading order QCD predictions on the q² dependence of nonsinglet moments of quark fragmentation functions, yielding a value of Λ ≈ 0.6 GeV.     

Equilibrium temperature of hadrons

The temperatureT of hadrons frome ⁺ e ^? annihilation is analyzed using the SPEAR and the PLUTO data. Thermal equilibrium is found for π,K and ρ andT～E _c.m ^α with α=0.31±0.05. A discussion is given on the equipartition of energy between broad resonances and particles from their strong decay, and its application to estimate the quark mass difference:m _s?m_u=0.11 andm _c?m_u=1.60 GeV.     

Study of transverse momenta of charged hadrons produced in νp and\bar vp charged current interactions

Data from a neutrino and antineutrino hydrogen experiment with BEBC are used to investigate transverse properties of the produced charged hadrons. Measurements are presented on average transverse momenta of charged pions as functions of Feynman-x and the hadronic mass, on the transverse momentum flow within an event and on jet-related quantities. The main features of the data are well described by the LUND model. The data favour a version of the model in which soft gluon effects are included and the primordial transverse momentum of the quarks in the proton is small. Effects from 1^st order QCD (hard gluon emission) are negligible.     

Two types of hadrons

Resonances and enhancements in meson–meson scattering can be divided into two classes distinguished by their behavior as the number of colors (N_c) in QCD becomes large: The first are ordinary mesons that become stable as N_c→∞. This class includes textbook mesons as well as glueballs and hybrids. The second class, extraordinary mesons, are enhancements that disappear as N_c→∞; they subside into the hadronic continuum. This class includes indistinct and controversial objects that have been classified as mesons or meson–meson molecules. Peláez's study of the N_c dependence of unitarized chiral dynamics illustrates both classes: the p-wave ππ and Kπ resonances, the ρ(770) and K^*(892), behave as ordinary mesons; the s-wave ππ and Kπ enhancements, the σ(600) and κ(800), behave like extraordinary mesons. Ordinary mesons resemble Feshbach resonances while extraordinary mesons look more like effects due to potentials in meson–meson scattering channels. I build and explore toy models along these lines. Finally I discuss some related dynamical issues affecting the interpretation of extraordinary mesons.     

Quadrupole moments of hadrons

We study an Abelian Higgs model in three, four and five dimensions using the mean field perturbation expansion with covariant gauge fixing. In four and five dimensions the mean field analysis shows three phases; a confined phase, a Coulomb phase with massless spin waves, and a Higgs phase in which the spin waves aquire a mass. The Higgs and confined phases are shown to be connected. In three dimensions we find a single phase.     

Color models of hadrons

The evidence for a three-valued “color” degree of freedom in hadron physics is reviewed. The structure of color model is discussed. Consequences of color models for elementary particle physics are discussed, including saturation properties of hadronic states, π^o → 2ψ and related decays, leptoproduction, and lepton pair annihilation. Signatures are given which distinguish theories with isolated colored particles from those in which color is permanently bound.     

Leptonic decays of hadrons

The theory of semi-leptonic weak interactions is reviewed and confronted with present experimental data. The theoretical points emphasized are the basic tenets of the Cabibbo theory, the algebra of currents, and the relevance of strong interaction symmetries to the weak semi-leptonic amplitudes. The experimental data is discussed in detail, and future lines of investigation, necessary for testing detailed theoretical predictions and for resolving outstanding questions, are indicated.     

Physics of charmed hadrons

Basic experimental results on charmed-particle physics that have been obtained over the past few years are surveyed. Prospects for studying the properties of charmed particles in the near future are discussed.