uming that the charge asymmetry parameter obeys a binomial distribution, as originally proposed by Chou and Yang, we have calculated the forward-backward multiplicity correlation as well as individual characteristics of single hemisphere distribution for pp̅ collision to the TeV region. With a two-term negative binomial distribution as a description for the charged multiplicity distribution in the full phase space, the calculated forward-backward correlation is non-linear. The deviation from the usually assumed linear form is likely distinguishable by experiments.
We present and study the results for the standard model process e+e− → ννbb at c.m. energies 150 ≤ √ s(GeV) ≤ 240 and for Higgs boson masses 60 GeV ≤ mH ≤ 110 GeV, obtained from all tree-level diagrams and including the most important radiative corrections. The matrix elements have been calculated by the ‘spinor bracket’ method without neglecting masses, which is presented in detail. The √ s-dependence and the interference properties of the Higgs boson contributions and of various coherent background contributions to the total cross section are examined and compared. The important differential distributions for the Higgs boson and the background components are studied, providing information useful for choosing cuts in Higgs searches. We also examine the effect of a minimal set of cuts and evaluate the importance of the WW fusion for detecting a higher mass Higgs boson at LEP II.
For an electron-photon collider the complete tree-level cross sections of the reaction gamma e --> nu b (b) over bar W are computed at center-of-mass energies between 0.5 and 2.0 TeV, for top masses of 160 to 200 GeV and Higgs masses between 80 and 140 GeV within the Standard Model. It is shown that most of the nu b (b) over bar W events are due to Higgs and Z/gamma* production (with H, Z/gamma* --> b (b) over bar decay) while top production (with t --> bW decay) is about 50% smaller. Multiperipheral background and interferences are small, respectively negligible, in the energy range studied. By convoluting the basic cross sections with an energy spectrum of the backscattered photon beam, and inserting linear collider luminosities as anticipated in present designs, realistic nu b (b) over bar W event rates are estimated, This results in large event rates for gamma e --> nu tb and gamma e --> nu HW. We estimate that the CKM matrix element \V-tb\ can be probed from the vtb final state to an accuracy of 1-3% at root s(e+e-) greater than or similar to 1 TeV. Assuming an effective Lagrangian based on dimension-6 operators we discuss the sensitivity for detecting deviations of the HWW coupling from the Standard Model in the reaction gamma e --> nu HW.
Inclusive K^0 and Λ photoproduction has been investigated at HERA with the H1 detector at an average photon-proton center of mass energy of 200 GeV in the transverse momentum range 0.5 <p_t <5 GeV. The production rates as a function of p_t and center of mass rapidity are compared to those obtained in deep inelastic scattering at Q^2=23 GeV^2. A similar comparison is made of the rapidity spectra of charged particles. The rate of strangeness photoproduction is compared with pp̅ measurements. The observations are also compared with next-to-leading order QCD calculations and the predictions of a Monte Carlo model.
In this paper we investigate the effects of heavy Majorana neutrinos in the reaction e + e − → W + W −. We consider neutrino masses in the 1–10 TeV region. We show that at LEP II and NLC energies it is possible to use this processes to verify indirect evidence of heavy neutral particles with mixing angles of the order sin2 α = 0.01. We discuss the unitarity restrictions that can be obtained for vector singlet and fermion-mirror-fermion models.
A non-relativistic, QCD-based, potential quark model for the proton and the neutron inevitably predicts a spin-0 diquark structure with an rms radius of the order of 0.35 fm or smaller. We prove this by solving the (S wave}) hamiltonian by De Rüjula et al. with variational methods. It is essential to include all quark interactions and to use realistic test wave–functions. The protondelta mass difference, the magnetic moments and the nucleon charge radii can be reproduced only with wave functions that contain a mixture of quark–diquark and three–quark states. Approaches with just a quark–diquark component give incorrect magnetic moments, while those without diquarks lead to a too low proton–delta mass difference.
The momentum distributions of partons in bound nucleons are known to depend significantly on the size of the nucleus. The Fourier transform of the momentum ( x Bj ) distribution measures the overlap between Fock components of the nucleon wave function which differ by a displacement of one parton along the light cone. The magnitude of the overlap thus determines the average range of mobility of the parton in the nucleon. By comparing the Fourier transforms of structure functions for several nuclei we study the dependence of quark mobility on nuclear size. We find a surprisingly small nuclear dependence (< 2% for He, C and Ca) for displacements t = z ≲ 2.5 fm, after which a nuclear suppression due to shadowing sets in. The nuclear effects observed in momentum space for x Bj ≲ 0.4 can be understood as a reflection of only the large distance shadowing in coordinate space.
Any calculation based on a quark-gluon Lagrangian to which pion fields are added as explicit degrees of freedom, leads to results having a flavor structure different from that in a pure quark-gluon QCD Lagrangian. We show however (for baryon magnetic moments) that there is no ''paradox'': The flavor terms apparently violating QCD can be rewritten so as to duplicate terms with allowed flavor structure. We show this by the method of general parametrization and display explicitly the doubly counted terms. It follows that if some pion exchanage contribution is assumed, it is impossible in any way to extract its amount univocally.
The production of the $J^{P}={1⩈er 2}^{+}$ octet baryons Λ and Ξ−, the $J^{P}={3⩈er 2}^{+}$ decuplet baryons Σ(1385)±Ξ(1530)0, and Ω−, and the $J^{P}={3⩈er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z0 decays. The integrated rates and the differential cross-sections as a function of x E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ− baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ−, Σ(1385)±Ξ(1530)0, and Λ(1520) are also compared to the predictions of an analytical QCD formula.
Data are presented on the reaction e+e− → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z° boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible ‘X’ particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z° is measured to be Nv = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 − 8 × 10−6 depending on its mass), production of an invisible ‘X’ particle (σ, < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10-6 μB).
It is shown that the hadron production in high energy pp andcollisions, calculated by assuming that particles originate in hadron gas fireballs at thermal and partial chemical equilibrium, agrees very well with the data. The temperature of the hadron gas fireballs, determined by fitting hadron abundances, does not seem to depend on the centre of mass energy, having a nearly constant value of about 170 MeV. This value is in agreement with that obtained in e(+)e(-) collisions and supports a universal hadronization mechanism in all kinds of reactions consisting in a parton-hadron transition at critical values of temperature and pressure.
We use (fermion) mass perturbation theory for the massive Schwinger model to compute the boson-boson bound state mass in lowest order. For small fermion mass the lowest possible Fock state turns out to give the main contribution and leads to a second order result for the bound state mass.
The small x behaviour of the structure function h(1)(x, Q(2)) is studied within the leading logarithmic approximation of perturbative QCD. There are two contributions relevant at small x. The leading one behaves like (1/x)(0) i.e. it is just a constant in this limit. The second contribution, suppressed by one power of x, includes the terms summed by the GLAP equation. Thus for h(1)(x, Q(2)) the GLAP asymptotics and Regge asymptotics are completely different, making h(1)(x, Q(2)) quite an interesting quantity for the study of small x physics.
We analyze gauge parameter dependence by using an algebraic method which relates the gauge parameter dependence of Green functions to an enlarged Slavnov-Taylor identity.In the course of the renormalization it turns out that gauge parameter dependence of physical parameters is already restricted at the level of Green functions.In a first step we consider the on-shell conditions which we find to be in complete agreement with these restrictions to all orders of perturbation theory.The fixing of the coupling, however, is much more involved outside the complete on-shell scheme.In the Abelian Higgs model we prove that this fixing can be properly chosen by requiring the Ward identity of gauge invariance to hold in its tree form to all orders of perturbation theory.
The electroproduction of rho mesons with proton diffractive dissociation for Q^2 > 7 GeV^2 and the elastic electroproduction of Phi mesons for Q^2 > 6 Gev^2 are studied in e^+ p collisions at HERA with the H1 detector, for an integrated luminosity of 2.8 pb-1. The dependence of the cross sections on P_t^2 and Q^2 is measured, and the vector meson polarisation obtained. The cross section ratio between proton dissociative and elastic production of rho mesons is measured and discussed in the framework of the factorisation hypothesis of diffractive vertices. The ratio of the elastic cross section for Phi and rho meson production is investigated as a function of Q^2.
The q-deformed harmonic oscillator is studied in the light of q-deformed phase space variables. This allows a formulation of the corresponding Hamiltonian in terms of the ordinary canonical variables $x$ and $p$. The spectrum shows unexpected features such as degeneracy and an additional part that cannot be reached from the ground state by creation operators. The eigenfunctions show lattice structure, as expected.
In reference to the recently observed high Q(2), large x events in deep-inelastic positron-proton scattering at HERA, various leptoquark and supersymmetric scenarios are discussed. We study the impact of virtual leptoquark or R-parity breaking squark exchange as well as generic contact interaction on the production of quark-antiquark pairs in e(+)e(-) annihilation, in particular at LEP2.
In the literature, the notion of eikonalization is often used as synonymous of unitarization or, at least, as implying that unitarity is not violated. This, to the very least, appears to be wishful thinking. We discuss the properties of various types of eikonalization within a unified treatment. Linear trajectories with intercept larger than unity (so popular nowadays) lead to small asymptotic violations of unitarity even after eikonalization. Classes of eikonalizations in which the Odderon could dominate over the Pomeron are given; even so the maximal Odderon is still excluded by eikonalization.
An improved version of the ``pop-corn'' model for baryon production in quark and gluon jets is presented. With a reduced number of parameters the model reproduces well both production rates for different baryon species and baryon momentum distributions. Predictions are presented for a set of baryon-antibaryon correlations.
