Four-fermion production at $\gamma\gamma$ colliders: 1. Lowest-order predictions and anomalous couplings

We have constructed a Monte Carlo generator (the corresponding FORTRAN code can be obtained from the authors upon request) for lowest-order predictions for the processes and in the standard model and extensions thereof by an effective coupling as well as anomalous triple and quartic gauge-boson couplings. Polarization is fully supported, and a realistic photon beam spectrum can be taken into account. For the processes all helicity amplitudes are explicitly given in a compact form. The presented numerical results contain, in particular, a survey of cross sections for representative final states and their comparison to results obtained with the program package Whizard/Madgraph. The impact of a realistic beam spectrum on cross sections and distributions is illustrated. Moreover, the size of various contributions to cross sections, such as from weak charged- or neutral-current, or from strong interactions, is analyzed. Particular attention is paid to W-pair production channels where we investigate the impact of background diagrams, possible definitions of the W-pair signal, and the issue of gauge-invariance violation caused by finite gauge-boson widths. Finally, the effects of triple and quartic anomalous gauge-boson couplings on cross sections as well as the possibility to constrain these anomalous couplings at future colliders are discussed.Received: 19 May 2004, Published online: 16 July 2004     

Double vector-charmonium production in electron-positron annihilation into two photons at $$\sqrt s = 10.6$$ GeV

In experimentally studying the exclusive production of two \(c\bar c\) mesons in electron-positron annihilation, the BELLE Collaboration obtained results that differ substantially from theoretical predictions. Recently, it was assumed that a significant part of this discrepancy can be explained by the process e⁺e^? → 2γ* → 2J/ψ, and its cross section was published. It is shown here that these results are incorrect (the cross sections are overestimated). The correct values of the cross sections for the double production of various vector charmonia are given.     

Neutral strange particle production in proton-proton collisions at\sqrt s = 63 GeV

The inclusive cross section for the production ofK _s ⁰ mesons, Λ and \(\bar \Lambda\) particles in proton-proton interactions at \(\sqrt s = 63\) GeV is presented. The produced particles have been detected in the full phase space. Behaviour of the longitudinal and transversal depandences of the cross sections are discussed. The total production cross sections for _s ⁰ mesons and Λ particles was determined to \(\sigma _{{\rm K}_S^0 } = (25.5 \pm 1.4)\) mb andσ _Λ =(7.8±1.2) mb respectively. A strong energy dependence of the production cross sections is observed.     

Pomeron and odderon in high energypp andp\bar p elastic scattering

High energypp and data on elastic scattering and total cross sections are analyzed in a model including the pomeron, odderon and secondary reggeons. A dipole model is used for the pomeron and for the odderon. By construction, our (bare) pomeron ansatz produces a single dip, as observed experimentally. The model reproduces the logarithmically rising cross sections with a unit pomeron intercept, but better fits are obained when a small non-zero value of the parameter = _p (0) is allowed for. Predictions for the future accelerators (UNK, LHC, SSC) are given.On leave of absence from the Institute for Theoretical Physics, Kiev-130, USSR     

Inelastic $J/\psi$ and $\Upsilon$ hadroproduction

We consider the prompt hadroproduction of and the states caused by the fusion of a symmetric colour-octet state, (gg)_8s , and an additional gluon. The cross sections are calculated in leading-order perturbative QCD. We find a considerable enhancement in comparison with previous perturbative QCD predictions. Indeed, the resulting cross sections are found to be consistent with the values measured at the Tevatron and RHIC, without the need to invoke non-perturbative colour-octet type of contributions.Received: 16 October 2004, Revised: 10 November 2004, Published online: 11 January 2005     

Physical criteria for the reliability of data on the photodisintegration of the <Superscript>89</Superscript>Y nucleus

Experimental photonuclear reaction cross sections obtained in experiments using quasimonoenergetic annihilation, monoenergetic tagged photons, and bremsstrahlung γ-radiation are analyzed using physical criteria for the reliability of data on the ⁸⁹Y nucleus. It is found that the reliability of data on the cross sections of partial reactions (γ, 1n) and (γ, 2n), obtained by means of photoneutron multiplicity sorting, is highly doubtful. Reliable cross sections of reactions (γ, 1n) and (γ, 2n) are obtained using the experimental–theoretical method (ETM) for evaluating using both experimental cross sections of neutron yield reaction σ^exp(γ, xn) that are free of neutron multiplicity problems, and theoretically calculated F _i ^theor ratios of the cross sections of definite (i) partial reactions to cross section σ^theor(γ, xn). It is shown that the evaluated cross sections differ noticeably from the experimental data.     

General features of\bar pp interactions at 7.3 GeV/c

Absolute inclusive cross sections for \(\bar pp\) interactions at 7.3 GeV/c are given. The data cover prong cross sections,V ⁰, γ production and inclusive charged particle (p/π) production. Separation has been made into annihilation and non-annihilation components. Inclusive π⁺, π^? production in the processes of \(\bar pp\) annihilation and non-annihilation are compared with simple quark models.     

Baryonic resonance production in\bar p p interactions at 32 GeV/c

The inclusive production of (1232) in \(\bar p\) p interactions at 32 GeV/c is studied using data collected in a bubble chamber experiment with a statistics of ～0.7 events/μb. Total and topological cross sections are evaluated and compared to existing data at other energies. The distributions of reduced longitudinal momentum and rapidity show evidence for some central production. Total cross sections for (∑ ⁺(1385)+cc) and (∑ ^?(1385)+cc) are also presented.     

Measurement of hadron and lepton-pair production in e+e- collisions at \sqrt{s}=192-208 GeV at LEP

Hadron production and lepton-pair production in e⁺e^- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies . Using a total integrated luminosity of 453 pb^-1, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally, the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle. An overall good agreement is found with Standard Model predictions.     

Model-independent analysis of Higgs spin and CP properties in the process \boldsymbol{e}^{+} \boldsymbol{e}^{-} \to\boldsymbol{t}\bar{\boldsymbol{t}} \boldsymbol{\Phi}

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a $t\bar{t}$ pair in high-energy e ⁺ e ^? collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top–electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top-quark pair.     

Annihilation and topological cross sections forpp and\bar p p interactions at 200 GeV/c

The results of an analysis of streamer chamber data from the NA5 experiment are presented. Topological cross sections forpp and \(\bar p\) p interactions and strange neutral particle production at 200 GeV/c have been measured and ( \(\bar p\) p?pp) difference cross sections have been determined. Multiplicity moments were calculated.     

The Reliability of Cross Sections of Partial Photoneutron Reactions for <Superscript>98</Superscript>Mo

The cross sections of partial photoneutron reactions for ⁹⁸Mo were evaluated. These cross sections are free from the shortcomings of various methods for neutron multiplicity determination used at the beams of quasimonoenergetic annihilation photons and bremsstrahlung radiation. New data on the cross sections of reactions (γ, 1n), (γ, 2n), and (γ, 3n) were obtained using the experimental–theoretical method for evaluation of cross sections of partial reactions satisfying the introduced physical reliability criteria. It is demonstrated that considerable deviations of the experimental cross sections from the evaluated ones result from an inaccurate sorting of neutrons between channels with a multiplicity of 1, 2, and 3.     

The standard model process e^ + e^ - \to \nu \bar \nu b\bar b and its Higgs signal at LEP II

We present and study the results for the standard model process $e^ + e^ - \to \nu \bar \nu b\bar b$ at c.m. energies 150 ≤ √s(GeV) ≤ 240 and for Higgs boson masses 60 GeV ≤ m _H ≤ 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.     

Four-fermion production at $\gamma\gamma$ colliders: 2. Radiative corrections in double-pole approximation

The electroweak radiative corrections to within the electroweak standard model are calculated in double-pole approximation (DPA). Virtual corrections are treated in DPA, leading to a classification into factorizable and non-factorizable contributions, and real-photonic corrections are based on complete lowest-order matrix elements for . Soft and collinear singularities appearing in the virtual and real corrections are combined alternatively in two different ways, namely by using the dipole subtraction method or by applying phase-space slicing. The radiative corrections are implemented in a Monte Carlo generator called Coffer - the computer code can be obtained from the authors upon request - which optionally includes anomalous triple and quartic gauge-boson couplings in addition and performs a convolution over realistic spectra of the photon beams. A detailed survey of numerical results comprises corrections to integrated cross sections as well as to angular, energy, and invariant-mass distributions. Particular attention is paid to the issue of collinear safety in the observables.Received: 3 June 2005, Published online: 5 August 2005     

Factorization theorems for high energy nn, \gamma p and \gamma\gamma scattering

The robustness of the factorization theorem for total cross sections, for nn (the even portion of pp and scattering), and scattering, originally proved by Block and Kaidalov using an eikonal formalism, is demonstrated. Factorization theorems for the nuclear slope parameter B and , the ratio of the real to the imaginary portion of the forward scattering amplitude, are derived under very general conditions, using analyticity and the optical theorem.Received: 19 February 2003, Revised: 10 July 2003, Published online: 19 September 2003Work partially supported by Department of Energy contract DA-AC02-76-Er02289 Task D.     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

Exclusive leptoproduction of \rho^0 mesons from hydrogen at intermediate virtual photon energies

Measurements of the cross section for exclusive virtual-photoproduction of mesons from hydrogen are reported. The data were collected by the HERMES experiment using 27.5 GeV positrons incident on a hydrogen gas target in the HERA storage ring. The invariant mass W of the photon-nucleon system ranges from 4.0 to 6.0 GeV, while the negative squared four-momentum of the virtual photon varies from 0.7 to 5.0 GeV. The present data together with most of the previous data in the intermediate W-domain are well described by a model that infers the W-dependence of the cross section from the dependence on the Bjorken scaling variable x of the unpolarized structure function for deep-inelastic scattering. In addition, a model calculation based on Off-Forward Parton Distributions gives a fairly good account of the longitudinal component of the production cross section for GeV. Received: 25 April 2000 / Revised version: 3 July 2000 / Published online: 25 September 2000     

Studies in\bar p p annihilation

Evidence is presented that \(\bar p\) p annihilation proceeds via the formation of two jets, with average transverse momentum of the order of the nucleon mass. The implications of this behaviour is linked to the measured cross sections and multiplicities, and explanations for it have been sought in the underlying gluon and quark constituents of the \(\bar p\) p system. The confrontation of the suggested constituent mechanisms and experimental data lead to the concept that charm meson production may play a significant role in the \(\bar p\) p experiments at the highest available energies.     

Evaluated Integral Cross Sections of the <Superscript>3</Superscript>H(<Emphasis Type="Italic">t</Emphasis>,2<Emphasis Type="Italic">n</Emphasis>)<Superscript>4</Superscript>He Reaction in the Low-Energy Region Obtained with Regard to Electron Screening

procedure is considered for analyzing ³H(t,2n)⁴He reaction proceeding in a gas environment with regard to electron screening [1–4]. Results from such an analysis are presented. An electron screening potential of 121 eV is obtained. The magnitude of this potential is three times higher than the one given in [5]. Starting with a 100 eV energy of particle interaction the cross sections of ³H(t,2n)⁴He reaction are calculated using the above potential. The reaction rates are calculated using the evaluated cross sections in the lowenergy region. Enhancement factors for cross sections and reaction rates are defined.