QCD effects andb-tagging at LEP I

We analyze the impact of usingb-tagged samples in studying non-Abelian effects due to QCD ine ⁺ e ^? → 4jet events at √s=M _z ⁰, using angular variable analyses and comparisons withe ⁺ e ^? → 3jetγ events. We find that QCD effects are largely enhanced inb-quark samples with respect to ‘unflavoured’ ones, where energy-ordering is used to distinguish between gluon and quark jets. We show that theb-quark mass influences the angular distributions significantly and should not be neglected.     

Anomalous contributions to 95-195-195-1at high energies

We analyze the processe ⁺ e ^?→e ⁺ e ^? ? ⁺ ? ^? (?=e, μ, τ-leptons) considering several nonstandard contributions in order to search for new physics beyond the standard model. We are able to test compositeness up to the TeV mass scale at LEP II and CLIC energies.     

The triple regge limit of diffractive dissociation in deep inelastic scattering

We derive, within perturbative QCD, a formula for the inclusive cross section of the diffractive dissociation of the deep inelastic photon γ^*+q→X+q in the triple Regge limits?M ²?Q ²?Λ ². We use the leading ln(s/M ², ln(M ²/Q ²) approximation and derive an, expression for the triple Pomeron vertex. The Pomeron above this vertex is found to be of higher order than the BFKL Pomeron. The resulting formula for the cross section is infrared finite. We show that the Abramovsky-Gribov-Kanchelli cutting rules are satisfied, and we discuss implications for the Pomeron structure function.     

ππ partial waves from 0.6 to 1.8 GeV

We use high statistics π^?p → π^?π⁺n data at 17.2 GeV/c to calculate the ππ partial-wave amplitudes in the energy range 0.6<M_ππ< 1.8 GeV. We perform both energy-independent and energy-dependent analyses using Barrelet zero techniques. We find four possible solutions for the partial waves, each containing the leading ?, f, g resonances but with very different lower partial waves. Two solutions contain a ?' resonance in the g region, but it is not possible to establish the existence of other possible broad daughter resonances. We show that accurate measurements of π^?p → π⁰π⁰n should select the physical solution.     

Production of neutral MSSM Higgs bosons ine + e − collisions: a complete 1-loop calculation

We present the first complete 1-loop diagrammatic calculation of the cross sections for the neutral Higgs production processese ⁺ e ^?→Z ⁰ h ⁰ ande ⁺ e ^?→A ⁰ h ⁰ in the minimal supersymmetric standard model. We compare the results from the diagrammatic calculation with the corresponding ones of the simpler and compact effective potential approximation and discuss the typical size of the differences.     

The discrepancy between τ and e + e − spectral functions revisited and the consequences for the muon magnetic anomaly

We revisit the procedure for comparing the π π spectral function measured in τ decays to that obtained in e ⁺ e ^? annihilation. We re-examine the isospin-breaking corrections using new experimental and theoretical input and find improved agreement between the τ ^?→π ^? π ⁰ ν _τ branching fraction measurement and its prediction using the isospin-breaking-corrected e ⁺ e ^?→π ⁺ π ^? spectral function, though not resolving all discrepancies. We recompute the lowest order hadronic contributions to the muon g?2 using e ⁺ e ^? and τ data with the new corrections and find a reduced difference between the two evaluations. The new tau-based estimate of the muon magnetic anomaly is found to be 1.9 standard deviations lower than the direct measurement.     

Production of neutral MSSM Higgs bosons ine + e ? collisions: a complete 1-loop calculation

We present the first complete 1-loop diagrammatic calculation of the cross sections for the neutral Higgs production processese ⁺ e ^???Z ⁰ h ⁰ ande ⁺ e ^???A ⁰ h ⁰ in the minimal supersymmetric standard model. We compare the results from the diagrammatic calculation with the corresponding ones of the simpler and compact effective potential approximation and discuss the typical size of the differences.     

Non-perturbative QCD vacuum frome +e−→I=1 hadron data

We estimate the gluon vacuum condensate α _s 〈F ²〉 from thee ⁺e^?→I=1 hadron cross-section known below 2 GeV using moment sum rules ratios. We obtain α _s 〈F ²〉= (3.9±1.0)10^?2GeV⁴. We also re-evaluate the contribution of the dimension-six vacuum condensates to the above sum rule and test the factorization hypothesis of the four-quark operator. Useful rules for the evaluation of the dimension-six vacuum condensates contributions are given.     

Nuclear Corrections in ν A DIS and Their Compatibility with Global NPDF Analyses

We perform a global χ ²-analysis of nuclear parton distribution functions using data from charged current neutrino–nucleus (ν A) deep inelastic scattering (DIS), charged-lepton–nucleus (? ^± A) DIS, and the Drell–Yan (DY) process. We show that the nuclear corrections in ν A DIS are not compatible with the predictions derived from ? ^± A DIS and DY data. We quantify this result using a hypothesis-testing criterion based on the χ ² distribution which we apply to the total χ ² as well as to the χ ² of the individual data sets. We find that it is not possible to accommodate the data from ν A and ? ^± A DIS by an acceptable combined fit. This implies that either the twist-2 parton distribution functions in nuclei are not universal, or that higher-twist terms play a more important role in the nuclear environment and have to be taken into account.     

Heavy Majorana neutrinos in e + e − → W + W−

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 new study of Kπ scattering between 0.7 and 2 GeV/c2

We present new data on the reaction K⁺d → K⁺π^?p(p), at 5.44 GeV/c. This reaction is dominated by absorbed pion exchange and we have used the data to study K⁺π^? scattering between 0.7 and 2 GeV/c². We find the $\text{I=}\text{1}\text{2}$ s-wave Kπ phase shift increases approximately linearly with mass up to 1.45 GeV/c², and have evidence for a more rapid variation of the s-wave amplitude in the region of 1.5 GeV/c². The so-called “up” branches in the region of the K¹(890) and K¹(1400) are excluded, save for the possibility of narrow s-wave resonances of width <10 MeV/c². We have explained quantitatively every aspect of the data up to 2 GeV/c² with s-, p-, d- and f-waves, finding an f-wave resonance at a mass of ≈1.76 GeV/c² and with a width ≈300 MeV/c². We have obtained new resonance parameters for the K¹(1400) which differ substantially from the currently accepted values.     

QCD effects and b-tagging at LEP I

We analyze the impact of using b-tagged samples in studying non-Abelian effects due to QCD in e ⁺ e ^? → 4jet events at ${sqrt s=M_{Z^0}}$, using angular variable analyses and comparisons with e ⁺ e ^? → 3jetγ events. We find that QCD effects are largely enhanced in b-quark samples with respect to ‘unflavoured’ ones, where energy-ordering is used to distinguish between gluon and quark jets. We show that the b-quark mass influences the angular distributions significantly and should not be neglected.     

A study of hadronic decays of the ϒ′

We present a detailed study of the decays ?′ → π⁺π^?? and ?′ → π⁰π⁰?, where the ? decays subsequently to e⁺e^? or μ⁺μ^?. The results are obtained from a sample of 146 000 ?′ decays observed with the CUSB detector at the Cornell Electron Storage Ring. We derive branching fractions of (18.9 ± 2.6)% for ?′ → π′π^?? and (10.3 ± 2.3)% for ?′ → π⁰π⁰?, and determined partial widths for these decays. Invariant mass and angular distributions of both the π⁺π^? and π⁰π⁰ systems are presented. We also set a limit on the branching fraction for ?′ → η? of less than 0.2% at the 90% confidence level.     

The 1+− state and ψ spectroscopy

We suggest that ψ′ → ψ H^πO (where the ψH is the 1^+? state) may be an important decay mode of the ψ′(3685) and ψ″′ → ψ_H^η of the ψ″′ (4414). We also discuss ways to test the magnitude of the η?π^O transition in the ψ system.     

Analysis of solar-neutrino-induced ββ processes for several nuclei

We investigate neutrino-flux-induced ββ transitions in targets built of ^112,114,116Cd and ¹⁸O isotopes. In addition to the known β ^? β ^? channel, we consider new β ^? β ⁺ and β ^? β ⁺ γ modes of the neutrino-induced ββ process. A possibility of detection of the solar neutrinos via the induced ββ transitions of interest is discussed. We note that the β ^? part of the solar-neutrino-induced β ^? β ⁺ process in ¹⁸O was already discussed in connection with possible in fluence of high-energy electron production of this origin on the Super-Kamiokande results.     

Shape selection in non-Euclidean plates

We investigate isometric immersions of disks with constant negative curvature into R³, and the minimizers for the bending energy, i.e. the L² norm of the principal curvatures over the class of W^2,2 isometric immersions. We show the existence of smooth immersions of arbitrarily large geodesic balls in H² into R³. In elucidating the connection between these immersions and the non-existence/singularity results of Hilbert and Amsler, we obtain a lower bound for the L^∞ norm of the principal curvatures for such smooth isometric immersions. We also construct piecewise smooth isometric immersions that have a periodic profile, are globally W^2,2, and numerically have lower bending energy than their smooth counterparts. The number of periods in these configurations is set by the condition that the principal curvatures of the surface remain finite and grow approximately exponentially with the radius of the disk. We discuss the implications of our results on recent experiments on the mechanics of non-Euclidean plates.     

Factorization at higher twist in hadron-hadron scattering

We study one-loop soft gluon effects in a scalar quark QCD model of the Drell-Yan process. We find that factorization of the type suggested by Politzer holds at order m²/s, but fails at order m⁴/s². We suggest that this pattern holds to higher orders, and that the non-factoring terms are not suppressed by form factors. We compute the non-factoring contributions, and give a classical interpretation of our results.     

Two-pion production in photon-photon collisions

We calculate within chiral perturbation theory the cross section for γγ→π⁰π⁰ and γγ→π⁺π⁻ to next-to-leading order. The first process only depends on the one-loop contributions and forms a test of chiral perturbation theory. We also calculate the pion electromagnetic form factor and compare it to recent data.     

Production ofW-bosons in high energye + e − ande − p collisions

We study the processe ⁺ e ^?→W+hadrons from theZ ⁰-pole to the threshold region forW-pair production, keeping the widths of theZ ⁰ andW finite. Already slightly below threshold the cross section is strongly depressed. Also the total cross section at theZ ⁰-peak is very small. We present a simple model to account for this. We also give exact results to lowest order for the weak Compton processese ⁺ e ^?→e ⁺ W ^? v _e ande ^? p→pW ^? v _e and compare them with results obtained with the equivalent photon approximation.     

Spectral function sum rules for gluonic currents

We determine the masses and the decay amplitudes of the 2⁺⁺, 0^?+ and 0⁺⁺ gluonia in anSU(3) _c Yang-Mills theory. We estimate the so-called topological susceptibility of theU(1) sector. We discuss theSU(3) _F breaking effects to the η′(896) massrelation from current algebra and predict the η′ parameter values.