A reassessment of the O(αs2) three-jet cross section for e+e− annihilation

Results of a new evaluation of the O(α_s²) dressed three-jet cross section for e⁺e^? annihilation are summarized. For vanishing cutoffs, the different results in published three-jet cross section formulae are due to differing definitions of resolvable four-jet events. Subleading terms which were ignored in previous calculations are evaluated and found to be sizeable in the phase space region where three-jet events become more two-jet-like. A simple calculation demonstrates that α_s values determined according to the three-jet cross section formulae of Gutbrod, Kramer and Schierholz are systematically too large.     

Comparison of the dipole cascade model versus O(αs) matrix elements and colour interference in ee annihilation

We investigate the relationship between the exact second-order cross section in QCD and the dipole cascade model as implemented in ARIADNE. We show that there is generally good agreement (very good in case one would average over different states in phase space). The relation between the probabilities to produce some states depends upon the way the recoil problems are treated in the cascade. We exhibit some observable consequences of the interference effects between different colour ordering in the states.     

Correlator of the quark scalar currents and Γtot(H → hadrons) at O(αs) in pQCD

We present the results of the analytical evaluation of the massless four-loop

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(α³_s) correction to the correlator of the quark scalar currents and the Higgs decay rate into hadrons. In numerical form we found (in

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scheme) that Γ (H →

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b ) = (3G_F/4

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π) M_Hm²_b (M_H) [1 + 5.667α_s/π + (35.94 − 1.359n_f) (α_s/π)² + (164.139 − 25.771n_f + 0.259n²_f) (α_s/π)³] where n_f is the number of quark flavour and α_s = α_s(M_H).     

The heavy quarkonium spectrum at order mαslnαs

We compute the complete leading-log terms of the next-to-next-to-next-to-leading-order corrections to potential NRQCD. As a by-product we obtain the leading logs at O(mα_s⁵) in the heavy quarkonium spectrum. These leading logs, when Λ_QCDmα_s², give the complete O(mα_s⁵lnα_s) corrections to the heavy quarkonium spectrum.     

Search for γγ→ηb in ee collisions at LEP 2

A search for the pseudoscalar meson η_b is performed in two-photon interactions at LEP 2 with an integrated luminosity of 699 pb⁻¹ collected at e⁺e⁻ centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Γ_γγ(η_b)×BR(η_b→4 charged particles)<48 eV, Γ_γγ(η_b)×BR(η_b→6 charged particles)<132 eV are obtained at 95% confidence level, which correspond to upper limits of 9.0% and 25% on these branching ratios.     

The vector and axial-vector coupling constants of the nucleon in cavity QCD to order αs

The cavity regularization technique, originally developed for self-energies, is adapted to the calculation of vertex diagrams in the framework of cavity field theory. As a test of this method, the vector and axial-vector coupling constants of the nucleon are computed to order α_s Logarithmic divergences of the various Feynman diagrams cancel for massless quarks, yielding g_v = 1.0000 and g_A = 1.0883 + 0.2425α_s, independent of the gauge and renormalisation scheme.     

Subtle errors in αs determination using “corrected data” of energy-energy asymmetry

For the determination of α_s in the process of hadron production from electron-positron annihilation at 35 GeV, the complete second-order QCD calculation is used to study the corrections to the so-called “corrected data” of the asymmetry of the energy-energy correlation function (Asy). It is found that the correction in the values of α_s using the asymmetry method can be quite large while that for the new method, the planar triple energy correlation (PTC), is negligible.     

Observation of inclusive η production in ee annihilation at CM energies of 34 GeV

The inclusive production of η mesons at CM energies around 34 GeV has been studied for e⁺e⁻ annihilation into hadrons. The average number of η-mesons per event is found to be 0.72 ± 0.10 (stat.) ± 0.18 (syst.). The abundance of η's is studied as a function of event shape parameters and it is compared to the corresponding π⁰ rates.     

Gluonic three-jet cross section in hadron collisions at O(α s 4 ) with cone jet definition

The next-to-leading order three-jet cross section in hadron collisions is calculated in the simplified case, when the matrix elements of all QCD subprocesses are approximated by the pure gluon matrix element. The cone jet definition is used. Distribution of the three-jet invariant mass distribution is compared with experimental data obtained at the TEVATRON. The important property of reduced renormalization and factorization scale dependence of the next-to-leading order physical cross sections as compared to the Born cross section is demonstrated.     

Predictions for all processes ee → fermions + γ

The complete matrix elements for e⁺e⁻ → 4 and e⁺e⁻ → 4fγy are calculated in the Electroweak Standard Model for polarized massless fermions. The matrix elements for all final states are reduced to a few compact generic functions. Monte Carlo generators for e⁺e⁻ → 4f and e⁺e⁻ → 4fγ are constructed. We compare different treatments of the finite widths of the electroweak gauge bosons; in particular, we include a scheme with a complex gauge-boson mass that obeys all Ward identities. The detailed discussion of numerical results comprises integrated cross sections as well as photon-energy distributions for all different final states.     

A new measurement of the Li(d,p)Li cross section and consequences for Be(p,γ)B

A novel scheme for measuring the cross section of the ⁷Be(p,γ)⁸B reaction, the major source of high energy neutrinos from the sun, is presented. The scheme involves a strictly uniform particle beam and overcomes some of the recognized experimental uncertainties of previous measurements. A new measurement of σ[⁷Li(d,p)⁸Li] has been carried out using this setup, and the present value of σ[⁷Li(d,p)⁸Li] = 155(8) mb at the top of the E_d(lab.) = 776 keV resonance is compared with previous measurements. A new issue regarding both the (d,p) and (p,γ) reactions has been examined: reaction-product nuclei which are backscattered out of the target. Measurements and simulations carried out in the course of this investigation are presented and discussed in the context of possible effects on the measured cross sections of these reactions.     

αs from τ: a discussion of theoretical errors

Nominal errors on the determination of α_s(m_Z) from τ decay are so small that it may appear that this is the best method of measuring the strong coupling. While I agree that this way of determining α_s(m_Z) is a very good one, I think that the theoretical errors involved are larger than often asssumed, even if the QCD sum rule framework is accepted.     

A measurement of the η radiative width Γη→γγ

The radiative width of the η meson has been measured at PETRA in photon-photon collisions. The resulting value is Γ_η→γγ = 0.53±0.04±0.04 keV.     

Preequilibrium α-emission in the Au(p,αx)-reaction at Ep = 72 MeV

Proton-induced α-spectra from ¹⁹⁷Au have been measured at E_p = 72.3 MeV and the angle-integrated cross section is compared to an exciton model Monte-Carlo calculation and to the spectral distribution of α-particles emitted after the absorption of negative pions at rest.     

Upper limit on the decay Σ(1385)→Σγ and cross section for γΣ→Λπ

Coherent Λπ⁻ production on Pb of 600 GeV Σ⁻ hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)⁻→Σ⁻γ]<9.5 keV, and estimate the cross section for γΣ⁻→Λπ⁻ at  GeV to be 56±16 μb.     

Energy dependence of the C(O, α) reaction

The energy dependence of the ¹²C(¹⁶O, α) reaction was measured at incident energies of E_lab=112−191 MeV. In the range ofE_x(²⁴Mg)=30−56 MeV, the excitation energies of the structures in the inclusive α spectrum were found to vary continuously as a function of incident energy in this region. This fact indicates that these structures do not represent excitations in ²⁴Mg, but rather that they originate from a different process such as a sequential ejectile decay.     

Finite-temperature effect on broken UA(1) symmetry and the η′ mass

The U_A(1) symmetry-breaking effective lagrangian mediated by the instanton is calculated in the semiclassical approximation at finite temperature. It is found that the strength of the effective vertex decreases with increasing temperature up to the QCD scale. Also, we discuss the possible variation of the η′ and other pseudoscalar meson masses.     

On the O(αs) infra-red divergences in the axial gauge of QCD

We demonstrate the cancellation of infra-red divergences in the axial gauge of QCD in the first corrections to the deep inelastic quark structure function.     

Observation of χb production in the exclusive reaction ′→γγχb→γγ→γγ(eeorμμ−)

We report on the observation of 1 ³P_J (χ_b) production in the reaction ′→γχ_b→γγ→γγ(e⁺e⁻ or μ⁺μ⁻). The data were recorded with the nonmagnetic CUSB detector at the Cornell Electron Storage Ring, CESR. We observe 124 γγ events with either an electron or muon pair in the final state. In the γγ correlation plot about 40% of the events cluster around (120, 430) MeV.