Comparison of e+e− annihilation with QCD and determination of the strong coupling constant

We have analyzed 1113 events of the reaction e⁺e^? → hadrons at CM energies of 12 and 30 GeV in order to make a detailed comparison with QCD. Perturbative effects can be well separated from effects depending on the quark and gluon fragmentation parameters to yield a reliable measurement of the coupling constant α_S. At 30 GeV, the result is α_S = 0.17 ± 0.02 (statistical) ± 0.03 (systematic). QCD model predictions, using the fragmentation parameters determined along with α_S, agree with both gross properties of the final states and with detailed features of the three-jet states.     

The QCD effective coupling constant in e+e− annihilation

The QCD effective coupling constant α_s(Q²) is determined by comparing the O(α_s)² jet-distributions with the high-energy e⁺e^? data from PETRA. We get α_s(Q² = 1225 GeV²) = 0.125 ± 0.01, which corresponds to $\text{Λ}{}_{\mathrm{<mtext>MS</mtext>}}\text{= 110}{}^{\mathrm{+70}}{}_{\mathrm{?50}}\text{MeV}$ with five flavours.     

Extracting the width of giant resonances from the analysis of heavy ion inelastic scattering

The energy and percentage of the energy-weighted sum rule associated with low-lying collective modes and with the giant resonances, are input parameters of the coherent surface excitation model of heavy ion reactions of Broglia, Dasso and Winther. In the present letter we study how the magnitude of structures in the energy spectra associated with the excitation of giant resonances depend on the spreading widths of these modes.     

Determination of the average lifetime of bottom hadrons

We have determined the average lifetime of hadrons containing b quarks produced in e⁺e^? annihilation to be

$\text{τ}\text{B}\text{=}\text{1.83}\text{+0.83}\text{+0.37}\text{?}\text{?0.34}\text{×10}{}^{\mathrm{?12}}\text{s}$

. Our method uses charged decay products from both non-leptonic and semileptonic decay modes.     

Constraints on the decay rates of quarkonium

We derive inequalities between the leptonic decay rates of 1S and 2S states of quarkonium, when the binding potential is an increasing concave (convex) function of the inter-quark distance in a framework where some relativistic corrections have been made to the Van Royen-Weisskopf formula for these rates. Experimental decay rates of the γ and γ′ rule out the convex increasing potential.     

Inclusive electron production from heavy quarks in e+e− annihilation at 34.6 GeV center of mass energy

The production of electrons by bottom and charm hadrons has been studied in e⁺e^? annihilation at 34.6 GeV center of mass energy. It is observed that the b quark fragmentation function is peaked at large values of the scaling variable z with 〈z_b〉 = 0.84^{+0.15 + 0.15}_{?0.10 ? 0.11}. For c quarks 〈z_c〉 = 0.57^{+0.10 + 0.05}_{?0.09 ? 0.06} is observed. A forward-backward charge asymmetry of A = ?0.25 ± 0.22 was measured in b production.     

K0 production in e+e− annihilations at 30 GeV center of mass energy

Inclusive K⁰-production has been measured in e⁺e^- annihilation at a center of mass energy of about W = 30 GeV. The ratio of K⁰ + K⁰ production to μ⁺μ^- production is R_K0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than R_K0 at W = 7 GeV. The cross sections (s/β) dσ/dx is consistent with a scaling behaviour.     

Λ, Λ production in e+e− annihilation at 33 GeV centre of mass energy

Performing a PWA of the π^?π^?π⁺ system over the ^?tp/p range 0.2 to 0.4 GeV² we find evidence for a J^P = 0^? ,J^G=1^? meson of mass 1342 ± 20 MeV and width 220 ±70 MeV decaying into ?π. This state is produced by natural parity exchange with a slope similar to that of elastic scattering. It can be interpreted as a radial excitation of the π meson (π′).     

Jet flavor conversions in the quark-gluon plasma

A quark or gluon jet traversing through a quark-gluon plasma can be converted to a gluon or quark jet through scattering with the thermal quarks and gluons in the quark-gluon plasma. Their conversion rates due to two-body elastic and inelastic scattering have recently been evaluated in the lowest order in QCD. Including both energy loss and conversions of quark and gluon jets in the expanding quark-gluon plasma produced in relativistic heavy ion collisions, a net conversion of quark jets to gluon jets has been found. This reduces the difference between the nuclear modification factors for quark and gluon jets in heavy ion collisions and thus enhances the ratios of high transverse momentum protons and antiprotons to pions that are produced from the fragmentation of these jets. To account for the observed similar ratios in central Au + Au and p + p collisions at same energy requires, however, a much larger net quark to gluon jet conversion rate than that given by the lowest-order QCD, indicating the importance of higher-order processes and the strongly coupling properties of the quark-gluon plasma in describing the propagation of jets in the quark-gluon plasma. B.-W. Zhang: On leave from: Institute of Particle Physics, Huazhong Normal University, Wuhan 430079, China Correspondence: C.-M. Ko, Cyclotron Institute and Physics Department, Texas A&M University, College Station, TX 77843-3366, USA     

Experimental determination of the effective strong coupling constant

We present a first attempt to experimentally extract an effective strong coupling constant that we define to be a low Q²$Q^2$ extension of a previous definition by S. Brodsky et al. following an initial work of G. Grunberg. Using Jefferson Lab data and sum rules, we establish its Q²$Q^2$-behavior over the complete Q²$Q^2$-range. The result is compared to effective coupling constants inferred from different processes and to calculations based on Schwinger–Dyson equations, hadron spectroscopy or lattice QCD. Although the connection between the experimentally extracted effective coupling constants and the calculations is not established it is interesting to note that their behaviors are similar.     

On the model dependence of the determination of the strong coupling constant in second order QCD from e+e−-annihilation into hadrons

Hadronic events obtained with the CELLO detector at PETRA are compared with second order QCD predictions using different models for the fragmentation of quarks and gluons into hadrons. We find that the model dependence in the determination of the strong coupling constant persists when going from first to second order QCD calculations.     

Measurement of the ortho-para transition rate in the pμp molecule and deduction of the pseudoscalar coupling constant gpμ

The ortho-para transition rate in the pμp molecule has been found experimentally to be λ_OP = (4.1 ± 1.4) × 10⁴ s^?1. Our recent result for the muon capture rate in liquid hydrogen can now be interpreted to extract the ortho-molecular capture rate: λ_OM = (531 ± 33) s^?1. A deduction of the pseudoscalar coupling constant g_p^μ is presented: we find g_p^μ = 8.7 ± 1.9.     

An analysis of the charged and neutral energy flow in e+e− hadronic annihilation at 34 GeV,and a determination of the QCD effective coupling constant

Using both charged and neutral components, 2600 multihadronic e⁺e^? annihilation events, recorded at 34 GeV by the CELLO detector at PETRA, have been analysed in a calometric approach. The fraction of energy carried by gamma rays is measured to be f_γ = (26.0 ± 0.4 (stat) ± 4.0 (syst)%. The neutral energy flow is seen to follow closely the overall energy flow. From the corrected oblateness distribution, a first order determination of α_s is performed. The result is α_s = 0.16 ± 0.01 (stat) ± 0.03 (syst).     

Nonperturbative condensate contributions to the effective quark-gluon coupling

We study the effective quark-gluon coupling at low-energy scale, which is defined as the amplitude of a quark emitting or absorbing a gluon with some momentum at low-energy scale. This amplitude is determined from the fermionic three-point Green’s functions of QCD including the leading order contributions of nonperturbative condensates through use of the operator-product expansion. By this approach, we discuss the relationship between the constituent quark and the quark of QCD Lagrangian, and estimate the scale of chiral symmetry breaking and the size of a constituent quark in participating the strong interaction process, such as form factors and radii.     

Renormalization-scale independence of the physical cosmological constant

Treating the metric as a classical background field, we show that the cosmological constant does not run with the renormalization scale—contrary to some claims in the literature.     

Experimental verification of the dual unitarization scheme

The connection between particle production in antiproton-proton annihilation and non-diffractive proton-proton processes is discussed in the framework of the dual unitarization scheme. We calculate relative multiplicity moments for antiproton-proton annihilation using the moments of non-diffractive proton-proton interactions and find good agreement with experimental annihilation data.     

Experimental proof of the existence of the A1 meson

In partial wave analyses of the (π^?π^?π⁺) system, substantial shape changes of the 1⁺S (?π) intensity as a function of t, and relative phase changes of ≈ 90°, provide compelling evidence for a resonant A₁ of mass ≈ 1280 MeV and width ≈ 300 MeV.