Flavor changing neutral currents and multileptons in e+e- and vμN,vμN

New quarks and new flavor-changing neutral currents give multiple lepton plus hadron final states in e⁺e^-, $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$. We observe that (i) e⁺e^- is a favored place to search for their effects through inclusive ratios σ(e⁺e^-+x:σ (μ⁺μ^- +x): σ(e±μ±+x) and same sign leptons e±e±+x, μ±μ±+x,e±μ±+x. Above a new flavor threshold four charged lrpton final states may become important. (ii) Trilepton final states in $\text{v}{}_{\mathrm{\mu }}\text{N,}\text{v}{}_{\mathrm{\mu }}\text{N}$ are not sensitive to the presence of flavor-changing neutral currents. Much more sensitive are the processes $\text{v}{}_{\mathrm{\mu }}\text{N}$ are ⁺e^-+βand (for charm changing neutral currents) $\text{v}{}_{\mathrm{\mu }}\text{N→e}{}^{\mathrm{+}}\text{β}$.     

Rare decay modes of the K-mesons in the chiral lagrangian

The decays K_S → γγ, K_L → γγ and K_L → μ⁺μ⁻ are studied within the framework of chiral lagrangians. The one loop contribution to K_S → γγ turns out to be finite, giving an unambiguous prediction. The results also indicate that the long-distance dispersive part of K_L → μ⁺μ⁻ is the dominant one. As for K_L → γγ, a possible difficulty is pointed out with the recently published value ϑ ⋍ 20° for the η − η′ mixing angle.     

A determination of the total width of the ϒ(9.46) meson

Using the DASP detector at the DESY storage ring DORIS we have continued measuring e⁺e^? annihilations near and on the ?(9.46) resonance. From the cross sections for e⁺e^? → μ⁺μ^? and e⁺e^? → hadrons we obtain a μ⁺μ^? branching ratio for the ?(9.46) of (2.9 ± 1.3 ± 0.5) %, a leptonic width $\text{г}{}_{\mathrm{<mtext>ee</mtext>}}\text{= (1.35 ± 0.11 ± 0.22)}\text{keV}$ and a total width of (47_?15⁺³⁷ keV.     

Study of the process e + e − → π+π− in the energy region 400 < \sqrt s < 1000 MeV^\P

The cross section of the process e ⁺ e ^? → π⁺π^? was measured in the spherical neutral detector experiment at the VEPP-2M collider in the energy region $400 < \sqrt s < 1000 MeV$ . This measurement was based on about 12.4 × 10⁶ selected collinear events, which include 7.4 × 10⁶ e ⁺ e ^? → e ⁺ e ^?, 4.5 × 10⁶ e ⁺ e ^? → π⁺π^?, and 0.5 × 10⁶ e ⁺ e ^? → μ⁺μ^? selected events. The systematic uncertainty of cross section determination is 1.3%. The ρ-meson parameters were determined as m _ρ = 774.9±0.4±0.5 MeV, Γ _ρ = 146.5±0.8±1.5 MeV, and σ(ρ → π⁺π^?) = 1220 ± 7 ± 16 nb and the parameters of the G-parity suppressed decay ω → π⁺π^? as σ(ω → π⁺π^?) = 29.9 ± 1.4 ± 1.0 nb and φ_ρω = 113.5±1.3±1.7°.     

Positron production by muon neutrinos BEBC filled with a neon-hydrogen mixture

For e⁺ energy > 0.3 GeV and 10 GeV < visible energy < 100 GeV we find that: (i) $\text{? = (v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{e}{}^{\mathrm{+}}\text{)/(v}{}_{\mathrm{\mu }}\text{+}\text{Ne}\text{→ μ}{}^{\mathrm{?}}\text{) = (0.41 ± 0.15)\%}$; (ii) 1.2 ± 0.5 neutral strange particles are produced per μ^?e⁺ event; (iii) the lifetime of possible positron-parent particles is < 3 × 10^?10 s (90% C.L.); (iv) the cross section for direct e⁺ production via the neutral current is < 0.2 times that via the charged current (90% C.L.); (v) the cross section for producing heavy leptons, L⁺, decaying into e⁺ … is < 0.7 × 10^?3 times that for μ^?production, implying M(L⁺) > 10 GeV.     

Flavour-violating charged lepton decays in seesaw-type models

Analytic expressions of lepton-flavour- and lepton-number-violating decays of charged leptons are derived in the context of general SU(2)_L ⊗ U(1)_Y seesaw scenarios that are motivated by grand unified theories (GUT's) or superstring models, in which left-handed and/or right-handed neutral singlets are present. Possible constraints imposed by cosmology and low-energy data are briefly discussed. The violation of the decoupling theorem in flavour-dependent graphs due to the presence of heavy neutral leptons of Dirac or Majorana nature is emphasized. Numerical estimates reveal that the decays τ⁻ → e⁻ e⁻ e⁺or τ⁻ → e⁻ μ⁻ μ⁺ can be as large as ∼ 10⁻⁶, which may be observed in LEP experiments or other τ factories.     

On W±, Z0, γ self-interactions: High energy behaviour and tree unitarity bounds

We analyze the high-energy behaviour of vector boson scattering amplitudes within the framework of a recently suggested lagrangian model based on global weak isospin symmetry broken by electromagnetism. Requiring vanishing of the most strongly (as s²) rising contribution to vector boson scattering amplitudes leads to vector boson self-interactions dependent on a single parameter, for which the anomalous W^± magnetic moment, κ, can be chosen. Tree unitarity is violated at about 2 TeV for arbitrary κ as in the SU(2)_L × U(1)_Y theory for m_H → ∞. The model is well suited for significant tests of the vector boson sector of the SU(2)_L × U(1)_Y electroweak theory in processes such as e⁺e⁻ → W⁺W⁻.     

Observation of charmless B meson decays

Using the ARGUS detector at the e⁺e⁻ storage ring DORIS II, we have observed charmless decays of B mesons into the final states pp̄π^± and pp̄π⁺π⁻. The significance of the signal corresponds to more than five standard deviations. The branching ratios are (5.2±1.4±1.9)×10⁻⁴ for the three-body and (6.0±2.0±2.2)×10⁻⁴ for the four-body final state. These decays cannot proceed via the dominant b→c transitions, and we show that they are not the result of penguin-type processes. Thus, the observed decays must represent b→u quark transitions. Consequently, the Kobayashi-Maskawa matrix element V_ub is non-zero.     

Measurements of tau decay modes and a precise determination of the mass

The cross sections for e⁺e^? → e⁺(μ⁺ + non showering track + any photons have been measured for cm energies between 3.1 GeV and 5.2 GeV. We observe τ-pair production below the thresholdfor charm production and determine the τ mass to be 1.807 ± 0.020 GeV from a fit to the energy dependence of the cross section. The ration of the leptonic branching ratios B_μ/B_e = 0.92 ± 0.32 is consistent with eμ-universality. The following branching ratios are determined for a V-A coupling: $\text{B(τ → ν}{}_{\mathrm{\tau }}\text{e}\text{ν}\text{) = B(τ → ν}{}_{\mathrm{\tau }}\text{μ}\text{ν}\text{) = 0.182 + 0.028}$. B(τ → ν_τ + charged hadron + any photons) = 0.29 ± 0.11, B(τ → ν_τ + three or more charged hadrons + any photons) = 0.35 ± 0.11.     

A new measurement of the (K+ → e+v)(K+ → μ +v) branching ratio

The branching ratio $\text{R = Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{v)}\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→ μ}{}^{\mathrm{+}}\text{v)}$ has been measured with an improved version of the apparatus described elsewhere. From 404 observed K⁺ → e⁺v decays, R = (2.51 ± 0.15) × 10^?5 was obtained, to be compared with the value predicted for pure axialvector interaction and μ-e-universality, R_theor = 2.57 × 10^?5.     

Limits for short-lived neutral particles emitted in μ+ or π+ decay

In the data taken for the μ⁺ → e⁺e⁺e^- and π⁺ → e⁺νe⁺e^- experiments a search was made for neutral particles φ produced in the decay μ⁺ → e⁺φ or π⁺ → e⁺νφ with subsequent decay φ → e⁺e^-. No candidates were found, Upper limits for the branching ratios are given as a function of their masses and lifetimes. For lifetimes below 10⁻¹⁰ s limits down to 2 × 10⁻¹² are obtained.     

Measurement of the slope of the π0-electromagnetic form factor

Using a magnetic spectrometer, we have studied 30 000 π⁰ → e⁺e^?γ events coming from K_π2⁺ decays in flight. We find a positive value for the slope of the neutral-pion electromagnetic form factor: a = +0.10 ± 0.03 (or a = +0.05 ± 0.03 without radiative corrections). This value is higher than the predictions of vector meson models.     

Determination of the radiative widths of the η′ and A2 from two-photon exchange production

From the two-photon exchange processes e⁺e^? → e⁺e^?η' (958) → e⁺e^??⁰γ and e⁺e^? → e⁺e^?A₂ (1310) → e⁺e^?π⁺π^?π⁰ observed using the CELLO detector at PETRA the radiative widths of the η' and A₂ have been determined with the results: Γ_γγ(η') = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γ_γγ(A₂) = 0.59 ± 0.14[stat.] _?0.08^+0.31[syst.] keV.     

Four families of composite quarks and leptons

Four families of composite quarks and leptons, two standard and two non-standard, are found in a unique solution SU(3)_HC × SU(6)_L × SU(6)_R of a restricted 't Hooft anomaly-matching program. Testable predictions emerge, such as prohibition of μ → eγ, zero charge asymmetry in e⁺e^? → τ⁺τ^? in contrast to e⁺e^? → μ⁺μ^?, and a rich new hadron spectrum masses around M_W. A minimal set of spectator fermions contains color-singlet objects with fractional quark-like charges.     

Photo-Production of Muons

The total cross-section for the photo-production of muons in the reaction γ + e^? → μ^? + v_e + v_μ is calculated. The dependence of the total cross-section on the incident photon energy is explicitly shown.     

Measurement of e+e−→τ+τ− at high energy and properties of the τ lepton

The e⁺e^?→τ⁺τ^? process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R_τ=1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos²θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a_τ of the τ to the weak neutral current given by a_τ=?1.12 ± 0.57.     

A measurement of the reaction e+e- →e+e-η′ and the radiative width Γη′→γγ at petra

The reaction e⁺e^- → e⁺e^-η' has been observed in the JADE experiment at PETRA, by detecting the final state π⁺π^-γ, resulting from the decay η' → γ?⁰. The cross section was measured at an average beam energy of 17.15 GeV to be σ(e⁺e^- → e⁺e^-η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ_η'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.     

Measurement of η' → π+π−γ in γγ collisions

The production of the pseudoscalar meson η'(958) is observed in the reaction e⁺e−→ e⁺e⁻η′→e⁺e⁻π⁺π⁻γ with the ARGUS detector at DESY. We measure the product Γ_γγ(η')Br(η′ →ϱγ) to be 1.13±0.04±0.13 keV. Using the known branching ratio s, we calculate Γ_γγ(η′) to be 3.76±0.13±0.47 keV and Γ_η' to be 203±32 keV.     

Determination of the kinetic parameters of the isomerization reaction of ethyl isocyanide using HeI photoelectron spectroscopy

The use of HeI photoelectron spectroscopy (PES) for the kinetic study of chemical reactions was introduced previously by us. As another example of the determination of the kinetic parameters of a chemical reaction using the PES method, the isomerization reaction of ethyl isocyanide CH₃CH₂NC → CH₃CH₂CN is investigated. It is found to be first order and the kinetic equations at 193.6, 200.0 and 210.3°C can be expressed as ln R_{466.6 K} = − (7.600 ± 0.026) × 10⁻⁵t − 0.4350; ln R_{473.0 K} = − (1.329 ± 0.032) × 10⁻⁴ − 0.4375 and ln R_{483.3 K} = − (3.170 ± 0.052) × 10⁻⁴ − 0.4354, respectively. The rate constants of the reactions at 193.6, 200.0 reactions at 193.6, 200.0 and 210.3°C are respectively (7.600 ± 0.026) × 10⁻⁵, (1.329 ± 0.032) × 10⁻⁴ and (3.170 ± 0.052) × 10⁻⁴ s⁻¹. The calculated activation energy (E_a) of this isomerization reaction is 38.36 ± 0.32 kcal mol⁻¹. These results are also in excellent agreement with the results obtained by a traditional method. This means that PES is a valuable method for determining the kinetic parameters of chemical reactions. The value of the intercept in the kinetic equations is related to the logarithm of the ratio of the photoionization cross-section of the bands used. This also means that the relative photoionization cross-sections of the bands used for the sample studied are obtained in the kinetic study of a chemical reaction using the PES method.     

Finite corrections to quark fragmentation functions in perturbative QCD

The finite corrections of order α _s in perturbative QCD to the cross-sections for semi-inclusive hadron production from deep inelastic leptonhadron scattering and electron-positron annihilation are calculated. We define the effective quark fragmentation functions viae ⁺ e ^? → hadron +X including the finite terms in order to estimate these corrections for the reactions lepton + hadron → lepton + hadron + anything. Contrary to the leading term the next-to-leading order term does not factorize into parts depending on the target and the fragment, respectively. For the processese +p →e + π^± +X andv +p →μ ^? + π^± +X the finite corrections of order α _s turn out to be at most 20% in the range of momenta covered by present experiments.