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1.
New quarks and new flavor-changing neutral currents give multiple lepton plus hadron final states in e+e-, vμN, vμN. 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 vμN, vμN are not sensitive to the presence of flavor-changing neutral currents. Much more sensitive are the processes vμN are +e-+βand (for charm changing neutral currents) vμN→e+β.  相似文献   

2.
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 гee = (1.35 ± 0.11 ± 0.22) keV and a total width of (47?15+37 keV.  相似文献   

3.
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 φρω = 113.5±1.3±1.7°.  相似文献   

4.
《Nuclear Physics B》1995,437(3):491-519
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 τe e e+or τe μ μ+ can be as large as ∼ 10−6, which may be observed in LEP experiments or other τ factories.  相似文献   

5.
For e+ energy > 0.3 GeV and 10 GeV < visible energy < 100 GeV we find that: (i) ? = (vμ + Ne → μ?e+)/(vμ + Ne → μ?) = (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.  相似文献   

6.
《Nuclear Physics B》1988,299(1):7-20
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 mH → ∞. 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.  相似文献   

7.
《Physics letters. [Part B]》1988,209(1):119-126
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 Vub is non-zero.  相似文献   

8.
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 Bμ/Be = 0.92 ± 0.32 is consistent with eμ-universality. The following branching ratios are determined for a V-A coupling: B(τ → ντeν) = B(τ → ντμν) = 0.182 + 0.028. B(τντ + charged hadron + any photons) = 0.29 ± 0.11, B(τντ + three or more charged hadrons + any photons) = 0.35 ± 0.11.  相似文献   

9.
The branching ratio R = Γ(K+e+v)Γ(K+ → μ+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, Rtheor = 2.57 × 10?5.  相似文献   

10.
Using a magnetic spectrometer, we have studied 30 000 π0 → e+e?γ events coming from Kπ2+ 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.  相似文献   

11.
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: Γγγ(η') = 5.4 ± 1.0[stat.] ± 0.7[syst.] keV; Γγγ(A2) = 0.59 ± 0.14[stat.] ?0.08+0.31[syst.] keV.  相似文献   

12.
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 MW. A minimal set of spectator fermions contains color-singlet objects with fractional quark-like charges.  相似文献   

13.
The total cross-section for the photo-production of muons in the reaction γ + e? → μ? + ve + vμ is calculated. The dependence of the total cross-section on the incident photon energy is explicitly shown.  相似文献   

14.
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 Γη'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.  相似文献   

15.
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 Rτ=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 aτ of the τ to the weak neutral current given by aτ=?1.12 ± 0.57.  相似文献   

16.
《Physics letters. [Part B]》1987,199(3):457-461
The production of the pseudoscalar meson η'(958) is observed in the reaction e+e−→ e+eη′→e+eπ+πγ with the ARGUS detector at DESY. We measure the product Γγγ(η')Br(η′ →ϱγ) to be 1.13±0.04±0.13 keV. Using the known branching ratio s, we calculate Γγγ(η′) to be 3.76±0.13±0.47 keV and Γη' to be 203±32 keV.  相似文献   

17.
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 +pe + π± +X andv +pμ ? + 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.  相似文献   

18.
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 R466.6 K = − (7.600 ± 0.026) × 10−5t − 0.4350; ln R473.0 K = − (1.329 ± 0.032) × 10−4 − 0.4375 and ln R483.3 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 (Ea) 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.  相似文献   

19.
In film taken with BEBC filled with a Ne(74%mol)/H2 mixture and exposed to the CERN narrow-band neutrino beam (200 GeV), tenμ?μ+, one μ?μ+μ?and five μ?e+ events were found in the ν exposure and two μ+μ? events and one μ+e? event in the ν exposure. Assuming the same production mechanism for μμ and μe events, the relative rates, corrected for identification inefficiency and background, can be combined and are (1.3 ± 0.4)% for (μ?e+ + μ?μ+)/μ? in neutrino interactions, and (1.2 ± 0.5)% for (μ+e? + μ+μ?)/μ+ antineutrino interactions. Eight out of the sixteen μ??+ events have a V0, leading to a corrected K0-multiplicity of 1.7 ± 0.7. No evidence is found for heavy-lepton production.  相似文献   

20.
王青德  陆埮 《物理学报》1985,34(7):892-900
本文主要讨论了中子星内部发生从正常中子物态到π凝聚物态相变所产生的星体振动的阻尼,由弱作用反应u(p1)→u(p2)+e-+ve和u(p1)+e-→u(p2)+ve算出振动阻尼时标,并考虑了中子星内部的热演化。 关键词:  相似文献   

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