CP violation andZ boson decays

We present a general discussion ofCP-violating effects in the following two and three body decays of theZ boson:Z→l ⁺ l ^?,Z→l ⁺ l ^?γ, wherel=e, μ, τ andZ→2 jets,Z→ 2 jets+γ, andZ→ 3 jets. Experimental observables sensitive toCP violation in these decays are discussed systematically for the case that polarizations of final state particles are not observed. It is shown that the standard model predicts only extremely smallCP-violating effects for the above decays. PossibleCP-violating interactions beyond the standard model are parametrized in terms of aCP-odd effective Lagrangian containing coupling constants proportional to Λ _P ^-1 and Λ _P ^-2 . Here Λ _CP is the mass scale associated with the assumed new interactions. We give estimates of the bounds obtainable for Λ _CP in experiments at LEP1.     

Probing the weak boson sector inγe→Ze

We study possible deviations from the Standard Model in the reactionγe→Ze at a 500 GeVe ⁺ e ^? collider. As a photon source we use a laser backscattered photon beam. We investigate the most generalγZγ andγZZ vertices including operators up to energy-dimension-six which are Lorentz invariant. These vertices require four extra parameters; two are CP-conserving,h ₁ ^γ andh ₁ ^Z , and two are CP-violating,h ₂ ^γ andh ₂ ^Z . We present analytical expressions of the helicity amplitudes for the processγe→Ze for arbitrary values of anomalous couplings. Assuming Standard Model values are actually measured we present the allowed region in the (h ₁ ^γ ,h ₁ ^Z ) plane at the 90% confidence level. We then show how the angular correlation of theZ decay products can be used to extract detailed information on the anomalous (especially CP-violating)γZγ andγZZ couplings.     

Angular distributions of dileptons in polarized hadronic collisions: Test of electroweak gauge models

The angular distributions of high-mass dileptons with large transverse momentum produced in longitudinally polarized hadronic collisions, hadron +hadron→(γ^*,Z ₁ ⁰ ,Z ₂ ⁰ , ...)+X→l ⁺ l ^?+X, are calculated in the QCD lowest order. The formulas presented in general form, are applicable to any gauge model of underlying electroweak interactions. Numerical results are obtained for the angular distributions in \(\bar p\) p-collisions at \(\sqrt s = 540GeV\) for the Weinberg-Salam,SU(2)×U(1)×U(1)′ andSU(2)×SU(2)′×U(1) models. Clearly distinguishable signals are revealed.     

E2 andE3 transition strengths in some rare-earth nuclei

Coulomb excitation byα-particles of vibrational-like states in even-mass rare-earth nuclei is used to determine the reduced transition probabilitiesB(E2; 0 _gs ⁺ →2 _γ ⁺ ),B(E2; 0 _gs ⁺ →2 _β ⁺ ),B(E2; 2 _gs ⁺ →0 _β ⁺ ) andB(E2; 0 _gs ⁺ →3 _oct ^? ) in¹⁵⁰Nd,^{152, 154}Sm,^{154, 158}Gd,¹⁶⁴Dy and¹⁶⁶Er. TheB(Eλ; 0 _gs ⁺ →I=λ)-values range from 2.4 to 6.5 single-particle units for transitions to the 2 _γ ⁺ -states, 0.8 single-particle units for the 2 _β ⁺ -states and from 14.1 to 21.7 single-particle units for the 3^?-states.     

e + e −-Annihilation with polarized beams in the standard model and extended electroweak gauge models

We derive the general expressions for the differential cross section and final state polarization ine ⁺ e ^?→γ,Z ₁ ⁰ ,Z ₂ ⁰ , ...→ff (f: leptons and quarks) with several neutral bosons and with polarized beams. From this also the jet axis distributions ine ⁺ e ^? → 2 jets are obtained. The general formulas are applied to the standard model and extended gauge models of electroweak interactions with one neutral boson lighter than the standard modelZ ⁰. The models differ from each other in the coefficients of angular distributions at energies around the firstZ ⁰ resonance and beyond. Observable effects are expected in certain models already at energies up to 60 GeV if the firstZ ⁰ is not too heavy.     

Weak contributions to angular asymmetries ine + e − annihilation

We study the energy and polarization dependence of angular asymmetries ine ^? e ⁺→ψ,Z ⁰→f \(\bar f\) (f=lepton or quark). Through the fragmentation of the quarks the corresponding asymmetries are obtained for the jet axis ine ^? e ⁺→ψ,Z ⁰→(Σq \(\bar q\) )→2 jets, and for inclusively produced hadronsh(h=π⁺,K ⁺ and π⁺ +K ⁺) ine ^? e ⁺→ψ,Z ⁰→(Σq \(\bar q\) )→(h+X)_2jet. In the Weinberg-Salam model these asymmetries come out big enough to show up already at upper PETRA and PEP energies.     

Probing QCD via four-jet decays of theZ boson

For a quantitative analysis of the non-Abelian three-gluon vertex a continuous parameterisation of possible deviations from QCD is highly desirable. An almost unique extension of the three-gluon vertex is provided by the dimension-6 operator Tr(F _μ ^ν F _ν ^ρ F _ρ ^μ ). The effects of this interaction term on various observables ine ⁺ e ^?→γ,Z→4 jet production are studied in detail. Presente ⁺ e ^? data are expected to give rather weak bounds on such anomalous contributions to the triple gluon vertex.     

Nonfactorization and the decaysD s +→φπ +,φρ + andφl + ν l

Using the experimentally measured values ofx=A ₂(0)/A ₁(0) andy=V(0)/A ₁(0) and the measured ratiosR _st=Γ(D _s ⁺ →φl ⁺ ν _l)/Γ(D _ins ⁺ →φπ ⁺) andR _h=Γ(D _s ⁺ →φρ ⁺)/Γ(D _s ⁺ →φπ ⁺), we present evidence for significant nonfactorization contribution in the decay amplitude forD _s ⁺ →φπ ⁺. We analyze the role of nonfactorization inD _s ⁺ →φρ ⁺ and conclude that present data onR _h are consistent with factorization inD _s ⁺ →φρ ⁺. A measurement of polarization inD _s ⁺ →φρ ⁺ would greatly assist our analysis.     

Polarized bhabha scattering in multiboson electroweak gauge models

The general expression for the differential cross section of the reactione ⁺ e ^?→γ,Z ₁ ⁰ ,Z ₂ ⁰ , ..., →e ⁺ e ^? with an arbitrary initial polarization state is derived in the context of electroweak gauge models with more than one neutral boson. Angular distributions, azimuthal asymmetries in the case of natural polarization, and longitudinal polarization asymmetries for models of the typeSU(2)×U(1)×G (G=?(1),S?(2)) and left-right symmetric models are compared with the standard model results. For the angular distributions withe ^± having equal helicities a～10% deviation from the standard model is predicted already below 50 GeV for models of the first type withZ ₁ ⁰ masses up to 80 GeV. At energies around the firstZ ₁ ⁰ a study of azimuthal and polarization asymmetries yields the possibility of distinguishing between different models.     

Anomalous magnetic moment of theW-bosons and non-standardZ 0 W + W − coupling in polarizede − e + collisions

We study quantitatively the reactions \(e^ + e^ - \to W^ + e\bar \nu _e \) ,e _R ^? e ⁺ and the rare decay \(Z^0 \to W^ \pm l^ \mp \mathop {\nu _e }\limits^{( - )} \) forl=e, μ and τ, as a test for anomalous γW ⁺ W ^? andZ ⁰ W ⁺ W ^? structure. If κ denotes the anomalous magnetic moment of theW-boson and ω its anomalous coupling to theZ ⁰, values of |ω|>2.5 and |κ|>1.5 can be ruled out at LEP and SLC rather easily. This will put constraints on composite model building.     

Z 0 decay and electron positron annihilation into three gluons

After pointing out that the two-gluon decay mode of theZ ⁰ vanishes, we calculate, in detail, the differential and the total decay rates forZ ⁰→ggg. Using the standard Glashow-Weinberg-Salam model and Quantum Chromodynamics, we find a branching ratio of 1.8×10^?5. We also discussZ→ggγ andZ ⁰→γγγ. As a natural extension of this work, we present the details of a calculation of the differential and the total cross sections for the processe ⁺ e ^?→ggg mediated by a virtual photon in the continuum. A detailed comparison with \(e^ + e^ - \to q\bar qg\) and a brief discussion ofe ⁺ e ^?→ggγ ande ⁺ e ^?→γγγ are also given.     

Measuring theWW γ vertex in the processep→γϑX

We present a detailed analysis of the processep→γ?X as a means of studying the gauge structure of theWWγ vertex. We find that the differential cross section of highp _T photons offers a sensitive measure of anomalousWWγ couplings. At HERA \((\sqrt s = 314GeV)\) , after several years of running, theWWγ vertex can be measured to δκ_γ ? _?2.0 ^+2.9 and δλ_γ ? _?2.5 ^+3.0 (95% C.L.). Which offers an improvement over existing constraints from direct measurements using associatedWγ production in \(\bar pp\) collisions but is less sensitive than the competing process at HERA,ep→eWX. For a higher energyep collider, LEP-LHC \((\sqrt s = 1.3TeV)\) , theWWγ vertex can be measured to δδκ_γ ? ± 0.4 and δλκ_γ ? ± 0.1 at 95%C.L. which is more sensitive to λ_γ than the processe ⁺ e ^?→W ⁺ W ^? at the LEP200e ⁺ e ^? collider and is comparable to the LEP200 sensitivity to κ_γ. These values are also roughly comparable to the competing processep→eWX at LEP-LHC and to what is expected from associated γW production at the LHC and SSC for κ_γ but they are about half as sensitive to λ_γ as the LHC and SSC.     

Spinless bosons in electron-positron annihilation

The contributions to the processes \(e^ + e^ - \to \mu ^ + \mu ^ - ,q\bar q,\gamma \gamma ,e^ + e^ - \) , mediated by scalar and/or pseudoscalar bosons are calculated. The constraints on their coupling constants and their masses are investigated as they arise from the radiative decayZ ⁰→⁺ e ^? γ and from the experimental data for the annihilation processes into lepton, photon and quark pairs. Data one ⁺ e ^?→μ⁺ μ^?, γγ ande ⁺ e ^? seriously reduce the domain of coupling constants to leptons and photons still allowed by the probable value of the width ofZ ⁰→e ⁺ e ^? γ. Experimentse ⁺ e ^?→μ⁺ μ^?, γγ,e ⁺ e ^? at 45 GeV c.m.s. energy with a sensitivity of 10% will decide about the existence of a heavy spinless boson with the presumed phenomenological couplings to leptons and photons. Assuming universality of the coupling to leptons and quarks a conservative bound on the contribution toR arising from spinless boson exchange is already in conflict with the presumed radiative width ofZ ⁰→e ⁺ e ^? γ.     

Comparison ofW ±+jet andZ 0+jet production at hadron colliders

We analyse the lowest-order QCD production mechanisms forp \(\bar p\) →W ^±+jet andp \(\bar p\) →Z ⁰+jet to find possible differences in jet properties for the two processes.     

The quadrupole momentQ 2+ of32S

The static quadrupole moment of the first excited 2⁺ state in³²S was determined by comparing, in coincidence with³²S ions backscattered from⁶⁰Ni, the gamma-ray yields of the 2 ₁ ⁺ →0 ₁ ⁺ transitions in both nuclei for bombarding energies around 70MeV. Depending on the sign of the interference term for transitions via the second excited 2⁺ state in³²S, the following two values were determined:Q ₂ ⁺ =(?18±4)e·fm² andQ ₂₊=(?15±4)e·fm².     

Untersuchung des Zerfalls von134Cs durch γ-γ-Winkelkorrelationsmessungen

γ-γ-angular correlation measurements with Ge(Li) detectors and NaJ(Tl) detectors provided theE2/M1 mixing ratios of the following gamma transitions: 3 ₁ ⁺ →2 ₂ ⁺ (475.3 keV), 2 ₂ ⁺ →2 ₁ ⁺ (563.3 keV), 4 ₂ ⁺ →4 ₁ ⁺ (569.4 keV), 3 ₁ ⁺ →2 ₁ ⁺ (1,039 keV). The angular correlation measurements were only consistent with spin 3 of the 1,643 keV level. The half life of the 1,401 keV level was determined by delayed coincidence techniques to beT _1/2 (1,401 keV)≦30 ps.     

A coupled-channel treatment of Cabibbo-angle favoured (D,D s + )→VP decays

We have performed a two-channel calculation of Cabibbo-angle favoured decays,D _s ⁺ →VP. We find a satisfactory fit toS _s ⁺ →φπ ⁺,ρ ⁰ π ⁺ andK ⁺ \(\bar K^{ * 0} \) data from ARGUS and E-691. We have also studied Cabbibo-angle favouredD→VP decays in a coupled channel formalism. We coupleD→K ^*π,K _? and \(\bar K^0 \phi \) channels inI=1/2 state, andK ^*π andK _? channels inI=3/2 state. We leave the two channels, \(\bar K^0 \omega \) and \(\bar K^{ * 0} \eta \) out of our unitarization scheme. Particular attention is paid to the role of the weak annihilation term in these decays.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

Q^2 \to A\sqrt s Scaling law fore + e −→hadrons andpp collisions at high energy

It has been conjectured recently that multiparticle production in low momentum transfer hadronic collisions is due to gluon bremsstrahlung off highly virtual (mass \(\mu ^2 \sim \sqrt s \) ) quarks. The model gives a new scaling law: \(Q^2 \to A\sqrt s \) , for comparinge ⁺ e ^?→hadrons andpp non-diffractive inelastic data. The scaling law is tested for average multiplicities, plateau height and 〈p ₂ ^⊥ 〉. Fore ⁺ e ^? annihilation a parametrization of data based on perturbative QCD approach is used.