Lepton flavor violation: Constraints from the exotic μ−-eμ− conversion

The exotic neutrinoless μ^? → e ^? conversion is studied within conventional extensions of the standard model as well as in minimal supersymmetric models with R-parity-conserving and R-parity-violating mechanisms. The dependence on the nucleon and nuclear structure of the μ-e conversion rates is consistently taken into account. From the available experimental data on the branching ratio $R_{\mu e^ - }$ for the currently interesting nuclei ⁴⁸Ti and ²⁰⁸Pb, and from the experimental sensitivity for ²⁷Al, which has been employed as a target in MECO experiment at Brookhaven, we extract very severe constraints for the flavor violation parameters with our calculated transition matrix elements. We especially emphasize the constraints resulting for SUSY R-parity-violating parameters.     

Muon decay in orbit spectra for μ???e conversion experiments

In mixed-valence manganites, the doped iron species play the roles of simultaneous probes and ruiners for the orbital order occurring in the Mn-O electronic subsystem. We investigated the Mn^3?+?-based undoped system RBaMn₂O_5.5 and the half-doped systems RBaMn₂O₆, and RBaMn₂O₅ substituting a tiny portion of Mn^3?+? sites with Fe^3?+?. Single-site M?ssbauer spectra were observed at room temperature in the charge-orbitally ordered state, i.e., below T_COO, for R=Y, Sm, Gd. Size of the rare earth ion strongly influences the quadrupole splitting in RBaMn₂O₆, but not in RBaMn₂O₅.     

Nuclear matrix elements for the coherent μ-e conversion process

The lepton flavor-violating coherent (μ⁻, e⁻) conversion is investigated. Photonic and nonphotonic contributions arising in various gauge models are considered. The dependence of the conversion rate on the structure of the nucleus is given by the elastic form factors. These are obtained in the context of shell model taking into account finite-size effects or extracted from the electron scattering data whenever possible. The relevant branching ratios are studied throughout the periodic table.     

Signal for intermittency in e+e− reactions obtained from negative binomial fits

With a simple relation between the parameter k of the negative binomial distribution and the factorial moments 〈Fⁱ〉 we reanalyse published data from e⁺e⁻ reactions at √s=29 GeV on multiplicity distributions in rapidity bins to show that there is a significant rise of the 〈Fⁱ〉 with decreasing bin size δy along the thrust axis. The rise for δy<1 can be regarded as a signal for intermittency. For further discussion we compare the data with the Lund shower Monte Carlo. We suggest a direct measurement of factorial moments in e⁺e⁻ jets.     

e + e − multiplicity distribution from branching process

We present a multiplicity distribution which is a solution to the stochastic branching equation proposed by Giovannini. This solution is more commonly known as generalized multiplicities distribution (GMD) and has already been successfully applied to bothpp andp collisions. It assumes that shapes and energy dependence of distributions are basically determined by hard parton scattering and subsequent branching. We apply GMD to the recente ⁺ e ^– data by Tasso Collaboration.     

Noise conversion from pump to the passively mode-locked fiber lasers at 1.5 μm

We characterize the noise conversion from the pump relative intensity noise (RIN) to the RIN and phase noise of passively mode-locked lasers at 1.5 μm. Two mode locking mechanisms, nonlinear polarization rotation (NPR) and semiconductor saturable absorber mirror (SESAM), are compared for noise conversion for the first time. It is found that the RIN and the phase noise of both types of lasers are dominated by the noise converted from the pump RIN and thus, can be predicted with the measured pump RIN and noise conversion ratios. The SESAM laser is found to show an excess noise conversion from the laser RIN to the laser phase noise due to the slow saturable absorber effect.     

Search for the e + e − → K ± K S π ∓ process on the VEPP-2M e + e − collider

We report on the results of the search for the e ⁺ e ^? → K ^± K _S π ^? process. Data with an integrated luminosity of 1.36 pb^?1 collected in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider in the energy range from 1.36 to 1.38 GeV have been analyzed. The upper limits of the σ < 150 pb cross sections of the sought process have been established for an energy of 1.37 GeV at a confidence level of 90%.     

Annihilation mechanisms of e+e− and μ+μ− production in relativistic nuclear collisions

We revise the μ⁺μ^? and $q\bar q$ annihilation mechanisms of dilepton production during relativistic nuclear collisions. We focus on the modifications caused by the specific features of in-medium pion and quark states rather than by medium modification of the ρ-meson spectral density. The main ingreditent emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, “connects” the total 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the lepton pair production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.     

Study of conversion decays φ→ηe+e− and η→γe+e− in the experiment with SND detector at VEPP-2M collider

The conversion decays φ→ηe⁺e⁻ and η→γe⁺e⁻ were studied by the SND detector using φ-meson production in e⁺e⁻-annihilation at VEPP-2M collider. The branching ratios of these decays were measured: Br(φ→ηe⁺e⁻)=(1.19±0.19±0.07)×10⁻⁴ and Br(η→γe⁺e⁻)=(5.15±0.62±0.39)×10⁻³. The e⁺e⁻-pair mass spectra and transition form factors were also studied.     

Deduction of the quantum numbers of low-lying states of the (e+e+e−e−) system from symmetry consideration

The features of the low-lying spectrum and the complete set of quantum numbers of each of the low-lying states of a (e⁺e⁺e⁻e⁻) system have been deduced based on symmetry.     

P-invariance violation in the electrosplitting of6Li∶e− +6Li→e−+D+4He

P-odd polarization phenomena near the threshold of the reaction e^– +⁶Li e^– + D +⁴He, due to the P-odd nuclear forces, are studied in general. The analysis is performed in terms of structure functions and threshold electromagnetic form-factors.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 37–41, May, 1990.     

The reaction e− + p → Λ + ν and the contributions of the individual form factors to the differential cross section

We calculate the differential cross section for the weak, strangeness changing, electron scattering process, e⁻ + p → Λ + ν, for incoming electron energies of 0.5, 1.0, 2.0, 4.0, and 6.0 GeV. We obtain as well contributions of the individual form factors to the differential cross sections. We find that the differential cross sections peak as the maximal scattering angle for the Λ is approached and that the peak height increases as the electron energy is increased. The behavior of the differential cross section near the maximal angle is discussed as is the possibility of observing this reaction in a facility such as TJNAF.     

Tests for planar events in e+e− annihilation

We present a new class of observables which distinguish events containing two or three hadron jets from those containing a larger number. These observables, which essentially measure the coplanary of events, are calculable in QCD perturbation theory. Their use should allow the mechanism of

decay to be determined.     

e+ e− production from pp reactions at BEVALAC energies

We have performed a detailed study of dilepton production from pp collisions including the subthreshold ϱ production via baryonic resonances (N(1520), N(1700)) in addition to the conventional dilepton sources as π⁰, η, ω and Δ Dalitz decays and direct decays of vector mesons (ϱ, ω). The role of baryonic resonances in ϱ production from nucleon-nucleon collisions is studied in comparison to the DLS data which are well described.     

Possibility of distinguishing the contribution of neutral weak currents in e+e− → μ−μ+ experiments with transverse-polarized clashing beams

The process e⁺+e^{– –}+ ⁺ is studied on the basis of several models: the Weinberg- Salam model, the Lee-Prentki-Zumino model, the vector model, the X model, and under the assumption of a V-A structure of the neutral weak currents. Arbitrary polarizations of all the particles are taken into account simultaneously. Polarization effects are analyzed in detail for the case of transverse-polarized clashing beams, and various possibilities for distinguishing the contribution of neutral weak currents are identified. This possibility is very important not only for obtaining information about the structure of these currents but also for experimentally determining the sign of the weak-interaction constant. Calculations show that the neutral weak currents lead to significant polarization effects at attainable energies. These effects are very sensitive to the model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 22–27, April, 1978.The authors thank A. A. Sokolov for interest and a useful discussion.     

Searches for electroweak γ-Z-Z’ interference at the LEP2 e + e − collider

Indirect effects of the Z’ boson in the process e ⁺ e ^? → μ⁺μ^? as implemented at the LEP2 electron-positron collider are investigated in terms of new integrated observables σ^±. It is demonstrated that these observables furnish more definitive information about Z’-boson effects than the canonical observables σ_± and A _FB. It is established that the deviations Δσ^± induced by Z’ bosons show a specific energy dependence, which is determined primarily by the parameters of the Standard Model. This permits making unambiguous model-independent predictions. In particular, two points, $\sqrt {s_ + } \approx 78GeV$ and $\sqrt {s_ - } \approx 113GeV$ , are determined at which, respectively, σ₊ and σ_? vanish both in the Standard Model and in presence of the extra Z’ boson. These energy values can be of use in searches for phenomenological manifestations of alternative sources of new physics that are different from Z’.     

Possibility of distinguishing the effect of neutral weak currents in e+e− → μ−μ+ experiments with longitudinally polarized clashing beams

The process e⁺e^{– – +} for the case of longitudinal polarization of the initial and final particles is studied on the basis of several models: the Weinberg-Salam model, the Lee-Prentki-Zumino model, the vector model, the X model, and under the assumption of a V-A structure of the neutral weak currents. Polarization effects tn the differential and total cross sections for this process are analyzed in detail, and various possibilities for distinguishing the contribution of neutral weak currents are found. Calculations show that neutral weak currents lead to appreciable polarization effects at attainable energies and that these effects are very sensitive to the model. It is important to note that an experimental study of these effects can yield valuable information on not only the structure of the neutral weak currents but also the sign of the weak-interaction constant.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 31–36, April, 1978.The authors thank A. A. Sokolov for a useful discussion and for interest in this work.     

Measurement of the strong coupling α S from the three-jet rate in e+e−-annihilation using JADE data

We present a measurement of the strong coupling α _S using the three-jet rate measured with the Durham algorithm in $\mathrm{e^{+}e^{-}}$ -annihilation using data of the JADE experiment at centre-of-mass energies between 14 and 44 GeV. Recent theoretical improvements provide predictions of the three-jet rate in $\mathrm{e^{+}e^{-}}$ -annihilation at next-to-next-to-leading order. In this paper a measurement of the three-jet rate is used to determine the strong coupling α _S from a comparison to next-to-next-to-leading order predictions matched with next-to-leading logarithmic approximations and yields a value for the strong coupling consistent with the world average.