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.     

Effect of weak neutral currents in the process e− + p → e− + γ + X

Polarization effects in the inclusive process e^– + p e^– + + X due to the neutral current are studied in the framework of the Weinberg-Salam model. Expressions for the asymmetry parameters and the degree of circular polarization of the photons are obtained in the quark-parton picture. It is shown that measurement of such quantities gives additional information about the quark structure of the hadronic weak neutral current.Paper presented at the scientific session of the nuclear physics branch, USSR Academy of Sciences and the Moscow State University on Electromagnetic and Weak Interactions (Moscow, January 16–20, 1979).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 96–99, January, 1981.     

Forward circularly polarized photon emission in longitudinally polarized e+e− collisions

We discuss the emission of circularly polarized forward photons in high energy e⁺e⁻ collisions with longitudinally polarized beams. We find substantial asymmetry under inversion of longitudinal electron polarization, thus supporting the proposal that measurement of circular polarization of forward emitted photons may allow for monitoring of longitudinal beam polarization.     

Physics opportunities with polarized e − and e + beams at TESLA

Beam polarization at e⁺-e^– linear colliders will be a powerful tool for high precision analyses. Often it is assumed that the full information from polarization effects is provided by polarization of the electron beam and no further information can be obtained by the simultaneous polarization of the positrons. In this paper we point out the advantages of polarizing both beams, and summarize the polarization-related results of the Higgs, Electroweak, QCD, SUSY and Alternative Theories working groups of the ECFA/DESY workshop for a planned linear collider operating in the energy range s = 500-800 GeV.     

Vector boson pair production in e−e− collisions with polarized beams

The W-boson pair production in e⁻e⁻ collisions with polarized beams is investigated. The helicity amplitudes are derived for general couplings and the conditions for a good high-energy behaviour of the cross-section are given. The results are applied to the heavy vector boson production in the context of the left-right symmetric model. The Ward identities and the equivalence theorem are also discussed.     

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.     

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.     

Production of polarized baryons in polarized and unpolarizede + e − collisions

Polarized and unpolarizede ⁺ e ^? annihilation is considered in lowest order at energies 30–150 GeV taking γ andZ ⁰ exchange in the standardSU(2)×U(1) model into account. The fragmentation of polarized quarks into polarized baryons is described by two kinds of fragmentation functions; the first is based onSU(6) weights and empirical expressions for favoured and disfavoured fragmentation; the second is based upon a Monte Carlo model of the chain decay including helicities of quarks and hadrons. From the cross sections for \(e^ + e^ - \to q\bar q\) and the fragmentation functions we obtain predictions for the baryon polarization as function of the collision energy and of kinematical variables.     

Energy spectra and energy correlations in the decayH→ZZ→μ+μ−μ+μ−

It is shown that in the sequential decay $H \to ZZ \to (f_1 \bar f_1 ) + (f_2 \bar f_2 )$ , the energy distribution of the final state particles provides a simple and powerful test of theHZZ vertex. For a standard Higgs boson, the energy spectrum of any final fermion, in the rest frame ofH, is predicted to be dΓ/dx～1+β⁴?2(x?1)², with $\beta = \sqrt {1 - 4m_Z^2 /m_H^2 } $ and 1?β≤x=4E/m _H ≤1+β. By contrast, the spectrum for a pseudoscalar Higgs is dΓ/dx～β²+(x?1)². There are characteristic energy correlations betweenf ₁ andf ₂ and betweenf ₁ andf ₂. These considerations are applied to the “gold-plated” reactionH→ZZ→μ⁺μ^?μ⁺μ^?, including possible effects ofCP-violation in theHZZ coupling. Our formalism also yields the energy spectra and correlations of leptons in the decay $H \to W^ + W^ - \to l^ + v_l l^ - \bar v_l $ .     

Unique R-parity violating sneutrino exchange signatures at e + e − linear colliders with polarized beams

We examine the possibility of uniquely identifying the indirect effects of s-channel R-parity violation sneutrino exchange against other kinds of new physics that can be parametrized by the four-fermion contact interactions, by means of double polarization asymmetry at the International Liner Collider with both e ⁺ e ^? beams being polarized.     

Measurement of the forward-backward asymmetry of μ+μ− pairs in CMS

The measurement of the forward-backward asymmetry A _FB and the effective weak mixing angle with the Drell-Yan process at the LHC is presented. The samples of 2011 collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 5 fb^?1 and 1.1 fb^?1, were used. The results are consistent with the standard model expectations.     

Detecting Rare J/ψ → μ+μ− Events in the CBM Experiment

Physics of Particles and Nuclei Letters - A simple and efficient trigger for selecting the rare $${J mathord{left/ {vphantom {J psi }} right. kern-0em} psi } to {{mu }^{ + }}{{mu }^{ -...     

Hard bremsstrahlung amplitudes fore + e − collisions with polarized beams at LEP/SLC energies

Cross sections are presented for the processese ⁺ e ^?→e ⁺ e ^?γ ande ⁺ e ^?→f \(\bar f\) γ (wheref is any light fermion) in the form of helicity amplitudes in which all complex phase information is kept. Owing to a spcial choice of the bremsstrahlung polarization and the use of spinor techniques the resultant expressions are extremely compact and lend themselves to fast numerical evaluation. An algorithm is given to obtain from the helicity amplitudes the cross section for arbitrary polarization of the incominge ⁺ e ^? beams. Special attention is given to the case of bremsstrahlung at very small angles to the beams, where a complicated dependence on the electron mass has to be taken into account.     

Searching for the process e+e- → K+K-π0 in experiments with the spherical neutral detector at VEPP-2M

We have searched for the process e⁺e^- → K⁺K^-π⁰ at energies up to 1.38 GeVin an experiment with the spherical neutral detector at the VEPP-2M e⁺e^- collider. The upper limits of the cross sections for the processes σ(e⁺e →; φπ: → K⁺K^-π⁰) < 0.023 nb and σ(e⁺e^- → KK*(892) → K⁺K^-π⁰) < 0.059 nb have been established at a 95% confidence level.     

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.     

Investigation of the reaction e+e− → ηπ+π− in the energy range up to 1.4 GeV

The reaction e⁺e⁻ → ηπ⁺π⁻ has been studied with the Neutral Detector in the CM energy range 1.05–1.40 GeV at VEPP-2M. At the maximum energy the cross section exceeds the prediction of the vector dominance with one ϱ(770). The following upper limits for the electron width times branching ratio into ηπ⁺π⁻ have been obtained for a resonance with a mass of 1.28 GeV and width of 0.08 GeV observed with the Omega-spectrometer at CERN: Λ_ee·B_ηππ < 9 eV, and for a ϱ′(1250) with a mass of 1.26 GeV and width of 0.125 GeV: Λ_ee·B_ηππ < 14 eV at 90% confidence level.     

CP-violation effect in neutralino pair production in e+ −e− annihilation and the electric dipole moment of the electron

It is shown that in the supersymmetric extensions of the standard electroweak theory, the threshold behaviour of the cross section of production of two different neutralinos in e⁺ −e⁻ annihilation may be sensitive to the violation of CP invariance by the neutral gaugino-higgsino mass term. The corresponding CP violation effect may be substantial quite far from the threshold. A relation (although rather indirect) between the form of the behaviour of this section in the threshold region and the value of the electric dipole moment of the electron may exist.