$(τ^+τ^-)_b$ is an atom of simple hydrogenlike structure similar to positronium $(e^+e^-)_b$ and $(μ^+μ^-)_b$. In this paper energy levels and decay widths of different decay channels of $(τ^+τ^-)_b$ are given. Cross section of production of this atomic system in $e^+e^-$ annihilation taking into account radiative corrections is calculated. According to our estimates 886 $(τ^+τ^-)_b$ atoms may be produced at BEPCII and 29 $(τ^+τ^-)_b$ atoms are produced at VEPP-4M under the present experimental conditions.
We consider the electromagnetic production of positron and electron in collisions of slow heavy nuclei. This process is dominated by emission of positron, with the electron captured by nucleus.
In this work is presented several results for cross sections of exotic particles production in electron-positron collisions in future linear electron-positron colliders. It is shown that the central production of exotic leptons, dilatons, radions, axions and technipions in this type of collision can be measurable for the predicted kinematic parameters for linear colliders.
The total and differential cross sections for the production of $Ω_{scb}$ baryons in electron-positron collisions are calculated at the $Z$-boson pole.
A fully massive Monte Carlo program to compute all four-fermion processes in electron positron collisions, including Higgs boson production, is presented. Leading higher order effects are discussed and included.
In the current work, We investigated the production of neutral Higgs boson and two charged Charginos owing to electron-positron annihilation via different propagators
We calculated the cross section of double electron-positron pair production with two-electron capture for the collisions of Pb+Pb ions and we did our calculations at LHC energies. We applied a similar methodology for the calculation of bound-free electron-positron pair production. We used perturbation theory and implemented Monte Carlo integration techniques to calculate the lowest order Feynman diagrams. We also compared our double electron-positron pair production with two-electron capture cross section results obtained in the literature. These calculations may help us to learn more about st…
We investigate the potential of TESLA and JLC/NLC electron-positron linear collider designs to observe diquarks produced resonantly in processes involving hard photons.
We introduce a new, fully massive, Monte Carlo program to compute all four-fermion processes in electron-positron collisions, including Higgs production. We outline our strategy for the matrix element evaluation, the phase space generation and the implementation of the leading higher order effects, and show, where available, comparisons with existing results.
In this paper initial state radiation corrections to double production of charmonium mesons on one-photon electron-positron annihilation at center of mass energy $\sqrt{s}=10.6\GeV$ are studied. It is shown, that these corrections have noticeable effect and must be taken into consideration.
Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.
The emission of electron-positron pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field is analyzed. A significant increase of the total cross section of pair production in the subthreshold region is found for decreasing laser pulse duration even in case of moderate laser pulse intensities.
Expressions for Sudakov form factors for heavy quarks are presented. They are used to construct resummed jet rates in electron-positron annihilation. Predictions are given for production of bottom quarks at LEP and top quarks at the Linear Collider.
We consider the production of ultrarelativistic parapositronium and orthopositronium atoms in collisions of high energy electrons with laser photons. Our results demonstrate the opportunity of intensive positronium beam formation with Lorentz-factor 10^6 using laser beam conversion on high energy electrons at the future Electron Linear Accelerators.
We study the structures in cross sections and R ratios concerning electron-positron annihilation reactions, for open-strangeness, open-charm and open-beauty hadron-pair production, from the perspective of a recently developed production formalism. Special attention is paid to non-resonant contributions. Known, tentative, and yet unknown resonances are spotted, with estimates for their masses and widths.
We present the CoLoRFulNNLO method to compute higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the computation of event shape observables in electron-positron collisions at NNLO accuracy and validate our code by comparing our predictions to previous results in the literature. We also calculate for the first time jet cone energy fraction at NNLO.
The results of a complete one-loop calculation for the production of chargino pairs in electron-positron collisions, including the option of polarized beams, are presented. The calculation has been performed in the on-shell renormalization scheme. Applications to the integrated cross section, to the forward-backward asymmetry for unpolarized beams, and to the left-right asymmetry show that the higher-order effects have a sizeable influence on the theoretical predictions and therefore should be properly taken into account for detailed studies in the MSSM.
Process of muon (pion) pair production with small invariant mass in the electron-positron high-energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Dell-Yan picture for differential cross section is valid in the charge-even experimental set-up. Radiative corrections both for electron block and for final state block are taken into account.
We introduce a subtraction method for jet cross sections at next-to-next-to-leading order (NNLO) accuracy in the strong coupling and use it to compute event shapes in three-jet production in electron-positron collisions. We validate our method on two event shapes, thrust and C-parameter, which are already known in the literature at NNLO accuracy and compute for the first time oblateness and the energy-energy correlation at the same accuracy.
We present the contributions from all types of one-loop corrections to the scattering amplitude for the pair production of polarized charginos or neutralinos from polarized electron-positron annihilation. The contributions are classified in terms of ``prototypes'' distinguished by the number of particles inside the loops and their spins. The results are quoted in terms of the Veltman-Passarino functions in terms of general couplings and internal masses. The results can therefore be applied to any supersymmetric extension of the Standard Model or indeed to any polarized fermion pair production …
The validity of the equivalent-photon approximation for two-photon processes in electron--positron collisions is critically examined. Commonly used forms to describe hadronic two-photon production are shown to lead to sizeable errors. An improved two-photon luminosity function is presented, which includes beyond-leading-logarithmic effects and scalar-photon contributions. Comparisons of various approximate expressions with the exact calculation in the case of the total hadronic cross section are given. Furthermore, effects of the poorly known low-Q2 behaviour of the virtual hadronic cross sect…
Electron-positron pair production in space- and time-dependent electromagnetic fields is investigated. Especially, the influence of a time-dependent, inhomogeneous magnetic field on the particle momenta and the total particle yield is analyzed for the first time. The role of the Lorentz invariant $\mathbf{E}^2 - \mathbf{B}^2$, including its sign and local values, in the pair creation process is emphasized.
The scaling of charged hadron fragmentation functions to the Tsallis distribution for $0.01 \lessapprox x \lessapprox 0.2$ is presented for various $e^+e^-$ collision energies. A possible microcanonical generalisation of the Tsallis distribution is proposed, which gives good agreement with measured data up to $x\approx1$. The proposal is based on superstatistics and a $KNO$ like scaling of multiplicity distributions in $e^+e^-$ experiments.
Process of lepton pair production by polarized photon on nuclei can be used to measure the degree of linear polarization of high energy photon. The differential cross section and the analyzing power are calculated with taking into account higher powers of expansion on $Zα$. Pure Coulomb and screened potential are considered.
We present the calculation of gamma gamma -> 2e+e- process cross section. The construction are perfomed using both helicity amplitude method and method of precision covariant calculation. The magnitude of cross section is obtained by the Monte-Carlo method of numerical integration. Different energies, polarization states and kinematics cuts are considered.
We compute the electroweak ${\cal O}(α^3α_s)$ corrections to three-jet production and related event-shape observables at electron-positron colliders. We properly account for the experimental photon isolation criteria and for the corrections to the total hadronic cross section. Corrections to the three-jet rate and to normalised event-shape distributions turn out to be at the few-per-cent level.
The calculational precision of $\ee\to\tautau$ and $\ee\to\mumu$ production cross-sections in electron-positron annihilations at \roots = 10.58 \gev are studied for the \kk Monte Carlo simulation program. We determine $σ(\ee\to\tautau) = (0.919 \pm 0.003) \nb$ and $σ(\ee\to\mumu) = (1.147 \pm 0.005) \nb$, where the error represents the precision of the calculation.
The process of the muon (pion) pair production with small invariant mass in the electron--positron high--energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Drell--Yan picture for differential cross section is valid in the charge--even experimental set--up. Radiative corrections both for electron block and for final state block are taken into account.
Recent theory results on direct production of resonances with positive charge conjugation in electron-positron annihilation are reviewed. The strong model dependence is emphasized, with predictions varying between 0.03 eV and 0.43 eV for the charmonium state with $J^{PC} = 1^{++}$ and between 0.16 eV and 4.25 eV for the state with $J^{PC} = 2^{++}$. For the state with $J^{PC} = 0^{++}$ the cross section is of $\cal{O}$ $(m^2_e/M^2_χ)$ and thus negligeable for all practical purpose. The importance of the relative phase of the production amplitude is emphasized.
The electron-positron pair production by an electron in a strong magnetic field near the process threshold is considered. The process is shown to be more probable if the spin of the initial electron is oriented along the field. In this case, the probability of the process is $\sim10^{13} s^{-1}$ when the magnetic field strength is $H=4\cdot 10^{12}$ G.
A study of the dynamical fluctuation property of jets is carried out using the Monte Carlo method. The results suggest that, the anisotropy of dynamical fluctuations in the hadronic system inside jets, changes abruptly with the variation of the cut parameter y_cut. A transition point exists, where these fluctuations behave like those in soft hadronic collisions, i.e. being circular in the transverse plane with respect to dynamical fluctuations.
We discuss the possibility of detecting heavy spin-3/2 leptons at LEP2 and NLC energies. The angular distributions of primary ordinary leptons are shown to be a good measure to discriminate between a heavy spin-3/2 lepton and a similar nonstandard spin-1/2 signal.
The baryons containing two heavy quarks and a light quark are believed to have the diquark-quark structure and the diquark is composed of the two heavy quarks which is a spin-0 or spin-1 object. The superflavor symmetry can associate productions of such heavy baryon-antibaryon pair with the heavy meson productions. The whole scenario is presented in some details in this work, and the observation prospect in future experiments is discussed.
The recent measurements of azimuthal single spin asymmetries by the HERMES collaboration at DESY may shed some light on presently unknown fragmentation and distribution functions. We present a study of such functions and give some estimates of weighted integrals directly related to those measurements.
The non-perturbative electron-positron pair production in time-dependent electric fields is investigated. The quantum kinetic formalism is employed in order to calculate the electron density for various field configurations. The corresponding set of first order, ordinary differential equations is analyzed and numerically solved. The focus of this study lies on the dynamically assisted Schwinger effect in pulsed electric fields with at least two different time scales. Furthermore, interference effects arising in setups with multiple pulses are examined and first results for an optimization of t…
The problem of the backreaction during the process of electron-positron pair production by a circularly polarized electromagnetic wave propagating in a plasma is investigated. A model based on the relativistic Boltzmann-Vlasov equation with a source term corresponding to the Schwinger formula for the pair creation rate is used. The damping of the wave, the nonlinear up-shift of its frequency due to the plasma density increase and the effect of the damping on the wave polarization and on the background plasma acceleration are investigated as a function of the wave amplitude.
A new approach to phenomenological description of the charged particle multiplicity distributions in proton-(anti)proton and electron-positron collisions is presented. The observed features of the data are interpreted on the basis of stochastic-physical ideas of multiple production. Besides the processes of parton immigration and absorption, two and three patron incremental and decremental recombinations are considered. The complex behaviour of the multiplicity distributions at different energies is described by four parametric generalized hypergeometric distribution (GHD). Application of the …
The production of various heavy-quark-containing baryons in electron-positron annihilation is considered. On the basis of exact formulas that we obtained previously within full perturbation theory, new numerical calculations of the respective cross sections are performed, and simple approximate expressions are then constructed for the results of these calculations. The dependence of the total cross sections on the masses of constituent quarks is discussed. The application of the Peterson fragmentation function and a Reggeon-type fragmentation function to describing differential cross sections …
Spin and polarization effects and correlations between them in the processes of pair production by a photon and synchrotron radiation in a magnetic field are considered. Expressions for the probabilities of the processes with arbitrary polarizations of the particles are obtained. These expressions are analyzed in detail in both the lowest Landau levels and ultrarelativistic approximations.
We calculate the complete one-loop quantum corrections to the helicity eigenstate chargino pair production cross sections in polarized electron positron collisions, within the Minimal Supersymmetric Standard Model. We calculate the non-QED corrections using the helicity amplitudes formalism, and Dimensional Regularization to deal with ultraviolet divergences. We calculate QED corrections using the dipole subtraction formalism to extract soft and collinear divergences in Bremsstrahlung, canceling them with the infrared divergences from virtual QED corrections. We show numerical results for the …
We calculate the double charmonium production cross section within the framework of $4\times 4$ Bethe-Salpeter Equation in the electron-positron annihilation, at center of mass energy $\sqrt{s}= 10.6$GeV, that proceeds through the exchange of a single virtual photon. In this calculation, we make use of the full Dirac structure of 4D BS wave functions of these charmonia, with the incorporation of all the Dirac covariants (both leading and sub-leading). The calculated cross-sections for the double charmonium productions for final states, ($J/Ψ, η_c$); ($Ψ',η_c$) ; ($J/Ψ, η_c'$); and ($Ψ',η_c'$) …
We report on the analytic calculation of the second-order QCD corrections to semi-inclusive hadron production in electron-positron annihilation. The calculation of the single-particle inclusive cross-section in time-like kinematics is performed in Mellin N-space and uses an algorithmic evaluation of inclusive phase-space integrals, based on the unitarity cutting rules and integration-by-parts. We obtain splitting functions and coefficient functions up to second order in the strong coupling alpha_s. Our results are in agreement with earlier calculations in the literature by Rijken and van Neerv…
Two spin-dependent structure functions $\hat g_1$ and $\hat g_2$ for the inclusive spin-half baryon production in electron-positron annihilation are studied in the context of QCD factorization as well as in the naive quark parton model. As a result, it is found that the sum of $\hat g_1$ and $\hat g_2$ is related to $\hat h_1$ and $\hat g_T$, two quark fragmentation functions defined by Jaffe and Ji. In connection with the measurement of quark fragmentation functions, the possible phenomenological consequences are discussed.
We consider the electromagnetic production of positron in collision of slow heavy nuclei, with the simultaneously produced electron captured by one of the nuclei. The cross-section of the discussed process exceeds essentially the cross-section of $e^+e^-$ production.
It is shown that $BR(χ_{b1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 3.3\cdot 10^{-7}$, $BR(χ_{b1}(2P)\rightarrow Z\rightarrow e^+e^-)\simeq 4.1\cdot 10^{-7}$ and $BR(χ_{c1}(1P)\rightarrow Z\rightarrow e^+e^-)\simeq 10^{-8}$ that give a good chance to search for the direct production of pseudovector $^3P_1$ heavy quarkonia in $e^+e^-$ collisions ($e^+e^-\rightarrow Z\rightarrow ^3P_1$) even at current facilities not to mention $b$ and $c-τ$ factories. Leading radiative corrections to annihilation of quarkonia in QCD are discussed.
We propose the characterization of fragmentation functions by the energy fraction x, a hadron takes away from the energy of the jet measured in the frame co-moving with the jet. Besides, we propose the usage of the jet mass as the fragmentation scale Q. We show that these two Lorentz-invariant variables emerge naturally in a microcanonical ensemble with conserved fourmomentum. Then, we construct a statistical hadronisation model, in which, two features of the hadronic final states in various high-energy reactions (power law spectra and negative-binomial multiplicity distributions) can be conne…
A possibility of a verification of CPT-invariance of QED for bound states by example of muonium or antimuonium produced in reactions of scattering of electrons or positrons by nuclei is considered. The number of events of the muonium production is estimated for contemporary accelerators. The method of the detection of muonium by measuring of oscillations of the decay curve caused by the interference between the ground and excited state of muonium is suggested. The admixture of the excited muonium to the final state is calculated.
We discuss the pair production of gluinos in electron-positron annihilation at LEP, in a model with soft supersymmetry breaking, allowing for mixing between the squarks. In much of the parameter space of the Minimal Supersymmetric Model (MSSM) the cross section corresponds to a $Z$ branching ratio above $10^{-5}$, even up to $10^{-4}$. A non-observation of gluinos at this level restricts the allowed MSSM parameter space. In particular, it leads to lower bounds on the soft mass parameters in the squark sector.
One kind of particularly interesting pseudoscalar particles, called axion-like particles (ALPs), have rich physical phenomenology at high- and low-energy collider experiments. After discussing most of single production channels of ALP at electron-positron colliders, we investigate the possibility of detecting this kind of new particles through the W$^{+}$W$^{-}$ fusion process e$^{+}$e$^{-}$ $\rightarrow$ $\overlineν_{e}$$ν_{e}a$ $(\rightarrow γγ)$ at the CLIC. The 3$σ$ and 5$σ$ bounds on the ALP parameter space at the three energy stages of the CLIC are obtained. We find that the bounds given…
The final-state interaction effects on the inclusive two-particle production in electron-positron annihilation are investigated within the context of the one-photon annihilation approximation. Such effects are characterized by one structure function in the decomposition of the hadronic tensor. On the basis of the positivity, we derived an inequality to bound this structure function. The price to access it experimentally is to polarize longitudinally one of the initial-state beam, to say, the electron beam, and measure the corresponding single spin asymmetry. By combining the Callan-Gross relat…
The processes of muons (tau) and charged pions pairs production at electron-positron annihilation with first order radiative corrections are considered. The calculation results are presented assuming the energies of final particles (cms implied) to be not far significantly from threshold production. The invariant mass distributions for the muon (tau) and pion pairs are obtained both for the initial and final state radiation. Some analytical calculations are illustrated numerically. The pions were assumed to be point-like objects and scalar QED was applied for calculation. The QED radiative cor…
The lowest order radiative correction to the differential cross-section of process of muon pair production with emission of hard photon at high energy electron-positron annihilation are calculated. Taking into account the emission of additional soft and hard photon the cross-section can be put in the form of Drell-Yan process in leading logarithmical approximation. Applying the crossing transformation we obtain the cross section of radiative electron-muon high-energy scattering process. Virtual and soft photon emission contributions of non-leading form are tabulated for several typical kinemat…
