Deviation from the standard model in the decay <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">νγ</Emphasis>

A precise investigation of radiative pion decay (π⁺ → e⁺νγ) in a pion beam from the meson factory of the Paul Scherrer Institute (Switzerland) was performed by the PIBETA Collaboration with the aid of the PIBETA detector. This resulted in finding 41 601 events of radiative pion decay in three kinematical regions. The absolute values of the branching ratio for radiative pion decay were determined in each of these regions. To a precision approximately four times higher than that known previously, the ratio of the axial-vector to the vector form factor was found to be γ ≡ F _A /F _V = 0.443 (15), the latter being fixed at F _V = 0.0259. The number of events found in the kinematical region specified by photon energies of E_γ > 55.6 MeV, positron energies of E _e > 20.0 MeV, and angles of θ_{γ, e} > 40° between the momenta of the corresponding particles (B region) was 5233. In region B, the measured branching ratio for radiative pion decay, R_π→evγ(expt) = 11.6(3) × 10^?8, proved to be smaller by eight standard deviations than that which follows from the Standard Model, R_π→evγ (theor) = 14.34(1) × 10^?8.     

Near-threshold radiative 3<Emphasis Type="Italic">π</Emphasis> production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

We consider the π⁺π^?π₀γ final state in electron-positron annihilation at c.m.s. energies not far from the threshold. Both initial-and final-state radiations of the hard photon are considered, but without interference between them. The amplitude for the final-state radiation is obtained by using the effective Wess-Zumino-Witten Lagrangian for pion-photon interactions valid for low energies. In real experiments, energies are never so small that ρ and ω mesons would have a negligible effect. So a phenomenological Breit-Wigner factor is introduced in the final-state radiation amplitude to account for the vector mesons' influence. Using radiative 3π production amplitudes, a Monte Carlo event generator was developed which could be useful in experimental studies.     

Higher <Emphasis Type="Italic">η</Emphasis><Subscript>c</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) and <Emphasis Type="Italic">η</Emphasis><Subscript>b</Subscript>(<Emphasis Type="Italic">nS</Emphasis>) mesons

The hyperfine splittings in heavy quarkonia are studied in a model-independent way using experimental data on dielectron widths. Relativistic correlations are taken into account together with the smearing of spin-spin interaction. The radius of smearing is fixed by known G/ψ−η _c(1S), ψ(2S)−η _c′(2S) splittings, which appears to be small, r _ss ≅ 0.06 fm. Nevertheless, even with such a small radius, substantial suppression of hyperfine splittings (∼50%) is observed in bottomonium. For nS b states (n = 1, 2, ..., 6), our predicted splittings (in MeV) are 28, 12, 10, 5, 6, 3. For the 3S and 4S charmonium states, the splittings 16(2) and 12(4) MeV are obtained. The text was submitted by the authors in English.     

Laser control of the low-temperature <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript>+O<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> reaction

The dissociative recombination theory of slow electrons with molecular ions in a strong monochromatic light field is developed. Classifications of all possible transitions and reaction mechanisms are presented. The potential energy curves of the oxygen molecule O₂^** dissociative states and partial cross sections are calculated.     

Possible tetraquark states in the <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">χ</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis>1</Subscript> invariant-mass distribution

In this article, we assume that there exist hidden charmed tetraquark states with spin–parity J ^P=1⁻, and we calculate their masses with the QCD sum rules. The numerical result indicates that the masses of the vector hidden charmed tetraquark states are about M _Z =(5.12±0.15) GeV or M _Z =(5.16±0.16) GeV, which are inconsistent with the experimental data on the π ⁺ χ _c1 invariant-mass distribution. The hidden charmed mesons Z ₁, Z ₂ or Z may be scalar hidden charmed tetraquark states, hadro-charmonium resonances or molecular states.     

On mass corrections to the decay <Emphasis Type="Italic">P</Emphasis> → <Emphasis Type="Italic">l</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">l</Emphasis><Superscript>−</Superscript>

The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar meson decay into a lepton pair, P → l ⁺ l ⁻. The full resummation of the terms ln(m _l ²/Λ²)(m _l ²/Λ²) ⁿ and (m _l ²/Λ²) ⁿ to the decay amplitude is performed, where m _l is the lepton mass and Λ ≈ m _ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e ⁺ e ⁻ channel is negligible and, for the μ⁺μ⁻channel, its order is of a few percent. The text was submitted by the authors in English.     

Electroproduction of <Emphasis Type="Italic">D</Emphasis>*<Superscript>±</Superscript> mesons at high energies

A comparative analysis of the predictions of the collinear parton model and the k _T -factorization approach is performed for the case of the D*-meson electroproduction at the HERA ep collider. It is shown that, owing to effectively taking into account, in noncollinear distributions, next-order corrections in the strong coupling constant α _s , the k _T -factorization approach increases, in contrast to the predictions of the collinear parton model, the absolute value of the cross sections for charmed-meson electroproduction by approximately a factor of 1.5 to 2. As a result, the agreement with experimental data is improved. This is not so only for the pseudorapidity spectrum, whose shape differs considerably from the experimental one and depends greatly on the choice of parametrization of the noncollinear gluon distribution within the proton.     

Two-photon production of vector resonance in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> collisions

A parameterization of the amplitude of the two-photon production of 1⁺⁺ and 1^?+ vector resonances V in the e ⁺ e ^? → e ⁺ e ^? V reaction has been obtained. The differential (in momentum transfer) scattering cross section dσ/dQ ² has been found for this reaction in the equivalent-photon approximation. The result obtained is model-independent.     

Contribution of final-state interaction to the branching ratio of <Emphasis Type="Italic">B</Emphasis>→<Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis><Emphasis Type="Italic">D</Emphasis>

To test the validity of perturbative QCD (pQCD) and investigate its range of application, one should look for a suitable process. B→J/ψ D is a promising candidate. The linear momentum of the products is relatively small, so that there may exist a region where exchanged gluons are soft and the perturbative treatment may fail, so that the non-perturbative effect would be significant. We attribute such non-perturbative QCD effects to the long-distance final-state interaction (FSI) which is estimated in this work. We find that the contribution from the FSI to the branching ratio is indeed sizable and may span the rather wide range of 10⁻⁶∼10⁻⁵ and cover a region where the pQCD prediction is of the same order. A more accurate measurement of its branching ratio may provide important information about the application region of pQCD and help to clarify the picture of inelastic rescattering (i.e. FSI), which is generally believed to play an important role in B decays.     

On the question of supersymmetric particles production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

Some aspects of supersymmetric particles pair production in e ⁺ e ^?-annihilation in processes \(e^ + + e^ - \to \tilde l^ + + \tilde l^ -\), \(e^ + + e^ - \to \tilde \chi ^ + + \tilde \chi ^ -\) are studied. Aparatus, in which long-lived charged particles deceleraition and accumulation take place, is considered. Binding energy of a negatively charged particle with nucleus is obtained. Probability of β-decay of a nucleus bounded with a long-lived negatively charged particle is considered.     

Investigation of the process <Emphasis Type="Italic">J/ψ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> with the KEDR detector

The product of the electron width of the J/ψ meson and the probability for its decay to an electron-positron pair was measured by using data from the KEDR experiment at the VEPP-4M electron-positron collider. The result was Γ _ee × Γ _ee /Γ = 0.3392 ± 0.0068(stat.) ± 0.0063(syst.) keV.     

Rare radiative leptonic decays <Emphasis Type="Italic">B</Emphasis><Stack><Subscript>d,s</Subscript><Superscript>0</Superscript></Stack> → ℓ<Superscript>+</Superscript>ℓ<Superscript>−</Superscript><Emphasis Type="Italic">γ</Emphasis>

The rare radiative leptonic decays \(\bar B_{d,s}^0 \to \ell ^ + \ell ^ - \gamma \) are studied. The contributions to the respective amplitude from the emission of photons from the quark loop, bremsstrahlung from leptons, and weak-annihilation effects are taken into account in relevant calculations. Results are presented for the partial widths and distributions of leptons in the final state. It is shown that the previously disregarded contributions of vector resonances associated with virtual-photon emission from the light valence quark of the B meson have a significant effect on the mass spectra of dileptons.     

Measurement of the cross sections for <Emphasis Type="Italic">π</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript> production in <Emphasis Type="Italic">pp</Emphasis> collisions at energies below 1 GeV

The cross sections for the reaction pp → ppπ ⁺ π ^? are measured at several values of the incident-proton energy. The resulting values are compared with other results, including values obtained previously for a deuteriumtarget, as well as with the predictions of a theoreticalmodel. This comparison reveals that, at energies below 850 MeV, the use of the impulse approximation in extracting the cross sections for double pion production on a free nucleon from data obtained with deuteron targets is illegitimate.     

On <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> pair production by colliding electromagnetic pulses

Electron-positron pair production from vacuum in an electromagnetic field created by two counterpropagating focused laser pulses interacting with each other is analyzed. The dependence of the number of produced pairs on the intensity of a laser pulse and the focusing parameter is studied with a realistic three-dimensional model of the electromagnetic field of the focused wave, which is an exact solution of the Maxwell equations. It has been shown that e⁺e^? pair production can be experimentally observed when the intensity of each beam is I～10²⁶ W/cm², which is two orders of magnitude lower than that for a single pulse.     

Inclusive production of vector charmonium in two-photon <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

One of the processes involving the inclusive production of the vector-charmonium states J/ψ. and ψ(2S) in two-photon electron-positron annihilation at \(\sqrt s = 10.6 GeV\) is studied on the basis of the singlet model. Analytic expressions are derived for respective differential cross sections, and numerical values of the total cross sections are given, along with graphs that represent the distributions of cross sections in the scattering angle and in the vector-meson energy. It is shown that these distributions differ substantially from the analogous distributions for charmonium production in one-photon electron-positron annihilation. For this reason, the process under consideration can readily be isolated despite the smallness caused by an extra power of α.     

Production of triply charmed Ω<Subscript>ccc</Subscript> baryonsin <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> annihilation

The total and differential cross sections for the production of triply charmed Ω_ccc baryons in e⁺e^? annihilation are calculated at the Z-boson pole.     

Search for <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript> → <Emphasis Type="Italic">ϕ</Emphasis>µµ decay at the Large Hadron Collider

As B _s -mesons will be produced abundantly at the LHC, the observability of the flavour-changing-neutral-current decay mode B _s → ϕμ⁺μ⁻ has been studied in CMS at the LHC centre-of-mass energy of 10 TeV. With an integrated luminosity of 100 pb⁻¹, an upper limit of 6.7 × 10⁻⁶ on the branching ratio is expected to be obtained. The potential at 7 TeV with a luminosity of 1 fb⁻¹ is expected to be better.     

Quark-hadron duality and production of charmonia and doubly charmed baryons in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> anninhilation

The cross sections for the production of charmonia and doubly charmed baryons in e ⁺ e ^? annihilation at an interaction energy of \(\sqrt s \) = 10.6 GeV are predicted under the assumption of quark—hadron duality. The method used is shown to remove some contradictions between experimental data and perturbative QCD.