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.     

The cusp effect in <Emphasis Type="Italic">η</Emphasis>′→<Emphasis Type="Italic">η</Emphasis><Emphasis Type="Italic">π</Emphasis><Emphasis Type="Italic">π</Emphasis> decays

Strong final-state interactions create a pronounced cusp in η′→η π ⁰ π ⁰ decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π ⁺ π ⁻ threshold.     

Scalar mesons in <Emphasis Type="Italic">η</Emphasis>′ → <Emphasis Type="Italic">ηπ</Emphasis><Superscript>0</Superscript><Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript> decay

The decay η′ → ηπ ⁰ π ⁰ is studied in the framework of isobar model. It is shown, that good agreement with the experiment is achieved if α ₀- and σ-meson contributions are taken into account. The contribution of α ₀-meson is dominant, but σ-meson is necessary to reproduce the form of the Dalitz plot. Instead of the usual Breit-Wigner form of σ-meson propagator we use parametrization of the ππ-amplitude, which satisfies analyticity, crossing, unitarity and chirality constraints. This amplitude has a pole in the complex plane, which corresponds to σ-meson and describe experimental data on ππ-scattering in K _e4 decay.     

Understanding jet shapes with <Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript>–<Emphasis Type="Italic">h</Emphasis><Superscript>±</Superscript> correlations

Angular correlations involving energetic particles associated with partonic jet fragmentation provide an important opportunity to study the hot nuclear matter produced in A+A collisions, particularly when compared against a p+p reference. Recent results from di-hadron correlations suggest that jet observables from A+A and p+p differ considerably at low p _T but approach comparable values as p _T increases above 7 GeV/c, providing clues on the nature of partonic energy loss and the medium response. The most recent π ⁰-triggered jet correlation results from the PHENIX experiment are presented, as well as a quantitative study of the jet-peak widths and shapes.     

Fluctuations of charged-particle multiplicities over narrow rapidity intervals in <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">A</Emphasis> collisions at 40 GeV/<Emphasis Type="Italic">c</Emphasis>

Maximum fluctuations of charged-particle multiplicities over narrow rapidity intervals are investigated for high-P_⊥ processes in π^?A collisions (where A=H, D, C, Cu, Pb) at 40 GeV/c. The observed fluctuations are studied by the method of factorial moments. The results show that the factorial moments 〈F _i 〉 vary in proportion to a power of the rapidity gap δy. This suggests that there are dynamical fluctuations in the processes under study. The experimental data are compared with theoretical results obtained on the basis of the model of quark-gluon strings by using the FRITIOF-7.02 package.     

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.     

Elliptic flow of ν ands <Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript> mesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeVmesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeV

Elliptic flow of ν and π ⁰ mesons emitted at midrapidity are studied in collisions of 1.9 A GeV ⁵⁸Ni+⁵⁸Ni and 2 A GeV ⁴⁰Ca+^natCa. The observed anisotropy corresponds to a negative elliptic flow signal for ν mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for π ⁰ mesons. This may indicate that ν mesons freeze out earlier from the central interaction region than pions.     

Independent <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript>-meson production in <Emphasis Type="Italic">pp</Emphasis> interactions

It is shown that experimental data on the multiparticle production of negatively charged pions in proton-proton interactions at \(\sqrt s \leqslant 30 GeV\) do not involve significant indications of the existence of anycorrela tions between negatively charged pions, apart from those that are associated with momentum conservation and with interference. The multiplicity distributions in rapidity intervals, forward-backward correlations, and two-particle rapidity and transverse-momentum correlations do not contradict the independent production of negatively charged pions. No constraints on the multiplicity distributions of product particles follow from their independent production.     

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 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.     

The <Emphasis Type="Italic">A</Emphasis> dependence of <Emphasis Type="Italic">K</Emphasis><Superscript>0</Superscript> and Λ Neutrinoproduction on nuclei

The A dependence of the production of K ⁰ and Λ is investigated for the first time in neutrino-nuclear reactions using the data obtained with the SKAT bubble chamber. An exponential parametrization (∼A ^β) of the particle yields results in = 0.20 ± 0.05 for V ⁰ particles (K ⁰ and Λ), while for π ⁻ mesons the A dependence is much weaker ( = 0.068 ± 0.007). A nuclear enhancement of the ratio K ⁰/π ⁻ is found; this ratio increases from 0.055 ± 0.013 for vN interactions up to 0.070 ± 0.011 at A ≈ 21 and 0.099 ± 0.011 at A ≈ 45. It is observed that the multiplicity rise of V ⁰ occurs predominantly in the backward hemisphere of the hadronic system. It is shown that the A dependence of the Λ⁰ and π ⁻ yields can be reproduced in the framework of a model incorporating the secondary intranuclear interactions of pions originating from the primary vN interactions. The text was submitted by the authors in English.     

Polarization observables <Emphasis Type="Italic">P</Emphasis> + <Emphasis Type="Italic">A</Emphasis> and (<Emphasis Type="Italic">P</Emphasis> + <Emphasis Type="Italic">A</Emphasis>)σ in 200-MeV proton inelastic scattering

Experimental and calculated data on inelastic scattering of polarized protons are presented as polarization-analyzing-power combinations P + A and (P + A)σ for the 0⁺ → 1⁺, T = 1 transition in ¹²C. Data on the polarization P and the function (P ? A)σ are also reported. Microscopic calculations have been performed using the DWBA program with the G-matrix interaction based on the Paris and Bonn potentials. A significant difference between the effective interaction with density correction and free NN interaction has been demonstrated. It is established that the (P + A)σ combination is especially sensitive to systematic variations in the density dependence in effective NN interactions.     

Lie Superalgebra Structures in <Emphasis Type="Italic">H</Emphasis><Superscript>⋅</Superscript> (<Emphasis Type="Italic">g</Emphasis>;<Emphasis Type="Italic">g</Emphasis>)

Let g=vect(M) be the Lie (super)algebra of vector fields on any connected (super)manifold M; let - be the change of parity functor, C ⁱ and H ⁱ the space of i-chains and i-cohomology. The Nijenhuis bracket makes into a Lie superalgebra that can be interpreted as the centralizer of the exterior differential considered as a vector field on the supermanifold associated with the de Rham bundle on M. A similar bracket introduces structures of DG Lie superalgebra in L ^* and for any Lie superalgebra g. We use a Mathematica-based package SuperLie (already proven useful in various problems) to explicitly describe the algebras l ^* for some simple finite dimensional Lie superalgebras g and their relatives - the nontrivial central extensions or derivation algebras of the considered simple ones.     

ALICE-PHOS: acceptance and efficiency correction factors <Emphasis Type="Italic">p</Emphasis>−<Emphasis Type="Italic">p</Emphasis>→<Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript>+<Emphasis Type="Italic">X</Emphasis> at 10 TeV

In ultra-relativistic Heavy-Ion Collisions (HIC), the properties of the quark gluon plasma (QGP) can be explored, in particular, via measurements of neutral pions. The π ⁰ is an important probe for both proton and heavy ion physics. In the former case, π ⁰ production provides an important mean of testing pQCD as well as useful data to constrain current and future theoretical models. In the latter case, π ⁰ measurements will serve as a baseline for exploring the nature of the HIC hard scattering. In the ALICE experiment, π ⁰ mesons are identified as they decay into two photons (π ⁰→γ γ) using the high-resolution photon spectrometer (PHOS). PHOS will measure π ⁰ transverse momentum over a wide range, from hundreds of MeV/c to several tens of GeV/c. An estimation of π ⁰ production cross-section in proton–proton collisions is calculated in a next-to-leading order (NLO) approximation and first presented. The π ⁰ geometrical acceptance and the identification efficiency along with the analysis on the invariant mass are the two important correction factors for obtaining a realistic π ⁰ spectrum discussed in this paper.     

Strong decay Δ<Superscript>++</Superscript>→<Emphasis Type="Italic">p</Emphasis><Emphasis Type="Italic">π</Emphasis> with light-cone QCD sum rules

We calculate the strong coupling constant g _{ΔN π} and study the strong decay Δ⁺⁺→p π with light-cone QCD sum rules. The numerical value of the strong coupling constant g _{ΔN π} is consistent with the experimental data. The small discrepancy may be due to the failure to take into account perturbative corrections.     

Tagged-weak <Emphasis Type="Italic">π</Emphasis> method

A new “tagged-weak π method” is proposed for determination of electromagnetic transition probabilities B(E2) and B(M1) of the hypernuclear states with lifetimes of ∼10⁻¹⁰ s. With this method, we are planning to measure B(E2) and B(M1) for light hypernuclei at JLab. The results of Monte Carlo simulations for the case of E2(5/2⁺, 3/2⁺ → 1/2⁺) transitions in _Λ⁷He hypernuclei are presented.     

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.