Scalar mesons in the decays η′ → 3π0 and η′ → π0π+π?

The decays η → 3π ⁰ and η → π ⁰ π ⁺ π ⁻ are considered within the isobar model. It is shown that, in order to explain the branching ratio and the shape of the Dalitz plot for the decay η′ → 3π ⁰, it is sufficient to take into account the contributions of the σ and a ₀ mesons. The inclusion of the σ meson is necessary for reproducing the shape of the distribution over the Dalitz plot. The branching ratio for the decay η′ → π ⁰ π ⁺ π ⁻ is obtained. The predictions for the distributions over the Dalitz plot for this decay are presented. These predictions depend strongly on model parameters.     

π+π+ and π+π? Colliding in Noncommutative Space

By studying the scattering process of scalar particle pion on the noncommutative scalar quantum electrodynamics, the non-commutative amendment of differential scattering cross-section is found, which is dependent of polar-angle and the results are significantly different from that in the commutative scalar quantum electrodynamics, particularly when cosθ∼±1. The non-commutativity of space is expected to be explored at around Λ_NC∼TeV.     

Novel insights into the γγ?→π0 transition form factor

BaBar’s observation of significant deviations of the pion transition form factor (TFF) from the asymptotic expectation with Q ²>9 GeV² has brought about a serious crisis to the fundamental picture established for such a simple q[`(q)]q\bar{q} system by perturbative QCD, i.e. the dominance of collinear factorization at high momentum transfers for the pion TFF. We show that non-factorizable contributions due to open flavors in γγ ^∗→π ⁰ could be an important source that contaminates the pQCD asymptotic limit and causes such deviations with Q ²>9 GeV². Within an effective Lagrangian approach, the non-factorizable amplitudes can be related to intermediate hadron loops, i.e. K ^(∗) and D ^(∗) etc., and their corrections to the π ⁰ and η TFFs can be estimated.     

ω(→ π+π?π0) meson photoproduction on proton

The cross-section for the π ⁺ π ⁻ π ⁰ invariant mass distribution in the γp reaction in the GeV region is calculated. This reaction is assumed to proceed through the formation of the ω-meson in the intermediate state, because the production cross-section for this meson in the γp reaction in the GeV region is significant and it has a large branching ratio (88.8%) in the π ⁺ π ⁻ π ⁰ channel. The cross-sections for this reaction are calculated using the energy-dependent reaction amplitude, f _γp→ωp(0), extracted from the latest ω-meson photoproduction data. We use established procedure to calculate other factors, like width and propagator of the ω-meson, so that our calculation can provide reliable cross-section. The calculated results reproduce the measured π ⁺ π ⁻ π ⁰ invariant mass distribution spectra in the γp reaction.     

K+→π+π0e+e?: a novel short-distance probe

We study the decay K ⁺→π ⁺ π ⁰ e ⁺ e ⁻, currently under analysis by the NA62 Collaboration at CERN. In particular, we provide a detailed analysis of the Dalitz plot for the long-distance, γ ^∗-mediated, contributions (Bremsstrahlung, direct emission and its interference). We also examine a set of asymmetries to isolate genuine short-distance effects. While we show that charge asymmetries are not required to test short distances, they provide the best environment for its detection. This constitutes by itself a strong motivation for NA62 to study K ⁻ decays in the future. We therefore provide a detailed study of different charge asymmetries and the corresponding estimated signals. Whenever possible, we make contact with the related processes K ⁺→π ⁺ π ⁰ γ and K _L →π ⁺ π ⁻ e ⁺ e ⁻ and discuss the advantages of K ⁺→π ⁺ π ⁰ e ⁺ e ⁻ over them.     

Analysis of the decays ψ′ → J/ψπ+π? and η′c → ηcπ+π? with the heavy-quark symmetry

In this article, we study the decays ψ′ → J/ψπ ⁺ π ⁻ and η′_c → η _c π ⁺ π ⁻ by taking into account the chiral symmetry breaking effects, the final-state interactions and the heavy-quark symmetry. We can confront the predictions of the η′_c → η _c π ⁺ π ⁻ decay width and differential decay width with the experimental data in the future, and obtain powerful constraints on the chiral breaking effects and the final-state interactions, and test the heavy-quark symmetry.     

S wave of pion-pion scattering from data on the reaction π?p → π0π0n

The results of recent experiments performed at KEK, Brookhaven National Laboratory, the Institute for High-Energy Physics (Protvino), and CERN to study the reaction π ⁻ p → π ⁰ π ⁰ n are analyzed in detail. For S-wave pion-pion scattering in the channel of isospin I=0, new data are obtained for the phase shift δ ₀ ⁰ and the inelasticity parameter η ₀ ⁰ . Difficulties that arise in using, for the amplitudes of the S and D waves of the final π ⁰ π ⁰ system, physical solutions selected on the basis of partial-wave analyses are discussed. It is noteworthy that other solutions are preferable in principle in the region of the invariant mass m of the π ⁰ π ⁰ system above 1 GeV. With the aim of clarifying the situation and further studying the properties of the f ₀(980) resonance, it is proposed to perform, in the reaction π ⁻ p → π ⁰ π ⁰ n, an especially careful examination of the m region in the vicinity of the threshold. __________ Translated from Yadernaya Fizika, Vol. 67, No. 7, 2004, pp. 1380–1391. Original Russian Text Copyright ? 2004 by Achasov, Shestakov.     

Power corrections in e+e?→π+π?,K+K? and B→Kπ,ππ

CLEO-c measurements of the timelike form factors F _π , F _K at ?s=3.671\sqrt{s}=3.671 GeV provide a direct probe of power corrections (PC’s) at energies near m _B . PC’s in F _π,K and B→Kπ,ππ are separated into perturbative and soft parts. In F _π,K the latter are ≥O(10) larger. A PC fit to the B→Kπ,ππ data also yields a ≥O(10) soft-to-perturbative hierarchy for the QCD penguin PC’s. Hence, both can be attributed to dominance of the soft-overlap between energetic (approximately) back-to-back collinear partons, and consistency of the B→Kπ,ππ fit with the Standard Model appears to be naturally realized. The CP asymmetries S_{Ks p⁰}S_{K_{s} \pi^{0}}, C_{Ks p⁰}C_{K_{s} \pi^{0}} are well determined, providing a clean test for new physics.     

Towards extraction of π+p and π+π+ cross-sections from charge exchange processes at the LHC

We study the possibilities to analyse the data on leading neutrons production at first LHC runs. These data could be used to extract from it π ⁺ p and π ⁺ π ⁺ cross-sections. In this note we estimate relative contributions of π, ρ and a ₂ reggeons to charge exchanges and discuss related problems of measurements.     

On the possibility to measure the π0→γγ decay width and the γ?γ→π0 transition form factor with the KLOE-2 experiment

A possibility of KLOE-2 experiment to measure the width \varGamma_{p⁰ ?gg}\varGamma_{\pi^{0} \to\gamma\gamma} and the π ⁰ γγ ^∗ form factor F(Q ²) at low invariant masses of the virtual photon in the space-like region is considered. This measurement is an important test of the strong interaction dynamics at low energies. The feasibility is estimated on the basis of a Monte-Carlo simulation. The expected accuracy for \varGamma_{p⁰ ?gg}\varGamma_{\pi^{0} \to\gamma\gamma} is at a per cent level, which is better than the current experimental world average and theory. The form factor will be measured for the first time at Q ²≤0.1 GeV² in the space-like region. The impact of these measurements on the accuracy of the pion-exchange contribution to the hadronic light-by-light scattering part of the anomalous magnetic moment of the muon is also discussed.     

Anomalous dipion invariant mass distribution of the ?(4S) decays into ?(1S)π+π? and ?(2S)π+π?

To solve the discrepancy between the experimental data on the partial widths and lineshapes of the dipion emission of ϒ(4S) and the theoretical predictions, we suggest that there is an additional contribution, which had not been taken into account in previous calculations. Noticing that the mass of ϒ(4S) is above the production threshold of B[`(B)]B\bar{B}, the contribution of the sequential process \varUpsilon(4S)? B[`(B)]? \varUpsilon(nS)+S?\varUpsilon(nS)+p⁺p^-\varUpsilon(4S)\to B\bar{B}\to \varUpsilon(nS)+S\to\varUpsilon(nS)+\pi^{+}\pi^{-} (n=1,2) may be sizable, and its interference with that from the direct production would be important. The goal of this work is to investigate if a sum of the two contributions with a relative phase indeed reproduces the data. Our numerical results on the partial widths and the lineshapes d\varGamma(\varUpsilon(4S)?\varUpsilon(2S,1S)p⁺p^-)/d(m_p⁺p^-)d\varGamma(\varUpsilon(4S)\to\varUpsilon(2S,1S)\pi^{+}\pi^{-})/d(m_{\pi ^{+}\pi^{-}}) are satisfactorily consistent with the measurements; thus the role of this mechanism is confirmed. Moreover, with the parameters obtained by fitting the data of the Belle and BaBar collaborations, we predict the distributions dΓ(ϒ(4S)→ϒ(2S,1S)π ⁺ π ⁻)/dcosθ, which have not been measured yet.     

ρ(ω) → π0π0γ, ρ(ω) → ηπ0γ decays in the local quark Nambu-Jona-Lasinio model

The branching ratios and photon spectra of the rare processes ρ(ω) → π ⁰ π ⁰ γ, ρ(ω) → ηπ ⁰ γ are calculated in the framework of the standard local quark Nambu-Jona-Lasinio model. Three types of diagrams are considered: the quark box and the pole diagrams with scalar (σ, α ₀(980)) and vector (ρ, ω) mesons. The obtained estimates for the widths of the processes ρ(ω) → π ⁰ π ⁰ γ are in satisfactory agreement with existing experimental data. Predictions are made for the widths of the processes ρ(ω) → ηπ ⁰ γ. The text was submitted by the authors in English.     

Delicate interplay between the D0D?0, ρ0J/ψ, and ωJ/ψ channels in the X(3872) resonance

The nature of the X(3872) enhancement is analyzed in the framework of the Resonance-Spectrum Expansion, by studying it as a regular J ^PC =1⁺⁺ charmonium state, though strongly influenced and shifted by open-charm decay channels. The observed but Okubo–Zweig–Iizuka-forbidden ρ ⁰ J/ψ and ωJ/ψ channels are coupled as well, but effectively smeared out by using complex ρ ⁰ and ω masses, in order to account for their physical widths, followed by a rigorous algebraic procedure to restore unitarity. A very delicate interplay between the D ⁰ D ^∗0, ρ ⁰ J/ψ, and ωJ/ψ channels is observed. The data clearly suggest that the X(3872) is a very narrow axial-vector c[`(c)]c\bar{c} resonance, with a pole at or slightly below the D ⁰ D ^∗0 threshold.     

Strong decays Σ*→Σπ,Λπ and related strong coupling constant

We calculate the strong coupling constant g among the decuplet baryons, the octet baryons and the pseudoscalar mesons in the heavy baryon chiral perturbation theory with the light-cone QCD sum rules, and we study the strong decays Σ ^*→Λ π,Σ π. The numerical value of the strong coupling constant g is consistent with our previous calculation; the central values lead to small SU(3) breaking effects, less than 6%; and no definitive conclusion can be drawn due to the large uncertainties.     

T-Odd correlation in K+ → π0l+νγ decays beyond the standard model

The T-odd correlation in the decays K ⁺ → π ⁰ l ⁺ νγ (l = e, μ) is investigated as a function of the parameters of the effective Lagrangian. It is shown that the T-odd correlation offers a good indicator of new physics in the vector and pseudovector sectors of the model under consideration. In the scalar and pseudoscalar sectors, investigation of the T-odd correlation gives no way to improve the current limits on the parameters of various extensions of the Standard Model. __________ Translated from Yadernaya Fizika, Vol. 67, No. 5, 2004, pp. 1025–1032. Original Russian Text Copyright ? 2004 by Braguta, Likhoded, Chalov.     

Measurement of inclusive π 0 production in hadronic Z 0 decays

An analysis is presented of inclusiveπ ⁰ production inZ ⁰ decays measured with the DELPHI detector. At low energies,π ⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to ) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy forqq andbb events. The number ofπ ⁰’s per hadronicZ ⁰ event isN(π ⁰)/Z _had ⁰ =9.2±0.2(stat)±1.0(syst) and forbb events the number ofπ ⁰’s is N(π ⁰)/bb=10.1±0.4(stat)±1.1(syst). The ratio of the number ofπ ⁰’s inbb events to hadronicZ ⁰ events is less affected by the systematic errors and is found to be 1.09±0.05±0.01. The measuredπ ⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in theξ _p=ln(1/x_p) distribution isξ* _p =3.90 _−0.14 ^+0.24 . The average number ofπ ⁰’s from the decay of primary B hadrons is found to be N(B→π ⁰ X)/B hadron=2.78±0.15(stat)±0.60(syst).     

Bs0 → μ+μ? in LHCb

Due to its sensitivity to New Physics contributions, the branching ratio of the very rare decay B _s ⁰ → μ ⁺ μ ⁻ is one of the most interesting measurements using the first data from the LHC accelerator. The analysis strategy for the study of this channel in the LHCb experiment is presented, as well as a review of the potential of the experiment in such study, using the latest simulations. With four months of nominal data taking, any enhancement from the Standard Model prediction can be excluded.     

Electron-impact excitation of the S°, P°, and D° doublet levels of cobalt atoms

The excitation of transitions from the ² S ^∘, ² P ^∘, and ² D ^∘ levels of the cobalt atom is studied by the method of extended crossing beams. Seventy-six excitation cross sections are measured at an exciting electron energy of 50 eV. Nine optical excitation functions are recorded in the electron energy region of 0–200 eV. Possible channels of excitation of levels under study are discussed.     

Analysis of the decay B0→χclπ0 with light-cone QCD sum rules

In this article,we calculate the contribution from the nonfactorizable soft hadronic matrix element to the decay B~0→χc1~π~0 with the light-cone quantum chromo-dynamic(QCD) sum rules.The numerical results show that its contribution is rather large and should not be neglected.The total amplitudes lead to a branching fraction which is in agreement with the experimental data marginally.