Study of B c → J / ψ π , η c π decays with?perturbative?QCD?approach

The B _c →J/ψ π, η _c π decays are studied with the perturbative QCD approach. It is found that the form factors and for the B _c →J/ψ, η _c transitions and the branching ratios are sensitive to the parameters ω, v, f _J/ψ and , where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively, and f _J/ψ and are the decay constants of the J/ψ and η _c mesons, respectively. The large branching ratios and the clear signals of the final states make the B _c →J/ψ π, η _c π decays the prospective channels for measurements at the hadron colliders.     

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.     

Rare decays of Λ b → Λ γ and Λ b → Λ l + l ? in universal extra-dimension model

The exclusive weak decay of Λ _b →Λ γ and Λ _b →Λ l ⁺ l ⁻ are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the branching ratio of Λ _b →Λ γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ _b →Λ l ⁺ l ⁻. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ _b →Λ μ ⁺ μ ⁻ is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ _b decays are not a useful tool to provide any valuable information for the universal extra-dimension model.     

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.     

Radiative scalar-meson decays f0(980) → ρ(ω)γ and a0(980) → ρ(ω)γ within the local Nambu-Jona-Lasinio model

The widths with respect to the radiative decays f ₀(980) → ργ and a ₀(980) → ωγ were calculated within the local Nambu-Jona-Lasinio model. The contributions of both quark and meson loops were taken into account. The latter and the former play a dominant role for the radiative decays of, respectively, the f ₀(980) and the a ₀(980) meson.     

Di-jet production in γ γ collisions at LEP2

The production of two high-p _T jets in the interactions of quasi-real photons in e ⁺ e ⁻ collisions at from 189 GeV to 209 GeV is studied with data corresponding to an integrated e ⁺ e ⁻ luminosity of 550 pb⁻¹. The jets reconstructed by the k _⊥ -cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p _T , above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum of the jets and is compared to perturbative QCD calculations. Deceased     

Reaction e + e ? → π + π ? π + π ? at energies of √ s ≤ 1 GeV

The e ⁺ e ⁻ → π ⁺ π ⁻ π ⁺ π ⁻ cross section is calculated for energies of 0.65 ≤ √s ≤ 1 GeV in the framework of the generalized hidden local symmetry model. The calculations are compared with the data of CMD-2 and BaBaR. It is shown that the inclusion of heavy isovector resonances ρ(1450) and ρ(1700) is necessary for reconciling calculations with the data. It is found that, at √s ≈ 1 GeV, the contributions of the above resonances are much larger, by a factor of 30, than the ρ(770) one, and amount to a considerable fraction ∼0.3–0.6 of the latter at √s ∼ m _ρ. The text was submitted by the authors in English.     

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.     

α-particle spectrum in the reaction p + 11B → α + 8Be* → 3α

Using a simple phenomenological parametrization of the reaction amplitude we calculated α-particle spectrumin the reaction p + ¹¹B → α + ⁸Be* → 3α at the resonance proton energy of 675 keV. The parametrization includes Breit-Wigner factor with an energy-dependent width for intermediate ⁸Be* state and the Coulomb and the centrifugal factors in α-particle-emission vertices. The shape of the spectrum consists of a well-defined peak corresponding to emission of the primary α and a flat shoulder going down to very low energy. We found that below 1.5MeV there are 17.5% of α’s and below 1MeV there are 11% of them. The text was submitted by the author in English.     

Simulation study of χc→J/Ψ+γ detection with J/Ψ→e+e? in pp collisions in the ALICE experiment at LHC

We present Monte Carlo preliminary results about the feasibility to detect the χ _c family in p-p collisions at 14 TeV in the ALICE Central Barrel at CERN LHC. The χ _c1 and χ _c2 were forced to decay in the radiative channel J/Ψ+γ→e ⁺ e ⁻+γ and were merged with a proton-proton non-biased collision. After Monte Carlo transport and simulation of the detector response, the e ⁺, e ⁻ and converted γ were reconstructed and identified in the ALICE ITS, TPC and TRD detectors. Separate signals corresponding to γ from χ _c1 and from χ _c2 were observed. The position and relative weight of the fit to gaussians agreed with the input values within the statistical limits. An erratum to this article can be found at     

Learning about flavour structure from τ→eβγ and μ→eγ?

Current and upcoming experiments should improve the sensitivity to e _α →e _β γ decays by an order of magnitude. This paper assumes that one of the τ→e _β γ decays is observed, and explores the structure and consequences of the required new flavoured couplings. In simple models (a low-scale seesaw, leptoquarks) it is shown that the dipole vertex function is proportional to a product of flavoured matrices from the Lagrangian (a “Jarlskog-like” invariant), provided that the loop particles are weakly coupled to the Higgs. Secondly, if the dipole vertex function has a hierarchical structure, this might imply that only some of the τ→e _β γ modes can be observed, due to the “approximate zero” implied by the bound on μ→eγ. The assumptions underlying this potential test of a hierarchical structure are discussed.     

B ?→ K 1*? (1270)(→ ρ 0 K ?) ? + ? ? in LEET

Flavor changing neutral current (FCNC) decays of the B-meson are a very useful tool for studying possible physics scenarios beyond the standard model (SM), where of the many FCNC modes radiative, purely leptonic and semi-leptonic decays of the B-meson are relatively clean tests. Within this context, the BELLE collaboration has measured the process B→K ^* γ and also searched for the B→K ₁(1270)γ process. Theoretical analyses of these processes are yielding similar values of the relevant form factors. In this work we have used this upper bound in studying the angular correlations for the related semi-leptonic decay mode B ⁻→K ₁⁻(1270)(→ρ ⁰ K ⁻)ℓ ⁺ ℓ ⁻, where we have used the form factors that have already been estimated for the B→K ₁(1270)γ mode. Note that the additional form factors that are required were calculated using large energy effective theory (LEET).     

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.     

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.     

Angular distributions of leptons from J/ψ’s produced in 920?GeV fixed-target proton-nucleus collisions

A study of the angular distributions of leptons from decays of J/ψ’s produced in p-C and p-W collisions at has been performed in the J/ψ Feynman-x region −0.34<x _F <0.14 and for J/ψ transverse momenta up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3×10⁵ J/ψ’s reconstructed in both the e ⁺ e ⁻ and μ ⁺ μ ⁻ decay channels, indicate that J/ψ’s are produced polarized. The magnitude of the effect is maximal at low p _T . For p _T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises. Many thanks to Antonio Vitale (1943–2008). Deceased. Supported by the Foundation for Fundamental Research on Matter (FOM), 3502 GA Utrecht, The Netherlands. Visitor from Dipartimento di Energetica dell’ Università di Firenze and INFN Sezione di Bologna, Italy. Visitor from P.N. Lebedev Physical Institute, 117924 Moscow B-333, Russia. Visitor from Moscow Physical Engineering Institute, 115409 Moscow, Russia. Visitor from Moscow State University, 119992 Moscow, Russia. Visitor from Institute for High Energy Physics, Protvino, Russia. Visitor from High Energy Physics Institute, 380086 Tbilisi, Georgia. Also from Fondazione Giuseppe Occhialini, 61034 Fossombrone (Pesaro Urbino), Italy. Supported by the CICYT contract AEN99-0483. Supported by the German Research Foundation, Graduate College GRK 271/3.     

J/ψ azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158?GeV per nucleon

The J/ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/ψ mesons at SPS energies. Hence, the measurement of J/ψ elliptic anisotropy, quantified by the Fourier coefficient v ₂ of the J/ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/ψ suppression observed in Pb-Pb collisions. We present the measured J/ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v ₂ as a function of the collision centrality and of the J/ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p _T sub-samples. The extracted v ₂ values are significantly larger than zero for non-central collisions and are seen to increase with p _T.     

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.     

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.     

B meson distribution amplitude from B→γ?ν

We reconsider the utility of the radiative decay B→γℓν with an energetic photon in the final state for determining parameters of the B-meson light-cone distribution amplitude. Including 1/m _b power corrections and radiative corrections at next-to-leading logarithmic order, we perform an improved analysis of the existing BABAR data. We find a provisional lower limit on the inverse moment of the B meson distribution amplitude, λ _B , which, due to the inclusion of radiative and power corrections, is significantly lower than the previous result. More data with large photon energy are, however, required to obtain reliable results, as should become available in the future from SuperB factories.