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1.
The decays η → 3π 0 and ηπ 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.  相似文献   

2.
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,ππ are separated into perturbative and soft parts. In F π,K the latter are ≥O(10) larger. A PC fit to the B,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,ππ fit with the Standard Model appears to be naturally realized. The CP asymmetries SKs p0S_{K_{s} \pi^{0}}, CKs p0C_{K_{s} \pi^{0}} are well determined, providing a clean test for new physics.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
The ratio of the ψ′ over the J ψ production cross section in the dielectron channel has been measured in $ \sqrt s $ \sqrt s = 200 GeV p + p collisions with the PHENIX detector at RHIC. The analysis is based on fitting of the dielectron invariant mass spectra in the area around the J ψ and ψ′ signals in order to extract a ratio ψ′ over J ψ of 0.019 ± 0.005 (stat) ± 0.002 (sys) and a fractional feed-down contribution to J ψ from ψ′ of 8.6 ± 2.5%.  相似文献   

6.
In this article, we study the decays ψ′ → J/ψπ + π and ηcη 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 ηcη 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.  相似文献   

7.
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.  相似文献   

8.
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 ΛNC∼TeV.  相似文献   

9.
Monte-Carlo generator with photon jets radiation in collinear regions for the process e + e γγ is described in detail. Radiative corrections in the first order of α are treated exactly. Large leading logarithmic corrections coming from collinear regions are taken into account in all orders of α by applying the Structure Function approach. Theoretical precision of the cross section with radiative corrections is estimated to be 0.2%. This process is considered as an additional tool to measure luminosity in forthcoming experiments with the CMD-3 detector at the e + e collider VEPP-2000.  相似文献   

10.
11.
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 pπ 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 pπ 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.  相似文献   

12.
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(mp+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 (ϒ(4S)→ϒ(2S,1S)π + π )/dcosθ, which have not been measured yet.  相似文献   

13.
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.  相似文献   

14.
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.  相似文献   

15.
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.  相似文献   

16.
We present an analysis with improved sensitivity to the light charged Higgs (mH+ < mt-mbm_{H^{+}} < m_{t}-m_{b}) searches in the top quark decays tbH +b(τ + ν τ )+c.c. in the t[`(t)]t\bar{t} and single t/[`(t)]t/\bar{t} production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio B (H+ ?t+nt) @ 1{\mathcal{B}} (H^{+} \to\tau^{+}\nu_{\tau})\simeq1 over almost the entire allowed tanb\tan\beta range. Noting that the τ + arising from the decay H +τ + ν τ are predominantly right-polarized, as opposed to the τ + from the dominant background W +τ + ν τ , which are left-polarized, a number of H +/W +τ + ν τ discriminators have been proposed and studied in the literature. We consider hadronic decays of the τ ±, concentrating on the dominant one-prong decay channel τ ±ρ ± ν τ . The energy and p T of the charged prongs normalised to the corresponding quantities of the ρ ± are convenient variables which serve as τ ± polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays tbH + (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system determined using Lagrange multipliers.  相似文献   

17.
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.  相似文献   

18.
19.
A possibility of KLOE-2 experiment to measure the width \varGammap0 ?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 \varGammap0 ?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.  相似文献   

20.
Contact interactions are searched for using the differential cross sections for the reactionse + e e + e ,e + e µ + µ ,e + e + ande + e measured at 12 energies around theZ peak and corresponding to about 20 pb–1 of cumulated luminosity. Four-fermion contact term models assuming various chiralities of lepton currents are fitted to the lepton data and lower limits on the energy scale of such terms are set at 95% c.l. The limits vary in the range 0.9–4.7 TeV, depending on the model and on the lepton flavour. Theee contact terms are searched for assuming various chiralities. Limits on the energy scale between 79 and 130 GeV are extracted from the data. The results are compared and combined with those reported at lower energies.Deceased  相似文献   

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