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.     

e+e－→π+π－π+π－形状因子拟合

基于BABAR实验组对e⁺e^－→π⁺π^－π⁺π^－的反应截面的测量结果, 用VMD模型给出的理论截面拟合实验数据, 首次从单一反应道得到π⁺π^－π⁺π^－末态形状因子的所有参数值.     

Search for and study of low-mass scalar mesons in reactions np → npπ+π? at neutron beam momentum Pn = (3.83 ± 0.12) GeV/c

The results of a search for and study of the scalar 0⁺ [0⁺⁺] σ₀ mesons in a π⁺π⁻ system produced in the reaction np → npπ⁺π⁻ at the quasi-monochromatic neutron beam momentum P _n = (3.83 ± 0.12) GeV/c are presented as derived from analyzing the data obtained during the exposure of a 1-meter hydrogen bubble chamber at the Laboratory of High Energy, Joint Institute for Nuclear Research (LHE JINR). It is found that there is a significant bump in the effective mass distribution at M_{p⁺ p^-} = (404 ±5)MeV/c²M_{\pi ^ + \pi ^ - } = (404 \pm 5)MeV/c^2 and Γ_res^exp = (14±5.4) MeV/c ², which is observed with more than four standard deviations from the background. The spin of this resonance is estimated to be most likely equal to zero. Its quantum numbers are found to be 0⁺ [0⁺⁺].     

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).     

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).     

J/ψ→π03(π+π－)分支比的测定

用BESⅠ的7.8×10⁶J/ψ数据更为精确地测定了J/ψ→π⁰3(π⁺π^－)和J/ψ→ω²(π⁺π^－)的分支比(Br(J/ψ→π⁰3(π⁺π^－))=(2.52±0.06±0.43)%,Br(J/ψ→π⁰3(π⁺π^－))=(1.31±0.09±0.21)%.同时对4π不变质量谱和ωππ不变质量谱进行研究分析,试图观察是否存在有兴趣的信号.     

在J/ψ衰变与ρ→π+π–π0衰变中的ρ–ω干涉

通过分析J/ψ→π⁺π^-π^{0π0来研究ρω干涉.利用描述J/ψ衰变的一般的唯象模型对PDG-2002关于J/ψ衰变到PP和PV的实验数据做了拟合(P表示赝标介子,V表示矢量介子) ,得到ρ0→π+π-π0反常大的分支比～10-3—10-2.理论的分析结果也与这一反常大的分支比相符合.同时,得到了合理的ηη′混合角和组分夸克质量比:θ=-19.68°±1.49°,m_u/m_s≈0.6 .}     

a2(1320)→π+π+π－过程的三体振幅分析

对a₂(1320)→π⁺π⁺π^－过程的衰变振幅进行张量分析,展示了如何得到三体衰变振幅.     

Effect of unitarization on the amplitudes for the decays K10 → π+π? and K+ → π+π+π?

The unitarization of the amplitude for the decay process K ₁⁰ → π⁺π⁻ and allowance for the rescattering of final-state pions in the decay process K ⁺ → π⁺π⁺π⁻ make it possible to evaluate, by using the parameters extracted from data on K → 2π decays, the K ⁺ → π⁺π⁺π⁻ decay width. The result agrees with the experimental width value at a level of a few percent. Allowance for corrections for higher order terms of the momentum expansion of the amplitude for the decay process K ⁺ → π⁺π⁺π⁻ leads to the slope-parameter value of g ₊₊₋^th = 0.2182, which agrees with its experimental counterpart, g ₊₊₋^exp = 0.2154 ± 0.0035.     

ρ0 production the reaction ξξ→3π+3π?ξξ→ρ0ρ0(1700)

We have studied the ⁰ production rate in the reaction 3⁺3^– in the energy range 1.6W 7.5 GeV with the CELLO detector at PETRA. Our analysis points to a substantial yield of ^00+– events in particular atW >4.0 GeV. We give cross sections for the ⁰2⁺2^– and ^00+– final states and calculate upper limits for the reaction ⁰⁰ (1700) ^00+–.Now at CERN     

AGS能量下π－π－的Bose—Einstein关联

全同粒子间的玻色-爱因斯坦关联可以用来研究相对论性核碰撞中次级粒子源分布及有关的物理问题.本文用强子级联模型(HCM)模拟²⁸Si(14.6A GeV/c)+Au反应,得到π^－粒子的freeze-out状态,进而计算了π^－π^－关联函数,取得与实验一致的结果.还计算了freeze—out π^－源的均方根线度,并讨论了它与拟合方法抽取的源参数间的关系.     

Non-factorizable contributions in D0→π+π- decay

We have analyzed the D^0→π^+π^- decay with α_s corrections in quantum chromodynamic (QCD) factorization and with the soft-gluon corrections in the light cone QCD sum rules. The soft-gluon effects are firstly calculated in the decay channel. The results show that once the factorization contributions, the α_s corrections, and the soft-gluon effects are all considered, we can satisfactorily explain the experimental data in the decay channel.     

τ→π±2π0v结构函数的测量

首次对τ→π^±2π⁰v衰变的结构函数进行了模型无关的实验测量,并与KS模型、IMR模型和Feindt模型进行了比较,在误差范围内,三种理论模型与实验结果一致.与OPAL组测量的τ→3π^±v道的结构函数相比,在0.52范围内未发现明显差异.     

CP -violation effects in the decays B ? → D * K *? and method for determining the weak phase γ

A method for determining the angle γ and the ratio of the amplitudes A _λ(B ⁻ → K ^*−) and A _λ)B ⁻ → D ^*0 K ^*−), r _Bλ, for all three vector-meson polarization states by using the decays B ^∓ → D ^* K ^*∓ is proposed. This method relies on the interference between the decays B ⁻ → D ^*0 K ^*− and B ⁻ → K ^*−, which arises if D ^*0 and decay to D ⁰/ π ⁰ and D ⁰/ γ, whereupon D ⁰ and mesons decay to common final hadron states. The doubly Cabibbo-suppressed modes of D ⁰-meson decay are chosen here to specify such final states. Original Russian Text ? V.A. Kovalchuk, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 4, pp. 754–763.     

通过τ→a1v→π±π0π0v道测量由Z0衰变的τ的极化不对称性

利用L3合作组1992年和1993年的数据,通过τ→a₁v→π^±π⁰π⁰v道测量了由Z⁰衰变的τ的极化不对称性A_pol=－0.239±0.126±0.100,其中第一项误差为统计误差,第二项误差为系统误差.由此推断有效电弱混合角sin²θ_w=0.2197±0.0219.     

Final-state interactions in the decay B 0→ η c K *

We study the final-state rescattering effects in the decay B ⁰→η _c K ^*. The numerical results indicate that the corrections are comparable with the contribution from the naive factorizable amplitude, and the total amplitudes can accommodate the experimental data.     

On the spin correlations of muons generated in the annihilation process e + e ? → μ+μ?

Using the technique of helicity amplitudes, the electromagnetic process e ⁺ e ⁻ → μ⁺μ⁻ is theoretically investigated in the one-photon approximation. The structure of the triplet states of the final (μ⁺μ⁻) system is analyzed. It is shown that in the case of unpolarized electron and positron the finalmuons are also unpolarized, but their spins are strongly correlated. Explicit expressions for the components of the correlation tensor of the final (μ⁺μ⁻) system are derived. The formula for the angular correlation at the decays of final muons μ⁺ and μ⁻, produced in the process e ⁺ e ⁻ → μ⁺μ⁻, is obtained. It is demonstrated that spin correlations of muons in the process of electron-positron pair annihilation have the purely quantum character, since one of the incoherence inequalities for the correlation-tensor components is always violated. The additional contribution of the weak interaction of lepton neutral currents through the virtual Z ⁰ boson is considered; it is established that, taking into account the weak interaction, the qualitative character of the muon spin correlations does not change. The text was submitted by the authors in English.     

π+介子光生中的π-π作用效应

在对于质子上的π⁺光生过程作了一般考虑以后,我们从Mandelstam表示出发,进而采用Cini-Fubini近似,导出了关于π光生幅的同位标部分的公式。按照核子电磁结构的新数据,我们选取π-π作用的I=J=l共振的参数为t_r=22,α_v=1.52,b_v=1.60,计算了(dσ)/(dΩ)(90°),(dσ_‖)/(dσ_⊥)(90°)以及三个能量下的角分布。结果表明,在加入π-π作用之后,与实验之间的调合比之Chew等的结果有很大的改进,所定出的γ+π→π+π的耦合常数约为∧≈-2.8e,这与时行的结果大致相符。     

The 16 O( e, e‘ pp) 14 C reaction to discrete final states

Differential cross-sections for exclusive ¹⁶O(e,epp)¹⁴C processes are computed within a distorted-wave framework which includes central short-range correlations and intermediate excitations. The cross-sections are compared to high-resolution data from the MAMI facility at Mainz for a central energy and momentum transfer of MeV and MeV, respectively. A fair agreement between the numerical calculations and data is reached when using spectroscopic information extracted from a ¹⁵N C experiment. The comparison between the calculations and the data provides additional evidence that short-range correlations exclusively affect nucleon pairs with a small center-of-mass momentum residing in a relative S state.Received: 3 September 2003, Revised: 2 December 2003, Published online: 18 June 2004PACS: 24.10.-i Nuclear-reaction models and methods - 21.60.-n Nuclear-structure models and methods - 25.30.Fj Inelastic electron scattering to continuum     

Deexcitation of K π = 0 2+ , 0 3+ , and 21/+ levels by M 1 transitions in nonspherical even-even nuclei

The signs of the experimental values of the multipole-mixture parameters δ are compared with the signs of ℛ = Σa _i μ _i for (2⁺0₂−2⁺0₁) and (2⁺0₃−2⁺0₁) transitions and with the signs of = Σa _i [(μ _i + μ _kν ) or (μ _kπ − 1/2)] for (2⁺2₁−2⁺0₁) transitions in nonspherical even-even nuclei, where a _i is the contribution of the ith pair of quasiparticles to the wave function for 2⁺0₂, 2⁺0₃, and 2⁺2₁ single-phonon states according to the quasiparticle-phonon model and μ is the magnetic moment for the corresponding Nilsson state. Original Russian Text ? A.M. Demidov, L.I. Govor, V.A. Kurkin, I.V. Mikhailov, 2009, published in Yadernaya Fizika, 2009, Vol. 72, No. 2, pp. 228–235.