Charm mixing from BABAR

We present recent results from BABAR experiment for D⁰－D⁰ mixing measurements. Mixing parameters can be measured in different ways using different D⁰ decay modes, here we discuss the most sensitive analyses such as D⁰→K⁺π^－ where we had the first evidence of charm mixing, the measurement of the ratio of lifetimes of the decays D0→K⁺K^－ and D⁰→π⁺π^－ relative to D⁰→K^－π⁺, the time dependent Dalitz plot analysis of D⁰→K⁺π^－π⁰. New limits on CP-violating time-integrated asymmetries in D0→K⁺K^－ and D0→π⁺π^－ are also discussed. The analyses presented are based on 384 fb^－1 data collected with the BABAR detector at the PEP-II asymmetric B Factory.     

K介子稀有衰变及其对Multiscale WalkingTechnicolor模型的限制

在多标度人工色模型框架下计算了荷电PG玻色子π±1和π±8对K介子稀有衰变过程K⁺→π⁺νν,K_L→π⁰νν和K_L→μ⁺μ^－的企鹅图贡献.计算结果表明:(a)荷电PG玻色子可以对K介子稀有衰变分枝比给出1～3个量级的增强;(b)根据现有实验数据,K.Lane等人提出的多标度人工色模型基本被排除.     

Measuring D0-D0 mixing in D→f0(980) K and more

We investigate the D⁰-D⁰ mixing through the doubly Cabibbo suppressed (DCS) channel D0→f₀(980)K^*0 and its charge conjugate channel, in which the K^*0 meson is reconstructed in both K⁺π^－ and K_Sπ⁰ final state. Although the decay D⁰→f₀(980)K^* has a small branching ratio, the final state mesons are relatively easy to identify. The f₀(980) meson can be replaced by the S-wave π⁺π^－ state, or a longitudinally polarized vector meson ρ⁰. All mixing parameters, including the mass difference and decay width difference, can be extracted by studying the time-dependent decay width of these channels. We show that the method is valid in all regions for mixing parameters and it does not depend on the strong phase difference.     

Kl3介子衰变

本文通过强作用K-π中间态,利用色散关系理论计算了Г(K_μ3⁺)/Г(K_α3⁺),Г(K₂⁰→πμ⁺ν)/Г(K₂⁰→πe⁺ν),{Г(K₂⁰→πe⁺ν)+Г(K₂⁰→πe^-ν)}/Г(K_α3⁺)分支比及K_μ3⁺衰变中的μ谱,当选择定则|ΔI|=1/2及ΔS=+ΔQ被破坏,并且I_z=1/2及I_z=3/2的振幅f^{3/2 1/2}(0)及f^{3/2 3/2}(0)不等时,上述分支比与实验能很好符合。在本文的理论中,形式因子不是常数。     

The study of B→K()l+l- decays in family non-universal Z' models

In a combined investigation of B→K^(*)l⁺l^- decays, constraints on the related couplings in family non-universal Z' models are derived. We find that within the allowed parameter space, the recently observed forward-backward asymmetry in the B→K^(*)l⁺l^- decay can be explained by flipping the signs of the Wilson coefficients C₉^eff and C₁₀. With the obtained constraints, we also calculate the branching ratio of the B_s→μ⁺μ^- decay. The upper bound of our prediction is nearly an order of magnitude smaller than the upper bound given by the CDF Collaboration recently.     

Mini-review of rare charmonium decays at BESⅢ

Recently, the LHCb experiment announced 3.5σ evidence for direct CP violation in D⁰ decay by looking at the difference between A_CP(D⁰→K⁺K^-) and A_CP(D⁰→π⁺π^-). This is the rst evidence of CP violation in a charm system, which may indicate new physics beyond the Standard Model. Motivated by this measurement, we review rare processes in charmonium decay, especially, the weak decay, C or P violated decay, and lepton avor violated decays. In case the new physics appears in charm sector, these rare decays of charmonium states will provide an opportunity to search for signi cant contributions from physics beyond the Standard Model. With huge J/ψ and ψ(2S) samples in BES0 experiment, the rare decays may be feasible.     

New data on the p + N → [Σ0K+] + N reaction at E p= 70 GeV and the search for exotic baryons

New data for the diffractive reaction p+N→ [Σ⁰ K ⁺] +N at E _p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous study of this reaction. In the mass spectrum M(Σ⁰ K ⁺) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P ² _T < 0.01 GeV². The possibility of the Coulomb production mechanism for X(1810) is discussed. Received: 28 April 1999     

Formation of the XeI excimer sustained by dielectric barrier discharge in Xe／I2 at low pressure

Dielectric barrier discharge is used to study the mechanism of XeI excimer formation in the mixture of Xe and I₂ at low pressures (<1330 Pa). Fluorescence emission in the spectral region of 200－260 nm is examined. We report on the characteristics of the 253 nm emission intensity which varied with different total pressure. The results indicate that under the present experimental conditions, electron impact is the major reaction producing the excimer XeI(B), interpreted as Xe⁺+I₂^-→XeI(B)+ I^*, then radiating 253 nm fluorescence from transition B→X. The 253 nm emission increases with the total gas pressure up to a maximum value at a pressure of about 540 Pa, then decreases as the gas pressure is further increased. The 206 nm emission is determined by I^* from ionic recombination between Xe⁺ and I₂^-. This result differs from previous works under other experimental conditions.     

INFLUENCE OF C+-IMPLANTATION DOSE ON BLUE EMISSION AND MICROSTRUCTURES OF Si-BASED POROUS β-SIC

Crystal Si were implanted with different doses of C⁺ from 10¹¹ to 10¹⁷ cm^-2 at an energy of 50 keV. β-SiC precipitates were formed by thermal annealing at 1050 ℃ for 1 h and porous structures were prepared by electrochemical anodization. Under the excitation of ultraviolet, the samples, with C⁺ dose ≥10¹⁵ cm^-2 have intense blue emission which is stronger than the photoluminescence (PL) intensity of reference porous silicon (PS), and increases as C⁺ dose increases; the samples with C⁺ dose ≤10¹⁴ cm^-2 show similar PL spectra to those of PS. The blue peak intensity in PL spectra is correlated with the TO phonon absorption strength of β-SiC in infrared absorption spectra. The transmission electron microscopy study shows that the blue peak is also correlated with the microstructures. Because porous β-SiC is nanometer in size, it is suggested that the quantum confinement effect be responsible for the blue light emission.     

OZI rule violation in p¯p annihilation into φππ by two step processes

The φπ⁺π⁻ production in pˉp annihilation at rest is strongly enhanced by a two step mechanism with intermediate KˉKππ states. The relative yield of the φ production due to the resonant final state interaction decreases with increasing total energy of the pˉp system. Received: 4 August 1997     

The chiral-bag model andK→2π decays

Nonleptonic kaon decays (K→2π) have been analyzed using the chrial-bag model. This continues the research of nonleptonic decays by the authors (Ref. [7] below). The results obtained are in qualitative agreement with those based on QCD-duality. the decay amplitudeA(K ⁺→π⁺π⁰) (ΔI=3/2) can be explained while the ΔI=1/2 decay amplitudes are 4 to 5 times smaller then the observed values. The ratio ofK ⁰ decay amplitudes ξ=|A(K ⁰→π⁺π^?)/A(K ⁰→π⁰π⁰| is larger than one, as it is experimentally. This is an improvement in comparison with MIT-bag model, where ζ was always smaller than one, even if ΔI=1/2 pieces in the theoretical expressions were enhanced.     

Search for the Decays D+→φe+ν,D+→φK－π+e+ν,D0→φK－e+νand D0→φK－μ+ν

We report the results of a search for the semileptonic decays D⁺→e⁺ν,D⁺→K^－π⁺e⁺ν,D⁰→K^－e⁺ν and D⁰→K^－μ⁺ν using the BES detector at the BEPC e⁺e^－ Collider. Using a data sample of 22.3pb^－1 collected at the center of mass energy s=4.03GeV, we select 2472±87D 0 tag DX and 7628±149D 0 tag DX singly tagged D events, where the X could be γ, π 0 and/or π^±. Based on the method of "combined D⁺and D⁰ single and double tags", we determine that 2471±218 D⁺X and 7629±251 D⁰ X are contained in the recoil side of the singly tagged neutral and charged D mesons, respectively. No events for the 4 semileptonic decay modes are observed in the recoil side of the tagged D mesons. The 90% confidence level upper limits of B(D⁺→e⁺ν)<1.38%,B(D⁺→K^－π⁺e⁺ν)<2.01%,B(D⁰→K^－e⁺ν)<0.53% and B(D⁰→K^－μ⁺ν)<0.53% are determined from the search for the semileptonic decays of D⁺ and D⁰.     

A simple chiral Lagrangian approach toK→πππ decays andε′+0−

We analyse theK→πππ decays in the framework of a chiral Lagrangian supplemented by the 1/N expansion (N being the number of colors). The measuredK _L →π⁺π⁰π⁺ Dalitz plot is very well reproduced. Contrary to a recent claim, the Li-Wolfenstein relation between the CP impurities associated with theK→πππ(ε′_+0?) and theK→ππ(ε′) decay amplitudes is rather stable against isospin-breaking effects and higher-order (in the chiral expansion) weak operator corrections. We also predict a branching ratio of 2.1 10^?7 for the CP-conservingK _S →π⁺π⁰π⁺ decay.     

Estimate of the probability of K+→μ+νμγ decay

About 100 000 K⁺-decays were observed in a magnetic spectrometer with streamer chambers. The estimation for the radiative decay K⁺→μ⁺ν_μγ, R^exp = [W(K⁺→μ⁺ν_μγ)]/[W(K⁺→all)]=(5.8±3.5) x 10^?3, at E_γ ? 9 MeV was obtained and the ratio R = [W(K⁺→π⁺π°)]/[W(K⁺→μ⁺ν_μ)] = 0.328 ± 0.005 was measured.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Coherent production of theK −π+π− system inK −d interactions at 4.5 GeV/c

After summarizing the properties of the socalled Dalitz Array (DA), which is a genuine characteristics of a resonance, we determine those of the well known ε, γ, andA ₂ resonances produced in theK ^? p→π⁺π^?π⁰ Λ final state at 4.2 Ge V/c. A tentative measurement of the DA of theA ₁ meson produced backwards in the reactionK ^? p→π⁺π⁺π^?Σ^? is also presented. The data for this analysis come from the high statistics (130 events/μb) experiment performed by the ACNO Collaboration.     

Hyperfeinstrukturuntersuchung des 6p 2 P 3/2-Terms im Au I-Spektrum durch Resonanzstreuung von Licht

From about 6×10⁶ stoppingK ^?-meson reactions in the Saclay 80 cm hydrogen bubble chamber 70Σ ^?→Λe^?¯ν and 11Σ⁺→Λe⁺ν decays have been identified. The ratio of the vector to axial vector coupling constant has been determined,f ₁/g ₁=?0.22±0.28, consistent with the predictionf ₁=0 of the CVC-theory. The branching ratios for the two decay modes are,Γ(Σ ^?→Λe^?ν)/Γ(Σ^?→ all modes)=(0.69±0.12). 10^?4,Γ(Σ⁺→Λe⁺ν)/Γ(Σ⁺→ all modes)=(0.29±0.10). 10^?4. The ratio, Γ(Σ⁺→Λe⁺)/Γ(Σ^?→Λe^?v)=0.69±0.18, agrees with the phase space ratio, 0.61, therefore a theory that includes no second class currents is consistent with the data.     

K→ππγ and chiral perturbation theory

Weak radiative decaysK _L,S →π⁺π^?γ andK ⁺→π⁺π⁰γ are reexamined. The electromagnetic form factors and long-distance contributions to the direct photon emission are evaluated using the higher order effective chiral Lagrangian. We find that (1) the naive soft-pion theorem cannot be applied to the magnetic-type transition amplitude, (2) the shortdistance contribution toK _L →π⁺π^?γ is comparable to or even bigger than the long-distance one, (3) the ΔI=1/2 enhancement persists in the decayK ⁺→π⁺π⁰γ, (4) to the order of 1/Λ _χ ² (Λ _χ being the chiral-symmetry breaking scale) the direct photon emission amplitude does not receive a contribution from penguin operators, and (5) the 1/N _c expansion improves the discrepancy between theory and experiment.     

Measurement of the branching ratio for Υ(1S) state intoπ + π − andsearch for decaysΥ(1S)→π + π −,K + K −,p \bar p

In the experiment withe ⁺ e ^?-beams performed at the VEPP-4 storage ring with the MD-1 detector we have measuredB _μμ, the branching ratio for the decay of Υ(1S) state intoμ ⁺ μ ^?. We obtainedB _μμ=(2.12+0.20+0.10)%. It is shown that the continuum and resonance interference should be taken into account. For the first time the upper limits on the branching ratio for the decaysΥ→π ⁺ π ^?,K ⁺ K ^?,p \(\bar p\) have been measured: Br(Υ→π ⁺ π ^?)<5·10^?4, Br(Υ→K ⁺ K ^?)<5·10^?4, Br(Υ→p \(\bar p\) <9·10^?4 (90% CL).     

Bounds on the masses of neutral generation-changing gauge bosons

The existence of several generations of quarks and leptons suggests the possibility of a gauge symmetry connecting the different generations. The neutral gauge bosons of such a scheme would mediate rare processes such as K_L⁰→μ^±, K⁺→π⁺e^?π⁺, μN→eN and would contribute to ΔM(K_S⁰?K_L⁰). We study these and other processes within a simple theoretical framework and derive bounds involving the masses and coupling constants of the generation-changing gauge bosons and various generation-mixing angles. The lower bounds for the relevant masses lie in the 10–100 TeV region. Various remarks concerning the relevance of these bounds to currently popular theoretical ideas and to future experiments are presented.