Superallowed 0+ → 0+ beta-decay and CKM unitarity

Precise measurements of the ft-values for superallowed nuclear β-decay yield results that support conservation of the weak vector current but violate the unitarity of the Cabibbo-Kobayashi-Maskawa matrix by more than two standard deviations. This apparent violation of the Standard Model has led to considerable theoretical and experimental activity largely focussed on reducing uncertainties in the small correction terms that account for charge-dependent nuclear effects. This activity is outlined and the prospects for future sharpening of the unitarity test are assessed. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: hardy@comp.tamu.edu     

Supersymmetric Box Contributions toe + e −→Z 0 h 0 ande + e −→A 0 h 0

Within the MSSM we calculate the electroweak 1-loop box contributions to the processese ⁺ e ^–Z ⁰ h ⁰ ande ⁺ e ^–Z ⁰ h ⁰. We present detailed results for c.m. energies and as well as for tan =2 and tan =50. The box contributions to the processe ⁺ e ^–Z ⁰ h ⁰ are, depending on and tan , of the order –2 to –20% and toe ⁺ e ^– A ⁰ h ⁰ of 2 to 10%.     

Production of a0 +-mesons in the reaction pp↦da0 +

We investigate the reaction pp↦da ₀ ⁺ at COSY and SIS energies together with accompanying background reactions and inclusive particle yields. The a ₀ ⁺ is considered as a usual u quark model state with two decay channels a ₀ ⁺↦K ⁺ and a ₀ ⁺↦π⁺η. Calculated cross-sections for a ₀ ⁺ production as well as for the corresponding non-resonant channels pp↦dK ⁺ and pp↦dπ⁺η are compared. Especially, in case of the final channel dπ⁺η, high statistics measurements are necessary to extract the a ₀ ⁺ signal from the high non-resonant background. Received: 20 December 2000 / Accepted: 7 May 2001     

Investigation of isospin forbidden 0+ → 0+ Fermi beta decays with Pyatov method

In the present work, the matrix elements, isospin impurities and log ft values of the isospin forbidden 0⁺ → 0⁺ beta decays have been investigated. The calculated results have been compared with available experimental and another theoretical data. The isotopic invariance of the Hamiltonian has been restored by Pyatov method. Within the quasi-particle random phase approximation (QRPA), the computations have been performed both in presence and absence of the pairing interactions.     

e+e-→e+e-π0π0 at DAΦNE

The production of the σ(500) meson in γγ→π⁰π⁰ is studied. In particular, the KLOE data collected during the DAΦNE run at are appropriate to this purpose because of the strong reduction of kaon backgrounds. PACS 12.39.-x     

On polarization of strange baryons in reactions p + p↦p + Λ0 + K+ and p + p↦p + Σ0 + K+ near thresholds

Polarization properties of strange baryons produced in pp reactions, p + p↦p + Λ⁰ + K⁺ and p + p↦p + Σ⁰ + K⁺, near thresholds of the final states pΛ⁰K⁺ and pΣ⁰K⁺ are analysed relative to polarizations of colliding protons. The cross-sections for pp reactions are calculated within the effective Lagrangian approach accounting for strong pp rescattering in the initial state of colliding protons with a dominant contribution of the one-pion exchange and strong final-state interaction of daughter hadrons (Eur. Phys. J. A 9, 425 (2000)). Received: 22 October 2001 / Accepted: 14 November 2001     

Zum experimentellen Nachweis von Zweiquantenzerfall beim 0+-0+-Übergang des Zr90

With a scintillation coincidence spectrometer it has been tried to detect double quantum emission in the 0⁺-0⁺ transition of the first excited level of Zr⁹⁰. An effect, probably due to double quantum emission gives 2·10^?3 for this decay mode. This level is reached byβ-decay of Y⁹⁰. From a measurement of the positron annihilation radiation it follows, that (3,4±0,4)·10^?5 pairs deexciting this level are created perβ-decay of Y⁹⁰.     

Annihilation of + \bar p + p → e + + e ? + π0 and + \bar p + p → γ + π0 through an ω-Meson intermediate state

The s-channel annihilation of a proton and an antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such a mechanism is expected to play a role at moderate values of the total energy $ \sqrt s $ , when the pion is emitted in the angular region around 90° in the center-of-mass system. A fair comparison with the existing data is obtained taking scattering and annihilation channels into account. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.     

Search for the rare decays K(L)→π0π0μ+μ- and K(L)→π0π0X0→π0π0μ+μ-

The KTeV E799 experiment has conducted a search for the rare decays, K(L)→π(0)π(0)μ(+)μ(-) and K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-), where the X(0) is a possible new neutral boson that was reported by the HyperCP experiment with a mass of (214.3 ± 0.5) MeV/c(2). We find no evidence for either decay. We obtain upper limits of Br(K(L)→π(0)π(0)X(0)→π(0)π(0)μ(+)μ(-)) < 1.0 × 10(-10) and Br(K(L)→π(0)π(0)μ(+)μ(-)) < 9.2 × 10(-11) at the 90% confidence level. This result rules out the pseudoscalar X(0) as an explanation of the HyperCP result under the scenario that the dsX(0) coupling is completely real.     

Partition temperatures ofK 0 andΛ 0 fromπ + p collisions

The rapidity distributions of inclusive ⁺ p ^–,K ⁰, ⁰ andK ^* (892) atP _1ab=16 GeV/c of CERN experiments, are analyzed using the covariant partition temperatureT _p model. In the fireball system, apart fromK ^* (892),T _p ^* m, no indication of thermal equilibrium, the average momentum ofK ⁰ and ⁰ being approximately equal and in the opposite direction, the entropy density is practically the same forK ⁰ and ⁰ but less than that of ^–. It is found that the principle of equipartition holds rather for the momenta of ,K, and in the fireball system.     

Study of Exclusive Hadronic Decays for D0→Ks0π+π- and D0→Ks0K+K- and Their Resonant Structures

We report the results of an experimental study of the exclusive hadronic decays for D0→K0 sπ+π - and K 0 sK +K - and their resonant structures using BES-Ⅰ detector at the BEPC Collider. Using the data sample of 22.3 pb -1 collected at the center-of-mass energy s=4.03 GeV, we measured the branching fraction for D 0→K 0π +π - to be (5.32±0.53±0.40)%, the branching fractions for the decays D 0→ K *-π +, D 0→K 0ρ 0 and D 0→K 0(π +π -) non-resonant to be (6.05±0.32±0.49)%, (1.17±0.17±0.13)% and (1.35±0.22±0.17)%, respectively. We measured the branching fractions Br(D 0→f) to be (1.04±0.24± 0.16)% for f=K 0K +K -, (1.12±0.34±0.15)% for f=K0, and (0.27±0.13±0.03)% for f=K 0(K+K-)non-.     

遍举衰变过程D0→Ks0π+π–和D0→Ks0K+K–及其共振态结构的实验研究

利用北京谱仪(BES–Ⅰ)在北京正负电子对撞机(BEPC)e+e–质心系能量为4.03GeV处采集的积分亮度为22.3pb–1的数据,研究了D0→K0sπ+π–,D0→K0sK+K–的衰变及其末态的共振结构.实验测得D0→K0sπ+π–过程的分支比为(5.32±0.53±0.40)%;D0→K–π+,D0→K0ρ0和D0→K0s(π+π–)non resonance过程的分支比分别为(6.05±0.32±0.49)%,(1.17±0.17±0.13)%和(1.35±0.22±0.17)%;测得D0→K0sK+K–,D0→K0和D0→K0(K+K–)non?的分支比分别为(1.04±0.2?4±0?.16)%,(1.12±0.34±0.15)%和(0.27±0.13±0.03)%.     

TheK S 0 →π0 l + l − andK L 0 →π0 l + l − decays in the standard model and the extended Nambu-Jona-Lasinio model

TheK _S ^{0 0} l ⁺ l ^– andK _L ^{0 0} l ⁺ l ^– decays are considered within the framework of the Standard model in the one-photon exchange approximation, i.e.K _S,L ^{0 0}+ *⁰ +l ⁺ l ^–. To evaluate the low-energy matrix elements of theK ⁰(¯K ⁰)⁰+ * transitions, the constituentquark-loop approximation, based on the extended Nambu-Jona-Lasino (NJL) model, is used. The obtained results are compared with other theoretical estimates and the experimental bounds.     

On the reactions p + p↦p + Λ + K+ and p + p↦p + Σ0 + K+ near thresholds

The cross-sections for the reactions of the strange production p + p ↦ p + Λ + K⁺ and p + p ↦ p + Σ⁰ + K⁺ near thresholds of the final states pΛK⁺ and pΣ⁰K⁺ are calculated in the effective Lagrangian approach. Our approach is based on the dominant contribution of the one-pion exchange and strong interaction of the colliding protons in the initial state. The theoretical values of the cross-sections agree reasonably well with the experimental data. The polarization properties of the Λ- and Σ⁰-hyperons are discussed.     

Comparison ofW ±+jet andZ 0+jet production at hadron colliders

We analyse the lowest-order QCD production mechanisms forp \(\bar p\) →W ^±+jet andp \(\bar p\) →Z ⁰+jet to find possible differences in jet properties for the two processes.     

The e + e −→π0π0γ process below 1.0 GeV

The e ⁺ e ^?→π⁰π⁰ γreaction was studied in the energy range 0.36–0.97 GeV on a VEPP-2M e ⁺ e ^? collider with an SND detector. The decay probabilities were found to be B(ω→ π⁰π⁰γ)= (7.8 ±2.7±2.0)×10^?5 and B(π→ π⁰π⁰γ)= (4.8 _?1.8 ^+3.4 ±0.2)×10^?5.     

遍举衰变过程D~0→K_s~0π~+π~-和D~0→K_s~0K~+K~-及其共振态结构的实验研究(英文)

利用北京谱仪 (BES -Ⅰ )在北京正负电子对撞机 (BEPC)e+ e-质心系能量为 4 .0 3GeV处采集的积分亮度为 2 2 .3pb-1的数据 ,研究了D0 →K0sπ+ π-,D0 →K0sK+ K-的衰变及其末态的共振结构 .实验测得D0 →K0sπ+ π-过程的分支比为 (5 .32± 0 .5 3± 0 .4 0 ) % ;D0 →K -π+ ,D0 →K0 ρ0 和D0 →K0s(π+ π-)non resonance过程的分支比分别为 (6 .0 5± 0 .32± 0 .4 9) % ,(1.17± 0 .17± 0 .13) %和 (1.35± 0 .2 2± 0 .17) % ;测得D0 →K0sK+ K-,D0 →K0 和D0 → K0 (K+ K-) non 的分支比分别为 (1.0 4± 0 .2 4± 0 .16 ) % ,(1.12± 0 .34± 0 .15 ) %和 (0 .2 7± 0 .13±0 .0 3) % .     

碰撞能对O++DH (v=0, j=0)→OD++H的准经典轨线

运用准经典轨线的方法,基于RODRIGO势能面,研究反应体系O⁺+DH (v=0, j=0)→OD⁺+H的立体动力学性质. 对描述k-j′两矢量相关和k-k′-j′三矢量相关的分布函数P(θr)和P(φr)以及产物转动取向参数进行了详细的讨论,发现极化微分反应截面呈现有趣的现象. 计算了反应几率与反应截面. O⁺+DH (v=0, j=0)→OD⁺+H反应的立体动力学性质对体系的碰撞能非常敏感.