Single decay-lepton angular distributions in polarizede + e − →\overline {tt} and simple angular asymmetries as a measure of CP-violating top dipole couplingsand simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of $\overline {tt} $ to a photon, and an analogous ‘weak’ dipole coupling to the Z, CP violation in the process e⁺e^? → $\overline {tt} $ results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when eithert or $\overline t $ decays leptonically, including $\mathcal{O}$ (α_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of thet or $\overline t $ , are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at √ s = 500 GeV with integrated luminosity 500 fb^? and also at √s = 1000 GeV with integrated luminosity 1000 fb^? have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.     

CP violation with beautiful baryons

CP violation can be studied in modes of charmed or bottom baryons when a decay process is compared with its charge-conjugated partner. It can show up as a rate asymmetry and in a study of other decay parameters. Neither tagging nor time-dependences are required to observeCP violation with modes of baryons, in contrast to the conventionalB ⁰ modes. Numerous modes of bottom baryons have the potential to show largeCP-violating effects within the Standard Model. Those effects can be substantial for modes with aD ⁰, which is seen in a final state that can also be fed from a \(\bar D^0 \) . For instance, a comparison of theΛ _b→Λ _CP ⁰ with the \(\bar \Lambda _b \to \bar \Lambda D_{CP}^0 \) process can show sizeableCP violation. HereD _CP ^o denotesCP eigenstates ofD ⁰, which occur at a few percent. Six related processes, such asΛ _b→ΛD ⁰, \(\Lambda _b \to \Lambda \bar D^0 \) ,Λ _b→Λ _CP ⁰ , and their charge-conjugated counterparts, can extract ?, which is the most problematic angle of the unitarity triangle and which is conventionally probed with theB _s→ρ⁰ K _S asymmetry. HereD ⁰ andD ^?0 are identified by their charged kaon or lepton. We predictB(Λ _b→ΛD ⁰)～10^?5, thusB(Λ _b→Λ _CP ⁰ )～10^?7. Under favourable circumstances,CP violation can occur at the few tens of percent level. Thus 10²–10³ Λ _b→Λ _CP ⁰ decays start probing ?. Tables list many additional modes with typical branching ratios at the 10^?5–10^?6 level, with large detection efficiencies (in contrast to theD _CP ⁰ ), and with potentially largeCP-violating effects, such as Ξ _b ⁰ →ΛΨ, Λ?, ΛK^*0; Ξ _b ^? →ΛK^(*)?, Ξ^?K_s, Ξ^?K^*0, Ω _b ^? →Ξ^?φ, Ξ^?ρ⁰, ΛK^(*)?, ΩK_s, Ω^?K^*0.     

Is there a puzzle in the π0→e + e − decay?

We show the importance of precise experimental cuts in π⁰→e ⁺ e ^? decay measurements. Similar cuts have little effect in η(K _L ⁰ )→μ⁺μ^? decays.     

Leptonic CP violation in leptoquark models

We study the leptonic CP violation effects in leptoquark models. We show that in general the leptoquark contribution to the longitudinal muon polarization effect inη→μ ⁺ μ ^? decay is very small and in a model which has no couplings induced by the leptoquark between different generations, both the electric dipole moment of electron or muon and longitudinal polarization of electron in π⁰,η→e ⁺ e ^? decays can be large.     

Measurement of charged kaon semileptonic decay branching fraction K^ - \to e^ - \bar \nu _e \pi ^0 using ISTRA+ detector

The ratio of branching fractions for \(K^ - \to e^ - \bar \nu _e \pi ^0\) andK ^? → π^?π⁰ decays has been measured using the ISTRA+ spectrometer. The result of our measurement is the following: $$\mathcal{R}_{Ke_3 /K_{2\pi } } = 0.2423 \pm 0.0015(stat.) \pm 0.0037(syst.).$$ Using the current PDG value for the K _2π branching fraction, this result leads to the measured K _e3 branching fraction of Br(K _e3) = 0.0501 ± 0.0009 and to the value of |V _us |f ₊(0) = 0.2115 ± 0.0021.     

Excitation and structure of hypernuclear resonances in (K −,π ¯0)-reactions on 1p-shell nuclei

The available experimental data on the excitation functions (EF) of the 1p-shellΛ-hy-pernuclei in (K ^?, π^?) reactions atθ _π = 0^° has been analysed in terms of shell model and weak coupling scheme. It is substantiated by the experimental data on the neutron spectroscopic factors and on the fragmentation of nuclear hole excitations. The pronounced nuclear spectroscopic characteristics in the hypernuclear spectra are indicative of a weak coupling ofΛ-hyperon with nuclear subsystem. The analysis has made it possible to determine the difference is single-particle energies ofΛ-hyperon in the 1p- and 1s-states and to obtain additional evidence for the smallness of theΛ-nucleus spin-orbit interaction. The resonance structure of EF of hypernuclei, which were not studied in (K ^?,π ₀ ^? ) reactions, is predicted. The interrelated aspects of the studies of the (K ^?,π ₀ ^? ), (K ^?,π ₀ ^? β^′), and (K ^?, π⁺) reactions which are of interest to spectroscopy ofΛ-andΣ-hypernuclei are discussed.     

Measurement of the masses and lifetimes of the charmed mesonsD 0,D + andD s +

We present the final results on the measurement of the masses and lifetimes of the mesonsD ⁰,D ⁺ andD _s ⁺ in the NA32 experiment at the CERN SPS, using silicon microstrip detectors and charge-coupled devices for vertex reconstruction. We measure the following lifetimes: \(\tau _{D^0 } = 3.88 \pm _{0.21}^{0.23} \cdot 10^{ - 13} s\) using a sample of 479D°→K ^?π⁺π^?π⁺ and 162D°→K ^?π⁺ decays; \(\tau _{D^ + } = 10.5 \pm _{0.72}^{0.77} \cdot 10^{ - 13} s\) with a sample of 317D ⁺→K ^?π⁺π⁺ decays; \(\tau _{D_s^ + } = 4.69 \pm _{0.86}^{1.02} \cdot 10^{ - 13} s\) with a sample of 54D _s ⁺ →K ⁺ K ^?π⁺ decays. We measure the following masses:m _D ⁰=1864.6±0.3±1.0 MeV,m _D ⁺=1870.0±0.5±1.0 MeV and \(m_{D_s^ + } \) =1967.0±1.0±1.0 MeV.     

A coupled-channel treatment of Cabibbo-angle favoured (D,D s + )→VP decays

We have performed a two-channel calculation of Cabibbo-angle favoured decays,D _s ⁺ →VP. We find a satisfactory fit toS _s ⁺ →φπ ⁺,ρ ⁰ π ⁺ andK ⁺ \(\bar K^{ * 0} \) data from ARGUS and E-691. We have also studied Cabbibo-angle favouredD→VP decays in a coupled channel formalism. We coupleD→K ^*π,K _? and \(\bar K^0 \phi \) channels inI=1/2 state, andK ^*π andK _? channels inI=3/2 state. We leave the two channels, \(\bar K^0 \omega \) and \(\bar K^{ * 0} \eta \) out of our unitarization scheme. Particular attention is paid to the role of the weak annihilation term in these decays.     

Contributions of parity-violating baryon matrix elements to nonleptonic charmed-baryon decays

Baryon-baryon matrix elements of the parity-violating charm-changing weak Hamiltonian are calculated using the MIT bag model. The changes in thes- andp-wave amplitudes of Cabibbo-favored nonleptonic decays of charmed baryons due to these parity-violating baryon transition elements are in general not substantially significant. However, they can overwhelm or be comparable to the contributions arising from the parity-conserving matrix elements for some reactions such as thes-wave amplitude ofΛ _c ⁺ →Ξ ⁰ K ⁺ and Δ⁺⁺ K ^? and thep-wave amplitude ofΛ _c ⁺ →∑ ⁰π⁺.     

Study of Σ* Resonances from K − N → πΛ Reactions

In order to know more about some Σ resonances and distinguish various models of hadron structures, an analysis is performed for the reactions K ^? n → π ^? Λ and K ^? p → π ⁰ Λ, using an effective Lagrangian approach. The differential cross sections and Λ polarizations from two experiments are analyzed with the c.m. energy between 1,550 and 1,676 MeV. Our study strongly support the existence of a ${J^P = {1\over 2}^+ \Sigma}$ resonance with mass near 1,633 MeV and width about 120 MeV, which is compatible with the three-star ${\Sigma(1660){1\over 2}^+}$ in PDG. Meanwhile, no evidence is found for the two-star ${\Sigma(1620){1\over 2}^-}$ listed in PDG.     

Radiative decays of ρ and ω mesons

The results of the measurements of radiative decays of ρ and ω mesons with the Neutral Detector at thee ⁺ e ^? collider VEPP-2M are presented. The branching ratio of the decay ω→π ⁰γ was measured with higher than in previous experiments accuracy: $${\rm B}(\omega \to \pi ^0 \gamma ) = 0.0888 \pm 0.0062$$ . The ρ⁰→π ⁰ γ branching ratio was measured for the first time: $$B(\rho ^0 \to \pi ^0 \gamma ) = (7.9 \pm 2.0) \cdot 10^{ - 4} $$ . The decays ρ, ω→ηγ were studied. Their branching ratios with the assumption of constructive ρ?ω interference are: $$\begin{gathered} B(\omega \to \eta \gamma ) = (7.3 \pm 2.9) \cdot 10^{ - 4} , \hfill \\ B(\rho \to \eta \gamma ) = (4.0 \pm 1.1) \cdot 10^{ - 4} \hfill \\ \end{gathered} $$ . The branching ratios of ρ, ω→ηγ and ω→e ⁺ e ^? decays were also measured: $$\begin{gathered} B(\omega \to \pi ^ + \pi ^ - \pi ^0 ) = 0.8942 \pm 0.0062, \hfill \\ B(\omega \to e^ + e^ - ) = (7.14 \pm 0.36) \cdot 10^{ - 5} \hfill \\ \end{gathered} $$ . The upper limit for the ω→π ⁰ π ⁰ γ branching ratio was placed: B(ω→π ⁰ π ⁰ γ)<4·10^?4 at 90% confidence level.     

Remarks about the counting of\bar vv generations using thee + e − →γZ 0 process

In the present note we further explore the possibility of measuring the number of \(\bar vv\) generations by means of \(Z^0 \to \bar vv\) decays. We investigate in particular the case where the radiative transitionse ⁺ e ^? →γZ ⁰ are studied on theZ ⁰ resonance itself. The various background reactions are discussed as well as the statistical significance that can be obtained for an additional \(\bar vv\) generation.     

Recent Studies of Hypernuclei Formation with Electron Beams at MAMI

At the Mainz Microtron MAMI exploratory experiments on the spectroscopy of mesonic weak decays (MWD) of electroproduced Λ-hypernuclei were performed. A unique setup was realized to use the broad momentum-band kaon spectrometer Kaos at zero degree angle with respect to the high-intensity electron beam direction to tag strangeness producing processes. A sample of order 10³ MWD from a beryllium target was collected by the coincidence technique with the high-resolution multi-spectrometer facility of the A1 Collaboration. It is conjectured that this sample contains monochromatic two-body decays from stopped hyperfragment decays as well as a wide momentum distribution of quasi-free produced Λ- and Σ-hyperon decays and three-body decays from hyperfragments. Stopped hyperfragments will be identified as monochromatic peaks in the π ^? momentum spectrum from which their masses can be extracted with a precision of 50 keV/c ².     

Average temperature and multiplicities ofe + e − annihilation

Hadron temperatures ofe ⁺ e ^?→h \(\bar h\) from PEP experiments at 29 GeV are estimated using theP _⊥ distribution; rather small fluctuations are found for temperatures of π,K,..., Ξ with respect to the average \(\bar T = 196 \pm 7\) MeV. A semi-empirical formula including quark content ofh is proposed to account for multiplicities of π,K, ..., Δ in terms of a unique temperature \(\bar T\) . The formula is further extended to charmed particlesD, F, J/Ψ andΛ _c without free parameters. The property \(\bar T\) ~E _cm ^1/4 holds for other experiments of DESY andCESR.     

On some properties of the neutron in the statistical model

Using the statistical model to arrive at |ψ(r)|² the square modulus of theS state wavefunction of the neutron, the electric dipole moment |d _n ^e | of the neutron as well as its baryon number violating lifetime have been estimated. The baryon asymmetry of the universe depending on |d _n ^e | has also been studied in this context.     

Search for CP violation in Z0 → τ + τ − and an upper limit on the weak dipole moment of the τ lepton

An improved test of invariance in the reaction e⁺e^? τ ⁺ τ ^? on the Z0 peak is performed using the data sample recorded between 1991 and 1995 with the OPAL detector at LEP. Optimal observables, requiring the reconstruction of the τ flight direction and spin, have been used for different final state topologies. From the non-observation of violation we derive 95% confidence level upper limits on the real and imaginary parts of the weak dipole moment of the τ lepton of |Re(d _τ ^w (m _Z ² | < 5.6 × 10^?18 e cm and |Im(d _τ ^w (m _Z ² ))| < 1.5 × 10^?17 e cm, respectively.     

Baryon pairs production ine + e − annihilation at\sqrt s = 2.4 GeV

Search for baryon pairs production ine ⁺ e ^? annihilation at \(\sqrt s = 2386 MeV\) is reported. The data relate to a luminosity of 161 nb^?1 collected by the DM2 experiment at DCI, the Orsay colliding ring. First measurements of directe ⁺ e ^? annihilation into \(\Lambda \bar \Lambda \) and ofe ⁺ e ^?→ \(p\bar p\) at this energy are presented. First observation of a goode ⁺ e ^?→ \(n\bar n\) candidate is reported and upper limits are given fore ⁺ e ^?→ \(n\bar n, \Lambda \bar \sum ^0 + c.c.\) and \(\Sigma ^0 \bar \Sigma ^0 \) .     

Measurement of various decay modes of charmed particlesD 0,D +,D s + andΛ s c

In the CERN NA 32 experiment a high-resolution silicon vertex detector and a purely topological approach have been used to investigate various decays of charmed particles. We observe ～620 fully reconstructed decays ofD ⁰ in 12 channels and determine the branching ratios. For fourD ⁰ decay modes involving a single (unseen) π⁰ the small and narrowD ^*+?D ⁰ mass difference is used to measure their branching ratios. We also observe ～280 fully reconstructedD ⁺ decays in 10 channels, ～90D _s ⁺ decays in 11 channels as well as 160Λ _s ^c and 18 decay channels ofD ⁺. For theD _s ⁺ , we measure the branching fractions within a subset of 16 three- and five-prong decay channels. For theΛ _s ^c , we determine the branching fractions within a sample of 11 three- and five-prong decay channels, nearly all involving a proton.     

Effects of anomalousZ 0 decays on neutrino counting near theZ 0 peak

We study the implications of the anomalousZ ⁰ decays on neutrino counting ine ⁺ e ^? collisions. The \(Z^0 \to l\bar l\gamma \) vertex is parametrized by an effective Lagrangian,L _eff, satisfyingU(1)_em gauge invariance, CP and chirality conservation. The parameters ofL _eff are constrained by the ratio \(\Gamma (Z \to l\bar l\gamma )/\Gamma (Z \to l\bar l)\) , Bhabba scattering, and low energyv _µ e scattering data. We find that the effect on neutrino counting can be significant but depends on the magnitude and relative signs of the parameters inL _eff. We also find that accurate measurements of the cross-section \(\sigma (e^ + e^ - \to v\bar v\gamma )\) at theZ ⁰ peak can be used as a sensitive test for new physics.