Fixed-t partial wave analysis of πN scattering

The last full Karlsruhe PW analysis of πN scattering was finished ca. 20 years ago. After that a huge pile of new accurate πN scattering data has emerged, with which the old analysis is not completely compatible. We are making a highly modernized version of the old analysis to all (recent and old) data, aiming to pay particular attention to the discrepancies between different data sets and to the handling of the experimental errors as well as to the electromagnetic corrections and the effects of isospin breaking.     

X → 2γ from π p → neutral meson + neuron at 3.8 GeV/c

We report on a measurement for the branching-ratio X⁰ → 2γ/X⁰ ar all. Our result is X⁰ → 2γ/X⁰ → all = (2.9 ± 0.9)%.     

Relativistic field-theoretical equations for the three-body multichannel πN and γN scattering reactions and propagator of the Δ-resonance

A new form of the relativistic three-body equations for the coupled πN and γN scattering reactions with three particle final states ππN and γπN is suggested. These equations are derived in the framework of the time-ordered three dimensional field theory. The solutions of the considered equations satisfy the unitarity condition and are exactly gauge invariant. The form of these three-body equations is does not depend on the choice of the model of Lagrangian and is also the same for the formulations with and without quark degrees of freedom.

The effective potentials of the suggested equations are defined by the vertex functions with two on-mass shell particles. It is emphasized that these input vertex functions can be constructed from experimental data. Special attention is given to the construction of the propagator of the Δ-resonance in the framework of the separable πN potential model. The strong dependence of the multichannel πN and γN cross sections on the form of the Δ-resonance propagator[2] is discussed.

The used formulation of the relativistic three-dimensional and three-body equations allows us to overcome a number of approximations which are usually used by practical calculations of the πN and γN scattering reactions.     

Pion-pion amplitude from the πN→ππN reaction

The possibilities of extracting parameters of ππ interaction from the experimental data on the πN→ππN reaction are analyzed in detail. The interval 300<P_lab<500 MeV/c is shown to be the smoothness domain of the πN→ππN amplitude. The expression for the background part of the amplitude is developed model-independently. The ππ scattering is described by four parameters to be extracted from experimental data (along with 11 background parameters).     

πN scattering and electromagnetic corrections in the perturbative chiral quark model

We apply the perturbative chiral quark model to give predictions for the electromagnetic O(p²) low-energy couplings of the ChPT effective Lagrangian that define the electromagnetic mass shifts of nucleons and first-order (e²) radiative corrections to the πN scattering amplitude. We estimate the leading isospin-breaking correction to the strong energy shift of the π⁻p atom in the 1s state, which is relevant for the experiment “Pionic Hydrogen” at PSI.     

Contrasting N→Δ and N→N parity-violating asymmetries in nuclei

Several perspectives that can be opened by studying the electroexcitation of the delta via parity-violating electron scattering from nuclei are examined, working within the context of the relativistic Fermi-gas model. A strong enhancement of the left–right asymmetry in the delta sector compared with that in the quasielastic regime is found and the potential to find clear signatures for the axial-vector contributions of the nucleon-to-delta transition to the asymmetry identified at specific low momentum transfer kinematics. Possibilities of probing the deformation of the delta are also explored, and using both the proton and nuclei as targets, the ability to study the asymmetry on neutrons is studied.     

Supersymmetric contributions to direct CP violation in K→ππγ decays

We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′_+−γ and the differential width asymmetry of K^±→π^±π⁰γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays.     

Model amplitude analysis of πp→ππn

We present an amplitude analysis of the process π⁻p→π⁺π⁻n at 15 GeV/c assuming spin and phase coherence of the production amplitude. The bearing of the results on aspects of dipion production phenomenology is discussed.     

Multi-Regge analysis of the pp→ppππ reaction at 8.1 GeV/c

We present here an analysis of the reaction pp→ppπ⁺π⁻ at 8.1 GeV/c in terms of the two multi-Regge models proposed by Chan, ;oskiewicz and Allison and by Berger et al. in which we introduce some modifications to improve the agreement between experimental data and theoretical results. Comparison between various experimental distributions and corresponding theoretical curves is satisfactory with a very simple parametrization in both models.     

Note on the angular analysis of the decay J/ψ→f(→ππ)+γ

We derive the general (4-parameter) angular decay distribution for the cascade decay J/ψ→f(→ππ)+γ and determine its angular coefficients from the absorptive and dispersive contributions of the lowest order QCD diagram.     

Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

Perturbative QCD correction to the B → π transition form factor

We report on the perturbative O(_s) correction to the light-cone QCD sum rule for the B → π transition form factor f⁺. The correction to the product f_Bf⁺ in leading twist approximation is found to be about 30%, that is similar in magnitude to the corresponding O(_s) correction in the two-point sum rule for f_B. The resulting cancellation of large QCD corrections in f⁺ eliminates one important uncertainty in the sum-rule prediction for this form factor.     

Regge-pole description of γN→πN backward-scattering data

Baryon Regge-pole contributions to u-channel helicity amplitudes for the γN→πN processes are derived, with attention to kinematic singularities and threshold conditions. An N, Nγ and Δδ Regge-exchange model is proposed that describes the backward scattering data on γp→π^op and γp→π⁺n at high energy. The N and Nγ trajectories are found to be nearly degenerate, with residues in the ratio β(Nγ)/β(N)≈0.6. Structure in the differential cross sections is explained as dominance at small u giving way to dominance at large u. An isoscaar-isovector admixture for the γ-coupling to is required by the fits. The solution extrapolates through the mean γp→π^op 180^o differential cross section at intermediate energies, as required by duality.     

A limit on the lepton-family number violating process π → μe

A FNAL E799 Collaboration has carried out a search for the lepton-family number violating decay π⁰ → μ^±e using π⁰'s produced from K_L → π⁰π⁰π⁰ decays in flight. No events were observed. Assuming that lepton-family number violation is charge independent, the 90% confidence level upper limit on

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was determined to be 8.6 × 10⁻⁹.     

A Partial Wave Analysis of the Reaction π+p→ (π+π−π0) Δ++ at 16 GeV/c

A partial wave analysis of the 3π-system has been performed for the reaction π⁺p→ (π⁺π^?π⁰) Δ⁺⁺ (1232) at 16 GeV/c. Beside the well-established A₂⁰ (1300), the resonant state ω* with isospin I = 0 and spin-parity J^P = 3^? decaying mainly into (?π) has been found. Its mass and width have been determined to be M = (1.71 ± 0.03) GeV and Γ = (0.22 ± 0.10) GeV. The cross section for the reaction π⁺p→ ω* (1700) Δ⁺⁺ (1232) is σ = (12 ± 6) μb.     

CP test in J/ψ→γφφ decay

We propose to test CP symmetry in the decay J/ψ→γφφ, for which large data sample exists at BESII, and a data sample of 10¹⁰ J/ψ's will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of J/ψ, electric- and chromo-dipole moment can be probed at order of 10⁻¹³ e cm. In the near future with a 10¹⁰ data sample, these moments can be probed at order of 10⁻¹⁴ e cm.     

Measurement of the slope parameter for the neutral pion spectrum in KL → πππ decay

The π⁰ spectrum in the K_L⁰ → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M² ≈ 1 + 2a₀(M_K/M_π²)(2T_π⁰−T_π⁰max) + a₁(M_K²/M_π⁴)(2T_π⁰−T_π⁰max)². We obtained a₀ = −0.282 ± 0.011 and a₁ consistent with zero.