Some comments on the π-3He-3H coupling constant

Some comments are made on recent determinations of the -³He-³H coupling constant. It is pointed out how the impulse approximation and the elementary particle method treat differently two step processes like radiative pion or muon capture and photo pion production.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.This work is part of the research program of the Stichting FOM, financially supported by the Stichting Z. W. O.     

CP-violation in B → π+π- and the unitarity triangle

We analyze the extraction of weak phases from CP-violation in B → π⁺π^- decays. We propose to determine the unitarity triangle by combining the information on mixing-induced CP-violation in B → π⁺π^-, S, with the precision observable sin2β obtained from the CP-asymmetry in B → ψK_S. It is then possible to write down exact analytical expressions for and as simple functions of the observables S and sin2β and of the penguin parameters r and ϕ. As an application clean lower bounds on and can be derived as functions of S and sin2β, essentially without hadronic uncertainty. Computing r and ϕ within QCD factorization yields precise determinations of and since the dependence on r and ϕ is rather weak. It is emphasized that the sensitivity to the phase ϕ enters only at second order and is extremely small for moderate values of this phase, predicted in the heavy-quark limit. Transparent analytical formulas are further given and discussed for the parameter C of direct CP-violation in B → π⁺π^-. Predictions and uncertainties for r and ϕ in QCD factorization are examined in detail. It is pointed out that a simultaneous expansion in 1/m_b and 1/N leads to interesting simplifications. At first order infrared divergences are absent, while the most important effects are retained. Independent experimental tests of the factorization framework are briefly discussed. Received: 16 April 2005, Revised: 6 August 2005, Published online: 21 November 2005 PACS: 11.30.Er, 12.15.Hh, 13.25.Hw     

Double- π0 photoproduction from the deuteron

The photoproduction of two neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to 820 MeV with the TAPS spectrometer at MAMI (Mainz Microtron). The total cross-section was determined and used to deduce the cross-section from the neutron. Due to the good statistical quality of the data Dalitz plots for the three particles in the exit channel (π⁰π⁰ N) could be constructed. The invariant mass distributions derived from them are presented in this paper. They indicate that the important reaction mechanism in the second resonance region is a sequential decay pattern involving the population of the Δ(1232)-resonance as an intermediate state. Received: 5 June 2000 / Accepted: 4 September 2000     

Threshold π0 photoproduction from the Skyrmion

The Skyrme model for nucleons is used to calculate threshold π⁰ photoproduction off a proton. It was found that the anomalous part of the electromagnetic current yields an important contribution to the photoproduction amplitude, roughly of the same magnitude normally ascribed to ω meson exchange. Agreement with the experimental threshold cross section can thus be achieved without invoking ω exchange.     

Yrast states in the π- particle ν- hole nucleus 65 146 Tb81

The nucleus ¹⁴⁶Tb was studied from in beam γγ-and conversion electron measurements. The level scheme was established up to ～5MeV above the (πh_11/2 vd _3/2 ^?1 )_5? β-isomer. In addition to the known (πh_11/2 vh _11/2 ^?1 )₁₀₊ E3-isomer, the 8⁺ and 11⁺ members of this configuration were located. The levels at the yrast line are dominated by the couplings of the πh_11/2 vh _11/2 ^?1 valence nucleons to the collective 3^? octupole state and to the πh_11/2d _5/2 ^?1 and πh_11/2g _7/2 ^?1 particle-hole excitations of ¹⁴⁶Gd.     

Measurement of the parity-violating asymmetry in inclusive electroproduction of π- near the Δ0 resonance

The parity-violating (PV) asymmetry of inclusive π- production in electron scattering from a liquid deuterium target was measured at backward angles. The measurement was conducted as a part of the G0 experiment, at a beam energy of 360 MeV. The physics process dominating pion production for these kinematics is quasifree photoproduction off the neutron via the Δ0 resonance. In the context of heavy-baryon chiral perturbation theory, this asymmetry is related to a low-energy constant d(Δ)- that characterizes the parity-violating γNΔ coupling. Zhu et al. calculated d(Δ)- in a model benchmarked by the large asymmetries seen in hyperon weak radiative decays, and predicted potentially large asymmetries for this process, ranging from A(γ)-=-5.2 to +5.2 ppm. The measurement performed in this work leads to A(γ)-=-0.36±1.06±0.37±0.03 ppm (where sources of statistical, systematic and theoretical uncertainties are included), which would disfavor enchancements considered by Zhu et al. proportional to V(ud)/V(us). The measurement is part of a program of inelastic scattering measurements that were conducted by the G0 experiment, seeking to determine the N-Δ axial transition form factors using PV electron scattering.     

Study of fermilab data for the reaction π−p → π0n

Fermilab data for the angular distribution measurements of the reaction ^–p ⁰n are investigated and it is shown that a good fit with experiment is obtained by using a simple Regge pole model with phenomenological residue functions. The energy dependence in this case is found to be different from that for the d/dt data obtained at Serpukhov.Work supported by the Pakistan Science Foundation under contract No. P-PU-PHY(11/1).     

Fission probabilities across the π-nucleon delta resonance

Cross-sections for the π⁺-induced fission of ²⁰⁹Bi and ²³⁵U have been measured in small steps across the 3-3 resonance to search for any mechanisms that might signal a change in the reaction mechanism across a region where strong coupling of available energy into nuclear excitation can be expected. The bismuth data are found to be in good agreement with a statistical calculation not including new mechanisms. Received: 15 August 2000 / Accepted: 23 January 2001     

The π-electron spectra of the benzene N-heterocyclics

The π-electron spectra of the nitrogen heterocyclics are discussed on the basis of a perturbation applied to the spectra of the corresponding aromatic hydrocarbons. The frequency of the first π→π band in pyridine is the same as that of the corresponding band in benzene, because of the accidental cancellation of a first-order blue shift by a second-order red shift. The first-and second-order shifts are related to two perturbation parameters, and these are obtained from experiment by examining the spectra of the benzene heterocyclics. These parameters can then be satisfactorily related to one another by assuming a perturbation field of the form exp (?2ηr)/r and by allowing for the C-N bond being shorter than the C-C bond in benzene.     

Single and double πo-photoproduction from the deuteron

Photoproduction of neutral pions from the deuteron has been studied for incident photon energies from 200 MeV to 792 MeV with the TAPS detector at the Mainz MAMI accelerator. Total and differential cross sections covering the full angular range have been obtained for coherent and incoherent single π^o-photoproduction. Good agreement between model predictions and the data was found for the coherent process. The incoherent cross section in the energy region of the Δ(1232)-resonance is overestimated by existing models. A comparison to model predictions indicates that final state interaction effects are much more important than for the coherent reaction. However, the angular dependence of the data in the Δ-peak region follows the pattern expected from the dominant excitation of the M₁₊-multipole on the free nucleon. The energy and angular dependence of single π^o-photoproduction in the second resonance region is remarkably different from the reaction on the free proton, indicating a strong nuclear effect. Finally the total cross section for double π^o-photoproduction from the deuteron has been measured for the first time and was used to estimate the cross section for double π^o-photoproduction from the neutron. Received: 24 June 1999 / Revised version: 30 August 1999     

Contributions of γd → πNN + π0 d channels to the spin asymmetry and the Gerasimov-Drell-Hearn integral for the deuteron

Contributions from the semi-exclusive channels γd → π^± NN + π⁰ d and γd → π⁰ X (X=pn or d) to the deuteron spin asymmetry and the Gerasimov-Drell-Hearn (GDH) integral are explicitly evaluated using an enhanced elementary pion photoproduction operator and a realistic, high-precision potential model for the deuteron wave function. The sensitivity of the results to the elementary pion photoproduction operator is also investigated and considerable dependence is found. Results for the deuteron GDH integral are compared with the measurements from A2 and GDH@MAMI Collaborations.     

Elastic π±-d and π±-4He scattering below 70 MeV

Elastic scattering differential cross section data of ^± d at 65 MeV and ^{± 4}He at 51 MeV are presented and compared respectively to fully relativistic 3-body and optical potential calculations including true pion absorption.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

New Measurement of the π0 radiative decay width

High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV to extract the π0→γγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.     

On the calculation of proton-proton coupling by π-electrons

A new method for molecular dynamics computer simulations, called the multiple time-step (MTS) method, is described, in which two or more time steps of different lengths are used to integrate the equations of motion in systems governed by continuous potential functions. With this method computing speeds have been increased by factors of three to eight over conventional molecular dynamics methods in simulations of monatomic and polyatomic fluids, with only marginal increases in computer storage.     

Coherent and incoherent π0 photoproduction from the deuteron

Differential cross-sections for the reactions d (γ,π⁰)d and d (γ,π⁰)pn have been measured at MAMI with the TAPS detector setup in the energy range 140 MeV < E _γ < 306 MeV. By use of the Glasgow tagging spectrometer an 0.8 MeV energy resolution for photons incident on the target was achieved. The π⁰ missing energy resolution was sufficient for a reliable separation of coherent and incoherent channels. The data for the break-up channel exhibit very strong final state interaction effects, whereas the observed angular dependence of the inclusive process d (γ,π⁰)X is in quantitative agreement with predictions for a quasi-free process. The observed absolute d (γ,π⁰)X cross-sections, on the other hand, are significantly smaller than predicted by the quasi-free process for E _γ >∼ 250 MeV. Associating this failure with the π⁰ photoproduction on the neutron would suggest that its cross-section is up to 25% below the presently believed value. Received: 13 February 2001 / Accepted: 13 April 2001     

A new interpretation of the πN σ-term

An explicit relation between the σ-term, the S-wave πN scattering length a⁽⁺⁾ and the range parameter b⁽⁺⁾ is established. The range term is shown to be the dominant feature. The important P-wave background terms in the extrapolation of the physical amplitude to the Cheng-Dashen point are shown to be very small if a path v²+2mv_B≅0, i.e., with cos θ≅0, is chosen. This avoids the compensating cancellations between large numbers typical of other procedures. Correction terms are also shown to be small using physical arguments. The present relation is in a convenient form for phenomenological applications.     

Nuclear structure effects in light π- mesoatoms

Performing the angle transformation from pion-nucleon to pion-nucleus CMS frame the first order pion-nucleus optical potential receives also a contribution due to nucleonic Fermi motion. The corresponding term is always repulsive and reflects the nuclear spin-orbital interaction playing an important role particularly for nuclei with half-filled valence shells. We demonstrate the effects due to this term yielding a contribution to the level shifts and widths of pionic atoms. Such ideas allow one to explain theA-dependence of 2p-level energy shifts for most of the s-d shell-mesoatoms.Dedicated by the co-authors to the memory of M. Gmitro.Two authors (A. C. and R. M.) are grateful to Prof. H. J. Leisi, Prof. M. P. Locher and Dr. P. F. A. Goudsmit for stimulating discussions and hospitality extended to them during their stay at Paul Scherrer Institute.     

Search for the f1(1285) → π+π-π0 decay with the VES detector

The isospin-violating decay f ₁(1285) → π⁺π^-π⁰ has been studied at the VES facility. This study is based on the statistics acquired in π^- Be interactions at 27, 36.6 and 41 GeV/c in the diffractive reaction π^- N → (f ₁π^-)N . The f ₁(1285) → π⁺π^-π⁰ decay is observed. The preliminary ratio of decay probabilities BR(f ₁(1285) → π⁺π^-π⁰) to BR(f ₁(1285) → ηπ⁺π^-)^. BR(η → γγ) is ∼ 2% . Original article based on material presented at HADRON 2007.     

Study of theK + K − π+ π− system centrally produced in the reactions π+ p→π+(K + K − π+ π−)p andpp→p(K + K − π+ π−)p at 85 GeV/c

The reactions π⁺ p→π⁺(K ⁺ K ^? π⁺ π^? p andpp→p(K ⁺ K ^? π⁺ π^?)p where the (K ⁺ K ^? π⁺ π^?) system is centrally produced have been studied at 85 GeV/c. 48% of the final state proceeds through single or double vector meson resonant production i.e.,K ^*0(890) (37%), ? (4%),ρ ⁰ (7%). Evidence is found for associatedK ^*0 (890) \(\bar K\) ^*o (890) production (6.4±1.1%) with a cross section ten times higher than that found for associated ? ? production in the same experiment.     

Signature of the ηNN configurations in coherent πphotoproduction on the deuteron

The photoproduction of a neutral pion on the deuteron is considered in the energy region around the η threshold, where a bump-like structure was observed at very backward pion angles. Different dynamical aspects which may be responsible for this phenomenon are analysed within a theoretical frame which includes intermediate ηNN configurations. The results show, in particular, that a three-body treatment of the ηNN interaction is of special importance.