Cross sections and asymmetries for elastic π3He scattering in the energy region around the Δ resonance

For a polarized target, π³He interaction is studied in the fixed-center approximation with all rescatterings included. Only the P ₃₃ wave is taken for the πN interaction. The nuclear wave function is taken either as a sum of Gaussian functions or as a Faddeev wave function in the s-wave approximation. The differential cross sections and asymmetries for elastic π⁺³He scattering at the laboratory energies of T _π, 180, and 256 MeV are calculated. The results are compared with experimental data.     

Positivity as a constraint on the positions of the zeros of theK − p forward scattering amplitude

Stringent constraints on the positions of the zeros of theK ^? p forward scattering amplitude in the complex energy plane are obtained using only information on the modulus of the amplitude on its cuts, together with the requirement of positivity of the imaginary part of the amplitude in the physical region.     

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130?525 MeV using the large Mainz NaI(T1) spectrometer atΘ _p ^lab =37.1°. Three separate reaction channels were identified, viz.⁴He(γ,p)t two-body breakup,⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

Determination of the πN charge exchange scattering amplitude from the experimental data at high energies

The difference between theπ ⁺ p andπ ^? p diffraction peaks is used for an estimate of the imaginary part of the charge exchange scattering amplitude. The imaginary part has a narrow peak in the forward direction and passes over to negative values at a momentum transfert of about ?0.15(GeV/c)². If the charge exchange amplitude is dominated by the contribution of theρ Regge pole, the peak is mainly due to thet-dependence of the residue function and a narrow forward peak is expected in the charge exchange angular distribution.     

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.     

P-Odd effects in the γ+He4 → He4 + π0 reaction

P-Odd effects with the elastic photoinformation of neutral pions in He⁴ nuclei are due to the interference of the P-odd amplitude of weak interaction with the P-even amplitude of strong interaction, and originate only for polarized photons. It is shown that close to the reaction threshold P-odd effects should be small. The interference amplitude of the mechanisms corresponding to exchange with a Regge or-pole and a neutral Z-boson at high energies is studied. P-Odd effects in this case increase with increase of energy of the interacting particles and with the square of the imparted momentum. P-Odd effects due to interference of the s ingle-photon and Z-boson mechanisms are also investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 71–76, September, 1978.     

Analyticity of scattering for the ϕ4 theory

We consider scattering for the equation (+m ²)+³=0 on four-dimensional Minkowski space. Form>0, one-to-one and onto wave operatorsW _± :HH are known to exist for all 0, whereH denotes the Hilbert space of finite-energy Cauchy data. We prove that the maps (,u)W _± (u) and (,u)(W _± )^–1 (u) are continuous from [0, )×H toH, and extend to real-analytic functions from an open neighborhood of {0}×H×{0}×H to the Hilbert spaceH _–1 of Cauchy data with Poincaré-invariant norm. Form=0, wave operatorsW _± are known to exist as diffeomorphisms ofH for all 0, where hereH denotes the Hilbert space of finite Einstein energy Cauchy data. In this case we prove that the maps (,u)(W _± ) (u) and (,u)(W _± )^–1 (u) extend to real-analytic functions from a neighborhood of [0, )×H×H toH.     

Charge-symmetry-breaking effects from phase-shift analysis of elastic π± He scattering

A phase-shift analysis of elastic π^±4 He scattering at energies 20–160 MeV was performed to determine pure hadronic phase shifts. No statistically significant difference between the hadronic phase shifts deduced from π⁺⁴ He and π⁻⁴ He scattering was observed.     

Model-independent extraction of two-photon effects in elastic electron–proton scattering

We address the discrepancy between the Rosenbluth and polarization transfer data for the electromagnetic form factors of the nucleon. Assuming that the effect of two-photon corrections on the polarization transfer data is negligible, we obtain a model-independent estimate of the two-photon correction Δ2γ${\Delta }^{2\gamma }$. We analyze the polarization transfer data and the cross section data separately using dispersion relations. A central value as well as an error estimate for Δ2γ${\Delta }^{2\gamma }$ is then obtained from a comparison of the two analyses. The resulting values for Δ2γ${\Delta }^{2\gamma }$ are in good agreement with direct calculations available in the literature.     

T invariance and polarization effects in the reactions p+3He → π++4He and π++4He → p+3He

On the basis of T invariance, it is established that the dependence of the effective cross section for a binary reaction of the a+b → c+d type on the polarization vectors of primary particles a and b determines completely the polarization vectors and spin correlations for the same particles in the inverse reaction c+d → a+b induced by collisions between unpolarized primary particles c and d. By using the formalism of helicity amplitudes, polarization effects are studied in the process p+³He → π⁺+⁴He and in the inverse process π⁺+⁴He → p+³He. It is shown that, in the reaction π⁺+⁴He → p+³He, the spins of the final-state particles (proton and ³He nucleus) are strongly correlated. An expression for the correlation tensor is obtained for arbitrary values of the (p, ³He) emission angle.     

On applicability of the Glauber model for pion elastic scattering by helium in the δ33 resonance region

Elastic scattering of pions by³He and⁴He in the region of the first pion-nucleon resonance is calculated within the Glauber theory. The spin-flip and charge-exchange effects are fully taken into account. Calculated results are compared with experiment and with predictions obtained using the optical model. Some conclusions are drawn concerning the validity of approximations used in deriving the two models. The calculations make clearer some of the limitations of using the Glauber model for very low energies.On leave fromInstitute of Nuclear Physics, e — Prague, Czechoslovakia.     

Possibility of T-violating P-conserving magnetism and its contribution to the T-odd P-even neutron–nucleus forward elastic scattering amplitude

T-violating P-even magnetism is considered. The magnetism arises from the T-violating P-conserving vertex of a spin 1/2 particle interaction with the electromagnetic field. The vertex vanishes for a particle on the mass shell. Considering the particle interaction with a point electric charge we have obtained the T-violating P-even spin dependent potential, which is inversely proportional to the cubed distance from the charge. The matrix element of this potential is zero for particle states on the mass shell; nevertheless, the potential contributes to the T-odd P-even neutron forward elastic scattering amplitude by a deformed nucleus with spin . The contribution arises if we take into account incident neutron plane wave distortion by the strong neutron interaction with the nucleus. Received: 29 August 2000 / Revised version: 22 January 2001 / Published online: 23 March 2001     

A quark model of the meson fragmentation region in πp collisions

A model is explored in which the fragmentation region is populated by the hadronization of a string which stretches from a fast forward quark to a quark in the backward hemisphere of the p collision. This model is a part of more complicated models which have been studied elsewhere. It successfully fits observed inclusive production of ⁰-mesons, ⁰-mesons and -mesons, and agrees with the result that their production in p collisions is harder than in electron-position annihilation if: (a) the forward quark has an initial momentum which is at least 0·9 of that of the ⁰-mesons (b) gluon radiation is weaker than in electron-positron annihilation.     

Regge analysis of the ππ scattering amplitude

The theoretical predictions for the subtraction constants lead to a very accurate dispersive representation of the ππ scattering amplitude below 0.8 GeV. The extension of this representation up to the maximum energy of validity of the Roy equations (1.15 GeV) requires a more precise input at high energies. In this paper we determine the trajectories and residues of the leading Regge contributions to the ππ amplitude (Pomeron, f and ρ), using factorization, phenomenological parametrizations of the πN and NN total cross sections at high energy, and a set of sum rules which connect the high and low energy properties of ππ scattering. We find that nonleading Regge terms are necessary in order to achieve a smooth transition from the partial waves to the Regge representation at or below 2 GeV. We obtain thus a Regge representation consistent both with the experimental information at high energies and the Roy equations for the partial waves with ℓ≤4. The uncertainties in our result for the Regge parameters are sizable, but in the solutions of the Roy equations these only manifest themselves above the K[`]KK\hspace {0.03cm}\overline {\rule [0.7em]{0.6em}{0em}}\hspace {-0.8em}K threshold.     

S-ware πN scattering effects in the nuclear three-body force

We examine the contributions of the off-mass-shell,s-wave N scattering amplitude terms in the Tucson-Melbourne two-pion-exchange three-body force to the trion binding energy. While thea andc terms are not as important as thep-wave terms, they comprise a nonnegligible part of the three-nucleon force which produces nonperturbative effects in the triton wave function.     

On determination of the 2p-energy level shift and width for π−-4He atom

The strong interaction shift and width in the 2p-level of the pionic helium have been deduced from the analysis of the low-energy -⁴He scattering data. The obtained values are: _2p=4·0 × × 10^–3 eV and _2p=1·6 × 10^–3 eV. The analysis has been performed within the framework of the UST approach.Presented at the IV International Symposium Mesons and Light Nucler, Bechyn, Czechoslovakia, September 5–10, 1988.