An interpretation of high-energy inelastic interactions of pions with heavy emulsion nuclei

An analysis of the basic characteristics of secondary particles created in the interaction of pions with heavy emulsion nuclei at the highest accelarator energies available is presented. Calculations were performed with an intra-nuclear cascade model using the Monte-Carlo method, taking into account the “trailing effect”. Emission of slow particles from the excited residual nucleus was calculated using Weisskopf's evaporation theory. The theoretical results were compared with experimental results at 17.2 and 60 GeV interactions.     

Nuclear interactions of 200 GeV protons in emulsion

Proton-nucleus interactions have been studied in nuclear emulsion exposed to the NAL 200 GeV proton beam. The inelastic mean free path is found to be 35.5 ± 0.8 cm and the average shower particle multiplicity is 12.9 ± 0.2. The angular distribution reveals some characteristics features of proton-nucleus interactions.     

Nuclear electroproduction of negative pions below threshold

We calculate the electroproduction of negative pions into bound atomic states. The effect of the strong π-nucleus interaction is included in the calculation.     

Nuclear relativistic hartree-fock approximation with effective pions

The effect of an interaction between the ??- and ??-meson fields, as well as that of the mixture of pseudoscalar (PS) and pseudovector (PV) couplings for the ??N vertex on the shell structure of finite nuclei are analyzed in the framework of different nonlinear nuclearmodels based on the relativistic Hartree-Fock approximation. For the case of a dominant ??N PV coupling, it is found that if the ??-?? interaction generates an effective pion mass increasing with the nuclear density, the unrealistic effect of pions on the shell structure can be strongly reduced, keeping, roughly, the contribution of pions to the total binding energy. The ??N PS coupling increases slightly the spin-orbit splittings and the binding energy of the single-particle levels.     

Elastic scattering of positive pions by O between 80 and 340 MeV

Angular distributions of cross sections for π⁺ elastic scattering by ¹⁶O have been measured between 14° and 138° at five energies (79, 114, 163, 240 and 343 MeV). They are compared to calculations using a first-order static model and an isobar doorway model. Phase-shift analyses have been done using the theoretical inputs as guidelines. The validity of these models is discussed.     

J/psi polarization in 800-GeV p-Cu interactions

We present measurements of the polarization of the J/psi produced in 800-GeV proton interactions with a copper target. Polarization of the J/psi is sensitive to the ccmacr; production and hadronization processes. A longitudinal polarization is observed at large x(F), while at small x(F) the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus p(T).     

Final-state interactions in radiative production of pions in colliding-beam experiments

The contribution of final state interactions of the pions in the process e⁺e^?→ππγ are calculated. It is noted that this may be used A) to obtain the zero isospin ππ s-wave in the ?-region, or B) if knowledge of this wave is assumed, to obtain a good estimate of the background for e⁺e^? → ππ     

Investigation of semicoherent interactions of 1-GeV protons with silicon

An experiment on studying the ²⁸Si(p, p′ γ ₀ X)²⁴Mg semicoherent reaction is carried out at the MAG setup on the 1-GeV proton beam of the U-10 ITEP accelerator. Two particles, proton and γ-ray photon, which accompanies the transition of the ²⁴Mg* nucleus from the first excited state to the ground state, are detected. When the events with the proton emission angle from 3° to 6.5° are selected, the following four processes are observed: the direct knockout of a nuclear α cluster by a proton, the formation of a _ΔSi isobaric nucleus, the formation of a Δ₁₂₃₂ isobar, and the production of a π ⁰ meson at rest in the nuclear coordinate system. The cross sections for the indicated processes are obtained.     

Nuclear pions and the Gottfried and Bjorken sum rules

The thermodynamic potential (TDP) of the boson sector of the Weinberg-Salam model in an external uniform magnetic field at finite temperature and nonzero chemical potential is calculated in one-loop approximation. In the high temperature limit with the use of Mellin summation technique explicit expressions for the thermodynamic potential are obtained to analyze its new minimum, different from the ordinary Higgs one. This new minimum is due to the root singularity in the oneloop expression for the TDP, originating as a consequence of the tachyonic mode in the spectrum of gauge boson in the magnetic field. It is demonstrated that in the high temperature limit the Higgs minimum possesses properties common with the ordinary superconductors and Abelian Higgs model. The influence of the magnetic field on the Higgs minimum is indirect and has a sufficiently complicated character. The presence of the non-zero chemical potential lowers the critical temperature leading to the disappearance of the Higgs minimum.     

Nuclear interactions of 21 GeV/c protons and 50 GeV/c negative pions in emulsions exposed in a strong magnetic field

Incoherent nuclear interactions of 21 GeV/c protons and 50 GeV/cπ ^?-mesons in emulsions exposed in a strong (180 kG) magnetic field have been investigated. The following topics are covered: the multiplicity of various types of charges secondaries, general features of one-particle rapidity and transverse momentum distributions, energy partitions among secondaries, characteristics of the leading particles and relativistic recoil protons, correlation relations. The experimental data are compared with predictions of current models of nuclear production.     

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/cπ⁺p and K^?p interactions (2 × 10⁶ and 10⁶ pion pair combinations, respectively) and in a smaller sample of $\text{p}\text{p}$ annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.     

Scattering of pions on pions in threshold region

It is shown that the integral equations for isoscalar-scattering, obtained from the Mandelstam representation by the method of so-called differential approximation, admit the threshold behaviour of partial amplitudes which is in agreement with the quantum theory of scattering and, moreover, they also admit solutions with other possible threshold behaviours. This result does not depend on whether the conformal mapping technique is used or not.     

Nuclear γ-rays induced by pions stopping in 55Mn

Stopping pions have been shown to excite the 126 keV level in a target of ⁵⁵Mn. A nonlinear variation of yield of the γ-ray versus target thickness suggests that the principal mechanism responsible for the excitation is a two-stage process. The production mechanism for the same γ-ray seen elsewhere in kaonic atoms experiments is discussed.     

QCD interactions of heavy mesons with pions by light-cone sum rules

Light-cone QCD sum rules are employed to compute the strong coupling constants: , and , where and are negative and positive parity and doublets. The couplings are calculated both for finite values of the heavy quark mass and in the infinite heavy quark mass limit, deriving sum rules for . Received: 30 May 1997 / Revised version: 7 October 1997 / Published online: 23 February 1998