Effects In Pair Production Research Articles

A simple method of studying atomic screening effects in pair production

The development of a simple method for an atomic pair production experiment is described. The preliminary results obtained by removing various experimental difficulties and errors are presented to justify the suitability of the method over other more expensive pair detection systems reported in recent literature.

Weak interaction asymmetries in pp̄ colliding beams

Charge asymmetry and polarization effects in lepton pair production in pp̄ collisions are investigated in order to distinguish between the standard unified model of electromagnetic and weak interactions and possible alternatives.

Photon circular polarization as a neutral current effect in bremsstrahlung and pair production

Neutral-current induced photon circular polarization effects in bremsstrahlung and pair production are calculated to the first order in the weak interaction. The effects are found to be of the same order of magnitude as corresponding lepton-helicity effects. Numerical results are presented for the Weinberg-Salam model. A brief discussion of the pure electromagnetic photon circular polarization effects is given.

Screening effects in pair production near threshold

Pair production cross sections near threshold have been calculated numerically in partial waves for a screened central potential, permitting a comparison of theory with recent experiments. Exchange effects are found to remain small. The level of agreement with experiment is variable and does not suggest any systematic trends. A more approximate theory of screening, energy-shift screening theory (EST), identifying screened cross sections with Coulomb cross sections of shifted spectrum energy ${V}_{0}$, is in agreement with the full calculation if the proper choice is made for the energy shift ${V}_{0}$; however, the procedure becomes more delicate as threshold is approached. A previous attempt to apply EST to threshold experiments made an incorrect choice for ${V}_{0}$.

Polarization effects in massive lepton pair production

We study massive lepton pair production in various hadronic collisions h 1 h 2 → ℓ ℓ X with one hadron polarized. Interesting spin-dependent effects are expected from current ideas used to explain the unpolarized cross sections. We suggest the confrontation of these predicted effects with feasible experiments.

Screening versus confinement

The influence of vacuum polarization on a confinement picture is discussed. The pair-production effects on the potential between two external charges are analyzed in the Schwinger model. Depending on the order of magnitude of the fermion mass, one obtains two clearly distinguished behaviors for the potential reflecting screening or confinement. In exceptional situations one finds colorless "quarks."

Scale violating effects in large qT muon pair production

We compare the hard scattering and DDT approaches to large q T and large M muon pair production, the former being valid at all q T but only to first order in α s, the latter including a sum over all orders but being valid only for q T << M. The DDT formula is rederived in the common domain of applicability of the two approaches. A numerical study indicates that the higher order effects are important for comparison with experiment.

Gluon effects in muon pair production

Cross section formulas for muon pair production in hadron-hadron collisions arising from quark + antiquark → off-shell photon + gluon and gluon + quark → off-shell photon + quark subprocesses are derived in the parton model. Predictions based on QCD agree rather well with the observed transverse momentum distribution of the pair.

Neutral-current effects in Bethe-Heitler pair production

We consider Bethe-Heitler pair production in which the exchanged photon is replaced with a neutral weak intermediate boson. The interference between this and the pure Bethe-Heitler amplitudes contributes to an asymmetry between the lepton pairs and, in addition, the leptons acquire a finite longitudinal polarization. Both effects are calculated and numerical examples are given in the standard Weinberg-Salam model.

Approach to scaling in deep inelastic scattering and lepton pair production

The covariant parton model is used to investigate the approach to scalling in deep inelastic lepton scattering and in lepton pair production by hadron beams. The subasymptotic effects in these two reactions are controlled by rather different features. Of particular importance for lepton pair production is how far the partons are off shell before they annihilate, while for deep inelastic scattering what matters is rather the mass of the parton after it has absorbed the virtual photon. There are uncertainties because of problems with gauge invariance, but it seems that subasymptotic effects in lepton pair production may be large even at SPS/Fermilab energies. Transverse momentum and x distributions of partons in hadrons are discussed in a very simple model. In particular it is found that, while the model is constructed such that F 2( x) ∼ (1 − x) 3 as x → 1, for values of x up to 0.85 F 2( x) is better approximated by (1 − x) 4.

Determination of detector efficiencies for gamma ray energies up to 12 MeV II. Monte Carlo calculation

By means of the Monte Carlo method the absolute intrinsic double escape peak efficiencies of a planar Ge(Li) detector and a cylindrical detector with an active volume of 26 cm 3 for gamma ray energies up to 12 MeV and the absolute full energy peak efficiencies of a cylindrical detector with an active volume of 42 cm 3 for gamma ray energies up to 3 MeV have been calculated. The evaluated efficiencies were compared with experimental values known from literature. An overall very satisfactory agreement was found taking multiple scattering of secondary particles produced in gamma ray interaction events, the creation of bremsstrahlung and the theoretical energy range relations into account avoiding crude approximations in the treatment of the usual interaction processes such as the photoelectric effect, the Compton scattering effect, the pair production effect, and the annihilation of the positron. The production of triplets and the annihilation in flight had no remarkable influence on the calculated efficiencies in the gamma ray energy range considered.

Lepton coupling in the proposed medium interaction and breakdown of muon-electron universality

It is argued from analyses of experimental data that the gauge bosons B which mediate the proposed medium interactions may couple to a doublet of the muon and heavy muon but not to the electron. This conjectured μ-B gauge coupling seems to explain the apparent small breakdown of μ-e universality observed in elastic and inelastic $mu$+p scattering and leptonic decay of phi meson. The mass of B is estimated to be around 4 GeV. It is also shown that the anomalous bump (after psi and psi' are subtracted) indicated in muon pair production in high-energy hadron collisions can be explained qualitatively as an effect of muon pair production via a virtual B boson. Several other consequences of the $mu$-B coupling are discussed.

Comments on Screening and Shell-Ratio Effects in Single-Quantum Pair Annihilation

We show that atomic-electron screening and subshell-ratio effects in single-quantum pair annihilation, reported by Broda and Johnson and by Sheth and Swamy, have a simple origin observed also in pair production and atomic photoelectric effect. In all three processes, the characteristic distances are small on an atomic scale, but large on a nuclear scale; wave functions have a point-Coulomb shape, but not the point-Coulomb normalization. Atomic-electron screening effects cause appreciable modifications of the total pair-annihilation cross section for positron energies below $1.5{m}_{ e}{c}^{2}$ in heavy elements ($Z&gt;47$). For low-$Z$ elements, screening effects are always important. The ${n}^{3}$ rule of Bethe for subshell ratios is good only for low-$Z$ elements (where $n$ is the prinicipal quantum number); we find that the subshell ratio between the $K$ and ${L}_{I}$ single-quantum pair-annihilation cross sections is well predicted by the square of the ratio of the $K$ and ${L}_{I}$ bound-electron wave-function normalizations.

On screening effects in pair production at intermediate and high energies

The effect of screening in atomic field pair production is calculated in Born approximation without approximation as to energy or angle and compared with the results of previous calculations based on the high energy approximation. The difference between the two calculations is comparable to the errors in recent experiments. The effect of nuclear excitation on the total pair production cross section is also investigated, but is found to be extremely small.

Electron-hole pair production and gunn effect in InSb

A study of the low and high field transport properties, the Gunn effect and avalanche breakdown as a function of pressure in n-InSb has been used to obtain information about the properties of higher conduction band minima and impurity levels associated with them.

Discontinuous behaviour in large angle proton-proton elastic scattering at high energies

Measurements of elastic proton-proton differential cross sections for angles between 65° and 90° c.m.s. have been made at 8, 9, 10, 11, 14, 15 and 21 GeV/ c. The shape of the angular distribution is found to change suddenly between 8 and 11 GeV/ c. An interpretation of this discontinuous behaviour in terms of the reactive effects of baryon-antibaryon pair production is proposed.

Coherent Bremsstrahlung and Pair Production in the Diamond Crystal in Graphical Representation between 1 and 40 GeV

The paper supplies numerical information on coherent effects of bremsstrahlung and electron pair production in diamond crystals in the energy range from 1 to 40 GeV. The information is collected in a number of graphs and tables showing the intensity and polarization of bremsstrahlung and the cross section and asymmetry ratio for pair production as a function of crystal orientation. The basic formulas for the interpretation of the diagrams are given. The experimental problem of a precise orientation of the crystal, which is closely connected with the production of coherent radiation, is discussed on the basis of these formulas.

Circular Polarization of High-EnergyγRays by Birefringence in Crystals

It was shown in a previous work that thick single crystals can be used as polarizers and polarimeters for highenergy gamma rays because of coherence effects in pair production. As a consequence of the effects previously discussed, it is shown here that single crystals are also birefringent. This makes it possible to use a crystal of appropriate thickness as the high-energy analog of a quarter-wave lengih plate to convert linear into circular polarization, and vice versa. In this way it will be possible to produce and analyze circularly polarized gamma beams of very high energy. (H.D.R.)

New Method for Producing and Analyzing Linearly Polarized Gamma-Ray Beams

The new method for the production and analysis of a polarized beam of high-energy gamma rays is based on observable interference effects in high-energy electron pair production on crystals. Due to these effects the absorption rate of very high-energy photon in crystal line matter depends on their linear polarization. Epuations are derived for the computation of the polarization and intensity loss. plot is presented of the intensity loss as a function of the imum value E. Values of E at different energies for the optimum value of the angle alpha at that energy are tabulated for copper and silicon crystals. Plots are also given of E as a function of alpha in copper for the photon energy, omega , equal to 6 Bev, and of E as a function of omega at alpha = 3.7 m rad. finally, the method by which the device can be used as a polarimeter is described. (H.D.R.)

Interference effects of bremsstrahlung and pair production in crystals

Interference effects of bremsstrahlung and pair production in crystals