Channeling radiation from 2 to 20 GeV/c electrons and positrons (II).: Axial case

Radiation spectra for GeV electrons and positrons have been measured in a broad range of incidence angles in Si and Ge crystals. An enhancement up to a factor of 50 is found for axially channeled particles. In nearly all cases, the very low-energy part of the photon spectra is strongly reduced either due to equalization in the doughnut or due to the strong multiple scattering from the atomic rows. For large incident angles to the axis, the reduction is due to the so-called Landau-Pomeranchuk effect. For proper channeled positrons, stable oscillations give rise to a peak in the photon spectra. In the transition region from axial to planar channeling, the photon spectra change from being structureless to showing pronounced peaks from the first harmonics. The experimental results are compared to both classical and quantal calculations.     

New approximation for the interaction potential of light channeled particles with crystals

A new approximation for the continuous interaction potentials of atomic planes and strings with channeled electrons and positrons in crystals is proposed. A model in which atomic electron distributions within a certain atomic subshell are assumed to be exponentially decaying is used. Contrary to the Thomas-Fermi (TF) and Thomas-Fermi-Dirac (TFD) models this approach takes into account the shell structure of atoms in reasonably good agreement with the Hartree-Fock method (HF). Simple analytical expressions for the continuous plane (string) potentials are given. Calculations of several planar potentials for positrons channeled in silicon and tungsten are presented. Results are compared with widely known Lindhard and Molière approximations. Some estimates of the Kumakhov spontaneous radiation intensity under positron planar channeling conditions in the classical approximation are also given.     

Emission of photons by positrons channeled in single crystals near an energy of 100 GeV

Emission by 120-GeV positrons in the channeling regime in the (011) plane of a silicon single crystal has been considered. Trajectories of positrons under different initial conditions have been calculated within the theory of nonlinear oscillations. The amplitude distribution function of channeled particles has been determined taking into account the nonlinearity of their motion. The intensity of radiation under various initial conditions has been calculated by two different methods. These results can be useful for comparison with experimental data at energies of positrons beginning with 100 GeV and higher.     

Bending of high energy beams using axial and planar channeling

A very strong and dramatic bending effect has been found for 12 GeV/c positive particles channeled along crystal axes and planes. For a combination of axial and planar channeling the bending efficiency is 5–10%. The maximum bending angle was 52 mrad obtained over a 20 mm long 〈111〉 Si-crystal. The axial channeling is also able to bend negative particles.     

Angular distributions of channeled pions and protons up to 250 GeV/c

Channeling phenomena are observed for positive particles of momentum up to 250 GeV/c in a germanium crystal. The polar angular distributions of the channeled particles are compared with theoretical predictions based on a diffusion model. The results indicate that at high particle energy there may be additional mechanisms besides those operative at low energy leading to dechanneling of the particles. In spite of this, channeling effects are observed for particles incident at up to several times the critical angle, in contrast with the results from low energy channeling. Statistical equilibrium in the azimuthal angular distribution has also been observed at all measured beam momenta to about twice the calculated channeling critical angle. The breakdown of statistical equilibrium for the 2 cm crystal used occurs at an incident angle 2–3 times smaller than predicted theoretically.     

Higher moments of the pion multiplicity distribution in proton-proton interactions at 12 and 24 GeV/c

Results on higher moments of the pion multiplicity distribution are presented for pp interactions at 12 and 24 GeV/c incident lab momentum. A simple parametrization for the pion multiplicity distribution is established at 12 and 24 GeV/c and is then used to discuss the energy dependence of higher moments in a range from 4 to about 500 GeV/c incident lab momentum.     

Experimental observation of a copious yield of electrons with small transverse momenta in pp collisions at high energies

Inclusive electron and positron emission have been observed for θ_cm = 30° and S = 2800 GeV² at the CERN Intersecting Storage Rings (ISR). Over the transverse momentum interval 0.2 GeV/c < p_T < 1.5 GeV/c, electrons and positrons, which are equal in number within the experimental accuracies, appear to grow with respect to other particles (pions) approximately like 1/p_T. We are unable to explain their number and p_T-dependence in terms of “conventional” mechanisms.     

General characteristics of\bar pp interactions at low energies in terms of principal axis and impact parameter variables

The reaction configuration in momentum and position space has been investigated in detail from exclusive final states in \(\bar pp\) interactions at centre of mass energies 2.01 and 2.96 GeV. In momentum space one finds a tendency towards a planar configuration at low multiplicities. In position space, one sees the average impact parameter decreasing with increasing multiplicity. At large multiplicities, events become more phase-space like i.e., more central whereas at lower multiplicities the effect ofp _t damping can be seen.     

Proton-proton elastic scattering and nucleon resonance production at high energies

Angular distributions of proton-proton elastic scattering have been measured for incident beam momenta of 10.0, 12.0, 14.2 and 24.0 GeV/c over a range of lab scattering angles from 12 to 152 mrad. This is equivalent to a range of four-momentum transfer squared from about 0.1 to 6.7 GeV² at the highest momentum. Nucleon resonance production in the two-body reaction p + p → p + X has been studied at 24.0 GeV/c incident momentum from 13.5 to 112 mrad by measuring the proton momentum spectra from the elastic peak down to a momentum corresponding to a missing mass of about 2.6 GeV. The new data are compared with previous results and theoretical models.     

A study of final states with a large transverse momentum particle from proton-proton collisions at 24 GeV/c

Events with a large transverse momentum (>1 GeV/c) pion or nucleon have been selected from the data of a high-statistics pp bubble chamber experiment (√s=6.84 GeV). Only events in which all secondary particles could be identified were used. One finds that fewer pions are produced in the azimuthal hemisphere containing the large transverse momentum particle than in the opposite hemisphere. An indication for coplanarity is found. Most pions associated with a large transverse momentum pion are emitted with small absolute c.m. rapidities, whereas those associated with large transverse momentum nucleons show some back-to-back structure. Various results of this investigation are similar to those obtained at the ISR. Most of the findings are compatible with predictions from an independent emission model.     

Analysis of the reaction np → dπ+π− below 3.5 GeV/c

The reaction np → dπ⁺π^? was studied from threshold up to 3.5 GeV/c neutron beam momentum. Cross-section values for this reaction are evaluated as a function of the beam momentum. The deuteron production features and the enhancement observed in the dπ mass spectrum at 2.17 GeV are adequately described in terms of an OPE model and nucleon-nucleon final-state interactions.     

正弦平方势与沟道辐射的谱线展宽

利用曾经提出的正弦平方势解析地处理了非线性效应和偶极效应对沟道谱线宽度的影响, 解释了正电子能量在5 GeV附近的Si (110)面沟道辐射谱特征. The spectral properties of the planar channeling radiation of positron have been investigated by using Sine squared Potential. At positron energy of 5 GeV a sharp line has been explained for the planar channeling radiation in Si(110 ). It is that theoretic results are compatible to the experiments.     

The anomalous PAMELA effect and its explanation

The anomalous effect discovered in the PAMELA experiment includes the unusual behavior of the ratio r of fluxes of Galactic positrons to the total flux of Galactic positrons and electrons. According to theory, the value of r should decrease with increasing energy E of these particles. The experiment has shown, however, that in the energy range of 0.1 GeV < E < 5 GeV, the value of r declines; then, beginning with E > 5 GeV and up to E ≈ 150 GeV (measurements have been conducted only up to this energy level), we observe its growth. An explanation for this phenomenon is given.     

A study of e+e− pairs in the mass range 11 to 25 GeV/c2 at the CERN intersecting storage rings

A sample of 58e⁺e^? events with an invariant mass greater than 11 GeV/c² produced in pp collisions at a centre-of-mass energy of 62.3 GeV is discussed. The cross sections are presented as a function of the mass and transverse momentum. The electron pairs produced with a mean transverse momentum of 2.50 ± 0.25 GeV/c.     

PAMELA spectrometer data processing

The international space experiment PAMELA was started in the mid-2006 and was finished in the beginning of 2016. The main objective of the experiment was the study of the cosmic ray spectra and elemental composition (including antiproton and positron spectra) in a wide energy range. The main instrument of the PAMELA device is a spectrometer including several detectors. Since the case in point here is the technique of processing the results for high-energy particles (protons, α-particles with energies E ≥ 50 GeV/nucleon, electrons and positrons with E ≥ 50 GeV), the three detectors were mostly used in data processing: a tracker placed into a dc magnetic field, a calorimeter, and a neutron detector. A relatively simple technique for separating electrons and positrons from the total flux of charged particles arriving at the spectrometer and a technique for determining the energy of these particles and constructing their energy spectra are described. This paper is based on the results presented in [1].     

Resonance structure in the γγ invariant mass spectrum in pC, dC, and dCu interactions

Along with ?? ⁰ and ?? mesons, a resonance structure in the invariant mass spectrum of two photons atM _??? = 360 ± 7 ± 9 MeV is observed in dC interactions at momentum 2.75 GeV/c per nucleon. This resonance structure is not observed in pC collisions at the beam momentum 5.5 GeV/c. The result obtained in the reaction dC is confirmed by the second experiment carried out on the deuteron beam at momentum 3.83 GeV/c per nucleon with a copper target. Some other checks of the observed effect are presented.     

Single Regge pole model for large angle elasticp-p scattering at high energies

The elastic proton-proton angular distribution at large momentum transfers (?t?8 (GeV/c)²) and energies above 10 GeV laboratory momentum can be understood in the framework of a single Regge pole model.     

Photoproduction of charged pions from deuterium at gamma-energies from 900 to 1,800 MeV and pion angles between 65 and 125°

The cross sections for production of pions, kaons, protons, antiprotons and deuterons at zero production angle have been measured in proton-nucleus collisions at 70 GeV in the momentum range of secondaries from 1.5 up to 3 GeV/c. Thin Al, Cu and W targets have been used in these measurements. The data onA-dependence of the production cross sections and particle yield ratios in momentum range from 1.35 up to 3.0 GeV/c are presented.     

Spatial dependent diffusion of cosmic rays and the excess of primary electrons derived from high precision measurements by AMS-02

The precise spectra of Cosmic Ray(CR) electrons and positrons have been published by the measurement of AMS-02. It is reasonable to regard the difference between the electron and positron spectra(?Φ = Φ_(e-)-Φ_(e+)) as being dominated by primary electrons. The resulting electron spectrum shows no sign of spectral softening above 20 GeV, which is in contrast with the prediction of the standard model of CR propagation. In this work, we generalize the analytic one-dimensional two-halo model of diffusion to a three-dimensional realistic calculation by implementing spatial variant diffusion coefficients in the DRAGON package. As a result, we can reproduce the spectral hardening of protons observed by several experiments, and predict an excess of high energy primary electrons which agrees with the measurement reasonably well. Unlike the break spectrum obtained for protons, the model calculation predicts a smooth electron excess and thus slightly over-predicts the flux from tens of GeV to 100 GeV. To understand this issue, further experimental and theoretical studies are necessary.