Electron-positron Beams Research Articles

Azimuthal asymmetry in meson productions in electron-nucleon deep inelastic scattering by HERMES

The spin structure of the nucleon is studied with deep inelastic scattering by HERMES. The electron (positron) beam at 27.6 GeV, polarized internal gas targets, and wide acceptance magnetic spectrometer with a ring imaging Cherenkov counter for the particle identification are the important ingredients of the experiment. The observation of significant azimuthal asymmetry in pion productions is reported. The measurement of the quark transverse spin distribution h 1( x) which is underway is discussed.

Electron (positron) beam polarization by Compton scattering on circularly polarized laser photons

In a number of papers an attractive method of laser polarization of electrons (positrons) at storage rings or linear colliders has been proposed. We show that these suggestions are incorrect and based on errors in simulation of multiple Compton scattering and in calculation of the Compton spin-flip cross sections. We argue that the equilibrium polarization in this method is zero.

DEPOLARIZATION AND LUMINOSITY ISSUES IN A HIGH ENERGY LINEAR COLLIDER

In the next energy frontier of an electron–positron (electron–electron) linear collider its demand of both extreme high energy and high luminosity leads to a high production of W+W- (W- particles). In order to delineate processes of interest, it is advantageous to polarize the electron and positron beams, as this tends to suppress the above known processes and thus heightens the sensitivity to the sought-after processes. We investigate the possible depolarization of the electron (positron) beams in the acceleration stages as well as in the collision point. We take the example of the laser wakefield accelerator design at 5 TeV center of mass energy of colliding beams. We find that in this design the spin depolarization due to the stage jitter noise is certainly negligible, and the depolarization due to the self-generated fields at the collision point is still tolerable. We also consider several lower energy scenarios as they might be possible to achieve in a single beam driven acceleration stage.

The structure study of thin cadmium and copper sulphide films by diffraction of synchrotron radiation

Crystalline structure and phase composition of thin CdS, Cu 2S and Cd(Cu)S films were investigated using diffraction of synchrotron radiation (SR). These films were synthesized by RPECVD using nontraditional volatile sulphur-containing precursors. The diffraction measurements were performed at the station “Anomalous Scattering”, existed at the second canal of colliding electron–positron beam accelerator VEPP-3 of Siberian center of SR (Institute of Nuclear Physics of SB RAS, Novosibirsk, Russia). It was established that these films have a high transmittance in the visible range of spectra. This type of substrate material was found to determine the structure of sulphide films. The deviation of lattice parameters of cadmium and copper sulphides in thin film state obtained on Si(1 0 0) substrates from following the parameters in bulk state probably connects with lattice mismatch of silicon substrate and hexagonal structure of growing sulphide films.

The structure study of thin boron and silicon carbonitride films by diffraction of synchrotron radiation

Crystalline structure and phase composition of thin boron and silicon carbonitride films were investigated using diffraction of synchrotron radiation (SR). These films were synthesized by RPECVD using nontraditional volatile precursors. The diffraction measurements were performed at the station “Anomalous Scattering”, existed at the second canal of colliding electron–positron beam accelerator VEPP-3 of the Siberian center of SR (Institute of Nuclear Physics of SB RAS, Novosibirsk, Russia). The formation of polycrystalline novel phase not coinciding with known phases of boron carbide and boron nitride was observed in boron carbonitride films by diffraction experiments. The boron carbonitride films are not a mixture of boron carbide and boron nitride phases. We propose that these films are probably BCN phase. The X-ray diffraction and RHEED investigations revealed fine crystals of hexagonal Si 3N 4 phase in amorphous matrix of silicon carbonitride films.

Two dimensional localization of electrons and positrons under high counting rate

The construction of two wire chambers for high counting rate application is reported. Each chamber includes three wire planes – one anode and two orthogonal cathodes – in which the wires operate as independent proportional counters. One of the chambers is rotated with respect to the other, so that four position coordinates may be encoded for a charged particle crossing both chambers. Spatial resolution is determined by the wire pitch: 1 mm for cathodes, 2 mm for anodes. 320 electronic channels are involved in the detection system readout. Global counting rates in excess of 10 7 events per second have been measured, while the average electron–positron beam intensity may be as high as 3×10 7 events per second.

NLO QCD corrections and triple gauge boson vertices at the NLC

We study NLO QCD corrections as relevant to hadronic W decay in W pair production at a future 500 GeV electron-positron linac, with particular emphasis on the determination of triple gauge boson vertices. We find that hard gluon bremstrahlung may mimic signatures of anomalous triple gauge boson vertices in certain distributions. The size of these effects can strongly depend on the polarisation of the initial electron positron beams.

A laser-based beam profile monitor for the SLC/SLD interaction region

Beam size estimates made using beam-beam deflections are used for optimization of the Stanford Linear Collider (SLC) electron-positron beam sizes. Typical beam sizes and intensities expected for 1996 operations are 2.1 × 0.6 μm ( x, y) at 4.0 × 10 10 particles per pulse. Conventional profile monitors, such as scanning wires, fail at charge densities well below this. The laser-based profile monitor uses a finely-focused 350-nm wavelength tripled YLF laser pulse that traverses the particle beam path about 29 cm away from the e +/e − IP. Compton scattered photons and degraded e +/e − are detected as the beam is steered across the laser pulse. The laser pulse has a transverse size of 380 nm and a Rayleigh range of about 5 μm.

Gamma-ray emission of blazars by a relativistic electron–positron beam

Gamma-ray emission of blazars by a relativistic electron–positron beam

A Signature of Relativistic Electron-Positron Beams in BL Lacertae Objects

view Abstract Citations (13) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Signature of Relativistic Electron-Positron Beams in BL Lacertae Objects Xie, G. Z. ; Liu, B. F. ; Wang, J. C. Abstract BL Lacertae objects have been observed to vary in all wavebands on various timescales ranging from years to hours. Compton Gamma Ray Observatory (CGRO) observations have revealed intense γ-ray emission from several BL Lac Objects. We show here that there is a significant correlation between the Doppler-corrected minimal X-ray luminosity and the equivalent timescale of X-ray variability extrapolated from the observed optical variability for BL Lac objects. We interpret this as evidence for relativistic electron-positron beams in BL Lac objects. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176463 Bibcode: 1995ApJ...454...50X Keywords: ELEMENTARY PARTICLES; GALAXIES: BL LACERTAE OBJECTS: GENERAL; GALAXIES: JETS; RADIATION MECHANISMS: NONTHERMAL full text sources ADS | data products SIMBAD (46) NED (45) HEASARC (1)

Gluon bremsstrahlung from massive quarks in high energy collisions of polarized electrons and positrons.

The gluon bremsstrahlung cross section ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}qq\ifmmode\bar\else\textasciimacron\fi{}g, including effects of finite quark and antiquark masses, is calculated for arbitrarily spin-polarized electron-positron beams. Mass effects and polarization effects are given and are shown to have a sizable influence on the cross section. It is shown, however, that for the left-right asymmetry ${\mathit{A}}_{\mathit{L}\mathit{R}}$ the mass corrections and radiative corrections vanish at the ${\mathit{Z}}^{0}$ pole. The use of longitudinal polarized electrons in measurements of the forward-backward asymmetry ${\mathit{A}}_{\mathit{F}\mathit{B}}$ may give sizable enhancements.

Stability of a relativistic rotating electron-positron jet

In the force-free approximation, an electron-positron jet is shown to be stable to axisymmetric perturbations for all velocities of longitudinal motion and rotation. The stability of the jet is a result of the shear of the magnetic field, which prohibits the convective motion of a charged fluid in the radial direction. The dispersion curves ω=ω(k∥) have a minimum for k∥ 0 ≃1/R, where R is the jet radius. This results in the accumulation of perturbations inside the jet with wavelengths of the order of the jet radius. This type of oscillatory structure is observed in kiloparsec jets, in particular in 3C 273, which is evidently an electron-positron beam

Interpretation of Some Properties of Extragalactic Jets in the Context of a Two Component Model

We have studied a sample of extragalactic jets within the context of a two component model. This model supposes the existence of two flows in the extragalactic jets. An electron-positron fast beam coming from the internal regions of the accretion disk, responsible for the VLBI jet at the parsec scale and for the observed superluminal speeds. A second slow component, responsible for the jet observed at larger scales. The fast beam is destroyed when the parallel magnetic field is smaller than a critical value, BII < Bcrit = 3.2 × 10−3np1/2, where np is the density of the background thermal plasma of the slow component.

Gamma-ray emission of active galactic nuclei as a signature of relativistic electron-positron beams

Gamma-ray emission from extragalactic sources is interpreted as the Doppler-boosted annihilation and inverse Compton radiation from a relativistic electron-positron beam. We argue that Doppler boosting is required to avoid a strong depletion by γ-γ pair production, but even so, the compactness cannot be smaller than unity at light-week scale with a reasonable Doppler factor. This strongly suggests the existence of a beamed electron-positron source. The case of the quasar 3C 279 is investigated in detail. We show that one can easily account for the observed luminosity and variability time scale with reasonable values of the plasma density and bulk Lorentz factor of the beam, in accordance with previous estimates based upon observations at other wavelengths (radio and X-rays)

Creation of excited leptons in colliding electron-positron beams

The generalized model assuming the existence of internal substructures in intermediate (virtual) leptons is used to calculate the differential cross section of the electroweak annihilation of unpolarized, longitudinally polarized and transversely polarized electrons and positrons with the formation of a lepton-antilepton pair and a photon in the final state. It is shown that there is a real possibility of experimental investigation of the internal substructure of particles (if such a structure does exist at all) in colliding beams with particle energies E≥100 BeV. The parameters of the model under consideration are calculated.

Energetic particle beams in quasars and active galactic nuclei

New developments of a two-flow model for extragalactic jets are presented. We study the possibility of ascribing Very Long Baseline Interferometry (VLBI) jet features and superluminal motion to beams of relativistic particles streaming through an ambient plasma such as a wind from the accretion disc. It is shown that stability of the beams relative to the excitation of Langmuir and Alfvénic waves can be ensured in the case of electron–positron beams with bulk Lorentz factor γ smaller than 43 (the square root of proton to electron mass ratio) as long as the magnetic field parallel to the beams and jets is larger than a critical value |${B}_\text{c}=3.2\times{10}^{-3}\,n_\text{p}^{1/2},\,\text{where}\,{n}_\text{p}$| is the density of the ambient plasma. Conversely, electron–positron beams with higher bulk Lorentz factor, and electron–proton beams are rapidly destroyed. Therefore we propose that electron–positron beams with |$\gamma \leq 43$| are responsible for VLBI features. Two main models for VLBI structures are then expected according to the relative values of parallel magnetic field and ambient plasma density close to the central engine, corresponding to two different regimes for the beams, namely propagation when |$B\gt{B}_\text{c}$| and dissolution when |$B\lt{B}_\text{c}.$|

The optical jet of 3C273: an electron-positron plasma beam viewed by the light of its quasar?

The nearby bright quasar 3C273 has an extended multiband jet whose spatial pattern of intensity differs strongly from band to band. We propose that only the radio power of the jet is accounted for by the usual synchrotron model. All the higher energy photons seen are instead secondary, misdirected photons from the bright quasar core scattered our way by material within the jet. This model gives a good account of form, spectrum, polarization and intensity pattern along the jet in all the higher bands. Dust cannot plausibly scatter the X-rays seen, but Thomson scattering fits all bands well

Relativistic electron-positron beam formation in the framework of the two-flow model for active galactic nuclei

A model is proposed for relativistic beam formation in active galactic nuclei, in which electrons and positrons are generated by pair cascade on the UV photons of the accretion disk. In situ turbulent acceleration by Alfven waves in a pair plasma balances the Compton losses and prevents annihilation. The origin of the turbulence is in the subrelativistic MHD accretion ejection flow, which guarantees an extended energy reservoir up to distance level, easily achieved, the pair creation becomes catastrophic, and so the dramatic increase of the relativistic pressure expels the pair plasma along the widening flux tubes.

Fast-digitizing and track-finding electronics for the vertex detector in the Opal experiment at the Large Electron Positron Collider (LEP) at CERN

The vertex detector front-end electronics are described. It comprises fast analog-to-digital conversion circuits and a fast programmable track trigger processor. The function of the electronics is to examine, within one large electron-positron beam crossing (22 mu s), data generated in the detector for the evidence of charged particle tracks. Measurements of ionization drift times are based on a gated 93-MHz oscillator synchronized to a precision crystal clock and give points in space. The axial positions of these points along the detector are found by analyzing the difference in time of arrivals of signals at the ends of the detector (z by timing). Particle tracks are found by 36 track finders operating in parallel and are matched by semicustom coincidence chips. The track information is used in the first stage of data reduction in the Opal experiments (the first-level trigger).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A determination of αstrong with transversally polarized beams at LEP1

We propose a new and rather unbiased way of determining the value of the strong coupling constant α s if transversally polarized electron-positron beams were available at LEP1. The ratio of azimuthal asymmetries for the production of hadrons to muons in e +e − annihilation is independent of any cut-off procedure and is very sensitive to the value of α s. Moreover we show that on top of Z resonance, it is free from any ambiguity stemminf from standard model unknown parameters or the possible presence of New Physics.