multi-GeV Electrons Research Articles

Material budget imaging with multi-GeV electrons - calibration and applications for 2D material scanning

The technique of material budget imaging (MBI) uses multi-GeV electrons to directly measure the material budget ϵ = x/X 0 of a material with thickness x and its radiation length X 0. The beam particles are deflected by multiple Coulomb scattering and the deflection angle distribution is centered at zero with a width depending on the traversed material. Hence, a reconstruction of kink angles using individual electron trajectories measured in high resolution beam telescopes allows to estimate the material budget by applying appropiate models of multiple scattering theory, such as the Highland formula. Measurements at the DESY II testbeam were performed with various materials in terms of thickness and type for a calibration of the MBI technique. The material budget is an important quantity for the design of high-energy particle detectors. Therefore, the material budget of unknown materials can be experimentally measured as well as complex material distributions can be imaged in 2D.

Application of material budget imaging for the design of the ATLAS ITk strip detector

The technique of material budget imaging (MBI) allows to experimentally assess the material budget ϵ = x/X 0 of a material with thickness x and its radiation length X 0. Here, multi-GeV electrons from a test beam facility such as the DESY-II test beam are used. This novel technique exploits the fact that the beam particles are deflected by multiple Coulomb scattering following a distribution of the deflection angle with a center at zero and a width depending on the traversed material. By reconstructing the individual kink angles from the measured particle trajectories in a high resolution beam telescope, the material budget can be extracted by applying appropriate models of multiple scattering theory, such as the Highland formula.On the one hand, various materials with known material budgets were measured to calibrate the MBI technique and study also different systematic effects such as the beam telescope’s acceptance and the variation of the beam energy. On the other hand, a number of material samples planned in the design of the local support structures of the new ATLAS Inner Tracker (ITk) strip detector were investigated to extract the according radiation length values not known beforehand.This paper shows therefore the potential of the MBI technique to give an input for the design of high-energy particle detectors by providing experimentally measured numbers of the radiation length for various material compounds with not a-priori known X 0 values.

Nonlinear Compton scattering of polarized photons in plane-wave backgrounds

We investigate the phenomenology of nonlinear Compton scattering of polarized photons by unpolarized electrons in plane-wave backgrounds. The energy and angular spectra of polarized photons are calculated for linearly and circularly polarized pulses, monochromatic fields and constant crossed field backgrounds. When the field intensity is in the weakly nonlinear regime, photons in different polarization states are predicted to possess very different energies and angular distributions. We explain this difference by calculating the spectrum for nonlinear Thomson scattering in a linearly polarized monochromatic background and projecting the electron's trajectory onto the different polarization directions. Finally, we calculate a scenario for multi-GeV electrons and, by considering the energy and angular-resolved photon polarization purity, find one can achieve a GeV-photon beam with polarization purities of over $90%$.

Dark matter, millicharges, axion and scalar particles, gauge bosons, and other new physics with LDMX

The proposed LDMX experiment would provide roughly a meter-long region of instrumented tracking and calorimetry that acts as a beam stop for multi-GeV electrons in which each electron is tagged and its evolution measured. This would offer an unprecedented opportunity to access both collider-invisible and ultra-short lifetime decays of new particles produced in electron (or muon)-nuclear fixed-target collisions. In this paper, we show that the missing momentum channel and displaced decay signals in such an experiment could provide world-leading sensitivity to sub-GeV dark matter, millicharged particles, and visibly or invisibly decaying axions, scalars, dark photons, and a range of other new physics scenarios.

Exploration of Strong Field Physics with Multi-PW Lasers

At the Center for Relativistic Laser Science (CoReLS) petawatt (PW) lasers have been developed for the investigations of strong field physics. The CoReLS has successfully upgraded one of the existing PW laser beamlines to a 4 PW laser at 20 fs. From laser-driven charged-particle acceleration experiments, multi-GeV electrons and 90-MeV protons can be generated using the laser wakefield acceleration and the radiation pressure acceleration schemes, respectively. The GeV electron beam can be, in turn, used for Compton backscattering with another PW laser. Such a Compton scattering process can be examined for other quantum electrodynamics (QED) effects, including the radiation reaction effect and the Breit-Wheeler pair production process. PW lasers have, thus, offered new opportunities to pursue novel physics research in relativistic plasma physics, strong field quantum electrodynamics, nuclear physics and laboratory astrophysics.

Observation of deflection of a beam of multi-GeV electrons by a thin crystal.

We report on an experiment performing channeling and volume reflection of a high-energy electron beam using a quasimosaic, bent silicon (111) crystal at the End Station A Test Beam at SLAC. The experiment uses beams of 3.35 and 6.3 GeV. In the channeling orientation, deflections of the beam of 400 μrad for both energies with about 22% efficiency are observed, while in the volume-reflection orientation, deflection of the beam by 120 μrad at 3.35 GeV and by 80 μrad at 6.3 GeV is observed with 86%-95% efficiency. Quantitative measurements of the channeling efficiency, surface transmission, and dechanneling length are taken. These are the first quantitative measurements of channeling and volume reflection using a primary beam of multi-GeV electrons.

Radiation from multi-GeV electrons and positrons in periodically bent silicon crystal

A periodically bent Si crystal is shown to efficiently serve for producing highly monochromatic radiation in a gamma-ray energy spectral range. A short-period small-amplitude bending yields narrow undulator-type spectral peaks in radiation from multi-GeV electrons and positrons channeling through the crystal. Benchmark theoretical results on the undulator are obtained by simulations of the channeling with a full atomistic approach to the projectile-crystal interactions over the macroscopic propagation distances. The simulations are facilitated by employing the MBN Explorer package for molecular dynamics calculations on the meso-, bio- and nano-scales. The radiation from the ultra-relativistic channeling projectiles is computed within the quasi-classical formalism. The effects due to the quantum recoil are shown to be significantly prominent in the gamma-ray undulator radiation.

A positron source using an axially oriented crystal associated to a granular amorphous converter

A non-conventional positron source using the intense γ radiation from an axially oriented monocrystal which materializes into e+e− pairs in a granular amorphous converter is described. The enhancement of photon radiation by multi-GeV electrons crossing a tungsten crystal along its <111> axis is reported. The resulting enhancement of pair production in an amorphous converter placed 2 meters downstream, is also reported. Sweeping off the charged particles from the crystal by a bending magnet upstream of the converter allows a significant reduction of the deposited energy density. Substituting a granular target made of small spheres for the usual compact one, makes the energy dissipation easier. The deposited energy and corresponding heating are analyzed and solutions for cooling are proposed. The configurations studied here for this kind of positron source allow its consideration for unpolarized positrons for the ILC.

Multicentimeter long high density magnetic plasmas for optical guiding

We present a platform for producing long plasma channels suitable for guiding lasers over several centimeters by applying magnetic fields to limit the radial heat flux from a preforming laser beam. The resulting density gradient will be used as an optical plasma waveguide. The plasma conditions have been chosen to be consistent with the requirements for laser wakefield acceleration where multi-GeV electrons are predicted. A detailed description of the system used to produce the high (5 T) magnetic fields and initial results that show a 5 cm long plasma column are discussed.

Polarimetry of coherent bremsstrahlung by analysis of the photon energy spectrum

A method of coherent bremsstrahlung (CB) polarimetry based on the analysis of the shape of the photon energy spectrum is presented. The influence of a number of uncertainty sources, including the choice of atomic form-factors, has been analyzed. For a CB source consisting of a diamond radiator and multi-GeV electrons, an absolute accuracy of polarimetry at the level of 0.01–0.02 is attainable.

Results on the coherent interaction of high energy electrons and photons in oriented single crystals

The CERN-NA-59 experiment examined a wide range of electromagnetic processes for multi-GeV electrons and photons interacting with oriented single crystals. The various types of crystals and their orientations were used for producing photon beams and for converting and measuring their polarisation.The radiation emitted by 178GeV unpolarised electrons incident on a 1.5cm thick Si crystal oriented in the Coherent Bremsstrahlung (CB) and the String-of-Strings (SOS) modes was used to obtain multi-GeV linearly polarised photon beams.A new crystal polarimetry technique was established for measuring the linear polarisation of the photon beam. The polarimeter is based on the dependence of the coherent pair production (CPP) cross section in oriented single crystals on the direction of the photon polarisation with respect to the crystal plane. Both a 1mm thick single crystal of Germanium and a 4mm thick multi-tile set of synthetic Diamond crystals were used as analyzers of the linear polarisation.A birefringence phenomenon, the conversion of the linear polarisation of the photon beam into circular polarisation, was observed. This was achieved by letting the linearly polarised photon beam pass through a 10cm thick Silicon single crystal that acted as a “quarter wave plate” (QWP) as suggested by Cabibbo et al.

New Fermi smearing approach for scattering of multi-GeV electrons by nuclei

The cross section for electron scattering by nuclei at high momentum transfers is calculated within the Fermi smearing approximation (FSA), where binding effects on the struck nucleon are introduced via the relativistic Hartree approximation (RHA). The model naturally preserves current conservation, since the response tensor for an off-shell nucleon conserves the same form that for a free one but with an effective mass. Different parameterizations for the inelastic nucleon structure function, are analyzed. The smearing at the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on $^{56}$Fe are well reproduced for all measured geometries for the first time, as is evident from the comparison with previous calculations.

Radiation emission and its influence on the motion of multi-GeV electrons and positrons incident on a single diamond crystal

A few years ago the CERN NA-43 collaboration installed an upgraded detector system which allows a detailed analysis of the particle motion before, during and after penetration of a crystal. Also, essentially perfect diamond crystals were produced by the collaborators from Schonland Research Centre. These facts have led to new and very detailed investigations of QED-processes in strong crystalline fields. Along axial directions the radiation emission is enhanced by more than two orders of magnitude. For incidence on a 0.7 mm thick diamond crystal of well-aligned 149 GeV electrons, 35% give rise to a high energy photon peak at ≃120 GeV. For 243 GeV electrons and ≃200 GeV photons, this number decreases to 25% – which may be an indication of quantum suppression. Different measurements of the photon multiplicities show that in most cases positrons and electrons emit equal number of photons. The dramatic radiation emission leads to a strong reduction in transverse energy and all electrons incident within the critical angle are captured to high lying channeling states and exit at channeling angles corresponding to their final energy – a completely new result for negatively charged particles. For the first time, we present an analysis where the photon is used as a `messenger' for the transverse energy of the electron during the formation time and we conclude that the more energetic photons are created closer to the string and emitted in the axial direction – in contrast to earlier calculations using the Dirac equation. The strongly enhanced radiation emission leads to angular cooling for electrons but angular heating for positrons and we show that at higher electron energies the cooling becomes stronger as expected from theory. For electrons, the radiative cooling gives rise to a capture of above-barrier particles into the channeled beam. The total radiative energy loss is shown as not to follow the γ 2-law expected from classical electrodynamics, but turns over towards the γ 2/3-law as found from a full QED calculation. Detailed comparisons of doughnut formation for e +, e − just before radiation emission and behind the crystal show large differences in equalization – evidence that the hard photons are emitted in the first part of the crystal.

Radiation emission and related processes for multi-GeV electrons and positrons in aligned crystals

Presented are theoretical results concerning the powerful influence of radiation emission on angular and spatial distributions of multi-GeV electrons and positrons in strong crystalline fields of axially oriented single crystals. The reduction/increase of the average angle between the particle velocity and the axial direction are shown to occur depending on the particle charge sign, angle of incidence, crystal type, and amount of radiative energy loss. This results in angular “cooling/heating” of the particle beam. A radiative capture of random particles into channeling regime is found to play an increasing role with increasing incident energy, leading to appearance of specific features in angular dependencies of physically observable quantities like angular spread of the beam, average energy loss, and yield of inelastic processes on crystal nuclei. This has been confirmed by recent experimental results of the NA-43 group at CERN.

Radiation Emission and Its Influence on the Motion of Multi-GeV Electrons and Positrons in Strong Crystalline Fields

Presented is the first experimental demonstration of a dramatic radiative redistribution in transverse states for multi-GeV electrons/positrons, interacting with strong crystalline fields. Detailed analysis of energy loss, photon multiplicities, and scattering distributions leads to new physical insight into open questions such as radiative cooling/heating of the beams in aligned crystals, validity of the constant-field approximation, radiative capture of random particles (``feed in'') into channeled states, and the Landau-Pomeranchuk effect in multiphoton radiation spectra.

Axial channeling and radiation of multi-GeV electrons

Channeling and radiation of intense γ-photons are discussed for 150 GeV and 1 TeV electrons, based on the synchrotron approximation for radiation. The dechanneling function and the lifetime of the electrons in a channel are calculated. Theoretical results for photon spectra are compared with the experiment for Si and Ge single crystals of different thicknesses. The photon multiplicity is discussed in detail.

Radiation emission and shower formation in strong crystalline fields

Abstract When multi-GeV electrons and positrons penetrate single crystals near axial/planar directions dramatic effects appear. The large gamma factors (105−106) enhance the electric fields along axes/planes to overcritical values within the electron restframe. Overcritical in this context means that perturbation theory (used hitherto) is no longer applicable, but a full description of QED in strong fields has to be used. Bremsstrahlung becomes a highly non-perturbative process resulting in a much enhanced cross section. Originally a peak in the photon spectra from 150 GeV electrons penetrating Ge-crystals was detected. In the literature different suggestions for processes leading to this peak is found, i.e. “new” physics, radiation cooling, multiphotons etc. Along axial/planar directions these effects were investigated in detail by our CERN-collaboration (NA-43) and surprising effects were found. 150 GeV axially channeled electrons radiate 80% of the total energy Eo in 1 mm Ge – 20 times more than in amo...

Probing nuclear structure with multi-GeV electrons

We consider several options for probing nuclear structure and perturbative QCD using high energy lepton beams. We conclude that there exists a good case for a dedicated electron facility with available electron energy of 10 to 20 GeV.

Hadronic physics with multi-GeV electrons

Hadronic physics with multi-GeV electrons

Plasma model of microwave background and primordial elements: an alternative to the big bang

A plasma model of the origin of the light elements and the microwave background is presented. In contrast to the conventional Big Bang hypothesis, the model assumes that helium, deuterium and the microwave background were all generated by massive stars in the early stages of galaxy formation. The microwave background is scattered and isotropized by multi-GeV electrons trapped in the jets emitted by active galactic nuclei. The model produces reasonable amounts of heavy elements, accurately predicts the gamma-ray background intensity and spectrum, and explains the statistics of quasars, compact and extended radio sources.