Compton Scattering Cross Section Research Articles

Exclusive processes in ep collisions at the EIC and LHeC: A closer look on the predictions of saturation models

The exclusive production of vector mesons and photons in $ep$ collisions is investigated considering three phenomenological saturation models based on distinct assumptions for the treatment of the dipole-hadron scattering amplitude. The latest high precision HERA data for the reduced and vector meson cross sections are used to update the saturation model proposed by Marquet Peschanski, and Soyez, which predicts that the saturation scale is dependent of the squared momentum transfer $t$. The Marquet-Peschanski-Soyez predictions for the photon virtuality, energy and $t$ dependencies of the exclusive $\ensuremath{\rho}$, $J/\mathrm{\ensuremath{\Psi}}$, and deeply virtual Compton scattering cross sections are presented and a detailed comparison with the results derived using the impact parameter saturation models is performed. Our results indicate that a future experimental analysis of the $t$ distribution $d\ensuremath{\sigma}/dt$ for exclusive processes in the kinematical range that will covered by the EIC and LHeC, considering the distinct photon polarizations and large values of $t$, will be able to discriminate between the distinct approaches for the QCD dynamics at high energies.

Determining the ratio of the number of recoil electrons to the number of photoelectrons using a new method

The problem in question is relevant due to discrepancy between the results of theoretical and known experimental studies of various interactions of ionizing emission photons with substances, in particular, photo effect and Compton scattering of these photons. The study aimed at carrying out specific measurements using a new method of simultaneously determining the ratio of the number of recoil electrons to the number of photoelectrons. Analysis of the results showed that there are significant discrepancies between theoretical calculations and experimental data. New values of simultaneously measured ratios of cross-sections for heavy atoms using a method invented by the author, and old measurements of these ratios for light atoms usingWilson cloud chamber, when compared with theoretical calculations, show that a significant (by one order and more) one-direction discrepancy is seen for X-ray and gamma emissions over a range of energies in question.It is shown that these discrepancies might be attributed to the fact that an atomic electron is in a free state for a while. Compton scattering occurs with a free electron; photo effect involves only bound electrons. Therefore, Compton scattering cross section is proportional to a period of time, during which electron was in a free state, whereas photo effect cross section is proportional to a time period, during which electron was in a bound state. The article materials might be helpful to perform both fundamental, and applied studies on interaction of light quanta with substance including modelling the phenomena under examination.

Deeply virtual Compton scattering using a positron beam in Hall-C at Jefferson Lab

We propose to use the High Momentum Spectrometer of Hall C combined with the Neutral Particle Spectrometer (NPS) to perform high precision measurements of the Deeply Virtual Compton Scattering (DVCS) cross section using a beam of positrons. The combination of measurements with oppositely charged incident beams is the only unambiguous way to disentangle the contribution of the DVCS\(^2\) term in the photon electroproduction cross section from its interference with the Bethe-Heitler amplitude. This provides a stronger way to constrain the Generalized Parton Distributions of the nucleon. A wide range of kinematics accessible with an 11 GeV beam off an unpolarized proton target will be covered. The \(Q^2-\)dependence of each contribution will be measured independently.

On the relativistic impulse approximation for the calculation of Compton scattering cross sections and photon interaction coefficients used in kV dosimetry

We calculate differential and integrated cross sections for the Compton interaction as well as mass attenuation (), mass energy-transfer (), and mass energy-absorption () coefficients, within the relativistic impulse approximation (RIA) using Compton profiles (CPs) obtained from unrestricted Hartree–Fock electron densities. We investigate the impact of using molecular as opposed to atomic CPs on dosimetric photon interaction coefficients for air, water and graphite, and compare our cross sections to the simpler Waller–Hartree (WH) and Klein–Nishina (KN) formalisms. We find that differences in and resulting from the choice of CPs within the RIA are small relative to the differences between the RIA, WH, and KN calculations. Surprisingly, although the WH binding corrections seem accurate when considering , there are significant discrepancies between the WH and RIA results when we look at . The WH theory can differ substantially from the predictions of KN and the RIA in the tens of keV range (e.g. 6%–10% at 20 keV), when Compton scattering becomes the dominant interaction mechanism. For lower energies, the disagreement further grows to about one order of magnitude at 1 keV. However, since the photoelectric effect transfers more energy than the Compton interaction in the tens of keV range and below, the differences in the total values resulting from the choice of Compton models (KN, WH, or RIA) are not larger than 0.4%, and the differences between WH and the other two theories are no longer prominent.

Time-dependent QED approach to x-ray nonlinear Compton scattering

Motivated by a recent experiment [Fuchs et al., Nat. Phys. 11, 964 (2015)], we theoretically investigate the process of x-ray nonlinear Compton scattering (XNLC). Our approach is based on the time-dependent Schr\odinger equation for an atomic system subject to an intense x-ray pulse, and explicitly accounts for the spontaneous scattering into a quantized photonic mode. We employ our framework to study multiple nonlinear scattering scenarios. Initially, we consider soft x rays at $500\phantom{\rule{0.16em}{0ex}}\text{eV}$ photon energy to scatter nonlinearly off a helium target. For this, we find that XNLC is dominated by certain third-order processes rather than the na\{\i}vely expected mechanisms pertaining to the lowest order of perturbation theory. Subsequently, we apply our model to XNLC in helium at $4.0\phantom{\rule{0.16em}{0ex}}\text{keV}$ photon energy and beryllium at $9.7\phantom{\rule{0.16em}{0ex}}\text{keV}$. Contrary to the conclusions drawn from the experimental observations, our results suggest a good agreement of the XNLC spectrum with simple, free-electron model predictions. Moreover, our studies reveal striking qualitative similarities of linear and nonlinear Compton scattering cross sections in this regime.

Resonant Inverse Compton Scattering Spectra from Highly Magnetized Neutron Stars

Abstract Hard, nonthermal, persistent pulsed X-ray emission extending between 10 and ∼150 keV has been observed in nearly 10 magnetars. For inner-magnetospheric models of such emission, resonant inverse Compton scattering of soft thermal photons by ultrarelativistic charges is the most efficient production mechanism. We present angle-dependent upscattering spectra and pulsed intensity maps for uncooled, relativistic electrons injected in inner regions of magnetar magnetospheres, calculated using collisional integrals over field loops. Our computations employ a new formulation of the QED Compton scattering cross section in strong magnetic fields that is physically correct for treating important spin-dependent effects in the cyclotron resonance, thereby producing correct photon spectra. The spectral cutoff energies are sensitive to the choices of observer viewing geometry, electron Lorentz factor, and scattering kinematics. We find that electrons with energies ≲15 MeV will emit most of their radiation below 250 keV, consistent with inferred turnovers for magnetar hard X-ray tails. More energetic electrons still emit mostly below 1 MeV, except for viewing perspectives sampling field-line tangents. Pulse profiles may be singly or doubly peaked dependent on viewing geometry, emission locale, and observed energy band. Magnetic pair production and photon splitting will attenuate spectra to hard X-ray energies, suppressing signals in the Fermi-LAT band. The resonant Compton spectra are strongly polarized, suggesting that hard X-ray polarimetry instruments such as X-Calibur, or a future Compton telescope, can prove central to constraining model geometry and physics.

PantherPix hybrid pixel γ-ray detector for radio-therapeutic applications

This work focuses on the design of a semiconductor pixelated γ-ray camera with a pixel size of 1 mm2. The cost of semiconductor manufacturing is mainly driven by economies of scale, which makes silicon the cheapest semiconductor material due to its widespread utilization. The energy of γ-photons used in radiation therapy are in a range, in which the dominant interaction mechanism is Compton scattering in every conceivable sensor material. Since the Compton scattering cross section is linearly dependent upon Z, it is less rewarding to utilize high Z sensor materials, than it is in the case of X-ray detectors (X-rays interact also via the photoelectric effect whose cross section scales proportional to Zn, where n is ≈ 4,5). For the stated reasons it was decided to use the low Z material silicon (Z = 14) despite its worse detection efficiency. The proposed detector is designed as a portal detector to be used in radiation cancer therapy. The purpose of the detector is to ensure correct patient alignment, spatial dose monitoring and to provide the feedback necessary for an emergency shutdown should the spatial dose rate profile deviate from the treatment plan. Radiation therapy equipment is complex and thus failure prone and the consequences of malfunction are often life threatening. High spatial resolution and high detection efficiency are not a high design priority. The detector design priorities are focused up on radiation hardness, robustness and the ability to cover a large area cost efficiently. The quintessential idea of the PanterPix detector exploits the relaxed spatial resolution requirement to achieve the stated goals. The detector is composed of submodules, each submodule consisting of a Si sensor with an array of fully depleted detection diodes and 8 miniature custom design readout ASICs collecting and measuring the minuscule charge packets generated due to ionization in the PN junctions.

Compton profiles of some composite materials normalized by a new method

Recently, we have shown that as a novel approach, in the case of samples which can be treated as pure incoherent scatterers, the effective atomic number Zeff itself could be conveniently used to normalize their un-normalized Compton profiles. In the present investigation, we have attempted to examine the efficacy of this approach. For this purpose, we have first determined the single differential Compton scattering cross sections (SDCS) of the elements C and Al as well as of some H, C, N and O based polymer samples such as bakelite, epoxy, nylon and teflon which are pure incoherent scatterers. The measurements were made at 120° in a goniometer assembly that employs a high resolution high purity germanium detector. The SDCS values were used to obtain the Zeff and the un-normalized Compton profiles. These Compton profiles were separately normalized with their Zeff values (for Compton scattering) as well as with the normalization constant obtained by integrating their Hartree-Fock Biggs et al Compton profiles based on the mixture rule. These two sets of values agreed well within the range of experimental errors, implying that Zeff can be conveniently used to normalize the experimental Compton profiles of pure incoherent scatterers.

Hard X-ray quiescent emission in magnetars via resonant Compton upscattering

Non-thermal quiescent X-ray emission extending between 10 keV and around 150 keV has been seen in about 10 magnetars by RXTE, INTEGRAL, Suzaku, NuSTAR and Fermi-GBM. For inner magnetospheric models of such hard X-ray signals, inverse Compton scattering is anticipated to be the most efficient process for generating the continuum radiation, because the scattering cross section is resonant at the cyclotron frequency. We present hard X-ray upscattering spectra for uncooled monoenergetic relativistic electrons injected in inner regions of pulsar magnetospheres. These model spectra are integrated over bundles of closed field lines and obtained for different observing perspectives. The spectral turnover energies are critically dependent on the observer viewing angles and electron Lorentz factor. We find that electrons with energies less than around 15 MeV will emit most of their radiation below 250 keV, consistent with the turnovers inferred in magnetar hard X-ray tails. Electrons of higher energy still emit most of the radiation below around 1 MeV, except for quasi-equatorial emission locales for select pulse phases. Our spectral computations use a new state-of-the-art, spin-dependent formalism for the QED Compton scattering cross section in strong magnetic fields.

Compton scattering from He4 at 61 MeV

The Compton scattering cross section from He4 has been measured with high statistical accuracy over a scattering angle range of 40∘−159∘ using a quasimonoenergetic 61-MeV photon beam at the High Intensity Gamma-Ray Source. The data are interpreted using a phenomenological model sensitive to the dipole isoscalar electromagnetic polarizabilities (αs and βs) of the nucleon. These data can be fit with the model using values of αs and βs that are consistent with the currently accepted values. These data will serve as benchmarks of future calculations from effective field theories and lattice quantum chromodynamics.Received 22 August 2017DOI:https://doi.org/10.1103/PhysRevC.96.055209©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNuclear reactionsPhotonuclear reactionsPolarization phenomenaPropertiesA ≤ 5Nuclear Physics

Hard Spectral Tails in Magnetars

AbstractPulsed non-thermal quiescent emission between 10 keV and around 150 keV has been observed in ~10 magnetars. For inner magnetospheric models of such hard X-ray signals, resonant Compton upscattering of soft thermal photons from the neutron star surface is the most efficient radiative process. We present angle-dependent hard X-ray upscattering model spectra for uncooled monoenergetic relativistic electrons. The spectral cut-off energies are critically dependent on the observer viewing angles and electron Lorentz factor. We find that electrons with energies less than around 15 MeV will emit most of their radiation below 250 keV, consistent with the observed turnovers in magnetar hard X-ray tails. Moreover, electrons of higher energy still emit most of the radiation below around 1 MeV, except for quasi-equatorial emission locales for select pulses phases. Our spectral computations use new state-of-the-art, spin-dependent formalism for the QED Compton scattering cross section in strong magnetic fields.

Attosecond x-ray scattering from a particle-hole wave packet

We investigate the imaging of electron wave-packet dynamics by measuring the pattern of inelastically scattered photons. For this purpose, we develop a theory of time-resolved Compton scattering. We demonstrate that, by using a sufficiently short x-ray pulse, the scattering cross section directly reflects the instantaneous momentum density of the electron. Therefore, we propose time-resolved Compton scattering as a tool to image electron wave-packet dynamics in momentum space. To illustrate this, we simulate electron wave packets in argon by using the time-dependent configuration-interaction singles method. Specifically, we consider coherent particle-hole wave packets, where the hole is in either the $3p$ or the $3s$ shell, and the particle (the excited electron) is either in a Rydberg state or in the continuum. Our calculations confirm that the dynamics of electron wave packets can indeed be imaged by measuring the doubly differential Compton scattering cross section. When the x-ray detector has no energy resolution at all, the contribution of Compton scattering to the differential scattering cross section becomes stationary. In that case, the motion of the particle and the hole can no longer be inferred from the scattering pattern.

Master formulas for the dressed scalar propagator in a constant field

The worldline formalism has previously been used for deriving compact master formulas for the one-loop N-photon amplitudes in both scalar and spinor QED, and in the vacuum as well as in a constant external field. For scalar QED, there is also an analogous master formula for the propagator dressed with N photons in the vacuum. Here, we extend this master formula to include a constant field. The two-photon case is worked out explicitly, yielding an integral representation for the Compton scattering cross section in the field suitable for numerical integration in the full range of electric and magnetic field strengths.

Determination of the scalar polarizabilities of the proton using beam asymmetry $\Sigma_{3}$ Σ 3 in Compton scattering

The scalar dipole polarizabilities, $\alpha_{E1}$ and $\beta_{M1}$, are fundamental properties related to the internal dynamics of the nucleon. The currently accepted values of the proton polarizabilities were determined by fitting to unpolarized proton Compton scattering cross section data. The measurement of the beam asymmetry $\Sigma_{3}$ in a certain kinematical range provides an alternative approach to the extraction of the scalar polarizabilities. At the Mainz Microtron (MAMI) the beam asymmetry was measured for Compton scattering below pion photoproduction threshold for the first time. The results are compared with model calculations and the influence of the experimental data on the extraction of the scalar polarizabilities is determined.

Inverse Compton power and cooling time in a quantum Fermi-Dirac plasma including the quantum degeneracy pressure

The inverse Compton power is investigated in relativistically degenerate quantum Fermi-Dirac plasmas including the influence of quantum statistical degeneracy pressure. The ordinary and double Compton scattering cross sections, the inverse Compton power, and the cooling time are obtained in Fermi-Dirac plasmas. It is shown that the differential Compton scattering cross section has a maximum at the small wave number domain. However, the differential Compton scattering cross section increases with an increase of the wave number in the case of a large relativistic degeneracy parameter. It is interesting to note that the differential Compton scattering cross section in the backward scattering region is greater than that in the forward scattering region when the degeneracy pressure is large. It is also shown that the double Compton scattering process is quite suppressed in the forward scattering domain. It is also shown that the inverse Compton power increases with an increase of the relativistic degeneracy parameter. It is also shown that the influence of the relativistic degeneracy on the inverse Compton power is more significant for small plasmon energies. In addition, it is found that the cooling time due to the inverse Compton process decreases with an increase of the relativistic degeneracy parameter.

Resonant Compton Scattering of Photons by Helium Atoms in Lorentzian Astrophysical Plasmas

We investigate the effects of Lorentzian astrophysical plasmas on resonant Compton scattering of photons by the helium ground and excited states. The bound-excited states energies in the plasma environments are obtained by using highly correlated exponential wave functions in the framework of Ritz variational method. The resonance Compton scattering cross sections in Lorentzian plasmas between the \(\hbox {1s}^{2}{\,}^{1}\hbox {S}\) and 1s2p \(^{1}\hbox {P}\), 1s2s \(^{1}\hbox {S}\) and 1s3p \(^{1}\hbox {P}\), 1s3s \(^{1}\hbox {S}\) and 1s3d \(^{1}\hbox {D}\) states are reported as a function of the spectral index and plasma parameter. The nonthermal character of the Lorentzian plasmas shows interesting features on the resonant Compton scattering cross sections.

Resonant Compton scattering of photons by He(1s2 1S) in astrophysical plasmas

SynopsisThe nonthermal effect on resonant Compton scattering of photons by the He (1s2 1S) ground state is investigated in Lorentzian astrophysical plasmas using exponential correlated basis functions and with a variational technique. The nonthermal character of the Lorentzian plasma enhances the resonant Compton scattering cross sections.

Gyromagnetic gs factors of the spin-1/2 particles in the (1/2+-1/2--3/2-) triad of the four-vector spinor, ψμ, irreducibility and linearity

The gauged Klein–Gordon equation, extended by a gsσμνFμν/4 interaction, the contraction of the electromagnetic field strength tensor, Fμν, with the generators, σμν/2, of the Lorentz group in (1/2, 0) ⊕ (0, 1/2), and gs being the gyromagnetic factor, is examined with the aim to find out as to what extent it qualifies as a wave equation for general relativistic spin-1/2 particles transforming as (1/2, 0) ⊕ (0, 1/2) and possibly distinct from the Dirac fermions. This equation can be viewed as the generalization of the gs = 2 case, known under the name of the Feynman–Gell-Mann equation, the only one which allows for a bilinearization into the gauged Dirac equation and its conjugate. At the same time, it is well-known a fact that a gs = 2 value can also be obtained upon the bilinearization of the nonrelativistic Schrödinger into nonrelativistic Pauli equations. The inevitable conclusion is that it must not be necessarily relativity which fixes the gyromagnetic factor of the electron to g(1/2) = 2, but rather the specific form of the primordial quadratic wave equation obeyed by it, that is amenable to a linearization. The fact is that space-time symmetries alone define solely the kinematic properties of the particles and neither fix the values of their interacting constants, nor do they necessarily prescribe linear Lagrangians. Information on such properties has to be obtained from additional physical inputs involving the dynamics. We here provide an example in support of the latter statement. Our case is that the spin-1/2- fermion residing within the four-vector spinor triad, ψμ ~ (1/2+-1/2--3/2-), whose sectors at the free particle level are interconnected by spin-up and spin-down ladder operators, does not allow for a description within a linear framework at the interacting level. Upon gauging, despite transforming according to the irreducible (1/2, 1) ⊕ (1, 1/2) building block of ψμ, and being described by 16-dimensional four-vector spinors, though of only four independent components each, its Compton scattering cross sections, both differential and total, result equivalent to those for a spin-1/2 particle described by the generalized Feynman–Gell-Mann equation from above (for which we provide an independent algebraic motivation) and with g(1/2-) = -2/3. In effect, the spin-1/2- particle residing within the four-vector spinor effectively behaves as a true relativistic "quadratic" fermion. The g(1/2-) = -2/3 value ensures in addition the desired unitarity in the ultraviolet. In contrast, the spin-1/2+ particle, in transforming irreducibly in the (1/2, 0) ⊕ (0, 1/2) sector of ψμ, is shown to behave as a truly linear Dirac fermion. Within the framework employed, the three spin sectors of ψμ are described on equal footing by representation- and spin-specific wave equations and associated Lagrangians which are of second-order in the momenta.

Non-thermal shielding effects on the Compton scattering power in astrophysical plasmas

The non-thermal shielding effects on the inverse Compton scattering are investigated in astrophysical non-thermal Lorentzian plasmas. The inverse Compton power is obtained by the modified Compton scattering cross section in Lorentzian plasmas with the blackbody photon distribution. The total Compton power is also obtained by the Lorentzan distribution of plasmas. It is found that the influence of non-thermal character of the plasma suppresses the inverse Compton power in astrophysical Lorentzian plasmas. It is also found that the non-thermal effect on the inverse Compton power decreases with an increase of the temperature. In addition, the non-thermal effect on the total Compton power with Lorentzan plasmas increases in low-temperature photons and, however, decreases in intermediate-temperature photons with increasing Debye length. The variation of the total Compton power is also discussed.

Influence of electron-neutral collisions on the Compton scattering cross section and the Salpeter structure factor in warm collisional plasmas

The electron-neutral collision effects on the Compton scattering process are investigated in warm collisional plasmas. The Compton scattering cross section in warm collisional plasmas is obtained by the Salpeter structure factor with the fluctuation-dissipation theorem and the plasma dielectric function as a function of the electron-neutral collision frequency, Debye length, and wave number. It is shown that the influence of electron-neutral collision strongly suppresses the Compton scattering cross section in warm collisional plasmas. It is also found that the electron-neutral collision effect on the differential Compton scattering cross section is more significant in forward scattering directions. We show that the differential Compton scattering cross section has a maximum at the scattering angle φ=π/2. In addition, we find that the electron-neutral collision effect on the total Compton scattering cross section increases with increasing Debye length and wave number. The variation of the Compton scattering cross section due to the change of collision frequency and plasma parameters is also discussed.