Single Differential Cross Sections Research Articles

Measurement of high-Q 2 charged current deep inelastic scattering cross sections with a longitudinally polarised positron beam at HERA

Measurements of the cross sections for charged current deep inelastic scattering in e+p collisions with a longitudinally polarised positron beam are presented. The measurements are based on a data sample with an integrated luminosity of 132 pb^-1 collected with the ZEUS detector at HERA at a centre-of-mass energy of 318 GeV. The total cross section is presented at positive and negative values of the longitudinal polarisation of the positron beams. The single-differential cross-sections ds/dQ^2, ds/dx and ds/dy are presented for Q^2 > 200 GeV^2. The reduced cross-section is presented in the kinematic range 200 < Q^2 < 60,000 GeV^2 and 0.006 < x < 0.562. The measurements agree well with the predictions of the Standard Model. The results are used to determine a lower limit on the mass of a hypothetical right-handed W boson.

Inelastic production of J/ψ mesons in photoproduction and deep inelastic scattering at HERA

A measurement is presented of inelastic photo- and electroproduction of J/psi mesons in ep scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and double differential cross sections are determined and the helicity distributions of the J/psi mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using a k_T factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.

Ionization of molecular hydrogen by 5 MeV/u bare fluorine ion and electron interference

Electrons emitted from H2 in collisions with 5 MeV/u F9 + ions were measured in the energy range from 1 to 300 eV and a wide range of emission angles between 20° and 160°. The measured energy and angular distributions of double-differential cross sections (DDCSs) of these electrons are compared with the molecular continuum distorted wave-eikonal initial state (CDW-EIS) calculation. The observed energy and angular distributions can be explained, in general, with the help of the two-centre effect which is included in the CDW-EIS model. In addition, the DDCS ratios of molecular-to-atomic hydrogen exhibit an oscillatory structure which is discussed in terms of Young-type electron interference. We have obtained the frequencies of such oscillations and studied their angular dependence. The single-differential cross sections (SDCSs) are deduced by integrating the DDCSs over solid angle and emission energy. We demonstrate that the SDCS ratio spectra also preserve the signature of interference to some extent. The asymmetry parameter, derived only from the molecular cross sections for forward and backward angles, shows an oscillatory behaviour as a function of electron velocity. This is understood in terms of the interference effect superimposed with the post-collisional two-centre effect.

First measurement of the muon neutrino charged current quasielastic double differential cross section

A high-statistics sample of charged-current muon neutrino scattering events collected with the MiniBooNE experiment is analyzed to extract the first measurement of the double differential cross section (d2σdTμdcosθμ) for charged-current quasielastic (CCQE) scattering on carbon. This result features minimal model dependence and provides the most complete information on this process to date. With the assumption of CCQE scattering, the absolute cross section as a function of neutrino energy (σ[Eν]) and the single differential cross section (dσdQ2) are extracted to facilitate comparison with previous measurements. These quantities may be used to characterize an effective axial-vector form factor of the nucleon and to improve the modeling of low-energy neutrino interactions on nuclear targets. The results are relevant for experiments searching for neutrino oscillations.9 MoreReceived 12 February 2010DOI:https://doi.org/10.1103/PhysRevD.81.092005©2010 American Physical Society

Measurement of direct photon pair production cross sections in [formula omitted] collisions at [formula omitted

We present a measurement of direct photon pair production cross sections using 4.2 fb−1 of data collected with the D0 detector at the Fermilab Tevatron pp¯ Collider. We measure single differential cross sections as a function of the diphoton mass, the transverse momentum of the diphoton system, the azimuthal angle between the photons, and the polar scattering angle of the photons. In addition, we measure double differential cross sections considering the last three kinematic variables in three diphoton mass bins. The results are compared with different perturbative QCD predictions and event generators.

Failure of the multiple peaking approximation for fast capture processes at milliradian scattering angles

The first Born approximation is examined for different fast capture processes for the $p+\mathrm{He}$ system at incident energies of about 1 MeV. Calculations have been performed for the singly differential cross section (SDCS) for scattering angles 0--0.5 mrad in the laboratory frame. In the case of transfer ionization, we observe that the two-step-2 mechanism has a dominant contribution to the SDCS for the kinematics considered in this work. The present investigation demonstrates that the multiple peaking approximation is a very crude method which fails to describe the SDCS even at scattering angles below 0.5 mrad. We have also presented a doubly differential cross section for the fixed emission energy of 600 eV and compared our results with other theoretical calculations and experiments.

Measurement of the [formula omitted] meson production cross section and [formula omitted] at high [formula omitted] in ep scattering at HERA

The inclusive production of D∗±(2010) mesons in deep-inelastic e±p scattering is measured in the kinematic region of photon virtuality 100<Q2<1000 GeV2 and inelasticity 0.02<y<0.7. Single and double differential cross sections for inclusive D∗ meson production are measured in the visible range defined by |η(D∗)|<1.5 and pT(D∗)>1.5 GeV. The data were collected by the H1 experiment during the period from 2004 to 2007 and correspond to an integrated luminosity of 351 pb−1. The charm contribution, F2cc¯, to the proton structure function F2 is determined. The measurements are compared with QCD predictions.

Time-dependent close-coupling calculations of the double photoionization of He@C60

The double photoionization of a He atom enclosed in a ${\mathrm{C}}_{60}$ molecule, He@C${}_{60}$ was investigated using the time-dependent close-coupling method with the ${\mathrm{C}}_{60}$ molecule represented by a spherical shell potential and the He atom treated nonperturbatively. Comparisons are made with the double photoionization of a bare He atom. The ratio of the total double photoionization cross section of He@C${}_{60}$ to that of a bare He atom is found to exhibit oscillations due to reflection of a slow electron. This is confirmed by calculations of the single energy differential cross section that peaks at unequal energy sharing when one of the ejected electrons has an energy comparable to the ${\mathrm{C}}_{60}$ well depth. Triple differential cross sections are found to be shifted in magnitude, but unchanged in shape from the bare He atom.

Single-differential and integral cross sections for electron-impact ionization for the damage of carbon clusters irradiated with x-ray free-electron lasers

Single-differential and integral cross sections for electron-impact ionization of the C atom and its ions were calculated with the binary-encounter-dipole model [Y.-K. Kim and M. E. Rudd, Phys. Rev. A 50, 3954 (1994)] to study the distribution of free-electron energies in carbon clusters after being irradiated with an x-ray free-electron laser (XFEL). The averaged energies of the secondary electrons for the C atom, and ${\mathrm{C}}^{1+}$, ${\mathrm{C}}^{2+}$, and ${\mathrm{C}}^{3+}$ ions were about $20$, $70$, $160$, and $200$ eV, respectively, when incident electron energy was about $20$ keV, while those energies were in the order of tens of electronvolts when the incident electron energy was about $250$ eV. The damage to carbon clusters irradiated with the XFEL was also investigated with time-dependent rate equations, considering photoionization, Compton scattering, Auger decay, and electron-impact ionization of the C atom and its ions. The results show that the electron-impact ionization becomes a more important process as the x-ray flux decreases, while the effect of Auger decay gradually appears as the x-ray flux increases. The energy dependence of the incident x ray was also investigated to evaluate the resolution of the diffraction pattern. These results indicate that we should make the XFEL pulse a few fs and about $16$ keV to suppress damage and obtain desired resolution of the diffraction pattern.

Tracing fingerprints of young type interferences in angular distributions of ejected electrons from molecular targets

Interference patterns in angular distributions of ionized electrons due to coherent emission from the proximities of the nuclei of molecular hydrogen are investigated in (e,2e) collisions. It is shown that double and single differential cross sections show signatures of this effect.

Double photoionization of helium including quadrupole radiation effects

Non-perturbative time-dependent close-coupling calculations are carried out for the double photoionization of helium including both dipole and quadrupole radiation effects. At a photon energy of 800 eV, accessible at current synchrotron light sources, the quadrupole interaction contributes around 6% to the total integral double photoionization cross section. The pure quadrupole single energy differential cross section shows a local maximum at equal energy sharing, as opposed to the minimum found in the pure dipole single energy differential cross section. The sum of the pure dipole and pure quadrupole single energy differentials is insensitive to non-dipole effects at 800 eV. However, the triple differential cross section at equal energy sharing of the two ejected electrons shows strong non-dipole effects due to the quadrupole interaction that may be experimentally observable.

Near-threshold electron impact ionization of Ne and Xe

Doubly differential cross-sections for the single electron impact ionization of Ne and Xe have been measured at several energies below the second ionization energy. The results indicate that the ionization of Ne is strongly influenced by the polarization of the ionized 22P3/2,1/2 core, where as this influence is significantly reduced for Xe. Single differential cross-sections are derived from the doubly differential cross-sections and for Xenon these show profiles similar to Helium ("smile"), whereas for Neon they show a dissimilar profile ("frown").

Rule of electron-impact ionization for the damage of C, N and O clusters irradiated by XFEL

Single differential and integral cross sections in electron-impact ionization of atoms and ions of C, N and O are calculated with the binary encounter dipole model (Kim Y-K. and Rudd M. E., 1994 Phys. Rev. A, 50 3954) to study electron-energy distribution in the C, N and O clusters irradiated by an X-ray free electron laser (XFEL). The damages to the C, N and O clusters irradiated by XFELs are also investigated with time-dependent rate equations, considering photo-ionization, Compton scattering, Auger decay and electron-impact ionization of the atoms and ions of C, N and O. We found that the electron-impact ionization is important process to estimate the damage of carbon clusters irradiated by XFEL.

Probing Young-type interference effect on angular distributions of e-DDCS using fast electrons as projectile

We have studied Young-type interference in the energy and angular distributions of double differential cross sections (DDCS) of electrons emitted in single-ionization of H2, induced by 8 keV electron impact. The first-order interference is derived from the energy distribution of DDCS and the resulting ratio-spectra (H2-to-2H) exhibit oscillating behaviour. The signature of first-order interference is also demonstrated in the DDCS-spectra as a function of emission angle. We have shown that the constructive interference prevails in soft- and binary-collision regions. The single differential cross sections obtained by integrating the DDCSs over energy and solid angle also preserve the information on interference.

Fast electron impact ionization of endohedral atoms

The differential generalized oscillator strengths (GOS's) for ionization of the s-subshells of the He and Ne atoms encapsulated inside a fullerene, C60 cage, along with the single differential cross sections for ionization by fast electrons, are calculated. It is shown that the modulation of the wave function of the ejected electron caused by the interference between the direct ejection and the waves scattered by the fullerene shell results in confinement resonances in the GOS's and the resulting impact ionization cross sections. When the energy transfer to the target is close to that of the giant plasmon resonance in C60, the interchannel interaction of the atomic ionization channels with the C60 ionization channels significantly influences the cross section for electron impact ionization of the confined atom.

Measurement of high-Q 2 neutral current deep inelastic e − p scattering cross sections with a longitudinally polarised electron beam at HERA

Measurements of the neutral current cross sections for deep inelastic scattering in e^- p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential cross-sections dsigma/dQ^2, dsigma/dx and dsigma/dy and the double-differential cross sections in Q^2 and x are measured in the kinematic region y < 0.9 and Q^2 > 185 GeV^2 for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements are based on an integrated luminosity of 169.9 pb^-1 taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318 GeV. The structure functions xF_3 and xF_3^{\gamma Z} are determined by combining the e^- p results presented in this paper with previously measured e^+ p neutral current data. The asymmetry parameter A^- is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The measurements agree well with the predictions of the Standard Model.

Near-threshold electron impact doubly differential cross sections for the ionization of neon and xenon

Normalized doubly differential cross sections (DDCSs) for the electron impact single ionization of Ne and Xe are presented. The Ne measurements are taken at incident energies of 23.5 eV, 25 eV, 30 eV and 40 eV while the Xe measurements are taken at 14 eV, 15 eV and 20 eV. Scattering angles in the experiment range from 15° to 120°. The measurements use a moveable target method for an accurate determination of the experimental background. Normalization of the differential data is initially made to available experimental cross sections for excitation of the ground np6 to the np5 (n + 1)s excited states of the noble gas and then, if necessary after integration, to available experimental total ionization cross sections. We show that our single differential cross sections, derived from integrating the DDCSs, show a convex profile (frown) for Ne whereas they are concave (smile) for Xe similar to what is observed for He and we suggest a tentative mechanism for this effect.

Fast-electron impact ionization of molecular hydrogen: energy and angular distribution of double and single differential cross sections and Young-type interference

We report the energy and angular distribution of absolute double differential cross sections (DDCSs) of ejected electrons in collisions of 8 keV projectile electrons with molecular hydrogen. The ejected electrons with energy between 1 eV and 400 eV and ejection angles between 30° and 150° are detected. The measured data are compared with the theoretical calculations based on two-effective centre (TEC) model. The first-order interference is derived from the energy distribution of DDCS and the resulting ratio spectra (H2 to 2H) exhibit oscillating behaviour. The signature of first-order interference is also demonstrated in the DDCS spectra as a function of the ejection angle. We have shown that the constructive interference prevails in soft- and binary-collision regions. The single differential cross sections (SDCS) are deduced by integrating the DDCS over the solid angle as well as ejection energy. We demonstrate that the SDCS and corresponding ratio spectra also preserve the signature of interference.

Time-dependent treatment of two-photon resonant single and double ionization of helium by ultrashort laser pulses

We report the results of accurate time-dependent calculations of two-photon ionization of helium by ultrashort pulses. Ionization amplitudes and generalized cross sections are extracted from the wave function using exterior complex scaling. For photon energies above the first ionization threshold, two-photon single ionization is enhanced by core excited resonances, in processes visible with pulses as short as 2 fs, when the photon frequency is equal to a transition energy in ${\text{He}}^{+}$. We explore the dependence of the total cross section in the vicinity of the threshold for sequential double ionization on pulse duration. A signature in the single differential cross section of two-photon sequential ionization with the ground state of the ion as the intermediate state is seen to be suppressed by sufficiently short pulses in favor of the nonsequential process, while the triple differential cross section shows that attosecond pulses can access different electron dynamics than those of longer duration. The peaks in the single differential cross section due to sequential ionization with the excited intermediate states of the ion are observed to occur at energies displaced by about 2 eV from the expected values by interference effects between continuum channels.

Theoretical investigations of electron emission after water vapour ionization by light ion impact

An ab initio quantum-mechanical treatment is applied for treating the ionization process of water vapour by light ions. In this theoretical model, the initial state of the system is composed of a projectile and a water target described by a plane wave and an accurate one-centre molecular wave function, respectively, whereas the final state is constituted by a slow ejected electron and a scattered projectile represented by a Coulomb wave and a plane wave, respectively. The obtained results are compared to available experimental data in terms of doubly differential cross sections ( DDCS), singly differential cross sections ( SDCS) and total cross sections ( TCS). A good agreement is generally found especially for the SDCS and the TCS.