Infrared safety in factorized hard scattering cross-sections

The rules of soft-collinear effective theory can be used naïvely to write hard scattering cross-sections as convolutions of separate hard, jet, and soft functions. One condition required to guarantee the validity of such a factorization is the infrared safety of these functions in perturbation theory. Using e⁺e⁻$e^{+}{e}^{-}$ angularity distributions as an example, we propose and illustrate an intuitive method to test this infrared safety at one loop. We look for regions of integration in the sum of Feynman diagrams contributing to the jet and soft functions where the integrals become infrared divergent. Our analysis is independent of an explicit infrared regulator, clarifies how to distinguish infrared and ultraviolet singularities in pure dimensional regularization, and demonstrates the necessity of taking zero-bins into account to obtain infrared-safe jet functions.     

Infrared laser emission in two-photon pumped sodium vapour

We report infrared laser emission in the region of 3 to 5 μm from sodium vapour optically pumped by a pulsed dye laser with wavelengths ranging from 585 to 610nm. Twophoton excitation processes are believed to be responsible for the primary excitation. Both molecular transitions (4 to 5 μm) between high lying states, and atomic transitions (5² S _1/2−4² P _3/2,1/2 at 3.41 μm) have been identified.     

Infrared characterization of silicon dioxide films obtained by chemical vapour deposition

Summary In this work we report new FTIR absorbance measurements due to Si−O stretching bond, Si−O−Si and O−Si−O bending bonds of silicon dioxide amorphous films. We compare the optical results obtained from films grown by APCVD, LPCVD, PACVD and thermal oxidation techniques. The effect of thermal annealing on optical obsorbance structures has been studied. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Optical reaction cross-sections for light projectiles

The optical reaction cross-sections forn, p,²H,³He,³He and⁴He for several global optical potentials available in the literature have been parametrized in terms of simple empirical expressions which are smooth functions of the target mass number and the projectile energy. The empirical forms are 5–10% accurate over the periodic table and energy-range upto 50 MeV. They can be conveniently used in calculations where the optical reaction cross-sections are required as input. The calculation of proton spectra in the (n, p) reaction at 14 MeV is discussed.     

Bidimensional planar micro-optics for optochemical absorbance sensing

A new approach for developing optochemical absorbance sensors is presented. The method is based on a planar micro-optic circuit in which an optochemically active membrane that responds to selective compounds is deposited in the device, yielding a part of the guiding planar structure. In this way the optical field is confined in the direction transverse to the substrate and controlled in the lateral direction by means of planar micro-optics components. High sensitivity of the device can be easily obtained because of the relatively long light paths through the membrane, and the response time is low because the analyte has to diffuse through a several-micrometer-thin membrane. Experimental results of measurements of the concentration of potassium are also presented to verify the possibilities of these devices as specific absorbance sensors.     

Neutral current cross-sections for neutrinos on protons

Defining the ratiosr _p =σ(vp →vx)/σ(vp →μ ⁻ x) and we obtain the bounds 0.28 ⩽r _p ⩽ 0.61 and using only the parton model and the data of CDHS group with iron target. We also give the complete set of parton-model relations which would allow the determination of all the neutral-current coupling constants from inclusive cross sections alone.     

Effective potential for water vapour

A suitable temperature dependence is introduced into the force parameters of the Lennard-Jones potential by taking the free-energy average of the Rowlinson potential. The resulting temperature-dependent parameters are used to calculate the effective potential, which is plotted for water vapour at a few different temperatures. The temperature-dependence of the second virial coefficient is shown for the cases of temperature-independent and temperature-dependent parameters of which the latter agrees very well with experimental results.     

Excitation-autoionization cross-sections and rate coefficients for Ge-like ions

Results of cross-section and rate coefficient calculations for electron impact direct and indirect ionization of ions belonging to the GeI isoelectronic sequence (ground 3d104s24p2) are presented. The cross-sections are given at near threshold energies for the five ions Kr4+, Mo10+, Xe22+, Pr27+ and Dy34+. The rate coefficients are computed for all the ions from Kr4+ to U60+ in the GeI sequence at seven electron temperatures (kTe = 0.1EI, 0.3EI, 0.5EI, 0.7EI, EI, 2EI and 10EI, where EI is the first ionization energy). The calculations include the contribution of direct ionization (DI) calculated with the Lotz formula approximation and the contributions of excitation-autoionization (EA) calculated in the framework of the distorted wave (DW) approximation for the 4s-nl, 3d-nl and 3p-nl resonant inner-shell excitations. The ionization enhancement due to the EA channels is shown as a function of Z along the GeI isoelectronic sequence.     

Effective potential for ammonia vapour

The modified free-energy averaged potential for water vapour is extended to NH₃ vapour. The resulting temperature-dependent parameters are used to compute the second virial coefficient of NH₃ vapour which agrees with experimental results particularly at higher temperatures.     

Mixing and quenching cross-sections for atomic collision processes

A general model for determining the mixing and quenching cross-sections for atomic collision processes is described taking into account a great number of levels.     

Total cross-sections of various homogeneous substances for ultracold neutrons

By transmission measurements at the time-of-flight spectrometer for ultracold neutrons at the FRM Munich, the total cross-sections of gold, aluminium and copper were determined as a function of neutron energy in the range 10^?7<E<5× 10^?4eV and the temperature range 33–303 °K. No significant deviations from the expected 1/v dependence of the cross-sections were found if the neutron velocityv is corrected for the index of refraction. From the measured total cross-sections at low temperature the following values for the thermal capture cross-sections could be calculated: $$Au:99.3 \pm 0.5b;Al:227 \pm 6mb;Cu:3.77 \pm 0.12b.$$ For aluminium in addition a value of 389±50 °K for the Debye temperature at 298 °K could be obtained from the temperature dependence of the total cross-sections. Additional measurements on glass, mica and air also showed proportionality of the total cross-sections to 1/v.     

Collision cross-sections for scattering of electrons from NO molecule

Electron-NO scattering is investigated in the energy range 2–1000eV by using a parameter-free spherical complex optical potential (SCOP) approach in the fixed nuclei approximation. The real part of the optical potential consists of three potentials namely, the static, the exchange and the polarization. For the imaginary part of the SCOP, we employ a semi-empirical model absorption potential. The molecular charge density function is calculated from a single-configuration molecular orbital based on Slater type orbitals. The various potential terms are then determined from these charge density functions. Calculations of the elastic (with and without absorption effects), total absorption, momentum transfer and differential cross-sections are obtained and compared with the available theoretical results and experimental measurements.     

Determination of charm production cross-sections for neutrinos and antineutrinos

It is shown that existing data for production rates of opposite-sign dileptons by neutrinos and antineutrinos are mutually consistent when acceptance corrections are calculated using a standard four-quark parton model, and a flat fragmentation function for charmed quarks. Together with a corrected cross-section, model calculations which adequately describe the data are presented.     

Antiresonance of Raman cross-sections for nonpolar phonons in CdS

The nonpolar optic phonons of E₂ symmetry in CdS are shown to exhibit a pronounced decrease in Raman cross-section at certain excitation energies. For the E₂ phonon branch at 43 cm⁻¹ the minimum cross-section occurs for laser excitation ∼0.18 eV below the band gap, and cross-section vs. excitation energy near this antiresonant minimum can be described by an equation of the form used by Ralston et al. for transverse polar phonon cross-sections. For the E₂ mode at 256 cm⁻¹ the antiresonance occurs at wavelengths longer than 6328 Å.     

Total electron ionization cross-sections for molecules of astrochemical interest

ABSTRACT

We describe a newly upgraded instrument for measuring absolute total electron ionization cross-sections over the energy range from 0 to 300?eV, and present cross-sections for nine previously unstudied molecules, as well as several small molecules for which comparison data is available. The measured cross-sections are compared with the predictions of the BEB model, and show reasonable agreement with the model, albeit peaking at higher electron energies than predicted by the model. We show that the maxima in the cross-sections follow an additivity model, such that the molecular cross-sections can be expressed as a sum over contributions from the constituent atoms. These contributions have been determined from a global fit to the data for all molecules studied, and allow maximum cross-sections to be predicted for molecules that have not been studied to date. We demonstrate the expected correlation between the maximum ionization cross-section and the molecular polarisability, and show that the atomic contributions to the cross-section show a similar dependence on the atomic polarisability. The observed correlation can be used as an alternative method for predicting unknown maximum cross-sections.