Cross Section Momentum Research Articles

Critical positions and spin polarisation for electrons scattered by potassium atoms

ABSTRACT The critical points were calculated using the Dirac equation and real optical potential model, in addition to calculating differential, integrated elastic, transfer momentum and viscosity cross sections, and Sherman function for elastic scattering of Potassium atoms at the range 4 to 150 eV and in the angular range θ = 0–180°. We obtained two critical positions (38.1 eV, 141.1°) and (128.1 eV, 120.2°) at these positions we obtained the highest polarisation of spin, and the amplitude of the spin–flip is greater than the amplitude of the direct scattering. This study is considered the first calculation of the critical points in the differential cross sections for electron scattering by potassium atom.

Measurement and interpretation of differential cross sections for Higgs boson production at [formula omitted

Differential Higgs boson (H) production cross sections are sensitive probes for physics beyond the standard model. New physics may contribute in the gluon-gluon fusion loop, the dominant Higgs boson production mechanism at the LHC, and manifest itself through deviations from the distributions predicted by the standard model. Combined spectra for the H→γγ, H→ZZ, and H→bb‾ decay channels and the inclusive Higgs boson production cross section are presented, based on proton-proton collision data recorded with the CMS detector at s=13TeV corresponding to an integrated luminosity of 35.9fb−1. The transverse momentum spectrum is used to place limits on the Higgs boson couplings to the top, bottom, and charm quarks, as well as its direct coupling to the gluon field. No significant deviations from the standard model are observed in any differential distribution. The measured total cross section is 61.1±6.0(stat)±3.7(syst)pb, and the precision of the measurement of the differential cross section of the Higgs boson transverse momentum is improved by about 15% with respect to the H→γγ channel alone.

Global Political Risk and Currency Momentum

Using a measure of political risk, relative to the United States, that captures unexpected political conditions, we show that political risk is priced in the cross section of currency momentum and contains information beyond other risk factors. Our results are robust after controlling for transaction costs, reversals, and alternative limits to arbitrage. The global political environment affects the profitability of the momentum strategy in the foreign exchange market; investors following such strategies are compensated for the exposure to the global political risk of those currencies they hold, that is, the past winners, and exploit the lower returns of loser portfolios. The risk compensation is mainly justified by the different exposures of foreign currencies in the momentum portfolio to U.S. political shocks, which is the main component of global political risk.

Keep Up the Momentum

The momentum risk premium is one of the most important alternative risk premia alongside the carry risk premium. However, it appears that it is not always well understood. For example, is it an alpha or a beta exposure? Is it a skewness risk premium or a market anomaly? Does it pursue a performance objective or a hedging objective? What are the differences between time-series and cross-section momentum? What are the main drivers of momentum returns? What does it mean when we say that it is a convex and not a concave strategy? Why is the momentum risk premium a diversifying engine, and not an absolute return strategy? The goal of this paper is to provide specific and relevant answers to all these questions. The answers can already be found in the technical paper Understanding the Momentum Risk Premium published recently by Jusselin et al. (2017). However, the underlying mathematics can be daunting to readers. Therefore, this discussion paper presents the key messages and the associated financial insights behind these results. Among the main findings, one result is of the most importance. To trend is to diversify in bad times. In good times, trend-following strategies offer no significant diversification power. Indeed, they are beta strategies. This is not a problem, since investors do not need to be diversified at all times. In particular, they do not need diversification in good times, because they do not want that the positive returns generated by some assets to be cancelled out by negative returns on other assets. This is why diversification may destroy portfolio performance in good times. Investors only need diversification in bad economic times and stressed markets. This diversification asymmetry is essential when investing in beta strategies like alternative risk premia. On the contrary, this diversification asymmetry is irrelevant when investing in absolute return strategies. However, we know that generating performance with alpha strategies is much more difficult than generating performance with beta strategies. Therefore, beta is beautiful, but convex beta is precious and scarce. Among risk premia, momentum is one of the few strategies to offer this diversification asymmetry. This is why investing in momentum is a decision of portfolio construction, and not a search for alpha.

Particle Simulations of the Effects of Atomic Oxygen on Ion Thruster Plumes

Ion thruster plumes interacting with ambient atomic oxygen are simulated using direct simulation Monte Carlo/particle-in-cell code with automatic mesh refinement/octree grids. Because of the disparity among the species concentrations and velocities, particle weighting factors with multiple species weighting time steps have been used. To calculate the elastic cross section for collisions, the variable hard sphere collision cross section was compared with the higher-fidelity Lennard–Jones model and found to agree well at the relevant collision energies. Because momentum and charge exchange cross sections for and O are not available in the literature, analytic approaches were used to infer these values. The simulations provide a number of interesting results about the role of and collisions. The effect of incoming freestream atomic oxygen direction on the ion thruster plume at 185 and 300 km altitudes was studied by changing the plume angle with respect to the freestream atomic oxygen, corresponding to satellite orientation change in orbit. It was observed that the freestream atomic oxygen affects the backflux of Xe at the lower altitude. This effect lessens as the altitude increases and is not observable at 300 km, and it was observed that Xe fluxes scale in a linear fashion with the density of O. The spatial distribution of the xenon ion fluxes was not influenced by collisions with freestream atomic oxygen.

Energy dependence of forward-rapidity mathrm {J}/psi and psi mathrm {(2S)} production in pp collisions at the LHC

We present results on transverse momentum (p_{mathrm {textsc {t}}}) and rapidity (y) differential production cross sections, mean transverse momentum and mean transverse momentum square of inclusive mathrm {J}/psi and psi mathrm {(2S)} at forward rapidity (2.5<y<4) as well as psi mathrm {(2S)}-to-mathrm {J}/psi cross section ratios. These quantities are measured in pp collisions at center of mass energies sqrt{s},=5.02 and 13 TeV with the ALICE detector. Both charmonium states are reconstructed in the dimuon decay channel, using the muon spectrometer. A comprehensive comparison to inclusive charmonium cross sections measured at sqrt{s},=2.76, 7 and 8 TeV is performed. A comparison to non-relativistic quantum chromodynamics and fixed-order next-to-leading logarithm calculations, which describe prompt and non-prompt charmonium production respectively, is also presented. A good description of the data is obtained over the full p_{mathrm {textsc {t}}} range, provided that both contributions are summed. In particular, it is found that for p_{mathrm {textsc {t}}}>15 GeV/c the non-prompt contribution reaches up to 50% of the total charmonium yield.

Effect of electromagnetic dipole dark matter on energy transport in the solar interior

In recent years, a revised set of solar abundances has led to a discrepancy in the sound-speed profile between helioseismology and theoretical solar models. Conventional solutions require additional mechanisms for energy transport within the Sun. Vincent et al. have recently suggested that dark matter with a momentum or velocity dependent cross section could provide a solution. In this work, we consider three models of dark matter with such cross sections and their effect on the stellar structure. In particular, the three models incorporate dark matter particles interacting through an electromagnetic dipole moment: an electric dipole, a magnetic dipole or an anapole. Each model is implemented in the DarkStec stellar evolution program, which incorporates the effects of dark matter capture and heat transport within the solar interior. We show that dark matter with an anapole moment of ∼ 1 GeV−2 or magnetic dipole moment of ∼ 10−3μp can improve the sound-speed profile, small frequency separations and convective zone radius with respect to the Standard Solar Model. However, the required dipole moments are strongly excluded by direct detection experiments.

Global Political Risks in the Currency Market

Using a measure of global political risk, relative to the U.S., that captures unexpected political conditions, we show that political risk is priced in the cross section of currency momentum and contains information beyond other risk factors. Our results are robust after controlling for transaction costs, reversals and alternative limits to arbitrage. The global political environment affects the profitability of the momentum strategy in the foreign exchange market; investors following such strategies are compensated for the exposure to the global political risk of those currencies they hold, i.e., the past winners, and exploit the lower returns of loser portfolios.

Measurement of the cross section of high transverse momentum [formula omitted] production in proton–proton collisions at [formula omitted] with the ATLAS detector

This Letter reports the observation of a high transverse momentum Z→bb¯ signal in proton–proton collisions at s=8 TeV and the measurement of its production cross section. The data analysed were collected in 2012 with the ATLAS detector at the LHC and correspond to an integrated luminosity of 19.5 fb−1. The Z→bb¯ decay is reconstructed from a pair of b-tagged jets, clustered with the anti-kt jet algorithm with R=0.4, that have low angular separation and form a dijet with pT>200 GeV. The signal yield is extracted from a fit to the dijet invariant mass distribution, with the dominant, multi-jet background mass shape estimated by employing a fully data-driven technique that reduces the dependence of the analysis on simulation. The fiducial cross section is determined to beσZ→bb¯fid=2.02±0.20 (stat.) ±0.25 (syst.)±0.06 (lumi.) pb=2.02±0.33 pb, in good agreement with next-to-leading-order theoretical predictions.

Differentiation of alkane isomers through binding energy spectra and total momentum cross sections

The C1s binding energy spectra and total orbital momentum cross sections of small saturated alkanes (up to six carbons) and their isomers are investigated and used to differentiate their structural differences. The present study discovers that the impact of isomerization of alkanes on the carbon core shell is more significant than the elongation of the linear carbon chain. C1s binding energies are capable of serving as excellent indicators for isomers, whereas information on valence space such as valence binding energy spectra and valence momentum distributions is more sensitive to the length of the alkane chains. It further reveals that the terminal carbons exhibit smallest IPs for the alkanes but with a similar chemical environment as all their IPs are in the vicinity of 289.50 eV (±0.45 eV). The largest C1s chemical shift for the isomers is 0.88 eV (neopentane) which is nearly three times larger than the linear alkanes which is 0.30 eV. The inner valence bonding energy spectra clearly show a dependence on the number of carbons with a decreasing HOMO–LOMO energy gap of 9.91 eV for methane but 7.63 eV for hexane. The total momentum distributions are also proportional to the number of electrons but the isomers present small differences in the low momentum region which correspond to the long range in coordinate space.

Heat flux effect in laminar flow of a water/alumina nanofluid

The paper aims at the assessment, through a numerical procedure, of the heat flux effect over the heat transfer coefficient for the internal undeveloped laminar flow of a water/alumina nanofluid. The adopted model assumes the nanofluid as a mixture of a base fluid and nanoparticles, with the relative motion originating in both Brownian and thermophoretic diffusion. The paper reports thermal convective results from the flow of the nanofluid in a 1010mm length and 4.5mm diameter pipe under different heating/cooling rates. Velocity and concentration fields have also been obtained along the length of the pipe. It has been found that the heat flux affects the nanoparticles concentration in the wall region as a result of thermophoretic diffusion driving force which is counterbalanced by Brownian diffusion as soon as the concentration gradient is established. Due to the effect of variable nanoparticles concentration and temperature in the wall region, cross section momentum and heat transfer are affected. Driven by thermophoretic diffusion, the wall region is depleted of nanoparticles under heating conditions, causing a convective heat transfer increment whereas the thermal conductivity diminishes. An opposite trend has been observed under cooling. According to the obtained results, enhancements of the nanofluid Nusselt number with respect to that of the base fluid (water) occur in the range of low Graetz numbers whereas generalized decrements are observed in the higher range.

Transverse momentum cross section ofe+e−pairs in theZ-boson region frompp¯collisions ats=1.96 TeV

The transverse momentum cross section of $e^+e^-$ pairs in the $Z$-boson mass region of 66-116 GeV/$c^2$ is precisely measured using Run II data corresponding to 2.1 fb$^{-1}$ of integrated luminosity recorded by the Collider Detector at Fermilab. The cross section is compared with quantum chromodynamic calculations. One is a fixed-order perturbative calculation at ${\cal O}(\alpha_s^2)$, and the other combines perturbative predictions at high transverse momentum with the gluon resummation formalism at low transverse momentum. Comparisons of the measurement with calculations show reasonable agreement. The measurement is of sufficient precision to allow refinements in the understanding of the transverse momentum distribution.

Ultra-low-energy electron scattering cross section measurements of Ar, Kr and Xe employing the threshold photoelectron source

A new experimental technique for the measurements of the total cross section for electron scattering from atoms and molecules at very low energy is described. Momentum transfer cross sections for scattering from Ar, Kr and Xe at very low energies were carefully derived using the modified effective range theory from the recently measured total cross sections, which were obtained with a new experimental technique utilizing the threshold photoelectron source. A significant discrepancy between the momentum cross sections derived from the present analysis and those determined in the previous electron swarm studies was found at energies below 100 meV. The findings emphasize the need of further high precision experiments in the very low energy region as well as re-analysis of the previous swarm data.

Heavy flavour decay muon production at forward rapidity in proton–proton collisions at [formula omitted

The production of muons from heavy flavour decays is measured at forward rapidity in proton–proton collisions at s=7 TeV collected with the ALICE experiment at the LHC. The analysis is carried out on a data sample corresponding to an integrated luminosity Lint=16.5 nb−1. The transverse momentum and rapidity differential production cross sections of muons from heavy flavour decays are measured in the rapidity range 2.5<y<4, over the transverse momentum range 2<pt<12 GeV/c. The results are compared to predictions based on perturbative QCD calculations.

Calculation of electronic transport coefficients of Ag and Au plasma

The thermoelectric transport coefficients of silver and gold plasma have been calculated within the relaxation-time approximation. We considered temperatures of 10-100 kK and densities of ρ </~ 1 g/cm(3). The plasma composition was calculated using a corresponding system of coupled mass action laws, including the atom ionization up to +4. For momentum cross sections of electron-atom scattering we used the most accurate expressions available. The results of our modeling have been compared with other researchers' data whenever possible.

Properties of jets measured from tracks in proton-proton collisions at center-of-mass energys=7 TeVwith the ATLAS detector

Jets are identified and their properties studied in center-of-mass energy sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-kt algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.

Integral and Momentum Cross Sections for Electron Elastic and Vibrational Excitation Scattering with Nitrogen in the Energy Range 5–30 eV

Integral and momentum transfer cross sections are calculated in the energy range from 5 to 30 eV and compared with other calculated and measured data. The overall agreement between our present results and various theoretical and experimental results are obtained. The present results are obtained by solving integrodifferential body-frame vibrational close-coupling equations. Distributed spherical Gaussian correlation-polarization model potentials with high-order terms and exact exchange effects in a single-configuration Slater determinant are used. The analytic Born completion method is also used to calculate high-order scattering matrix elements.

State-selective charge exchange from Na(3s) and Na*(3p) by highly charged ions

State-selective charge exchange cross sections and momentum spectra are calculated for collisions of Xe18+ and Xe54+ ions with Na(3s) and Na*(3p) over the energy range of 0.1–10.0 keV/amu. The classical trajectory Monte Carlo method is used which includes all two-body interactions. The n-level cross sections are found to be rather insensitive to collision energy below 1 keV/amu. In contrast, the transverse momentum cross sections for specific n-levels change rapidly with energy. However, this latter variation in energy is found to be in general agreement with simple scaling rules. Experimental state-selective data are available for Xe18+ over a limited energy range; they are found to be in reasonable accord with the calculations.

Differential cross sections for electron elastic scattering and vibrational v = 1 excitation in nitrogen in the energy range from 5 to 20 eV measured over an angular range of 10°–180°

Absolute differential cross sections for elastic electron scattering and vibrational, v = 0 → 1, excitation in nitrogen have been measured in the scattering angle range from 10° to 180° and at incident electron energies between 5 eV and 20 eV. The magnetic angle-changing technique has been applied to access the range of scattering angles between 90° and 180°. Integral and momentum cross sections have also been derived by integration of the measured differential cross sections. A comparison with recent theoretical calculations of elastic and vibrational cross sections is presented.

Theory of nano optical manipulation by designed light fields under excitonic resonance conditions

AbstractWe theoretically study the resonant radiation force on a nanoparticle confining an exciton under the irradiation of various light sources that consist of Laguerre‐Gaussian beams (LGB) with doughnut‐shaped intensity distribution on a beam cross‐section and optical orbital angular momentum (OAM) around light axis. As a result, we have clarified possibilities of novel types of nano optical manipulation as follows: (A) Size‐selective control of rotational motion of nano‐objects can be realized by changing light frequency near the exciton resonance in multiple optical potential wells in a standing wave field composed of counter‐propagating LGBs with the same OAM. (B) Spiral‐shaped optical traps can be formed by the combination of LGBs with different OAMs. Obtained results will drastically expand the degrees of freedom of resonant nano optical manipulation by incorporating the control technique of the rotational motion in addition to those of the translational and the relative motions. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)