Predictions For Cross Sections Research Articles

Decoupling theoretical uncertainties from measurements of the Higgs boson

We develop a technique to present Higgs coupling measurements, which decouple the poorly defined theoretical uncertainties associated to inclusive and exclusive cross section predictions. The technique simplifies the combination of multiple measurements and can be used in a more general setting. We illustrate the approach with toy LHC Higgs coupling measurements and a collection of new physics models.

Test of statistical model cross section calculations forα-induced reactions onAg107at energies of astrophysical interest

Astrophysical reaction rates, which are mostly derived from theoretical cross sections, are necessary input to nuclear reaction network simulations for studying the origin of $p$ nuclei. Past experiments have found a considerable difference between theoretical and experimental cross sections in some cases, especially for ($\alpha$,$\gamma$) reactions at low energy. Therefore, it is important to experimentally test theoretical cross section predictions at low, astrophysically relevant energies. The aim is to measure reaction cross sections of $^{107}$Ag($\alpha$,$\gamma$)$^{111}$In and $^{107}$Ag($\alpha$,n)$^{110}$In at low energies in order to extend the experimental database for astrophysical reactions involving $\alpha$ particles towards lower mass numbers. Reaction rate predictions are very sensitive to the optical model parameters and this introduces a large uncertainty into theoretical rates involving $\alpha$ particles at low energy. We have also used Hauser-Feshbach statistical model calculations to study the origin of possible discrepancies between prediction and data. An activation technique has been used to measure the reaction cross sections at effective center of mass energies between 7.79 MeV and 12.50 MeV. Isomeric and ground state cross sections of the ($\alpha$,n) reaction were determined separately. The measured cross sections were found to be lower than theoretical predictions for the ($\alpha$,$\gamma$) reaction. Varying the calculated averaged widths in the Hauser-Feshbach model, it became evident that the data for the ($\alpha$,$\gamma$) and ($\alpha$,n) reactions can only be simultaneously reproduced when rescaling the ratio of $\gamma$- to neutron width and using an energy-dependent imaginary part in the optical $\alpha$+$^{107}$Ag potential.......

Automatic computations at next-to-leading order in QCD for top-quark flavor-changing neutral processes

Computations at next-to-leading order in the Standard Model offer new technical challenges in the presence of higher dimensional operators. We introduce a framework that, starting from the top-quark effective field theory at dimension six, allows one to make predictions for cross sections as well as distributions in a fully automatic way. As an application, we present the first complete results at next-to-leading order in QCD for flavor-changing neutral interactions including parton shower effects, for $tZ$, $th$, $t\ensuremath{\gamma}$ associated production at the LHC.

Computational Modeling of Hole Distortion in Extruded Microstructured Optical Fiber Glass Preforms

Extrusion of glass preforms that are used to draw microstructured optical fibers was simulated using computational mechanics. The study focused on a preform with a cross-section geometry that contains 36 holes arranged in three hexagonal rings. Symmetry allowed for the modeling of a 30° portion of the cross section, which included five holes within this reduced computational domain. The simulations took into account flow through an array of 13 feed holes, flow along five circular pins to create the holes, exit from the die, and the development of a constant profile for the cross section of the preform. The primary concern in the study was exploring the capacity of the model to reproduce the observed distortion of the extruded holes, i.e., the difference between the holes that develop and the negative of the pin arrangement, by taking into account the complexity of the flow. The key features that describe the model are viscous flow, uniform temperature, interface slip using the Navier friction model, and the assumption of a steady-state solution. Validation of the procedure was based on a comparison between the predicted cross section and an actual preform. The results show that distortion of the holes is rather sensitive to the level of friction, which provides insight into reducing the magnitude of distortion in future experimental work.

Impact of Reaction Cross Section on the Unified Description of Fusion Excitation Function

A systematics of over 300 complete and incomplete fusion cross section data points covering energies beyond the barrier for fusion is presented. Owing to a usual reduction of the fusion cross sections by the total reaction cross sections and an original scaling of energy, a fusion excitation function common to all the data points is established. A universal description of the fusion exci- tation function relying on basic nuclear concepts is proposed and its dependence on the reaction cross section used for the cross section normalization is discussed. The pioneering empirical model proposed by Bass in 1974 to describe the complete fusion cross sections is rather successful for the incomplete fusion too and provides cross section predictions in satisfactory agreement with the observed universality of the fusion excitation function. The sophisticated microscopic transport DYWAN model not only reproduces the data but also predicts that fusion reaction mechanism disappears due to weakened nuclear stopping power around the Fermi energy.

Spatial Asymmetry of Heavy Nuclei as Essential Feature for Predictions of Compound Nuclear cross Sections and Decay Rates

Cross sections for neutron capture in the range of unresolved resonances and average level distances near the neutron emission threshold are simultaneously predicted for more than 140 spin-0 target nuclei with A >50. In nearly all these nuclei a combined description of photon strength, level density and Maxwellian averaged radiative neutron capture is presented, which only needs very few fit parameters, which are global for the full range in A. To reach that it is essential that the requirements of spherical or axial symmetry are given up.

Fusion cross sections for reactions involving medium and heavy nucleus-nucleus systems

Existing data on near-barrier fusion excitation functions of medium and heavy nucleus-nucleus systems have been analyzed using a simple diffused barrier formula derived assuming the Gaussian shape of the barrier height distributions. Fusion cross section is obtained by folding the Gaussian barrier distribution with the classical expression for the fusion cross section for a fixed barrier. The energy dependence of the fusion cross section, thus obtained, provides good description to the existing data on near-barrier fusion and capture excitation functions for medium and heavy nucleus-nucleus systems. The fusion or capture cross section predictions are especially important for planning experiments for synthesizing new super-heavy elements.

Photoelectric disintegration ofO16

The photoelectric cross section of $^{16}\mathrm{O}(\ensuremath{\gamma},\ensuremath{\alpha})^{12}\mathrm{C}$ is estimated to be larger than the radiative capture cross section of $^{12}\mathrm{C}(\ensuremath{\alpha},\ensuremath{\gamma})^{16}\mathrm{O}$. The predicted cross section and the angular distribution of the $\ensuremath{\alpha}$ particle are illustrated for the future experiment. The cross section just above the $\ensuremath{\alpha}$-particle threshold is found to be dominated by the $E2$ excitation.

Squark and gluino production cross sections in [Formula: see text] collisions at [Formula: see text] and [Formula: see text] TeV.

We present state-of-the-art cross section predictions for the production of supersymmetric squarks and gluinos at the upcoming LHC run with a centre-of-mass energy of sqrt{s} = 13 and 14 TeV, and at potential future pp colliders operating at sqrt{s} = 33 and 100 TeV. The results are based on calculations which include the resummation of soft-gluon emission at next-to-leading logarithmic accuracy, matched to next-to-leading order supersymmetric QCD corrections. Furthermore, we provide an estimate of the theoretical uncertainty due to the variation of the renormalisation and factorisation scales and the parton distribution functions.

Soft gluon resummation for gluon-induced Higgs Strahlung

We study the effect of soft gluon emission on the total cross section predictions for the $gg\to HZ$ associated Higgs production process at the LHC. To this end, we perform resummation of threshold corrections at the NLL accuracy in the absolute threshold production limit and in the threshold limit for production of a $ZH$ system with a given invariant mass. Analytical results and numerical predictions for various possible LHC collision energies are presented. The perturbative stability of the results is verified by including universal NNLL effects. We find that resummation significantly reduces the scale uncertainty of the $gg\to HZ$ contribution, which is the dominant source of perturbative uncertainty to $ZH$ production. We use our results to evaluate updated numbers for the total inclusive cross section of associated $pp \to ZH$ production at the LHC. The reduced scale uncertainty of the $gg\to HZ$ component translates into a decrease of the overall scale error by about a factor of two.

Two-neutron transfer in Sn isotopes beyond theN=82shell closure

We have performed microscopic distorted-wave Born approximation calculations of differential cross sections for the two reactions $^{136}\mathrm{Sn}(p,t)^{134}\mathrm{Sn}$ and $^{134}\mathrm{Sn}(t,p)^{136}\mathrm{Sn}$, which are within reach of near-future experiments with radioactive ion beams. We have described the initial and final nuclear states in terms of the shell model, employing a realistic low-momentum two-body effective interaction derived from the CD-Bonn nucleon-nucleon potential that has already proved quite successful in describing the available low-energy spectrum of $^{134}\mathrm{Sn}$. We discuss the main features of the predicted cross sections for the population of the low-lying yrast states in the two nuclei considered.

Next-to-leading orderγγ+2−jetproduction at the LHC

We present next-to-leading order QCD predictions for cross sections and for a comprehensive set of distributions in diphoton + 2-jet production at the Large Hadron Collider. We consider the contributions from loop amplitudes for two photons and four gluons, but we neglect top quarks. We use BlackHat together with SHERPA to carry out the computation. We use a Frixione cone isolation for the photons. We study standard sets of cuts on the jets and the photons, and also sets of cuts appropriate for studying backgrounds to Higgs-boson production via vector-boson fusion.

Predictions for the spatial distribution of gluons in the initial nuclear state

We make predictions for the t-differential cross section of exclusive vector meson production (EVMP) in electron-ion collisions, with the aim of comparing DGLAP evolution to CGC models. In the current picture for the high-energy nucleus, nonlinear effects need to be understood in terms of low-$x$ gluon radiation and recombination as well as how this leads to saturation. EVMP grants experimental access to the edge region of the highly-boosted nuclear wavefunction, where the saturation scale for CGC calculations becomes inaccessible to pQCD. On the other hand, DGLAP evolution requires careful consideration of unitarity effects. The existing $J/{\psi}$ photoproduction data in ep collisions provides a baseline for these theoretical calculations. Under different small-$x$ frameworks we obtain a measurable distinction in both the shape and normalization of the differential cross section predictions. These considerations are relevant for heavy ion collisions because the initial state may be further constrained, thus aiding in quantitative study of the quark-gluon plasma.

Symmetry- and solvent-dependent photophysics of fluorenes containing donor and acceptor groups.

Three two-photon absorption (2PA) dyes (donor-π-donor (DPA2F), donor-π-acceptor (AF240), and acceptor-π-acceptor (BT2F); specifically, D is Ph2N-, A is 2-benzothiazoyl, and the π-linker is 9,9-diethylfluorene) are examined in a variety of aprotic solvents. Because the 2PA cross section is sensitive to the polarity of the local environment, this report examines the solvent-dependent linear photophysics of the dyes, which are important to understand before probing more complex solid-state systems. The symmetrical dyes show little solvent dependence; however, AF240 has significant solvatochromism observed in the fluorescence spectra and lifetimes and also the transient absorption spectra. A 114 nm bathochromic shift is observed in the fluorescence maximum when going from n-hexane to acetonitrile, whereas the lifetimes increase from 1.25 to 3.12 ns. The excited-state dipole moment for AF240 is found to be 20.1 D using the Lippert equation, with smaller values observed for the symmetrical dyes. Additionally, the femtosecond transient absorption (TA) spectra at time zero show little solvent dependence for DPA2F or BT2F, but AF240 shows a 52 nm hypsochromic shift from n-hexane to acetonitrile. Coupled with the solvatochromism in the fluorescence and large excited-state dipole moment, this is attributed to formation of an intramolecular charge-transfer (ICT) state in polar solvents. By 10 ps in AF240, the maximum TA in acetonitrile has shifted 30 nm, providing direct evidence of a solvent-stabilized ICT state, whose formation occurs in 0.85-2.71 ps, depending on solvent. However, AF240 in nonpolar solvents and the symmetrical dyes in all solvents show essentially no shifts due to a predominantly locally excited (LE) state. Preliminary temperature-dependent fluorescence using frozen glass media supports significant solvent reorganization around the AF240 excited state in polar solvents, and may also support a twisted intramolecular charge-transfer (TICT)-state contribution to the stabilization. Finally, time-dependent density functional theory calculations support ICT in AF240 in polar media and also allow prediction of the 2PA cross sections in the 0-0 band, which are much larger for AF240 than the symmetrical dyes.

SU‐E‐T‐323: The FLUKA Monte Carlo Code in Ion Beam Therapy

Purpose:Monte Carlo (MC) codes are increasingly used in the ion beam therapy community due to their detailed description of radiation transport and interaction with matter. The suitability of a MC code demands accurate and reliable physical models for the transport and the interaction of all components of the mixed radiation field. This contribution will address an overview of the recent developments in the FLUKA code oriented to its application in ion beam therapy.Methods:FLUKA is a general purpose MC code which allows the calculations of particle transport and interactions with matter, covering an extended range of applications. The user can manage the code through a graphic interface (FLAIR) developed using the Python programming language.Results:This contribution will present recent refinements in the description of the ionization processes and comparisons between FLUKA results and experimental data of ion beam therapy facilities. Moreover, several validations of the largely improved FLUKA nuclear models for imaging application to treatment monitoring will be shown. The complex calculation of prompt gamma ray emission compares favorably with experimental data and can be considered adequate for the intended applications. New features in the modeling of proton induced nuclear interactions also provide reliable cross section predictions for the production of radionuclides. Of great interest for the community are the developments introduced in FLAIR. The most recent efforts concern the capability of importing computed‐tomography images in order to build automatically patient geometries and the implementation of different types of existing positron‐emission‐tomography scanner devices for imaging applications.Conclusion:The FLUA code has been already chosen as reference MC code in many ion beam therapy centers, and is being continuously improved in order to match the needs of ion beam therapy applications.Parts of this work have been supported by the European FP7 project ENVISION (grant agreement no. 241851).

Influence of multiphonon excitations and transfer on the fusion of Ca+Zr

Fusion data for $^{48}$Ca+$^{90,96}$Zr are analyzed by coupled-channels calculations that are based on the M3Y+repulsion, double-folding potential. By applying a previously determined nuclear density of $^{48}$Ca, the neutron densities of the zirconium isotopes are adjusted to optimize the fit to the fusion data, whereas the proton densities are determined by electron scattering experiments. It is shown that the fusion data can be explained fairly well by including couplings to one- and two-phonon excitations of the reacting nuclei and to one- and two-nucleon transfer reactions but there is also some sensitivity to multiphonon excitations. The neutron skin thicknesses extracted for the two zirconium isotopes are consistent with anti-proton measurements. The densities of the zirconium isotopes are used together with the previously determined nuclear density of $^{40}$Ca to calculate the M3Y+repulsion potentials and predict the fusion cross sections of $^{40}$Ca+$^{90,96}$Zr. The predicted cross sections for $^{40}$Ca+$^{90}$Zr are in reasonable agreement with the data when the influence of multiphonon excitations and a modest transfer is considered. The prediction of the $^{40}$Ca+$^{96}$Zr fusion cross section, on the other hand, is poor and under-predicts the data by 30 to 40%. Although couplings to transfer channels with positive $Q$ values were expected to play an important role, they are not able to explain the data, primarily because the predicted Coulomb barrier is about 1.5 MeV too high. Possible reasons for this failure are discussed.

Effects of autoionizing states on two-photon double ionization of the H2 molecule

We report angle-resolved and angle-integrated cross sections for two-photon double-ionization of H by a strong laser pulse. The effect of doubly excited states on the predicted cross sections is addressed.

Improved Nuclear Inputs for Nuclear Model Codes Based on the Gogny Interaction

The need for cross sections far from the valley of stability, for applications such as nuclear astrophysics or future nuclear facilities, challenges the robustness as well as the predictive power of nuclear reaction models. Traditionally, cross section predictions rely on more or less phenomenological approaches, depending on parameters adjusted to generally scarce experimental data or deduced for systematic relations. While such predictions are expected to be reliable for nuclei not too far from the experimentally accessible regions, they are clearly questionable when dealing with exotic nuclei. To improve the predictive power of nuclear model codes, one should use more fundamental approaches, relying on sound physical bases, when determining the nuclear inputs (ingredients) required by the reaction model. Thanks to the high computer power available today, all these major ingredients have been microscopically or semi-microscopically determined, starting from the information provided by a Skyrme effective (and efficient) nucleon-nucleon interaction. These microscopic inputs have shown their ability to compete with the traditional classical methods as such, but also when they are used in actual nuclear cross sections calculations. We will discuss the current efforts made to improve the predictive power of such microscopic inputs using a more coherent nucleon-nucleon interaction, namely the finite-range Gogny force.

Complete and incomplete fusion of weakly bound nuclei

Existing quantum mechanics methods to study fusion reactions with weakly bound nuclei cannot evaluate separately the complete fusion and the incomplete fusion cross sections. We develop a semiclassical procedure that can calculate these cross sections, apply it to $^{6,7}\mathrm{Li}+^{209}\mathrm{Bi}$ collisions at energies just above the barrier, and show that its predictions for the different fusion cross sections are in good agreement with the data. We find that the contribution from the sequential fusion of the Li fragments to the complete fusion cross section is substantial in the case of $^{6}\mathrm{Li}$, reaching almost 40% of that from the direct process, which illustrates the importance of calculating correctly the different components of the fusion cross section.

Next-to-leading order QCD corrections to di-photon production in association with up to three jets at the Large Hadron Collider

We present the computation of next-to-leading order (NLO) QCD corrections to di-photon production in association with two or three hard jets in pp collisions at a center-of-mass energy of 8 TeV. The inclusion of NLO corrections is shown to substantially reduce the theoretical uncertainties estimated from scale variations on total cross section predictions. We study a range of differential distributions relevant for phenomenological studies of photon pair production in association with jets at the LHC. Using an efficient computational set-up we performed a detailed study of uncertainties due to parton distribution functions. The computation of the virtual corrections is performed using new features of the C++ library NJET.