Gamma Cross Section Research Articles

Measurement of Zgamma gamma production in pp collisions at sqrt{s}= 13 TeV with the ATLAS detector

Cross-sections for the production of a Z boson in association with two photons are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb^{-1} recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated Z(rightarrow ell ell )gamma gamma cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the Zgamma gamma system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

Differential cross-section measurements of the 11B(d, pγ1,2)12B reactions for analytical applications

In the present work, the 11B(d, pγ)12B differential cross-sections for gamma- rays originating from the first two excited states of the 12B at 953 and 1674 keV were measured in the energy range Ed,lab = 671–1990 keV with steps of 30 or 40 keV at a detection angle of 90°. The target was a thin natB2O3 film evaporated onto a self-supporting Ag layer. The thick target gamma-ray yields were measured in the same experimental setup using a pressed pellet made of natB powder. The obtained results were compared with the existing data in literature. The validity of measured cross-sections was checked through a thick target benchmarking experiment.

STRAUM-MATXST: A code system for multi-group neutron-gamma coupled transport calculation with unstructured tetrahedral meshes

In this paper, a new multi-group neutron-gamma transport calculation code system STRAUM-MATXST for complicated geometrical problems is introduced and its development status including numerical tests is presented. In this code system, the MATXST (MATXS-based Cross Section Processor for SN Transport) code generates multi-group neutron and gamma cross sections by processing MATXS format libraries generated using NJOY and the STRAUM (SN Transport for Radiation Analysis with Unstructured Meshes) code performs multi-group neutron-gamma coupled transport calculation using tetrahedral meshes. In particular, this work presents the recent implementation and its test results of the Krylov subspace methods (i.e., Bi-CGSTAB and GMRES(m)) with preconditioners using DSA (Diffusion Synthetic Acceleration) and TSA (Transport Synthetic Acceleration). In addition, the Krylov subspace methods for accelerating the energy-group coupling iteration through thermal up-scatterings are implemented with new multi-group block DSA and TSA preconditioners in STRAUM.

Study of the process e^+e^- rightarrow eta eta gamma in the energy range sqrt{s} = text{1.17--2.00 }\xa0GeV with the SND detector

The process e^+e^-rightarrow eta eta gamma is studied in the center-of-mass energy range 1.17–2.00 GeV using data with an integrated luminosity of 201 pb^{-1} collected by the SND detector at the VEPP-2000 e^+e^- collider. The e^+e^-rightarrow eta eta gamma cross section is measured for the first time. It is shown that the dominant mechanism of this reaction is the transition through the phi eta intermediate state. Our result on the e^+e^-rightarrow eta eta gamma cross section is consistent with the e^+e^-rightarrow phi eta measurement in the phi rightarrow K^+ K^- mode. The search for radiative processes contributing to the e^+e^-rightarrow eta eta gamma cross section is performed, and no significant signal is observed.

A phenomenological analysis of the nonperturbative QCD contributions for the photon wave function

The photon – induced interactions, present in ep, eA, pp, pA, AA and e^+ e^- collisions, are expressed within the color dipole approach in terms of the photon wave function, which describes the transition of the photon into a quark – antiquark color dipole. Such quantity is usually calculated using perturbation theory assuming that long distance corrections associated to strong interactions can be neglected. In this paper we investigate the impact of these nonperturbative QCD (npQCD) corrections to the description of the photon wave function for dipoles of large size in several observables measured at HERA, LEP and LHC. We assume a phenomenological ansatz for the treatment of these npQCD corrections and constrain the free parameters of our model using the experimental data for the photoproduction cross section. The predictions for the gamma gamma cross section, exclusive rho production in ep collisions and the rapidity distribution for the rho production in PbPb collisions are compared with the data. We demonstrate that the inclusion of the nonperturbative QCD corrections improves the description of processes that are dominated by large dipoles.

Constraining level densities through quantitative correlations with cross-section data

The adopted level densities (LD) for the nuclei produced through different reaction mechanisms significantly impact the calculation of cross sections for the many reaction channels. Common LD models make simplified assumptions regarding the overall behavior of the total LD and the intrinsic spin and parity distributions of the excited states. However, very few experimental constraints are taken into account: LD at neutron separation energy coming from average resonance spacings, whenever they have been previously measured, and the sometimes subjective extrapolation of discrete levels. These, however, constrain the LD only for very specific spins, parities and excitation energies. This work aims to establish additional experimental constraints on LD through quantitative correlations between cross sections and LD. This allows for the fitting and determination of detailed structures in LD. For this we use the microscopic Hartree-Fock-Bogoliubov (HFB) LD to associate variations predicted by the model with the structure observed in double-differential spectra at low outgoing neutron energy, which is dominated by the LD input. We also use \nuc{56}{Fe} ($n,p$) as an example cross sections are extremely sensitive to LD. For comparison purposes we also perform calculations with the GC model. With this approach we are able to perform fits of the LD based on actual experimental data, constraining the model and ensuring its consistency. This approach can be particularly useful in extrapolating the LD to nuclei for which high-excited discrete levels and/or resonance spacings are unknown. It also predicts inelastic gamma cross sections that can significantly differ from more standard phenomenological LD.

Constraining top-quark couplings combining top-quark and varvec{B} decay observables

We present a first, consistent combination of measurements from top-quark and B physics to constrain top-quark properties within the Standard Model Effective Field Theory (SMEFT). We demonstrate the feasibility and benefits of this approach and detail the ingredients required for a proper combination of observables from different energy scales. Specifically, we employ measurements of the tbar{t}gamma cross section together with measurements of the bar{B}rightarrow X_sgamma branching fraction to test the Standard Model and look for new physics contributions to the couplings of the top quark to the gauge bosons within SMEFT. We perform fits of three Wilson coefficients of dimension-six operators considering only the individual observables as well as their combination to demonstrate how the complementarity between top-quark and B physics observables allows to resolve ambiguities and significantly improves the constraints on the Wilson coefficients. No significant deviation from the Standard Model is found with present data.

First application of the Oslo method in inverse kinematics

The gamma -ray strength function (gamma SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton–gamma coincidence events from the mathrm {d}(^{86}mathrm {Kr}, mathrm {p}gamma )^{87}mathrm {Kr} reaction were measured at iThemba LABS and the gamma SF and NLD in ^{87}mathrm {Kr} was obtained. The low-energy region of the gamma SF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The gamma SF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain (mathrm {n},gamma ) cross sections of nuclei using the TALYS reaction code. These results are compared to ^{86}mathrm {Kr}(n,gamma ) data from direct measurements.

Ratio method for estimating uncertainty in calculated gamma cascades

The assessment of uncertainty on deduced quantities obtained through both measurement and modeling must include contributions from both components. There are several methods to estimate the uncertainty due to modeling, such as the parametric uncertainty and that stemming from model bias. However, in the case where experimental data exists for partial cross sections, such as discrete gammas emitted in the de-excitation of the product nucleus following the reaction, the discrepancy between the measured and modeled gamma cascades provides more information and allows for uncertainty estimation that can account for all types of model and data uncertainty. This work presents a method for estimating that uncertainty, using ratios of gammas to get a measure of the accuracy of different parts of the modeled gamma cascade. The gamma with the lowest intensity uncertainty is shown to be the best for determining the channel cross section with realistic uncertainties, indicating that it should be used rather than the most intense gamma or a sum of gammas. This method provides both a simple procedure for calculating realistic uncertainties and identifies the best gamma for use in converting a set of measured partial gamma cross sections to the deduced total channel cross section.

Coupled Neutron and Gamma Heating Calculation Based on VARIANT Transport Solutions

For accurate assessment of nuclear heating in fast reactors, a new coupled neutron and gamma heating calculation scheme has been developed based on VARIANT nodal transport solutions of neutron and gamma flux distributions. The MC2-3 code was extended to generate multigroup neutron and gamma cross sections and kinetic energy release in materials (KERMA) factors, and a utility program CURVE was developed to reconstruct detailed pin and duct wall powers from VARIANT output files. The improved heating calculation scheme has been verified against MCNP6 Monte Carlo reference solutions for the Advanced Burner Test Reactor (ABTR) and Experimental Breeder Reactor II (EBR-II) benchmark problems. Compared to the existing coupled heating calculation method based on DIF3D diffusion theory solutions, the new heating calculation scheme utilizes more accurate gamma cross sections and KERMA factors, accounts for the transport effects, and eliminates the approximations in the existing pin power reconstruction scheme. As a result, it produces more accurate assembly and pin power distributions. For both the ABTR and EBR-II problems, the maximum assembly power error was ~1% in fuel assemblies and ~2% in instrumented structure assemblies, and the maximum error in pin segment powers in an axial node of fuel assembly was ~4%. In the blankets of the EBR-II problem, the maximum error in pin segment powers was increased to ~8%, mainly due to the lower power level and the relatively large error in the nodal power of the VARIANT solution.

Calculation of photon pulse height distribution using deterministic and Monte Carlo methods

Abstract Radiation transport techniques which are used in radiation detection systems comprise one of two categories namely probabilistic and deterministic. However, probabilistic methods are typically used in pulse height distribution simulation by recreating the behavior of each individual particle, the deterministic approach, which approximates the macroscopic behavior of particles by solution of Boltzmann transport equation, is being developed because of its potential advantages in computational efficiency for complex radiation detection problems. In current work linear transport equation is solved using two methods including collided components of the scalar flux algorithm which is applied by iterating on the scattering source and ANISN deterministic computer code. This approach is presented in one dimension with anisotropic scattering orders up to P8 and angular quadrature orders up to S16. Also, multi-group gamma cross-section library required for this numerical transport simulation is generated in a discrete appropriate form. Finally, photon pulse height distributions are indirectly calculated by deterministic methods that approvingly compare with those from Monte Carlo based codes namely MCNPX and FLUKA.

Improved calculation of displacements per atom cross section in solids by gamma and electron irradiation

Several authors had estimated the displacements per atom cross sections under different approximations and models, including most of the main gamma- and electron-material interaction processes. These previous works used numerical approximation formulas which are applicable for limited energy ranges. We proposed the Monte Carlo assisted Classical Method (MCCM), which relates the established theories about atom displacements to the electron and positron secondary fluence distributions calculated from the Monte Carlo simulation. In this study the MCCM procedure is adapted in order to estimate the displacements per atom cross sections for gamma and electron irradiation. The results obtained through this procedure are compared with previous theoretical calculations. An improvement in about 10–90% for the gamma irradiation induced dpa cross section is observed in our results on regard to the previous evaluations for the studied incident energies. On the other hand, the dpa cross section values produced by irradiation with electrons are improved by our calculations in about 5–50% when compared with the theoretical approximations. When thin samples are irradiated with electrons, more precise results are obtained through the MCCM (in about 20–70%) with respect to the previous studies.

Gamma Heating Rate Evaluation for Material Irradiation Test in the Joyo Experimental Fast Reactor

The evaluation of the spatial distribution of gamma heating in fast reactors requires consideration of all the gamma intensity components. However, the delayed gamma ray yield data of all actinides are not included in evaluated nuclear data files such as ENDF or JEDNL. In this study, new neutron and gamma cross section constants considering the delayed gamma ray based on JENDL-3.2 and JENDL-4.0 were developed. Neutron and gamma ray coupling calculations for the Joyo experimental fast reactor core revealed that the gamma flux increased by approximately 40% when the delayed gamma intensities in both JENDL-3.2 and JENDL-4.0 were considered. The calculated gamma heating rates were verified by comparison with the measured data obtained by on-line irradiation rigs. It was confirmed that the calculated gamma heating rates agreed with the measurements to within 3–12%.

Monte Carlo calculations for dose rate at indoors exposed by distributed Cs-137 activities

The correlation of dose rates inside of the typical Japanese house to different distributions of Cs-137 activities outside are calculated by using the Monte Carlo code MVP with its attached gamma cross section library for aiming at the planning of decontamination strategies and setting the priorities in order to decrease the amounts of waste soil effectively, which will be disposed and stored for a long time with shield. The study is summarized that (1) the decontamination of the roof is not effective in decreasing the dose rate of indoors when surrounding field is contaminated, (2) the plowing of wide area will decrease the dose rate by one tenth even if the depth is only 5 cm, (3) the dose rate of the 2nd floor is higher than that of the 1st floor in some decontamination cases.

Soft-gluon resummation for high-pTinclusive-hadron production at COMPASS

We study the cross section for the photoproduction reaction gamma N -> h X in fixed-target scattering at COMPASS, where the hadron h is produced at large transverse momentum. We investigate the role played by higher-order QCD corrections to the cross section. In particular we address large logarithmic "threshold" corrections to the rapidity dependent partonic cross sections, which we resum to all orders at next-to-leading accuracy. In our comparison to the experimental data we find that the threshold contributions are large and improve the agreement between data and theoretical predictions significantly.

Gamma transport and diffusion calculation capability coupled with neutron transport simulation in KARMA 1.2

KAERI has developed a lattice transport calculation code KARMA (Kernel Analyzer by Ray-tracing Method for fuel Assembly) and its library generation system. Recently, the library generation system has been extended to include a gamma cross section generation capability and a gamma transport/diffusion calculation module has been implemented in KARMA 1.2. The method of characteristics for the neutron transport calculation to estimate eigenvalue has been utilized to predict gamma flux distribution and energy deposition. In addition, the coarse mesh finite difference method with diffusion approximation has also been utilized to estimate gamma flux distribution and energy depositions for each coarse mesh with homogenized pins as a computationally efficient alternative. This paper describes the procedure to generate neutron induced gamma production and gamma cross section data, and the methods to predict gamma flux distribution, gamma energy deposition and gamma smeared pin power distribution. The computational results for benchmark problems show that the gamma library and gamma simulation in KARMA are reasonable. And it is noted that gamma smeared power distributions predicted by coarse mesh diffusion calculation are very accurate compared to the results of transport calculation.

130 GeV dark matter and the Fermi gamma-ray line

Based on tentative evidence for a peak in the Fermi gamma-ray spectrum originating from near the center of the galaxy, it has been suggested that dark matter of mass ~130 GeV is annihilating directly into photons with a cross section ~24 times smaller than that needed for the thermal relic density. We propose a simple particle physics model in which the DM is a scalar X, with a coupling lambda_X X^2|S|^2 to a scalar multiplet S carrying electric charge, which allows for XX -> gamma gamma at one loop due to the virtual S. We predict a second monochromatic photon peak at 114 GeV due to XX-> gamma Z. The S is colored under a hidden sector SU(N) or QCD to help boost the XX -> gamma gamma cross section. The analogous coupling lambda_h h^2 |S|^2 to the Higgs boson can naturally increase the partial width for h -> gamma gamma by an amount comparable to its standard model value, as suggested by recent measurements from CMS. Due to the hidden sector SU(N) (or QCD), S binds to its antiparticle to form S-mesons, which will be pair-produced in colliders and then decay predominantly to XX, hh, or to glueballs of the SU(N) which subsequently decay to photons. The cross section for X on nucleons is close to the Xenon100 upper limit, suggesting that it should be discovered soon by direct detection.

High resolution measurement of neutron inelastic scattering cross-sections for 23Na

The neutron inelastic scattering cross-section of 23Na has been measured in response to the relevant request of the OECD–NEA High Priority Request List, which requires a target uncertainty of 4% in the energy range up to 1.35MeV for the development of sodium-cooled fast reactors. The measurement was performed at the GELINA facility with the Gamma Array for Inelastic Neutron Scattering (GAINS), featuring eight high purity germanium detectors. The setup is installed at a 200m flight path from the neutron source and provides high resolution measurements using the (n,n′γ)-technique. The sample was an 80mm diameter metallic sodium disk prepared at IRMM. Transitions up to the seventh excited state were observed and the differential gamma cross-sections at 110° and 150° were measured, showing mostly isotropic gamma emission. From these the gamma production, level and inelastic cross-sections were determined for neutron energies up to 3838.9keV. The results agree well with the existing data and the evaluated nuclear data libraries in the low energies, and provide new experimental points in the little studied region above 2MeV. Following a detailed review of the methodology used for the gamma efficiency calibrations and flux normalization of GAINS data, an estimated total uncertainty of 2.2% was achieved for the inelastic cross-section integrals over the energy ranges 0.498–1.35MeV and 1.35–2.23MeV, meeting the required targets.

Xenon diffusion studies with prompt gamma activation analysis

Developing a better understanding of xenon transport through porous systems is critical to predicting how this gas will enter the atmosphere after a below ground nuclear weapons test. Radioxenon monitoring is a vital part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System. This work details the development of prompt gamma activation analysis for measuring the diffusion rates of xenon and argon gases through a porous medium. The University of Texas at Austin maintains a prompt gamma activation analysis facility with a peak neutron flux of ~1.5 × 107 cm−2 s−1 and a beam diameter of 1 cm. Due to the relatively large prompt gamma cross sections of many stable xenon isotopes at thermal and sub-thermal neutron energies, prompt gamma activation analysis is a suitable technique for in situ non-destructive analysis of natural xenon. A test chamber has been designed and constructed to utilize prompt gamma activation analysis to measure xenon and argon diffusion through geological materials (e.g., sand, soil, etc.). Initial experiments have been conducted to determine the detection limits for stable gas measurements. The results from these experiments will be utilized to benchmark parts of a xenon transport model that is being used to determine diffusion coefficients for xenon and argon.

Sensitivity of isolated photon production at TeV hadron colliders to the gluon distribution in the proton

We compare the single inclusive spectra of isolated photons measured at high transverse energy in proton-antiproton collisions at sqrt(s)=1.96 TeV with next-to-leading order perturbative QCD predictions with various parametrizations of the parton distribution functions (PDFs). Within the experimental and theoretical uncertainties, the Tevatron data can be reproduced equally well by the recent CTEQ6.6, MSTW08 and NNPDF1.2 PDF sets. We present also the predictions for isolated gamma spectra in proton-proton collisions at sqrt(s)=14TeV for central (y=0) and forward (y=4) rapidities relevant for LHC experiments. Different proton PDFs result in maximum variations of order 30% in the expected E_T-differential isolated gamma cross sections. The inclusion of the isolated photon data in global PDF fits will place extra independent constraints on the gluon density.