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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Measurement of the semileptonic $ \mathrm{t}\overline{\mathrm{t}} $ + γ production cross section in pp collisions at $ \sqrt{s}=8 $ TeV

A measurement of the cross section for top quark-antiquark ( $ \mathrm{t}\overline{\mathrm{t}} $ ) pairs produced in association with a photon in proton-proton collisions at $ \sqrt{s}=8 $ TeV is presented. The analysis uses data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.7 fb$^{1}$. The signal is defined as the production of a $ \mathrm{t}\overline{\mathrm{t}} $ pair in association with a photon having a transverse energy larger than 25 GeV and an absolute pseudorapidity smaller than 1.44. The measurement is performed in the fiducial phase space corresponding to the semileptonic decay chain of the $ \mathrm{t}\overline{\mathrm{t}} $ pair, and the cross section is measured relative to the inclusive $ \mathrm{t}\overline{\mathrm{t}} $ pair production cross section. The fiducial cross section for associated $ \mathrm{t}\overline{\mathrm{t}} $ pair and photon production is found to be 127 ±27 (stat+syst) fb per semileptonic final state. The measured value is in agreement with the theoretical prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Database work for the new cross section standards evaluation

An effort is now underway to produce a new evaluation of the neutron standards. It is important to maintain experimental programs to increase the quality and extend the database for the neutron cross section standards in order to improve evaluations of them that will be used to convert cross section measurements made relative to those standards. Measurements have been made for most of the standard cross sections since the last evaluation of the standards. The improved database includes the cross sections for the H(n,n), 6Li(n,t), 10B(n,αγ), 10B(n,α), C(n,n), Au(n,γ), 235U(n,f) and 238U(n,f) standard reactions and ratios among them. The database also includes the 238U(n,γ) and 239Pu(n,f) cross sections in addition to the standard cross sections. Those data were included since there are many ratio measurements of those cross sections with the standards and absolute data are available for them.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Collisional Cross-Sections with T-Wave Ion Mobility Spectrometry without Experimental Calibration

A method for relating traveling-wave ion mobility spectrometry (TWIMS) drift times with collisional cross-sections using computational simulations is presented. This method is developed using SIMION modeling of the TWIMS potential wave and equations that describe the velocity of ions in gases induced by electric fields. The accuracy of this method is assessed by comparing the collisional cross-sections of 70 different reference ions obtained using this method with those obtained from static drift tube ion mobility measurements. The cross-sections obtained here with low wave velocities are very similar to those obtained using static drift (average difference = 0.3%) for ions formed from both denaturing and buffered aqueous solutions. In contrast, the cross-sections obtained with high wave velocities are significantly greater, especially for ions formed from buffered aqueous solutions. These higher cross-sections at high wave velocities may result from high-order factors not accounted for in the model presented here or from the protein ions unfolding during TWIMS. Results from this study demonstrate that collisional cross-sections can be obtained from single TWIMS drift time measurements, but that low wave velocities and gentle instrument conditions should be used in order to minimize any uncertainties resulting from high-order effects not accounted for in the present model and from any protein unfolding that might occur. Thus, the method presented here eliminates the need to calibrate TWIMS drift times with collisional cross-sections measured using other ion mobility devices. .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Nuclear Forensics and Radiochemistry: Cross Sections

The neutron activation of components in a nuclear device can provide useful signatures of weapon design or sophistication. This lecture will cover some of the basics of neutron reaction cross sections. Nuclear reactor cross sections will also be presented to illustrate the complexity of convolving neutron energy spectra with nuclear excitation functions to calculate useful effective reactor cross sections. Deficiencies in the nuclear database will be discussed along with tools available at Los Alamos to provide new neutron cross section data.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Measurements of the pp → WZ inclusive and differential production cross sections and constraints on charged anomalous triple gauge couplings at $\sqrt{s} $ = 13 TeV

The WZ production cross section is measured in proton-proton collisions at a centre-of-mass energy $\sqrt{s} =$ 13 TeV using data collected with the CMS detector, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The inclusive cross section is measured to be $\sigma_{\text{tot}}$(pp $\to$ WZ$)$ = 48.09 $^{+1.00}_{-0.96}$ (stat) $^{+0.44}_{-0.37}$ (theo) $^{+2.39}_{-2.17}$ (syst) $\pm$ 1.39 (lumi) pb, resulting in a total uncertainty of $-$2.78/$+$2.98 pb. Fiducial cross section and ratios of charge-dependent cross section measurements are provided. Differential cross section measurements are also presented with respect to three variables: the Z boson transverse momentum $p_\mathrm{T}$, the leading jet $p_\mathrm{T}$, and the $m$(WZ) variable, defined as the invariant mass of the system composed of the three leptons and the missing transverse momentum. Differential measurements with respect to the W boson $p_\mathrm{T}$, separated by charge, are also shown. Results are consistent with standard model predictions, favouring next-to-next-to-leading-order predictions over those at next-to-leading order. Constraints on anomalous triple gauge couplings are derived via a binned maximum likelihood fit to the $m$(WZ) variable.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Measurements of production cross sections of 10Be and 26Al by 120GeV and 392MeV proton bombardment of 89Y, 159Tb, and natCu targets

The production cross sections of 10 Be and 26 Al were measured by accelerator mass spectrometry using 89 Y, 159 Tb, and nat Cu targets bombarded by protons with energies Ep of 120GeV and 392MeV. The production cross sections obtained for 10 Be and 26 Al were compared with those previously reported using Ep=50MeV–24GeV and various targets. It was found that the production cross sections of 10 Be monotonically increased with increasing target mass number when the proton energy was greater than a few GeV. On the other hand, it was also found that the production cross sections of 10 Be decreased as the target mass number increased from that of carbon to those near the mass numbers of nickel and zinc when the proton energy was below approximately 1GeV. They also increased as the target mass number increased from near those of nickel and zinc to that of bismuth, in the same proton energy range. Similar results were observed in the production cross sections of 26 Al, though the absolute values were quite different between 10 Be and 26 Al. The difference between these production cross sections may depend on the impact parameter (nuclear radius) and/or the target nucleus stiffness.

120 GeV proton↗
DOE OSTI2013

Photoionization and photoabsorption cross sections for the aluminum iso-nuclear sequence

K-shell photoionization and photoabsorption cross sections are presented for Li-like to Na-like Al. The calculations are performed using the Breit–Pauli R-matrix method where the effects of radiation and Auger dampings are included. We provide electronic data files for the raw cross sections as well as those convolved with a Gaussian of width ΔE/E=10{sup −4}. In addition to total cross sections for photoabsorption and photoionization, partial cross sections are available for photoionization.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Experimental cross sections for L-shell x-ray production and ionization by protons

Tables of compiled cross sections list data for production of individual line and total L x-rays as well as for ionization of L subshells and the total L shell. The present cumulative compilation covers some six decades of measurements on targets from {sub 10}Ne to {sub 95}Am bombarded by protons ranging from 10 keV to 1 GeV. It includes data published in the period 1954–1992 from tables published in this journal, cross sections that were not reported in those tables, and new data from works published after 1992. Existing empirical, semiempirical, and theoretical analyses based on, and relative to, the pre-1993 database are reviewed. The experimental details are summarized for pre-1993 articles that were not referenced in previous compilations and, continuing the practice of these compilations, for each new publication. Covering the period 1954–December 2012, the present tabulation collects (not counting 2519 new data for L{sub β1,3,4}, L{sub β2,15},L{sub γ1}, L{sub γ2,3}, and L{sub γ4,4{sup ′}} x ray production) circa 15 500 experimental cross sections and enlarges the database from the previously published tables by 94%. -- Highlights: •An updated database is presented, increasing by 94% the earlier pre-1993 database. •The update has 40% more data from the pre-1993 period, absent in prior compilations. •The growth and possible saturation in the number of data is illustrated. •Ionization cross sections are reconverted to x-ray production cross sections. •Elements and ion energies are identified where measurements are still necessary.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Effect of wave function on the proton induced L XRP cross sections for {sub 62}Sm and {sub 74}W

The L{sub k}(k= 1, α, β, γ) X-ray production cross sections have been calculated for {sub 74}W and {sub 62}Sm at different incident proton energies ranging 1-5 MeV using theoretical data sets of different physical parameters, namely, the Li(i=1-3) sub-shell X-ray emission rates based on the Dirac-Fork (DF) model, the fluorescence and Coster Kronig yields based on the Dirac- Hartree-Slater (DHS) model and two sets the proton ionization cross sections based on the DHS model and the ECPSSR in order to assess the influence of the wave function on the XRP cross sections. The calculated cross sections have been compared with the measured cross sections reported in the recent compilation to check the reliability of the calculated values.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2019

Extraction and Parametrization of Isobaric Trinucleon Elastic Cross Sections and Form Factors

By mining data from Jefferson Lab Hall A experiment E08-014 a new 3 He elastic cross section was extracted from a large quasielastic background. This measurement was taken with an initial beam energy of 3.356 GeV and an angle of 20.51°. The cross section was found to be 1.345 × 10 -6 µb/sr ± 0.086 × 10 -6 µb/sr at Q 2 = 34.19 fm -2 . This new data point falls approximately halfway between the first and second diffractive minima of the 3 He form factors. When combined with recent high Q 2 3 He elastic cross section measurements from Jefferson Lab and MIT-Bates this new data point improves our knowledge of the cross section and form factors at large momentum transfers. The new high Q 2 data motivate a reanalysis of the 3 He elastic cross section world data and provide an improved understanding of the magnetic form factor in particular. For this analysis the elastic cross section world data for 3 He, and its mirror nuclei 3 H, were collected. The world data spans a time frame from 1965 to 2016. The dataset contains electron energy ranges from tens of MeV to above 12 GeV for measurements performed at many different facilities. The world data were then fit using a sum of Gaussians parametrization which allowed for the extraction of both targets’ magnetic and electric form factors which were then used to calculate charge densities and radii. The new charge and magnetic form factors for 3 H and the charge form factor for 3 He are in good agreement with the 1994 fits from Amroun et al . However, the addition of the new high Q 2 data has caused the 3 He magnetic form factor’s first diffractive minimum to shift up in Q 2 by 1-3 fm -2 while also decreasing the magnitude of the magnetic form factor above Q2 ≈ 20 fm -2 . The first diffractive minima for 3H are located at Q2 ≈ 13 fm -2 and Q 2 ≈ 23-24 fm -2 for the charge and magnetic form factors respectively. The first diffractive minima for 3 He are located at Q 2 ≈ 11 fm -2 and Q 2 ≈ 17-20 fm -2 for the charge and magnetic form factors respectively. The charge radius for 3 He was found to be 1.90 fm ± 0.00144 fm in reasonable agreement with past measurements, and the charge radius for 3 H was found to be 2.02 fm ± 0.0133 fm which is much larger than past measurements. However, each of these charge radii has an additional uncertainty that must be applied to them due to allowing all parameters to float freely during the sum of Gaussians fitting procedure. This additional uncertainty should be small for 3 He, but it is likely quite significant for 3 H and would help bring this charge radius closer to agreement with past measurements that made different fitting choices. Unfortunately, this analysis was unable to quantify this additional uncertainty. The new form factor fits were compared to modern theoretical predictions from the 2016 paper of Marcucci et al . The ‘conventional’ theoretical approach applied in this paper modelled two and three-body nucleon interactions with relativistic corrections and was reasonably successful at predicting the charge form factors of 3 H and 3 He. χEFT predictions were also often successful. However, while the ‘conventional’ approach still performed best, theory failed to accurately predict the magnetic form factors of either 3 H or 3 He. The first diffractive minimum of the new 3 He magnetic form factor fits actually moved further away from theory. This disagreement between theory and experiment provides motivation for new asymmetry measurements using polarized 3 He and a polarized electron beam. When the beam is scanned in Q 2 on the target the sign of the asymmetry will flip at the form factor minima pinning down their true location.

Barcus, Scott↗
DOE OSTI2020

First Measurement of Differential Charged Current Quasielasticlike $\nu_{\mu}$ -Argon Scattering Cross Sections with the MicroBooNE Detector

We report on the first measurement of flux-integrated single differential cross sections for charged-current (CC) muon neutrino ($\nu_{\mu}$) scattering on argon with a muon and a proton in the final state, 40 Ar $(\nu_{\mu},μp)X$. The measurement was carried out using the Booster Neutrino Beam at Fermi National Accelerator Laboratory and the MicroBooNE liquid argon time projection chamber detector with an exposure of 4.59 × 10 19 protons on target. Events are selected to enhance the contribution of CC quasielastic (CCQE) interactions. The data are reported in terms of a total cross section as well as single differential cross sections in final state muon and proton kinematics. We measure the integrated per-nucleus CCQE-like cross section (i.e., for interactions leading to a muon, one proton, and no pions above detection threshold) of (4.93 ± 0.76 stat ± 1.29 sys )×10 -38 cm 2 , in good agreement with theoretical calculations. The single differential cross sections are also in overall good agreement with theoretical predictions, except at very forward muon scattering angles that correspond to low-momentum-transfer events.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1989

The abundance of N-14 at the cosmic-ray source - A study using new fragmentation cross sections

The abundance of N-14 at the Galactic cosmic ray source was examined using new fragmentation cross sections measured by the University of New Hampshire group for 12 different source nuclei (ranging from C-12 to Ni-58) which cover about 70 percent of all cosmic-ray nuclei arriving at earth. A new cross-section program was used to estimate unmeasured cross sections. These cross sections were then incorporated into a Galactic propagation program to calculate the interstellar production of B and N. Results indicate that atomic selection effects alone cannot explain adequately the observed depletion of N-14 relative to O-16 in the cosmic-ray source with respect to the solar corona, indicating that some part of this depletion must have a nuclear/nucleosynthetic origin.

Gupta, M.↗
DOE OSTI2024

Cross Section Evaluation for Exclusive Channels of K+Λ and K+Σ0 Electroproduction off Protons Using CLAS Detector Data

In this work, a method for evaluating the cross sections of electroproduction of K+Λ0 and K+Σ0 off protons in the region of invariant masses of final hadrons MK + MY <W < 2.65 GeV (MK and MY being the masses of the kaon and hyperon, respectively) and squares of four-momentum transfers of virtual photons, i.e., photon virtualities 0 < Q2 < 5 GeV2, is developed based on experimental data of these exclusive channels’ cross sections measured by the CLAS detector in Hall B at Jefferson Lab. A set of algorithms has been implemented to evaluate the differential cross sections of these channels, along with their statistical and systematic uncertainties. A program was developed for the evaluation of differential cross sections and structure functions using C++ and Python libraries. An interactive website was created for working with the program, enabling the analysis of one-dimensional and two-dimensional dependences of structure functions and differential cross sections. The evaluation of differential cross sections for the K+Λ and K+Σ0 electroproduction channels is necessary for extracting the structure function σLT from the data on the polarization asymmetry of electroproduction reactions of these final states with longitudinally polarized electrons. The obtained results are also important for the development of realistic Monte Carlo event generators in planning future experiments and for evaluating the efficiency of detecting final particles when extracting reaction cross sections from experimental data.

Golda, A. V.↗
DOE OSTI2019

Measurement of inclusive very forward jet cross sections in proton-lead collisions at $ \sqrt{s_{\mathrm{NN}}} $ = 5.02 TeV

Measurements of differential cross sections for inclusive very forward jet production in proton-lead collisions as a function of jet energy are presented. The data were collected with the CMS experiment at the LHC in the laboratory pseudorapidity range –6.6 < η < –5.2. Asymmetric beam energies of 4 TeV for protons and 1.58 TeV per nucleon for Pb nuclei were used, corresponding to a center-of-mass energy per nucleon pair of $ \sqrt{s_{\mathrm{NN}}} $ = 5.02 TeV. Collisions with either the proton (p+Pb) or the ion (Pb+p) traveling towards the negative η hemisphere are studied. The jet cross sections are unfolded to stable-particle level cross sections with p$_{T}$ ≳ 3 GeV, and compared to predictions from various Monte Carlo event generators. In addition, the cross section ratio of p+Pb and Pb+p data is presented. The results are discussed in terms of the saturation of gluon densities at low fractional parton momenta. None of the models under consideration describes all the data over the full jet-energy range and for all beam configurations. Discrepancies between the differential cross sections in data and model predictions of more than two orders of magnitude are observed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2021

High-resolution Laboratory Measurements of K-shell X-ray Line Polarization and Excitation Cross Sections in Helium-like S XV Ions

We report measurements of electron-impact excitation cross sections for the strong K-shell n = 2 -> 1 transitions in S XV, using the LLNL EBIT-I electron beam ion trap, two crystal spectrometers, and the EBIT Calorimeter Spectrometer. The cross sections are determined by direct normalization to the well-known cross sections of radiative electron capture, measured simultaneously. Using contemporaneous polarization measurements with the two crystal spectrometers, whose dispersion planes are oriented parallel and perpendicular to the electron beam direction, the polarization of the direct excitation line emission is determined, and in turn the isotropic total cross sections are extracted. We further experimentally investigate various line-formation mechanisms, finding that radiative cascades and collisional inner-shell ionization dominate the degree of linear polarization and total line emission cross sections of the forbidden line, z.

atomic data↗
DOE OSTI2021

High-resolution Laboratory Measurements of K-shell X-Ray Line Polarization and Excitation Cross Sections in Helium-like S XV Ions

We report measurements of electron-impact excitation cross sections for the strong K-shell n = 2 → 1 transitions in S xv, using the LLNL EBIT-I electron beam ion trap, two crystal spectrometers, and the EBIT Calorimeter Spectrometer. The cross sections are determined by direct normalization to the well-known cross sections of radiative electron capture, measured simultaneously. Using contemporaneous polarization measurements with the two crystal spectrometers, whose dispersion planes are oriented parallel and perpendicular to the electron beam direction, the polarization of the direct excitation line emission is determined, and in turn the isotropic total cross sections are extracted. We further experimentally investigate various line-formation mechanisms, finding that radiative cascades and collisional inner-shell ionization dominate the degree of linear polarization and total line-emission cross sections of the forbidden line, z.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Monoenergetic photon-induced fission cross-section ratio measurements for U 235 , U 238 , and Pu 239 from 9.0 to 17.0 MeV

Background: High-accuracy data are needed to advance microscopic descriptions of the nuclear fission process, to improve the predictive precision of phenomenological models, and for applications in nuclear energy and homeland security. Purpose: In this work, the main goal is to provide high-accuracy cross-section data for photofission of 235 U, 238 U, and 239 Pu in the energy range from the fission threshold to the high-energy tail of the giant dipole resonance. These new data should contribute significantly to the reduction of the systematic uncertainty in evaluated photofission cross-section databases. Method: Cross-section ratios for photofission of the “big three” actinide nuclei were measured using a quasimonoenergetic photon beam and dual-fission chambers. The measurements were performed at the HIγS facility using a photon beam produced from Compton backscattering of free-electron laser light. The dual-fission chamber enabled simultaneous counting of fission events from two targets. This method allows for cross-section ratio measurements with very small systematic errors. The largest source of systematic error in the determination of the cross-section ratios is the uncertainty in the ratio of the target thicknesses. Results: We report photon-induced fission cross-section ratios for σ[ 235 U(γ,f) / 238 U(γ,f)] , σ[235U(γ,f) / 239 Pu(γ,f)] , and σ[ 238 U(γ,f) / 239 Pu(γ,f)] at photon energies from 9.0–17.0 MeV. More than 20 data points were measured for each ratio, and the systematic uncertainties are less than 2%. Conclusion: The present photofission cross-section ratio data sets are compared to ratios computed from previous measurements, to the corresponding neutron-induced fission cross-section ratios, and to ratios computed from evaluated databases. Finally, the data obtained in this work for σ[ 235 U(γ,f) / 238 U(γ,f)] are consistent with the existing data, while for σ[ 235 U(γ,f) / 239 Pu(γ,f)] and σ[ 238 U(γ,f) / 239 Pu(γ,f)] the present data are systematically lower.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

Note: Absolute photoionization cross-section of the vinyl radical

This work measures the absolute photoionization cross-section of the vinyl radical (σvinyl(E)) between 8.1 and 11.0 eV. Two different methods were used to obtain absolute cross-section measurements: 193 nm photodissociation of methyl vinyl ketone (MVK) and 248 nm photodissociation of vinyl iodide (VI). The values of the photoionization cross-section for the vinyl radical using MVK, σvinyl(10.224 eV) = (6.1 ± 1.4) Mb and σvinyl(10.424 eV) = (8.3 ± 1.9) Mb, and using VI, σvinyl(10.013 eV) = (4.7 ± 1.1) Mb, σvinyl(10.513 eV) = (9.0 ± 2.1) Mb, and σvinyl(10.813 eV) = (12.1 ± 2.9) Mb, define a photoionization cross-section that is ~1.7 times smaller than a previous determination of this value.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗