Total Cross Section Measurements Research Articles

Photoproduction of $\eta$ η mesons from the neutron: Cross sections and double polarization observable E

Photoproduction of $\eta$ mesons from neutrons} \abstract{Results from measurements of the photoproduction of $\eta$ mesons from quasifree protons and neutrons are summarized. The experiments were performed with the CBELSA/TAPS detector at the electron accelerator ELSA in Bonn using the $\eta\to3\pi^{0}\to6\gamma$ decay. A liquid deuterium target was used for the measurement of total cross sections and angular distributions. The results confirm earlier measurements from Bonn and the MAMI facility in Mainz about the existence of a narrow structure in the excitation function of $\gamma n\rightarrow n\eta$. The current angular distributions show a forward-backward asymmetry, which was previously not seen, but was predicted by model calculations including an additional narrow $P_{11}$ state. Furthermore, data obtained with a longitudinally polarized, deuterated butanol target and a circularly polarized photon beam were analyzed to determine the double polarization observable $E$. Both data sets together were also used to extract the helicity dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$. The narrow structure in the excitation function of $\gamma n\rightarrow n\eta$ appears associated with the helicity-1/2 component of the reaction.

Adiabatic-nuclei calculations of positron scattering from molecular hydrogen

The single-center adiabatic-nuclei convergent close-coupling method is used to investigate positron collisions with molecular hydrogen (${\mathrm{H}}_{2}$) in the ground and first vibrationally excited states. Cross sections are presented over the energy range from 1 to 1000 eV for elastic scattering, vibrational excitation, total ionization, and the grand total cross section. The present adiabatic-nuclei positron-${\mathrm{H}}_{2}$ scattering length is calculated as $A=\ensuremath{-}2.70{a}_{0}$ for the ground state and $A=\ensuremath{-}3.16{a}_{0}$ for the first vibrationally excited state. The present elastic differential cross sections are also used to ``correct'' the low-energy grand total cross-section measurements of the Trento group [A. Zecca et al., Phys. Rev. A 80, 032702 (2009)] for the forward-angle-scattering effect. In general, the comparison with experiment is good. By performing convergence studies, we estimate that our ${R}_{m}=1.448{a}_{0}$ fixed-nuclei results are converged to within $\ifmmode\pm\else\textpm\fi{}5%$ for the major scattering integrated cross sections.

Total cross sections for ultracold neutrons scattered from gases

We have followed up on our previous measurements of upscattering of ultracold neutrons (UCNs) from a series of gases by making measurements of total cross sections on the following gases hydrogen, ethane, methane, isobutene, n-butane, ethylene, water vapor, propane, neopentane, isopropyl alcohol, and He3. The values of these cross sections are important for estimating the loss rate of trapped neutrons due to residual gas and are relevant to neutron lifetime measurements using UCNs. The effects of the UCN velocity and path-length distributions were accounted for in the analysis using a Monte Carlo transport code. Results are compared to our previous measurements and with the known absorption cross section for He3 scaled to our UCN energy. We find that the total cross sections for the hydrocarbon gases are reasonably described by a function linear in the number of hydrogen atoms in the molecule.Received 12 July 2016DOI:https://doi.org/10.1103/PhysRevC.95.015501©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectroweak interactions in nuclear physicsNeutron physicsNucleon induced nuclear reactionsTechniquesNeutron scatteringNuclear Physics

First results of total and partial cross-section measurements of the 107Ag(p,γ)108Cd reaction

The γ process is assumed to play an important role in the nucleosynthesis of the majority of the p nuclei. Since the network of the γ process includes so many different reactions and - mainly unstable - nuclei, cross-section values are predominantly calculated in the scope of the Hauser-Feshbach statistical model. The values heavily depend on the nuclear-physics input parameters. The results of total and partial cross-section measurements are used to improve the accuracy of the theoretical calculations. In order to extend the experimental database, the 107 Ag(p,γ )108 Cd reaction was studied via the in-beam method at the high-efficiency HPGe γ -ray spectrometer HORUS at the University of Cologne. Proton beams with energies between 3.5 MeV and 5.0 MeV were provided by the 10 MV FN-Tandem accelerator leading to the determination of four new total cross-section values. After slight adjustments of the nuclear level density and γ -ray strength function an excellent agreement between theoretical calculations and experimentally deduced values for both total and partial cross sections has been obtained.

V+jets from CMS

The production of vector bosons (V = W, Z, or γ) in association with jets is a stringent test of perturbative QCD and is a background process in searches for new physics. Total and differential cross-section measurements of vector bosons produced in association with jets (and heavy flavour quarks) are presented. The data have been recorded with the CMS detector at the LHC and are compared to next-to(-next-to)-leading-order calculations and event simulations that devise matrix element calculations interfaced with parton showers.

Probing the Higgs self coupling via single Higgs production at the LHC

We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production ($gg{\rm F}$, VBF, $WH$, $ZH$, $t\bar tH$) and decay ($\gamma \gamma$, $WW^{*}/ZZ^{*}\to 4f$, $b\bar b$, $\tau \tau$) modes at the LHC and then estimate the sensitivity to the trilinear coupling via a one-parameter fit to the single Higgs measurements at the LHC 8 TeV. We find that the bounds on the self coupling are already competitive with those from Higgs pair production and will be further improved in the current and next LHC runs.

Neutron Total Cross Sections and Resonance Parameters of Palladium

Measurements of neutron total cross sections of palladium in the energy region from 0.2 to 120 eV have been performed by using the time-of-flight method at the Pohang Neutron Facility. A group of high-purity natural palladium metallic plates with thicknesses of 0.5 and 1.0 mm is used for the neutron transmission measurement. Resonance parameters of 104Pd, 105Pd, 106Pd, 108Pd, and 110Pd in the neutron energy range below 120 eV were extracted from the transmission ratios by using the multilevel R-matrix SAMMY code. The present results are compared with the evaluated data from ENDF/B-VII.1 and previous experimental data. The statistical analysis for nearest-neighbor level spacings in 105Pd has been carried out to compare with the Wigner distribution.

A Modified activation method for reaction total cross section and yield measurements at low astrophysically relevant energies

The activation method is proposed for collection of the sufficient statistics during the investigation of the nuclear astrophysical reactions at low energies with the short-living residual nuclei formation. The main feature is a multiple cyclical irradiation of a target by an ion beam and measurement of the radioactivity decay curve. The method was tested by the yield measurement of the 12C(p,γ)13N reaction with detecting the annihilation γγ- coincidences from 13N(β+ν)13C decay at the two-arm scintillation spectrometer.

Determination of the $$^6$$ 6 He Nuclear Radius from the Total Reaction Cross Section of $$^6$$ 6 He + $$^9$$ 9 Be

A new method to obtain the nuclear radius from low energies total reaction cross section measurements is presented. Elastic scattering angular distributions of \(^6\)He on \(^9\)Be at two energies, namely, E\(_\mathrm {cm}= 9.72\) and 12.78 MeV, were analysed previously and the total reaction cross sections obtained are used to assess the \(^6\)He nuclear interaction radius. A comparison with the radius of the \(^6\)He obtained at higher energies is presented.

Validation of Cross Sections for Monte Carlo Simulation of the Photoelectric Effect

Several total and partial photoionization cross section calculations, based on both theoretical and empirical approaches, are quantitatively evaluated with statistical analyses using a large collection of experimental data retrieved from the literature to identify the state of the art for modeling the photoelectric effect in Monte Carlo particle transport. Some of the examined cross section models are available in general purpose Monte Carlo systems, while others have been implemented and subjected to validation tests for the first time to estimate whether they could improve the accuracy of particle transport codes. The validation process identifies Scofield's 1973 non-relativistic calculations, tabulated in the Evaluated Photon Data Library(EPDL), as the one best reproducing experimental measurements of total cross sections. Specialized total cross section models, some of which derive from more recent calculations, do not provide significant improvements. Scofield's non-relativistic calculations are not surpassed regarding the compatibility with experiment of K and L shell photoionization cross sections either, although in a few test cases Ebel's parameterization produces more accurate results close to absorption edges. Modifications to Biggs and Lighthill's parameterization implemented in Geant4 significantly reduce the accuracy of total cross sections at low energies with respect to its original formulation. The scarcity of suitable experimental data hinders a similar extensive analysis for the simulation of the photoelectron angular distribution, which is limited to a qualitative appraisal.

Fast neutron measurements at the nELBE time-of-flight facility

The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf has been rebuilt. A new enlarged experimental hall with a flight path of up to 10 m is available for neutron time-of-flight experiments in the fast energy range from about 50 keV to 10 MeV. nELBE is intended to deliver nuclear data of fast neutron nuclear interactions e.g. for the transmutation of nuclear waste and improvement of neutron physical simulations of innovative nuclear systems. The experimental programme consists of transmission measurements of neutron total cross sections, elastic and inelastic scattering cross section measurements, and neutron induced fission cross sections. The inelastic scattering to the first few excited states in 56 Fe was investigated by measuring the gamma production cross section with an HPGe detector. The neutron induced fission of 242 Pu was studied using fast ionisation chambers with large homogeneous actinide deposits.

Measurements of the jet and vector boson in association with jets production, extraction ofαsand PDF constraints at CMS

We present CMS results about measurements of cross sections for jet production, which allow basic tests of perturbative QCD predictions. Results include recent jet, dijet, and multijet differential cross sections, and hadronic event shape measurements in pp collisions at a centre-of-mass energy of 7 and 8 TeV, using data collected in the CMS experiment. Total and differential cross section measurements of vector bosons production in association with jets and heavy flavour quarks are also presented. The experimental results are compared to leading and next-to-leading order calculations, both at parton level and in event generators where matrix element calculations are interfaced with parton showers. Recent CMS results related to the extraction of the strong coupling constant and extraction of αS and PDF are discussed.

Measurement of the inclusive electron neutrino charged current cross section on carbon with the T2K near detector.

The T2K off-axis near detector ND280 is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies ∼1 GeV as a function of electron momentum, electron scattering angle, and four-momentum transfer of the interaction. The total flux-averaged ν(e) charged current cross section on carbon is measured to be ⟨σ⟩(ϕ)=1.11±0.10(stat)±0.18(syst)×10⁻³⁸ cm²/nucleon. The differential and total cross-section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is 1.23×10⁻³⁸ cm²/nucleon and the GENIE prediction is 1.08×10⁻³⁸ cm²/nucleon. The total ν(e) charged current cross-section result is also in agreement with data from the Gargamelle experiment.

Central-field model for the γ spectrum of positrons annihilating on rare-gas atoms

A central field model is used to study the two-photon positron annihilation spectrum for the rare gas atoms He, Ne, Ar, Kr, and Xe at energies close to thermal. Correlation effects are incorporated with a semiempirical polarization potential. The $\ensuremath{\gamma}$ spectrum is given, with values reported for individual subshells. The predicted full widths at half-maximum (FWHM) for all systems are typically $5%--20%$ larger than the experimental values reported using the positron trap at the University of California, San Diego, while, with the exception of neon, generally being $2%--10%$ smaller than the FWHMs measured at University College London. The detailed spectrum for xenon is reported and the likelihood of core annihilation's making a measurable contribution to the observed Doppler spectrum is discussed. The $\ensuremath{\gamma}$ spectra are found to be insensitive to variations in the scattering potential and whether the target is represented by a Hartree-Fock or a Dirac-Fock wave function. The model potential used in the solution of the positron-atom Schr\odinger equation provides a reasonable fit to recent total elastic cross-section measurements reported by the Australian National University and University of Trento groups.

Erratum to: Neutron total cross-section measurements with the 6Li-ZnS(Ag) scintillator (BC702) employing a neutron and noise separation technique

Erratum to: Neutron total cross-section measurements with the 6Li-ZnS(Ag) scintillator (BC702) employing a neutron and noise separation technique

EPECUR setup for the search for narrow baryon resonances in pion-proton scattering

EPECUR experimental setup is aimed at the search of narrow resonant states by precision measurement of differential and total reaction cross sections of pion-nucleon interaction with 1 MeV pion energy steps. In five years passed from the idea of the experiment till the start of the data taking in April of 2009, a new apparatus was build from scratch at the universal beam line 322 of ITEP proton synchrotron U-10. The setup is essentially a non-magnetic spectrometer with a liquid hydrogen target based on the large aperture drift chambers with hexagonal structure. The unique properties of the beam line allow individual pion momentum measurement with the accuracy better than 0.1%. The momentum tagging is done with 1 mm pitch proportional chambers located in the first focus of the beam line. The design of numerous subsystems of the setup is based on modern electronic components including microprocessors and FPGA. All the subsystems are tuned and tested both individually and as parts of the whole working setup. The distributed data acquisition system uses widely spread USB and Ethernet protocols, which allows to achieve high performance and take full advantage of the industrial solutions.

Isotopic Mo Neutron Total Cross Section Measurements in the Energy Range 1 to 620 keV

A series of new total cross section measurements for the stable molybdenum isotopes of 92,94,95,96,98,100Mo covering the energy range between 1 keV and 620 keV was performed at the Gaerttner LINAC Center at Rensselaer Polytechnic Institute. New high-accuracy resonance parameters were extracted from an analysis of the data using the multilevel R-matrix Bayesian code SAMMY. In the unresolved resonance region, average resonance parameters and fits to the total cross sections were obtained using the Bayesian Hauser-Feshbach statistical model code FITACS.

Neutron total cross-section measurements with the 6Li-ZnS(Ag) scintillator (BC702) employing a neutron and noise separation technique

The neutron total cross-section of natural Dy has been measured in the energy region from 0.01 to 100 eV by using the neutron time-of-flight method at Pohang Neutron Facility, which consists of an electron linear accelerator, a water-cooled Ta target with a water moderator, and a timeof- flight path with an 11-m length. A 6Li-ZnS(Ag) scintillator with a diameter of 12.5 cm and a thickness of 1.5 cm has been used as a neutron detector, and a metallic Dy plate has been used for the neutron transmission measurement. The background level has been determined by using notch filters of Co, Ta, and Cd sheets. In order to reduce the gamma rays from bremsstrahlung and from neutron capture, we have employed a neutron-gamma separation system based on their different pulse shapes.

Fluctuations Above the Resonance Range in Evaluated Data of 55Mn

The evaluation procedures for 55Mn are elaborated, focusing on the issues related to the fluctuations in the cross sections above the resolved resonance range. Smooth cross sections are defined in the unresolved resonance range, based on the resolution-broadened total cross section measurements, where relevant. Above this energy fluctuations in the measured total cross section are introduced by scaling all reaction cross sections, but preserving the resolution-broadened total cross section. Special procedures are designed to match the observed structure in the average cosine of scattering by adjusting the ratio of the shape-elastic and compound-elastic contributions to the elastic scattering cross sections. The evaluated data file is being assembled and subjected to rigorous testing, verification and validation.

Progress of Filtered Neutron Beams Development and Applications at the Horizontal Channels No.2 and No.4 of Dalat Nuclear Research Reactor

The neutron filter technique has been applied to create mono-energetic neutron beams with high intensity, at the horizontal channels No.2 and No.4 of the Dalat nuclear research reactor. The mono-energetic neutron beams that have been developed for researches and applications are thermal (0.025eV), 24keV, 54keV, 59keV, 133keV and 148keV. The relative intensities of main peak in filtered neutron energy spectra and the collimated neutron fluxes at the sample irradiation positions are 90 ¸ 96% and 2.8×105 ¸ 7.8×106 n/cm2.s, respectively. Monte Carlo simulations and transmission calculations were performed to each neutron energy beam for optimal design of geometrical structure and neutron filter materials. These filtered neutron beams have been applied efficiently for experimental researches on neutron total and capture cross sections measurements, and elemental analysis in various kinds of samples based on the prompt gamma neutron activation analysis method. This paper reviews the progress of filtered neutron beams development and its applications for past many years at the Dalat nuclear research reactor.