Total Cross Section Measurements Research Articles

Nuclear and Coulomb interactions in coherent fragmentation of relativistic nuclei in a photoemulsion

The role of the nuclear and Coulomb interactions in coherent fragmentation of relativistic nuclei is discussed with the cluster-model analysis of the experimental data on the fragmentation of 7Li (P = 3A GeV/c) via the 3H + 4He channel in photoemulsion used as an example. The calculated electromagnetic contribution of ∼10% to the cross section is not in conflict with the photoemulsion data and the upper estimate of ∼40% derived from the earlier measurements of total cross sections for fragmentation of light nuclei using the counter technique. The observed irregularities in the differential cross section for 7Li fragmentation with a separated Coulomb peak at a very small momentum transfer Q are ascribed to the overlap of nuclear diffraction patterns arising from light (C, N, O) and heavy (Ag, Br) photoemulsion nuclei. The predicted diffraction cross sections in the inelastic channel drastically differ from the usual shape of nuclear diffraction in an elastic channel. For pure targets, they have a shape of oscillations with a few peaks of comparable intensity and show strong dependence on the form of the surface nuclear density and radii of the intranuclear cluster and target nucleus. The probability for two-body clustering in 7Li is estimated at about 0.7.

Analysis of theη′photoproduction off the proton and preliminary beam asymmetry results at the GRAAL experiment

Differential and total cross section measurements on eta' photoproduction were published by the CLAS Collaboration (M. Dugger et al., Phys. Rev. Lett. 96, 062001 (2006) and M. Williams et al., Phys.Rev.C80, 045213 (2009)) for center-of-mass energies from near the threshold up to 2.84 GeV, and by the CB-ELSA-TAPS Collaboration (V. Crede et al., Phys. Rev. C80, 055202 (2009)) up to 2.36 GeV and also making a precise threshold scan of the differential cross section in the 1446 -1527.4 MeV gamma beam energy range. However, the wide information about reaction cross sections are not sufficient to understand the role of resonances involved in the process. Different theoretical works stressed the importance to have also polarization observables in order to solve the ambiguity in the choice of the parameters used in their models. We present the analysis of the eta' photoproduction off the proton, identifying the meson via the gamma gamma, pi(0)pi(0)eta, and pi(+)pi(-)eta decay modes by using the GRAAL apparatus; and we show the preliminary GRAAL results on the beam asymmetry Sigma from the threshold (1.446 GeV) up to 1.5 GeV.

Low-energy positron and electron scattering from nitrogen dioxide

Total cross section (TCS) measurements for positron scattering from nitrogen dioxide (NO2) are presented in the energy range 0.2–40 eV. The TCS, the elastic integral and differential cross sections, and the integral cross section accounting of all the inelastic processes (including positronium formation) have also been computed using the independent atom model with screening corrected additivity rule (IAM-SCAR) for incident energies from 1 to 1000 eV. A qualitative level of agreement is found between the present TCS experiment and theory at the common energies. As no previous measurements or calculations for positron–NO2 scattering exist in the literature, we also computed the TCS for electron collisions with NO2 employing the IAM-SCAR method. A comparison of those results to the present positron cross sections and the earlier electron-impact data and calculations is provided. To investigate the role that chemical substitution plays in positron scattering phenomena, we also compare the present positron–NO2 data with the TCSs measured at the University of Trento for positron scattering from N2O and CO2.

Neutron total cross section measurements of gold and tantalum at the nELBE photoneutron source

Neutron total cross sections of 197Au and natTa have been measured at the nELBE photoneutron source in the energy range 0.1–10MeV with a statistical uncertainty of up to 2% and a total systematic uncertainty of 1%. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5ps) with a short flight path of 7m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources.

Interpretation of the measurements of total, elastic, and diffractive cross sections at LHC

Recently at LHC one has obtained measurements of the total, elastic and diffractive cross sections in pp collisions at very high energy. The total cross section is in good agreement with predictions based on a leading behavior \sigma_{tot} (s) \propto (\ln s/s_0)^2, on the other hand the elastic cross section is lower than most expectations and the diffractive cross section is higher. It is remarkable that the ratio (\sigma_{el} + \sigma_{diff})/\sigma_{tot} calculated combining the results of the TOTEM and ALICE detectors is 0.495^{+0.05}_{-0.06}, very close to the maximum theoretically allowed value of 1/2 known as the Miettinen Pumplin bound. In this work we discuss these results using the frameworks of single and multi--channel eikonal models, and outline the main difficulties for a consistent interpretation of the data.

Results of total cross section measurements for 197Au in the neutron energy region from 4 to 108 keV at GELINA

Transmission measurements have been performed to determine the total cross section for neutron-induced reactions with 197Au in the energy region from 4keV to 108keV. The experiments were carried out at a 50m measurement station of the time-of-flight facility GELINA using a 6Li glass scintillator. The average total cross section as a function of neutron energy was derived after correcting the observed average transmission for cross section fluctuations due to resonance structures. The results have been compared with literature data and with the total cross section resulting from a dispersive coupled-channel optical model potential. The neutron strength function for s -wave neutrons and an orbital-independent scattering radius, together with their covariance matrix, have been derived in the neutron energy region between 4keV and 108keV through a parameterization of the total cross section based on a nuclear reaction theory.

Absolute total ionization cross sections of uracil (C4H4N2O2) in collisions with MeV energy highly charged carbon, oxygen and fluorine ions

Ionization and fragmentation of uracil molecules (C4H4N2O2, m = 112 amu) in collisions with fast highly charged C, O and F ions have been investigated using a time-of-flight mass spectrometer. The measurement of total ionization cross sections (TCS) is reported for different charge states (q), such as Fq + with q = 5–8; Oq + with q = 5,7; Cq + with q = 5 and 6. These studies reveal a (q/v)∼1.5 dependence of TCS, in contrast, to the well-known q2-dependence in ion–atom collisions. Scaling properties of the TCS with projectile energy and charge states are obtained. The experimental results for TCS measurements are compared with the theoretical calculations performed within classical and quantum mechanical frameworks. The trends in energy dependence of the TCSs is qualitatively well reproduced by the different models and more specifically by the classical description, which provides the best agreement with measurements.

AN UPDATED ANALYSIS ON THE RISE OF THE HADRONIC TOTAL CROSS-SECTION AT THE LHC ENERGY REGION

A forward amplitude analysis on pp and [Formula: see text] elastic scattering above 5 GeV is presented. The dataset includes the recent high-precision TOTEM measurements of the pp total and elastic (integrated) cross-sections at 7 TeV and 8 TeV. Following previous works, the leading high-energy contribution for the total cross-section (σ tot ) is parametrized as ln γ(s/sh), where γ and sh are free real fit parameters. Singly-subtracted derivative dispersion relations are used to connect σ tot and the rho parameter (ρ) in an analytical way. Different fit procedures are considered, including individual fits to σ tot data, global fits to σ tot and ρ data, constrained and unconstrained data reductions. The results favor a rise of the σ tot faster than the log-squared bound by Froissart and Martin at the LHC energy region. The parametrization for σ tot is extended to fit the elastic cross-section (σ el ) data with satisfactory results. The analysis indicates an asymptotic ratio σ el /σ tot consistent with 1/3 (as already obtained in a previous work). A critical discussion on the correlation, practical role and physical implications of the parameters γ and sh is presented. The discussion confronts the 2002 prediction of σ tot by the COMPETE Collaboration and the recent result by the Particle Data Group (2012 edition of the Review of Particle Physics). Some conjectures on possible implications of a fast rise of the proton–proton total cross-section at the highest energies are also presented.

Response of CR39 detector to 5 A GeV Si14+ ions and measurement of total charge changing cross-section

In the present work, response of CR39 track etch detector was obtained by cone-height measurement technique. CR39 track etch detector was used to identify the incident charged particles and their fragments by the measurements of cone-height of tracks using an optical microscope DM6000 M and automated image analyzer system installed with Leica QWin Plus software. The CR39 detector was calibrated and the response points were fitted with a linear relation and all the points are within the limits of the experimental errors. The charge resolution of the detector was calculated to be 0.2e. The response function is obtained and fitted with a linear relation which is good throughout Z/β=6.1–14.1. The experimental value of the total charge changing cross-section of 5A GeV Si14+ ion beam in polyethylene and CR39 combined target is σtot=(734±128)mb. The total charge changing cross-section is compared with the experimental results of others based on cone base-area measurement technique and also fitted by the Bradt–Peters geometrical cross-section.

Implications of a Froissart bound saturation ofγ*−pdeep inelastic scattering. II. Ultrahigh energy neutrino interactions

In Part I (in this journal) we argued that the structure function $F_2^{\gamma p}(x,Q^2)$ in deep inelastic $ep$ scattering, regarded as a cross section for virtual $\gamma^*p$ scattering, has a saturated Froissart-bounded form behaving as $\ln^2 (1/x)$ at small $x$. This form provides an excellent fit to the low $x$ HERA data, including the very low $Q^2$ regions, and can be extrapolated reliably to small $x$ using the natural variable $\ln(1/x)$. We used our fit to derive quark distributions for values of $x$ down to $x=10^{-14}$. We use those distributions here to evaluate ultra-high energy (UHE) cross sections for neutrino scattering on an isoscalar nucleon, $N=(n+p)/2$, up to laboratory neutrino energies $E_\nu \sim 10^{16}$-$10^{17}$ GeV where there are now limits on neutrino fluxes. We estimate that these cross sections are accurate to $\sim$2% at the highest energies considered, with the major uncertainty coming from the errors in the parameters that were needed to fit $F_2^{\gamma p}(x,Q^2)$. We compare our results to recently published neutrino cross sections derived from NLO parton distribution functions, which become much larger at high energies because of the use of power-law extrapolations of quark distributions to small $x$. We argue that our calculation of the UHE $\nu N$ cross sections is the best one can make based the existing experimental deep inelastic scattering data. Further, we show that the strong interaction Froissart bound of $\ln^2 (1/x)$ on $F_2^{\gamma p}$ translates to an exact bound of $\ln^3E_\nu$ for leading-order-weak $\nu N$ scattering. The energy dependence of $\nu N$ total cross section measurements consequently has important implications for hadronic interactions at enormous cms (center-of-mass) energies not otherwise accessible.

Cross sections for positron scattering from ethane

We report experimental and theoretical cross sections for positron scattering from the fundamental organic-chemistry molecule ethane (C${}_{2}$H${}_{6}$). The experimental total cross sections (TCSs) were obtained using a linear transmission technique, for energies in the range 0.1--70 eV and with an energy resolution of $\ensuremath{\sim}$0.25 eV (full width at half maximum). Agreement, over the common energy range, with the earlier TCS measurements of Floeder et al. [J. Phys. B 18, 3347 (1985)] is excellent, while both the present results and those of Floeder et al. are consistently higher in magnitude than the data of Sueoka and Mori [J. Phys. B 19, 4035 (1986)]. The present calculations employed the Schwinger multichannel method and were performed in the static plus polarization approximation for energies up to 10 eV. Our calculated elastic integral cross sections (ICSs) indicate a Ramsauer-Townsend minimum at around 1.4 eV in the ${A}_{g}$ scattering symmetry, and a virtual state. In addition we calculated from our scattering cross section a scattering length of $\ensuremath{-}$13.83${a}_{0}$. Agreement between our measured TCS and calculated elastic ICS is found to be only qualitative, although this is perhaps not so surprising given the TCS below 10 eV in principle includes contributions from rotational, vibrational, and electronic-state excitation and positronium formation whereas the calculation does not.

Luminosity-independent measurements of total, elastic and inelastic cross-sections at

The TOTEM experiment at the LHC has performed the first luminosity-independent determination of the total proton-proton cross-section at . This technique is based on the optical theorem and requires simultaneous measurements of the inelastic rate – accomplished with the forward charged-particle telescopes T1 and T2 in the range 3.1 < |η| < 6.5 – and of the elastic rate by detecting the outcoming protons with Roman Pot detectors. The data presented here were collected in a dedicated run in 2011 with special beam optics (β* = 90 m) and Roman Pots approaching the beam close enough to register elastic events with squared four-momentum transfers |t| as low as 5·10−3 GeV2. The luminosity-independent results for the elastic, inelastic and total cross-sections are σel = (25.1 ± 1.1) mb, σinel = (72.9 ± 1.5) mb and σtot = (98.0 ± 2.5) mb, respectively. At the same time this method yields the integrated luminosity, in agreement with measurements by CMS. TOTEM has also determined the total cross-section in two complementary ways, both using the CMS luminosity measurement as an input. The first method sums the elastic and inelastic cross-sections and thus does not depend on the ρ parameter. The second applies the optical theorem to the elastic-scattering measurements only and therefore is free of the T1 and T2 measurement uncertainties. The methods, having very different systematic dependences, give results in excellent agreement. Moreover, the ρ-independent measurement makes a first estimate for the ρ parameter at possible: |ρ| = 0.145 ± 0.091.

Reaction mechanisms in the scattering of exotic nuclei

This paper describes the evolution of our understanding of the reaction mechanisms involved in the scattering of exotic nuclei starting from the first measurements of reaction cross sections in the 1980s up to the most recent and advanced exclusive experiments for dripline unbound nuclei. We shall mainly cover nuclear and Coulomb breakup reactions, elastic scattering and total reaction cross sections measurements. Some open problems like kinematical effects on core parallel momentum distributions, the existence of a proton halo, the determination of the ground state of unbound nuclei such as 13Be, will be discussed in detail. A general framework for the reaction theory will be used, based on a time dependent perturbation theory approach and when suitable on its eikonal limit.

Positron scattering from noble gases

We have extended the nonrelativistic convergent close-coupling (CCC) method to the calculation of positron scattering from noble gases within the single-centre approximation. Good agreement is found with the available measurements of total cross sections and elastic differential cross sections for Ne, Ar, Kr and Xe.

High-order Harmonic Spectroscopy : Experimental and Theoretical study of Cooper Minimum in Argon

We study the Cooper minimum in HHG from argon atoms using long wavelength laser pulses. We find that the minimum in high harmonic spectra is systematically shifted with respect to total photoionization cross section measurements. We use a semi-classical theoretical approach based on Classical Trajectory Monte Carlo and Quantum Electron Scattering methods (CTMC-QUEST) to model the experiment. Our study reveals that the shift between photoionization and high harmonic emission is due to several effects: the directivity of the recombining electrons and emitted polarization, and the shape of the recolliding electron wavepacket.

Beryllium and Graphite Neutron Total Cross-Section Measurements from 0.4 to 20 MeV

The Gaerttner Laboratory electron linear accelerator at Rensselaer Polytechnic Institute was used in the measurement of the neutron total cross section of natural beryllium and carbon (graphite) in the energy range of 0.4 to 20 MeV. Neutron transmission measurements were made using the time-of-flight method with a 100-m flight path, fast detector response and electronics, and a narrow neutron pulse width to provide good energy resolution. A method was developed to determine the time-dependent background component associated with the transmission measurement using a combination of experimental data and Monte Carlo methods. The signal-to-background ratio combined with low counting statistics error resulted in low uncertainties and highly accurate data. The graphite measurement, showing excellent agreement with the current evaluations, provided a verification of the accuracy in the measurement and analytical methods used. The measurements of beryllium resulted in an accurate measurement of total cross section, showing some deviations with commonly used evaluations and better agreement with ENDF/B-VI.8. These results can be used for the improvement of future neutron cross-section evaluations of beryllium.

Rovibrationally selected ion-molecule collision study using the molecular beam vacuum ultraviolet laser pulsed field ionization-photoion method: Charge transfer reaction of N2+(X 2Σg+; v+ = 0–2; N+ = 0–9) + Ar

We have developed an ion-molecule reaction apparatus for state-selected absolute total cross section measurements by implementing a high-resolution molecular beam vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) ion source to a double-quadrupole double-octopole ion-guide mass spectrometer. Using the total cross section measurement of the state-selected N(2)(+)(v(+), N(+)) + Ar charge transfer (CT) reaction as an example, we describe in detail the design of the VUV laser PFI-PI ion source used, which has made possible the preparation of reactant N(2)(+)(X (2)Σ(g)(+), v(+) = 0-2, N(+) = 0-9) PFI-PIs with high quantum state purity, high intensity, and high kinetic energy resolution. The PFI-PIs and prompt ions produced in the ion source are shown to have different kinetic energies, allowing the clean rejection of prompt ions from the PFI-PI beam by applying a retarding potential barrier upstream of the PFI-PI source. By optimizing the width and amplitude of the pulsed electric fields employed to the VUV-PFI-PI source, we show that the reactant N(2)(+) PFI-PI beam can be formed with a laboratory kinetic energy resolution of ΔE(lab) = ± 50 meV. As a result, the total cross section measurement can be conducted at center-of-mass kinetic energies (E(cm)'s) down to thermal energies. Absolute total rovibrationally selected cross sections σ(v(+) = 0-2, N(+) = 0-9) for the N(2)(+)(X (2)Σ(g)(+); v(+) = 0-2, N(+) = 0-9) + Ar CT reaction have been measured in the E(cm) range of 0.04-10.0 eV, revealing strong vibrational enhancements and E(cm)-dependencies of σ(v(+) = 0-2, N(+) = 0-9). The thermochemical threshold at E(cm) = 0.179 eV for the formation of Ar(+) from N(2)(+)(X; v(+) = 0, N(+)) + Ar was observed by the measured σ(v(+) = 0), confirming the narrow ΔE(cm) spread achieved in the present study. The σ(v(+) = 0-2; N(+)) values obtained here are compared with previous experimental and theoretical results. The theoretical predictions calculated based on the Landau-Zener-Stückelberg formulism are found to be in fair agreement with the present measured σ(v(+) = 1 or 2; N(+)). Taking into account of the experimental uncertainties, the measured σ(v(+) = 1 or 2, N(+)) for N(+) = 0-9 at E(cm) = 0.04-10.0 eV are found to be independent of N(+).

Measurement of total and partial charge changing and charge pick-up cross-sections for 300A MeV Fe26+ beam in Al with a new system of analysis

In the present study, total and partial charge changing cross-sections of 300AMeV Fe26+ ion beam in aluminum target were measured by a new system of analysis installed with the Leica QWin Plus software. The CR39 nuclear track detectors were used to identify the incident charged particles and their fragments. The CR39 detectors just before and just after the target were calibrated and found to have the same charge response and the charge resolution, which were 0.19e and 0.20e, respectively. The response points were fitted with a polynomial of degree one and all the points are within the limits of experimental errors. The value of total charge changing cross-section was calculated to be σtot=(1663±236)mb. To determine the partial charge changing cross-sections for ΔZ=−23,−22,…,−1, number of events corresponding to each fragment were determined from multiple Gaussian fitting of diameter distributions within 95.5% confidence levels and the numbers of incident and survived beam ions were counted within 99.7% confidence levels. Charge pick-up cross-section for ΔZ=+1 was calculated and is (92±6)mb.

Calibration of CR39 detectors with new system for Fe26+ ion beam and measurement of total charge changing cross-section in Al target

Abstract In the present study, CR39 track etch detector was calibrated with a new system and the total charge changing cross-section of 300 A MeV Fe 26+ ion beam in aluminum target was measured. The CR39 nuclear track detectors were used to identify the incident charged particles and their fragments using an optical microscope DM6000 M and automated image analyzer system installed with Leica QWin Plus software. The CR39 detectors before and after the target were calibrated and found to have the same charge response; the charge resolution in both of the detectors were 0.19e and 0.20e, respectively. The calibration points were fitted with a polynomial of degree one and all the points are within the limits of the experimental errors. The response functions were also obtained and fitted with a polynomial of degree three which are quite good throughout Z / β = 4.6 to 41.4. The value of the total charge changing cross-section is σ tot = (1663 ± 236) mb. The total charge changing cross-section was compared with the experimental results of others and also fitted by the Bradt-Peters geometrical cross-section.

Positron scattering from chiral enantiomers

We report on total cross section measurements for positron scattering from the chiral enantiomers ($+$)-methyl ($R$)-2-chloropropionate and (--)-methyl ($S$)-2-chloropropionate. The energy range of the present study was 0.1--50 eV, while the energy resolution of our incident positron beam was \ensuremath{\sim}0.25 eV (FWHM). As positrons emanating from \ensuremath{\beta} decay in radioactive nuclei have a high degree of spin polarization, which persists after moderation, we were particularly interested in probing whether the positron helicity differentiates between the measured total cross sections of the two enantiomers. No major differences were, however, observed. Finally, quantum chemical calculations, using the density functional theory based B3LYP-DGTZVP model within the gaussian 09 package, were performed as a part of this work in order to assist us in interpreting some aspects of our data.