Ratio Of Total Cross Sections Research Articles

Total hadronic cross sections at high energies in holographic QCD

We present our analysis on high energy hadron–hadron scattering in the framework of the holographic QCD. Combining the Brower–Polchinski–Strassler–Tan Pomeron exchange kernel and gravitational form factors of the involved hadrons which are obtained by using the bottom-up AdS/QCD models in the five-dimensional AdS space, we calculate the total cross sections at high energies. We show that our calculations for the nucleon–nucleon scattering agree with the experimental data including the recent ones taken by the TOTEM collaboration at the LHC. The present framework is applicable to any high energy process, in which the strong interaction can be approximated by the Pomeron exchange. We present the results for the pion–nucleon and pion–pion scattering as examples, which can be obtained without any additional parameter because all the adjustable parameters are fixed via the analysis on the nucleon–nucleon scattering. The resulting total cross section ratios are σtotπN/σtotNN=0.63 and σtotππ/σtotNN=0.45, respectively.

Correlations among elastic and inelastic cross-sections and slope parameter

We discuss the unitarity motivated relations among the elastic cross-section, slope parameter and inelastic cross-section of the high energy pp interaction. In particular, the MacDowell-Martin unitarity bound is written down in another form to make a relation between the elastic and inelastic quantities more transparent. On the basis of an unitarity motivated relation we argue that the growth with energy of the elastic to total cross-section ratio is a consequence of the increasing with energy of the inelastic interaction intensity. The latter circumstance is an underlying reason for the acceleration of the slope parameter growth, for the slowing of the growth of the elastic to total cross-section ratio and for other interesting phenomena, which are observed in the TeV energy range. All of this confirms the old idea that the elastic scattering is a shadow of the particle production processes.

Integral particle reflection coefficient for oblique incidence of photons as universal function in the domain of initial energies up to 300 keV

In this paper we present the results of calculations and analyses of the integral particle reflection coefficient of photons for oblique photon incidence on planar targets, in the domain of initial photon energies from 100 keV to 300 keV. The results are based on the Monte Carlo simulations of the photon reflection from water, concrete, aluminum, iron, and copper materials, performed by the MCNP code. It has been observed that the integral particle reflection coefficient as a function of the ratio of total cross-section of photons and effective atomic number of target material shows universal behavior for all the analyzed shielding materials in the selected energy domain. Analytical formulas for different angles of photon incidence have been proposed, which describe the reflection of photons for all the materials and energies analyzed.

Next-to-leading orderW+5-jet production at the LHC

We present next-to-leading order QCD predictions for the total cross section and for a comprehensive set of transverse-momentum distributions in W + 5-jet production at the Large Hadron Collider. We neglect the small contributions from subleading-color virtual terms, top quarks and some terms containing four quark pairs. We also present ratios of total cross sections, and use them to obtain an extrapolation formula to an even larger number of jets. We include the decay of the $W$ boson into leptons. This is the first such computation with six final-state vector bosons or jets. We use BlackHat together with SHERPA to carry out the computation.

Photon albedo coefficients as functions of μ/Zeff parameter

This paper presents the results of the analyses of photon reflection from planar targets for normal photon incidence and for different shielding materials (water, concrete, aluminum, iron, and copper), in the range of the initial photon energies from 20 keV to 300 keV. Calculations of photon reflection parameters based on the results of Monte Carlo simulations of the photon transport have been performed using MCNP4C code. Integral reflection coefficients, presented as functions of the ratio of total cross-section of photons and effective atomic number of target material, show universal behaviour for all the analyzed shielding materials in the selected energy domain.

A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at [formula omitted] with ATLAS

The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb−1. The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with pT>30 GeV to be 8.73±0.30(stat)±0.40(syst) in the electron channel, and 8.49±0.23(stat)±0.33(syst) in the muon channel.

An Assessment of Acceleration Techniques in Scattering Source Iterations

Discrete ordinates solutions of the neutron transport equation require the solution of the within-group transport equation by the method of iteration on the scattering source. Scattering source iterations are hampered by extremely slow convergence rates when the medium is highly scattering. Among the methods proposed for the acceleration of the scattering source iterations, the coarse mesh rebalance and the diffusion synthetic acceleration techniques appear to be the most prominent ones. Thus, one or the other has been adopted in most of the SN codes. The numerical studies concerning the effectiveness of these acceleration methods have been made mostly for the planar geometry. There are some studies also for the multidimensional Cartesian geometries. In this study we have tried to assess the merits of these acceleration techniques in a curvilinear coordinate system that is spherical geometry. The performance of both of the acceleration methods have been determined by varying the scattering to total cross section ratio, the mesh size, the degree of anisotropy in scattering for a uniform spherical system. Then the study is extended to multiregion systems some of which are diffusive and in some of which transport effects are important.

A simple method to evaluate double ionization of He by swift highly charged ions

Double ionization of He by impact of multiply charged ions is studied. Perturbative and non-perturbative regimes are analysed discriminating the influence of post-collisional effects. A simple exponential approximation, based on known theoretical or experimental single ionization cross sections and Bohr and Linhard predictions of the electron release distance, is shown to give an adequate description of existing experimental data. Saturation effects are shown to play an important role in the total cross section ratios of double and single ionization for non-perturbative collisions.

Energy transfer of highly vibrationally excited azulene. III. Collisions between azulene and argon

The energy transfer dynamics between highly vibrationally excited azulene molecules (37 582 cm(-1) internal energy) and Ar atoms in a series of collision energies (200, 492, 747, and 983 cm(-1)) was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. The angular resolved collisional energy-transfer probability distribution functions were measured directly from the scattering results of highly vibrationally excited azulene. Direct T-VR energy transfer was found to be quite efficient. In some instances, nearly all of the translational energy is transferred to vibrational/rotational energy. On the other hand, only a small fraction of vibrational energy is converted to translational energy (V-T). Significant amount of energy transfer from vibration to translation was observed at large collision energies in backward and sideway directions. The ratios of total cross sections between T-VR and V-T increases as collision energy increases. Formation of azulene-argon complexes during the collision was observed at low enough collision energies. The complexes make only minor contributions to the measured translational to vibrational/rotational (T-VR) energy transfer.

On the universality of cross sections of hadron–hadron (nuclei) collisions at superhigh energies

We analyze the interplay of the hard and soft interaction dynamics in the onset of the black body limit in the high energy hadron–hadron and hadron–nucleus collisions. We demonstrate that hard interactions of large x partons with the strong small x gluon fields result in a faster increase of the range of the impact parameters where interaction reaches the unitarity limit. At superhigh energies, far above the Greizen–Zatsepin–Kuzmin limit, the radius of hadronic interactions, proportional to ln(s/s0), significantly exceeds static radii of the interacting hadrons (nuclei) and the dependence of the high energy elastic hadron–hadron scattering cross section on the impact parameter b becomes universal leading to the ratios of total cross sections of hadron–hadron, hadron–nucleus, nucleus–nucleus collisions becoming equal to one. The same universality is also expected for the ratio of structure functions: F2A(x,Q2)/F2N(x,Q2)→1 at very small x. We analyze how increase of the interaction radii with energy changes the energy dependence of total, absorption and inelastic cross sections, and the distribution over the number of wounded nucleons in proton–nucleus collisions.

Electron capture byNe4+ions from atomic hydrogen

Using the Oak Ridge National Laboratory ion-atom merged-beams apparatus, the absolute total electron-capture cross section has been measured for collisions of ${\mathrm{Ne}}^{4+}$ with hydrogen and deuterium at relative energies in the center-of-mass frame between 0.10 and 1006 eV/u. Comparison with previous measurements shows large discrepancies between 80 and 600 eV/u. For energies below $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$, a sharply increasing cross section is attributed to the ion-induced dipole attraction between the reactants. Multichannel Landau-Zener calculations are performed between 0.01 and 5000 eV/u and compare well to the measured total cross sections. Below $\ensuremath{\sim}5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$, the present total cross section calculations show a significant target isotope effect. At 0.01 eV/u, the H:D total cross section ratio is predicted to be $\ensuremath{\sim}1.4$ where capture is dominated by transitions into the ${\mathrm{Ne}}^{3+}$ $(2{s}^{2}2{p}^{2}3d)$ configuration.

Measurement of the 8Li( α, n) 11B reaction cross sections of astrophysical interest

An accurate exclusive measurement of the 8 Li( α , n) 11 B reaction cross sections has been carried out successfully by using a highly efficient detector system and high-purity low energy 8 Li-beam. The excitation function obtained with high statistics in the energy region from 0.9 to 2.7 MeV in the center-of-mass system is reported. The present cross sections show that the averaged ratio of total cross section to the inverted neutron capture cross section is 4 ∼ 5. Some details of the experimental method are also described.

Total electron-impact ionization cross sections of helium

By accurate measurement of total cross section ratios for electron-impact ionization and photoionization, total electron-impact ionization cross sections of He were determined. Relative standard uncertainties as low as 1.6 to 2% in the electron energy range from 100 to 4000 eV were achieved using published cross section data for photoionization. Results are discussed in terms of theoretical predictions and by comparison with former experimental results. The data are in excellent agreement with the results by Rejoub et al (2002 Phys. Rev. A 65 042713) and represent an accurate and reliable database for testing theoretical models.

Measurements of electron-impact ionization cross sections of argon, krypton, and xenon by comparison with photoionization

Ratios of total cross sections for electron-impact ionization and photoionization in Ar, Kr, and Xe in the energy range from 140 to 4000 eV for electrons and from 16 to 1012 eV for photons were measured. Comparatively low relative standard uncertainties of 1.3--1.9 % were achieved using an apparatus combining two recent instrumental developments. The first is associated with a highly accurate device for the determination of soft-x-ray and vacuum-UV photon flux, a cryogenic electrical substitution radiometer. The second is an upgraded ionization chamber for the precise comparison of total-ion yields for electron and photon impact. On the basis of our measured cross-section ratios and well-known total photoionization cross-section data, we deduced absolute total electron-impact ionization cross sections of the rare gases with relative standard uncertainties as low as 2%.

Measurement of Partial-Wave Contributions inpp→ppπ0

We report a measurement of the spin-dependent total cross section ratios delta_sigma_T/sigma_tot and delta_sigma_L/sigma_tot of the pp --> pp pi^0 reaction between 325 MeV and 400 MeV. The experiment was carried out with a polarized internal target in a storage ring. Non-vertical beam polarization was obtained by the use of solenoidal spin rotators. Near threshold, the knowledge of both spin-dependent total cross sections is sufficient to deduce the strength of certain participating partial waves, free of any model.

Measurement of the longitudinal cross-section using the direction of the thrust axis in hadronic events at LEP

In the process e +e −→hadrons, one of the effects of gluon emission is to modify the (1+cos 2 θ) form of the angular distribution of the thrust axis, an effect which may be quantified by the longitudinal cross-section. Using the OPAL detector at LEP, we have determined the longitudinal to total cross-section ratio to be σ L/ σ tot=0.0127±0.0016±0.0013 at the parton level, in good agreement with the expectation of QCD computed to O(α s 2) . Comparisons at the hadron level with Monte Carlo models are presented. The dependence of the longitudinal cross-section on the value of thrust has also been studied, and provides a new test of QCD.

Measurements of electron-impact ionization cross sections of neon by comparison with photoionization

A method and apparatus have been developed for precise measurements of the ratios of total cross sections for electron-impact ionization and photoionization in rare gases based on the comparison of the total ion yields of the two ionization processes. Low uncertainties for the cross-section ratios are achieved above all by using a cryogenic electrical substitution radiometer as a primary detector standard in the soft-x-ray and vacuum ultraviolet spectral ranges in order to determine the impinging photon flux. On the basis of our measured cross-section ratios and well-known total photoionization cross sections we deduce absolute total electron-impact ionization cross sections of rare gases. As a result we present ratios of total electron-impact ionization cross sections to total photoionization cross sections and deduce total electron-impact ionization cross sections of neon in the energy range of electrons from 140 to 4000 eV and of photons from 100 to 1500 eV. Relative uncertainties as low as 1.3% for the cross-section ratios and 2.8% for the total electron-impact ionization cross sections have been achieved. A comparison of our cross-section data with published experimental and theoretical data is presented.

Measurement of the longitudinal, transverse and asymmetry fragmentation functions at LEP

The fragmentation function for the process e+e−→h+X, whereh represents a hadron, may be decomposed into transverse, longitudinal and asymmetric contributions by analysis of the distribution of polar production angles. A number of new tests of QCD have been proposed using these fragmentation functions, but so far no data have been published on the separate components. We have performed such a separation using data on charged particles from hadronic Z0 decays atOpal, and have compared the results with the predictions of QCD. By integrating the fragmentation functions, we determine the average charged particle multiplicity to be\(\overline {n_{ch} } = 21.05 \pm 0.20\). The longitudinal to total cross-section ratio is determined to be σL/σtot=0.057±0.005. From the longitudinal fragmentation function we are able to extract the gluon fragmentation function. The connection between the asymmetry fragmentation function and electroweak asymmetrics is discussed.

Measurement of low energy K+ total cross sections on N=Z nuclei.

The total cross sections for ${\mathit{K}}^{+}$ on deuterium, $^{6}\mathrm{Li}$, $^{12}\mathrm{C}$, $^{28}\mathrm{Si}$, and $^{40}\mathrm{Ca}$ have been measured at four-momenta in the range of 480--714 MeV/c. The experimental technique was of the standard transmission type. Because of its long mean free path in nuclear matter at low energies the ${\mathit{K}}^{+}$ can be expected to probe the entire volume of the nucleus. Indeed we found that, to better than 10% \ensuremath{\sigma}(${\mathit{K}}^{+}$A)=A\ensuremath{\sigma}(${\mathit{K}}^{+}$N) up to A=40. This feature was used to study more delicate effects of the nuclear medium. Special emphasis was placed on measuring the total cross section ratios of ${\mathit{K}}^{+}$A to ${\mathit{K}}^{+}$ D with a precision of \ensuremath{\le}2%. This ratio is a good measure of nuclear medium effects because many experimental as well as theoretical systematic uncertainties cancel in the ratio. We discuss the medium dependence as a function of A. The data do not agree with calculations which include only conventional medium effects. This points towards the need of unconventional nuclear medium effects such as partial quark deconfinement, mass rescaling of nuclear pionic fields or pion excess in nuclei. Thus far only calculations based on unconventional medium effects for $^{12}\mathrm{C}$ exist. Calculations for the other nuclei are needed before quantitative conclusions can be drawn.

Chiral quark model and hadron scattering.

Hadron scattering at large and small distances is simultaneously described in the framework of the unitarization method based on a generalized reaction matrix. The assumed dynamics of hadron interactions is inspired by the ideas of the chiral quark models. The proposed model for hadron interactions is based on geometrical notions of the interactions of constituent quarks similar to those used by Chou and Yang for the description of hadronic interactions. This model allows us to reproduce the ${\mathrm{ln}}^{2}s$ growth of the total cross sections as well as regularities in the behavior of differential cross sections, in particular, its power-law falloff at fixed angles. It also allows us to get the correct values for the total cross-section ratios of hyperon-proton and proton-proton interactions and to estimate the total cross-section values for interactions of the hadrons containing heavy quarks.