Sigma Tot Research Articles

On the Discrepancy of pp, Formulap Total Cross Sections at s = 1.8 TeV between E710, E811 and CDF

Based on the previous approach, we have investigated a possibility to resolve the discrepancy between the E710, E811 and CDF at sqrt s =1.8TeV, using the experimental data of the pp, pbar p total cross sections sigma tot(+) and rho(+)$ ratio up to the SPS experiments (sqrt s = 0.9TeV) as inputs. We predict sigma tot(pbar p) and rho(pbar p) at the Tevatron energy(sqrt s=1.8TeV) as sigma tot(pbar p)=75.9+- 1.0mb, rho(pbar p)=0.136+- 0.005. It turns out that only the data of E710 is consistent with the prediction in the one standard deviation. So we can conclude that E710 is preferable but we can exclude neither CDF nor E811 results.

Single- and double-electron detachment in collisions of two negative hydrogen ions

Employing the crossed-beams technique in conjunction with a beam-pulsing method, we have measured absolute cross sections sigma tot for the process H-+H- to H0+... for CM energies between 2.5 and 100 keV. Combining the present results with our previously measured cross sections for double-electron detachment ( sigma 00) and triple-electron detachment ( sigma 0+). We obtain cross sections sigma 0- for the single-electron detachment process from the relation sigma 0-= sigma tot- sigma 00- sigma 0+ The experimental data of singleand double-electron detachment are well described by theoretical results based on the non-stationary tunnelling approach. Both cross sections are calculated for CM energies between 0.15 and 300 keV. A new two-electron simultaneous transition mechanism is introduced. The importance of this process for the theoretical assessment of the experimental results is discussed.

The Bethe theory for dissociative excitations and ionisation of H2+(1sσg) by electron impact

The revised Bethe theory due to Inokuti et al (1978) for the inelastic scattering of charged particles by atoms and molecules is applied to H2+ (1s sigma g). In the 'reflection' approximation, the cross sections for the sum of all the discrete excitations sigma ex, ionisation sigma i and total excitations sigma tot given in an asymptotic expression with the three constants (the so-called Born asymptote) instead of two constants (the so-called Bethe asymptote) are accurately calculated. The Bethe asymptotes are given for comparison with the less accurate ones reported by Peek (1974). It is shown that the ionisation cross sections given by the Born asymptote including the free-electron exchange correction are most compatible with the experimental data, but the ones given by the Bethe asymptote are only valid at high incident energies. The calculated sigma ex and sigma tot are also shown to be in excellent agreement with the experimental data at incident energies above 50 eV.

Transcapillary clearance of albumin in rat skeletal muscle monitored by external detection. Effects of alterations in capillary surface area.

The effects of noradrenaline (NA)-induced vasoconstriction on the transcapillary passage of albumin was evaluated by an external detection technique, allowing repetitive measurements of albumin clearance (Cl) during various conditions (in the same animal). Six isolated rat hindquarters were perfused with serum-albumin solutions during maximal vasodilation (papaverine 90 microM) and Cl was determined at different net filtration rates (Fv) induced by elevations of venous pressure. Then, the perfusate was changed to one of similar composition but containing noradrenaline (2-4 microM), and the procedure of determining Cl vs. Fv was repeated. Tissue accumulation of [99mTc]albumin was expressed in terms of clearance, using the isogravimetric Cl of defined muscle samples during maximum vasodilation in separate experiments as reference, the latter being 0.0246 +/- 0.0012 ml min-1 per 100 g. Noradrenaline caused an increase in vascular resistance from 2 to 14 mmHg min 100 g ml-1, while the Cl vs. Fv relationship was shifted downwards in a fashion parallel with the control Cl vs. Fv curve. For Fv = 0, Cl was 0.0101 +/- 0.0014 ml min-1 per 100 g during NA challenge. The average reflection coefficient for albumin (sigma tot) was 0.92 +/- 0.01 irrespective of vascular tone. Thus, both albumin clearance and the capillary filtration coefficient (CFC) seem to vary in direct proportion to the capillary surface area available for exchange.

Energy-gain spectroscopy measurements of single-electron capture by Ar6+in Ne and Ar

State-selective absolute capture cross sections sigma n,l for Ar6+ on neon and argon have been measured in the velocity interval from 0.01 to 0.03 au. Only reaction channels corresponding to curve crossings between 5 and 15 au approximately are found to be important. In contrast to findings at higher velocities, the summed cross sections sigma n and sigma tot increase strongly with velocity. Some special features of the partial cross sections are discussed.

Method for determining photoelectron angular distribution, total cross section and excitation beam polarisation from measurement of the integrated flux into selected solid angles

Detector geometries may be chosen to determine the total cross section sigma tot, the asymmetry parameter beta and the photo polarisation p while achieving good experimental statistics by using large acceptance angles in gas-phase photoemission experiments, in which the emitted electron current distribution is described by sigma tot(1+ beta P2(cos gamma ))/4 pi , where gamma is the angle between the emitted electron and the direction of one of the polarisation components of the photon beam. When a cylindrical mirror analyser (CMA) with variable acceptance geometry is used, it is possible to determine sigma tot, beta and the incident light polarisation p by measuring the flux with several different restricted (vignetted) annular rings whose polar and azimuthal angular acceptance ranges are appropriately chosen. The mathematical structure of this problem precludes determination of sigma tot, beta and p from the measured photocurrent using a CMA having its aperture vignetted only in the azimuthal or polar angle.

Absolute ionisation functions for electron impact with barium

Absolute ionisation functions sigma n+(E)(n=1,2,3,4) and the total ionisation function sigma tot(E) for electron impact with barium have been determined for energies up to 600 eV. Modified crossed-beam techniques were applied using the excitation function of the light from the resonance transition as a reference standard for the cross sections. A time-of-flight device was used to separate ions with different charges.

Electron-loss cross sections for negative ions at high energies

Total electron-loss cross sections sigma tot and sigma -11, respectively, have been measured with different combinations of H-, F-, S-, Cl-, Se-, Br-, I- in the following target gases: H2, He, O2, N2 and Ar. The energy range was extended from 20 to 220 keV. The measured cross sections for H- are compared with other data and theoretical approximations; for all other negative ions the cross sections are presented without comparison because calculations are not available.

Prediction of elastic and total cross sections using the Reggeon-photon coupling analogy

The Reggeon-photon coupling analogy, which relates the coupling of the natural-parity trajectories (P,f, omega , rho ,A2) at any vertex to that of the photon, is used to predict successfully a wide variety of elastic and total cross sections. As a special case, the authors predict the cross sections for gamma p to Vp where V is any vector meson ( rho , omega , phi , psi , Upsilon or their daughters) and thence obtain an excellent prediction of the recently measured sigma tot( gamma p) at high energies.

Elastic scattering and the Reggeon-photon coupling analogy

The gamma -analogy hypotheses for Reggeon couplings are used to predict the dominant P, f, omega , rho and A2 exchanges in pi +or-p, K+or-p, pp and pp elastic scattering. The couplings are all determined by the vector-meson-photon couplings fomega gamma and frho gamma , with only a small allowance for f- omega degeneracy breaking. Then the only unknown is the P:f ratio. When this has been determined (as a function of t) the authors can predict successfully sigma tot and d sigma /dt for all the above processes, and make reasonable estimates of the decay rates for rho , f, g, h to pi pi and f, A2, omega *, g, h to KK.