Dσ dΩ Research Articles

Search of the tensor glueball: The identification of resonances in the mass region 1.9–2.4 GeV

The result of the partial wave analysis of Crystal Barrel data on pp → π 0π 0,ηη and ηη′ combined with earlier data on dσ dΩ and polarization for pp → π −π + is presented. The polarization data separate cleanly states with L = J ± 1, while Crystal Barrel data provide possibility to define quark content of the observed resonances. Along with other states, four I = 0, J PC = 2 ++ resonances are identified. All 2 + resonances have flavour composition close to n n = ( u u + d d )/ 2 , with rather little s s component. The possible nonet classification of the found states is discussed.

Experimental study of the 3He(γ, pp)n reaction with polarized photons

The experimental study of the reaction 3He(γ, pp)n is being carried out in the photon energy range E γ = 200–500 MeV at the Tokyo 1.3 GeV electron synchrotron. By use of the tagged and linearly polarized photon beam, and the π-sr magnetic spectrometer TAGX, a kinematically complete measurement of the reaction 3He(γ, pp)n will be made. The high statistics measurements of dσ dΩ and Σ of the reaction 3He(γ, pp)n will clarify the photon absorption mechanism.

The cross-section for magnetic Compton scattering up to 1 MeV

The energy dependence of the magnetic Compton cross-section was measured with elliptically polarised synchrotron radiation at five energies from 245.2 to 1000.5 keV at the European Synchrotron Radiation Facility (ESRF) using a recently installed superconducting wavelength shifter, the sample was ferromagnetic iron. These measurements more than double the highest photon energy previously used in synchrotron radiation studies. It was found that the integrated intensity of the spin-dependent scattering was well described by the formulae for the differential cross-section, dσ dΩ , for free, stationary electrons. The optimisation of experiments designed to yield the spin-dependent Compton profile from the double differential cross-section, d 2σ dΩ dω is discussed.

Scalar and vector meson production and two-step processes in the ( K−, K+) reaction on 12C

The double strangeness exchange reaction ( K −, K +) is investigated with respect to the sub-threshold production of scalar and vector mesons ( f 0/ a 0/ φ) decaying into K + K − and the two-step processes induced by intermediate mesons and Ξ − hyperons at p k − = 1.66 GeV/ c using a scintillating fiber active target. The differential cross section ( 〈 dσ dΩ L 〉) averaged over the angular interval (2.3° ⩽ θ K + L ⩽ 14.7°) for the sub-threshold f 0/ a 0/ φ meson production with the K + K − decay is 11 ± 6 μb/sr at 0.6 ⩽ p K 1 < 0.95 GeV/ c. The present result differs significantly from the theoretical calculation which predicts the contribution of the f 0/ a 0/ φ meson production to be predominant in the ( K −, K +) reaction below p K + = 0.95 GeV/ c. We found a sizable contribution from two-step ( K −, K + processes, characterized by production of two S = −1 hyperons, consistent with the result of the intra-nuclear cascade (INC) model calculation with respect to the meson-induced hyperon (or hyperon resonance) pair production in the momentum region 0.6 ⩽ p K + < 0.95 GeV/ c. The observed enhancement of the cross section for the two-step ΛΛ production beyond the prediction of the INC model at p K + ⋍ 1.1 GeV/c could be due to the Ξ − p → ΛΛ reaction in 12C.

Signatures from polarization observables for photon absorption on a [formula omitted] proton pair

Photoabsorption on a bound 1S 0 proton pair has been investigated with respect to possible specific signatures from polarization observables. Assuming the dominance of any two of the three lowest possible multipoles (E1,E2,M2) we obtain simple forms for the differential cross section dσ dΩ , the photon polarization asymmetry Σ and the proton polarization P y . Specifically we find distinct relations between dσ dΩ and Σ. They may be applied to test the assumption of a dominance of the two-body process in (γ, pp) reactions in nuclei.

DWIA calculations for deuteron inelastic scattering at intermediate energies

We have developed a DWIA method to calculate ( d, d′ ) inelastic scattering at intermediate energies. Comparison is made to existing data for 12C( d, d′) at 400 MeV for dσ dΩ , A y , A yy , P y , K y y and the spin-flip probability. All observables are correctly reproduced.

Binary encounter electron emission in collisions of highly charged ions with helium gas targets

The energy and angular distribution of δ-electrons produced in collisions of bare argon projectiles with helium gas targets are reported. Double differential electron emission cross sections, d 2 σ dE e dΩ e , have been measured as a function of the electron emission energy, E e, and the polar electron emission angle, V e. The major interest was directed upon the angular dependence of the integrated single differential emission cross sections of the binary encounter (BE) electrons, dσ(Θ e ) dΩ e . The cross sections are compared with electron argon scattering data (calculated and tabulated in Phys. Rev. A 15 (1977) 2173 [1]) as well as experimental data derived from light ion impact on helium (ionic charge q≤9+). The theoretical results are calculated with the impulse approximation (IA) model developed by Lee et al. (Phys. Rev. A 41 (1990) 4816 [2]). Even for higher ionic charge states the measured BE electron emission cross sections are well described by the IA model and are found to scale quadratically with the ionic charge state, q 2, and the projectile energy, E p 2.

Angular distributions for H − formation from interaction of H 2+ with Kr

Differential cross sections were determined for the production of H − fragments produced by the collision of H 2 + on Kr at projectile energies between 1.0 to 5.0 keV and for scattering angles from −4° to 4°. The H − distributions are observed to fit to the scaling law ( 1 E ) dσ dω = F(Eθ 2) , where E is the incident energy. Two structures found at 4.0 and 7.3 eV yield information about the production of H −. These are associated with the direct dissociation and predissociative states of H 2 + interacting with the target.

Back-angle anomaly 16O + 28Si and phenomenological effective surface potential

The connection between the equations of classical hydrodynamics describing the flow of a liquid and the quantum-mechanical Schrödinger equation is discussed. A non-linear form of the latter is derived. The non-linearity of the Schrödinger equation is approximated by a phenomenological potential which is used to compute the differential cross-section ( dσ dΩ ) for the elastic scaterring of 16O on 28Si.

Fractal internal interfaces in nanostructured amorphous SiAu-alloys

Small Angle Neutron Scattering (SANS) was employed to characterize the microstructure of nanostructured amorphous Si 1-xAu x alloys (0.1 <×<0.35). Contrast variation of SANS by immersion in liquids has been shown to be a powerful tool to identify the scattering contributions in these nanostructured samples. At small values of the momentum transfer Q the SANS intensity decreases according to a power law dσ(Q)dΩ ∼ Q −3.37 due to the scattering of a surface fractal structure of dimension D S = 2.63. This fractal structure is the internal surface between regions of highly densified amorphous material and agglomerates of free volumes, forming a system of interconnected channels across the whole sample. Filling the pore system with a contrast liquid leads to a strong change of the scattering intensity, while the exponent α = 3.37 of the low Q power law remained unchanged. The results verify the fractal nature of the internal surface, as well as the microstructural concept of dense nanometer-sized amorphous grains embedded in a less dense “matrix” formed by grain boundaries and free volumes. Using C 6D 12, CS 2 and D 20, a molecule-size effect of different access to smaller pores was observed.

Formula omitted

Recent data from expt PS 172 at LEAR are presented. Data for both dσ dΩ and A on have been measured for π − π + and K − K + final states at 20 momenta from 360 to 1550 MeV/c over the centre of mass angular range 1° to 169°.

Neutral pion production in the reactions 16O+ 27Al, 58Ni, 208Pb at Elab=95 MeV/nucleon

The production of neutral pions has been studied in the 16O+ 27Al, 58Ni, 208Pb reactions at 95 MeV/nucleon. Inclusive pion differential distributions dσ dp t , dσ dT π , and dσ dΩ have been measured by detecting the two-pion decay γ-rays in a setup of 8 lead glass Cherenkov detector telescopes. The data are discussed in the framework of a moving thermal source model. It is shown that the shape of the pion energy spectra is better described if mean field effects on the primary pion-production cross section and pion reabsorption are included in the calculation.

Premiere observation de la production de π0 dans la reaction d+d→ α+ π0 interdite par la conservation de la symetrie de charge et mesure de la reaction d+d→ α+ γ

The reaction d+d→ α+ π 0 which is in clear violation of charge symmetry conservation, has been observed for the first time at a laboratory energy of 1.10 GeV in an experiment carried out at the Saturne synchroton at Saclay. The number of π 0's detected corresponds to a differential cross section dσ dΩ ∗(π 0) = 0.97 ± 0.20 ± 0.15 pb/sr at a centre-of-mass angle of θ c. m. = 107°, where the first error bar refers to the statistical uncertainty and the second to the systematic. The reaction d+d→ α+ γ was measured simultaneously with the π 0 production, leading to a differential cross section of dσ dΩ ∗(γ) = 0.82±0.18±0.10 pb/sr at the slightly larger angle of θ c. m. = 110°. The available predictions of theoretical models of charge symmetry breaking, based upon η/ π mixing, fall an order of magnitude below our measurement. However, these predictions for the η/ π mixing level might be boosted by the η threshold (1.121 GeV) proximity, where this experiment is performed.

Angular distributions of H − fragments from H +2 on Mg at low keV collisions

Three interesting structures have been observed on the angular distributions of the H − fragments produced by the collision of H + 2 on Mg at projectile energies of 1, 2, 3, 4 and 5 keV. The good matching of the distributions to the a scaling law ( 1 E inc ) dσ dω = ƒ(E inc θ 2 ) indicates that the same mechanism is acting over this range of energies. The mechanism proposed for the production of H − is through the predissociative states of H + 2 interacting with the target.

Cross section measurements of the 1H( 4He, 4He) 1H elastic recoil reaction for ERD analysis

The non-Rutherford differential cross section of the 1H( 4He, 4He) 1H reaction utilized in elastic recoil detection (ERD) analysis has been measured in the 0.9–3.4 MeV energy and 16°–41° recoil angle range. The results for the differential recoil cross section vs energy (lab) and recoil angle were fitted on a second-order surface, yielding dσ dω = 89.1E 2 − 0.119θ 2 − 455.7E + 10.2θ−1.38θE + 693 , where E is the energy [MeV], θ the recoil angle [deg] and dσ dω the differential cross section [10 −31 m 2/sr], all in the laboratory system.

A 36S(d,p) study with high energy resolution

The reaction 36 S( d, p ) has been studied at E d = 20 MeV with enriched 36S using H 2S gas targets and the Q3D magnetic spectrograph. We identify 35 excited states in 37S. Angular distributions for dσ dΩ(θ) and A y ( θ) yield quantum numbers J θ and spectroscopic factors for most of them. Comparison is made to the distribution of strength in 41Ca. From an additional ( d,d ′ ) experiment at E d = 23 MeV we derive multipole moments for the 2 + 1 and 3 − 1, state in 36S.

Polarization measurement of atomic hydrogen beam spin-exchanged with optically oriented sodium atoms

The spin-exchange reaction between hydrogen atoms and optically oriented sodium atoms was used to produce a polarized atomic hydrogen beam. The electron-spin polarization of the atomic hydrogen beam, which underwent the spin-exchange reaction with the optically oriented sodium atoms, was measured. A beam polarization of −(8.0 ± 0.6)% was obtained when the thickness and polarization of the sodium target were (5.78 ± 0.23) × 10 13 atoms/cm 2 and −(39.6 ± 1.6)%, respectively. The value of the spin-exchange cross section in the forward scattering direction, whose scattering angle in the laboratory system was less than 1.0°, was obtained from the experimental results as Δσ ex = ∫ dσ dω dω θ lab =0 →1.0° =(3.39±0.34)× −15 cm 2. This value is almost seven times larger than the theoretical value calculated from the NaH potential. The potential was computed quantum mechanically in the space of the appropriate wave functions of the hydrogen and the sodium atoms.

Effects of collective excitations in the elastic scattering of vector polarized deuterons

Abstract The differential cross sections, dσ(θ) dΩ , and the vector analysing powers, iT 11 ( θ ), for 12 MeV vector polarized deuterons scattered elastically from 40 Ar, 46,48,50 Ti, 52,54 Cr, 54,56 Fe, 58,60 Ni, 76,78,80,82 Se and 90 Zr were analysed assuming two-channel, 0 1 + −2 1 + , coupling. In contrast with the results of conventional optical model analysis for the same isotopes, the two-channel potential parameters are found to be described well without B (E2; 0 + −2 + ) dependence.

Frictional forces for deep inelastic heavy ion collisions of deformed nuclei and application to 238U on 238U

For the description of deep inelastic reactions between deformed nuclei we present a classical model with frictional forces. The frictional forces and moments are derived from an extended double-folding model of Tsang and have a finite range. The frictional forces dissipate energy and angular momentum. In order to show the symmetries of the frictional forces and to simplify dynamical calculations we develop a multipole expansion of the frictional forces and moments. The model is applied to the deep inelastic reaction of 238U on 238U at E lab = 7.42 MeV/amu. By averaging over the initial orientations of the intrinsic symmetry axes of the deformed nuclei, we calculate the double-differential cross section d 2σ dE dθ cm , the differential one dσ dΩ , and th total one for the deep inelastic collision.

Backward pion-deuteron elastic scattering from 1.75 to 3.1 GeV/ c

Measurements of the differential cross section for π −d elastic scattering in the backward angular region (−1 ⩽ cos θ cms ⩽ −0.98) are presented. These measurements were made at nine incident pion momenta P π ranging from 1.75 to 3.09 GeV/ c and at the largest values of q 2 [up to 7 (GeV/ c) 2] ever reached experimentally; here q 2 is the momentum transfer squared. The differential cross section was found to decrease rapidly with increasing momentum dσ dΩ cms (180°) ∼ P −15.7 π, dσ dt ∼ (q 2) −12.8 . The data are compared with predictions of Regge and quark bag models.