Search

Differential cross sections and photon-beam asymmetries for the γ[over →]p→π^{-}Δ^{++}(1232) reaction have been measured for 0.7cosθ_{π}^{c.m.}1 and E_{γ}=1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross-section data are obtained in this kinematical region, and the asymmetry data for 1.5E_{γ}(GeV)2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure uu[over ¯] quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at E_{γ}=1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of π exchange in the t channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions producing a dd[over ¯] or an ss[over ¯] quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural-parity exchanges are needed to reproduce the present data.

The ϕ-Λ(1520) interference effect in the γp→K^{+}K^{-}p reaction has been measured for the first time in the energy range from 1.673 to 2.173 GeV. The relative phases between ϕ and Λ(1520) production amplitudes were obtained in the kinematic region where the two resonances overlap. The measurement results support strong constructive interference when K^{+}K^{-} pairs are observed at forward angles but destructive interference for proton emission at forward angles. Furthermore, the observed interference effect does not account for the sqrt[s]=2.1 GeV bump structure in forward differential cross sections for ϕ photoproduction. This fact suggests possible exotic structures such as a hidden-strangeness pentaquark state, a new Pomeron exchange, or rescattering processes via other hyperon states.

The test of the local hidden variable theories involving strongly interacting pairs of massive spin-\(\frac{1}{2}\) hadrons, in a nearly loophole-free experimental setting is reported. The spin correlation function is deduced to be Cexp(π/4) = −0.73 ± 0.08. This result is in agreement with non-local quantum mechanical prediction and it violates the Bell’s inequality of CBell(π/4) ≥ −0.5 at a confidence level of 99.3%.

A new result for the transverse mu^+ polarization, P_T, in the decay K^+ --> pi^0 mu^+ nu has been obtained in the KEK E246 experiment. Combined with our earlier result, P_T = (-1.12 +- 2.17(stat) +- 0.90(syst))x10^{-3} and Im(\xi) = (-0.28 +- 0.69(stat) +- 0.30(syst))x10^{-2}, which are consistent with no T-violation., Comment: 5 pages, 2 figures, to be published in the Proceedings of the PANIC02, Osaka, Sept 30 - Oct 4, 2002

Gamow-Teller (GT) states with ${J}^{\ensuremath{\pi}}$ = 1${}^{+}$ excited by a $(p,n)$-type charge-exchange reaction on $N=Z$ nuclei with ground-state isospin $T=0$ have isospin $T=1$, while $M1$ states excited by inelastic scattering of electrons or protons can have either $T=0$ or $T=1$. The latter are the isobaric analog states of the GT states. By comparing the GT states observed in the good-resolution ${(}^{3}\mathrm{He},t)$ reaction at 150 MeV/nucleon with the $M1$ states observed in inelastic electron and proton reactions, the isospin structure of the ${1}^{+}$ states in ${}^{28}\mathrm{Si}$ has been determined. From an analysis of the strengths of corresponding ${1}^{+}$ states observed in the ${(}^{3}\mathrm{He},t)$ and ${(e,e}^{\ensuremath{'}})$ reactions, the spin and orbital contributions to the $M1$ excitations have been deduced.

The exclusive reaction γp→K(+)π(-)Σ(+) was measured for the first time using linearly polarized photons at beam energies from 1.85 to 2.96 GeV. Angular distributions in the rest frame of the K(+)π(-) system were fitted to extract spin-density matrix elements of the K(*0) decay. The measured parity spin asymmetry shows that natural-parity exchange is dominant in this reaction. This result clearly indicates the need for t-channel exchange of the κ(800) scalar meson.

It is pointed out that the y-dependence of the differential cross-section for various types of neutrinos on the electron promises to be a sensitive testing ground of the electroweak Standard Model at KAON in Vancouver. Estimates of the flux requirements are given and the feasibility of such experiments is discussed.

The first measurements of elastic photon scattering on complex nuclei from 150 MeV to the Δ(1232) (Eγ = 300 MeV) are compared with theoretical calculations. Data on 4He at the Δ peak are in agreement with a Δh calculation, but substantial disagreement occurs at lower energies that is at least partly due to the approximate treatment of non-resonant parts of the elementary nucleon amplitude. An impulse approximation calculation which includes meson exchange provides an adequate description of the data at 187 MeV on 4He. Improved data on the proton at 20–30° and 120–140° at a range of energies are in agreement with a recent dispersion relation calculation. Data taken on 12C are still too preliminary to report, due to the difficulty of eliminating inelastic contributions.

This is the first measurement of the total cross section σ( 4 He (γ npp)n) in the range of 135–455 MeV. The σ, which cannot be reproduced by any model, has similar E γ dependence to γ T (γ 4 He → all channels). The averaged ratio σ( 4 He(γ, npp)n)/ σ T (γ 4 He → all channels) = (2.3 ± 0.3)% is compared with a cascade-model calculation in which quasi-free pion production followed by pion reabsorption is assumed.

Differential cross sections and photon-beam asymmetries for the gamma(p)--K{+}Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6cos(theta){c.m.}{K}1. A new bump structure was found at W approximately 2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with Jor=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with Jor=5/2 or by a new reaction process, for example, an interference effect with the phi photoproduction having a similar bump structure in the cross sections.

Photoproduction of Lambda(1520) with liquid hydrogen and deuterium targets was examined at photon energies below 2.4 GeV in the SPring-8 LEPS experiment. For the first time, the differential cross sections were measured at low energies and with a deuterium target. A large asymmetry of the production cross sections from protons and neutrons was observed at backward K+/0 angles. This suggests the importance of the contact term, which coexists with t-channel K exchange under gauge invariance. This interpretation was compatible with the differential cross sections, decay asymmetry, and photon beam asymmetry measured in the production from protons at forward K+ angles.

This is the first kinematically complete measurement of the 4He(γ, npp)n reaction in the energy range of 135–455 MeV. The ordered-momentum spectra and the double-differential cross sections are compared with the calculations which assume that photons are absorbed either on two- (np or pp), three- (npp), or four-nucleon systems. The ordered-momentum spectra below 400 MeV are reproduced well by pp and/or npp absorption but not by np absorption only.

The angular distributions for coherent photon scattering from {sup 4}He were measured at average laboratory bremsstrahlung energies of 187, 235, and 280 MeV. The experiment was performed at the Saskatchewan Accelerator Laboratory using the new high duty factor electron beam. The scattered photons were observed with a high-resolution NaI(Tl) total absorption scintillation detector. These measurements are intended to investigate modification of the {Delta} properties inside the nuclear medium and the treatment of nonresonant contributions to the scattering cross sections. The results are compared to theoretical calculations in the isobar-hole model. Clear deviations from the theory are evident at all energies, especially at 187 MeV.

The Sigma(1385) resonance, or Sigma;{*}, is well known as part of the standard baryon decuplet with spin J=3/2. Measurements of the reaction gammap--K;{+}Sigma;{*0} are difficult to extract due to overlap with the nearby Lambda(1405) resonance. However, the reaction gamman--K;{+}Sigma;{*-} has no overlap with the Lambda(1405) due to its charge. Here we report the first measurement of cross sections and beam asymmetries for photoproduction of the Sigma;{*-} from a deuteron target. The cross sections at forward angles range from 0.4 to 1.2 mub, with a broad maximum near E_{gamma} approximately 1.8 GeV. The beam asymmetries are negative, in contrast with positive values for the gamman--K;{+}Sigma;{-} reaction.

We have built an efficient trigger system for the π sr spectrometer, TAGX, which has been constructed for experiments with a high-duty (10%) tagged photon beam. In order to get a reasonable event rate for the on-line data acquisition, a heavy quantum-electrodynamical (QED) background has been effectively reduced at the triggering stage. The design and fabrication of the trigger system are described along with its performances in the 4 He(γ, pn) and 4 He(γ, pp) experiments.

In27Al(p, γ)28Si reaction, a narrow resonance was located for the incident proton energyEp=3.785 MeV. It is tentatively identified as the analogue of the 5.91 MeV level in28Al. It is found to populate only levels of high spin (J≥3) and the angular distributions are consistent with spin-parity assignment ofJπ=3+ for the resonance. Gamma-decay strengths and branching ratios are deduced. The transition strengths from the otherJπ=3+,T=1 are compiled and compared against the strength expected from the positron decay of the ground state of28P (Jπ=3+). It is apparent that there is considerable configuration mixing among theJπ=3+,T=1 levels in28Si.

Inclusive inelastic electron scattering off the deuteron under 180 degrees has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm;{-1} and 0.74 fm;{-1} with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn--dgamma of big-bang nucleosynthesis over most of the relevant temperature region. Results from potential model calculations and (for q=0.27 fm;{-1}) from pionless nuclear effective field theory are in excellent agreement with the data.

Differential cross sections and photon-beam asymmetries have been measured for the gamma n --K+ Sigma- and gamma p --K+Sigma0 reactions separately using liquid deuterium and hydrogen targets with incident linearly polarized photon beams of E gamma = 1.5-2.4 GeV at 0.6cos ThetacmK1. The cross section ratio of sigma K+ Sigma-/sigma K+ Sigma0, expected to be 2 on the basis of the isospin 1/2 exchange, is found to be close to 1. For the K+ Sigma- reaction, large positive asymmetries are observed, indicating the dominance of K* exchange. The large difference between the asymmetries for the K+ Sigma- and K+ Sigma0 reactions cannot be explained by simple theoretical considerations based on Regge model calculations.

A search for T-violating transverse muon polarization (P(T)) in the K+-->pi(0)mu(+)nu decay was performed using kaon decays at rest. A new improved value P(T)=-0.0017+/-0.0023(stat)+/-0.0011(syst) was obtained giving an upper limit |P(T)

The detector built at KEK to search for T-violating transverse muon polarization in K+ --> pi0 mu+ nu (Kmu3) decay of stopped kaons is described. Sensitivity to the transverse polarization component is obtained from reconstruction of the decay plane by tracking the mu+ through a toroidal spectrometer and detecting the pi0 in a segmented CsI(Tl) photon calorimeter. The muon polarization was obtained from the decay positron asymmetry of muons stopped in a polarimeter. The detector included features which minimized systematic errors while maintaining high acceptance., Comment: 56 pages, 30 figures, submitted to NIM

Beam polarization asymmetries for the p(gamma--,K+)Lambda and p(gamma--,K+)Sigma(0) reactions are measured for the first time for E(gamma)=1.5-2.4 GeV and 0.6cos((theta(c.m.)(K+))1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective-Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are thus far undiscovered.

In a kinematically complete experiment at the Mainz microtron MAMI, pion angular distributions of the $^3$He(e,e'$\pi^+)^3$H reaction have been measured in the excitation region of the $\Delta$ resonance to determine the longitudinal ($L$), transverse ($T$), and the $LT$ interference part of the differential cross section. The data are described only after introducing self-energy modifications of the pion and $\Delta$-isobar propagators. Using Chiral Perturbation Theory (ChPT) to extrapolate the pion self energy as inferred from the measurement on the mass shell, we deduce a reduction of the $\pi^+$ mass of $\Delta m_{\pi^+} = (-1.7^{+ 1.7}_{- 2.1})$ MeV/c$^2$ in the neutron-rich nuclear medium at a density of $\rho = (0.057^{+ 0.085}_{- 0.057})$ fm$^{-3}$. Our data are consistent with the $\Delta$ self energy determined from measurements of $\pi^0$ photoproduction from $^4$He and heavier nuclei., Comment: Elsart, 12 pages and 4 figures, Correspondent: Professor Dr. Dr. h.c. mult. Achim Richter, richter@ikp.tu-darmstadt.de, submitted to Phys. Rev. Lett

The 48Ca(e,e(')n) reaction has been investigated for excitation energies 11-25 MeV and momentum transfers 0.22-0.43 fm(-1) at the superconducting Darmstadt electron linear accelerator S-DALINAC. Electric dipole and quadrupole plus monopole strength distributions are extracted from a multipole decomposition of the spectra. Their fragmented structure is described by microscopic calculations allowing for coupling of the basic particle-hole excitations to more complex configurations. Comparison of the excitation spectrum of the residual nucleus 47Ca with statistical model calculations reveals a 39(5)% contribution of direct decay to the damping of the giant dipole resonance.

It is argued that in microscopic physics the discussions of wave-particle duality are not meaningful. This reasoning is based on the observation that waves are a conglomeration of coherent disturbances in a many body system and as such they do not represent individual entities. Newtonian kinematics have no predictive power and they do not offer a physical description of participants in an interaction, except to say that they obey the conservation laws. The point-particle concept is an unnecessary complication in physics.

The spin and parity of the 6.2 MeV level in 59Cu, populated by (p,γ) reaction, are found to be Jπ = 9/2+. The previously known two g9/2 fragments are situated 0.7 MeV higher in excitation energy. A description, consistent with (3He,d), (p,p′γ), and (p,γ) data, indicates the presence of isospin mixing and core polarization in these three states.

The gamma decay properties of 10.43-, 10.1-, 9.7-, 9.51-, and 8.91-MeV levels are studied by the 13C(p, γ) reaction. The natural widths, gamma decay widths, branching ratios, and multipole mixing ratios are determined. The gamma branching ratios are generally in good agreement with earlier works. However, it is found that the previous (p, γ) measurements overestimated the gamma transition strengths. The results are compared with shell model calculations. Also, a phenomenological description is attempted for a few 14N levels.

Inelastic electron–scattering form factors have been measured for 63,65Cu levels below 4 MeV excitation energy for momentum transfers q −1. The data obtained, along with the results from previous work, were used to test the validity of simple weak-coupling model predictions. It was found that while the weak-coupling model is only partially successful in describing the properties of the low-lying levels in those nuclei, the properties of the 65Cu levels are well described as two valence neutrons coupled to 63Cu levels over a wide range of momentum transfers.

Gamma decay schemes and angular distributions have been measured for g9/2 isobaric analogue resonances (IAR) in the 64,66Zn(p,γ) reactions. In 65Ga, the IAR is seen to be fragmented into four components at resonance energies ER = 6.810, 6.819, 6.830, and 6.835 MeV, and two fragments are observed in 67Ga at ER = 8.554 and 8.569 MeV. The total analogue–antianalogue M1 strengths are, respectively, 7 and 4% of the single particle estimates in 65Ga and 67Ga. These results are examined in the light of a model proposed by Aleshin. In 65Ga, the level at 1.286 MeV is determined to have a spin of 9/2 from angular distributions. This level is most likely a member of [Formula: see text] multiplet.

Isobaric analog resonances in /sup 6/9Ga corresponding to the ground (1/2/sup -/) and first excited (9/2/sup +/) parent states of /sup 6/9Zn have been studied by the /sup 6/9Zn(p,..gamma..) reaction. The ..gamma.. decay of the gound state of /sup 6/9Zn is compared with the ..beta.. decay of the parent isobaric analog state. The latter is a pure Gamow-Teller transition to the ground (3/2/sup -/) and third (3/2/sup -/) excited states, while both Gamow-Teller and Fermi matrix elements can contribute in the decay to the second excited (1/2/sup -/) state of /sup 6/9Ga. The M1 decay widths obtained from the ..gamma.. decay of the J/sup ..pi../ = 1/2/sup -/ isobaric analog state are in good agreement with the widths extracted from the logft values in the first two of the three ..beta..-decay branches. However, the M1 decay width to the third excited state disagrees with the value deduced from the logft value of the ..beta.. decay of the /sup 6/9Zn g.s. to this state. In addition, the M1 transition strength of the 9/2/sup +/ (T/sub greater-than/) state to the 9/2/sup +/ (T/sub less-than/) state in /sup 6/9Ga has been measured and is compared with the recently published systematic trends for themore » analog to antianalog transition in other f-p shell nuclei.« less

In the 13C(α, γ)17O reaction, measurements of E1 transition strengths from the 11.078 and 9.148 MeV (Jπ = 1/2−) levels to the 0.871 MeV level give (10.4 ± 1.6) × 10−3and (2.4 ± 0.5) × 10−3 e2 fm2, respectively. The ratio of these transition strengths results in a polarization charge epol ≈ −0.6. The E1 transition strength from the 11.078 MeV level is in excellent agreement with the core-polarization calculation of Towner and Hardy. The asymmetry for the corresponding isovector E1 transitions in 17O and 17F is found to be [Formula: see text], comparable in magnitude with the asymmetry for the analogous [Formula: see text] decays of 17N and 17Ne.

The resonances at Ep = 3.249 and 3.253 MeV in 64Zn(p,γ) are identified as fragments of the d5/2 isobaric analogue resonance from (p,p′γ) angular distributions. Gamma decay schemes and angular distributions are measured. In 65Ga, the level at 2.21 MeV is assigned a spin of Jπ = 5/2−. From angular distributions and symmetry potential considerations, the level at 2.82 MeV is considered to be the antianalogue state. The analogue–antianalogue transition strength is found to be compatible with single nucleon transfer data, thus showing that the interference effects from core polarized components arc negligible in this case.

A successful technique to overcome the difficulties in preparing self-supporting carbon targets using isotopic carbon in powder form is described. Using this technique, targets up to thicknesses of 140 μg/cm2 were prepared by e−-gun evaporation. Elemental purity, durability and uniformity of these targets have been tested using the protons from a Van de Graaff accelerator. Their performance has been compared with commercially available targets.

A second-order DWBA analysis is performed for the 124,130 Te(p, t) 122,128 Te reactions at E p = 51.9 MeV. It is found that the (p, t) excitations of one-phonon 2 1 + and 3 1 − states in 122 Te receive large contributions from inelastic two-step processes, while those of 128 Te receive dominant contributions from one-step processes.

The decay of131Ba has been studied by Ge(Li) detector supplemented by Ge(Li)-Ge(Li) fast-slow coincidence and NaI(Tl)-NaI(Tl) sum-coincidence spectrometer. The existence of 31 gamma rays and the levels at 78.8, 123.5, 133.4, 215.7, 373.0, 585.0, 620.0, 696.3 and 1084.4 keV have been confirmed. No evidences are found for the level at 1170 keV and 215.7−78.8 and 696.3−373.0 transitions. Some transitions are found to be connected with the impurities which were attributed to131Ba decay in earlier studies. The relative intensities and conversion coefficients have been determined and multipolarities of some of the transitions infered from the comparison of the conversion coefficients with the theoretical values.

The radioactive decay of 16.1 d 99Rh has been studied using a Ge(Li)-Ge(Li) coincidence spectrometer and a NaI(Tl)-NaI(Tl) sum-coincidence spectrometer. Evidence for the existence of a new γ-ray of energy 910.8 keV is obtained. A level scheme for 99Ru is established. Four new cascade transitions from the energy levels at 850.3, 1000.2, 1295.2 and 1382.9 keV are reported. The relative intensities and energies of all the γ-transitions are determined. The half-life of the 89.4 keV level is measured using the delayed coincidence method. The value obtained is 20.5±0.1 nsec.

The gamma decay of Ep = 3.77 MeV resonance in 13C(p,γ)14N has been measured. From the measured excitation functions, the natural width of the resonance was deduced to be 1.2 ± 0.4 keV. The resonance is found to strongly populate the 3.945 MeV level, in addition to the gs transition. Gamma angular distribution measurements determined the resonance spin as 3+. The reduced proton width is found to be 0.5% of the single particle unit. The transition strengths are measured to be B(E2) = 0.45 ± 0.07 and 3.0 ± 0.8 Wu for transitions to ground state and the level at 3.945 MeV, respectively.

With the use of Ge(Li) detectors for gamma ray yield measurements, several resonances were located in proton-induced reactions on a /sup 27/Al target for bombarding energies of E/sub p/ = 3.1--3.6 MeV (E/sub x/ = 14.62--15.04 MeV in /sup 28/Si). Decay modes of the resonances were determined.

It is shown that the reduction in the strengths of analog-antianalog ..gamma.. transitions (M1) can be understood without taking recourse to the presence of core polarized states. The results of calculations for various transitions are presented and compared with experimental data.

The /sup 119,117/Sn(p,t) reactions have been studied at E/sub p/ = 52 MeV. The angle integrated cross sections (10/sup 0/ < or = theta/sub c.m./ < or = 50/sup 0/) for l = 0 and 2 transfers have been compared with the corresponding ones in the neighboring even isotopes. About a 50% reduction in strength for g.s. (l = 0) transitions in odd isotopes has been observed. It is in agreement with the interpretation of Fleming et al. as due to a blocking effect. However, in contrast to the observation of Fleming et al., it is argued that such blocking may not be present for l = 2 transitions in these nuclei.

Differential cross sections of (p, t) reactions exciting the 2+1 states in Te (A = 128 − 120), Sn (116 and 114) and Cd (114 and 112) have been measured at Ep = 52 MeV. The observed differences of the angular distributions are interpreted by taking into account the two-step processes through inelastic scattering channels.

An experimental level scheme has been determined for 147Pm from an investigation of the decay of 147Nd which employed a high resolution Ge(Li) detector and a sum-coincidence spectrometer with fast-slow coincidence. Conclusive evidence is presented for the existence of levels in 147Pm at 182,228�5,275,319�5 and 725 keY besides the six already established levels, while no evidence is found for another six levels suggested by some earlier workers. Thirty-two y-ray transitions and their cascade relations have been established, and relative intensities have been determined for most of the transitions.