共查询到20条相似文献,搜索用时 15 毫秒
1.
A differential cross section for π-meson production in peripheral heavy-ion collisions is formulated within the context of a particle-hole model in the Tamm-Dancoff approximation. This is the first attempt at a fully quantum-mechanical particle-hole calculation for pion production in relativistic heavy-ion collisions. The particular reaction studied is an 16O projectile colliding with a 12C target at rest. In the projectile we form a linear combination of isobar-hole states, with the possibility of a coherent isobar giant resonance. The target can be excited to its giant M1 resonance (Jπ = 1+, T = 1) at 15.11 MeV, or to its isobar analog neighbours, 12B at 13.4 MeV and 12N at 17.5 MeV. The theory is compared to recent experimental results. 相似文献
2.
Y. Eisenberg B. Haber U. Karshon J. Mikenberg S. Pitluck E.E. Ronat A. Shapira G. Yekutieli 《Physics letters. [Part B]》1974,48(4):354-358
In a high statistics experiment a large dσ/dt′ slope of (23.7 ± 3.2) GeV?2 is obtained in the forward direction. The natural parity exchange cross-section shows a dip at t′ ≈ 0.2 GeV2 and peak at ≈ 0.6 GeV2. The ?o is separated from the S-wave background and we obtain ?00F ≈ 0.94, at t′ = 0. 相似文献
3.
《Physics letters. [Part B]》1986,179(4):403-408
A search for two exotic decay modes of the ϒ(1S) meson has been made using the ARGUS detector at the e+e− storage ring DORIS II at DESY. The first was ϒ(1S) decays into weakly interacting particles, for which an upper limit of 2.3% at the 90% CL on the branching ratio is found. The second mode was ϒ(1S)→γa, where a is a neutral particle with mass less than 1.5GeV/c2, that either decays inside the detector or is sufficiently long-lived to escape detection. For short-lived particles a decaying into an e+e− pair, upper limits on the BR(ϒ(1S)→γa) of 3.1 × 10− at the 90% CL are found. The upper limit without restriction on the lifetime of a is found to be 1.3 × 10−3. Limits for other decay modes are also given. 相似文献
4.
《Nuclear Physics A》1998,641(4):476-498
We calculate the momentum-dependent potentials for K+ and K− mesons in a dispersion approach at nuclear density ϱ0 using the information from the vacuum K+N and K−N scattering amplitudes, however, leaving out the resonance contributions for the in-medium analysis. Whereas the K+ potential is found to be repulsive (≈ + 25 MeV) and to show only a moderate momentum dependence, the K− self-energy at normal nuclear matter density turns out to be ≈ − 140 ± 25 MeV at zero momentum roughly in line with K− atomic data, however, decreases rapidly in magnitude for higher momenta. The antikaon production in p + A reactions is calculated within a coupled channel transport approach and compared to the data at KEK including different assumptions for the antikaon potentials. Furthermore, detailed predictions are made for p+12C and p+207Pb reactions at 2.5 GeV in order to determine the momentum-dependent antikaon potential experimentally. 相似文献
5.
The proposal of hunting theH-particle taking advantage of antiproton annihilation at rest on3He is discussed. The obtained K* beam should allow one to obtain a flux ofΞ ? with momentum low enough to optimize the fusion probability (ΞN) to give anH. The experimental apparatus to detectH-events as the only missing mass of the fully reconstructed reaction¯p 3He →KKπ + H is the OBELIX Spectrometer at LEAR. A detailed Monte Carlo simulation of the overall acceptance of OBELIX for the above reaction is performed. The obtained final rate shows the feasibility of the experiment also in a not dedicated detector like OBELIX. 相似文献
6.
Marek Grinberg 《Journal of luminescence》2011,131(3):433-437
Emission related to rare earth ions in solids takes place usually due to 4fn→4fn and 4fn−15d1→4fn internal transitions. In the case of band to band excitation the effective energy transfer from the host to optically active impurity is required. Among other processes one of the possibilities is capturing of the electron at the excited state and the hole at the ground state of impurity.The latest results on high pressure investigations of luminescence related to Pr3+ and Eu2+ in different lattices are briefly reviewed. The influence of pressure on anomalous luminescence and 4fn−15d1→4fn luminescence in BaSrF2:Eu2+ and LiBaF3:Eu2+ systems and Pr3+ 4fn→4fn emission quenching is presented and discussed. A theoretical model describing the impurity-trapped exciton as a system where a hole is localized at the impurity and an electron is captured by Coulomb potential at Rydberg-like states is developed. The results show the importance of local lattice relaxation for the creation of stable impurity-trapped exciton states. The ligands shifts create a potential barrier that controls the effect of mixing between the Rydberg-like electron and localized electron wave functions. 相似文献
7.
From optical and thermal bleaching experiments it is concluded that the 400 nm absorption band which appears in Al2O3 after γ-irradiation is a composite V band. One of its components is attributed to the V-OH center which also is responsible for a localized vibrational band at 3316 cm-11 analogous to the one observed for the VOH center in MgO. The irradiation also results in electron trapping at Cr3+ impurity ions to produce a band at 227 nm. Annealing at 170°C destroys the V-OH center by releasing holes which convert the Cr2+ to Cr3+ with an attendant thermoluminescence. 相似文献
8.
P.C. Bruton C.S. Curran J.K. Davies T. Ekelöf S.M. Fisher E. Hagberg A.J. Herz F.F. Heymann D.C. Imrie S. Kullander G.J. Lush J.P. Nassalski A.L. Read 《Nuclear Physics B》1978,142(4):365-380
Proton-helium elastic scattering and coherent single-pion production have been studied at 18.6 GeV/c in the four-momentum transfer region (?0.06, ?0.17) GeV/c2. The elastic t-distribution has a somewhat steeper slope than is predicted by the Glauber approximation. The invariant-mass distribution of the Nπ system agrees with the double Regge-pole model except at about 1.65 GeV/c2 where an enhancement presumably due to N1 resonances is seen. The model also predicts the correct magnitude of the slope for nπ+α events. By using our cross sections at t′ = ?0.06 (GeV/c)2 where the impulse approximation should be valid, the isospin-zero exchange elementary cross section for the nπ+ production is evaluated. The inelastic angular distributions are consistent with several spinparity states contributing at all Nπ masses. 相似文献
9.
Four sets of NMR signals, two each, from 55Mn and 75As nuclei have been observed. The temperature dependences of 55Mn resonances have been studied from 77 to 311 K and that of 75As, from 77 K to about 250 K. The results show that there is a phase transition at T1 ≈ 220 K. This transition may be due to introduction of a local spontaneous distortion in the region of the domain walls in the lattice, resulting in lowering of symmetry at low temperatures. Another possibility is the canting of spins which would lower the magnetic group symmetry. The observed resonances have been assigned to arise from the nuclei at the edge and the centre of the domain walls at temperatures T >T1 and from two types of wall edges with inequivalent orientation of atomic spins at T < T1. The isotropic hyperfine field at 0 K obtained by extrapolating the resonance frequencies are 227 and 285.1 kOe at 55As nuclei, respectively. The anisotropy in the hyperfine field is nearly zero at 55Mn nuclei and about 5.8 kOe at 75As nuclei at 0 K. 相似文献
10.
R. Brandelik W. Braunschweig K. Gather V. Kadansky K. Lübelsmeyer P. Mättig H.-U. Martyn G. Peise J. Rimkus H.G. Sander D. Schmitz A. Schultz von Dratzig D. Trines W. Wallraff H. Boerner H.M. Fischer H. Hartmann G. Zobernig 《Physics letters. [Part B]》1980,94(1):91-95
Inclusive K0-production has been measured in e+e- annihilation at a center of mass energy of about W = 30 GeV. The ratio of K0 + K0 production to μ+μ- production is RK0 = 5.6 ± 1.1 (statist. error) ± 0.8 (system.error) This value is about a factor of three higher than RK0 at W = 7 GeV. The cross sections (s/β) dσ/dx is consistent with a scaling behaviour. 相似文献
11.
P. Bosetti H. Kirk M. Matziolis H. Nowak H.J. Schreiber K. Böckmann R. Hartmann J. Bartke M.J. Counihan S. Humble D.R.O. Morrison R. Stroynowski H. Wahl T. Hirose J. Stiewe A.A. Azooz T.C. Bacon M. Gorski 《Nuclear Physics B》1974,81(1):61-69
Data are presented on the reactions K?p → Δ++ + anything at 10 and 16 GeV/c and π?p → Δ++ + anything at 16 GeV/c. In the K?p reaction, scaling is observed between 10 and 16 GeV/c in the variable M2/s. The scaling occurs at relatively low values of M in marked contrast to the reaction π+p → Δ++ + anything. This result can be explained by duality arguments on a triple Regge picture, since the exchanged reggeon-incident particle scattering is exotic. Comparison of the π?p reaction, which is similarly exotic, with the K?p reaction at the same energy gives further evidence for factorization in pomeron-dominated inclusive reactions. 相似文献
12.
The second-order Born-approximation treatment of Cutler and Schucan was applied to inelastic electron scattering data on 6Li, 60Ni, and 114Cd acquired at low momentum transfers. The form factors as a function of momentum transfer q in the range of 0.25–0.57 fm?1 were obtained by angular distribution measurements performed at incident energies of 30 to 60 MeV. The correlation between two parameters deduced from the measurements, the reduced transition probability B(E2↑) and the transition radius R(2)tr, is discussed. It is suggested that inelastic electron scattering data at low-q is best used either in conjunction with an accurate value of B(EL↑) (available from the model-independent analysis of “photon” experiments at zero momentum transfer) to allow accurate determination of R(2)tr, or in conjunction with high-q inelastic electron scattering data to allow accurate determination of B(EL↑) as well as R(2)tr. 相似文献
13.
J. Eickmeyer S. Michalowski N. Mistry R. Talman K. Ueno 《Physics letters. [Part B]》1976,63(1):104-106
The total cross-section for production of hadrons by inelastic electron scattering at 3.2° from hydrogen and deuterium has been measured in the Q2 range 0.015 GeV2 to 0.1 GeV2, at virtual photon energies ranging from 2 GeV to 8.5 GeV. The transition to photoproduction is observed to be smooth, the ratio σD/σH being about 1.85 in this range. No evidence is seen for a conjectured rapid Q2-dependence of this ratio at low Q2. 相似文献
14.
Stephen R. Cotanch 《Nuclear Physics A》1978,308(3):253-262
The K+ meson (kaon) inelastic excitation of low-lying (Ex = 0–15 MeV) T = 0 collective states in 16O is theoretically studied as a function of energy and momentum transfer. The distorted wave impulse approximation is used to calculate angular distributions and total inelastic cross sections for exciting the first Jπ = 2+, 3?, 4+ and 5? states at lab energies from threshold to 400 MeV. The distortions are represented in a Kisslinger-type optical potential constructed from elementary K+-nucleon amplitudes. Total nuclear elastic and reaction K+-nucleus cross sections are computed to demonstrate sensitivity to choice in K+-nucleon amplitudes. Fermi motion effects are also assessed using a simple averaging procedure. The weak absorption character of the kaon is reflected in the inelastic calculations which predict selective excitation of low spin states at low momentum transfer and high spin states at high momentum transfer. 相似文献
15.
Strange mesons are considered to be sensitive to in-medium modifications. Theory predicts a repulsive K + N potential and an attractive K ? N potential in dense matter. A repulsive K + N potential would repel the K + mesons from the bulk of the nucleons and therefore cause a preferred out-of-plane emission of K + mesons at midrapidity and a directed flow opposite to the nucleons at target and projectile rapidity. One of observables to probe in-medium effects is the azimuthal emission pattern of K + mesons in heavy ion collisions. KaoS collaboration has measured the azimuthal distributions of K + mesons in Au + Au reactions at 1.5 A GeV and Ni + Ni reactions at 1.93 A GeV. Data show that K + mesons exhibit a pronounced enhancement at ${\phi = {90}^\circ}$ , i.e. perpendicular to the reaction plane. The data have also been fitted using the first two components of a Fourier series to get the directed flow v 1 and elliptic flow v 2. We used the quantum molecular dynamics model based on the covariant kaon dynamics to simulate the Au + Au collisions at 1.5 A GeV and the Ni + Ni collisions at 1.93 A GeV, to analyze the azimuthal distributions of K + mesons, and to calculate v 1 and v 2 of K + mesons. Calculated results with a repulsive in-medium K + N potential can reasonably describe the features of KaoS data. This indicates that the azimuthal distribution is one of sensitive probes to extract information on in-medium properties at high densities. 相似文献
16.
《Journal of Magnetic Resonance (1969)》1979,33(2):445-455
The method of calculating the pseudocontact shift of lanthanide shift reagents as a power series of T−n, the reciprocal of temperature, developed by Bleaney has been extended to the T−3 term. Using crystal field parameters reported in the literature, it is found that the T−3 term is no more than 10% of the T−2 term in magnitude at room temperature for all ions to which the theory is applicable. The calculations show that even though the pseudocontact shift cannot be fitted exactly to a T−2 temperature dependence, the simple equation for the T−2 term is adequate for estimating the actual shift at room temperature to an accuracy of 10 to 20%. 相似文献
17.
Energy and angular dependences for the electron impact excitation of the Helium 23 S, 21 S, 23 P, and 21 P states have been measured using monochromatic (0.05 eV) electrons in the energy range from 19 to 23 eV and for scattering angles ranging from 0 to 110°. The structures near the 23 S-threshold have been analyzed in terms of resonant and non resonant i.e. direct scattering phase shifts. The first peak in this excitation function at 19.95 eV is mostly due to the rapid change with collision energy of the directs-wave phase of the inelastic scattering, which in turn is a consequence of the existence of the 22 S-resonance at 19.3 eV. The energy position and behaviour with collision energy of the first peak at 20.7 eV in the 21 S-channel is in agreement with the predictions for the existence of a virtual resonance state ofBurke et al. A term sceme of the He? resonances with assignments of configurations is presented. 相似文献
18.
The 20 h95gTc decay to levels of95Mo has been investigated studyingγ-singles andγγ-coincidences. The first excited state of95Mo at 204 keV, previously assumed to be populated in the95m Tc decay only, is found to be fed by aγ-transition of 870 keV deexciting the level at 1074 keV which is populated in the95g Tc decay. More over three newγ-transitions of 477, 786 and 1552 keV deexciting the level at 1552 keV have been found. For the levels at 1074 and 1552 keV the range of possibleJ π assignments could be reduced. 相似文献
19.
H. Baltzer K. Freitag C. Günther P. Herzog J. Manns U. Müller R. Paulsen P. Sevenich T. Weber B. Will 《Zeitschrift für Physik A Hadrons and Nuclei》1995,352(1):47-67
The electron-capture decay of228Pa to levels in228Th has been studied using mass-separated sources and high-resolutionγ-ray and conversion-electron spectroscopy. A level at 979.5 keV is assigned as 2+ member of a second excited Kπ=0+ band, with the 0+ band head at 938.6 keV. The 2+ and 3+ members of a second excited Kπ=2+ band at 1153.5 and 1200.5 keV, which decay by strongE0 transitions to the 969 keVγ-vibrational band, are confirmed. In addition we tentatively propose a Kπ=1+ band at 944 keV. The Kπ=0?, 1? and 2? members of the octupole quadruplet are confirmed, and theγ decay of these levels is analysed in an approach, in which the mixing of the octupole bands by the Coriolis interaction is taken into account. It is suggested that octupole correlations might be important for theE1 transition moments. A total of 29 levels is observed between ~1.4 and ~2.0 MeV, for which the nuclear structure, and the possible assignment to rotational bands, is unclear. 相似文献
20.
Rotational sidebands in 166Er were observed using the 24 MeV 164Dy(α, 2nγ) reactions. The ground-state band was observed up to spin 16+ and does not backbend. A strong backbend is, however, observed in a Kπ = (O+) sideband, indicating that the 12+ state of the previously unknown S-band is at 2656 keV. The γ-band shows significant rotational alignment above I = 10+. Levels of at least two negative-parity bands, one of which is primarily the Kπ = 2? octupole vibration, are also observed. 相似文献