We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic ...events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).
Bose-Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of H, Formula omittedH, ...He, He, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose-Einstein correlations. One distribution is derived from unlike-sign hadron pairs, and the second is derived from mixing like-sign pairs from different events. The extraction procedure used simulations incorporating the experimental setup in order to correct the results for spectrometer acceptance effects, and was tested using the distribution of unlike-sign hadron pairs. Clear signals of Bose-Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
The beam-helicity asymmetry in associated electroproduction of real photons,
ep
→
e
γπ
N
, in the Δ(1232)-resonance region is measured using the longitudinally polarized Hera positron ...beam and an unpolarized hydrogen target. Azimuthal Fourier amplitudes of this asymmetry are extracted separately for two channels,
ep
→
e
γπ
0
p
and
ep
→
e
γπ
+
n
, from a data set collected with a recoil detector. All asymmetry amplitudes are found to be consistent with zero.
The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a ...negligible residual vector polarization enabled the first measurement of the tensor asymmetry A{sub zz}{sup d} and the tensor structure function b{sub 1}{sup d} for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV{sup 2}<<Q{sup 2}><5 GeV{sup 2}. The quantities A{sub zz}{sup d} and b{sub 1}{sup d} are found to be nonzero. The rise of b{sub 1}{sup d} for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.
Ratios of the ψ′ over the J/ψ production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA ...storage ring. The ψ′ and J/ψ states were reconstructed in both the μ+μ- and the e+e- decay modes. The measurements covered the kinematic range -0.35≤xF≤0.1 with transverse momentum pT≤4.5 GeV/c. The angular dependence of the ratio has been used to measure the difference of the ψ′ and J/ψ polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is Rψ′(μ)/Rψ′(e)=1.00±0.08±0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B′(μ)B(e))/(B(μ)B′(e)), of ψ′ and J/ψ in the two channels. The ψ′ to J/ψ production ratio is almost constant in the covered xF range and shows a slow increase with pT.
The results on DD-reaction yield enhancement from the Ti/TiO
2
:D
x
heterostructure by H
+
and N
+
ion beams in the energy range of 10–25 keV are presented. Neutron and proton fluxes weremeasured ...using a neutron detector based onHe-3 counters and a CR-39 plastic track detector. Measurements showed significant DD-reaction yield enhancement effects. The screening potential for this heterostructure under these experimental conditions was determined as
U
e
= 796 eV.
Deuterium-loaded BeO films were produced by sputtering the beryllium target with 10 keV Ne ions in D
2 gas at a pressure of approximately 1 Pa. The sputtered beryllium reacts – on the substrate ...surface – with the residual oxygen, thus forming a beryllium oxide layer. Biasing the substrate negatively with respect to the target provides the simultaneous bombardment of the growing film surface with D ions formed by Ne–D
2 collisions. Substrate potential governs the maximum energy of ions striking the growing film surface while its size governs the flux density. According to X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA) and reflection high energy electron diffraction (RHEED) data, the beryllium is deposited in the form of polycrystalline hcp-BeO layers with negligible (about 1 at.%) carbon and neon retention. Thermal desorption spectroscopy (TDS) data shows a strong deuterium bonding, with a desorption peak at 950 K, in the films deposited at −50 and −400 V substrate potentials. In addition, a relatively high ratio D/BeO≈0.2 has been found in the BeO films even at a substrate temperature of 800 K. Microstructural features of mixed Be–C–O films are presented as well.
The results on DD-reaction yield enhancement from the Pd/PdO:D
x
heterostructure by N
+
and Ne
+
ion beams in the energy range of 10–25 keV are presented. Neutron and proton fluxes were measured ...using a neutron detector based on He-3 counters and a CR-39 plastic track detector. Measurements showed significant DD-reaction yield enhancement effects. The screening potential for this heterostructure under these experimental conditions was determined as
U
e
= 897 eV.
The results of measurements of the DD-reaction yields from the Pd/PdO:D
x
heterostructure in the energy range of 10–25 keV are presented. The neutron and proton fluxes are measured using a neutron ...detector based on He-3 counters and a CR-39 plastic track detector. Comparisons with calculations show significant effects of DD-reaction yield amplification. The screening potential for this heterostructure under these experimental conditions is estimated as
U
e
= 630–980 eV.
At the ion accelerator HELIS at the LPI, the neutron yield is investigated in DD reactions within a polycrystalline deuterium-saturated CVD diamond, during an irradiation of its surface by a ...deuterium ion beam with the energy less than 30 keV. The measurements of the neutron flux in the beam direction are performed in dependence on the target angle, \b{eta}, with respect to the beam axis. These measurements are performed using a multichannel detector based on He3 counters. A significant anisotropy in neutron yield is observed, it was higher by a factor of 3 at \b{eta}=0 compared to that at \b{eta} = +-45{\deg}. The possible reasons for the anisotropy, including ion channeling, are discussed.
PDF
