Magneto-Optic Trapping of β-Decaying 38Km, 37K From an On-Line Isotope Separator

A magneto-optic trap (MOT) can provide a well-polarized, backing-free, localized source of radioactive atoms for β-decay experiments. We have trapped approximately 6000 atoms of 38Km ( t1/2 = 0.925s) and 2000 atoms of 37K (1.226 s) produced at the TRIUMF on-line separator TISOL in a vapor-cell MOT. We have measured optical isotope shifts and deduced the nuclear charge radii, which show an unusual lack of change at the neutron number N = 20 shell closure. Plans include a search for scalar contributions to the β+- ν correlation in the 0+→0+ decay of 38Km

Polyethylene Based Ionomers as High Voltage Insulation Materials

Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6\ub710−14\ua0S\ua0m−1 at 70\ua0\ub0C and an electric field of 30\ua0kV\ua0mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts

Comparison of energy flows in deep inelastic scattering events with and without a large rapidity gap

Energy flows in deep inelastic electron-proton scattering are investigated at a centre-of-mass energy of 269 GeV for the range Q2 ≥ 10 GeV2 using the ZEUS detector. A comparison is made between events with and without a large rapidity gap between the hadronic system and the proton direction. The energy flows, corrected for detector acceptance and resolution, are shown for these two classes of events in both the HERA laboratory frame and the Breit frame. From the differences in the shapes of these energy flows we conclude that QCD radiation is suppressed in the large-rapidity-gap eents compared to the events without a large rapidity gap. © 1994

Extraction of the gluon density of the proton at x

The gluon momentum density xg(x, Q2) of the proton was extracted at Q2 = 20 GeV2 for small values of x between 4 × 10-4 and 10-2 from the scaling violations of the proton structure function F2 measured recently by ZEUS in deep inelastic neutral current ep scattering at HERA. The extraction was performed in two ways. Firstly, using a global NLO fit to the ZEUS data on F2 at low x constrained by measurementsfrom NMC at larger x; and secondly using published approximate methods for the solution of the GLAP QCD evolution equations. Consistent results are obtained. A substantial increase of the gluon density is found at small x in comparison with the NMC result obtained at larger values of x. © 1995

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the γp centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton. © 1995

Inclusive jet differential cross sections in photoproduction at HERA

Inclusive jet differential cross sections for the reaction ep → jet + X at Q2 below 4 GeV2 have been measured with the ZEUS detector at HERA using an integrated luminosity of 0.55 pb-1. These cross sections are given in the kinematic region 0.2 \u3c y \u3c 0.85, for jet pseudorapidities in the ep-laboratory range -1 \u3c ηjet \u3c 2 and refer to jets at the hadron level with a cone radius of one unit in the η - θ plane. These results correspond to quasi-real photoproduction at centre-of-mass energies in the range 130-270 GeV and, approximately, for jet pseudorapidities in the interval -3 \u3c ηjet(λp CMS) \u3c 0. These measurements cover a new kinematic regime of the partonic structure of the photon, at typical scales up to ∼300 GeV2 and photon fractional momenta down to xγ ∼ 10-2. Leading logarithm parton shower Monte Carlo calculations, which include both resolved and direct processes and use the predictions of currently available parametrisations of the photon parton distributions, describe in general the shape and magnitude of the measured ηjet and Etjet distributions. © 1995

Observation of events with a large rapidity gap in deep inelastic scattering at HERA

In deep inelastic, neutral current scattering of electrons and protons at s=296 GeV, we observe in the ZEUS detector events with a large rapidity gap in the hadronic final state. They occur in the region of small Bjorken x and are observed up to Q2 of 100 GeV2. They account for about 5% of the events with Q2≥10 GeV2. Their general properties are inconsistent with the dominant mechanism of deep inelastic scattering, where color is transferred between the scattered quark and the proton remnant, and suggest that the underlying production mechanism is the diffractive dissociation of the virtual photon. © 1993

Initial study of deep inelastic scattering with ZEUS at HERA

Results are presented on neutral current, deep inelastic scattering measured in collisions of 26.7 GeV electrons and 820 GeV protons. The events typically populate a range in Q2 from 10 to 100 GeV2. The values of x extend down to x ∼ 10-4 which is two orders of magnitude lower than previously measured at such Q2 values in fixed target experiments. The measured cross sections are in accord with the extrapolations of current parametrisations of parton distributions. © 1993

Observation of hard scattering in photoproduction at HERA

We report a study of electron proton collisions at very low Q2, corresponding to virtual photoproduction at centre of mass energies in the range 100-295 GeV. The distribution in transverse energy of the observed hadrons is much harder than can be explained by soft processes. Some of the events show back-to-back two-jet production at the rate and with the characteristics expected from hard two-body scattering. A subset of the two-jet events have energy in the electron direction consistent with that expected from the photon remnant in resolved photon processes. © 1992