1807085
Simulations of slow positron production using a low-energy electron accelerator.
Monte Carlo simulations of slow positron production via energetic electron interaction with a solid target have been performed. The aim of the simulations was to determine the expected slow positron beam intensity from a low-energy, high-current electron accelerator. By simulating (a) the fast positron production from a tantalum electron-positron converter and (b) the positron depth deposition profile in a tungsten moderator, the slow positron production probability per incident electron was estimated. Normalizing the calculated result to the measured slow positron yield at the present AIST linear accelerator, the expected slow positron yield as a function of energy was determined. For an electron beam energy of 5 MeV (10 MeV) and current 240 μA (30 μA), production of a slow positron beam of intensity 5 × 10(6) s(-1) is predicted. The simulation also calculates the average energy deposited in the converter per electron, allowing an estimate of the beam heating at a given electron energy and current. For low-energy, high-current operation the maximum obtainable positron beam intensity will be limited by this beam heating.
31219355
New scheme for positron accumulation in ultrahigh vacuum.
A new positron accumulation scheme compatible with ultrahigh vacuum conditions has been developed, which is realized by preparing a high density electron plasma as high as approximately 10(11) cm(-3) and an ion cloud as energy absorbers. The present accumulation rate normalized by the intensity of 22Na positron source is (3.6+/-0.3)x10(2)e(+)/s/mCi, which is more than one and a half orders of magnitude higher than other ultrahigh vacuum compatible schemes so far reported.
31299789
Electron cooling of high-energy protons in a multiring trap with a tank circuit monitoring the electron-plasma oscillations.
Electron cooling of energetic protons in a multiring trap was investigated experimentally with a tank circuit monitoring electron-plasma oscillations in the trap. The energy of protons was determined by time-of-flight measurements. It is found that a simple model can explain the qualitative behavior of both electron and proton energy when the initial energy of protons is less than 2 keV. Monitoring the electron-plasma temperature with a tank circuit can be an effective tool when energetic particles are electron cooled in a multiring trap.
121059853
Space-charge effects in the catcher gas cell of a rf ion guide
Slow radioactive ion beams have been produced with an overall efficiency of 4% by thermalizing energetic ions produced by a projectile fragment separator in a He-gas cell and guiding them to a vacuum vessel by dc and rf fields. Space charge was observed to have a limiting effect. Since the ionization of He atoms by energetic ions creates a region of high space charge, many thermalized ions of interest are pushed toward the walls of the gas cell. Such losses have been investigated for different incoming ion intensities.
117228255
Response of the D0 Muon Chamber to changes in voltage, incident angle, gas composition, and oxygen contamination
The measured space point resolution of a D0 Muon Chamber is /+-/0.31 mm perpendicular to the anode wire and 2.7 mm parallel to the wire. A voltage change of 1 kV, which changes the gas gain by a factor of 50, only causes a change of drift velocity of 12%. Tracks inclined of 45/degree/ have a resolution worse than those of 0/degree/ by a factor 3 /+-/ 2. A change in gas composition from CO/sub 2/(10%) to CO/sub 2/(11%) decreases the gas gain by 17 /+-/ 5%, and decreases drift velocity by 0.2 /+-/ 0.2%. The effect of an oxygen contamination of 3200 ppM is to change the mean pulse height by 45% over the 5 cm width of the cell. 4 refs., 15 figs.
119054052
Search for W pair production with dilepton decay modes at D0
We present the results of a search of 13.5 pb{sup {minus}1} of p{bar p} collisions at {radical}s = 1.8 TeV for WW {yields} dileptons + X using the DO detector. One WW {yields} e{mu}v{bar v} + X candidate was found with an expected background of about 0.96 {plus_minus} 0.44 events. One WW {yields} e{mu}v{bar v} + candidate was found with an expected background of about 1.23 {plus_minus} 0.87 events. The 95% C.L. upper limit for the W pair production cross section is 133 pb without background subtraction. Making the constraint {kappa} = 1 ({Delta}{kappa} = 0) implies {minus}2.6 {le} {gamma} {le} 2.7 (95% C.L.) and making the constraint {gamma} = 0 implies {minus} 3.3 {le} {Delta}{kappa} {le} 3.5 (95% C.L.) assuming {kappa}{sub {gamma}} = {kappa}{sub {Zeta}} and {lambda}{sub {gamma}} = {lambda}{sub {Zeta}}. We also present the contour of excluded couplings when {kappa} and {lambda} are allowed to simultaneously vary from their standard model values.