119087432
Ionization chambers for monitoring in high-intensity charged particle beams
Radiation-hard ionization chambers were tested using an intense electron beam from the accelerator test facility at the Brookhaven National Laboratory. The detectors were designed to be used as the basic element for monitoring muons in the Main Injector Neutrino beamline at the Fermi National Accelerator Laboratory. Measurements of linearity of response, voltage dependence, and the onset of ionization saturation as a function of gap voltage were performed.
118737108
Search for single top production with the D0 detector at the Fermilab Tevatron Collider
We attempt to identify a single top signal in the muon + jets data collected using the D0 detector at the Fermilab Tevatron at a center-of-mass energy of {radical}s = 1.8 TeV from 1992-96. The data corresponds to an integrated luminosity of 103.7 pb{sup -1}. While resolving a signal has proved impossible, we are able to place an upper limit on the production cross section for single top events using these data. The cross section for production of single top via 95% p{bar p} {yields} tb and p{bar p} {yields} qtb is less than 78 pb at the 95% confidence level based on muon + jets data only.
54041161
An optical readout TPC (O-TPC) for studies in nuclear astrophysics with gamma-ray beams at HIγS1
We report on the construction, tests, calibrations and commissioning of an Optical Readout Time Projection Chamber (O-TPC) detector operating with a CO2(80%) + N2(20%) gas mixture at 100 and 150 Torr. It was designed to measure the cross sections of several key nuclear reactions involved in stellar evolution. In particular, a study of the rate of formation of oxygen and carbon during the process of helium burning will be performed by exposing the chamber gas to intense nearly mono-energetic gamma-ray beams at the High Intensity Gamma Source (HI?S) facility. The O-TPC has a sensitive target-drift volume of 30x30x21 cm3. Ionization electrons drift towards a double parallel-grid avalanche multiplier, yielding charge multiplication and light emission. Avalanche-induced photons from N2 emission are collected, intensified and recorded with a Charge Coupled Device (CCD) camera, providing two-dimensional track images. The event's time projection (third coordinate) and the deposited energy are recorded by photomultipliers and by the TPC charge-signal, respectively. A dedicated VME-based data acquisition system and associated data analysis tools were developed to record and analyze these data. The O-TPC has been tested and calibrated with 3.183 MeV alpha-particles emitted by a 148Gd source placed within its volume with a measured energy resolution of 3.0%. Tracks of alpha and 12C particles from the dissociation of 16O and of three alpha-particles from the dissociation of 12C have been measured during initial in-beam test experiments performed at the HI?S facility at Duke University. The full detection system and its performance are described and the results of the preliminary in-beam test experiments are reported.
182311735
e(L) e(R) transitions due to thermal magnetic field fluctuations in the early universe and the upper bound on Majorana neutrino masses from B-L conservation
45505198
Enhanced dark matter annihilation rate for positron and electron excesses from Q-ball decay.
We show that Q-ball decay in Affleck-Dine baryogenesis models can account for dark matter when the annihilation cross section is sufficiently enhanced to explain the positron and electron excesses observed by PAMELA, ATIC, and PPB-BETS. For Affleck-Dine baryogenesis along a d=6 flat direction, the reheating temperature is approximately 30 GeV and the Q-ball decay temperature is in the range of 10-100 MeV. The lightest supersymmetric particles produced by Q-ball decay annihilate down to the observed dark matter density if the cross section is enhanced by a factor approximately 10(3) relative to the thermal relic cross section.
1977978
Flat direction condensate instabilities in the MSSM
Coherently oscillating scalar condensates formed along flat directions of the MSSM scalar potential are unstable with respect to spatial perturbations if the potential is flatter than φ2, resulting in the formation of non-topological solitons such as Q-balls. Using the renormalization group we calculate the corrections to the φ2 potential for a range of flat directions and show that unstable condensates are a generic feature of the MSSM. Exceptions arise for an experimentally testable range of stop and gluino masses when there are large admixtures of stops in the flat direction scalar.
5395080
Symmetry non-restoration via order 10(-10) B and L asymmetries
It has been observed that a large lepton asymmetry, n(L)/s approximate to 0.1, can prevent the Higgs expectation value from going to zero at high temperature, resulting in the non-restoration of the SU(2) x U(1) gauge symmetry and other symmetries. This could allow for the elimination of domain walls and other dangerous topological defects. Here we show that if the reheating temperature after inflation, T-R is sufficiently low then symmetry non-restoration will occur with an asymmetry of the order of the observed baryon asymmetry, n(B)/s approximate to 10(-10). For this to occur T-R less than or similar to 1 GeV is necessary. Remarkably, this happens to be the reheating temperature expected in Affleck-Dine baryogenesis along a d = 6 flat direction of the MSSM. As an example, we show that this can neatly solve the Z(3), domain wall problem of the NMSSM.