11472673
Calibration of the beam-position monitor system for the SLAC PEP-II B Factory
The beam-position monitors (BPM) for the PEP-II B Factory consist of four 1.5-cm diameter button style pickups mounted on the diagonals of the quadrupole vacuum chambers. Before installation of the vacuum chambers in the quadrupole assemblies, the electrical center of the BPMs is measured with respect to the mechanical center in a calibration test stand. In this paper the calibrations test stand is described and the precision and accuracy of the calibrations are presented. After installation of the quadrupole assemblies in the PEP-II tunnel, the passive attenuation for each channel of the system is measured to preserve the accuracy of the calibration. Finally, the active electronics includes an on-board calibrator. Results for these portions of the calibration are presented.
118623913
A Blind Search for Pulsars in EGRET Data using a Time Differencing Technique
Most of the sources in the galactic plane detected by the EGRET instrument on board the Compton Gamma‐Ray Observatory still remain unidentified. The energy spectra of some of the sources suggest that the gamma‐ray emission originates from pulsars. Detecting pulsed gamma‐ray emission without prior knowledge of the pulsar spin parameters is exceedingly difficult. Standard pulsar blind searches rely on the execution of long FFTs, which use a large amount of computational power. We present a pulsar blind search, based on our Time Differencing Technique, that can be carried out more economically, in this example on a standard office PC. To prove the concept of this search method we conducted a blind periodicity search on all 271 sources from the 3rd EGRET catalog.
15057663
Linac Coherent Light Source Undulator RF BPM System
The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL) when it becomes operational in 2009. The LCLS is currently in the construction phase. The beam position monitor (BPM) system planned for the LCLS undulator will incorporate a high-resolution X-band cavity BPM system described in this paper. The BPM system will provide high-resolution measurements of the electron beam trajectory on a pulse-to-pulse basis and over many shots. The X-band cavity BPM size, simple fabrication, and high resolution make it an ideal choice for LCLS beam position detection. We will discuss the system specifications, design, and prototype test results.
15325639
A Fresh Look at Diffuse Gamma-ray Emission from the Inner Galaxy
The Energetic Gamma-Ray Experiment Telescope (EGRET) experiment onboard the Compton Gamma-Ray Observatory (CGRO) has provided the most precise measurements of the -ray sky to date. The EGRET measurements of the diffuse emission across the sky show an excess above 1 GeV. This "GeV excess" has been a topic of great debate and interest since its original discovery by Hunter et al. in 1997. We have modified the GLAST simulation and reconstruction software to model the EGRET instrument. This detailed modeling has allowed us to explore the parameters of the EGRET instrument, in both its beam-test configuration and in-orbit on CGRO, in greater detail than has previously been published. We have found that the GeV excess is significantly increased when previously unaccounted for instrumental effects are considered. We will present a new measurement of diffuse -ray emission in the inner Galaxy.
110121135
FEEDBACK SYSTEMS IN THE SLC
Two classes of computer-controlled feedback have been implemented to stabilize parameters in subsystems of the SLC: (1) ''slow'' (time scales approx. minutes) feedback, and (2) ''fast'', i.e., pulse-to-pulse, feedback. The slow loops run in a single FEEDBACK process in the SLC host VAX, which acquires signals and sets control parameters via communication with the database and the network of normal SLC microprocessors. Slow loops exist to stabilize beam energy and energy spread, beam position and angle, and timing of kicker magnets, and to compensate for changes in the phase length of the rf drive line. The fast loops run in dedicated microprocessors, and may sample and/or feedback on particular parameters as often as every pulse of the SLC beam. The first implementations of fast feedback are to control transverse beam blow-up and to stabilize the energy and energy spread of bunches going into the SLC arcs. The overall architecture of the feedback software and the operator interface for controlling loops are discussed.
122398457
Fermi Gamma‐ray Space Telescope, Introduction and Highlights from the First Eight Months
The Fermi Gamma‐ray Space Telescope, formerly named GLAST, is a mission in low‐Earth orbit to observe gamma rays from the cosmos in the broad energy range from 20 MeV to >300 GeV, with supporting observations of gamma‐ray bursts from 8 keV to 30 MeV. The telescope far surpasses previous generations in its ability to detect and localize faint gamma‐ray sources, as well as its ability to see 20% of the sky at any instant and scan the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi has opened a new and exciting window on a wide variety of exotic astrophysical objects, including pulsars, black holes, active galactic nuclei, and gamma‐ray bursts, and it will enable new research on such topics as the origin and circulation of cosmic rays and searches for hypothetical new phenomena such as annihilation of supersymmetric dark matter.
17372933
MAGE - a GEANT4-based Monte Carlo framework for low-background experiments
A Monte Carlo framework, MaGe, has been developed based on the Geant4 simulation toolkit. Its purpose is to simulate physics processes in low-energy and low-background radiation detectors, specifically for the Majorana and Gerda $^{76}$Ge neutrinoless double-beta decay experiments. This jointly-developed tool is also used to verify the simulation of physics processes relevant to other low-background experiments in Geant4. The MaGe framework contains simulations of prototype experiments and test stands, and is easily extended to incorporate new geometries and configurations while still using the same verified physics processes, tunings, and code framework. This reduces duplication of efforts and improves the robustness of and confidence in the simulation output.
122426348
Pion Charge Exchange Scattering at High-Energies
We report on a study of pion charge-exchange scattering carried out at Fermilab in the energy range 20 to 200 GeV. The results can be described remarkably well by a simple Regge-pole model. The charge-exchange cross sections in the forward direction lead to a prediction for the difference in total cross sections of ..pi../sup -/p and ..pi../sup +/p which is in satisfactory agreement with direct measurements of this difference in another experiment at Fermilab. (AIP)
115852024
Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm
Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper.
17422475
Probing the Nature of the G1 Clump Stellar Overdensity in the Outskirts of M31
We present deep Hubble Space Telescope ACS observations of the G1 clump, a distinct stellar overdensity lying at similar to 30 kpc along the southwestern major axis of M31, close to the G1 globular cluster ( from the work of Ferguson and coworkers). Our well-populated color-magnitude diagram reaches similar to 7 mag below the red giant branch tip with 90% completeness, and allows the detection of various morphological features that can be used to derive detailed constraints on the age and metallicity of the constituent stellar population. We find that the color-magnitude diagram is best described spread in metallicity is constrained to be P = 0.5 dex. The star formation rate in this region has declined over time, with the bulk of the stellar mass having formed > 6 Gyr ago. Nonetheless, a nonnegligible mass fraction (approximate to 10%) of the population has formed in the last 2 Gyr. We discuss the nature of the G1 clump in light of these new stellar population constraints and argue that the combination of stellar content and physical size make it unlikely that the structure is the remnant of an accreted dwarf galaxy. Instead, the strong similarity between the stellar content of the G1 clump and that of the M31 outer disk suggests that the substructure is a fragment of the outer disk, perhaps torn off from the main body during a past accretion/merger event; this interpretation is consistent with extant kinematical data. If this interpretation is correct, our analysis of the stellar content provides further evidence that the outskirts of large disk galaxies have been in place for a significant time. (Less)
119898563
Inclusive eta production at large transverse momenta
We have measured the ratio of inclusive production of eta to ..pi../sup 0/ at transverse momenta above 1.5 GeV/c. Results are presented for various meson and proton beams with momenta of 100, 200, and 300 GeV/c incident upon a hydrogen target. The eta/..pi../sup 0/ production ratio is found to be independent of incident beam momentum and of the transverse and longitudinal momenta of production. The ratio for pion- and proton-induced reactions is 0.44 +- 0.05; for kaons, it is 0.74 +- 0.12.