55027916
Design and initial commissioning of beam diagnostics for the PEP-II B factory
PEP II is a 2.2-km-circumference collider with a 2.1-A, 3.1-GeV positron ring (the Low-Energy Ring) 1 m above a 1-A, 9-GeV electron ring (the High-Energy Ring); both are designed for 3 A maximum. We describe the beam diagnostics for HER commissioning, starting in May 1997. LER commissioning will follow in 1998. The beam size and pulse duration are measured using near-UV synchrotron light extracted by grazing-incidence mirrors that must withstand 200 W/cm.
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.
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.
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.
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.
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.
123273188
COMPARISON OF HIGH TRANSVERSE MOMENTUM PI0 PRODUCTION FROM PI-, K-, P, AND ANTI-P BEAMS.
We compare high-transverse-momentum (P/sub perpendicular/) inclusive ..pi../sup 0/ production from ..pi../sup -/, K/sup -/, p, and p beams, at 100 and 200 GeV/c, for center-of-mass (c.m.) angles ranging from 2/sup 0/ to 115/sup 0/, and P/sub perpendicular/ .. ..pi../sup 0/X)/sigma (..pi..p ..-->.. ..pi../sup 0/X) decreases with increasing P/sub perpendicular/, and changes dramatically with c.m. angle. Also, the ratios sigma (K/sup -/p ..-->.. ..pi../sup 0/X)/sigma (..pi../sup -/p ..-->.. ..pi../sup 0/X) and sigma (pp ..-->.. ..pi../sup 0/X)/sigma (pp ..-->.. /sup 0/X) are approximately constant. The measurements are consistent with a theoretical viewpoint in which constituents of the incident hadrons undergo a hard-scattering subprocess.
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.
16316489
Constraints on Galaxy Formation from Stars in the Far Outer Disk of M31
Numerical simulations of galaxy formation within the cold dark matter (CDM) hierarchical clustering framework are unable to produce large disk galaxies without invoking some form of feedback to suppress gas cooling and collapse until a redshift of unity or below. An important observational consequence of delaying the epoch of disk formation until relatively recent times is that the stellar populations in the extended disk should be of predominantly young-to-intermediate age. We use a deep Hubble Space Telescope/Wide Field Planetary Camera 2 archival pointing to investigate the mean age and metallicity of the stellar population in a disk-dominated field at 30 kpc along the major axis of M31. Our analysis of the color-magnitude diagram reveals the dominant population to have a significant mean age (greater than or similar to8 Gyr) and a moderately high mean metallicity ([Fe/H] similar to -0.7); tentative evidence is also presented for a trace population of ancient (greater than or equal to 10 Gyr) metal-poor stars. These characteristics are unexpected in CDM models, and we discuss the possible implications of this result as well as alternative interpretations.
119074148
A search for organic molecules in intermediate redshift DLAs
There has been a renewed interest in searching for diffuse interstellar bands (DIBs) due to their probable connection to organic molecules and, thus, their possible link to life in the Universe. Our group is undertaking an extensive search for DIBs in DLAs via QSO absorption-line systems. Six of our DLA targets are presented here. Our equivalent width (EW) limits for the 5780 DIB line strongly suggests that DIB abundance is below the Milky Way expected value or that metallicity plays a large role in DIB strengths.
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.