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We describe a setup to search for the existence of a massive gauge boson A', the "dark photon," mediating dark matter interactions with coupling strength [alpha]'. In certain models, the A' decays promptly but invisibly and might be discoverable in high luminosity collider experiments. Following a proposed setup by Wojtsekhowski et al. to use the VEPP-3 electron-positron storage ring at the Budker Institute for Nuclear Physics, we study whether an e+ + e- - A'+ -[gamma] signal could be seen over the quantum electrodynamic background. The proposed VEPP-3 setup is sensitive to an A' within the mass range mA = 5-20 MeV. Out of the two backgrounds, e++e- - 3[gamma] and e+ + e- - e+ + e- + [gamma], we find that the former process provides the dominant background for the A' signal. While positron bremsstrahlung events can be detected and suppressed in Wojtsekhowski's apparatus, the 3[gamma] cross-section has a large cross section in this range, "faking" an A'. We use Monte Carlo numerical integration techniques to calculate the cross sections and obtain reach plots, determining which values of mA' and a' could be discovered at 5[sigma] confidence. This background study can be used to improve the VEPP-3 proposal, and provides a valuable comparison study with the MIT-led DarkLight proposal to search for a dark photon in the same mass range.
The DarkLight experiment is searching for a dark force carrier, the A' boson, and hopes to measure its mass with a resolution of approximately 1 MeV/c 2 . This mass calculation requires precise reconstruction to turn data, in the form of hits within the detector, into a particle track with known initial momentum. This thesis investigates the appropriateness of the Billoir optimal fit to reconstruct helical, low-energy lepton tracks while accounting for multiple scattering, using two separate track parameterizations. The first method approximates the track as a piecewise concatenation of parabolas in three-dimensions, and (wrongly) assumes that the y and z components of the track are independent. When tested using simulated data, this returns a track which geometrically fits the data. However, the momentum extracted from this geometrical representation is an order of magnitude higher than the true momentum of the track. The second method approximates the track as a piecewise concatenation of helical segments. This returns a track which geometrically fits the data even better than the parabolic parameterization, but which returns a momentum which depends on the seeds to the algorithm. Some further work must be done to modify this fitting method so that it will reliably reconstruct tracks.
It's a future of hope and prosperity throughout the known star systems. The Earth Alliance has maintained an uneasy peace with alien races across the galaxy, but even its mighty starfleet can't hold back the raiders who have fought for control of the outer sectors and set their sights closer to the-Terran controlled systems. Commando Inc. was created to tackle those issues in which the Alliance was incapable of dealing with. From their secret base, buried deep within an asteroid, former covert military operative Mark Carson and his team, aboard the sentient starship Pulsar is all that stand between humanity and a never ending darkness. Now, an ancient horror has awoken and found its way into our galaxy. It's a threat that neither the Alliance nor Commando Inc., are prepared to face or comprehend. Planet by planet, the Alliance begins to fall. Friends become enemies as the future of Earth and the entire galaxy are at stake. Time is running out. No one is who they appear to be. The Alliance military is powerless. Mark Carson and his team are Earth's only hope, but how can they defeat an alien horror when they can't even trust their own?
A separate section of the journal, Molecular and developmental evolution, is devoted to experimental approaches to evolution and development.
This volume on Visual Psychophysics documents the current status of research aimed toward understanding the intricacies of the visual mechanism and its laws of operation in intact human perceivers. As can be seen from the list of contributors, the problems of vision engage the interest and experimental ingenuity of investi gators from a variety of disciplines. Thus we find authors affiliated with depart ments of biology, medical and physiological physics, ophthalmology, physics, physiology and anatomy, psychology, laboratories of neurophysiology, medical clinics, schools of optometry, visual and othcr types of research institutes. A continuing interplay between psychophysical studies and physiological work is everywhere evident. As more information about the physiological basis of vision accumulates, and new studies and analyses of receptor photochemistry and the neurophysiology of retina and brain appear, psychophysical studies of the intact organism become more sharply focused, sometimes more complex, and often more specialized. Technological advances have increased the variety and precision of the stimulus controls, and advances in measurement techniques have reopened old problems and stimulated the investigation of new ones. In some cases, new concepts are being drawn in to help further our under standing of the laws by which the visual mechanism operates; in other cases, ideas enunciated long ago have been reevaluated, developed more fully, and reified in terms of converging evidence from both psychophysical experiments and unit recordings from visual cells.