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A Design Report of the Baseline for PEP-X: an Ultra-Low Emittance Storage Ring

Description: Over the past year, we have worked out a baseline design for PEP-X, as an ultra-low emittance storage ring that could reside in the existing 2.2-km PEPII tunnel. The design features a hybrid lattice with double bend achromat (DBA) cells in two arcs and theoretical minimum emittance (TME) cells in the remaining four arcs. Damping wigglers are used to reduce the horizontal emittance to 86 pm-rad at zero current for a 4.5 GeV electron beam. At a design current of 1.5 A, the horizontal emittance increases, due to intrabeam scattering, to 164 pm-rad when the vertical emittance is maintained at a diffraction limited 8 pm-rad. The baseline design will produce photon beams achieving a brightness of 10{sup 22} (ph/s/mm{sup 2}/mrad{sup 2}/0.1% BW) at 10 keV in a 3.5-m conventional planar undulator. Our study shows that an optimized lattice has adequate dynamic aperture, while accommodating a conventional off-axis injection system. In this report, we present the results of study, including the lattice properties, nonlinear dynamics, intra-beam scattering and Touschek lifetime, RF system, and collective instabilities. Finally, we discuss the possibility of partial lasing at soft X-ray wavelengths using a long undulator in a straight section.
Date: June 2, 2010
Creator: Bane, Karl; Bertsche, Kirk; Cai, Yunhai; Chao, Alex; Corbett, Willian; Fox, John et al.
Partner: UNT Libraries Government Documents Department

Studying Gaugino mass in Semi-Direct Gauge Mediation

Description: We study gaugino mass generation in the context of semi-direct gauge mediation models, where the messengers are charged under both the hidden sector and the standard model gauge groups while they do not play important roles in dynamical supersymmetry breaking. We clarify the cancellation of the leading contributions of the supersymmetry breaking effects to the gaugino mass in this class of models in terms of the macroscopic effective theory of the hidden sector dynamics. We also consider how to retrofit the model so that we obtain the non-vanishing leading contribution to the gaugino mass.
Date: June 11, 2010
Creator: Ibe, M.; /SLAC; Izawa, K.-I.; /Kyoto U., Yukawa Inst., Kyoto /Tokyo U., IPMU; Nakai, Y.; /Kyoto U., Yukawa Inst., Kyoto et al.
Partner: UNT Libraries Government Documents Department

Measurement of the Branching Fraction for D8+ rarr tau+nu_tau and Extraction of the Decay Constant f_D_s

Description: The branching fraction for the decay D{sub s}{sup +} {yields} {tau}{sup +}{nu}{sub {tau}} with {tau}{sup +} {yields} e{sup +}{bar {nu}}{sub {tau}}, is measured using a data sample corresponding to an integrated luminosity of 427 fb{sup -1} collected at center of mass energies near 10.58 GeV with the BABAR detector at the PEP-II asymmetric-energy e{sup +}e{sup -} collider at SLAC. In the process e{sup +}e{sup -} {yields} c{bar c} {yields} D*{sub s}{sup +} {bar D}{sub TAG}{bar K}X, the D*{sub s}{sup +} meson is reconstructed as a missing particle, and the subsequent decay D*{sub s}{sup +} {yields} D{sub s}{sup +}{gamma} yields an inclusive D{sub s}{sup +} data sample. Here {bar D}{sub TAG} refers to a fully reconstructed hadronic {bar D} decay, {bar K} is a K{sup -} or {bar K}{sup 0}, and X stands for any number of charged or neutral pions. The decay D{sub s}{sup +} {yields} K{sub S}{sup 0}K{sup +} is isolated also, and from ratio of event yields and known branching fractions, {Beta}(D{sub s}{sup +} {yields} {tau}{sup +}{nu}{sub {tau}}) = (4.5 {+-} 0.5 {+-} 0.4 {+-} 0.3)% is determined. The pseudoscalar decay constant is extracted to be f{sub D{sub s}} = (233 {+-} 13 {+-} 10 {+-} 7) MeV, where the first uncertainty is statistical, the second is systematic, and the third results from the uncertainties on the external measurements used as input to the calculation.
Date: June 4, 2010
Creator: Lees, J.P.; Poireau, V.; Prencipe, E.; Tisserand, V.; /Annecy, LAPP; Garra Tico, J. et al.
Partner: UNT Libraries Government Documents Department

Investigation of novel decay B _____ ____(2S)____K at BaBar

Description: We investigate the undocumented B meson decay, B{sup +} {yields} {Psi}(2S){omega}K{sup +}. The data were collected with the BaBar detector at the SLAC PEP-II asymmetric-energy e{sup +}e{sup -} collier operating at the {gamma}(4S) resonance, a center-of-mass energy of 10.58 GeV/c{sup 2}. The {gamma}(4S) resonance primarily decays to pairs of B-mesons. The BaBar collaboration at the PEP-II ring was located at the SLAC National Accelerator Laboratory and was designed to study the collisions of positrons and electrons. The e{sup -}e{sup +} pairs collide at asymmetric energies, resulting in a center of mass which is traveling at relativistic speeds. The resulting time dilation allows the decaying particles to travel large distances through the detector before undergoing their rapid decays, a process that occurs in the in the center of mass frame over extremely small distances. As they travel through silicon vertex trackers, a drift chamber, a Cerenkov radiation detector and finally an electromagnetic calorimeter, we measure the charge, energy, momentum, and particle identification in order to reconstruct the decays that have occurred. While all well understood mesons currently fall into the qq model, the quark model has no a priori exclusion of higher configuration states such as qqqq which has led experimentalists and theorists alike to seek evidence supporting the existence of such states. Currently, there are hundreds of known decay modes of the B mesons cataloged by the Particle Data Group, but collectively they only account for approximately 60% of the B branching fraction and it is possible that many more exist.
Date: June 22, 2011
Creator: Schalch, Jacob & /SLAC, /Oberlin Coll.
Partner: UNT Libraries Government Documents Department

Diborane Electrode Response in 3D Silicon Sensors for the CMS and ATLAS Experiments

Description: Unusually high leakage currents have been measured in test wafers produced by the manufacturer SINTEF containing 3D pixel silicon sensor chips designed for the ATLAS (A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid) experiments. Previous data has shown the CMS chips as having a lower leakage current after processing than ATLAS chips. Some theories behind the cause of the leakage currents include the dicing process and the usage of copper in bump bonding, and with differences in packaging and handling between the ATLAS and CMS chips causing the disparity between the two. Data taken at SLAC from a SINTEF wafer with electrodes doped with diborane and filled with polysilicon, before dicing, and with indium bumps added contradicts this past data, as ATLAS chips showed a lower leakage current than CMS chips. It also argues against copper in bump bonding and the dicing process as main causes of leakage current as neither were involved on this wafer. However, they still display an extremely high leakage current, with the source mostly unknown. The SINTEF wafer shows completely different behavior than the others, as the FEI3s actually performed better than the CMS chips. Therefore this data argues against the differences in packaging and handling or the intrinsic geometry of the two as a cause in the disparity between the leakage currents of the chips. Even though the leakage current in the FEI3s overall is lower, the current is still significant enough to cause problems. As this wafer was not diced, nor had it any copper added for bump bonding, this data argues against the dicing and bump bonding as causes for leakage current. To compliment this information, more data will be taken on the efficiency of the individual electrodes of the ATLAS and CMS chips on this wafer. The electrodes will be ...
Date: June 22, 2011
Creator: Brown, Emily R. & /SLAC, /Reed Coll.
Partner: UNT Libraries Government Documents Department

The Black Hole in the Throat - Thermodynamics of Strongly Coupled Cascading Gauge Theories

Description: We numerically construct black hole solutions corresponding to the deconfined, chirally symmetric phase of strongly coupled cascading gauge theories at various temperatures. We compute the free energy as a function of the temperature, and we show that it becomes positive below some critical temperature, indicating the possibility of a first order phase transition at which the theory deconfines and restores the chiral symmetry.
Date: June 14, 2007
Creator: Aharony, Ofer; /Weizmann Inst. /Stanford U., ITP /SLAC; Buchel, Alex; Phys., /Western Ontario U. /Perimeter Inst. Theor.; Kerner, Patrick & U., /Western Ontario
Partner: UNT Libraries Government Documents Department

PyDecay/GraphPhys: A Unified Language and Storage System for Particle Decay Process Descriptions

Description: To ease the tasks of Monte Carlo (MC) simulation and event reconstruction (i.e. inferring particle-decay events from experimental data) for long-term BaBar data preservation and analysis, the following software components have been designed: a language ('GraphPhys') for specifying decay processes, common to both simulation and data analysis, allowing arbitrary parameters on particles, decays, and entire processes; an automated visualization tool to show graphically what decays have been specified; and a searchable database storage mechanism for decay specifications. Unlike HepML, a proposed XML standard for HEP metadata, the specification language is designed not for data interchange between computer systems, but rather for direct manipulation by human beings as well as computers. The components are interoperable: the information parsed from files in the specification language can easily be rendered as an image by the visualization package, and conversion between decay representations was implemented. Several proof-of-concept command-line tools were built based on this framework. Applications include building easier and more efficient interfaces to existing analysis tools for current projects (e.g. BaBar/BESII), providing a framework for analyses in future experimental settings (e.g. LHC/SuperB), and outreach programs that involve giving students access to BaBar data and analysis tools to give them a hands-on feel for scientific analysis.
Date: June 22, 2011
Creator: Dunietz, Jesse N. & /SLAC, /MIT
Partner: UNT Libraries Government Documents Department

Parallelizing AT with MatlabMPI

Description: The Accelerator Toolbox (AT) is a high-level collection of tools and scripts specifically oriented toward solving problems dealing with computational accelerator physics. It is integrated into the MATLAB environment, which provides an accessible, intuitive interface for accelerator physicists, allowing researchers to focus the majority of their efforts on simulations and calculations, rather than programming and debugging difficulties. Efforts toward parallelization of AT have been put in place to upgrade its performance to modern standards of computing. We utilized the packages MatlabMPI and pMatlab, which were developed by MIT Lincoln Laboratory, to set up a message-passing environment that could be called within MATLAB, which set up the necessary pre-requisites for multithread processing capabilities. On local quad-core CPUs, we were able to demonstrate processor efficiencies of roughly 95% and speed increases of nearly 380%. By exploiting the efficacy of modern-day parallel computing, we were able to demonstrate incredibly efficient speed increments per processor in AT's beam-tracking functions. Extrapolating from prediction, we can expect to reduce week-long computation runtimes to less than 15 minutes. This is a huge performance improvement and has enormous implications for the future computing power of the accelerator physics group at SSRL. However, one of the downfalls of parringpass is its current lack of transparency; the pMatlab and MatlabMPI packages must first be well-understood by the user before the system can be configured to run the scripts. In addition, the instantiation of argument parameters requires internal modification of the source code. Thus, parringpass, cannot be directly run from the MATLAB command line, which detracts from its flexibility and user-friendliness. Future work in AT's parallelization will focus on development of external functions and scripts that can be called from within MATLAB and configured on multiple nodes, while expending minimal communication overhead with the integrated MATLAB library.
Date: June 22, 2011
Creator: Li, Evan Y. & /SLAC, /Brown U.
Partner: UNT Libraries Government Documents Department

Geometric Transitions, Topological Strings, and Generalized Complex Geometry

Description: Mirror symmetry is one of the most beautiful symmetries in string theory. It helps us very effectively gain insights into non-perturbative worldsheet instanton effects. It was also shown that the study of mirror symmetry for Calabi-Yau flux compactification leads us to the territory of ''Non-Kaehlerity''. In this thesis we demonstrate how to construct a new class of symplectic non-Kaehler and complex non-Kaehler string theory vacua via generalized geometric transitions. The class admits a mirror pairing by construction. From a variety of sources, including super-gravity analysis and KK reduction on SU(3) structure manifolds, we conclude that string theory connects Calabi-Yau spaces to both complex non-Kaehler and symplectic non-Kaehler manifolds and the resulting manifolds lie in generalized complex geometry. We go on to study the topological twisted models on a class of generalized complex geometry, bi-Hermitian geometry, which is the most general target space for (2, 2) world-sheet theory with non-trivial H flux turned on. We show that the usual Kaehler A and B models are generalized in a natural way. Since the gauged supergravity is the low energy effective theory for the compactifications on generalized geometries, we study the fate of flux-induced isometry gauging in N = 2 IIA and heterotic strings under non-perturbative instanton effects. Interestingly, we find we have protection mechanisms preventing the corrections to the hyper moduli spaces. Besides generalized geometries, we also discuss the possibility of new NS-NS fluxes in a new doubled formalism.
Date: June 29, 2007
Creator: Chuang, Wu-yen & /SLAC /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

LSST Charge-Coupled Device Calibration

Description: The prototype charge-coupled device created at the Stanford Linear Accelerator Center for the Large Synoptic Survey Telescope must be tested to check its functionality and performance. It was installed into the Calypso telescope in Arizona in November of 2008 for this purpose. Since then it has taken many images of various astronomical objects. By doing photometry on standard stars in these images, we can compare our magnitude results to the known magnitudes of these stars. This comparison allows us to then determine the chip's performance and functional capabilities. Expecting to see first light in 2016, the Large Synoptic Survey Telescope (LSST) is an extremely large ground based telescope that anticipates funding and will be built in Chile. Described as 'Wide-Fast-Deep', the LSST will have an unprecedented wide field of view (ten square degrees for surveys), short exposures (fifteen to thirty seconds and still see faint objects), and the largest digital camera in the world. One of the goals hoped to be achieved with this camera is the measurement of dark matter using strong and weak gravitational lensing. Gravitational lensing occurs when a large cluster of galaxies distorts the light from a galaxy behind this cluster. This causes an arc of light to form around the cluster. By measuring the length of this arc, one can calculate how much matter should be present in the cluster. Since the amount that should be present is vastly greater than the amount of visible matter that can be seen, it is postulated that the difference between these two numbers is made up of dark matter. This is a direct way of measuring the amount of dark matter in the universe. Thousands of galaxy clusters will be seen with LSST, allowing precise measurements of strong lensing effects. Weak lensing is a much smaller effect, distorting ...
Date: June 22, 2011
Creator: Stout, Tiarra Johannas & /SLAC, /Idaho State U.
Partner: UNT Libraries Government Documents Department

Calculation of the Beam Field in the LCLS Bunch Length Monitor

Description: Maintaining a stable bunch length and peak current is a critical step for the reliable operation of a SASE based x-ray source. In the LCLS, relative bunch length monitors (BLM) right after both bunch compressors are proposed based on the coherent radiation generated by the short electron bunch. Due to its diagnostic setup, the standard far field synchrotron radiation formula and well-developed numerical codes do not apply for the analysis of the BLM performance. In this paper, we develop a calculation procedure to take into account the near field effect, the effect of a short bending magnet, and the diffraction effect of the radiation transport optics. We find the frequency response of the BLM after the first LCLS bunch compressor and discuss its expected performance.
Date: June 7, 2006
Creator: Stupakov, G.; Ding, Y.; Huang, Z. & /SLAC
Partner: UNT Libraries Government Documents Department

Analysis of Femtosecond Timing Noise and Stability in Microwave Components

Description: To probe chemical dynamics, X-ray pump-probe experiments trigger a change in a sample with an optical laser pulse, followed by an X-ray probe. At the Linac Coherent Light Source, LCLS, timing differences between the optical pulse and x-ray probe have been observed with an accuracy as low as 50 femtoseconds. This sets a lower bound on the number of frames one can arrange over a time scale to recreate a 'movie' of the chemical reaction. The timing system is based on phase measurements from signals corresponding to the two laser pulses; these measurements are done by using a double-balanced mixer for detection. To increase the accuracy of the system, this paper studies parameters affecting phase detection systems based on mixers, such as signal input power, noise levels, temperature drift, and the effect these parameters have on components such as the mixers, splitters, amplifiers, and phase shifters. Noise data taken with a spectrum analyzer show that splitters based on ferrite cores perform with less noise than strip-line splitters. The data also shows that noise in specific mixers does not correspond with the changes in sensitivity per input power level. Temperature drift is seen to exist on a scale between 1 and 27 fs/{sup o}C for all of the components tested. Results show that any components using more metallic conductor tend to exhibit more noise as well as more temperature drift. The scale of these effects is large enough that specific care should be given when choosing components and designing the housing of high precision microwave mixing systems for use in detection systems such as the LCLS. With these improvements, the timing accuracy can be improved to lower than currently possible.
Date: June 22, 2011
Creator: Whalen, Michael R. & /SLAC, /Stevens Tech.
Partner: UNT Libraries Government Documents Department

Axions in String Theory

Description: In the context of string theory, axions appear to provide the most plausible solution of the strong CP problem. However, as has been known for a long time, in many string-based models, the axion coupling parameter Fa is several orders of magnitude higher than the standard cosmological bounds. We re-examine this problem in a variety of models, showing that Fa is close to the GUT scale or above in many models that have GUT-like phenomenology, as well as some that do not. On the other hand, in some models with Standard Model gauge fields supported on vanishing cycles, it is possible for Fa to be well below the GUT scale.
Date: June 9, 2006
Creator: Svrcek, Peter; /Stanford U., Phys. Dept. /SLAC; Witten, Edward & /Princeton, Inst. Advanced Study
Partner: UNT Libraries Government Documents Department

Analysis of the Cause of High External Q Modes in the JLab High Gradient Prototype Cryomodule Renascence

Description: The Renascence cryomodule [1] installed in CEBAF in 2007 consists of 8 cavities as shown in Figure 1. The first three cavities (No.1-No.3) in the upstream end are of the Low Loss (LL) shape design, and the remaining 5 cavities (No.4-No.8) on the beam downstream end are the High Gradient (HG) shape design. The fundamental power couplers (FPCs) are the rectangular waveguides, and the little cylindrical structures are the HOM couplers. The locations of the FPC in the last four cavities are mirrored about the beam z axis. Cavities No.4 and No.5 form a back-to-back cavity pair. Among the HG cavities installed in the Renascence cryomodule, the only identifiable difference from their fabrication documentation is that cavity No.5 received an extra EBW pass on one equator weld, specifically cell 5. The non-uniform mechanical tuning required to compensate the fundamental mode tune and flatness for the extra shrinkage of this cell is believed to contribute the most significant differences from the other HG cavities. Beam based instability studies on this cryomodule in CEBAF have shown a significant beam breakup (BBU) threshold current reduction, well below design value. Frequency spectrum peaked by the off-sided beam power indicated the cause is due to abnormal high Q modes in the cavity No.5. Measured beam off-axis position at the cavity No.5 does not correspond to the shunt impedances calculated for an ideal cavity. Low power RF measurements have identified that the problematic modes are in the second dipole band (TM110 like). Three of the modes have external Qs two orders magnitude higher than the others, while the rest of modes in the first two dipole bands are normal in terms of the design values. The cause of this abnormality and the future impact on the BBU was not able to be resolved due to the ...
Date: June 27, 2008
Creator: Li, Z.; Akcelik, V.; Xiao, L.; Lee, L.; Ng, C.; Ko, K. et al.
Partner: UNT Libraries Government Documents Department

Stopping Gluinos

Description: Long lived gluinos are the trademark of split susy. They form R-hadrons that, when charged, efficiently lose energy in matter via ionization. Independent of R-spectroscopy and initial hadronization, a fraction of R-hadrons become charged while traversing a detector. This results in a large number of stopped gluinos at present and future detectors. For a 300 GeV gluino, 10{sup 6} will stop each year in LHC detectors, while several hundred stop in detectors during Run II at the Tevatron. The subsequent decays of stopped gluinos produce distinctive depositions of energy in calorimeters with no activity in either the tracker or the muon chamber.
Date: June 29, 2005
Creator: Arvanitaki, A.; Dimopoulos, S.; /Stanford U., Phys. Dept.; Pierce, A.; /SLAC /Stanford U., Phys. Dept.; Rajendran, S. et al.
Partner: UNT Libraries Government Documents Department

Sweet Spot Supersymmetry

Description: We find that there is no supersymmetric flavor/CP problem, {mu}-problem, cosmological moduli/gravitino problem or dimension four/five proton decay problem in a class of supersymmetric theories with O(1) GeV gravitino mass. The cosmic abundance of the nonthermally produced gravitinos naturally explains the dark matter component of the universe. A mild hierarchy between the mass scale of supersymmetric particles and electroweak scale is predicted, consistent with the null result of a search for the Higgs boson at the LEP-II experiments. A relation to the strong CP problem is addressed. We propose a parametrization of the model for the purpose of collider studies. The scalar tau lepton is the next to lightest supersymmetric particle in a theoretically favored region of the parameter space. The lifetime of the scalar tau is of O(1000) seconds with which it is regarded as a charged stable particle in collider experiments. We discuss characteristic signatures and a strategy for confirmation of this class of theories at the LHC experiments.
Date: June 6, 2007
Creator: Ibe, Masahiro; Kitano, Ryuichiro & /SLAC /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

Realistic Two-body Interactions in Many-nucleon Systems: Correlated Motion beyond Single-particle Behavior

Description: In the framework of the theory of spectral distributions we perform an overall comparison of three modern realistic interactions, CD-Bonn, CD-Bonn+3terms, and GXPF1 in a broad range of nuclei in the upper fp shell and study their ability to account for the development of isovector pairing correlations and collective rotational motion in many-particle nuclear systems. Our findings reveal a close similarity between CD-Bonn and CD-Bonn+3terms, while both interactions possess features different from the ones of GXPF1. The GXPF1 interaction is used to determine the strength parameter of a quadrupole term that augments an isovector-pairing model interaction with Sp(4) dynamical symmetry, which in turn is shown to yield a reasonable agreement with the experimental low-lying energy spectra of {sup 58}Ni and {sup 58}Cu.
Date: June 27, 2006
Creator: Sviratcheva, K.D.; Draayer, J.P. & /Louisiana State U. /Iowa State U. /LLNL, Livermore /SLAC
Partner: UNT Libraries Government Documents Department

Comparative Study of Various Algorithms for the Merging of Parton Showers and Matrix Elements in Hadronic Collisions

Description: We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW and MLM schemes using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.
Date: June 27, 2007
Creator: Alwall, J.; Hoche, S.; Krauss, F.; Lavesson, N.; Lonnblad, L.; Maltoni, F. et al.
Partner: UNT Libraries Government Documents Department

Comparing the Calibration and Simulation Data of the Cryogenic Dark Matter Search

Description: The Cryogenic Dark Matter Search, or CDMS, collaboration is preparing a new experiment called SuperCDMS. CDMS uses Germanium detectors to attempt the direct detection of dark matter. To do this, they measure the ionization and heat produced during an event where a WIMP scatters off of germanium crystal lattice. To prepare for the experiment the detectors are calibrated with various radioactive sources. The response of the detectors is also modeled by a Monte Carlo simulation. These simulations include modeling everything from the radiation production to the raw data collected by the detector. The experimental data will be used to validate the results of the detector simulation. This research will look only at the phonons produced during events that occur very close to the detector surface. From the raw data and simulation output three parameters will be determined: the rise time, the decay time, and time to position independence. It was found that the simulation's risetime and time to position independence was generally smaller than that of the data, while the decay time was found to be larger in the simulation than in the data. These differences show that the simulation is not complete. The difference in risetime implies that the phonons are not spread out enough when they reach the detector walls, which would be improved by a look at the Luke phonon and charge transport. The long decay time in the simulation implies that the rate phonons are being absorbed is underestimated. Finally, the small time to position independence in the simulation could be due to a low phonon scattering rate. A simple solution may be to alter the parameters that control the simulation, while still remaining physically sensible, to help match simulation and data.
Date: June 22, 2011
Creator: DiFranzo, Anthony & /SLAC, /Rensselaer Poly.
Partner: UNT Libraries Government Documents Department

Calibration Analyses and Efficiency Studies for the Anti Coincidence Detector on the Fermi Gamma Ray Space Telescope

Description: The Anti Coincidence Detector (ACD) on the Fermi Gamma Ray Space Telescope provides charged particle rejection for the Large Area Telescope (LAT). We use two calibrations used by the ACD to conduct three studies on the performance of the ACD. We examine the trending of the calibrations to search for damage and find a timescale over which the calibrations can be considered reliable. We also calculated the number of photoelectrons counted by a PMT on the ACD from a normal proton. Third, we calculated the veto efficiencies of the ACD for two different veto settings. The trends of the calibrations exhibited no signs of damage, and indicated timescales of reliability for the calibrations of one to two years. The number of photoelectrons calculated ranged from 5 to 25. Large errors in the effect of the energy spectrum of the charged particles caused these values to have very large errors of around 60 percent. Finally, the veto efficiencies were found to be very high at both veto values, both for charged particles and for the lower energy backsplash spectrum. The Anti Coincidence Detector (ACD) on the Fermi Gamma Ray Space Telescope is a detector system built around the silicon strip tracker on the Large Area Telescope (LAT). The purpose of the ACD is to provide charged particle rejection for the LAT. To do this, the ACD must be calibrated correctly in flight, and must be able to efficiently veto charged particle events while minimizing false vetoes due to 'backsplash' from photons in the calorimeter. There are eleven calibrations used by the ACD. In this paper, we discuss the use of two of these calibrations to preform three studies on the performance of the ACD. The first study examines trending of the calibrations to check for possible hardware degradation. The second study ...
Date: June 22, 2011
Creator: Kachulis, Chris & /SLAC, /Yale U.
Partner: UNT Libraries Government Documents Department

Supersymmetry with Small mu: Connections between Naturalness, Dark Matter, and (Possibly) Flavor

Description: Weak scale supersymmetric theories often suffer from several naturalness problems: the problems of reproducing the correct scale for electroweak symmetry breaking, the correct abundance for dark matter, and small rates for flavor violating processes. We argue that the first two problems point to particular regions of parameter space in models with weak scale supersymmetry: those with a small {mu} term. This has an interesting implication on direct dark matter detection experiments. We find that, if the signs of the three gaugino mass parameters are all equal, we can obtain a solid lower bound on the spin-independent neutralino-nucleon cross section, {sigma}{sub SI}. In the case that the gaugino masses satisfy the unified mass relations, we obtain {sigma}{sub SI} {approx}> 4 x 10{sup -46} cm{sup 2} (1 x 10{sup -46} cm{sup 2}) for fine-tuning in electroweak symmetry breaking no worse than 10% (5%). We also discuss a possibility that the three problems listed above are all connected to the hierarchy of fermion masses. This occurs if supersymmetry breaking and electroweak symmetry breaking (the Higgs fields) are coupled to matter fields with similar hierarchical structures. The discovery of {mu} {yields} e transition processes in near future experiments is predicted in such a framework.
Date: June 28, 2006
Creator: Kitano, Ryuichiro; /SLAC; Nomura, Yasunori & /UC, Berkeley /LBL, Berkeley
Partner: UNT Libraries Government Documents Department

Superpotentials for Quiver Gauge Theories

Description: We compute superpotentials for quiver gauge theories arising from marginal D-Brane decay on collapsed del Pezzo cycles S in a Calabi-Yau X. This is done using the machinery of A{sub {infinity}} products in the derived category of coherent sheaves of X, which in turn is related to the derived category of S and quiver path algebras. We confirm that the superpotential is what one might have guessed from analyzing the moduli space, i.e., it is linear in the fields corresponding to the Exts of the quiver and that each such Ext multiplies a polynomial in Exts equal to precisely the relation represented by the Ext.
Date: June 10, 2005
Creator: Aspinwall, Paul S.; /Stanford U., Phys. Dept. /SLAC /Duke U., CGTP; Fidkowski, Lukasz M. & /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

Clicks versus Citations: Click Count as a Metric in High Energy Physics Publishing

Description: High-energy physicists worldwide rely on online resources such as SPIRES and arXiv to perform gather research and share their own publications. SPIRES is a tool designed to search the literature within high-energy physics, while arXiv provides the actual full-text documents of this literature. In high-energy physics, papers are often ranked according to the number of citations they acquire - meaning the number of times a later paper references the original. This paper investigates the correlation between the number of times a paper is clicked in order to be downloaded and the number of citations it receives following the click. It explores how physicists truly read what they cite.
Date: June 22, 2011
Creator: Bitton, Ayelet & /UC, San Diego /SLAC
Partner: UNT Libraries Government Documents Department

Knot Undulator to Generate Linearly Polarized Photons with Low on-Axis Power Density

Description: Heat load on beamline optics is a serious problem to generate pure linearly polarized photons in the third generation synchrotron radiation facilities. For permanent magnet undulators, this problem can be overcome by a figure-8 operating mode. But there is still no good method to tackle this problem for electromagnetic elliptical undulators. Here, a novel operating mode is suggested, which can generate pure linearly polarized photons with very low on-axis heat load. Also the available minimum photon energy of linearly polarized photons can be extended much by this method.
Date: June 19, 2009
Creator: Qiao, S.; /Stanford U., Appl. Phys. Dept. /SLAC, SSRL /LBNL, ALS /Fudan U.; Ma, De-wei; Feng, Dong-lai; U., /Fudan; Hussain, Z. et al.
Partner: UNT Libraries Government Documents Department