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Single Bunch Stability to Monopole Excitation

Description: We study single bunch stability with respect to monopole longitudinal oscillations in electron storage rings. Our analysis is different from the standard approach based on the linearized Vlasov equation. Rather, we reduce the full nonlinear Fokker-Planck equation to a Schroedinger-like equation which is subsequently analyzed by perturbation theory. We show that the Haissinski solution [3] may become unstable with respect to monopole oscillations and derive a stability criterion in terms of the ring impedance. We then discuss this criterion and apply it to a broad band resonator impedance model.
Date: January 19, 1999
Creator: Podobedov, Boris
Partner: UNT Libraries Government Documents Department


Description: The design status and R and D plan of a 1.5 Angstrom SASE-FEL at SLAC, called the Linac Coherent Light Source (LCLS), are described. The LCLS utilizes one third of the SLAC linac for the acceleration of electrons to about 15 GeV. The FEL radiation is produced in a long undulator and is directed to an experimental area for its utilization. The LCLS is designed to produce 300 fsec long radiation pulses at the wavelength of 1.5 Angstrom with 9 GW peak power. This radiation has much higher brightness and coherence, as well as shorter pulses, than present 3rd generation sources. It is shown that such leap in performance is now within reach, and is made possible by the advances in the physics and technology of photo-injectors, linear accelerators, insertion devices and free-electron lasers.
Date: February 9, 1999
Creator: Cornacchia, Massimo
Partner: UNT Libraries Government Documents Department

Superlattice Photocathodes for Accelerator-Based Polarized Electron Source Applications

Description: A major improvement in the performance of the SLC was achieved with the introduction of thin strained-layer semiconductor crystals. After some optimization, polarizations of 75-85% became standard with lifetimes that were equal to or better than that of thick unstrained crystals. Other accelerators of polarized electrons, generally operating with a much higher duty factor, have now successfully utilized similar photocathodes. For future colliders, the principal remaining problem is the limit on the total charge that can be extracted in a time scale of 10 to 100 ns. In addition, higher polarization is critical for exploring new physics, especially supersymmetry. However, it appears that strained-layer crystals have reached the limit of their optimization. Today strained superlattice crystals are the most promising candidates for better performance. The individual layers of the superlattice can be designed to be below the critical thickness for strain relaxation, thus in principle improving the polarization. Thin layers also promote high electron conduction to the surface. In addition the potential barriers at the surface for both emission of conduction-band electrons to vacuum and for tunneling of valence-band holes to the surface can be significantly less than for single strained-layer crystals, thus enhancing both the yield at any intensity and also decreasing the limitations on the total charge. The inviting properties of the recently developed AlInGaAs/GaAs strained superlattice with minimal barriers in the conduction band are discussed in detail.
Date: March 22, 1999
Creator: Clendenin, James E
Partner: UNT Libraries Government Documents Department

High-power vacuum window in WR10

Description: Results are presented for fabrication and test of a WR10 waveguide window, for use in ultra-high vacuum at 91.4 GHz. Low-power bench measurements are compared with analytic and simulation results. Operation at approximately equal to 4-kW peak power, duty factor 10{sup {minus}6} and 10{sup {minus}9}-scale vacuum is noted.
Date: June 28, 1999
Creator: Hill, Marc E
Partner: UNT Libraries Government Documents Department

Recent QCD Results from SLD

Description: We present selected results on strong interaction physics from the SLD experiment at the SLAC Linear Collider. We report on several new studies of 3- and 4-jet hadronic Z{sup 0} decays, in which jets are identified as quark, antiquark or gluon. The 3-jet Z{sup 0} --> b anti-bg rate is sensitive to the b-quark mass; prospects for measuring m{sub b} are discussed. The gluon energy spectrum is measured over the full kinematic range, providing an improved test of QCD and limits on anomalous b anti-bg couplings. The parity violation in Z{sup 0} --> b anti-bg decays is consistent with electroweak theory plus QCD. New tests of T- and CP-conservation at the bbg vertex are performed. A new measurement of the rate of gluon splitting into b anti-b pairs yields g{sub b anti-b} = 0.0031 {+-} 0.0007 (stat.){+-} 0.0006 (syst.) (Preliminary). We also present a number of new results on jet fragmentation into identified hadrons. The B hadron energy spectrum is measured over the full kinematic range using a new, inclusive technique, allowing stringent tests of predictions for its shape and a precise measurement of (xB) = 0.714 {+-} 0.005(stat.) {+-} 0.007(syst.) (Preliminary). A detailed study of correlations in rapidity y between pairs of identified pi{sup {+-}}, K{sup {+-}} and p/anti-p confirms that strangeness and baryon number are conserved locally, and shows local charge conservation between meson-baryon and strange-nonstrange pairs. Flavor-dependent long-range correlations are observed for all combinations of these hadron species, yielding new information on leading particle production. The first study of correlations using rapidities signed such that y > 0 corresponds to the quark direction provides additional new insights into fragmentation, including the first direct observation of baryon number ordering along the q anti-q axis.
Date: September 27, 1999
Creator: Muller, David
Partner: UNT Libraries Government Documents Department

Measurement of subpicosecond electron bunch lengths

Description: A new frequency-resolved bunch-length measuring system has been developed at the Stanford SUNSHINE facility suitable for subpicosecond electron bunches. This method utilizes a far-infrared Michelson interferometer to measure coherent transition radiation emitted from electron bunches through optical auto-correlation. A simple and systematic way has also been developed to include interference effects caused by the beam splitter, so the electron bunch length can be easily obtained from the measurement. This autocorrelation method demonstrates subpicosecond resolving power that cannot be achieved by existing time-resolved methods.
Date: November 1, 1995
Creator: Lihn, Hung-chi; Bocek, D.; Kung, P.; Settakorn, C. & Wiedemann, H.
Partner: UNT Libraries Government Documents Department

1997 Annual Site Environmental Report (ASER)

Description: The SLAC program centers around experimental and theoretical research in elementary particle physics using accelerated electron beams and a broad program of research in atoms and solid-state physics, chemistry, and biology using synchrotron radiation from accelerated electron beams. There is also an active program in the development of accelerators, detectors, and new sources and instrumentation for synchrotron radiation research. The main instrument of research is the 3.2-km linear accelerator (linac) that generates high intensity beams of electrons and positrons up to 50 GeV, which are among the highest energy electron and positron beams available in the world. The linac is also used for injecting electrons and positrons into colliding-beam storage rings for particle physics research. The Positron-Electron Project (PEP) storage ring is about 800 meters in diameter. The PEP program was completed several years ago. PEP is now being upgraded to serve as an Asymmetric B Factory (or PEP-II) that will study the B meson. PEP-II will make use of much of PEP's existing equipment and infrastructure, and is scheduled for completion in 1998. A smaller storage ring, the Stanford Positron-Electron Asymmetric Ring (SPEAR) has its own smaller linac and a booster ring for injecting accelerated beams of electrons. SPEAR is fully dedicated to synchrotron radiation research. The synchrotron light generated by the SPEAR storage ring is used by the Stanford Synchrotron Radiation Laboratory (SSRL) to perform experiments. Scientists from all parts of the United States and from throughout the world participate in the experimental programs at SLAC.
Date: October 1, 1998
Creator: Holden, Gene
Partner: UNT Libraries Government Documents Department

CP Violation and B Physics

Description: This is a quick review of CP non-conservation in B physics. Several methods are described for testing the Kobayashi-Maskawa single phase origin of CP violation in B decays, pointing out some limitations due to hadronic uncertainties. A few characteristic signatures of new physics in B decay asymmetries are listed.
Date: August 17, 1999
Creator: Gronau, Michael
Partner: UNT Libraries Government Documents Department

Including Internal Losses In The Equivalent Circuit Model Of The SLAC Damped Detuned Structure (DDS)

Description: In the equivalent circuit model for the DDS originally presented no losses were explicitly included in the cell circuits or the manifold circuits. Damping via the manifolds was effected by imposing matching conditions (including the possibility of reflection) on the ends of the manifolds. In this paper we extend the circuit theory to include lossy circuit elements. We discuss and compare shunt conductance and series resistance models for the cells. Manifold damping is modeled by introducing a shunt conductance per unit length in the transmission line elements of the manifolds. We apply the theory to the mitigation of performance degradation associated with fabricationally desirable decoupling of several cells at the ends of the structure from the manifolds.
Date: April 1, 1999
Creator: Jones, Roger M
Partner: UNT Libraries Government Documents Department

Low alpha experiments at the ALS

Description: The authors present a modified, low alpha lattice for the Advanced Light Source where the quadrupole field strengths have been detuned to allow the momentum compaction factor to be varied smoothly from positive to negative values. With this low alpha lattice the authors decrease the momentum compaction factor by a factor of 5 to 0.0003 over normal operation resulting in a measured bunch length reduction of 2. They also measure the size the second order momentum compaction factor as well as store beam in a negative momentum compaction lattice. Streak camera measurements at positive and negative momentum compaction operation show longitudinal beam profile distributions that are in agreement with simulations by Fang et al.
Date: August 1, 1995
Creator: Robin, D.; Alvis, R.; Jackson, A.; Holtzapple, R. & Podobedov, B.
Partner: UNT Libraries Government Documents Department

Supersymmetric Higgs Pair Production at Hadron Colliders

Description: We study the pair production of neutral Higgs bosons through gluon fusion at hadron colliders in the framework of the Minimal Supersymmetric Standard Model. We present analytical expressions for the relevant amplitudes, including both quark and squark loop contributions, and allowing for mixing between the superpartners of left- and right-handed quarks. Squark loop contributions can increase the cross section for the production of two CP--even Higgs bosons by more than two orders of magnitude, if the relevant trilinear soft breaking parameter is large and the mass of the lighter squark eigenstate is not too far above its current lower bound. In the region of large tan{beta}, neutral Higgs boson pair production might even be observable in the 4b final state during the next run of the Tevatron collider.
Date: May 12, 1999
Creator: Mizukoshi, Jose
Partner: UNT Libraries Government Documents Department

Supersymmetric Higgs Boson Pair Production: Discovery Prospects at Hadron Colliders

Description: We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the Minimal Supersymmetric Standard Model. We perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is re-emphasized. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.
Date: September 15, 1999
Creator: Mizukoahi, Jose K.
Partner: UNT Libraries Government Documents Department

Perspectives on Epic Physics

Description: An electron-proton/ion polarized beam collider (EPIC) with high luminosity and center of mass energy square root s = 25 GeV would be a valuable facility for fundamental studies of proton and nuclear structure and tests of quantum chromodynamics, I review a sample of prospective EPIC topics, particularly semi-exclusive reactions, studies of the proton fragmentation region, heavy quark electroproduction, and a new probe of odderon/pomeron interference.
Date: July 14, 1999
Creator: Brodsky, Stanley J.
Partner: UNT Libraries Government Documents Department

Measurement of the running b-quark Mass using e{sup +}e{sup -} {yields} b{bar b}g events

Description: We have studied the determination of the running b-quark mass, m{sub b}(M{sub Z}), using Z{sup 0} decays into 3 or more hadronic jets. We calculated the ratio of {ge} 3-jet fractions in e{sup +}e{sup -} {yields} b{bar b} vs. e{sup +}e{sup -} {yields} q{sub l}{bar q}{sub l} (q{sub l} = u or d or s) events at next-to-leading order in perturbative QCD using six different infra-red- and collinear-safe jet-finding algorithms. We compared with corresponding measurements from the SLD Collaboration and found a significant algorithm-dependence of the fitted m{sub b}(M{sub Z}) value. Our best estimate, taking correlations into account, is m{sub b}(M{sub Z}) = 2.52 {+-} 0.27(stat.){sub -0.47}{sup +0.33}(syst.){sub -1.46}{sup +0.54}(theor.) GeV/c{sup 2}.
Date: June 2, 1999
Creator: Burrows, Phil
Partner: UNT Libraries Government Documents Department

Hadronic Charmless B Decays at the SLD

Description: Rare decays of beauty particles were studied in several two-body exclusive hadronic charmless modes using the 19.4 pb<sup>-1</sup> Z-pole data collected with the SLD detector at SLAC from 1993 to 1998. These decays are mediated by both tree level b {yields} u and one-loop penguin b {yields} s, d transitions. Upper limits for the branching ratios are set for the investigated modes B<sub>s</sub>, B<sub>0</sub> {yields} P<sup>+</sup>P<sup>-</sup>, B<sup>+</sup> {yields} V P<sup>+</sup> and B<sub>s</sub>, B<sup>0</sup> {yields} V V , where the pseudoscalar particle P<sup>+</sup> is either {pi}<sup>+</sup> or K<sup>+</sup> and the vector particle V is either {rho}<sup>0</sup>, K<sup>* 0</sup> or {phi}. Using an event selection algorithm consisting of a set of hard cuts combined with a set of discriminator functions, the efficiencies range between 24% and 37% with near zero background.
Date: September 2, 1999
Creator: Reinertsen, Per L
Partner: UNT Libraries Government Documents Department

Polarization Asymmetries in gamma e Collisions and Triple Gauge Boson Couplings Revisited

Description: The capability of the NLC run in the {gamma}e collision mode to probe the CP-conserving {gamma}WW and {gamma}ZZ anomalous couplings through the use of the polarization asymmetry is reviewed. When combined with other measurements, very strong constraints on both varieties of anomalous couplings can be obtained. We show that these bounds are complementary to those that can be extracted from data taken at the LHC.
Date: July 16, 1999
Creator: Rizzo, Thomas G.
Partner: UNT Libraries Government Documents Department

Direct Measurement of A{sub b} using Charged Kaons at the SLD Detector

Description: We report a new measurement of A{sub b} using data obtained by SLD in 1997-98. This measurement uses a vertex tag technique, where the selection of a b hemisphere is based on the reconstructed mass of the bottom hadron decay vertex. The method uses the 3D vertexing capabilities of SLD's CCD vertex detector and the small and stable SLC beams to obtain a high b-event tagging efficiency and purity of 78% and 97%, respectively. Charged kaons identified by the CRID detector provide an efficient quark-antiquark tag, with the analyzing power calibrated from the data. We obtain a preliminary result of A{sub b} = 0.997 {+-} 0.044 {+-} 0.067.
Date: July 29, 1999
Creator: Wright, Thomas R
Partner: UNT Libraries Government Documents Department

Impedance study for the PEP-II B-factory

Description: The paper summarizes results of the impedance studies of the components of the B-factory. The prime goal of this activity was to support the design of the vacuum chamber and, at the same time, to get a reasonable model of the machine impedance, which can be used later for detail studies of collective effects.
Date: June 1, 1995
Creator: Heifets, S.; Daly, C.E. & Ko, K.
Partner: UNT Libraries Government Documents Department

KEK ATF Injector Upgrade

Description: The main goal at the Accelerator Test Facility (ATF) at the KEK laboratory in Japan is to develop the technology that can stably supply the main linac with an extremely flat multi-bunch beam. The injector for this accelerator was upgraded to produce greater than 2 x 10{sup 10} in electrons a single bunch at 80 MeV in a very narrow bunch.
Date: March 24, 1999
Creator: Yeremian, anahid D
Partner: UNT Libraries Government Documents Department

Science and Paranormal Phenomena

Description: In order to ground my approach to the study of paranormal phenomena, I first explain my operational approach to physics, and to the ''historical'' sciences of cosmic, biological, human, social and political evolution. I then indicate why I believe that ''paranormal phenomena'' might-but need not- fit into this framework. I endorse the need for a new theoretical framework for the investigation of this field presented by Etter and Shoup at this meeting. I close with a short discussion of Ted Bastin's contention that paranormal phenomena should be defined as contradicting physics.
Date: June 3, 1999
Creator: Noyes, H. Pierre
Partner: UNT Libraries Government Documents Department

Computation of Nonlinear One-Turn Maps from Measurement with Model-Independent Analysis

Description: It is desirable to determine the nonlinear transformation maps, especially the one-turn map, of a storage ring from measured BPM data for nonlinear analysis in order to improve the machine performance. However, the accuracy of detecting the weak signals from nonlinear effects is often limited by the available BPM resolution. With the recent development of Model-Independent Analysis methods, which can significantly reduce BPM random noise via statistical analysis, it is possible to more accurately determine the nonlinear maps from measured data by using a large number of BPMs. Computational techniques and some simulation results for PEP-II will be presented.
Date: April 12, 1999
Creator: Wang, Chunxi
Partner: UNT Libraries Government Documents Department

Beam-Based Solenoid Compensation for the PEP-II

Description: Commissioning the compensation system of the solenoid in the BaBar detector presents a challenging problem due to the complexity of the system, which uses twelve normal quadrupoles and twelve skew quadrupoles in each ring. The setting of these skew quadrupoles needs to be readjusted according to the machine optical parameters since the machines always have some unknown errors. In this paper, we will describe a beam based method to match the coupling and optics in the interaction region to compensate for the optical effects due to the solenoid. The method has been successfully used to find the wrong polarities and the wrong scaling factor of the skew quadrupoles in the early stage of the commissioning. It is being refined to set the skew quadrupoles in the machines in order to reduce the beam size at the interaction point and improve the luminosity of PEP-II.
Date: August 26, 1999
Creator: Cai, Yunhai
Partner: UNT Libraries Government Documents Department

Physics and Government

Description: In defining the powers and duties of the three branches of government, the U.S. Constitution never explicitly referred to Science, except in the patent clause. But many technical responsibilities are implied in references to weights and measures, the census, and the like. Thomas Jefferson, John Adams, and in particular Benjamin Franklin, were highly literate in science, but it was their disciple, President John Quincy Adams who promoted as a matter of policy a direct role of the government in science--in particular with respect to astronomy, land surveys and navigation--all physical sciences. Some agencies of government--notably the National Bureau of Standards and the Department of Agriculture were founded in the early days of the Republic with scientific and technical missions. Since then the involvement of the government with science has waxed and waned but the major expansion of the interaction between physics and government occurred after World War II when physicists demonstrated the power of their craft during mobilization of science in support of the war effort. In discussing the interaction of physics with government we should distinguish ''science in government''--scientific input into policy making--from ''government in science,'' which is the support and management of that part of the overall scientific endeavor for which the government has responsibility. Let me turn first to the subject of physics in government. An overwhelming fraction of governmental decisions today have scientific and technical components; decisions ignoring these components are wasteful at best and can imperil the nation. For this reason governmental bodies at all levels solicit scientific advice--or at least give lip service to the need for such advice. When such advice was deliberately avoided, as President Reagan did before announcing his Strategic Defense Initiative in March 1983, the technically unattainable goal ''to make nuclear weapons impotent and obsolete'' was proclaimed.
Date: August 24, 1999
Creator: Hendry, Nancy H.
Partner: UNT Libraries Government Documents Department

Spin Structure Functions g{sub 1} and g{sub 2} for the Proton and Deuteron

Description: The experiment E155 at SLAC measured the spin structure functions g{sub 1} and g{sub 2} of the proton and deuteron. The experiment used deep inelastic scattering of 48.3 GeV longitudinally polarized electrons incident on polarized solid {sup 15}NH{sub 3} and {sup 6}LiD targets. The data taken by three independent spectrometers covered a kinematic range of 0.014 &lt; x &lt; 0.9 and 1 (GeV/c){sup 2} &lt; Q{sup 2} &lt; 40 (GeV/c){sup 2}. Due to the high luminosity and polarization available at SLAC the data on g{sub 1} are to date the most precise in this kinematic range. The x and Q{sup 2} dependence of g{sub 1} has been studied using NLO PQCD fits, allowing extraction of values for the Bjorken sum rule and quark and gluon spin contributions to the nucleon. Results are presented for g{sub 1} and g{sub 2} for the proton and deuteron.
Date: April 7, 1999
Creator: Mitchell, Gregory
Partner: UNT Libraries Government Documents Department