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Why e{superscript +}e{superscript -} {yields} t tbar is Different

Description: Unlike other examples of fermion pair production in e{sup +}e{sup -} collisions, we show that top-quark pairs are produced in an essentially unique spin configuration in polarized e{sup +}e{sup -} colliders at all energies. Since the directions of the electroweak decay products of polarized top-quarks are strongly correlated to the top-quark spin axis, this unique spin configuration leads to a distinctive topology for top-quark pair events which can be used to constrain anomalous couplings to the top-quark. A significant interference effect between the longitudinal and transverse W-bosons in the decay of polarized top-quarks is also discussed.
Date: February 18, 1999
Creator: Parke, Stephen
Partner: UNT Libraries Government Documents Department

An improved limit on jet handedness in Z{sup 0} decays

Description: We present the results of an improved search for jet handedness in hadronic decays of Z{sup degree} bosons collected by the SLD experiment at SLAC. Quark and antiquark jets, expected to be oppositely polarized in Z{sup degree} decays, were separated using the large forward-backward quark asymmetry induced by the highly polarized SLC electron beam. The larger data sample and beam polarization of the 1994/5 SLC/SLD run yield a factor of two improvement in our sensitivity to jet handedness. Assuming Standard Model values of quark polarizations we set an improved upper limit on the analyzing power of the handedness method.
Date: July 1995
Creator: Collaboration, The SLD
Partner: UNT Libraries Government Documents Department

Probing quartic couplings through three gauge boson production at an e{sup +}e{sup {minus}} linear collider

Description: We explore the capability of a 500 or 1000 GeV e{sup +} e{sup {minus}} linear collider to measure anomalous quartic gauge boson couplings. In the framework of a non-linear effective Lagrangian with a custodial SU(2) symmetry, there are only two next-to-leading order operators which contribute to quartic, but not to two- and three-gauge boson interactions. The limits on the coefficients of these operators from present and future e{sup +} e{sup {minus}} colliders are compared with those available from other sources.
Date: November 22, 1996
Creator: Dawson, S.; Likhoded, A.; Valencia, G. & Yushchenko, O.
Partner: UNT Libraries Government Documents Department

Studies of multiparticle production in hadronic Z{sup 0} decays

Description: Hadronic decays of Z{sup 0} bosons produced in e{sup +}e{sup {minus}} annihilation are ideal for testing QCD. This thesis presents a measurement of the charged-particle multiplicity distribution and the first experimental study of the ratio of cumulant to factorial moments, using hadronic Z{sup 0} decays collected by the SLD experiment at SLAC. The author finds that this ratio, as a function of the moment-rank q, decreases sharply to a negative minimum at q = 5, which is followed by quasi-oscillations. These features are in qualitative agreement with expectations from higher-order perturbative QCD. The author also presents an analysis of the intermittency in rapidity phase space using the method of scaled factorial moments. It is found that both parton cascade and hard-gluon radiations contribute to the growth of the moments by studying the event-shape and jet-topology dependencies. All aspects of the data appear to be reproduced reasonably well by the QCD-based Monte Carlo model.
Date: December 1, 1996
Creator: Zhou, Jingchen
Partner: UNT Libraries Government Documents Department

Issues and state of the art for short bunches in e{sup +}/e{sup {minus}} storage rings

Description: The potential of e{sup +}/e{sup {minus}} storage rings for producing short bunches is reviewed. We begin with a review of existing storage rings and proceed to discuss possible future developments. The effects which limit the production of short bunches in a ring are also discussed. Finally, the emission of coherent synchrotron radiation is examined.
Date: December 1, 1996
Creator: Murphy, J.B.
Partner: UNT Libraries Government Documents Department

Summary of recent color coherence results

Description: Recent experimental results on color coherence phenomena from e{sup +}e{sup -}, ep, and p{anti p} collisions are presented. The data are compared to analytic perturbative QCD calculations based on the modified leading logarithm approximation and the local parton hadron duality hypothesis.
Date: August 1, 1998
Creator: Varelas, N., University of Chicago
Partner: UNT Libraries Government Documents Department

Breakdown of conventional factorization for isolated photon cross sections

Description: Using {ital e{sup +}e{sup -} {r_arrow} {gamma} + X} as an example, we show that the conventional factorization theorem of perturbative QCD breaks down for isolated photon cross sections in a specific part of phase space. Implications are discussed.
Date: October 1996
Creator: Berger, E. L.; Guo, Xiaofeng & Qiu, Jianwei
Partner: UNT Libraries Government Documents Department

Top pair production in e+e- and {gamma}{gamma} processes

Description: We analyze spin correlations between top quark and anti-top quark produced at polarized e{sup +} e{sup -} and {gamma}{gamma} colliders. We consider a generic spin basis to find a strong spin correlation. Optimal spin decompositions for top quark pair are presented for e{sup +}e{sup -} and {gamma}{gamma} colliders. We show the cross- section in these bases and discuss the characteristics of results.
Date: February 1, 1998
Creator: Hori, M.; Kiyo, Y.; Kodaira, J.; Nasuno, T. & Parke, S.
Partner: UNT Libraries Government Documents Department

Two-detector Doppler broadening profiles in Al

Description: Low-background Doppler broadening profiles have been measured in Al. The KKR methodology has been used to calculate the profile and study the effect of positron-electron correlation.
Date: September 1997
Creator: Mijnarends, P. E.; Kruseman, A. C.; van Veen, A.; Ghosh, V. J.; Asoka-Kumar, P.; Bansil, A. et al.
Partner: UNT Libraries Government Documents Department

Next-to-leading order corrections to e{sup +}e{sup -} {yields} four jets

Description: I present a general purpose Monte Carlo program for calculating the next-to-leading order corrections to arbitrary four-jet quantities in electron-positron annihilation. In the current version of the program, some subleading in color terms are neglected. As an example, I calculate the four-jet rate in the Durham scheme as well as the Bengtsson-Zerwas angular distribution at O ({alpha}{sub s}{sup 3}) and compare the results to existing data.
Date: July 1, 1997
Creator: Signer, A.
Partner: UNT Libraries Government Documents Department

Low energy supersymmetry phenomenology

Description: The authors summarize the current status and future prospects for low energy (weak scale) supersymmetry. In particular, they evaluate the capabilities of various e{sup +}e{sup {minus}}, p{bar p} and pp colliders to discover evidence for supersymmetric particles. Furthermore, assuming supersymmetry is discovered, they discuss capabilities of future facilities to disentangle the anticipated spectrum of super-particles, and, via precision measurements, to test mass and coupling parameters for comparison with various theoretical expectations. The authors then comment upon the complementarity of proposed hadron and e{sup +}e{sup {minus}} machines for a comprehensive study of low energy supersymmetry.
Date: April 1, 1995
Creator: Baer, H.; Chen, C.H.; Bartl, A.; Feng, J.; Fujii, K.; Gunion, J. et al.
Partner: UNT Libraries Government Documents Department

Isolated prompt photon production

Description: We show that the conventionally defined partonic cross section for the production of isolated prompt photons is not an infrared safe quantity. We work out the case of e{sup +}e{sup -} {yields} {gamma} + X in detail, and we discuss implications for hadron reactions such as p{bar p} {yields} {gamma} + X.
Date: August 15, 1997
Creator: Berger, E.L.; Guo, Xiaofeng & Qiu, Jianwei
Partner: UNT Libraries Government Documents Department

On the robustness of the localized spatiotemporal structures in electron-positron-ion plasmas

Description: It is shown that, in an electron-positron plasma with a small fraction of ions, large-amplitude localized spatiotemporal structures (light bullets) can be readily generated and sustained. These light bullets are found to be exceptionally robust: they can emerge from a large variety of initial field distributions and are remarkably stable.
Date: April 1, 1998
Creator: Mahajan, S.M.; Berezhiani, V.I. & Miklaszewski, R.
Partner: UNT Libraries Government Documents Department

e{sup +}e{sup {minus}} collisions at the SLC: The left-right asymmetry

Description: The Sanford Linear Collider has operated successfully to produce over 50,000 Z{sup O}{prime}s with polarized electron beams. The asymmetry in the production of Z{sup O}{prime}s with respect to left and right handed electron beams has been measured, and a preliminary result is presented.
Date: February 1, 1994
Creator: Shapiro, G. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department

A Test of the Flavor Independence of Strong Interactions in e+e- Annihilation at the Z0 Pole

Description: This thesis presents a comparison of the strong coupling of the gluons to light (q<sub>l</sub> = u + d + s), c, and b quarks, determined from multijet rates in flavor-tagged samples of approximately 150,000 hadronic Z<sup>0</sup> decays recorded with the SLC Large Detector at the SLAC Linear Collider between 1993 and 1995. Flavor separation among primary q<sub>l</sub> {anti q<sub>l</sub>} , c{anti c} and b {anti b} final states was made on the basis of the reconstructed mass of long-lived heavy-hadron decay vertices, yielding tags with high purity and low bias against {>=} 3-jet final states. The data obtained imply no flavor dependence within our sensitivity.
Date: September 3, 1999
Creator: Muller, David
Partner: UNT Libraries Government Documents Department

Loaded delay lines for future RF pulse compression systems

Description: The peak power delivered by the klystrons in the NLCRA (Next Linear Collider Test Accelerator) now under construction at SLAC is enhanced by a factor of four in a SLED-II type of R.F. pulse compression system (pulse width compression ratio of six). To achieve the desired output pulse duration of 250 ns, a delay line constructed from a 36 m length of circular waveguide is used. Future colliders, however, will require even higher peak power and larger compression factors, which favors a more efficient binary pulse compression approach. Binary pulse compression, however, requires a line whose delay time is approximately proportional to the compression factor. To reduce the length of these lines to manageable proportions, periodically loaded delay lines are being analyzed using a generalized scattering matrix approach. One issue under study is the possibility of propagating two TE{sub o} modes, one with a high group velocity and one with a group velocity of the order 0.05c, for use in a single-line binary pulse compression system. Particular attention is paid to time domain pulse degradation and to Ohmic losses.
Date: May 1, 1995
Creator: Jones, R.M.; Wilson, P.B. & Kroll, N.M.
Partner: UNT Libraries Government Documents Department

Compensation of the {open_quotes}Pacman{close_quotes} tune spread by tailoring the beam current

Description: {open_quotes}Factory{close_quotes}-like e{sup +}-e{sup {minus}} colliders presently under design or construction achieve high luminosity by resorting to large numbers of closely-spaced bunches. The short bunch spacing implies that there are unavoidable parasitic collisions (PCs) in the neighborhood of the interaction point (IP). Since the bunch population of the beam is not uniform due to an intentional ion-clearing gap, the bunches at the head or tail of the train ({open_quotes}pacman bunches{close_quotes}) experience different beam-beam tune shifts than those away from the edges ({open_quotes}typical bunches{close_quotes}). The author presents here a method to minimize the vertical tune spread at the expense of increasing the horizontal tune spread (it is assumed that there is only one IP). Since the beam-beam dynamics for flat beams typically tolerates a significantly higher horizontal tune spread than a vertical tune spread, this method implies a net advantage. The author presents this discussion in the context of the PEP-II collider.
Date: April 1, 1995
Creator: Furman, M.A.
Partner: UNT Libraries Government Documents Department

e{sup +}e{sub {minus}} and ep options for the very large hadron collider.

Description: Although the linear collider is ultimately capable of higher energies, a circular e{sup +}e{sup {minus}} collider installed in the large tunnels of a Very Large Hadron Collider (VLHC) has attractive features, including very light magnet system and unchallenging vacuum requirements. An ep collider, built either in the 3 TeV booster or the large tunnel, could extend the HERA program beyond {radical}s {approximately} 1 TeV. Both machines could perhaps use the same rf system, first in the booster tunnel and then as part of the large collider.
Date: April 27, 1998
Creator: Norem, J.
Partner: UNT Libraries Government Documents Department

Supernova constraints on a superlight gravitino

Description: In supergravity models with low supersymmetry breaking scale the gravitinos can be superlight, with mass in the 10{sup -6} eV to few keV range. In such a case, gravitino emission provides a new cooling mechanism for protoneutron stars and therefore can provide constraints on the mass of a superlight gravitino. This happens because the coupling to matter of superlight gravitinos is dominated by its goldstino component, whose coupling to matter of superlight gravitinos is dominated by its goldstino component, whose coupling to matter is inversely proportional to the scale of supersymmetry breaking and increases as the gravitino mass decreases. Present observations therefore provide lower limits on the gravitino mass. Using the recently revised goldstino couplings, we find that the two dominant processes in supernova cooling are e{sup +} e{sup -} {yields} GG and {gamma}+e{sup -} {yields} e{sup -} GG. They lead to a lower limit on the supersymmetry breaking scale {Lambda}{sub s} from 160 to 500 GeV for core temperatures 30 to 60 MeV and electron chemical potentials 200 to 300 MeV. The corresponding lower limits on the gravitino mass are .6 - 6 x 10{sup -6} eV.
Date: October 1, 1997
Creator: Dicus, D. A.; Mohapatra, R. N. & Teplitz, V. L.
Partner: UNT Libraries Government Documents Department

Comparison of backgrounds in detectors for LHC, NLC and {mu}{sup +}{mu}{sup {minus}} colliders

Description: Background levels in detectors at future high-luminosity colliders of three different types - proton-proton, electron-positron, and muon- antimuon - are analyzed. Two sources - debris from the collision points and those from an accelerator tunnel - are studied. It is shown that hadron, electron and muon colliders are similar and very different at the same time with respect to background origin, integrated radiation levels and instantaneous rates of particles in the detectors. 23 refs., 11 figs., 4 tabs.
Date: March 1, 1996
Creator: Mokhov, N.V.
Partner: UNT Libraries Government Documents Department

Precise measurement of the left-right cross section asymmetry in Z boson production by E{sup +}e{sup {minus}} collisions

Description: The authors present a precise measurement of the left-right cross section asymmetry (A{sub LR}) for Z boson production by e{sup +}e{sup {minus}} collisions. The measurement was performed at a center-of-mass energy of 91.26 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (63.0 {+-} 1.1)%. Using a sample of 49,392 Z decays, they measure A{sub LR} to be 0.1628 {+-} 0.0071 (stat.) {+-} 0.0028(syst.) which determines the effective weak mixing angle to be sin{sup 2} {theta}{sub W}{sup eff} = 0.2292 {+-} 0.0009(stat.) {+-} 0.0004(syst.). They combine this result with the result obtained in 1992 and obtain sin{sup 2} {theta}{sub W}{sup eff} = 0.2294 {+-} 0.0010, which constitutes the best measurement of sin{sup 2} {theta}{sub W}{sup eff} in a single experiment presently available.
Date: September 1, 1994
Creator: Lath, A. & Collaboration, SLD
Partner: UNT Libraries Government Documents Department