21 Matching Results

Search Results

Advanced search parameters have been applied.

Precision measurements in supersymmetry

Description: Supersymmetry is a promising framework in which to explore extensions of the standard model. If candidates for supersymmetric particles are found, precision measurements of their properties will then be of paramount importance. The prospects for such measurements and their implications are the subject of this thesis. If charginos are produced at the LEP II collider, they are likely to be one of the few available supersymmetric signals for many years. The author considers the possibility of determining fundamental supersymmetry parameters in such a scenario. The study is complicated by the dependence of observables on a large number of these parameters. He proposes a straightforward procedure for disentangling these dependences and demonstrate its effectiveness by presenting a number of case studies at representative points in parameter space. In addition to determining the properties of supersymmetric particles, precision measurements may also be used to establish that newly-discovered particles are, in fact, supersymmetric. Supersymmetry predicts quantitative relations among the couplings and masses of superparticles. The author discusses tests of such relations at a future e{sup +}e{sup {minus}} linear collider, using measurements that exploit the availability of polarizable beams. Stringent tests of supersymmetry from chargino production are demonstrated in two representative cases, and fermion and neutralino processes are also discussed.
Date: May 1, 1995
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

Supersymmetry tests at future linear colliders

Description: If new particles are discovered, it will be important to determine if they are the supersymmetric partners of standard model bosons and fermions. Supersymmetry predicts relations among the couplings and masses of these particles. We discuss the prospects for tests of these relations at a future e+e- linear collider.
Date: December 1, 1994
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

Squark mass determination at a future linear collider

Description: Present mass limits allow the possibility that squarks may be produced at future linear e{sup +}e{sup {minus}} colliders. In this talk the authors discuss the prospects for precision studies of squark masses at such a facility. Both direct and cascade decay scenarios are discussed. By exploiting the clean environment and polarizable beams of linear e{sup +}e{sup {minus}} colliders, they find that squark mass determinations at the level of a few GeV are possible for a number of regions in parameter space.
Date: July 1, 1993
Creator: Feng, J. & Finnell, D.
Partner: UNT Libraries Government Documents Department

Lepton flavor violation at LEP II and beyond

Description: At present, two fundamental mysteries in particle physics are the origins of electroweak symmetry breaking and the fermion mass matrices. The experimental discovery of superpartners would represent enormous progress in the understanding of electroweak symmetry breaking, but would it also allow progress on the flavor problem? To date, nearly all experimental studies of supersymmetry have ignored the possibility of flavor mixings in the sfermion sector. However, since all superpartners must be given masses, all supersymmetric theories necessarily allow for the possibility of new flavor mixings beyond the standard model. In addition, there are now many supersymmetric theories of flavor, which predict a wide variety of superpartner flavor mixings. In this study, the author examines the possibility of measuring these mixings at LEP II and the Next Linear Collider (NLC). Rare flavor changing processes, such as {mu} {yields} e{gamma}, {tau} {yields} {mu}{gamma}, {tau} {yields} e{gamma}, b {yields} s{gamma}, and neutral meson mixing, already provide important constraints on the sfermion flavor mixings through the virtual effects of superpartners. However, as will be seen below, once superpartners are discovered, it will be possible to probe these mixings much more powerfully by directly observing the change in flavor occurring at the superpartner production and decay vertices.
Date: July 1, 1996
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

R-parity violation and sneutrino resonances at muon colliders

Description: In supersymmetric models with R-parity violation, sneutrinos may be produced as channel resonances at {mu}{sup +}{mu}{sup {minus}} colliders. The authors demonstrate that, for R-parity violating couplings as low as 10{sup {minus}4}, sneutrino resonances may be observed and may be exploited to yield high precision SUSY parameter measurements. The excellent beam energy resolution of muon colliders may also be used to resolve MeV level splitting between CP-even and CP-odd sneutrino mass eigenstates.
Date: January 1, 1998
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

Naturalness re-examined: Implications for supersymmetry searches

Description: The authors discuss the origin of focus points in the scalar mass RGEs of the MSSM and their implications for collider searches. The authors present a new exact analytic solution to the homogeneous system of scalar mass TGEs in the MSSM for general tan {beta}. This is then used to prove that the focus point for m{sup 2}{sub H{sub u}} depends only on the value of the top Yukawa coupling at the weak scale (not its value at the GUT scale) and is independent of the bottom Yukawa coupling.
Date: March 24, 2000
Creator: Feng, J.L.; Matchev, K.T. & Moroi, Takeo
Partner: UNT Libraries Government Documents Department

Supersymmetry at linear colliders: The importance of being e{sup {minus}}e{sup {minus}}

Description: Advantages of the e{sup {minus}}e{sup {minus}} option at linear colliders for the study of supersymmetry are highlighted. The fermion number violating process e{sup {minus}}e{sup {minus}} {yields} {tilde e}{sup {minus}}{tilde e}{sup {minus}} provides unique opportunities for studies of slepton masses and flavor mixings. In particular, slepton mass measurements at the 100 MeV level through threshold scans of scalar pair production may be possible. Such measurements are over an order of magnitude better than those possible in e{sup +}e{sup {minus}} mode, require far less integrated luminosity, and may lead to precise, model-independent measurements of tan {beta}. Implications for studying gauginos and the importance of accurate beam polarimetry are also discussed.
Date: March 1, 1998
Creator: Feng, J.L.
Partner: UNT Libraries Government Documents Department

Testing supersymmetry at the next linear collider

Description: If new particles are discovered, it will be important to determine if they are the supersymmetric partners of standard model bosons and fermions. Supersymmetry predicts relations among the couplings and masses of these particles. The authors discuss the prospects for testing these relations at a future e{sup +}e{sup {minus}} linear collider with measurements that exploit the availability of polarized beams.
Date: September 1, 1994
Creator: Feng, J. L.
Partner: UNT Libraries Government Documents Department

X-ray streak camera temporal resolution improvement using a longitudinal time-dependent field

Description: X-ray streak cameras (XSC) have been known to be one of the fastest detectors forultrafast X-ray science. A number of applications in material science, biochemistry, accelerator physics, require sub-picosecond resolution to study new phenomena. Inthis paper, we report on a new method which can potentially improve the temporal resolution of a streak camera down to 100 femtoseconds. This method uses a time-dependent acceleration field to lengthen the photoelectron bunch, significantlyimproving the time resolution as well as reducing the time dispersion caused byinitial energy spread and the effects fromthe space charge forces. A computer simulation of an XSC using this method shows significant improvement in the resolution.
Date: May 9, 2008
Creator: Qiang, Ji; Qiang, J.; Byrd, J.M.; Feng, J. & Huang, G.
Partner: UNT Libraries Government Documents Department

Progress on Modeling of Ultrafast X-Ray Streak Cameras

Description: Streak cameras continue to be useful tools for studying phenomena on the picoseconds time scale. We have employed accelerator modeling tools to understand and possibly improve the time resolution of present and future streak cameras. This effort has resulted in an end-to-end model of the camera. This model has contributed to the recent measurement of 230 fsec (FWHM) resolution measured at 266 nm in the Advanced Light Source Streak Camera Laboratory. We describe results from this model that show agreement with the experiments. We also extrapolate the performance of this camera including several possible improvements.
Date: June 22, 2007
Creator: Huang, G.; Byrd, J.M.; Feng, J.; Qiang, J. & Wang, W.
Partner: UNT Libraries Government Documents Department

Determining tan {beta} at the NLC with SUSY Higgs bosons

Description: The authors examine the prospects for determining tan {beta} from heavy Higgs scalar production in the minimal supersymmetric standard model at a future e{sup +}e{sup {minus}} collider. Their analysis is independent of assumptions of parameter unification, and they consider general radiative corrections in the Higgs sector. Bounds are presented for {radical}s = 500 GeV and 1 TeV, several Higgs masses, and a variety of integrated luminosities. For all cases considered, it is possible to distinguish low, moderate, and high tan {beta}. In addition, the authors find stringent constraints for 3 {approx_lt} tan{beta} {approx_lt} 10, and, for some scenarios, also interesting bounds on high tan {beta} through tbH{sup {+-}} production. Such measurements may provide strong tests of the Yukawa unifications in grand unified theories and make possible highly precise determinations of soft SUSY breaking mass parameters.
Date: July 1, 1997
Creator: Feng, J.L. & Moroi, Takeo
Partner: UNT Libraries Government Documents Department

Ultrafast magnetization dynamics studies using an x-ray streakcamera

Description: The spin dynamics of ferromagnetic thin films following an excitation by ultrashort 100-fs near-infrared laser pulses has recently received much attention. Here, a new approach is described using x-ray magnetic circular dichroism to investigated emagnetization and magnetization switching processes. In contrast to magneto-optical measurements, x-ray dichroism has the advantage of determining separately the spin and orbital components of the magnetic moment. The relatively low time resolution of the synchrotron x-ray probe pulses (80 ps FWHM) is overcome by employing an ultrafast x-ray streak camera with a time resolution of <1 ps. A description of the experimental setup including the x-ray/IR laser pulse synchronization and the streak camera is given.
Date: July 13, 2005
Creator: Bartelt, A.F.; Comin, A.; Feng, J.; Nasiatka, J.; Padmore, H.A.; Scholl, A. et al.
Partner: UNT Libraries Government Documents Department

An ultrafast x-ray detector system at an elliptically polarizingundulator beamline

Description: An ultrafast x-ray detector system is under development atLawrence Berkeley National Laboratory (LBNL) for application primarily tostudyies of ultrafast magnetization dynamics. The system consists of a fslaser, an x-ray streak camera and an ellipitically polarization undulator(EPU) beamline. Polarized x-rays from an EPU can be used to measure x-raymagnetic circular dichroism (XMCD) of a sample. XMCD has the uniqueability to independently measure orbit and spin magnetization withsub-monolayer sensitivity and element specificity. The streak camera hassimultaneously a sub-picosecond temporal resolution and a high spatialresolution. The combination of the streak camera and EPU allows us tostudy the transfer of angular momentum from spin to orbit to the latticein the sample on an ultrafast time scale. We describe here theperformance of the ultrafast detector, the laser and the x-raysynchronization system. The observation of the demagnetization process ofdifferent samples demonstrates the ability of the apparatus.
Date: May 1, 2007
Creator: Feng, J.; Comin, A.; Bartelt, A.F.; Shin, H.J.; Nasiatka, J.R.; Padmore, H.A. et al.
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

Element-specific spin and orbital momentum dynamics of Fe/Gdmultilayers

Description: The role of orbital magnetism in the laser-induced demagnetization of Fe/Gd multilayers was investigated using time-resolved X-ray magnetic circular dichroism at 2-ps time resolution given by an x-ray streak camera. An ultrafast transfer of angular momentum from the spin via the orbital momentum to the lattice was observed which was characterized by rapidly thermalizing spin and orbital momenta. Strong interlayer exchange coupling between Fe and Gd led to a simultaneous demagnetization of both layers.
Date: March 23, 2007
Creator: Bartelt, A.F.; Comin, A.; Feng, J.; Nasiatka, J.R.; Eimuller, T.; Ludescher, B. et al.
Partner: UNT Libraries Government Documents Department

Correlations between charged particles emitted in ion-molecule collisions

Description: A new experimental apparatus for studying correlations between charged particles emitted in ion-atom collisions is described. The apparatus consists of two channelplate detectors, each equipped with position sensitive anodes. Time correlated events in both detectors provide information about correlated charged particle emission. Initial test studies of dissociative double ionization for H{sub 2} and N{sub 2} targets are reported here.
Date: September 1, 1990
Creator: DuBois, R.D. (Pacific Northwest Lab., Richland, WA (USA)); Herrmann, R.; Doerner, R.; Euler, J.; Ullmann, K. (Frankfurt Univ. (Germany, F.R.). Inst. fuer Kernphysik) & Feng, J. (Lanzhou Univ., GS (China))
Partner: UNT Libraries Government Documents Department

DESIGN OF THE ITER IN-VESSEL COILS

Description: The ITER project is considering the inclusion of two sets of in-vessel coils, one to mitigate the effect of Edge Localized Modes (ELMs) and another to provide vertical stabilization (VS). The in-vessel location (behind the blanket shield modules, mounted to the vacuum vessel inner wall) presents special challenges in terms of nuclear radiation (~3000 MGy) and temperature (100oC vessel during operations, 200oC during bakeout). Mineral insulated conductors are well suited to this environment but are not commercially available in the large cross section required. An R&D program is underway to demonstrate the production of mineral insulated (MgO or Spinel) hollow copper conductor with stainless steel jacketing needed for these coils. A preliminary design based on this conductor technology has been developed and is presented herein.
Date: November 27, 2010
Creator: Neumeyer, C; Bryant, L; Chrzanowski, J; Feder, R; Gomez, M; Heitzenroeder, P et al.
Partner: UNT Libraries Government Documents Department

Progress on PEEM3 - An Aberration Corrected X-Ray PhotoemissionElectron Microscope at the ALS

Description: A new ultrahigh-resolution photoemission electron microscope called PEEM3 is being developed and built at the Advanced Light Source (ALS). An electron mirror combined with a much-simplified magnetic dipole separator is to be used to provide simultaneous correction of spherical and chromatic aberrations. It is installed on an elliptically polarized undulator (EPU) beamline, and will be operated with very high spatial resolution and high flux to study the composition, structure, electric and magnetic properties of complex materials. The instrument has been designed and is described. The instrumental hardware is being deployed in 2 phases. The first phase is the deployment of a standard PEEM type microscope consisting of the standard linear array of electrostatic electron lenses. The second phase will be the installation of the aberration corrected upgrade to improve resolution and throughput. This paper describes progress as the instrument enters the commissioning part of the first phase.
Date: May 20, 2006
Creator: MacDowell, Alastair A.; Feng, J.; DeMello, A.; Doran, A.; Duarte,R.; Forest, E. et al.
Partner: UNT Libraries Government Documents Department

An aberration corrected photoemission electron microscope at the advanced light source

Description: Design of a new aberration corrected Photoemission electron microscope PEEM3 at the Advanced Light Source is outlined. PEEM3 will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. The models to calculate the optical properties of the electron mirror are discussed. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system (50 nm) and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further.
Date: November 1, 2003
Creator: Feng, J.; MacDowell, A.A.; Duarte, R.; Doran, A.; Forest, E.; Kelez, N. et al.
Partner: UNT Libraries Government Documents Department