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Measurements of the CKM Angle beta

Description: In this article I report on new and updated measurements of the CP-violating parameter {beta}({phi}{sub 1}), which is related to the phase of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix of the electroweak interaction. Over the past few years, {beta} has become the most precisely known parameter of the CKM unitarity triangle that governs the B system. The results presented here were produced by the two B Factories, BABAR and Belle, based on their most recent datasets of over 600 million B{bar B} events combined. The new world average for sin2{beta}, measured in the theoretically and experimentally cleanest charmonium modes, such as B{sup 0} {yields} J/{Psi}K{sub S}{sup 0}, is sin 2{beta} = 0.685 {+-} 0.032. In addition to these tree-level dominated decays, independent measurements of sin2{beta} are obtained from gluonic b {yields} s penguin decays, including B{sup 0} {yields} {phi}K{sub S}{sup 0}, B{sup 0} {yields} {eta}'K{sub S}{sup 0} and others. There are hints, albeit somewhat weaker than earlier this year, that these measurements tend to come out low compared to the charmonium average, giving rise to the tantalizing possibility that New Physics amplitudes could be contributing to the corresponding loop diagrams. Clearly, more data from both experiments are needed to elucidate these intriguing differences.
Date: December 14, 2005
Creator: Bartoldus, Rainer
Partner: UNT Libraries Government Documents Department

Single-Spin Asymmetries and Transversity in QCD

Description: Initial- and final-state interactions from gluon exchange, normally neglected in the parton model, have a profound effect in QCD hard-scattering reactions, leading to leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, as well as nuclear shadowing and antishadowing-leading-twist physics not incorporated in the light-front wavefunctions of the target computed in isolation. The physics of such processes thus require the understanding of QCD at the amplitude level; in particular, the physics of spin requires an understanding of the phase structure of final-state and initial-state interactions, as well as the structure of the basic wavefunctions of hadrons themselves. I also discuss transversity in exclusive channels, including how one can use single-spin asymmetries to determine the relative phases of the timelike baryon form factors, as well as the anomalous physics of the normal-normal spin-spin correlation observed in large-angle proton-proton elastic scattering. As an illustration of the utility of light-front wavefunctions, the transversity distribution of a single electron is computed, as defined from its two-particle QED quantum fluctuations.
Date: December 14, 2005
Creator: Brodsky, S.J.
Partner: UNT Libraries Government Documents Department

Observation of Beam ION Instability in Spear3

Description: Weak vertical coupled bunch instability with oscillation amplitude at {mu}m level has been observed in SPEAR3. The instability becomes stronger when there is a vacuum pressure rise by partially turning off vacuum pumps and it becomes weaker when the vertical beam emittance is increased by turning off the skew quadrupole magnets. These confirmed that the instability was driven by ions in the vacuum. The threshold of the beam ion instability when running with a single bunch train is just under 200 mA. This paper presents the comprehensive observations of the beam ion instability in SPEAR3. The effects of vacuum pressure, beam current, beam filling pattern, chromaticity, beam emittance and bunch-by-bunch feedback are investigated in great detail. In an electron accelerator, ions generated from the residual gas molecules can be trapped by the beam. Then these trapped ions interact resonantly with the beam and cause beam instability and emittance blow-up. Most existing light sources use a long single bunch train filling pattern, followed by a long gap to avoid multi-turn ion trapping. However, such a gap does not preclude ions from accumulating during one passage of the single bunch train beam, and those ions can still cause a Fast Ion Instability (FII) as predicted by Raubenheimer and Zimmermann. FII has been observed in ALS, and PLS by artificially increasing the vacuum pressure by injecting helium gas into the vacuum chamber or by turning off the ion pumps in order to observe the beam ion instability. In some existing rings, for instance B factory, the beam ion instability was observed at the beginning of the machine operation after a long period of shutdown and then it automatically disappeared when the vacuum was better. However, when the beam emittance becomes smaller, the FII can occur at nominal conditions as observed in PLS, SOLEIL ...
Date: December 14, 2011
Creator: Teytelman, D.; Cai, Y.; Corbett, W. J.; Raubenheimer, T. O.; Safranek, J. A.; Schmerge, J. F. et al.
Partner: UNT Libraries Government Documents Department

An Optical Streaking Method for Measuring Femtosecond Electron Bunches

Description: The measurement of the ultra-short electron bunch length on the femtosecond time scale constitutes a very challenging problem. In the x-ray free electron laser facilities such as the Linac Coherent Light Source, generation of a sub-ten femtoseconds electron beam with 20pC charge is possible, but direct measurements are very difficult due to the resolution limit of the present diagnostics. We propose a new method here based on the measurement of the electron beam energy modulation induced from laser-electron interaction in a short wiggler. A typical optical streaking method requires a laser wavelength much longer than the electron bunch length. In this paper a laser with its wavelength shorter than the electron bunch length has been adopted, while the slope on the laser intensity envelope is used to distinguish the different periods. With this technique it is possible to reconstruct the bunch longitudinal profile from a single shot measurement. Generation of ultrashort x-ray pulses at femtoseconds (fs) scale is of great interest within synchrotron radiation and free electron laser (FEL) user community. One of the simple methods is to operate the FEL facility at low charge. At the Linac Coherent Light Source (LCLS), we have demonstrated the capability of generating ultrashort electron-beam (e-beam) with a duration of less than 10 fs fwhm using 20 pC charge. The x-ray pulses have been delivered to the x-ray users with a similar or even shorter pulse duration. However, The measurement of such short electron or x-ray pulse length at the fs time-scale constitutes a challenging problem. A standard method using an S-band radio-frequency (rf) transverse deflector has been established at LCLS, which works like a streak camera for electrons and is capable of resolving bunch lengths as short as 25 fs fwhm. With this device, the electrons are transversely deflected by the high-frequency time-variation ...
Date: December 14, 2011
Creator: Ding, Yuantao; Bane, Karl L.F.; Huang, Zhirong & /SLAC
Partner: UNT Libraries Government Documents Department