Exclusive Hadronic Final States in E+ E- Interactions at BaBar

The first observation of e{sup +}e{sup -} annihilation into states of positive C parity, {rho}{sup 0}{rho}{sup 0} and {phi}{phi}{sup 0} is reported. It is shown that these final states are produced through two-virtual-photon annihilation. this is based on the distributions of cos{theta}*, where {theta}* is the center-of-mass polar angle of {phi} or {rho}{sup 0}. The cross sections for the |cos{theta}*| < 0.8 are measured. In addition, the observation of another channel, e{sup +}e{sup -} {yields} {phi}{eta} near {radical}s = 10.58 Gev with a significance of 6.5{sigma} is discussed. The cross section of the later channel for |cos{theta}*| < 0.8 is measured, where {theta}* is the center-of-mass polar angle of {phi} meson

Experimental Tests of the GDH and Other Sum Rules at SLAC

Recent measurements from SLAC of the polarized nucleon structure functions g{sub 1} and g{sub 2} have been used to experimentally test the Bjorken, Ellis-Jaffe, Burkhardt-Cottingham, and Efremov-Leader-Teryaev sum rules. In the future, the SLAC E159 experiment will extend structure function measurements using real photons to 40 GeV, enabling a definitive test of the high energy convergence of the GDH sum rule for both proton and deuteron targets

Flux profile scanners for scattered high-energy electrons

The paper describes the design and performance of flux integrating Cherenkov scanners with air-core reflecting light guides used in a high-energy, high-flux electron scattering experiment at the Stanford Linear Accelerator Center. The scanners were highly radiation resistant and provided a good signal to background ratio leading to very good spatial resolution of the scattered electron flux profile scans.Comment: 22 pages, 17 figure

Liquid Hydrogen Target Experience at SLAC

Liquid hydrogen targets have played a vital role in the physics program at SLAC for the past 40 years. These targets have ranged from small "beer can" targets to the 1.5 m long E158 target that was capable of absorbing up to 800 W without any significant density changes. Successful use of these targets has required the development of thin-wall designs, liquid hydrogen pumps, remote positioning and alignment systems, safety systems, control and data acquisition systems, cryogenic cooling circuits and heat exchangers. Detailed operating procedures have been created to ensure safety and operational reliability.This paper surveys the evolution of liquid hydrogen targets at SLAC and discusses advances in several of the enabling technologies that made these targets possible

On the influence of the cosmological constant on gravitational lensing in small systems

The cosmological constant Lambda affects gravitational lensing phenomena. The contribution of Lambda to the observable angular positions of multiple images and to their amplification and time delay is here computed through a study in the weak deflection limit of the equations of motion in the Schwarzschild-de Sitter metric. Due to Lambda the unresolved images are slightly demagnified, the radius of the Einstein ring decreases and the time delay increases. The effect is however negligible for near lenses. In the case of null cosmological constant, we provide some updated results on lensing by a Schwarzschild black hole.Comment: 8 pages, 1 figure; v2: extended discussion on the lens equation, references added, results unchanged, in press on PR

The E158 experiment

We have carried out a precision measurement of the parity-violating asymmetry A PV in the scattering of longitudinally polarized electrons off electrons in a liquid-hydrogen target. The measurement was performed with the 50GeV beam line at SLAC. The final result with the full data set collected in three production runs is A PV = - 131±14 (stat) ±10 (syst) parts per billion. The result leads to new limits on possible contact interactions at the TeV scale. We discuss future prospects for more precise measurements

Using Boosted Decision Trees to Separate Signal and Background in B to XsGamma Decays

The measurement of the branching fraction of the flavor changing neutral current B {yields} X{sub s}{gamma} transition can be used to expose physics outside the Standard Model. In order to make a precise measurement of this inclusive branching fraction, it is necessary to be able to effectively separate signal and background in the data. In order to achieve better separation, an algorithm based on Boosted Decision Trees (BDTs) is implemented. Using Monte Carlo simulated events, ''forests'' of trees were trained and tested with different sets of parameters. This parameter space was studied with the goal of maximizing the figure of merit, Q, the measure of separation quality used in this analysis. It is found that the use of 1000 trees, with 100 values tested for each variable at each node, and 50 events required for a node to continue separating give the highest figure of merit, Q = 18.37

Space Charge Correction on Emittance Measurement of Low Energy Electron Beams

The goal of any particle accelerator is to optimize the transport of a charged particle beam along a set path by confining the beam to a small region close to the design trajectory and directing it accurately along the beamline. To do so in the simplest fashion, accelerators use a system of magnets that exert approximately linear electromagnetic forces on the charged beam. These electromagnets bend the beam along the desired path, in the case of bending magnets, and constrain the beam to the desired area through alternating focusing and defocusing effects, in the case of quadrupole magnets. We can model the transport of such a beam through transfer matrices representing the actions of the various beamline elements. However, space charge effects, produced from self electric fields within the beam, defocus the beam and must be accounted for in the calculation of beam emittance. We present below the preliminary results of a MATLAB code built to model the transport of a charged particle beam through an accelerator and measure the emittance under the influence of space charge effects. We demonstrate the method of correctly calculating the emittance of a beam under space charge effects using a least square fit to determine the initial properties of the beam given the beam size measured at a specific point after transport

Study of the Rare Decay B Mesons Decaying to X Mesons Positive And Negative Leptons at BABAR

Flavor-changing neutral current transitions are forbidden at tree level in the Standard Model and can only occur via higher order diagrams. Since the amplitudes for such loops are dominated by the heaviest known particles, and non-SM effects are expected to contribute at the same order as the SM, such processes are an ideal place to look for new physics. We present a measurement of the inclusive branching fraction for the flavor-changing neutral current process B {yields} X{sub s}{ell}{sup +}{ell}{sup -} with a sample of 81.9 fb{sup -1}, collected with the BABAR detector at the Stanford Linear Accelerator Center. The final state is reconstructed from e{sup +}e{sup -} or {mu}{sup +}{mu}{sup -} pairs and a hadronic system consisting of one K{sup {+-}} or K{sub s} and up to two pions, with at most one {pi}{sup 0}. They observe a signal of 40 {+-} 10(stat) {+-} 2(syst) events and extract a branching fraction {Beta}(B {yields} X{sub s}{ell}{sup +}{ell}{sup -}) = (5.6 {+-} 1.5(stat) {+-} 0.6(exp. syst) {+-} 1.1(model syst)) x 10{sup -6} for m{sub ll} > 0.2 GeV

Search for Neutral D Meson Mixing using Semileptonic Decays

Based on a 87 fb{sup -1} dataset, a search for D{sup 0}-{bar D}{sup 0} mixing is made using the semileptonic decay modes D*{sup +} {yields} {pi}{sup +} D{sup 0}, D{sup 0} {yields} [K/K*]e{nu} (+c.c.) at the B-Factory facility at the Stanford Linear Accelerator Center. These modes offer unambiguous initial and final-state charm flavor tags, and allow the combined use of the D{sup 0} lifetime and D*{sup +}-D{sup 0} mass difference ({Delta}M) in a global likelihood fit. The high-statistics sample of reconstructed unmixed semileptonic D{sup 0} decays is used to model both the {Delta}M distribution and the time-dependence of mixed events directly from the data. Neural networks are used both to select events and to fully reconstruct the D{sup 0}. A result consistent with no charm mixing has been obtained, R{sub mix} < 0.0047 (95% C.L.) and R{sub mix} < 0.0043 (90% C.L.). The lowest current published limit on semileptonic charm mixing is 0.005 (90% C.L.) (E791, E.M. Aitala et al. Phys.Rev.Lett. 77 2384 (1996)). The current best published limit using any analysis technique on the total rate of charm mixing is 0.0016 (95% C.L.) (Bab K{pi} mixing, B. Aubert et al., Phys. Rev. Lett. 91 171801 (2003))