D. Karlen

Radiative Bhabha scattering for singly tagged and untagged configurations

Abstract A method for simulating radiative Bhabha scattering for configurations where one or both electrons do not scatter appreciably is presented. Double radiative Bhabha scattering is included by using the equivalent photon approximation. Results from a Monte Carlo event generator are shown for two experimental configurations. When an electron and photon scatter at large angles, the contribution from order α 4 is large for low visible enegries. For the single photon configuration, the order α 4 correction is small.

THE CASE FOR A 500 GEV E+E- LINEAR COLLIDER

Several proposals are being developed around the world for an e+e- linear collider with an initial center of mass energy of 500 GeV. In this paper, we will discuss why a project of this type deserves priority as the next major initiative in high energy physics.

THE PERFORMANCE OF 'VIRTUAL PHASE' CCDs AS DETECTORS OF MINIMUM IONIZING PARTICLES

Abstract The Texas Instruments “Virtual Phase” CCD has been the basis of an ambitious design for a precision vertex detector to be used at the Stanford Linear Collider. The performance of this chip shows promise for future use in electron linear colliders. Experimental results are reported in addition to description of the electronic readout and preliminary mechanical design.

Measurement of the branching fraction for tau --->5 pi +/-( pi 0) nu tau and an upper limit on the nu tau mass.

The branching fraction for tau/sup -/..-->..5..pi../sup + -/(..pi../sup 0/)..nu../sub tau/ is measured from data accumulated with the Mark II detector at PEP. Four events are observed with an estimated hadronic background of (0.03/sub -0.02//sup +0.04/) events and a background from tau/sup -/..-->..e..pi../sup + -/..pi../sup 0/..nu../sub tau/ of (0.05/sub -0.04//sup +0.07/) events. This results in a measured branching fraction of (0.16 +- 0.08 +- 0.04)%. The candidate events are used to establish an upper limit of 125 MeV/c/sup 2/ on the ..nu../sub tau/ mass at the 95% confidence level.

A STUDY OF LOW Q**2 RADIATIVE BHABHA SCATTERING

This thesis presents a study of electron-positron scattering, via nearly real photon exchange, where in the process one or more high energy photons are produced. The motivations behind the work are twofold. Firstly, the study is a sensitive test of the theory of electron-photon interactions, quantum electrodynamics. A deviation from the theory could indicate that the electron is a composite particle. Secondly, a thorough understanding of this process is necessary for experiments to be done in the near future at the Stanford Linear Collider and the LEP facility at CERN. Calculations for the process to third and fourth order in pertubation theory are described. Methods for simulating the process by a Monte Carlo event generator are given. Results from the calculations are compared to data from the Mark II experiment at the PEP storage ring. The ratio of measured to calculated cross sections are 0.993 /+-/ 0.017 /+-/ 0.015 and 0.99 /+-/ 0.16 /+-/ 0.08 for final states with one and two observed photons respectively, where the first errors are statistical and the second systematic. The excellent agreement verifies the calculations of the fourth order radiative correction. No evidence for electron substructure is observed.

The Case for a 500 GeV e+e- Linear Collider

Several proposals are being developed around the world for an e+e- linear collider with an initial center of mass energy of 500 GeV. In this paper, we will discuss why a project of this type deserves priority as the next major initiative in high energy physics.

Refined measurement of theB-hadron lifetime

We report a new measurement of the average lifetime of hadrons containing bottom quarks. The B hadron decays are tagged by identifying leptons at high transverse momentum. From a fit to the lepton impact parameter distribution, the average B hadron lifetime is found to be (0.98 f 0.12 f 0.13) x lo-l2 sec. The lifetime of hadrons containing bottom quarks is a measure of the strength of the weak transitions between the bottom quark and the charm and up quarks. In terms of the 3 x 3 quark mixing matrix proposed by Kobayashi and Maskawaf the B hadron lifetime depends on the magnitude of the matrix elements Vub and &b. Studies of B semileptonic decay’ have shown that Iv&l is small compared to I&l, and therefore the B lifetime essentially measures II&l and limits lvUbl. The data used in this measurement were collected with the Mark II detector at the e+estorage ring PEP (EC, = 29 GeV). We have previously reported a B lifetime measurement3 based on a data sample of 80 pb-l. The present work: based on a data sample of 204 pb-l, includes the previous data and supersedes our earlier analysis. We use the same procedure of measuring the impact parameters of leptons produced in B decay. However, we have improved upon the previous result through direct measurement of the experimental resolution function, a more precise determination of the B production point, and a comprehensive analysis of inclusive lepton production. These improvements combined with the increased statistics make this measurement of the B lifetime the most precise from any experiment to date. The Mark II detector has been described in detail elsewhere.5 A high resolution drift chamber, known as the vertex chamber, is situated inside the main tracking chamber. The two drift chambers are immersed in a solenoidal magnetic field of 2.3 kG. Particle trajectories are measured with high precision in the (2, y) plane perpendicular to th e b earns, and the impact parameter is accurately determined in that plane. Electrons are identified over 64 % of the solid angle with a lead-liquid-argon calorimeter. Muons are identified over 44 % of the solid angle by-a system of hadron absorbers and proportional tubes.

A Refined Measurement of the

We report a new measurement of the average lifetime of hadrons containing bottom quarks. The B hadron decays are tagged by identifying leptons at high transverse momentum. From a fit to the lepton impact parameter distribution, the average B hadron lifetime is found to be (0.98 f 0.12 f 0.13) x lo-l2 sec. The lifetime of hadrons containing bottom quarks is a measure of the strength of the weak transitions between the bottom quark and the charm and up quarks. In terms of the 3 x 3 quark mixing matrix proposed by Kobayashi and Maskawaf the B hadron lifetime depends on the magnitude of the matrix elements Vub and &b. Studies of B semileptonic decay’ have shown that Iv&l is small compared to I&l, and therefore the B lifetime essentially measures II&l and limits lvUbl. The data used in this measurement were collected with the Mark II detector at the e+estorage ring PEP (EC, = 29 GeV). We have previously reported a B lifetime measurement3 based on a data sample of 80 pb-l. The present work: based on a data sample of 204 pb-l, includes the previous data and supersedes our earlier analysis. We use the same procedure of measuring the impact parameters of leptons produced in B decay. However, we have improved upon the previous result through direct measurement of the experimental resolution function, a more precise determination of the B production point, and a comprehensive analysis of inclusive lepton production. These improvements combined with the increased statistics make this measurement of the B lifetime the most precise from any experiment to date. The Mark II detector has been described in detail elsewhere.5 A high resolution drift chamber, known as the vertex chamber, is situated inside the main tracking chamber. The two drift chambers are immersed in a solenoidal magnetic field of 2.3 kG. Particle trajectories are measured with high precision in the (2, y) plane perpendicular to th e b earns, and the impact parameter is accurately determined in that plane. Electrons are identified over 64 % of the solid angle with a lead-liquid-argon calorimeter. Muons are identified over 44 % of the solid angle by-a system of hadron absorbers and proportional tubes.

B

We have searched for the lepton-flavor-violating decay D/sup 0/..-->..e/sup +- /..mu../sup minus-or-plus/ in 204 pb/sup -1/ of e/sup +/e/sup -/ annihilation data at E/sub c.m./ = 29 GeV from the Mark II detector. No candidates were found; we estimate an upper limit on the cross section times branching ratio of sigma(e/sup +/e/sup -/..-->..D/sup 0/,D-bar/sup 0/; inclusive)B(D/sup 0/..-->..e/sup +- /..mu../sup minus-or-plus/) ..e/sup +- /..mu../sup minus-or-plus/)<2.1 x 10/sup -3/. AE.

Hadron Lifetime

V o l u m e 160B, n u m b e r 1,2,3 PHYSICS LETTERS 3 October 1985 UPPER LIMIT O N B°B ° MIXING IN e + e - ANNIHILATION AT 29 GeV ~ T. SCHAAD, M.E. NELSON 1, G. ABRAMS, D. AMIDEI 2, A.R. BADEN, T. BARKLOW, A.M. BOYARSKI, J. BOYER, M. BREIDENBACH, P.R. BURCHAT, D.L. BURKE, F. BUTLER, J.M. D O R F A N , G.J. FELDMAN, G. GIDAL, L. G L A D N E Y 3, M.S. GOLD, G. GOLDHABER, L. G O L D I N G 4, j. HAGGERTY, G. HANSON, K. HAYES, D. HERRUP, R.J. HOLLEBEEK, W.R. INNES, J.A. JAROS, I. JURICIC, J.A. K A D Y K , D. KARLEN, S.R. KLEIN, A.J. L A N K F O R D , R.R. LARSEN, B.W. LECLAIRE, M. LEVI 5, N.S. LOCKYER 3, V. LIJTH, C. MATTEUZZI 5, R.A. ONG, M.L. PERL, B. RICHTER, K. RILES, M.C. ROSS, P.C. ROWSON, H. SCHELLMAN 2, W.B. SCHMIDKE, R. SCHWITTERS, P.D. SHELDON, G.H. TRILLING, C. DE LA VAISSIERE 6, D.R. WOOD, J.M. YELTON 7 and C. ZAISER Stanford Linear Accelerator Center, Stanford Unwerslty, Stanford, CA 94305, USA Lawrence Berkeley Laboratory and Department of Physws, Umverstty of Cahforma, Berkeley, CA 94720, USA Department of Physws, Harvard Unwerstty, Cambridge, MA 02138, USA Recewed 21 June 1985 The rate of ddepton production m the process e+e - --* hadrons at Vs- = 29 GeV is found to be m good agreement with predictions based on semdeptomc decays of bottom and charm hadrons. We determine that the average probability for a semdeptonlc decay of a hadron lnmally containing a b quark to produce a positive lepton is less than 0 12 at the 90% confidence level and set upper hmlts on B°B ° rmxing. New knowledge of the weak mixing angles, im- posed by the long B lifetime [1,2], a lower bound on the t quark mass [3], and a small ratio [4] of F(b-*u)/ P(b ~ c), has led to predictions that B 0 mesons and, to a much lesser extent, B 0 mesons should exhibit mixing [5,6]. B 0 ~0 mixing can lead to the production of like- sign dileptons in the process e+e - ~ BOBX -> BOBX l This work was supported in part by the Department of Energy, contracts DE-AC03-76SF00515 (SLAC), DE-AC03- 76SF00098 (LBL), and DE-AC02-76ER03064 (Harvard) Present address: California Institute of Technology, Pasadena, CA 91125, USA Present address Umverslty of Chicago, Clucago, IL 60637, USA. Present address University of Pennsylvania, Pluladelptua, PA 19104, USA. Present address Therma-Wave, Inc., Fremont, CA 94539, USA. Present address: CERN, CH-1211 Geneva 23, Switzerland. Present address: LPNHE, Umverslt6 Pierre et M a n e Cune, F-75230 Pans, France Present address Oxford Umverslty, Oxford, England £ - £ - X ,1. Recently, the CLEO collaboration ,2 has reported an upper limit on B0B 0 mixing from the rate of like.sign dileptons produced in the decay of the T(4s). The UA1 collaboration [8] has observed like-sign dimuon events, leading to speculations in the literature [9] that these events could arise from B s 0 - B - 0 s mixing. In this letter, we report a measurement of dflepton rates in e+e - annihilation at an energy above the B 0 production threshold. Here, we always imply the charge conjugate reaction. We use t h e Particle Data Group convention that B (B) hadrons in t h e absence of mixing decay into positive (negative) lep- tons. The t~pes_of neutral B m e s o n s are denoted by B~ = bd and B~ = bs. The CLEO collaboration has set an upper limit on the di- lepton ratio Y n q = ( N n q n q + N~O=O)/N~O~O = N~±/N +- ~a va~a nd~d ndDd The limit set isYB~ < 0.30 at 90% C L under the assump- tion of equal semileptortic branching ratios. Since the B m e s o n s are in an l = 1 state, mixing is suppressed by inter- ference effects (see ref. [12]) a n d Y B ~ = rd, where r d = 0370-2693/85/