197461838
A measurement of tau polarization at LEP
With a data sample of 86000 tau pairs collected in 1990 - 1993 the authors have measured the polarization of tau-leptons as a function of the production polar angle. They obtain for the ratio of vector to axial-vector weak neutral couplings for electrons g{sub Ve}/g{sub Ae}=0.0791{+-}0.0099(stat) {+-}0.0025 (syst) and taus g{sub V{tau}}/g{sub A{tau}} = 0.0752 {+-}0.063(stat){+-}0.0045(syst) consistent with the hypothesis of e - {tau} universality. Assuming universality of the e-{tau} neutral current the authors determine the effective electroweak mixing angle to be sin{sup 2}{theta}{sub W}{sup eff}=0.2309{+-}0.0016.
118099621
A measurement of the polarization asymmetry of the tau lepton using the L3 detector at LEP
With a data sample of e e events collected in the L detector at LEP during we did a measurement of the polarization of leptons as a function of the production polar angle with respect to the incident e beam direction We used the following prong decay channels e e and a As the result we obtained the asymmetries A and Ae Combining this with the previous data measurement by L we ob tained A and Ae These asymmetries gave the ratio of vector to axial vector weak neutral coupling con stants for electrons as g V g e A and for taus as g V g A The numbers are consistent with the hypothesis of e lepton universality Assuming the e neutral current universality the e ective electroweak mixing angle is calculated as sin e w Advisor Professor Aihud Pevsner
17667065
Review of Charm Semileptonic Decays and QCD
In this paper, we review recent progress in the field of semileptonic decays of charm mesons, including topics on the relative branching ratio and the form factors. The comparison between the experimental form factor measurements and the Lattice QCD calculations is emphasized.
197461838
A measurement of tau polarization at LEP
With a data sample of 86000 tau pairs collected in 1990 - 1993 the authors have measured the polarization of tau-leptons as a function of the production polar angle. They obtain for the ratio of vector to axial-vector weak neutral couplings for electrons g{sub Ve}/g{sub Ae}=0.0791{+-}0.0099(stat) {+-}0.0025 (syst) and taus g{sub V{tau}}/g{sub A{tau}} = 0.0752 {+-}0.063(stat){+-}0.0045(syst) consistent with the hypothesis of e - {tau} universality. Assuming universality of the e-{tau} neutral current the authors determine the effective electroweak mixing angle to be sin{sup 2}{theta}{sub W}{sup eff}=0.2309{+-}0.0016.
119805142
Recent FOCUS results on charm mixing and CP violation
We summarize recent results on CP violation and mixing based on a high statistics photo-produced charm sample collected by the FOCUS experiment. We compare the lifetimes of two neutral D meson decays: D0 → K−π+ and D0 → K−K+. A mixing parameter for the neutral D system (yCP) is obtained under the assumption that K−π+ is an equal mixture of CP odd and even eigenstates. In addition, we searched for a CP width asymmetry in D+ → K−K+π+, D0 → K−K+ and D0 → π−π+. We found no evidence for CP violation by comparing the decay rates for the particle and antiparticle.
119679827
RECENT FOCUS RESULTS ON CHARM MIXING
We present the recent result on CP mixing based on a high statistics photoproduced charm sample collected by the FOCUS experiment. We compare the lifetimes of two neutral D meson decays: D0→K- π+ and D0→K-K+. A mixing parameter for the neutral D system (yCP) is obtained under the assumption that K-π+ is an equal mixture of CP odd and even eigenstates.
122541104
Progress report on the Bates parity experiment
We are performing an experiment at the MIT Bates Linear Accelerator Center to measure the parity‐violating asymmetry in the elastic scattering of polarized electrons from carbon. The asymmetry, which is due to the isoscalar piece of the neutral weak current, is predicted to be about one part per million for our experimental conditions. We have recently obtained preliminary data with polarized electrons. This paper discusses the status of the experiment, with emphasis on our understanding of the most important systematic errors.
118190331
RADIATION REACTION IN CURVED SPACETIME
123227475
Results from the bates 12C parity experiment
Abstract We report the results of an experiment measuring the the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from 12 C nuclei. We obtain A exp = 0.60 ± 0.14 ± 0.02 ppm. The first error is statistical and the second is systematic. Using our measured beam polarization of 0.37 ± 0.02, we compute the isoscalar vector hadronic coupling constant γ to be 0.136 ± 0.032 ± 0.009. This agrees with the tree level Standard Model prediction of γ = 0.155 .
85450376
Simple “invariance” of two-body decay kinematics
We study the two-body decay of a mother particle into a massless daughter. We further assume that the mother particle is unpolarized and has a generic boost distribution in the laboratory frame. In this case, we show analytically that the laboratory frame energy distribution of the massless decay product has a peak, whose location is identical to the (xed) energy of that particle in the rest frame of the corresponding mother particle. Given its simplicity and \invariance" under changes in the boost distribution of the mother particle, our nding should be useful for the determination of masses of mother particles. In particular, we anticipate that such a procedure will then not require a full reconstruction of this two-body decay chain (or for that matter, information about the rest of the event). With this eventual goal in mind, we make a proposal for extracting the peak position by tting the data to a well-motivated analytic function describing the shape of such an energy distribution. This tting function is then tested on the theoretical prediction for top quark pair production and its decay, and it is found to be quite successful in this regard. As a proof of principle of the usefulness of our observation, we apply it for measuring the mass of the top quark at the LHC, using simulated data and including experimental eects. PACS numbers: 11.80.Cr It is very well-known that in the rest frame of a mother particle undergoing a two-body decay, the energy of each of the daughter particles is xed in terms of mother and the daughter particle masses. Turning this fact around, we can determine the mass of the mother particle if we can measure these rest-frame energies of the daughter particles. However, often the mother particle is produced in the laboratory with a boost, that too with a magnitude and direction which is (a priori) not known. Moreover, the boost of mother particles produced at hadron colliders is dierent in each event. Such a boost distribution depends on the production mechanism of the particle and on the structure functions of the hadrons in the initial state of the collision, and is thus a complicated function. In turn, the fact that the mother has a dierent boost in each event implies that when we consider the observed energy of the two-body decay product in the laboratory frame, we get a distribution in it. Thus it seems like the information that was encoded in the rest frame energy is lost, and we are prevented from extracting (at least at an easily tractable level) the mass of the mother particle along the lines described above. We show that, remarkably, if one of the daughter particles from the two-body decay is massless and the mother is unpolarized, then such is not the case. Specically, in this case, we demonstrate that the distribution of the daughter particle’s energy in the laboratory frame has a peak precisely at its corresponding rest-frame energy. This result is interesting per se. Furthermore, we expect that it will lead to formulation of new methods for mass measurements. Obviously, for this purpose, we need to be able to determine the location of this peak accurately from the observed energy distribution of the massless daughter. To this end, we propose and motivate an analytic function that can be used to t the data on the energy distribution and thus extract the peak position. We show that this function is a suitable one using the top quark decay, t! W b, as a test case, namely, it ts very well the theory prediction for energy spectrum of the resulting b-jets. Simulating a realistic experimental situation, we then show that we can extract the value of the top mass from the position of the peak in the b-jet energy distribution along with the well-measured mass of the W boson. Let us consider the decay of a heavy particle B of mass mB, i.e., B! Aa where a is a massless visible particle. For the subsequent arguments, the properties of the particle A (other than its mass denoted by mA) are irrelevant. In the rest frame of particle B, the energy of the particle a is simply given by E = m 2 m 2 2mB :
121056144
Operation of the LAMPF stopped muon channel for small gas targets
Abstract We describe the operation of the LAMPF stopped muon channel (SMC) in a mode that provides a small beam spot and a narrow momentum spread suitable for stopping negative muons in presently available optically pumped spin-exchange polarized gas targets. This technique is expected to be useful for the production of polarized muonic atoms. Monte Carlo studies of the channel are discussed, and we describe experimental results including measurements of the fraction of negative muon stops in a 6 cm 3 krypton target at 1 atm as a function of beam momentum.