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Register a new userDetector for measuring the $pi^+to e^+ u_e$ branching fraction
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Added by
Aleksey (aka Alexei) Sher (aka Cher)
Publication date
2015
fields
Physics
and research's language is
English
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The PIENU experiment at TRIUMF is aimed at a measurement of the branching ratio $R^{e/mu}$ = ${Gammabig((pi^{+} rightarrow e^{+} u_{e}) + (pi^{+} rightarrow e^{+} u_{e}gamma)big)}/{Gammabig((pi^{+} rightarrow mu^{+} u_{mu})+(pi^{+} rightarrow mu^{+} u_{mu}gamma)big)}$ with precision $<$0.1%. Incident pions, delivered at the rate of 60 kHz with momentum 75 MeV/c, were degraded and stopped in a plastic scintillator target. Pions and their decay product positrons were detected with plastic scintillators and tracked with multiwire proportional chambers and silicon strip detectors. The energies of the positrons were measured in a spectrometer consisting of a large NaI(T$ell$) crystal surrounded by an array of pure CsI crystals. This paper provides a description of the PIENU experimental apparatus and its performance in pursuit of $R^{e/mu}$.
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We report the first absolute measurement of the branching fraction of $Lambda^+_{c}rightarrow Lambda e^+ u_e$. This measurement is based on 567 pb$^{-1}$ of $e^+e^-$ annihilation data produced at $sqrt{s}=4.599$ GeV, which is just above the $Lambda^+_cbar{Lambda}^-_c$ threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be $mathcal B({Lambda^+_crightarrow Lambda e^+ u_e})=(3.63pm0.38({rm stat})pm0.20({rm syst}))%$, representing a more than twofold improvement in precision upon previously published results. As the branching fraction for $Lambda^+_{c}rightarrow Lambda e^+ u_e$ is the benchmark for those of other $Lambda^+_c$ semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.
The MEG (Mu to Electron Gamma) experiment has been running at the Paul Scherrer Institut (PSI), Switzerland since 2008 to search for the decay meg by using one of the most intense continuous $mu^+$ beams in the world. This paper presents the MEG components: the positron spectrometer, including a thin target, a superconducting magnet, a set of drift chambers for measuring the muon decay vertex and the positron momentum, a timing counter for measuring the positron time, and a liquid xenon detector for measuring the photon energy, position and time. The trigger system, the read-out electronics and the data acquisition system are also presented in detail. The paper is completed with a description of the equipment and techniques developed for the calibration in time and energy and the simulation of the whole apparatus.
The technique of discrimination of the $e^+e^-to e^+e^-$ and $e^+e^-to pi^+pi^-$ events in energy range $0.5 < sqrt{s} < 1$ GeV by energy deposition in the calorimeter of SND detector was developed by applying machine learning method. Identification efficiency for $e^+e^-to e^+e^-$ and $e^+e^-to pi^+pi^-$ events in the range from 99.3 to 99.8 % has been achived.
The lepton identification is essential for the physics programs at high-energy frontier, especially for the precise measurement of the Higgs boson. For this purpose, a Toolkit for Multivariate Data Analysis (TMVA) based lepton identification (LICH) has been developed for detectors using high granularity calorimeters. Using the conceptual detector geometry for the Circular Electron-Positron Collider (CEPC) and single charged particle samples with energy larger than 2 GeV, LICH identifies electrons/muons with efficiencies higher than 99.5% and controls the mis-identification rate of hadron to muons/electrons to better than 1%/0.5%. Reducing the calorimeter granularity by 1-2 orders of magnitude, the lepton identification performance is stable for particles with E > 2 GeV. Applied to fully simulated eeH/$mumu$H events, the lepton identification performance is consistent with the single particle case: the efficiency of identifying all the high energy leptons in an event, is 95.5-98.5%.
Based on a sample of 300 million $K_S$ mesons produced in $phi to K_L K_S$ decays recorded by the KLOE experiment at the DA$Phi$NE $e^+e^-$ collider we have measured the branching fraction for the decay $K_S to pi mu u$. The $K_S$ mesons are identified by the interaction of $K_L$ mesons in the detector. The $K_S to pi mu u$ decays are selected by a boosted decision tree built with kinematic variables and by a time-of-flight measurement. Signal efficiencies are evaluated with data control samples of $K_L to pi mu u$ decays. A fit to the reconstructed muon mass distribution finds $7223 pm 180$ signal events. Normalising to the $K_S to pi^+ pi^-$ decay events the result for the branching fraction is $mathcal{B}(K_S to pi mu u) = (4.56 pm 0.11_{rm stat} pm 0.17_{rm syst})times10^{-4}$.
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