Session G8: Electroweak Interactions I

Maximum Likelihood Analysis for the PEN Experiment

The experimental determination of the $\pi^+$ $\rightarrow$ $e^+\nu$ ($\pi_{\rm e2}$ decay) branching ratio is one of the best tests of lepton universality. The PEN experiment at PSI aims to measure this branching ratio with an order of magnitude improvement in the uncertainty, reaching $\Delta B/B \leq 5\times 10^{-4}$. The final branching ratio will be calculated using a maximum likelihood analysis and the Feldman-Cousins approach for calculating confidence limits. This analysis assigns each event to its most likely process ($\pi^+$ $\rightarrow$ $e^+\nu$, $\pi^+$ $\rightarrow$ $\mu^+\nu$, decay-in-flight, pile-up, etc.) using Monte Carlo verified probability distribution functions of our observables (energies, times, and target waveform pulse-shape analysis results). The current state of our preliminary maximum likelihood analysis will be presented.   

A Mini Time Projection Chamber for the PEN Experiment

The PEN experiment aims to measure the $\pi^+ \rightarrow e^+ \nu(\gamma )$ branching ratio with a relative uncertainty of $5\times 10^{-4}$ or smaller using a stopped beam approach. Achieving this precision requires strict control of many systematics, including pion decay vertex position and identification of decay-in-flight events. We have designed and implemented a miniature time projection chamber (50\,$\times$\,50\,$\times$\,50\,mm$^3$, with 4 anode readout wires) to track beam pions in order to control the aforementioned systematics. This paper discusses the performance of the MTPC during the fall 2009 data collection period at PSI.   

Overview of the Qweak Experiment at Jefferson Lab

The weak charge of the proton, $Q_{\rm weak}$, which measures the strength of the coupling of the $Z^0$ to the proton, is precisely predicted in the Standard Model. Any deviation from this predicted value would signal the presence of new physics. At tree level in the Standard Model, $Q_{\rm weak}$ is proportional to $1-4\sin^2 \theta_w$, which is a small number. Therefore, $Q_{\rm weak}$ is particularly sensitive to possible new physics. An experiment is being constructed at Jefferson Lab to determine $Q_{\rm weak}$ by measuring the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from the proton at very low momentum transfer. This small asymmetry, which arises due to electroweak interference, will allow us to determine the weak charge to a 4\% precision, which will probe new physics at the TeV scale. A toroidal magnetic spectrometer will focus scattered electrons from a hydrogen target onto a set of eight Cerenkov detectors, which will integrate the scattered flux of 800 MHz per detector. The physics goal of the experiment will be discussed, and an overview of the apparatus will be presented.   

Qweak: A Low Noise Experiment

The Q$_{Weak}$ experiment at Jefferson Lab will make a measurement of the weak charge of the proton with a 4\% combined statistical and systematic errors using parity-violating elastic e p scattering. The main technical challenge in this precision measurement arises from the extraction of the experimental asymmetry of 0.25 ppm from the scattering rates. The primary source of error comes from the counting statistics. Strategies will be used by the collaboration to minimize the effect of other random noise that are generated by the target density fluctuations, 60Hz pick up and the electronic modules. Custom low noise electronics built for us by TRIUMF includes an 18-bit, 500kHz sampling ADC and low noise preamplifire. Performance in realistic tests will be presented.   

Qweak Particle Tracking System

\mbox{$Q_{Weak}$} experiment at Jefferson lab will measure parity-violating elastic electron-proton scattering asymmetry at $Q^2 \simeq 0.03GeV/c^2$ to obtain the weak charge of the Proton, $Q_W$ to an accuracy of 4\%. An accurate value of $Q^2$ is required to measure the $Q_W$. A low beam-current counting- mode particle tracking system will measure the average $Q^2$ to an accuracy of $0.5$\%. A dedicated tracking software system will decode tracking detector signals to generate a set of electron hit data that will be used to derive individual electron tracks. This will enable us to calculate the scattering angle and interaction vertex, map the main detector response function, and correct the main detector signal for background contributions. A summary of the $Q_{Weak}$ tracking detectors and software system will be presented.   

A Precise Compton Polarimeter for Hall~C at Jefferson Lab

The $Q_{weak}$ experiment, scheduled to run in 2010--2012 in Hall~C at Jefferson~Lab, will measure the parity-violating asymmetry in elastic electron-proton scattering at 1.1\,GeV to determine the weak mixing angle $\sin^2 \theta_W$. The dominant experimental systematic uncertainty will be knowledge of the electron beam polarization. Following the accelerator upgrade to provide an 11\,GeV electron beam to Hall~C by 2014, parity-violating deep-inelastic scattering experiments will require a high-precision, continuous beam polarization measurement. With a new Compton polarimeter we aim to measure the beam polarization with a statistical precision better than 1\% in one hour and a systematic uncertainty of 1\% for an incident electron beam energy between 1.1\,GeV and 11\,GeV. A low-gain Fabry--P\'erot cavity laser system provides the circularly polarized photons. The scattered electrons are detected in radiation-hard diamond strip detectors, and read-out using FPGA logic boards. The photon detector uses a fast, undoped CsI crystal with sampling and integrating read-out. Coincident events are used to calibrate the detectors. The design and installation of the Compton polarimeter subsystems will be discussed.   

Data acquisition system for the electron detector in Compton polarimeter

The Q$_{weak}$ experiment will use a new Compton polarimeter for the non-invasive continuous measurement of the electron beam polarization. The Compton polarimeter will use four planes of multi-strip diamond detectors to detect the Compton scattered electrons and a CsI crystal to detect the back-scattered photons. The diamond detectors will be read out using custom-built electronic modules that chain together a preamplifier, a shaper and a discriminator for each micro-strip. The digitized signal will be processed by a general purpose logic module based on field programmable gate arrays which can handle very high rates of up to 100kHz. The data acquisition will be handled by the CEBAF online data acquisition package. We have assembled a data acquisition setup for the electron detector, along with a complete electronic readout chain for the same. The logic modules have been programmed to collect data in both single event mode and accumulation mode. The diamond detectors and the complete data acquisition system are being tested with various electron sources and cosmic rays. We will show preliminary results from these tests.   

An Overview of the Data Acquisition System in the KATRIN Experiment

The Karlsruhe Tritium Neutrino (KATRIN) Experiment is a next generation tritium $\beta$-decay experiment designed to make a model-independent measurement of the $\nu_{e}$-mass with an estimated sensitivity of 0.2 eV/$c^{2}$. This would represent an order of magnitude improvement in the $\nu_{e}$-mass sensitivity compared to previous tritium beta-decay experiments. The basic function of the Data Acquisition System (DAQ) is to process and store signals from all detector modules within the KATRIN experimental setup. In order to reach the specified $\nu_{e}$-mass sensitivity, the KATRIN DAQ must be able to process event rates over a range spanning a few mHz for $\nu_{e}$-mass measurements to MHz for calibration measurements. A multi-user graphical Object-oriented Real-time Control and Acquisition (ORCA) interface serves as the software that is employed to readout the DAQ electronics. In this talk, the KATRIN DAQ electronics as well as the ORCA software interface will be discussed.   

Development of a Data-Acquisition System for a Low-Background BEGe Detector

The broad energy germanium (BEGe) detector is a type of high purity germanium detector exhibiting sub-kiloelectronvolt energy thresholds while maintaining a large ($\sim$1 kg) detector mass. BEGe detectors show a factor $\sim$5 increase in charge drift times over traditional germanium detectors, greatly improving the ability to distinguish single site events from multi-site events. This feature in a single channel detector is particularly desirable in a neutrinoless double-beta decay experiment, where it could allow a significant reduction in background events from pulse-shape discrimination and a simplification in detector array design. The M\textsc{ajorana} collaboration has deployed a customized BEGe detector at Kimballton Underground Research Facility in Virginia to investigate the feasibility of using BEGe detectors in the search for neutrinoless double-beta decay in $^{76}$Ge. In order to make full use of the powerful pulse-shape event discrimination of BEGe detectors, a data acquisition system (DAQ) capable of digitizing extremely low-energy signals at 100MHz is required. We present an overview of the DAQ developed for this detector.