Search

We describe the design of a 20-liter test stand constructed to study fundamental properties of liquid argon (LAr). This system utilizes a simple, cost-effective gas argon (GAr) purification to achieve high purity, which is necessary to study electron transport properties in LAr. An electron drift stack with up to 25 cm length is constructed to study electron drift, diffusion, and attachment at various electric fields. A gold photocathode and a pulsed laser are used as a bright electron source. The operational performance of this system is reported., Comment: 18 pages, 11 figures, Accepted by JINST on May 31, 2016

The MicroBooNE experiment is designed to observe interactions of neutrinos with a Liquid Argon Time Projection Chamber (LArTPC) detector from the on-axis Booster Neutrino Beam (BNB) and off-axis Neutrinos at the Main Injector (NuMI) beam at Fermi National Accelerator Laboratory. The detector consists of a $2.5~m\times 2.3~m\times 10.4~m$ TPC including an array of 32 PMTs used for triggering and timing purposes. The TPC is housed in an evacuable and foam insulated cryostat vessel. It has a 2.5 m drift length in a uniform field up to 500 V/cm. There are 3 readout wire planes (U, V and Y co-ordinates) with a 3-mm wire pitch for a total of 8,256 signal channels. The fiducial mass of the detector is 60 metric tons of LAr. In a LArTPC, ionization electrons from a charged particle track drift along the electric field lines to the detection wire planes inducing bipolar signals on the U and V (induction) planes, and a unipolar signal collected on the (collection) Y plane. The raw wire signals are processed by specialized low-noise front-end readout electronics immersed in LAr which shape and amplify the signal. Further signal processing and digitization is carried out by warm electronics. We present the techniques by which the observed final digitized waveforms, which comprise the original ionization signal convoluted with detector field response and electronics response as well as noise, are processed to recover the original ionization signal in charge and time. The correct modeling of these ingredients is critical for further event reconstruction in LArTPCs., Comment: Presentation at the DPF 2015 Meeting of the American Physical Society Division of Particles and Fields, Ann Arbor, Michigan, August 4-8, 2015

We report the measurement of longitudinal electron diffusion coefficients in liquid argon for electric fields between 100 and 2000 V/cm with a gold photocathode as a bright electron source. The measurement principle, apparatus, and data analysis are described. Our results, which are consistent with previous measurements in the region between 100 to 350 V/cm [1] , are systematically higher than the prediction of Atrazhev-Timoshkin[2], and represent the world's best measurement in the region between 350 to 2000 V/cm. The quantum efficiency of the gold photocathode, the drift velocity and longitudinal diffusion coefficients in gas argon are also presented., Comment: Accepted by NIM on January 29th. 2016

We present new measurements of the single top quark production cross section in \ppbar collisions at $\sqrt{s} = 1.96 TeV$ using data corresponding to 5.4 \ifb of integrated luminosity collected by the {\dzero} detector at the Fermilab Tevatron collider. The large mass of the top quark, close to the electroweak symmetry-breaking scale, makes it a good candidate for probing physics beyond the Standard Model, including possible anomalous couplings. We examine the data to study the Lorentz structure of the $Wtb$ coupling, and find that the data prefer the left-handed vector coupling, and set upper limits on the anomalous couplings., Comment: 4 pages, Conference proceedings for XLVIIth Rencontres de Moriond: Electroweak Interactions and Unified Theories, La Thuile, Italy, March 2012