We present a detailed lattice calculation of the unpolarized isovector quark PDF from the largemomentum effective theory approach. In this calculation, the quasi-PDF is defined by a spatial correlator that is free from mixing with operators of the same dimension, and is nonperturbatively renormalized in a regularization-independent momentum subtraction scheme. The renormalized quasi-PDF is then matched to the MS PDF at one-loop order in perturbative QCD. The lattice simulation is done using Gaussian-momentum-smeared source at Mπ = 310 MeV with the nucleon momentum Pz ∈ {1.7, 2.15, 2.6} GeV. Five source-sink separations have been used in our analysis to control the systematics associated with excited-state contamination. The systematic errors due to renormalization and perturbative matching are carefully studied. The final result is in reasonable agreement with the PDF from the latest phenomenological analyses.

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We report the design, construction, and initial commissioning results of a large high pressure gaseous Time Projection Chamber (TPC) with Micromegas modules for charge readout. The detector vessel has an inner volume of about 600 L and an active volume of 270 L. At 10 bar operating pressure, the active volume contains about 20 kg of xenon gas and can image charged particle tracks. Drift electrons are collected by the charge readout plane, which accommodates a tessellation of seven Micromegas modules. Each of the Micromegas covers a square of 20 cm by 20 cm. A new type of Microbulk Micromegas is chosen for this application due to its good gain uniformity and low radioactive contamination. Initial commissioning results with 1 Micromegas module running with 1 bar argon and isobutane gas mixture and 5 bar xenon and trimethylamine (TMA) gas mixture are reported. We also recorded extended background tracks from cosmic ray events and highlighted the unique tracking feature of this gaseous TPC.

We analyze the lattice spacing dependence for the pion unpolarized matrix element of a quark bilinear operator with a Wilson link (parton quasidistribution functions operator, quasi-PDFs) in the rest frame, using 13 lattice spacings ranging from 0.032 to 0.121 fm. We compare results for three different fermion actions with or without good chiral symmetry on dynamical gauge ensembles from three collaborations. This investigation is motivated by the fact that the gauge link generates a 1=a divergence, the cancellation of which in many ratios can be numerically tricky. Indeed, our results show that this cancellation deteriorates with decreasing lattice spacing, and that the RI/MOM method leaves a linearly divergent residue for quasi-PDFs. We also show that in the Landau gauge the interaction between the Wilson link and the external state results in a linear divergence which depends on the discretized fermion action.