Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session Y3: Invited Session: The Structure of the Pion |
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Sponsoring Units: DNP Chair: Rolf Ent, Thomas Jefferson National Accelerator Facility Room: Holiday 2 |
Tuesday, April 14, 2015 1:30PM - 2:06PM |
Y3.00001: Basic Facts about the Pion Invited Speaker: Craig Roberts With discovery of the Higgs boson, the Standard Model of Particle Physics became complete. Its formulation and verification are a remarkable story. However, the most important chapter is the least understood. Quantum Chromodynamics (QCD) is that part of the Standard Model which is supposed to describe all of nuclear physics and yet, almost fifty years after the discovery of quarks, we are only just beginning to understand how QCD builds the basic bricks for nuclei: pions, neutrons, protons. QCD is characterised by two emergent phenomena: confinement and dynamical chiral symmetry breaking (DCSB), whose implications are truly extraordinary. This presentation will reveal how DCSB, not the Higgs boson, generates more than 98\% of the visible mass in the Universe, explain why confinement guarantees that condensates, those quantities that were commonly viewed as constant mass-scales that fill all spacetime, are instead wholly contained within hadrons; and, with particular focus on the pion, elucidate a range of observable consequences of these phenomena whose measurement is the focus of a vast international experimental programme. [Preview Abstract] |
Tuesday, April 14, 2015 2:06PM - 2:42PM |
Y3.00002: The pion form factor and deep exclusive pion production Invited Speaker: Tanja Horn Meson electroproduction data play an important role in our understanding of hadron structure and the dynamics that bind the basic elements of nuclear physics. Pion and kaon form factors are of particular interest as they are connected to the Goldstone modes of chiral dynamical symmetry breaking. The last decade saw a dramatic improvement in precision of charged pion form factor data and new results have become available on the pion transition form factor. Increasing the virtual photon mass in electron scattering experiments allows one to reach smaller distance scales. In this regime one becomes more and more sensitive to the partonic picture where hard and soft physics have been shown to factorize and Generalized Parton Distributions (GPDs) provide the most complete description of the non-perturbative physics. Recent data and prospects for deep exclusive pion electroproduction are presented. Experimental tests of our theoretical understanding of the reaction mechanism are shown including longitudinal-transverse separated charged-pion cross section data and ratios. The prospects to use projected charged- and neutral pion data to further determine the spin, charge-parity and flavor of GPDs, including the helicity-flip GPDs, are discussed. [Preview Abstract] |
Tuesday, April 14, 2015 2:42PM - 3:18PM |
Y3.00003: Precision Measurement of the Neutral Pion Lifetime Invited Speaker: Liping Gan As the lightest particle in the hadron spectrum, the $\pi^0$ meson plays an important role in understanding the fundamental symmetries of QCD at low-energy. The $\pi^0\rightarrow\gamma\gamma$ decay offers a key test of the QCD predictions based on the chiral anomaly and spontaneous chiral symmetry breaking. The theoretical calculations over the last decade have reached the precision of 1\% in the $\pi^0$ radiative decay width. The experimental measurement of this parameter with a comparable accuracy will be an important test of QCD. The PrimEx collaboration at Jefferson Lab developed and performed two experiments to measure the $\pi^0$ decay width via the Primakoff effect. The published result from the first experiment (PrimEx-I) has achieved the accuracy of 2.8\% in the total uncertainty. The second experiment (PrimEx-II) was carried out with a goal of 1.4\% precision. The preliminary results from the PrimEx-II experiment will be presented. [Preview Abstract] |
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