Transverse Momentum Dependence of Semi - Inclusive Pion and Kaon Production July 5 , 2011

1 Executive Summary E12-09-017 plans to make precise measurements of cross sections of semi-inclusive charged-pion (π ±) electroproduction at deep inelastic scattering kinematics and low transverse momentum (P h⊥) from hydrogen and deuterium targets. The experiment will simultaneously, albeit with a factor of ten lower rates, accumulate charged-kaon (K ±) cross secion measurements, and obtain high-precision measurements of the azimuthal single beam spin asymmetries at low P h⊥ , through the use of longitudinally polarized electron beams. The proposed measurements cover the range 0. The Hall C HMS spectrometer and the projected SHMS with its first-generation detector package will be used for electron and meson detection. The chosen setup of highly-focusing magnetic spectrometers with well-understood acceptances and redundant detector packages will allow precise determination of the P h⊥ dependence of the ratios of π + to π − cross sections. The proposed measurements correspond to a beam time request of 32 days, and assume a longitudinally polarized electron beam to also include azimuthal asymmetry measurements, beam energies of 8.8 and (predominantly) 11.0 GeV, and varying beam currents of up to 75 µA. The precision ratios will be combined with maps of the azimuthal asymmetries in semi-inclusive electroproduction of pions as approved for the unpolarized hydrogen target (E12-06-112, " Probing the Proton's Quark Dynamics in Semi-Inclusive Pion Production at 12 GeV ") and envisioned for the unpolar-ized deuteron target (LOI12-07-103, LOI12-09-005). In the context of a simple model, such combination of the proposed Hall C maps and the CLAS12 large-acceptance measurements constrain the initial transverse momentum widths of up and down quarks, and the transverse momentum widths of favored and unfavored fragmentation functions, respectively. We give a more detailed outline along the lines of this simple model below, using results of semi-inclusive pion electroproduction cross section measurements of the E00-108 experiment in Hall C, performed in 2003 with a 5.5 GeV beam energy, as an example. The latter also shows that although the physics proposed here benefits from its companion CLAS12 experimental program, it can stand on its own. The proposed cross section measurements will provide basic tests of the theoretical understanding of semi-inclusive deep inelastic scattering in terms of factorized parton distributions convoluted with fragmentation functions, augmenting the CLAS12 program with precision charged-pion and charged-kaon cross section ratios. These precision cross section measurements will provide a critical role in establishing and/or validating the entire semi-inclusive deep inelastic scattering program in …