( Resubmission of E 12 - 09 - 017 to Jefferson Lab PAC 37 ) Transverse Momentum Dependence of Semi - Inclusive Pion and Kaon Production December 1 , 2010

We propose to map the transverse momentum (Pt) dependence for semi-inclusive electroproduction of charged pions (π±) and, simultaneously albeit with a factor of ten lower rates, kaons (K±) from both proton and deuteron targets. The proposed measurements cover the range 0.2 < x < 0.5, 2 < Q < 5 GeV, 0.3 < z < 0.5, and Pt < 0.5 GeV. 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 Pt 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 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 semiinclusive electroproduction of pions as approved for the unpolarized hydrogen target (E12-06112, “Probing the Proton’s Quark Dynamics in Semi-Inclusive Pion Production at 12 GeV”) and envisioned for the unpolarized deuteron target (LOI12-07-103, LOI12-09-005 and a complementary CLAS12 proposal anticipated for PAC-38 emphasizing the deuteron/proton ratios and a complete (Pt, φ) coverage). 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 electroroduction 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 measurements emphasize the low Pt region, of scale Λ, as one-particle inclusive deep inelastic scattering off polarized and unpolarized nucleons have been the emphasis of recent theoretical studies. Such cross sections have been decomposed, using tree-level factorization, in terms of transverse-momentum-dependent parton distribution and fragmentation functions, for low transverse momentum of the scattered hadron [1]. Some of the kinematics benefit from overlap with the approved 12-GeV experiment E12-06104 (“Measurement of the Ratio R = σL/σT in Semi-Inclusive Deep Inelastic Scattering”). As compared to the conditionally approved experiment E12-09-017, we have made the following changes: • Recently, an NSF-MRI award was granted to augment the SHMS detection package with an aerogel detector, allowing simultaneous measurement of kaon cross sections. • Polarized electron beam has been included as the default, to obtain azimuthal beam asymmetry measurements at low Pt. • The kinematics and checkout are coordinated with the approved E12-06-104 experiment (“Measurement of the Ratio R = σL/σT in Semi-Inclusive Deep Inelastic Scattering”) and the companion PAC-37 proposal for a “Precise Measurement of π+/π− Ratios in Semiinclusive Deep Inelastic Scattering: Charge Symmetry Violating Quark Distributions” (a resubmittal of conditionally approved experiment E12-09-002). The collaborations have large overlap.