Semi-Inclusive Λ electroproduction in the Target Fragmentation Region A 12 GeV Proposal to Jefferson Lab PAC 42

Hadron production in Semi-Inclusive Deep Inelastic Scattering (SIDIS) is generally studied in the Current Fragmentation Region, where the detected hadron originates from the struck quark. Conversely, in the Target Fragmentation Region (TFR), the hadron is produced in the fragmentation process of the target remnants. Here, the SIDIS process can be described trough the so-called Fracture Functions, which represent the joint probability of producing the final hadron from the target remnants when a parton of the target nucleon is struck by the virtual photon in a hard scattering process. Like the ordinary parton distribution functions, the Fracture Functions are universal objects, thus they can be measured in one experiment at a given hard scale and then used to make predictions for other experiments, at another hard scale. We propose a study of these functions in the SIDIS electroproduction of Λ on a proton target, ep → e′ΛX. This process has two main advantages: (i) the TFR can be cleanly identified and (ii) the weak decay Λ → pπ− provides a way of measuring the final hadron polarization, allowing access to all the relevant Fracture Functions. The TFR will be identified through the cut on the Feynman-x variable xF < 0. The main focus of the proposal will be the measurement of the longitudinal spin transfer from the polarized beam to the Λ, which is sensitive to the ∆M Fracture Function, representing the probability of having a longitudinally polarized quark when a longitudinally polarized hadron is produced. Since the Λ spin mainly due to its strange quark, measurement of the Λ polarization can also provide information on the strange sea quark polarization in the nucleon. Measurements of the Lambda multiplicity will provide information on the unpolarized Fracture Function M . The study of its Q dependence also will test the perturbative framework implied by Fracture Functions, simultaneously encoding the information on the interacting parton and on the fragmentation of the spectator system. The measurements will be performed in the Hall B. We will use the 11 GeV polarized electron beam on an unpolarized hydrogen target and the CLAS12 detector to detect the scattered electron together with the proton and the pion from the Λ decay, with large coverage in the relevant kinematic variables. The CLAS12 central detector in particular will extend the detection of the low energy decay pion at large angles. The measurement will run simultaneously with the other approved experiments with unpolarized hydrogen target, thus no additional beam time is required.