Onset of the Color Transparency (CT) in Protons at 12 GeV in Hall C at Jefferson Lab (JLab)

CT is a unique prediction of QCD where the final (and/or initial) state interactions of hadrons with the nuclear medium are suppressed for exclusive processes at high momentum transfers. While this phenomenon has been observed for mesons, there has never been a conclusive observation for baryons. A clear signal of CT for baryons would be the first evidence of baryons fluctuating to a small size in the nucleus, and the onset would show the transition from partonic picture to quark-gluon degrees of freedom.

The experiment E12-06-107 searching for the onset of CT in protons, was completed in Hall C at JLab using the recently upgraded 12 GeV e^- beam. It used HMS and new SHMS spectrometers in coincidence to measure the ¹²C(e,e’p) proton knockout reaction. Data were collected on a ¹²C target over the range of Q² = 8 – 14.3 (GeV/c)² covering the region where a previous A(p,2p) experiment at BNL had observed an enhancement. Additional data on a ¹H target were collected to determine the elementary process. A rise in the Proton Transparency (PT) as a function of Q² is predicted to be a signature of the onset of CT.

This talk will summarize the status of the analysis and present preliminary results on hydrogen normalization and nuclear transparency.