Higher twist analysis of the proton g_1 structure function

We perform a global analysis of all available spin-dependent proton structure function data, covering a large range of Q^2, 1 < Q^2 < 30 GeV^2, and calculate the lowest moment of the g_1 structure function as a function of Q^2. From the Q^2 dependence of the lowest moment we extract matrix elements of twist-4 operators, and determine the color electric and magnetic polarizabilities of the proton to be chi_E = 0.026 +- 0.015 (stat) + 0.021/-0.024 (sys) and chi_B = -0.013 -+ 0.007 (stat) - 0.010/+0.012 (sys), respectively.