Systematic Errors in measurement of b1

[摘要] A class of spin observables can be obtained from the relative difference of or asymmetry between cross sections of different spin states of beam or target particles. Such observables have the advantage that the normalization factors needed to calculate absolute cross sections from yields often divide out or cancel to a large degree in constructing asymmetries. However, normalization factors can change with time, giving different normalization factors for different target or beam spin states, leading to systematic errors in asymmetries in addition to those determined from statistics. Rapidly flipping spin orientation, such as what is routinely done with polarized beams, can significantly reduce the impact of these normalization fluctuations and drifts. Target spin orientations typically require minutes to hours to change, versus fractions of a second for beams, making systematic errors for observables based on target spin flips more difficult to control. Such systematic errors from normalization drifts are discussed in the context of the proposed measurement of the deuteron b1structure function at Jefferson Lab.

[发布机构] Thomas Jefferson National Accelerator Facility, Newport News; VA; 23606, United States^1

[关键词] Absolute cross sections;Jefferson Lab;Normalization factors;Polarized beams;Spin observables;Spin orientations;Spin state;Structure functions