Transverse single spin asymmetry, AN, of very forward (η > 6) π0 production plays an important role to understand the production mechanism from the view points of particularly diffractive and non-diffractive interactions. However, it has never been measured in detail because non-zero AN of π0 has been usually interpreted by perturbative QCD framework. Since larger AN was observed by more isolated π0 than less isolated ones recently, the diffraction is emerging as a possible origin of the non-zero AN of π0. To disentangle this point, we installed a new electromagnetic calorimeter in the 0-degree area of STAR experiment and measured very forward π0 over the transverse momentum (pT) range of 0 < pT < 1 GeV/c in 510 GeV p↑+p collisions.
We report the first measurement of the AN in very forward π0 production and its preliminary result
as a function of pT recently released, which will provide more precise answer to the role of the
diffractive interaction in near future by combined analysis with other STAR detectors.