New Measurements of the Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering over a Range of Spin-0 Nuclei
D. Adhikari, H. Al-Bataineh, D. Androić, K. Aniol, David Armstrong, T. Averett, C. Ayerbe Gayoso, S. Barcus, Vincenzo Bellini, R. Beminiwattha, Jay Benesch, H. Bhatt, D. Bhatta Pathak, D. Bhetuwal, B. Blaikie, J. Boyd, Q. Campagna, A. Camsonne, G. D. Cates, Y. Chen, C. Clarke, J. C. Cornejo, S. Covrig Dusa, M. M. Dalton, P. Datta, A. Deshpande, D. Dutta, Charles Feldman, E. Fuchey, C. Gal, D. Gaskell, T. Gautam, Michael Gericke, C. Ghosh, I. Halilovic, O. Hansen, F. Hauenstein, W. Henry, C. J. Horowitz, Christopher Jantzi, Siyu Jian, S. Johnston, D. Jones, B. Karki, S. Kakkar, Sumudu Katugampola, C. E. Keppel, P. M. King, David E. King, Matthew Knauss, K. S. Kumar, T. Kutz, N. Lashley-Colthirst, Graham Leverick, H. Liu, N. Liyange, S. Malace, J. Mammei, R. Mammei, M. McCaughan, D. McNulty, D. Meekins, Carrington Metts, R. Michaels, M. Mihovilovič, M. M. Mondal, J. Napolitano, D. Nikolaev, M. N. H. Rashad, V. Owen, C. Palatchi, Jie Pan, B. Pandey, S. Park, K. Paschke, M. Petrusky, M. Pitt, S. Premathilake, A. J. R. Puckett, B. Quinn, R. Radloff, S. Rahman, A. Rathnayake, Brendan T. Reed, P. E. Reimer, R. K. Richards, S. Riordan, Y. Roblin, S. Seeds, A. Shahinyan, P. A. Souder, L. Tang, M. Thiel, Y. Tian, G. M. Urciuoli, E. W. Wertz, B. Wojtsekhowski, W Xiong, B. Yale, Ye Tao
Abstract
We report precision determinations of the beam-normal single spin asymmetries (A_{n}) in the elastic scattering of 0.95 and 2.18 GeV electrons off ^{12}C, ^{40}Ca, ^{48}Ca, and ^{208}Pb at very forward angles where the most detailed theoretical calculations have been performed. The first measurements of A_{n} for ^{40}Ca and ^{48}Ca are found to be similar to that of ^{12}C, consistent with expectations and thus demonstrating the validity of theoretical calculations for nuclei with Z≤20. We also report A_{n} for ^{208}Pb at two new momentum transfers (Q^{2}) extending the previous measurement. Our new data confirm the surprising result previously reported, with all three data points showing significant disagreement with the results from the Z≤20 nuclei. These data confirm our basic understanding of the underlying dynamics that govern A_{n} for nuclei containing ≲50 nucleons, but point to the need for further investigation to understand the unusual A_{n} behavior discovered for scattering off ^{208}Pb.