BOSTON — Eighteen people nationwide, more than half of whom live in Massachusetts, have been arrested in connection with an alleged drug trafficking and money laundering ring centered in Gardner, the U.S. Attorney said Tuesday. Eleven of the 18 charged live in the Bay State, in Gardner, Leominster, Winchendon, Phillipston, Fitchburg, Shirley, and Chicopee. The rest hail from New Jersey, Florida, Texas, Oklahoma, California, and Hawaii, U.S. Attorney Leah Foley said in a statement.