Federal health officials on Monday unveiled a new primary care experiment that seeks to pay doctors for providing stepped-up services that keep patients healthy and out of the hospital, an effort they say will transform basic medical services for tens of millions of American patients. The initiative, called CMS Primary Cares, includes five new payment options for small and large providers, allowing them to take varying levels of financial responsibility for improving care and lowering costs. It broadly seeks to change how primary care is delivered in the U.S. by rewarding doctors for improving management of patients with chronic illnesses such as diabetes and high blood pressure and averting expensive trips to the hospital.