In Massachusetts, leaving the scene of an accident that causes injury is a serious crime (unless you have to leave to get emergency medical attention). Call 911 and remain at the scene until the Worcester Police or the Massachusetts State Police arrive to investigate. The police will create an official accident report, which is a key piece of evidence in your case.
You also need to exchange contact and insurance information with the other driver. (If you don’t feel safe doing so right away, it’s OK to wait until the police arrive and secure the scene.) You should get names and contact information for any witnesses as well. Keep your comments at the scene brief – don’t say anything about fault, and don’t apologize. You’re not in a position to understand why the accident happened yet. Leave that to your attorney to investigate.
If you can do so, start gathering evidence at the scene. Take pictures of the vehicles involved, the surrounding circumstances, any visible injuries, property damage, and other evidence such as skid marks. It’s critical that you preserve this evidence before it’s lost or destroyed.