BOSTON — Massachusetts voters are heading to the polls today to decide which Republican and Democratic candidates will win their party primaries and go on to run in the state’s second special U.S. Senate election in four years.

The race to fill the seat formerly held by Secretary of State John Kerry has been overshadowed by the Boston Marathon bombings. A light turnout is expected.

The Republican candidates include former Navy SEAL Gabriel Gomez, former U.S. Attorney Michael Sullivan and state Rep. Daniel Winslow.

The Democratic primary is pitting congressmen Edward Markey and Stephen Lynch against each other.

A win would help Senate Democrats maintain a caucus edge of 55-45 as they press forward on issues including immigration.