They're accountable in the sense that they're all up for reelection. You can show up and demand an explanation of the bill status and the role they played. If you don't like it you can vote for someone else.
In practice I suspect very few people care all that much. Some do, of course, but for most it won't be top of their priority list.
This is the real challenge of democracy. We think of it in terms of yeah no votes, but the real work is done by the people choosing from millions of options to put the final up-down choice in front of you. Nobody has yet found a good way to do collaboration on that scale.
> demand an explanation of the bill status and the role they played
That's just what I meant. Can you know which senator voted how within that committee? Otherwise it'd be easy for them to say "well I voted for it of course!"
Do you know if that information will be public record in any way? If not, this seems like an awful lot of power in very few, non-accountable hands...