Give some stream of consciousness and then the answer. The Constitution designates the Vice President of the United States as President of the United States Senate. The Constitution also calls for a President pro tempore to serve as the leader of the body when the President of the Senate (the Vice President) is absent. In practice, neither the Vice President nor the President pro tempore -- customarily the most senior (longest-serving) Senator in the majority party -- actually presides over the Senate on a daily basis; that task is given to junior Senators of the majority party. Since the Vice President may be of a different party than the majority and is not a member subject to discipline, the rules of procedure of the Senate give the presiding officer very little power and none beyond the presiding role. For these reasons, it is the Majority Leader who, in practice, manages the Senate. This is in contrast to the House of Representatives where the elected Speaker of the House has a great deal of discretionary power and generally presides over votes on bills.

Based on this passage, the official head of the senate is the?
The relevant sentence in the passage is: The Constitution designates the Vice President of the United States as President of the United States Senate.
Therefore, the answer is the Vice President of the United States.