Performance and aging studies of BaBar resistive plate chambers

The BaBar detector is currently operating nearly 200 Resistive Plate Chambers (RPCs), constructed as part of an upgrade of the forward endcap, muon detector in 2002. Although the average RPC efficiency remains high, numerous changes in the RPC performance (increased currents and rates) have been observed. A few of the highest rate RPCs have suffered efficiency losses of more than 15%. Several types of efficiency loss have been observed. Tests with humidified gas have shown that some of the lost efficiency is recoverable. However, efficiency losses in the highest rate regions have not yet improved with humid gases.