The BABAR detector has operated nearly 200 Resistive Plate Chambers (RPCs), constructed as part of an upgrade of the forward endcap muon detector, for the past two years. The RPCs experience widely different background ; luminosity-driven singles rates (0.01-10 Hz/cm2) depending on position within the endcap. Some regions have integrated over 0.3 C/cm 2. RPC efficiency measured with cosmic rays is high ; stable. The average efficiency measured with beam is also high. However, a few of the highest rate RPCs have suffered efficiency losses of 5-15%. Although constructed with improved techniques ; minimal use of linseed oil, many of the RPCs, which are operated in streamer mode, have shown increased dark currents ; noise rates that are correlated with the direction of the gas flow ; the integrated current. Studies of the above aging effects are presented ; correlated with detector operating conditions. © 2005 Elsevier B.V. All rights reserved.
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