Study of HF production in BaBar Resistive Plate Chambers

TheBaBar detector has operated over 200 2nd generation Resistive Plate Chambers (RPCs)in the forward end caps ince 2002. Many chambers have increased noise rates and highvoltage currents. These aging symptoms are correlated with the integrated RPC current as expected, but also depend on the rate and direction of the gas flow, indicating that pollutants produced in the gas can accelerate aging of downstream RPC surfaces. HFproduced by decomposition of the Freon 134a component of the BaBar RPC gas inelectric discharges has been proposed as the main pollutant. This paper presents measurements of HFproduction and absorption rates in BaBar RPCs. Since many of the highest rate chambers in the forward end cap were onverted to avalanche mode operation, a comparison of HFproduction in streamer and avalanche mode RPC s is made. Correlations between the HF production rate and other chamber operating conditions were also explored