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 and luminosity-driven singles rates (0.01–10 Hz/cm 2 ) depending on position within the endcap. Some regions have integrated over 0.3 C/cm 2 . RPC efficiency measured with cosmic rays is high and 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 and minimal use of linseed oil, many of the RPCs, which are operated in streamer mode, have shown increased dark currents and noise rates that are correlated with the direction of the gas flow and the integrated current. Studies of the above aging effects are presented and correlated with detector operating conditions.

/pdf/performance-of-second-generation-babar-resistive-plate-18hifwd6ad.pdf

Performance of second generation BABAR resistive plate chambers

The commissioning of the RPC-based Muon detector in the BESIII experiment has been carried out. The RPC modules, front-end electronics, online and offline software of the muon system have been studied. The detector performances including efficiency, counting rate, noise ratio, spacial resolution, dark current, and muon charge ratio were obtained by cosmic ray data with and without magnetic field. The new operating high voltage and threshold were chosen after the scan experiment. The long-term stability of the BESIII RPCs made of bakelite without oil treatment was Studied. (C) 2008 Elsevier B.V. All rights reserved.

First results of the RPC commissioning at BESIII

Aging of glass RPCs has been extensively studied along the last years. Most authors refer effects such as an increase of dark counting rate, reduction of the counter efficiency and the appearance of deposits over the electrodes surfaces. Understanding the origin of these deposits and their effect on the counter performance is of considerable practical importance. In this study, aimed at timing RPCs operating in avalanche mode, we irradiated 0.3 mm gas gaps for 790 days of continuous operation at 300 Hz/cm 2 , corresponding to an accumulated charge of more than 20 mC/cm 2 . No evidence of any systematic long-term increase of dark current was found, but a visual inspection confirmed the existence of a bluish deposit over the glass electrodes. The identification of the deposit components was made by liquid extraction with organic solvents and subsequent analysis by gas chromatography with mass spectroscopy detection. The identified species are oligomers of tetrafluoroethylene.

A long-run study of aging in glass timing RPCs with analysis of the deposited material

The BaBar detector has operated over 200 2nd generation Resistive Plate Chambers (RPCs) in the forward endcap since 2002. Many chambers have increased noise rates and high voltage 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. HF produced by decomposition of the Freon 134a component of the BaBar RPC gas in electric discharges has been proposed as the main pollutant. This paper presents measurements of HF production and absorption rates in BaBar RPCs. Since many of the highest rate chambers in the forward endcap were converted to avalanche mode operation, a comparison of HF production in streamer and avalanche mode RPCs is made. Correlations between the HF production rate and other chamber operating conditions were also explored.

/pdf/study-of-hf-production-in-babar-resistive-plate-chambers-1nyas9yw0q.pdf

Study of HF production in 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.

/pdf/performance-and-aging-studies-of-babar-resistive-plate-1v2a0xy54x.pdf

Performance and Aging Studies of BaBar Resistive Plate Chambers

The muon and neutral hadron detector (instrumented flux return or IFR) in the forward endcap of the BaBar detector at SLAC was upgraded by the installation of a new generation of resistive plate chambers (RPCs) and by increasing the absorber. The chamber replacement was made necessary by the rapid aging and efficiency loss of the original BaBar RPCs. Based on our experience with those original RPCs and 24 RPCs with thinner linseed oil treatments, improvements in the design, construction, and testing of the new generation RPCs were implemented and are described in detail.

/pdf/babar-forward-endcap-upgrade-457q0pbyd1.pdf

BaBar forward endcap upgrade

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BaBar forward endcap upgrade