The Ohio State University               Department of Physics           BABAR


December 2002 groups from Italy (Ferrara, Padova) and the US (Princeton, Ohio State) proposed to replace the current BaBar Resistive Plate Chambers (RPC) in the instrumented flux return (IFR) gaps, used to detect muons and  neutral hadrons, with plastic Limited Streamer Tubes (LST). These web pages provide more detailed information on this project as well as the work done by the Ohio State group.
(2007 Update) This project is now complete. The last LST modules were installed during the 2006 shutdown in time for Run 6. A brief report on the LST Upgrade project can be found here.


LST Links

A “standard” LST  cell consists of a  silver plated sense wire 100 mm in diameter, located at the center of a cell of 9-mm square section.  A plastic (PVC ) extruded structure, or  “profile” contains 8 such cells, open on one side (fig. 2). The profile is coated with a resistive layer of graphite, having a typical surface resistivity between 0.2 and 1 MW/square. The profiles, coated with graphite and strung with wires, are inserted in plastic tubes (“sleeves”) of matching dimensions for containment of the gas mixture. Other components needed for the complete detector are end pieces with gas inlets, HV and ground connectors; spacers, which keep the wires at the centre of the cell and are installed typically every 40cm; small printed boards and their supports at the two ends of the profile for soldering the wires and providing electrical connections. If, as is likely, the dimensions of the tubes are modified, a new set of all these pieces will be designed. The signals for the measurement of one coordinate can be read directly from the wires, but it has become customary instead to read both coordinates with strip planes, thereby avoiding the complications of feed-throughs and blocking capacitors. For such tubes the operating voltage is typically 4.7kV; the plateaus are at least 200V wide; the signals on the wire are of the order of 150/200mV (over 50W), typically 50ns at the base, sometimes with an afterpulse; an average charge per pulse of 300pC can be assumed. The gas mixtures are strongly quenching: the original one (25% Ar, 75% n-pentane) being explosive has been replaced in accelerator use (SLD; ZEUS) by a non-flammable one based on CO2. The LST geometrical efficiency is limited by the  plastic sides of the cells (1mm thick) and  sleeves (1mm) to a worst-case value of 90%. Fortunately  this effect is mitigated by the fact that most tracks area not exactly orthogonal  to the profiles, and can be greatly reduced by increasing the cell size. Alternatively a double-layer geometry increases both efficiency and reliability, as long as the gap is thick enough to accommodate it.

More information on limited streamer tubes:


General BaBar LST Links (some are private)


High Voltage System

Gas and Efficiency Studies


Module Assembly

Test Tube Activities

Quality Control and Test Set-Ups

Contact Information

Mailing address        Professor Klaus Honscheid
                                Professor Richard Kass
                                Dept. of Physics
                                The Ohio State University
                                174 W 18th Avenue
                                Columbus, Ohio

Conference Room    (614) 292-2314

    (2029)                (614 292-6799

Fax:                        (614) 292-8261