Design and performance of a straw tube drift chamber

Drift chambers are now used in a lmost every h igh energy physics experiment. There are many different designs of drift chambers and one of them uses straw tubes as detector elements [1]. In this article, we repor t the design, construct ion, and per formance of large straw tube drift chambers used in the spect rometer a rm of E735 at the Fermi lab collider. E735 is an exper iment to s tudy low transverse m o m e n t u m particles to search for a phase t ransi t ion of h a d r o n gas to q u a r k g l u o n p lasma f rom the highest center of mass energy ~p interact ions [2]. We also present pre l iminary results of a s tudy done with 2 m m radius tubes which have a direct detector appl icat ion at the Superconduct ing Super Coll ider (SSC). Using straw tubes has several advantages. First, since the cells are isolated from one another , cross talk is minimized. If a sense wire is broken, then the channe l can be easily removed wi thout turning off all channels . Second, straw tubes can be pressurized for bet ter resolution, and for mechanical rigidity. Third, the resolut ion of tracks is independen t of a part icle 's incident angle, so one does not have to incorpora te angular correct ion factors when the drift dis tance is calculated from the drift time, as with typical drift chambers . This was the ma in reason we chose straw drift chambers since tracks in the spectrometer arm have large slopes. This article is organized as follows. In section 2, we discuss the design and const ruct ion of chambers , and in section 3, test ing and per formance of the chambers are discussed. In section 4 we describe a method to measure the drift velocity and resolution. Section 5 includes the track reconstruct ion in the chambers , and section 6 conta ins a s tudy done with 2 m m radius tubes, which may have a detector appl icat ion for the Superconducting Super Collider. The basic ingredient of the chamber is a 2.5 cm radius tube made of a luminized mylar. The wall of the tube consists of 0.018 m m of a luminum, 0.075 m m of paper and 0.075 m m of mylar, a thickness of about 0.04% of a rad ia t ion length. The tubes were wound by Stone Indust r ia l [3] with length of about 110 cm. The tubes are s trong enough to suppor t about 10 kg of weight placed on one end, and an internal pressure of at least 3 atm. The tubes are posi t ioned between two a luminum plates as shown in fig. 1. Two a luminum plates on bo th the top and the b o t t o m provide protec t ion for the tube ends, feed-throughs and electronics. The size of the holes and the dis tance between holes were milled to be be t te r than 0.1 mm. There are about 60 to 100 holes in each chamber . The holes in each chamber are in two staggered rows. After the holes were made, the center of each hole was measured with respect to a survey point to de termine the exact posi t ion of the sense wire. As shown in fig. 2, each tube is connected to the plates by means of a luminum end-pieces. A hose c lamp is used to ensure the mechanica l and electrical connect ion between the a luminum end-piece and the tube. Each a luminum piece is g rounded to the frame by a g round cable. A n end-piece made of delrin and a feedth rough are inserted in to the a luminum end-piece. 100 ~ m diameter gold plated C u B e wire is s t rung between feed-throughs under 250 g of tension. The elastic l imit of the wire is abou t 1000 g. C u B e wire is used because its thermal expans ion coefficient is close to tha t of the a luminum frame. A larger d iameter wire is chosen to provide a higher electric field near the outer wall of the tube. The drift velocity saturates if the electric field is high enough. Gas leakage, especially a round the ends of the tubes,