CMS Central Hadron Calorimeter

We present a description of the CMS central hadron calorimeter. We describe the production of the 1996 CMS hadron testbeam module. We show the results of the quality control tests of the testbeam module. We present some results of the 1995 CMS hadron testbeam. The design of the CMS detector starts with the 4 T solenoidal magnet of length 13 m and inner diameter 5.9 m. The magnet determines many of the features of the CMS calorimeters, since the CMS calorimeter is located inside the magnet. Figure 1 shows a quarter slice of the CMS up to the coil. The EM calorimeter, ECAL, consists of lead tungstate, PbW0 4 , crystals. The hadron calorimeter, HCAL, surrounds ECAL. The most important requirement of HCAL is to minimize the non-gaussian tails of the energy resolution function. Hence, HCAL design maximizes as much interaction length of material inside the magnetic coil as possible. Copper absorber satisfies this requirement, as well as being nonmag-netic. In addition, copper is fairly low Z, so it does not degrade the muon momentum measurement. Maximizing the amount of absorber before the magnet requires minimizing the amount of space devoted to active medium. The tile/fiber technology is an ideal choice. It consists of plastic scintillator tiles read out with embedded wave length shifting (WLS) fibers. This technology was first developed by the UA1 collaboration and at Protvino [1]. The system is being used in the upgrade of the CDF endcap calorimeter [2]. It enables HCAL to be easily built with a tower geometry readout. The entire HCAL area can be instrumented with no uninstrumented cracks. HCAL covers the pseudorapidity range |η| <3.0 with a barrel (central) and endcap hadron calorimeter. The barrel calorimeter covers 0< |η| <1.4, while the endcap calorimeter covers down to |η|=3.0. The region to |η|=5.0 is covered by a very forward calorimeter. HCAL is segmented into towers of granularity ∆η × ∆φ=0.087×0.087. This granularity is sufficient for good dijet mass resolution. The rest of this article will only discuss the barrel hadron calorime-ter. HCAL is built as 20 o wedges inside the magnet. Figure 2 shows a 20 o wedge, with ECAL on the right side and HCAL on the left side. The body of wedges are copper, but the inner and outer plates are stainless steel for structural strength. The wedges are bolted together. This enables the wedges to be assembled cheaply and minimizes …