Comparison of the multi-anode PMTs with the old HF PMTs by studying the collision data

Abstract

The Hadron Forward (HF) calorimeter of the CMS detector improves jet detection and missing transverse energy resolution in the high pseudorapidity range. HF employs photomultiplier tubes (PMT) that measure the Cerenkov light emitted by shower products in quartz fibers. Stray muons that hit a PMT window create high energy events that are difficult to reject. To alleviate this problem, the PMTs installed in the CMS will be replaced with those of better performance. From among various candidate PMTs, quad-anode Hamamatsu R7600U-200-M4 were chosen to replace the single-anode Hamamatsu R7525HA PMTs. The quad-anode PMTs o er the possibility to reject window events at the hardware level; muons hitting the window are localized to a single anode, while real events illuminate all four anodes. In 2011, eight such PMTs were installed in the readout boxes corresponding to the coordinates i = 67, i = 29; 30; 31; 32, which get very few hits on account of their location. The purpose of this thesis is to compare the response of the old and new PMTs to window hits using pulseshape analysis. It is shown that the new PMTs offer significantly better noise performance, simply by virtue of their thinner windows.