Identification and Filtering of Uncharacteristic Noise in the CMS Hadron Calorimeter

TL;DR

This paper presents the identification and filtering of uncharacteristic HCAL noise observed during CMS commissioning. It introduces algorithms to flag intermittent HPD/RBX noise, PMT window hits, ADC saturation, and persistent hot/dead channels, validates them on CRUZET/CRAFT and MC datasets, and demonstrates substantial reductions in fake MET at both trigger and offline levels. The results show effective noise suppression with limited impact on physics signals, indicating practical benefits for CMS MET-based triggers during early LHC data taking. The methods provide a framework for ongoing HCAL noise management and potential deployment at the trigger level to maintain data quality in high-rate environments.

Abstract

Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.

Figures (9)

• Figure 1: Quarter view of the CMS hadron calorimeter. The shading indicates the optical grouping of scintillator layers into different longitudinal readouts.
• Figure 2: HCAL noise rates from CRAFT data passing a 6 GeV jet trigger. Rates are plotted vs. (top) readout box energy and (bottom) missing transverse energy for all events with at least one HB/HE readout box containing more than 20 GeV of energy. Only channels with energy greater than 1 GeV are considered when calculating contributions to the readout box energy.
• Figure 3: Number of HCAL channels within a single RBX with energy greater than 1 GeV, for readout boxes with a total energy greater than 20 GeV. Data were collected from CRAFT events triggered on calorimeter jets with at least 6 GeV of transverse energy.
• Figure 4: Expected HCAL signal pulse shape, from (left) pion test beam data HBdesign and (right) a simulated QCD multi-jet sample . The tails of each pulse are shaded in black.
• Figure 5: Each figure shows a charge distribution from a single HB channel in a CRUZET event. Events were collected from a trigger that required a minimum energy of 10 GeV from any two neighboring HCAL towers. The channel on the left has no tail, while the (shaded) tail of the channel on the right is abnormally large. Both channels are flagged as noisy.