Energy weighting for the upgrade of the CMS HCAL
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ELEMENTARY PARTICLES AND FIELDS Experiment
Energy Weighting for the Upgrade of the CMS HCAL* 1) ¨ K. Borras1), D. Krucker , I. Melzer-Pellmann1) , M. Stein1)** , and P. Schleper2)
Received November 15, 2011
Abstract—In these simulation studies an energy weighting method is applied to the signals of the CMS hadronic calorimeter readout with a longitudinal segmentation for a possible future upgrade. Tabulated weighting factors are used to compensate for the different response of hadronic and electromagnetic energy depositions of simulated pion showers in the hadronic calorimeter. The weighting improves √ 2 the relative energy resolution: (σE /E) = ((92.2 ± 0.6)%/ E)2 + ((6.5 ± 0.1)%)2 (before weighting), √ (σE,weight /E)2 = ((85.4 ± 0.5)%/ E)2 + ((4.4 ± 0.1)%)2 (after weighting), where E in the square root has units of GeV. DOI: 10.1134/S1063778812090049
1. INTRODUCTION The hadronic calorimeter (HCAL) of CMS is a non-compensating sampling calorimeter with an e/π ratio of about 1.2 for 50-GeV pions [1]. Consequently, the response for electromagnetic energy depositions is larger than for hadronic ones which affects the energy measurement. An energy weighting method to compensate for the e/π ratio is possible if one can identify the electromagnetic- or hadroniclike origin of the energy deposition within a hadronic shower. For the CMS detector upgrade Phase I a longitudinal segmentation of the HCAL towers is under consideration, improving its longitudinal granularity by a factor of 4 (see Fig. 1). This offers the possibility to resolve parts of particle showers. A possible readout scheme (“1–4–4–8”) is investigated here, where each digit represents the number of calorimeter cells which are read out in one channel. Other possible readout schemes has been investigated, too. However, it turned out that the readout scheme “1–4–4–8” yields the best result for the weighting.
energy depositions and to find appropriate weighting factors for the compensation. The discrimination criterion is the energy density i /V i , ρi = Emeas
(1)
i is the measured energy and V i a measure where Emeas for the volume in arbitrary units, both for a readout channel i.
The weighting is based on the fact that the average energy density of electromagnetic depositions is larger than for hadronic ones. In a Monte-Carlo (MC) simulation it is possible to obtain weighting
2. THE METHOD AND REALIZATION The method of the tabulated weighting factors [2, 3] is a software-based method, aiming to compensate for the e/π ratio of a calorimeter. The basic idea is to distinguish between electromagnetic and hadronic
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The text was submitted by the authors in English. 1) DESY, Hamburg, Germany. 2) University of Hamburg, Germany. ** E-mail: [email protected]
Fig. 1. Sketch of a possible readout scheme (“1–4– 4–8”) for the CMS HCAL after the upgrade.
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ENERGY WEIGHTING
factors wi as a function of the energy density ρi : i Edep i i w ρ , Eshower = , i Emeas
σE/E, % 30
After w
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