Study of Noise inCMS Hadron Calorimeter

Kunal KothekarSeema Sharma, Sourabh Dube

XXI DAE-BRNS High Energy Physics Symposium, 2014

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Outline

➔ Introduction.

➔ Characteristics of Noise in the Hadron Calorimeter.

➔ Noise Rejection Criteria (or current Noise variables).

➔ Study of 2014 Cosmic Data.

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Motivation➔ The performance of CMS detector needs to be studied in the changing condition of 2015

LHC run.

➔ Analysis of Noise characteristics in the HCAL, is the part of detector performance studies.

➔ Its essential to remove such anomalous Noise signals so that they do not contribute to the measured energy attributed to collision events.

➔ The aim here is to evaluate the performance of noise rejection algorithms.

➔ Data taken in absence of proton beams is used to understand the noise.

➔ I will be presenting studies on 2014 cosmic data.

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The CMS Detector Overview

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Brief Introduction to the CMS Hadron Calorimeter ➔ The Hadron Calorimeter (HCAL) measures the energy of charged and neutral hadrons.

➔ HCAL is organized in four major sections,- Barrel(HB), covers range | η | ≤ 1.4- EndCap (HE), covers range 1.3 ≤ | η | ≤ 3.0 ,- Forward calorimeters(HF), covers range 2.9 ≤ | η | ≤ 5,- Outer calorimeter(HO), serves to detect escaped particles from inner calorimeter.

➔ There are 18 equal slices in φ direction for both HB and HE.

Longitudinal view of the CMS detector .

HB

HE

HF

HO

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➔ The front end electronics of each wedge are housed in a read out box(RBX).

➔ Each RBX contains four hybrid photo detector(HPD) which registers signals from eighteen towers at an fixed φ angle.

➔ Analog-to-digital converters(ADCs) digitize the signals.

➔ The ADC output of each calorimeter channel is computed every 25 ns(Time-slices).

The HCAL tower segmentation in the r, z plane for one-fourth of the HB,

HO, and HE detectors.

Read-Out Scheme for CMS Hadron Calorimeter

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➔ The CMS ECAL and HCAL occasionally record anomalous signals which can be misinterpreted as energy deposits.

➔ Such signals can contribute in false measurement of deposited Energy.

➔ Electronics and Detector noise observed in the HB and HE occurs randomly.

➔ There are several sources of the noise such as ion feedback, HPD Noise and RBX noise.

➔ Noise is classified on the basis of 'Hits' recorded in per HPD /per RBX.

➔ A Hit is defined as any channel in a HPD which records energy > 1.5 GeV

Noise in CMS Hadron Calorimeter

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➔ HPD Ion Feedback (1 − 9 hits/RBX) -Anomalous noise, in which liberated ion due to the thermal emission causes a cascade effect.-Dominates low energy spectrum of a noise.

➔ HPD Discharge (10 − 18 hits/RBX) - Noise probably related to misalignment of HPD with magnetic field.- Typically Only HPD in an RBX records hits in the discharge event.- Dominates high energy spectrum of a noise.

➔ RBX Noise (19 − 72 hits/RBX) - Anomalous noise characterized by a high multiplicity of hits in all four HPDs in an RBX.- Counter-intuitively it is not the highest energy component of anomalous noise

Sources of Noise in HCAL

Number of hits in a RBX with energy>10 GeV

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➔ The event filter to identify and reject noise events is based on channel multiplicity, total no. of zero ADC counts and the RBX pulse shape ratio(R45).

➔ An event is flagged as noise if any of the following conditions are met,

-at least 17 channels within an HPD with Echannel

> 1.5GeV, (HPDHits) or

-at least 10 channels within an HPD with Echannel

>1.5GeV, and there is no energy reported in the other HPDs contained in the same RBX,(HPDNoOtherHits) or

-at least 10 TSs within an RBX with zero ADC counts, and E(RBX) ≥ 10GeV,(MaxZeros) or

- More variables based on timing and pulse shape of the signal.

HCAL Noise Rejection Criteria

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Study of Cosmic Data 2014

➔ For the following study data has been taken from a dataset which was taken during last few months when there was no beam activated and magnet was off.

➔ This Data is then mostly a record of cosmic events and other noise, which is ideal for characterizing noise in the detector.

➔ For analysis purpose, a specific run from this dataset which is triggered on Minimum Bias trigger set, is studied here and the results are presented.

➔ Some terms which are used in the plots are,-Nominal MET(CaloMET) Missing transverse energy reconstructed using energy recorded in calorimeters.-RBXHits Number of channels in an RBX which has Energy > 1.5 GeV. -RBXEnergy Total energy of the rechits in this RBX.

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➔ Only RBX's which have energy > 15 GeV are considered here.

➔ All the events are triggered on the condition that Highest reconstructed Jet Pt > 20 GeV

➔ Work is going on to understand the various kind of noises seen in this data.

Noise CharacteristicsHighest RBX energy Recorded per event

CMS Work in Progress

Hits corresponding to Highest RBX energy Recorded

CMS Work in Progress

RBX Energy [GeV]

Number of Hits

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Variables used for Noise Identification

➔ ADC 0's Count (MaxZeros)-High multiplicity of identical zeros recorded in ADC's indicates Noise.-We reject those events in which at least 10 Maxzero's are present

➔ HPD Hit Multiplicity-Anomalous noise is characterized on the basis of Hit multiplicity.-We reject those events in which No. of hits are greater than 17

Number of Maxzeros

Rejected Events

ADC 0's Count

10 Number of Maxzeros

CMS Work in Progress

Number of HPD Hits 17

HPD Hit Multiplicity

Rejected Events

CMS Work in Progress

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HPDNoOtherHits-Anomalous noise is characterized on the basis of Hit multiplicity.-When there are multiple hits in a single HPD of an RBX, it indicates noise.-We reject such events, when there are more than 10 hits in a single HPD, when there are no other hits in that RBX

➔ More Variables based on timing and pulse shape of the signal are under study.

Variables used for Noise Identification

HPD Hit Multiplicity when no other Hits are found in an RBX

Rejected Events

CMS Work in Progress

Number of HPD Hits10

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Survived Events after Noise Cleaning

Accepted Events after applying Noise rejection criteria

CMS Work in Progress

All Events

Accepted Events

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Conclusion & Future Plans

➔ LHC is going to resume its operation at center-of-mass energy 13 TeV in a few months.

➔ Work is going on to understand HCAL noise characteristics.

➔ The total rate for noise with RBX Energy ERBX

> 100 GeV is observed to be ~4Hz in the 2009 CRAFT data, we are working to update the noise rate for 2014 cosmic data.

➔ One has to test, how much effective these algorithms would be, in new conditions like high beam energy and increased pile-up rate.

➔ Presented a preliminary study of cosmic data taken by CMS experiment. More work is in progress.