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CHALLENGES AND LIMITATIONS OF CURRENT CALORIMETERS
Roger Rusack – The University of Minnesota
Overview
§ What are the current calorimeters. § Experience and some problems seen.
What are the Current Calorimeters
§ CMS ú ECAL -‐ Lead Tungstate crystal calorimeter. ú HCAL – Brass – plasIc scinIllator and forward calorimeter steel – quartz fibers.
CMS Calorimeters ECAL – ~76,000 lead tungstate crystals
HF – quartz fiber Čerenkov calorimeter
Barrel and endcap hadron calorimeters – brass & scinIllator.
ResoluIon
ATLAS Calorimeters
ATLAS γ candidate γ candidate
πo candidate
Electronic Noise with <pile-‐up> = 14.
PoinIng
Check also with di-photon events(looking at z(1)-z(2) instead of the average)
same resolution for different pileup levels
27
ATLAS ECAL Performance
Limits to Liquid Argon
§ Current due to ionizaIon between plates. ú CriIcal charge density where electric fields across the gaps begin to sag and electron mobility decreases.
ú An issue in the forward calorimeter (FCAL) of ATLAS in the HL-‐LHC era.
§ Cryro Preamps
Problems in ExisIng CMS Calorimeters
§ CMS ECAL ú Signals seen in the avalanche photodiodes from neutrons.
ú Short-‐term changes due to ionizaIon radiaIon. ú Long-‐term damage caused by nuclear interacIons.
Timing
N!/eff A0 20 40 60 80 100
) [ns
]1-t 2(t!
0
0.5
1
1.5
2
2.5
3
3.5
4 / ndf 2" 6.632 / 15
N 0.2907± 27.45 C 0.02646± 0.2666
/ ndf 2" 6.632 / 15N 0.2907± 27.45 C 0.02646± 0.2666
CMS preliminary 2010ECAL Barrel
= 7 TeVs
4.5 GeV
RadiaIon Induced Light Loss
Long-‐Term Hadronic Damage
!1.5 2 2.5 3
0S
/S
-310
-210
-110
1
-1s-2, 5E+33 cm-1 10 fb
-1s-2, 1E+34 cm-1 100 fb
-1s-2, 2E+34 cm-1 500 fb
-1s-2, 5E+34 cm-11000 fb
-1s-2, 5E+34 cm-12000 fb
-1s-2, 5E+34 cm-13000 fb
Constant Term Changes
!1.5 2 2.5 3
/AA
"
-410
-310
-210
-110
1 -1s-2, 5E+33 cm-1 10 fb -1s-2, 1E+34 cm-1 100 fb
-1s-2, 2E+34 cm-1 500 fb -1s-2, 5E+34 cm-11000 fb
-1s-2, 5E+34 cm-12000 fb -1s-2, 5E+34 cm-13000 fb
Predicted variaIon of the constant term in the end-‐cap calorimeter due to the hadron induced damage.
InteracIons in the APDs
Seen early on in CMS. Made life very exciIng for short while. ExplanaIon is that these are mostly from knock-‐on protons from the epoxy used to couple the APD to the crystal.
SPIKES
Spikes
On detector suppression using energy deposiIon in surrounding crystals.
Offline signal Iming
CMS HCAL § Photodetector Experience
ú Hybrid PMTs found to have significant breakdown at intermediate B-‐fields (~2 T).
ú InstabiliIes in Hybrid PMTs response. ú Čerenkov radiaIon in glass of PMTs used to readout the HF calorimeter.
§ Light loss in fibers and plasIc scinIllator.
All these effects are being addressed in the Phase 1 upgrade of the CMS hadron calorimeter
Photodetector Stability
PMT Hits
ES (GeV)
EL (
GeV
)
Forward Calorimeter in CMS
-1Integrated luminosity, fb0 2 4 6 8 10 12
Rel
ativ
e si
gnal
stre
ngth
0.80.820.840.860.880.9
0.920.940.960.98
11.021.04
=2.9!=3.5..4.2!=5.1!
CMS Preliminary 2012
R7525 Hamamatsu (Single-anode PMTs)
PMT Hits
Light Loss in HF fibers.
Expected Effect on ResoluIon in HF
Damage to ScinIllator in Endcaps
500 4-‐1
1.
0.
.3
.6
1.
3000 4-‐1
CMS Upgraded Hadron Calorimeter Major detector changes that will be done in LS1 and LS2. New Photodetectors and increased segmentaIon. Solving unexpected problems with Vacuum PMT’s and Hybrid PMTs
Summary
§ Expect the unexpected. § Very mature technologies do really have fewer risks.
§ QualificaIon at the system level olen gets postponed but is very important.