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.