Hadronic Calorimeter Granularity

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In summary, the reason for lower granularity in the HCAL of ATLAS is due to the wider and deeper nature of hadronic showers compared to electromagnetic ones. This decision was made to balance cost and computing power, as both were limited. Although a finer granularity could increase precision, it would have been too expensive. Despite a 15 year gap in development, the ATLAS and ZEUS detectors have similar technologies. The main difference in resolution between the hadron calorimeters is not due to the calorimeter itself, but rather the variability of hadron showers. The choice to use a non-compensating calorimeter in ATLAS was also influenced by constructability and budget constraints. The resolution for electromagnetic showers in both detectors is similar, but
  • #1
ChrisVer
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Well that's a fast question, I mainly seek for a confirmation... Is it a fact that the reason behind having lower granularity for the HCAL in ATLAS is that the Hadronic Showers are in general wider and deeper than the Electromagnetic ones? So the HCAL doesn't need high granularity (dealing with wider) but rather radially extended (dealing with deeper) geometry?
 
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  • #2
It is a matter of cost and computing power. If both were unlimited...
Jets are wider than individual electrons/photons, and just a few analyses look into the jet substructure. Also, the energy resolution for jets is much worse (energy lost to neutrinos, neutral pions that form smaller electromagnetic showers with a different calorimeter response, ...).
 
  • #3
mfb said:
Also, the energy resolution for jets is much worse

But that's also cost. ATLAS could have made their calorimeter compensating (or at least more compensating), or they could have gone to very fine granularity so that particle flow works better. Both of these would be very expensive. If the budget is fixed, that choice would have meant something else would have to get worse, and the experiment didn't want to do that.
 
  • #4
You can increase the precision with a better granularity, but you'll never reach the precision of electromagnetic calorimeters for electromagnetic showers.
 
  • #5
mfb said:
but you'll never reach the precision of electromagnetic calorimeters for electromagnetic showers.

You'd be surprised. The ATLAS hadron calorimeter has a resolution of 19%/[itex]\sqrt{E}[/itex] and for the ZEUS EM calorimeter it's 18%/[itex]\sqrt{E}[/itex]. Not equal, but pretty close. The main reason hadron calorimeters have poorer resolution isn't the calorimeter - it's the hadrons. Hadron showers are all different, and that difference makes the resolution worse.
 
  • #6
Vanadium 50 said:
The main reason hadron calorimeters have poorer resolution isn't the calorimeter - it's the hadrons. Hadron showers are all different, and that difference makes the resolution worse.
That's what I said.

Also, there are 15 years of development between ATLAS and ZEUS.
 
  • #7
mfb said:
That's what I said.

Are you sure? It seemed to me you were discussing the calorimeter, not the particles it measured

mfb said:
Also, there are 15 years of development between ATLAS and ZEUS.

Despite the 15 years, those two detectors use very similar technologies. One could have built the ATLAS calorimeter in 1990. That said, I did pick an EM calorimeter favorable to my argument: ZEUS is compensating, and ATLAS is not.
 
  • #8
Vanadium 50 said:
Are you sure? It seemed to me you were discussing the calorimeter, not the particles it measured
Things I wrote so far:
  • Jets are wider than individual electrons/photons
  • Also, the energy resolution for jets is much worse (energy lost to neutrinos, neutral pions that form smaller electromagnetic showers with a different calorimeter response, ...).
  • but you'll never reach the precision of electromagnetic calorimeters for electromagnetic showers.
Yes I am sure I discussed the measured particles. And I never discussed the calorimeters - the third bullet point mentions them because the electromagnetic showers just happen to be in the part called electromagnetic calorimeter.
Vanadium 50 said:
One could have built the ATLAS calorimeter in 1990.
Was money the only difference? ATLAS electromagnetic calorimeter has (design) of about ##\sigma/E = 10\%/\sqrt E \oplus 0.6\%##, significantly better than 18%.
Also, where does the number for the hadronic calorimeter come from? The TDR expects 60%/sqrt(E) sampling term.

I wonder how the 40 MHz (low granularity, I know) readout would have worked.

Vanadium 50 said:
ZEUS is compensating, and ATLAS is not
I know.
 
  • #10
mfb said:
Also, where does the number for the hadronic calorimeter come from?

Electron test beam. That tells you for sure what the calorimeter is capable of as an instrument.

mfb said:
Was money the only difference?

That was part of it, sure, but I think constructability was at least as important. The "natural" HCal for ATLAS would have been LAr, like the endcap. The barrel, however, is huge, and so would need an even larger cryostat. If it could be built at all it would have to be built at CERN, and CERN had a lot on their plate. The TileCal, however, could be built in pieces around the world, and only the final assembly would need to be done at CERN.
 
  • #11
Vanadium 50 said:
Electron test beam. That tells you for sure what the calorimeter is capable of as an instrument.
Ah, so 18%/sqrt(E) are for the hadronic calorimeter with electromagnetic showers. That sounds more realistic.
 

Related to Hadronic Calorimeter Granularity

1. What is a Hadronic Calorimeter Granularity?

A Hadronic Calorimeter Granularity refers to the size of the individual cells or sampling units within a hadronic calorimeter. These cells are responsible for measuring the energy of hadronic particles, such as protons and neutrons, as they pass through the calorimeter.

2. Why is granularity important in a Hadronic Calorimeter?

The granularity of a Hadronic Calorimeter is important because it determines the level of precision and accuracy in measuring the energy of particles. A smaller granularity allows for a more precise measurement of the energy of individual particles, while a larger granularity may result in a loss of energy resolution.

3. How is the granularity of a Hadronic Calorimeter determined?

The granularity of a Hadronic Calorimeter is determined by the size and number of cells or sampling units within the detector. This is often optimized through simulations and experimental studies to find the optimal balance between resolution and cost.

4. What are some factors that can affect the granularity of a Hadronic Calorimeter?

The granularity of a Hadronic Calorimeter can be affected by various factors, such as the type of particle being measured, the energy range of the particles, and the desired energy resolution. Other factors may include the size and shape of the detector and the material used to construct it.

5. How does the granularity of a Hadronic Calorimeter impact particle detection?

The granularity of a Hadronic Calorimeter plays a crucial role in particle detection. A smaller granularity allows for the identification and measurement of individual particles, while a larger granularity may result in overlapping and inaccurate measurements. This can impact the overall performance and accuracy of the calorimeter in detecting and measuring particles.

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