How do these both detectors separate from each other? Of course I can derive the terms and this is, more or less, all I can look up: In an electromagnetic calorimeter the particles interact mostly electromagnetically and in a hadronic calorimeter they will do it via the strong force.

This rises the following question: Can gluons not be measured with an electromagnetic calorimeter?

How can I ensure that this will be possible with the help of a hadronic calorimeter? Hence, can't I measure charged particles and photons within a hadronic calorimeter?

The question is a bit connected to What exactly is measured in a e.g. hadronic calorimeter - momentum or energy of a particle?.

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    $\begingroup$ Not sure what you mean: gluons don't exist as free particles in a calorimeter of either kind, do they? $\endgroup$
    – user154997
    Nov 2, 2017 at 14:58
  • $\begingroup$ The main difference between them is the materials that are used. Materials that calorimeters are made of. $\endgroup$
    – Nemo
    Nov 2, 2017 at 15:03
  • $\begingroup$ You're right. I was looking for particles who interact via the strong force and exclued quarks because they have also electric charge. Didn't think further.. Nevertheless: How does the material influence a measurement? $\endgroup$
    – Ben
    Nov 2, 2017 at 15:16
  • $\begingroup$ Gluons are not a good example since they are confined inside hadrons. Gluons and quarks hadronize forming jets. $\endgroup$
    – Nemo
    Nov 2, 2017 at 15:16
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    $\begingroup$ Your question would make more sense with neutron instead of gluon: a hadronic calorimeter will detect a neutron whereas an electromagnetic calorimeter will not detect a neutral particle. $\endgroup$
    – user154997
    Nov 2, 2017 at 17:14

2 Answers 2


Let us take as an example proton proton scattering at LHC. The scatter is calculated to happen within a known volume, and the objective is to measure all outgoing particles' energy and momentum, and detectors are built around the interaction region in order to achieve this total knowledge of each interaction ( hopefully)

Here is the CMS detetor at LHC.

enter image description here

The silicon trackers catch all charge particles by the tracks they leave, and the momentum is measured by their curvature in the magnetic field. Neutral particles leave no track and have to be caught by special detectors. The photons deposit all their energy in the crystal electromagnetic calorimeter. The charged tracks also leave their trace but can be identified by the entering track, for electrons, which will also deposit all their energy in the electromagnetic calorimeter. The rest of the tracks create showers in the hadronic calorimeter, except for the muons which go all the way through to the muon detectors.

A hadronic signal in the hadron calorimeter which does not have a track input, is a neutron.

Gluons can only be identified in jets of charged and neutral paricles, as gluon jets.

Here is a candidate event for a higgs boson:


CMS-PHO-EVENTS-2011-010-9 - Small, Medium, Large, Original Real CMS proton-proton collision events in which 4 high energy electrons (green lines and red towers) are observed. The event shows characteristics expected from the decay of a Higgs boson but is also consistent with background Standard Model physics processes.

The red towers are in the electromagnetic calorimeter, and the association with the green charged tracks defines them as electrons. One must realize that a lot of computing using the data in the detectors is necessary to see these event displays.

You can check on a number of other events.

  • $\begingroup$ Thank you! I've some questions: Why are the green tracks not bended respectively where is the according magnetic field? to do that? Then, I feel your answer is more about the identification but how/why do I built a hcal different than an ecal? $\endgroup$
    – Ben
    Nov 3, 2017 at 14:47
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    $\begingroup$ Note that the ecal is made of crystals the hcal of a lot of mass with detectors in between. The crystals show the light of the secondary photons from the dominant electromagnetic interactions. The hcal bulk matter (brass+ plastic scintilator, see image above) allows for strong interactions having a high probability. They do not look bended because the image is small and the electrons (by choice looking for Higgs) are very high energy, in contrast to the rest of the charged tracks. There are many"spectator" tracks in high energy proton proton. $\endgroup$
    – anna v
    Nov 3, 2017 at 16:02

The magnetic constant accepted by treaty is a major stumbling block. The Higgs can be found such that :

91.165434070 GeV [1.25663706209E-6 / (4) (2.285514462E-7)] = 125.312993135 mz LEP mu o P-synchrotron LEP m-Higgs boson LHC watt/electron

(96485.3397794)(13.6056919364)(.007297352538)^2 (25812.8075694)/ (.001)(299792458)^2 =m-H F=kb Na Tk Eb alpha Rk = h/eV^2 gram C

I have several other solutions which I found prior to the July 4,2012 announcement at CERN and they all give the same mass for the Higgs boson.


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