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I wonder that nobody came up with this question in advance - maybe it is too obvious? However..

How can neutral particles be measured (with respect to their energy in a particle detector)? I know there is, for example, Kamiokande to observe neutrinos but I haven't seen something Kamiokande-like as part of a particle accelerator/detector like CMS, Desy etc. How do they measure those particles?

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Much more complicated experimental setups and analysis are used in hadron experiments, take cms for example:

CMS

Basically, when no charged track is seen in the silicon charged particle tracker, but energy is deposited in the calorimeters, and the directon of the momentum points to the tracking vertex, one assumes a neutral particle has been detected with the energy given by the calorimeter: gammas in the electromagnetic,neutrons in the hadronic calorimeter, the electromagnetic is built so as to see gammas but neutrons will have small probability of interaction, the hadronic has high probability of neutrons and other hadrons to interact. One then goes to analysis of the energetics of the event to fit specific hadrons to the assumed neutral tracks , and compares the distributions with monte carlo generated events to get solid numbers with their errors.

I should add that any missing energy from the primary interaction found after the analysis of the events, is attributed to neutrino or generally weakly interacting particles , which are sought after for new physics.

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  • $\begingroup$ Thanks a lot! Why is a neutron weakly affected by an electromagnetic calorimeter but more likely by a hadronic one? $\endgroup$ – Ben Aug 7 at 10:56
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    $\begingroup$ @Ben because the ,material for the detectors is chosen so that hadrons will have a high interaction crossection, whereas for the EM that photons and charged particles will have higher interaction crossection $\endgroup$ – anna v Aug 7 at 15:55
  • $\begingroup$ How in specific? Is it only a matter of the density? $\endgroup$ – Ben Aug 8 at 5:01
  • $\begingroup$ @Ben It depends on the material choice , have a look : cms.web.cern.ch/news/electromagnetic-calorimeter versus cms.web.cern.ch/news/hadron-calorimeter $\endgroup$ – anna v Aug 8 at 5:21
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    $\begingroup$ You can go to the CMS detector and find what things are made of. In the links I gave you it gives the basic reason,"scintilation of charged particles and large photon energy" for ECAl, for hadronic it is large density with scintilators in between Qarks and gluons cannot be measured except as jets of nomral hadrons, k, pi, proton neutron. They have large interaction with the nuclei, and the denser the more. cdsweb.cern.ch/record/922757/files/lhcc-2006-001.pdf $\endgroup$ – anna v Aug 8 at 10:49

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