# How does CERN model results?

Hi all,
I was wondering how CERN models their particle results as we see them in images.
As I understand it, Heisenberg's Uncertainty Principle tells us that we are unable to precisely observe subatomic or fundamental particles, as the energy would cause its velocity or position to alter. How, then, can they precisely model the results of their experiments? What methods do they use?

P.S. Apologies if any of my information is wrong, I'm still in high school so my knowledge is horrifyingly limited!
If I followed an incorrect format or posted in the wrong section, please let me know - this is my first time here.

mfb
Mentor
I was wondering how CERN models their particle results as we see them in images.
Which images? Event displays like these?
The uncertainty relation is completely negligible for these tracks - less than the size of an atom while the pictures show tracks with lengths of meters. The measurement uncertainties of the detectors is many orders of magnitude larger than the fundamental limit given by the uncertainty principle.

The measurement uncertainty of the detectors can be a challenge for the experiments. As an example, if you reconstruct the decay of a Higgs boson to two photons, you use the measured properties of the photons to calculate the Higgs boson mass. A hypothetical perfect detector would always get the same value within ~0.004% (the natural uncertainty of this value), in practice the measurements vary by about 1%. That makes it harder to see an excess of events at the Higgs mass - you need much larger datasets than you would with a "perfect" detector. Here is an example graph and some more details.

Imager, vanhees71, dlgoff and 1 other person
Which images? Event displays Like these?
The uncertainty relation is completely negligible for these tracks - less than the size of an atom while the pictures show tracks with lengths of meters. The measurement uncertainties of the detectors is many orders of magnitude larger than the fundamental limit given by the uncertainty principle.

The measurement uncertainty of the detectors can be a challenge for the experiments. As an example, if you reconstruct the decay of a Higgs boson to two photons, you use the measured properties of the photons to calculate the Higgs boson mass. A hypothetical perfect detector would always get the same value within ~0.004% (the natural uncertainty of this value), in practice the measurements vary by about 1%. That makes it harder to see an excess of events at the Higgs mass - you need much larger datasets than you would with a "perfect" detector. Here is an example graph and some more details.

Thank you

ZapperZ
Staff Emeritus
Hi all,
I was wondering how CERN models their particle results as we see them in images.

Since you're still in high school, then there is also another thing that you should learn. The work being done at CERN are not done only by CERN employees. All of the major scientific efforts at CERN (and at Fermilab, NASA, Super Kamiokande, etc...) are done by collaborators from institutions all over the world. Look at this, for example:

https://arxiv.org/pdf/1808.00336.pdf

Scroll down and look at the institutions that are represented within the "ATLAS collaboration". What percentage of these people are actually working for CERN directly?

I'm pointing this out because a lot of people, especially outside of physics and those who are still in high school, often do not realize that major scientific projects, while done under the banner of one organization, are often done by people from all over the world. You do not need to be working for CERN to work AT CERN. This applies to all the user facilities at various major scientific laboratories all around the world.

This is a very common misconception, and I thought that this is a good opportunity to highlight it since it is obviously happening here.

Zz.

vanhees71, odietrich, mfb and 1 other person