How do we find particles?

How do we know they are there? I am clear about Atomic Theory through the ages, but what about the elementary particles? And, how do we "shine light" on particles, as I know this as a way of fiding them (and am being confused about it)?
 

Astronuc

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Well discovery of radiation goes back to Roentgen (X-rays, 1895) and Henri Becquerel, Marie and Pierre Curie (discovered radioactivity, 1896) from uranium salts and other radioactive elements. Rutherford discovered alpha and beta 'rays' from uranium in 1897. J. J. Thomson determined q/m for 'cathode rays'.

Then Rutherford did work with alpha particles, which showed the mass of the atom was concentrated.

See this history of Cosmic Rays - http://en.wikipedia.org/wiki/Cosmic_ray
particularly - http://en.wikipedia.org/wiki/Cosmic_ray#History_of_cosmic_rays

In 1928, Dmitri Skobeltsyn obtained the first cloud-chamber photographs of cosmic rays. These indicated high energy particles, many of which were charged.

In 1931, Robert Van De Graff constructed the first high-voltage electrostatic generator for nuclear research, and the next year, 1932, Ernest Lawrence built the first cyclotron.

Chadwick discovered the neutron in 1932.

Then it was a matter of piecing together the puzzle and building bigger, higher energy machines.

The rest is history. :biggrin:
 
SizarieldoR said:
How do we know they are there? I am clear about Atomic Theory through the ages, but what about the elementary particles? And, how do we "shine light" on particles, as I know this as a way of fiding them (and am being confused about it)?

Bubble and cloud chambers and more advanced versions. Cloud chamber is pretty easy to do yourself if you havy any uranium (United Nuclear sells small quantities) and some dry ice + alcohol.

http://en.wikipedia.org/wiki/Cloud_chamber
http://en.wikipedia.org/wiki/Bubble_chamber
 
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ahrkron

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From the CERN website:

http://public.web.cern.ch/public/Content/Chapters/AboutCERN/HowStudyPrtcles/HowStudyPrtcles-en.html [Broken]
 
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ahrkron

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In summary, there are various ways to look for them, and they depend on the type of particle we talk about.

One example: when LHC turns on (in a year or so), the search for the Higgs boson will be based on trying to reconstruct it from its possible decay products. One smashes a proton vs another proton; out of the energy of the collision, some times (on in 10^12 or less) a Higgs boson is created, which will almost immediately decay (some times) into two Z bosons, which decay into two muons each.

You then look for events that have four muons, see if their combined 4-momenta add up to the known Z mass, then plot the combined mass of all 4 muons and see if there is a peak over the combinatoric background and over the known processes that can produce four muons from a single vertex.
 

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