Difference between revisions of "Cross section"
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| − | The '''cross section''' for a given process is a measure for the rate of interactions that | + | The '''cross section''' for a given process is a measure for the rate of interactions that originate from the process that can be quoted independently of the experimental set-up of the scattering experiment itself. It is denoted <math>\sigma</math>. In a hypothetical experiment in which a flux of particles <math>F</math> (incident particles per unit area per unit time) scatter at a rate <math>R</math> (scattered particles per unit time), the cross section is <math>\sigma = R/F</math>. |
| − | Cross sections are measured in units of area, where the special unit ''barn'' (b) is used with prefixes. Cross sections at the [[LHC]] can range from hundreds of millibarns (the total cross section of proton-proton collisions) down to fb or smaller for rare processes that are still considered to be measurable. | + | Cross sections are measured in units of area, where the special unit ''barn'' (b) is used with prefixes. A barn is 10<sup>−28</sup> m<sup>2</sup> (100 fm<sup>2</sup>). Cross sections at the [[LHC]] can range from hundreds of millibarns (the total cross section of proton-proton collisions) down to fb or smaller for rare processes that are still considered to be measurable. |
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| + | In calculations using [[natural units]] (with <math>\hbar = c = 1</math>), area has dimensions of 1/energy-squared, so units of [[GeV]]<sup>-2</sup> may be used. The conversion is 1 GeV<sup>-2</sup> = 0.389 mb. | ||
== Learn more == | == Learn more == | ||
* [https://en.wikipedia.org/wiki/Cross_section_(physics) Wikipedia article] | * [https://en.wikipedia.org/wiki/Cross_section_(physics) Wikipedia article] | ||
Latest revision as of 08:24, 7 April 2017
The cross section for a given process is a measure for the rate of interactions that originate from the process that can be quoted independently of the experimental set-up of the scattering experiment itself. It is denoted 
. In a hypothetical experiment in which a flux of particles 
(incident particles per unit area per unit time) scatter at a rate 
(scattered particles per unit time), the cross section is 
.
Cross sections are measured in units of area, where the special unit barn (b) is used with prefixes. A barn is 10−28 m2 (100 fm2). Cross sections at the LHC can range from hundreds of millibarns (the total cross section of proton-proton collisions) down to fb or smaller for rare processes that are still considered to be measurable.
In calculations using natural units (with 
), area has dimensions of 1/energy-squared, so units of GeV-2 may be used. The conversion is 1 GeV-2 = 0.389 mb.
