Difference between revisions of "Cross section"
(More about the definition and units of scattering cross sections) |
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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. In a hypothetical experiment in which a flux of particles ''F'' (particles per square area per unit time) scatter at a rate ''R'' (scattered particles per unit time), the cross section is 𝜎 = ''R''/''F''. |
| − | 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 ''ħ''=''c''=1) area has dimensions of 1/energy-squared, so units of GeV<sup>-2</sup>. 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] | ||
Revision as of 21:58, 6 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. In a hypothetical experiment in which a flux of particles F (particles per square area per unit time) scatter at a rate R (scattered particles per unit time), the cross section is 𝜎 = R/F.
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 ħ=c=1) area has dimensions of 1/energy-squared, so units of GeV-2. The conversion is 1 GeV-2 = 0.389 mb.
