# Infrared safety

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In [quantum field theory](/source/Quantum_field_theory), and especially [asymptotically free](/source/Asymptotically_free) [quantum field theories](/source/Quantum_field_theories), an [observable](/source/Observable) is **infrared safe** if it does not depend on the low energy/long distance physics of the theory. Such observables can therefore be calculated reliably using [perturbative](/source/Perturbative) methods and then compared to experiment.[1][2] An example of an observable which is infrared safe is the total [scattering cross-section](/source/Scattering_cross-section) for the collision of an [electron](/source/Electron) and a [positron](/source/Positron) to produce [hadrons](/source/Hadrons).[3]

## See also

- [Asymptotic freedom](/source/Asymptotic_freedom)
- [Infrared divergence](/source/Infrared_divergence)
- [Kinoshita–Lee–Nauenberg theorem](/source/Kinoshita%E2%80%93Lee%E2%80%93Nauenberg_theorem)

## References

1. Botje, Michiel. ["Quantum Chromo Dynamics, Section 7. Soft and Collinear Singularities"](http://www.nikhef.nl/~h24/qcdcourse/section-7.pdf). Retrieved May 30, 2014.

1. Soper, Davison. ["Jet Definitions"](http://particle.physics.ucdavis.edu/seminars/data/media/2006/dec/soper.pdf). Retrieved May 30, 2014.

1. Chris, Sachrajda. ["Standard Model of Particle Physics"](http://www2.ph.ed.ac.uk/sussp61/lectures/01_Sachradjda_StandardModel/standrews3.pdf). Retrieved May 30, 2014.

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