What's the advantage of gamma-gamma colliders? What new physics can be done with it?

Reference: http://www.slac.stanford.edu/pubs/beamline/26/1/26-1-kim.pdf

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    $\begingroup$ Details, please. The article would seem to answer your questions. Why doesn't it? Include this explanation in your question. $\endgroup$ – WhatRoughBeast Mar 30 '16 at 2:02
  • $\begingroup$ The academic papers may be too hard to understand, and only focus on a specific area. So I want to learn more. I hope someone can give a more general and easier to understand answer. $\endgroup$ – Ballistics Mar 30 '16 at 3:04

The strongest physics quest for a $\gamma\gamma$ collider is the production of Higgs bosons as the only particle in the final state, from a very well known initial state.

This is not achieved neither at future lepton colliders (ILC, CLIC, FCC-ee, CEPC) where the typical production by higgstrahlung comes with additional particles in the final state (carrying some uncertainty), and even less at proton colliders (LHC) where the initial state is unknown and there is additional noise from the proton remnants. Off course this didn't prevent its discovery, but makes precision studies much harder.

If the diphoton signal at $750~$GeV observed in the 2015 run of the LHC is confirmed, it would be a very strong push, although reaching that energy with a $\gamma\gamma$ collider is... let's say expensive!

  • $\begingroup$ Why is Higgs production a background? Wouldn't it be signal? $\endgroup$ – innisfree Apr 4 '16 at 13:18
  • $\begingroup$ @innisfree unlucky choice of words, my bad $\endgroup$ – DarioP Apr 4 '16 at 13:35
  • $\begingroup$ How can be the production of Higgs bosons in $\gamma\gamma$ colliders direct, if photons don't couple with the Higgs? $\endgroup$ – Bosoneando Jul 19 '16 at 23:54
  • $\begingroup$ @Bosoneando They couple through loops where typically a top quark or a W boson circulates; therefore, although technically not direct, still as clean as if it was. $\endgroup$ – DarioP Jul 20 '16 at 7:37
  • $\begingroup$ @DarioP exactly my point. The Feynman diagram for gluon fusion (which is the dominant mode at LHC) is exactly the same as the Feynman diagram for the photon fusion that you propose. By the way, in a $e^+e⁻$ collider, Higgs bosons are produced in simpler processes with no loops. See for example fig 2.6 in arxiv.org/abs/1306.6352v1 $\endgroup$ – Bosoneando Jul 20 '16 at 7:42

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