Editing Proton–proton chain (section)

==The PEP reaction==
[[File:Proton proton cycle.svg|thumb|300px|Proton–proton and electron-capture reactions in a star]]
A [[deuteron]] can also be produced by the rare pep (proton–electron–proton) reaction ([[electron capture]]):

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H + e- + H -> D + ve
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In the Sun, the frequency ratio of the pep reaction versus the {{nowrap|p–p}} reaction is 1:400. However, the [[neutrino]]s released by the pep reaction are far more energetic: while neutrinos produced in the first step of the {{nowrap|p–p}} reaction range in energy up to {{val|0.42|u=MeV}}, the pep reaction produces sharp-energy-line neutrinos of {{val|1.44|u=MeV}}. Detection of solar neutrinos from this reaction were reported by the [[Borexino]] collaboration in 2012.<ref>{{cite journal |last=Bellini |first=G. |display-authors=etal |date=2 February 2012 |title=First Evidence of pep Solar Neutrinos by Direct Detection in Borexino |journal=Physical Review Letters |volume=108 |issue=5 |pages=051302 |doi=10.1103/PhysRevLett.108.051302|arxiv= 1110.3230 |bibcode= 2012PhRvL.108e1302B |pmid=22400925|s2cid=118444784 }}</ref>

Both the pep and {{nowrap|p–p}} reactions can be seen as two different [[Feynman diagram|Feynman representations]] of the same basic interaction, where the electron passes to the right side of the reaction as a positron. This is represented in the figure of proton–proton and electron-capture reactions in a star, available at the NDM'06 web site.<ref>Int'l Conference on Neutrino and Dark Matter, 7 Sept 2006, [https://indico.ijclab.in2p3.fr/event/4364/contributions/14455/attachments/11714/13732/Martinez-P12-Vert-NDM06.pdf Session 14].</ref>