Formerly I thought that Delta minus baryon was discovered in cosmic rays. However I was mistaken. Wikipedia says that Delta states were "established experimentally at the University of Chicago cyclotron and the Carnegie Institute of Technology synchro-cyclotron in the mid-1950s using accelerated positive pions on hydrogen targets" and gives two references:

[1] H. L. Anderson, E. Fermi, E. A. Long, and D. E. Nagle, “Total Cross Sections of Positive Pions in Hydrogen.” Phys. Rev., 85, 936 (1952). and ibid. p. 934.

[2] J. Ashkin et al., “Pion Proton Scattering at 150 and 170 MeV.” Phys. Rev., 101, 1149 (1956).

Robert Cahn and Gerson Goldhaber in their book "The Experimental Foundations of Particle Physics" give the same references (see pages 99-113). However pions of various signs on hydrogen targets can produce $\Delta^{++}$, $\Delta^{+}$ and $\Delta^{0}$ particles only according to the following formation and decay reactions: \begin{gather} \pi^{+}+p\to\Delta^{++}\to\pi^{+}+p,\tag{1}\\ \pi^{0}+p\to\Delta^{+}\to\pi^{0}+p,\tag{2}\\ \pi^{-}+p\to\Delta^{0}\to\pi^{-}+p.\tag{3} \end{gather} The matter is that J. Beringer et al. (2012): in Particle listings $\Delta$(1232) do not provide any specific data for $\Delta^{-}$.

The $\Delta^{-}$ particles could be created by means of the reaction \begin{equation} \pi^{-}+n\to\Delta^{-}\to\pi^{-}+n.\tag{4} \end{equation} However, pure neutrons do not constitute a dense matter in order to form a target. They exist in the form of radiation emitted from nuclear reactors. Being neutral, neutrons cannot be compressed into dense beams. Therefore it is very difficult to implement the reaction (4) as well as to register and identify the neutron in its products.

If we use a deuterium target, then we would have two competing reactions: the reaction (4) and the following reaction \begin{equation} \pi^{-}+p\to\Delta^{0}\to\pi^{0}+n,\tag{5} \end{equation} both producing neutrons. So, is there an experimental technique for producing $\Delta^{-}$ baryons and clearly detecting the products of their decay? If not, this means that the data for $\Delta^{-}$ lifetime in Wikipedia are not experimental data.

  • $\begingroup$ Welcome to SE.Physics! Since this seems to be more of a question about the history of the study of Physics, as opposed to a question about Physics itself, it might be a better fit for SE.HistoryOfScienceAndMathematics. $\endgroup$
    – Nat
    Nov 9, 2018 at 23:59
  • 5
    $\begingroup$ I'm voting to close this question as off-topic because it's about history; according to the site consensus, those questions should be on HSM SE. $\endgroup$
    – user191954
    Nov 10, 2018 at 4:27
  • $\begingroup$ there is this journals.aps.org/prc/abstract/10.1103/PhysRevC.28.2064 which discusses delta- and might have references to original. needs access to a library and all these old articles need to dig in. $\endgroup$
    – anna v
    Nov 10, 2018 at 9:59
  • $\begingroup$ The question isn't about the way in which the particle was produced. Yes, it mentions the process, but the explicit question in the end (and the only question in the whole body) is "Who first experimentally observed that?" That's just history, not physics. $\endgroup$
    – user191954
    Nov 10, 2018 at 12:19
  • $\begingroup$ My question is about physics. I suspect that $\Delta^{-}$ is a white spot in experimental particle physics and I would like to make sure that it is really so. $\endgroup$ Nov 23, 2018 at 17:51


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