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.
This post imported from StackExchange Physics at 2019-02-02 19:53 (UTC), posted by SE-user Ruslan_Sharipov