Why this self-loop diagram is not included in $\phi^4$-theory of Peskin & Schroeder?

Consider a $$2\rightarrow2$$ scattering process in $$\phi^4$$-theory. On p. 326 in the book of Peskin & Schroeder, they consider the 3 1-loop corrections in the parenthesis:

My question is: Why don't they include below self-loop diagram?

Is this 0? Why?

Peskin & Schroeder (P&S) on p. 326 are discussing a connected, amputated 4-pt amplitude$$^1$$ $${\cal M}_4$$. It is clear from various places in the P&S textbook [see e.g. eq. (10.21)] that $${\cal M}_4$$ is an amputated amplitude. Now OP's self-loop diagram can be understood as an amputated diagram, so OP's question is still in principle a valid question.

However, P&S explain on p. 113-114 that such diagrams should be cut away. This is e.g. to avoid over-counting when we attach connected propagators $$G_c$$ to the external legs of the amputated amplitude $${\cal M}_4$$. [Technically, self-loop diagrams in principle contribute to the connected propagator $$G_c$$, but are typically cancelled via renormalization conditions on the self-energy, see e.g. eqs. (10.28) & (10.29) on p. 328.]

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$$^1$$ By the way, the last explicit diagram in P&S is not a 4-loop diagram: It denotes an interaction counterterm, cf. fig. 10.3 on p. 325 :-)

if you separate the new diagram you added to 2 diagram it means:

1. diagram of the first order
2. diagram with a 1 particle that scatter with itself and continue in its trajectory

the probability for a particle to continue its trajectory when it only "interacts" with itself is 1 due to conservation of momentum.

therefore the probability is the same and the physical meaning is the same as the first order diagram