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GATE 2020 PH – Question 31

Nuclear and Particle Physics · Conservation laws, isospin symmetry, charge conjugation, parity and time-reversal invariance. · 1 mark · Numerical answer

A particle Y undergoes strong decay $Y\to\pi^-+\pi^-$. Find its isospin.

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Correct answer: 2 to 2

Explanation

Each pion has isospin 1 and $I_3=-1$. The two-pion final state has $I_3=-2$. Adding two isospin-1 particles permits I = 0, 1 or 2, and only I = 2 can have projection −2. Strong decay conserves isospin, so the parent Y must also have I = 2.

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