# How is parity of the deuteron measured experimentally?

I'm reading Wong 'Introductory Nuclear Physics' and in chapter 3-1 he writes that "For the deuteron, it is known that the parity is positive. Let us see what we can learn from this piece of experimental information."

My question is, how is it known that the parity of the deuteron is positive? He is indicating that it is measured experimentally, what observable would indicate positive or negative parity?

I know that the intrinsic parity of the quarks are positive and anti-quarks are negative, which would directly lead to the parity of the proton/neutron system to be positive, but quarks weren't discovered until some time after the deuteron. Is there a way to measure parity in an experiment without going back to some theoretical declaration?

P.S. any recommendations for good graduate level nuclear physics textbooks?

• Sep 15, 2023 at 2:26
• I edited title to make it clear that this question seems to be specifically about the how the parity of the deuteron is measured experimentally. Its original title ("How is parity measured experimentally") sounds like a duplicate (and hence liable to be closed) of "How do you measure the parity of a particle?". Nov 19, 2023 at 14:38

Since the proton and neutron have positive parity, the parity of the deuteron is $$(-1)^L$$, where $$L$$ is the proton-neutron orbital angular momentum. As Bethe calculated as far back as 1940, the deuteron ground state is mostly L=0 with a bit of L=2, so the deuteron has positive parity. (The strong interactions that bind the deuteron can only mix states with the same parity.)
More direct evidence for positive parity of the deuteron comes from scattering experiments. For example, according to Landau & Smorodinsky, p. 15, as far back as the 1950s low energy scattering of neutrons by protons was consistent with the existence of a $$(1^+)^3S_1+^3D_1$$ positive parity deuteron, but not consistent with a $$(1^-)^1P_1$$ or $$(1^-)^3P_1$$ negative parity deuteron. More recently, there has been much theoretical and experimental work on the tiny parity-violation effects in $$n d$$, $$p d$$, $$e d$$, and $$\gamma d$$ scattering. Since the parity violation depends on the different parity states involved, they are effectively also precision measurements of the deuteron parity.
• As someone who spent several years working on parity violation in $np\to d\gamma$, I applaud this top-notch answer.