Deeply bound $π^{-}$ states in $^{207} Pb$ formed in the $^{208} Pb {(d,}^{3} He)$ reaction. I. Experimental method and results

The deeply bound pionic states

{(1 s, 2 p)}_{π^{-}} \otimes^{207} Pb

were observed for the first time, by investigating the

^{208} Pb {(d,}^{3} He)

reaction at a beam energy of

T_{d} = 604.3 MeV

and at ejectile angles around 0°. The measured momentum distribution of the

^{3} He

particles was used to determine the Q value spectrum in the region

- 145 MeV < Q < - 120 MeV

with a systematic uncertainty of ±120 keV and a full width at half maximum resolution of

480 \pm 60 keV .

This spectrum shows a prominent peak at

Q ≃ - 135.5 MeV,

corresponding to the pionic

2 p

state, coupled mainly to the

{3 p}_{1 / 2}

and

{3 p}_{3 / 2}

neutron hole states in

^{207} Pb .

A shoulder is seen on the tail of this dominant peak, and is attributed to the population of the pionic

1 s

state. The cross section for the continuum component at these high excitation energies is

d^{2} σ / (d Ω d E) = 4.7 μ b / s r MeV .

The net cross section for production of

π^{-}

states in the bound pion region

- 140 MeV < Q < - 133 MeV

above the continuum amounts to

d σ / d Ω = 76 μ b / s r .

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Deeply boundπ−states in207Pbformed in the208Pb(d,3He)reaction. I. Experimental method and results