Table 1 Gradients of the collisional shifts of the laser resonance frequencies of \(\bar{{\boldsymbol{p}}}{}^{{\bf{4}}}{\bf{H}}{{\bf{e}}}^{+}\) against target density (dν/dρ) and temperature (dν/dT)

From: High-resolution laser resonances of antiprotonic helium in superfluid 4He

Transition

dν/dρ (×10−21 GHz cm3)

dν/dT (GHz K−1)

(n, ℓ) → (n′, ℓ′)

Gas, supercritical

He I

Theory

He I

He II

(37, 35) → (38, 34)

−3.99(7)

−4.67(9)

−3.42

3.5(3)

0.75(7)

(39, 35) → (38, 34)

−4.52(8)

−4.5(2)

−4.05

3.9(7)

0.4(1)

  1. Experimental dν/dρ values measured in gaseous and supercritical helium, and He I targets at temperatures between T = 2.7 K and 4.2 K are compared with theoretical values18 calculated for binary collisions at T = 5.4 K. The dν/dT value in He I represents the best fit to data measured at temperatures between T = 2.2 K and 2.55 K. In He II targets, the dν/dT value decreased by a factor of 5–10 (see text).
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