Shift and broadening of resonance lines of antiprotonic helium atoms in liquid4He

Abstract

The shift and broadening of the resonance lines in the spectrum of antiprotonic helium atoms pHe + located in fluid and superfluid 4 He have been estimated. The contributions to the shift and broadening from collective degrees of freedom in liquid 4 He have been evaluated using the phenomenological response function. The shift due to collisions ofpHe + with 4 He atoms has been calculated in the quasistatic limit using the experimental pair-correlation function. It has been shown that an implantedpHe + atom establishes a good probe of liquid-helium properties, since this atom practically does not change the target structure.

Shift and broadening of resonance lines of antiprotonic helium atoms in solid helium

“…A similar study for liquid 4 He, presented in Ref. [1], showed that the shift is a linear function of density in normal-fluid 4 He and displays only small oscillations with temperature in superfluid 4 He. The pairdistribution function, which describes the atom distribution around a given particle, is very similar for both the normal-fluid and the superfluid helium at various temperatures and saturated-vapor pressure.…”

“…Thus, the knowledge of the pair-correlation function above this limit is not needed. The resonance-line shifts ∆E 0 which are presented in Table I display a clear nonlinear dependence on the target density, which is in contrast to the behavior of analogous line shifts in 4 He gas [5,6] and liquid 4 He above T = 2.17 K [1]. The absolute values of the reduced line shifts in solid helium are greater than the values of the corresponding line shifts in liquid 4 He (e.g., ∆E 0 /̺ = −0.427 GHz l/g for ̺ = 146 g/l at T = 2.27 K [1]).…”

“…In our case, we replace this atom by the implanted antiprotonic helium atom. However, this is a reasonable approximation since the probability density calculated for the two-particle systempHe + +He is very similar to g(r) at r 3Å [1]. In the literature, the data regarding the function g(r) are scarce.…”

“…III in the quasistatic approximation of Ref. [1] using the available pair-correlation functions g(r) for crystalline 4 He. It has been shown in Ref.…”

“…It has been shown in Ref. [1] that in the quasistatic limit of slow collisions the semiclassical expression for the collisional shift of Ref. [4] takes the form of a mean value of the interatomic potential, averaged over the spatial distribution of the perturbing helium atoms around the emitting antiprotonic atoms.…”