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Shift and broadening of resonance lines of the antiprotonic helium atoms in liquid He-4

The shift and broadening of the resonance lines in spectrum of the antiprotonic helium atoms $\bar{p}\mathrm{He}^{+}$ located in fluid and superfluid $^4$He have been calculated. The contributions to the shift and broadening from collective degrees of freedom in liquid $^4$He have been estimated using the phenomenological response function. Effects due to the interaction of $\bar{p}\mathrm{He}^{+}$ with a single $^4$He atom have been calculated in the quasistatic approximation using the experimental pair correlation function. It has been shown that an implanted $\bar{p}\mathrm{He}^{+}$ atom establishes a good probe of liquid helium properties, since this atom practically does not change the target structure.