Femtoscopy of stopped protons

The longitudinal proton-proton femtoscopy (Hanbury Brown–Twiss) correlation function, based on the idea that in a heavy-ion collision at $\sqrt{s}\lesssim 20\mathrm{GeV}$ stopped protons are likely to be separated in configuration space, is evaluated. It shows a characteristic oscillation which appears sufficiently pronounced to be accessible in experiment. The proposed measurement is essential for estimating the baryon density in the central rapidity region and can be also viewed as an (almost) direct verification of the Lorentz contraction of the fast-moving nucleus.

Figure 1

Femtoscopy correlation function for (a) $\sqrt{s}=20\mathrm{GeV}$ and (b) $\sqrt{s}=14\mathrm{GeV}$. The black dashed lines represent the result of our model calculation while the solid blue lines are obtained by doubling the value of width of the collision point distribution, ${\mathrm{\Gamma }}_c$.

Figure 2

Same as Fig. 1 but with strong and Coulomb interaction effects included.

Figure 3

Time integrated source function for stopped protons as a function of $z$ for (a) $\sqrt{s}=20\mathrm{GeV}$ and (b) $\sqrt{s}=14\mathrm{GeV}$. The black dashed lines represent the result of our model calculation while the blue solid lines are obtained by doubling the value of width of the collision point distribution, ${\mathrm{\Gamma }}_c$. The source functions shown are normalized to unity.