FIAS Scientific Report 2010 - Frankfurt Institute for Advanced Studies ...

Nuclear compression induced by a moving antiproton
Collaborators: A.B. Larionov 1,2 , I.N. Mishustin 1,2 , L.M. Satarov 1,2 , W. Greiner 1
1 Frankfurt Institute for Advanced Studies, 1 Kurchatov Institute, Moscow
Due to the strongly attractive real part of the ¯p-nucleus optical potential, an antiproton slowly moving in the
nuclear interior may create a local zone with enhanced nucleon density. We have considered this possibility
with a help of the GiBUU model. For this purpose a standard parallel ensemble simulation of the high-energy
antiproton induced reaction has been performed. The antiproton momentum and position at the annihilation
time moment have been stored in each parallel ensemble (or event). Assuming then, that the compression proceeds
mainly on the short piece of the ¯p trajectory before its annihilation, the antiproton has been reinitialized
in every annihilation event with the same momentum and position as at its annihilation. Then a new GiBUU
calculation with switched off annihilation has been done. Due to the coherent initialization of the antiproton at
the same position in all parallel ensembles, the mean field effects have been taken into account in full strength
in this calculation, which allows to calculate the nuclear response in a proper way. The survival probability
of the antiproton during the compressional evolution was calculated via the time-integrated annihilation width.
On the basis of these simulations we have evaluated the probability of ¯p-annihilation within a compressed
zone (ACZ) where maximum nucleon density ρmax exceeds a given value ρ. The results of calculations are
shown in the figure below. The various curves demonstrate how the results depend on model parameters characterizing
the ¯p optical potential, in particular the scaling factor ξ of the ¯p mean field (ξ = 1 corresponds to
the G-parity transformed nucleon mean fields). For the phenomenologically preferable value ξ = 0.22 (leading
to Re(Vopt) = −153 MeV) we find that annihilations at densities above 2ρ0 are predicted on the level of
10−4 ÷ 10−5 . Such events can be detected in the future FAIR experiments with the PANDA detector. With expected
¯p-beam luminosity L = 2 · 1032 cm−2 s−1 , the ACZ rate can be estimated on the level of a few hundred
events per second. Triggering on a fast proton in final state can, in principle, enhance the ACZ event fraction
by about one order of magnitude, while suppressing the rate by factor 103 . Certainly, further theoretical studies
are needed in order to find the best experimentally realizable ways to observe nuclear compression in ¯p-nucleus
collisions.
σ compr /σ ann
10 0
10 -2
10 -4
10 -6
10 -8
p - 16 O, 3 GeV/c
ξ=1
ξ=1, HO, m *
ξ=0.22
ξ=0.15
ξ=1, HO
10 -10
1 1.5 2
ρ/ρ0 2.5 3
Event-averaged probability of ¯p annihilation at ρmax > ρ vs ρ for ¯p 16 O collisions at plab = 3 GeV/c. The default choice
of parameters corresponds to ξ = 0.22.
Related talks and publications in 2010:
1. A.B. Larionov, I.N. Mishustin, L.M. Satarov, and W. Greiner, Possibility of cold nuclear compression in
antiproton-nucleus collisions, Phys. Rev. C 82, 024602 (2010).
2. A.B. Larionov, I.N. Mishustin, L.M. Satarov, and W. Greiner, Dynamical compression of the 16 O nucleus
by a moving antiproton, talk given at the meeting of the German Physical Society (DPG), Bonn, March
16, 2010.
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