# Nuclear Physics Seminar

##
Long-Range Rapidity Correlations in Heavy-Light Ion Collisions

### Doug Wertepny (OSU)

We study two-particle long-range rapidity correlations arising in
the early stages of heavy ion collisions in the saturation/Color
Glass Condensate framework, assuming for simplicity that one
colliding nucleus is much larger than the other. We calculate the
two-gluon production cross section while including all-order
saturation effects in the heavy nucleus with the lowest-order
rescattering in the lighter nucleus. We find four types of
correlations in the two-gluon production cross section: (i)
geometric correlations, (ii) HBT correlations accompanied by a
back-to-back maximum, (iii) away-side correlations, and (iv)
near-side azimuthal correlations which are long-range in
rapidity. The geometric correlations (i) are due to the fact that
nucleons are correlated by simply being confined within the same
nucleus and may lead to long-range rapidity correlations for the
produced particles without strong azimuthal angle dependence.
Somewhat surprisingly, long-range rapidity correlations (iii) and
(iv) have exactly the same amplitudes along with azimuthal and
rapidity shapes: one centered around Δ φ =π with the
other one centered around Δ φ =0 (here Δ φ is
the azimuthal angle between the two produced gluons). We thus
observe that the early-time CGC dynamics in nucleus-nucleus
collisions generates azimuthal non-flow correlations which are
qualitatively different from jet correlations by being long-range in
rapidity. If strong enough, they have the potential of mimicking the
elliptic (and higher-order even-harmonic) flow in the di-hadron
correlators: one may need to take them into account in the
experimental determination of the flow observables.

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