Abstract
In the framework of dense-dilute CGC approach we study fluctuations in the multiplicity of produced particles in p-A collisions. We show that the leading effect that drives the fluctuations is the Bose enhancement of gluons in the proton wave function. We explicitly calculate the moment generating function that resums the effects of Bose enhancement. We show that it can be understood in terms of the Liouville effective action for the composite field which is identified with the fluctuating density, or saturation momentum of the proton. The resulting probability distribution turns out to be very close to the gamma-distribution. We also calculate the first correction to this distribution which is due to pairwise Hanbury Brown-Twiss correlations of produced gluons.
Highlights
The study of correlations in p − A and p − p collisions has been a very active area in the last years due to the observation of the ridge correlations at the LHC
We show that the main contribution to multiplicity fluctuations arises form the Bose enhancement (BE) of gluons in the projectile wave function
We note that if we include the soft scales in the k integral, that is, take kmin ∼ Λ, the situation changes, and the Hanbury Brown–Twiss (HBT) effect becomes as important as the Bose enhancement
Summary
We calculate the multiplicity momentum generating function, using McLerran-Venugopalan (MV) model for the projectile and assuming that the target is very dense. The latter assumption allows us to employ the factorizable form for the averages of Wilson lines, as explained in Ref. IV, we calculate in closed form the momentum generating function that resums all BE contributions We relate it to the constrained effective potential approach proposed in Ref.
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