Abstract
In high-energy heavy-ion collisions, the correlations between the emitted particles can be used as a
probe to gain insight into the charge creation mechanisms. In this Letter, we report the first results of
such studies using the electric charge balance function in the relative pseudorapidity (η) and azimuthal
angle (ϕ) in Pb–Pb collisions at √sN N =2.76 TeV with the ALICE detector at the Large Hadron Collider.
The width of the balance function decreases with growing centrality (i.e. for more central collisions)
in both projections. This centrality dependence is not reproduced by HIJING, while AMPT, a model
which incorporates strings and parton rescattering, exhibits qualitative agreement with the measured
correlations in ϕ but fails to describe the correlations in η. A thermal blast-wave model incorporating
local charge conservation and tuned to describe the pT spectra and v2 measurements reported by ALICE,
is used to fit the centrality dependence of the width of the balance function and to extract the average
separation of balancing charges at freeze-out. The comparison of our results with measurements at lower
energies reveals an ordering with √sN N: the balance functions become narrower with increasing energy
for all centralities. This is consistent with the effect of larger radial flow at the LHC energies but also
with the late stage creation scenario of balancing charges. However, the relative decrease of the balance
function widths in η and ϕ with centrality from the highest SPS to the LHC energy exhibits only small
differences. This observation cannot be interpreted solely within the framework where the majority of the
charge is produced at a later stage in the evolution of the heavy-ion collision.
Original language | English |
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Pages (from-to) | 267-279 |
Number of pages | 13 |
Journal | Physics Letters B |
Volume | 723 |
Issue number | 4-5 |
DOIs | |
Publication status | Published - 2013 |