Rapidity correlations in the RHIC Beam Energy Scan.
Ayeh Jowzaee for the STAR Collaboration
ajowzaee@wayne.edu

A pair-normalized two-particle covariance versus the rapidity
of the two particles, called R$_2$, was originally studied
[1] in ISR and FNAL data in the 1970's and has recently seen
renewed interest [2] to study the dynamics of heavy-ion
collisions in the longitudinal direction. These rapidity
correlations can be decomposed onto a basis set of Legendre
polynomials with prefactors $\langle$a$_{\rm mn}$$\rangle$,
which can be considered the rapidity analog of the
decomposition of azimuthal anisotropies into a basis set of
cosine functions with prefactors v$_{\rm n}$. The
$\langle$a$_{\rm mn}$$\rangle$ values have been suggested [2]
to be sensitive to the number of sources, baryon stopping,
viscosities, and criticality. The rapidity correlations have
been measured by the STAR collaboration as a function of the
centrality and beam energy in the range of 7.7 to 200 GeV.
The experimental results and comparisons to those from the
UrQMD model will be presented.

[1] L. Fo\`{a}, Phys. Lett. C22, 1 (1975);
H. B\oggild, Ann. Rev. Nucl. Sci. 24, 451 (1974)
[2] T. Lappi and L. McLerran, Nucl. Phys. A 832, 330 (2010);
A. Bzdak and D. Teaney, Phys. Rev. C 87, 024906 (2013);
A. Monnai, B. Schenke, arXiv:1509.04103;
A. Bzdak, Volker Koch, and Nils Strodthoff, arXiv:1607.07375;
J. Jia, S. Radhakrishnan, and M. Zhou, Phys. Rev. C 93, 044905 (2016)