Longitudinal asymmetry and its effect on pseudorapidity distributions in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV

Submission Date:
22/10/2017
Article Information
Submission Form
System:
Pb-Pb
Energy:
2.76 TeV
Abstract Plain Text:
First results on the longitudinal asymmetry and its effect on the
pseudorapidity distributions in \PbPb collisions at \snn = 2.76 TeV at
the Large Hadron Collider are obtained with the ALICE detector.
The longitudinal asymmetry arises because of an unequal
number of participating nucleons from the two colliding nuclei, and is
estimated for each event by measuring the energy in the forward
neutron-Zero-Degree-Calorimeters (ZNs). The effect
of the longitudinal asymmetry is measured on the pseudorapidity distributions of
charged particles in the regions $|\eta| < 0.9$,  $2.8 < \eta < 5.1$ and
$-3.7 < \eta < -1.7$ by taking the ratio of the pseudorapidity distributions from events
corresponding to different regions of asymmetry.  The coefficients of
a polynomial fit to the ratio characterise the effect of the
asymmetry. A Monte Carlo simulation using a Glauber
model for the colliding nuclei is
tuned to reproduce the spectrum in the ZNs and provides
a relation between the measurable longitudinal asymmetry and the shift in
the rapidity ($y_{\mathrm{0}}$) of the participant zone formed by the
unequal number of participating nucleons.
The dependence of the coefficient of the linear term in the polynomial
expansion, $c_{\rm 1}$, on the mean value of $y_{\mathrm{0}}$ is investigated.