Centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at √ s N N = 5.02  TeV.

The pseudorapidity density of charged particles, d N ch / d η , at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of √ s N N = 5.02     TeV . For the 5% most central collisions, we measure a value of 1943 ± 54 . The rise in d N ch / d η as a function of √ s N N is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of d N ch / d η as a function of the average number of participant nucleons, ⟨ N part ⟩ , calculated in a Glauber model, is compared with the previous measurement at √ s N N = 2.76     TeV . A constant factor of about 1.2 describes the increase in d N ch / d η from √ s N N = 2.76 to 5.02 TeV for all centrality classes, within the measured range of 0%–80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.

The pseudorapidity density of charged particles,
d
N
ch
/
d
η
, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of
√
s
N
N
=
5.02
 
 
TeV
. For the 5% most central collisions, we measure a value of
1943
±
54
. The rise in
d
N
ch
/
d
η
as a function of
√
s
N
N
is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of
d
N
ch
/
d
η
as a function of the average number of participant nucleons,
⟨
N
part
⟩
, calculated in a Glauber model, is compared with the previous measurement at
√
s
N
N
=
2.76
 
 
TeV
. A constant factor of about 1.2 describes the increase in
d
N
ch
/
d
η
from
√
s
N
N
=
2.76
to 5.02 TeV for all centrality classes, within the measured range of 0%–80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.