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research
Measurement of two particle pseudorapidity correlations in Pb+Pb collisions at
s
N
N
\sqrt{s_{NN}}
s
NN
​
​
= 2.76 TeV with the ATLAS detector
Authors
Sooraj Radhakrishnan
Publication date
1 November 2015
Publisher
Doi
Cite
View
on
arXiv
Abstract
Two-particle pseudorapidity correlations, measured using charged particles with
p
T
>
p_{\mathrm{T}} >
p
T
​
>
0.5 GeV and
∣
η
∣
<
|\eta| <
∣
η
∣
<
2.4, from
s
N
N
\sqrt{s_{NN}}
s
NN
​
​
= 2.76 TeV Pb+Pb collisions collected in 2010 by the ATLAS experiment at the LHC are presented. The correlation function
C
N
(
η
1
,
η
2
)
C_N(\eta_1,\eta_2)
C
N
​
(
η
1
​
,
η
2
​
)
is measured for different centrality intervals as a function of the pseudorapidity of the two particles,
η
1
\eta_1
η
1
​
and
η
2
\eta_2
η
2
​
. The correlation function shows an enhancement along
η
−
≡
η
1
−
η
2
≈
\eta_- \equiv \eta_1 - \eta_2 \approx
η
−
​
≡
η
1
​
−
η
2
​
≈
0 and a suppression at large
η
−
\eta_-
η
−
​
values. The correlation function also shows a quadratic dependence along the
η
+
≡
η
1
\eta_+ \equiv \eta_1
η
+
​
≡
η
1
​
+
η
2
\eta_2
η
2
​
direction. These structures are consistent with a strong forward-backward asymmetry of the particle multiplicity that fluctuates event to event. The correlation function is expanded in an orthonormal basis of Legendre polynomials,
T
n
(
η
1
)
T
m
(
η
2
)
T_n(\eta_1)T_m(\eta_2)
T
n
​
(
η
1
​
)
T
m
​
(
η
2
​
)
, and corresponding coefficients
a
n
,
m
a_{n,m}
a
n
,
m
​
are measured. These coefficients are related to mean-square values of the Legendre coefficients,
a
n
a_n
a
n
​
, of the single particle longitudinal multiplicity fluctuations:
a
n
,
m
=
⟨
a
n
a
m
⟩
a_{n,m} = \langle a_na_m \rangle
a
n
,
m
​
=
⟨
a
n
​
a
m
​
⟩
. Significant values are observed for the diagonal terms
⟨
a
n
2
⟩
\langle a_n^2 \rangle
⟨
a
n
2
​
⟩
and mixed terms
⟨
a
n
a
n
+
2
⟩
\langle a_na_{n+2}\rangle
⟨
a
n
​
a
n
+
2
​
⟩
. Magnitude of
⟨
a
1
2
⟩
\langle a_{\mathrm{1}}^{\mathrm{2}} \rangle
⟨
a
1
2
​
⟩
is the largest and the higher order terms decrease quickly with increase in
n
n
n
. The centrality dependence of the leading coefficient
⟨
a
1
2
⟩
\langle a_{\mathrm{1}}^{\mathrm{2}} \rangle
⟨
a
1
2
​
⟩
is compared to that of the mean-square value of the asymmetry of the number of participating nucleons between the two colliding nuclei, and also to the
⟨
a
1
2
⟩
\langle a_{\mathrm{1}}^{\mathrm{2}} \rangle
⟨
a
1
2
​
⟩
calculated from HIJING.Comment: 4 pages, 3 figures, proceedings of the 7th International Conference on Hard and Electromagnetic Probes of High Energy Nuclear Collisions (Hard Probes 2015), Montrea
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Last time updated on 09/08/2016