2011 QCD and High Energy Interactions - Rencontres de Moriond ...

space-time region emitting bosons with overlapping wave functions increases with multiplicity,
whereas the correlation strength decreases. Both decrease with increasing momentum difference
kT . Anticorrelations between same-sign charged particles are observed for Q values above the
signal region, which can be seen in Fig. 6c showing the double ratio R(Q) 10 .
r (fm)
2.5 CMS - s = 7 TeV
2
1.5
1
0.5
0
(a) (b)
N range: (2 - 9)
ch
Nch
range: (10 - 24)
Nch
range: (25 - 80)
0.2 0.3 0.4 0.5 0.6 0.7
kT
(GeV)
1 CMS - s = 7 TeV
0.8
0.6
0.4
0.2
0
N range: (2 - 9)
ch
Nch
range: (10 - 24)
Nch
range: (25 - 80)
0.2 0.3 0.4 0.5 0.6 0.7
kT
(GeV)
T
Double ratio / 0.01 GeV
1.03
1.02
1.01
1
0.99
0.98
(c)
CMS -
s = 7 TeV
exponential
Eq. (4)
0.97
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Q (GeV)
Figure 6: Radius r (a), correlation strength λ (b), double ratio showing anticorrelations (c)
Near-side long-range particle correlations in proton data have first been reported by CMS 11 .
A ridge, a pronounced structure in high-multiplicity events for rapidity and azimuth differences
of 2.0 < |∆η| < 4.8 and ∆φ ≈ 0 has been found. Long- and short-range correlations in ion data
have also been studied 12 . The correlation functions of the 0-5% most central collisions show
characteristic features not present in minimum bias proton interactions (Fig. 7). The ridge is
most evident for pT ’s of the trigger particle between 2 and 6 GeV, but disappears at high pT .
References
2 pair
d N
dΔφ
trig
N 1
2 pair
d N
dΔφ
trig
N 1
6.5
6.0
0 < | Δη|
< 1
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trig
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T
T
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PbPb sNN
PYTHIA8 pp
= 2.76 TeV, 0-5%
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d N
dΔφ
s = 2.76 TeV
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trig
N 1
6.0
assoc
2 < p < 4 GeV/c
T
2 pair
d N
dΔφ
trig
N 1
6.5
6.0
∫
-1
CMS L dt = 3.1 μb
trig
trig
trig
6 < p < 8 GeV/c 7.0 8 < p < 10 GeV/c 7.0 10 < p < 12 GeV/c
T
T
T
2 pair
d N
dΔφ
0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3
| Δφ|
| Δφ|
| Δφ|
| Δφ|
| Δφ|
2 < | Δη|
< 4
2 pair
d N
dΔφ
Ntrig 1
6.0
5.8
trig
N 1
assoc
2 < p < 4 GeV/c
T
-1
CMS L dt = 3.1 μb
trig
2 < p < 4 GeV/c
T
6.4
trig
4 < p < 6 GeV/c
T
6.4
trig
6 < p < 8 GeV/c
T
6.4
PbPb s = 2.76 TeV, 0-5%
NN
6.2
PYTHIA8 pp s = 2.76 TeV
5-term Fourier fits
6.2
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2 pair
d N
dΔφ
Ntrig 1
6.0
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∫
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d N
dΔφ
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2 pair
d N
dΔφ
0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3 0 1 2 3
| Δφ|
| Δφ|
| Δφ|
| Δφ|
| Δφ|
Ntrig 1
6.0
5.8
trig
N 1
6.5
6.0
6.4
trig
8 < p < 10 GeV/c
T
2 pair
d N
dΔφ
Ntrig 1
6.2
6.0
5.8
trig
10 < p < 12 GeV/c
T
Figure 7: Short-range (0 < |∆η| < 1) and long-range (2 < |∆η| < 4) correlations in lead ion data
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