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

d
η
d N ch
.
1/ N ev
Ratio
1.8
1.6
1.4
1.2
1
0.8
0.6
0.8
]
3
c
-2
[mb GeV
3
/dp
σ
3
Ed
4.9
/GeV)
s
(a)
(
21
10
19
10
17
10
15
10
13
10
11
10
9
10
7
10
5
10
(a)
+ -
pp( p)
→ 0.5(h +h ) + X (| η| 500 MeV, | η | < 2.5
T
ATLAS s = 7 TeV
Data 2010
PYTHIA ATLAS AMBT1
PYTHIA ATLAS MC09
PYTHIA DW
PYTHIA 8
PHOJET
1.2 Data Uncertainties
MC / Data
1
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5
η
/d n ch
d N ev
⋅
1/ N ev
Ratio
1
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
1.5
1
0.5
2
10
2
10
nch
≥ 2, p > 100 MeV, | η | < 2.5
T
ATLAS s = 7 TeV
(c)
Data 2010
PYTHIA ATLAS AMBT1
PYTHIA ATLAS MC09
PYTHIA DW
PYTHIA 8
PHOJET
Data Uncertainties
MC / Data
20 40 60 80 100 120 140 160 180 200
n ch
Figure 2: Minimum bias pseudorapidity distributions at √ s = 0.9 TeV (a) and 7 TeV (b), multiplicity distribution
at √ s = 7 TeV (c)
components from beam-beam remnants. The dominant momentum flow defines three regions
in the plane transverse to the incoming beams. It is given by the direction of the highest-pT
track in ATLAS, whereas in CMS the leading track jet is used instead. The region within an
azimuthal angle difference of |∆φ| < 60 0 with respect to the leading object is called the toward
region, and the one opposite (|∆φ| > 120 0 ) the away region. The area in between, the transverse
region, is the one that is most sensitive to the UE.
ATLAS 5 and CMS 6 measured various properties of charged particles in the UE such as multiplicity
and transverse momentum distributions. Multiplicity and ΣpT densities as a function
of the leading-pT entity were also studied. There is a strong growth of UE activity with √ s.
ch
/ dN
ev
) dN
ev
(1/N
1
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
Data 7 TeV
Data 0.9 TeV
PYTHIA-6 Z1, 7 TeV
PYTHIA-6 Z1, 0.9 TeV
charged particles
(p > 0.5 GeV/c, | η|
< 2, 60°
< | Δ
T
leading track-jet p > 3 GeV/c
T
CMS Preliminary
φ|
< 120
° )
0 5 10 15 20 25 30
(a)
Nch
) [GeV/c]
φ
Δ
(
Δ
η
Δ
/
2
Δ Σp
T
ev
1 / N
2.5
2
1.5
1
0.5
(p
T
> 0.5 GeV/c, |
CMS Preliminary
Data 7 TeV
PYTHIA-6 D6T
PYTHIA-6 Z1
PYTHIA-8 4C
charged particles
η|
< 2, 60°
< | Δφ|
< 120°
)
0
0 20 40 60 80 100
Leading track-jet p [GeV/c]
T
(b)
) [GeV/c]
φ
Δ
(
Δ
η
Δ
/
T
p
Σ
2
Δ
ev
7/0.9 TeV 1/N
3.5
3
2.5
2
1.5
1
0.5
Data
PYTHIA-6 D6T
PYTHIA-6 Z1
PYTHIA-8 4C
CMS Preliminary
charged particles
(p > 0.5 GeV/c, | η|
< 2, 60°
< | Δφ|
< 120°
)
T
0
0 5 10 15 20 25
Leading track-jet p [GeV/c]
T
Figure 3: Underlying event multiplicites (a), average scalar momentum sum (b), multiplicity density ratio (c)
Fig. 3a shows the increase of the number of events for centre-of-mass energies from 0.9 to 7 TeV
(c)