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

SHERPA 9 MC generators but not by PYTHIA 10 which underestimates the measured cross
sections.
) [pb]
jet
N
≥
)+
-
e
+
e
→
*(
γ
(Z/
σ
Data / NLO
Data / MC
Data / MC
3
10
2
10
10
1
ATLAS Preliminary
∫
-1
L dt = 33 pb
anti-kt
jets, R = 0.4,
jets
p > 30 GeV
T
+ -
Z/ γ*(
→ e e ) + jets
Data 2010 ( s = 7 TeV)
Alpgen
Sherpa
Pythia
MCFM
1.6
1.4
1.2
1
0.8
0.6
1 2 Data 2010 ( s3=
7 TeV)
theoretical uncertainties
1.6
1.4
1.2
1
0.8
0.6
1.4
1.2
1
0.8
0.6
1 2 Data 2010 / Alpgen 3
Data 2010 / Sherpa
NNLO normalization
1 2 3
1 2 3
≥ Njet
0jets) [1/GeV]
)+ ≥
-
μ
+
*( → μ
/ σ (Z/ γ
T
d σ /dp
Data / NLO
Data / MC
Data / MC
10
10
10
-1
-2
-3
ATLAS Preliminary
∫
-1
L dt = 33 pb
Z/ γ*
+ ≥ 1 jet,
anti-kt
jets, R = 0.4,
jets
p > 30 GeV
T
+ -
Z/ γ*(
→ μ μ )+jets
Data 2010 ( s = 7 TeV)
Alpgen
Sherpa
MCFM
0.8
0.6
1
1.8
1.6
1.4
1.2
0.8
0.6
1
1.8
1.6
1.4
1.2
0.8
0.6
Data 2010 ( s = 7 TeV)
theoretical uncertainties
1
1.8
1.6
1.4
1.2
0.8
0.6
1
1.8
1.6
1.4
1.2
1.4
1.2
1
0.8
Data 2010 / Alpgen
Data 2010 / Sherpa
0.6
30 40 50 60 70 80 90 100 110 120
jet
p [GeV]
T
Figure 2: To the left (resp. right), measured cross section (black dots) in Z/γ ∗ (→ e + e − )+jets (resp. Z/γ ∗ (→
µ + µ − )+jets) production as a function of the inclusive jet multiplicity (resp. p jet
T ), for events with at least one
jet with p jet
T > 30 GeV and |ηjet | < 2.8 in the final state. The error bars indicate the statistical uncertainty
and the dashed areas the statistical and systematic uncertainties added in quadrature. The measurements are
compared to NLO pQCD predictions from MCFM (only available up to 2 jets), as well as the predictions from
ALPGEN, SHERPA, and PYTHIA. The shadowed areas around the ALPGEN and SHERPA predictions denote
a 5% uncertainty on the absolute normalization.
4 Measurement of diboson production (Wγ,Zγ,W + W − )
ATLAS has also performed the measurement of diboson production of high energy photons in
association with either a W or Z boson. Such measurements allow to test pQCD. Moreover,
the Wγ process includes a diagram sensitive to Triple Gauge boson Coupling (TGC) of the
electroweak sector. Events with W and Z bosons decaying into high-pT electrons and muons are
required in addition to have a photon with ET > 15 GeV located outside a cone of radius 0.7 in η
- φ space centered on the lepton(s) from the boson decay. To further reduce the background due
to photons from π0 and η decays, an isolation requirement of Eiso T < 5 GeV is applied. Eiso T is
the total transverse energy recorded in the calorimeter in a cone of radius 0.4 around the photon
direction (excluding a small window which contains the photon energy). E iso
T is corrected for the
leakage of the photon energy into the isolation cone and the contributions from the underlying
and pile-up activities in the event. A total of 95 (97) pp → eνγ + X (pp → µνγ + X) and
25 (23) pp → e + e − γ + X (pp → µ + µ − γ + X) event candidates are selected 11 . The measured
production cross sections, together with the kinematic distributions of the leptons and photons
in data signal candidate events, are found to agree with the O(ααs) Standard Model predictions
(see Table 1).