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

events / 5 GeV
data/MC
5
10
4
10
10
3
2
10
10
1
2
1
0
CMS preliminary
-1
36 pb at
s = 7 TeV
MT
> 50 GeV
data
W → μν
(MadGraph)
top
other backgrounds
50 100 150 200 250
leading jet ET
[GeV]
number of events
data/MC
6
10
5
10
10
4
3
10
2
10
10
1.5
1
0.5
data
W → μν
(MadGraph)
top
CMS preliminary
-1
36 pb at
jet
ET
s = 7 TeV
> 30 GeV
other backgrounds
0 1 2 3 4 5 6
exclusive jet multiplicity
Figure 1: Distributions of the ET for the leading jet (left) and number of reconstructed jets (right) in events
W → µν. The ratio between the data and the simulation is also shown.
remarkable also for the leading jet ET, which is shown for events with MT > 50 GeV in order
to further suppress the background. For each jet multiplicity, the number of signal events in the
W channels is determined with an unbinned extended maximum likelihood fit to the transverse
mass and the number of b-tagged jets in the event, in order to measure the top background.
The measured rates are corrected for the selection efficiency and unfolded for detector smearing
using matrix inversion with singular value decomposition. The final results are given for jet
counting at particle level in the lepton and jet acceptance to ease the comparison with theory.
As shown in Figure 2 for W signal, the results are found in agreement with the predictions from
MadGraph 8 , a multi-jet matrix element Monte Carlo matched with pythia 9 parton shower,
while the pythia parton shower alone underestimates the higher jet rates.
σ(W
+ ≥ n-jets)
σ(W
+ ≥ 0-jet)
≥ n-jets)
(n-1)-jets)
σ(W
+
σ(W
+ ≥
10
10
-1
-2
-3
10
0.2
0.1
0
data
energy scale
unfolding
MadGraph Z2
MadGraph D6T
Pythia Z2
-1
36 pb at
jet
ET
CMS preliminary
W →eν
s = 7 TeV
> 30 GeV
1 2 3 4
inclusive jet multiplicity, n
σ(W
+ ≥ n-jets)
σ(W
+ ≥ 0-jet)
≥ n-jets)
(n-1)-jets)
σ(W
+
σ(W
+ ≥
10
10
-1
-2
-3
10
0.2
0.1
0
data
energy scale
unfolding
MadGraph Z2
MadGraph D6T
Pythia Z2
-1
36 pb at
jet
ET
CMS preliminary
W →μν
s = 7 TeV
> 30 GeV
1 2 3 4
inclusive jet multiplicity, n
Figure 2: The ratio σ(W + n jets)/σ(W) and σ(W + n jets)/σ(W + (n − 1) jets) in the electron (left) and muon
(right) channel compared to expectations from simulations. The systematic uncertainty due to the jet energy
scale and the unfolding are shown, together with the total uncertainty.
3 W polarization
In pp collisions at the LHC the W’s recoiling against energetic jets are expected to exhibit a
sizable left-handed polarization, because of the dominance of quark-gluon initial states, along
with the V −A nature of the coupling of the W boson to fermions 6 . We measure the polarization