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

Data / MC
CMS preliminary, 2.9 pb
1.1
s = 7 TeV
1.08
MC scaled for FSR and QCD bkg
pT balance
1.06
1.04
1.02
1
0.98
0.96
anti-kT 0.5 PF
MPF
χ2
/ NDF = 14.2 / 12
20 30 40 50 100 200
γ
p (GeV)
-1
T
Absolute scale uncertainty [%]
10
9
8
7
6
5
4
3
2
1
0
-1
CMS preliminary, 2.9 pb
particle flow jets
Anti-k 0.5 & 0.7
T
Total uncert.
Total MPF
Photon scale
Extrapolation
Offset (+1PU)
Residuals
s = 7 TeV
20 30 100 200 1000 2000
p (GeV)
Figure 1: Left: Ratio between measured jet absolute energy scale with photon+jet events and the one predicted
by the MC simulation, as a function of photon pT. Results obtained with the Missing-ET Projection Fraction
(MPF) method (red) are compared to a traditional photon/jet balancing technique (blue). Right: Uncertainty
on the absolute scale measurement with the MPF method. Different sources of error are shown.
• an absolute correction, which addresses the non-compensating nature of the CMS calorimeters,
and uniforms the response as a function of jet transverse momentum.
The measurement of the relative and absolute corrections has been performed on the first
3 pb −1 of data recorder in 2010. The jet absolute correction is measured on photon+jet events,
in which the precision with which the photon is reconstructed in the crystal electromagnetic
calorimeter is exploited in order to infer the recoiling jet’s true momentum. The absolute
response is extracted making use of the knowledge of the full event missing transverse energy,
with a method know as the Missing-ET Projection Fraction (MPF) 2 . This method is particularly
suited for the Particle-Flow event reconstruction, which, through the use of the tracker, ensures
a relatively high response also in the case of soft radiation. It is therefore expected to be the
most insensitive to biases related to additional event activity.
Results obtained with the photon+jet pt balancing technique are shown in Fig. 1 (left),
where the MPF data/MC ratio (blue) is shown as a function of the photon transverse momentum.
Results obtained with a more traditional photon/jet balancing technique are shown as
comparison (red). The points are compatible with the Monte Carlo prediction. The estimated
systematic uncertainty on this measurement is shown in Fig. 1 (right). Various possible sources
resolution
T
jet p
0.3
0.2
0.1
-1
s=7 TeV, L=35.9 pb CMS preliminary 2010
total systematic uncertainty
MC truth (c-term added)
MC truth
data
0
50 100 200
CaloJets
(Anti-k R=0.5)
T
0 < | η|
≤ 0.5
p [GeV]
T
resolution
T
jet p
0.3
0.2
0.1
total systematic uncertainty
MC truth (c-term added)
MC truth
data
0
50 100 200
T
-1
s=7 TeV, L=35.9 pb CMS preliminary 2010
PFJets
(Anti-k R=0.5)
T
0 < | η|
≤ 0.5
p [GeV]
T
Figure 2: Jet transverse momentum resolution measurement with the dijet asymmetry method in the central part
of the detector (|η| < 0.5). Calorimeter jet results are shown on the left, Particle-Flow jets on the right.