Jet energy measurement with the ATLAS detector in proton-proton collisions at √s=7 TeV

The jet energy scale and its systematic uncer-
tainty are determined for jets measured with the ATLAS
detector at the LHC in proton-proton collision data at a
centre-of-mass energy of
√
s
=
7 TeV corresponding to
an integrated luminosity of 38 pb
−
1
. Jets are reconstructed
with the anti-
k
t
algorithm with distance parameters
R
=
0
.
4
or
R
=
0
.
6. Jet energy and angle corrections are deter-
mined from Monte Carlo simulations to calibrate jets with
transverse momenta
p
T
≥
20 GeV and pseudorapidities
|
η
|
<
4
.
5. The jet energy systematic uncertainty is estimated
using the single isolated hadron response measured
in situ
and in test-beams, exploiting the transverse momentum bal-
ance between central and forward jets in events with di-
jet topologies and studying systematic variations in Monte
Carlo simulations. The jet energy uncertainty is less than
2.5 % in the central calorimeter region (
|
η
|
<
0
.
8) for jets
with 60
≤
p
T
<
800 GeV, and is maximally 14 % for
p
T
<
30 GeV in the most forward region 3
.
2
≤|
η
|
<
4
.
5.
The jet energy is validated for jet transverse momenta up
to 1 TeV to the level of a few percent using several
in situ
techniques by comparing a well-known reference such as the
recoiling photon
p
T
, the sum of the transverse momenta of
tracks associated to the jet, or a system of low-
p
T
jets recoil-
ing against a high-
p
T
jet. More sophisticated jet calibration
schemes are presented based on calorimeter cell energy den-
sity weighting or hadronic properties of jets, aiming for an
improved jet energy resolution and a reduced flavour depen-
dence of the jet response. The systematic uncertainty of the
jet energy determined from a combination of
in situ
tech-
niques is consistent with the one derived from single hadron
response measurements over a wide kinematic range. The
nominal corrections and uncertainties are derived for iso-
lated jets in an inclusive sample of high-
p
T
jets. Special
cases such as event topologies with close-by jets, or selec-
tions of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed
and the corresponding uncertainties are determined.