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.