In-situ jet energy scale and jet shape corrections for multiple interactions in the first ATLAS data at the LHC

In-situ methods are presented for subtracting contributions to the measured jet energy due to multiple proton-proton interactions (pile-up) in the first data collected with the ATLAS detector in proton-proton collisions at the LHC at a center-of-mass energy of $\sqrt{s} = 7$ TeV. Such events deposit diffuse soft radiation in the calorimeter that is uncorrelated with jets from the hard-scattering. This introduces an offset which can be, on average, subtracted from the measured jet energy. Two approaches to deriving and applying this offset correction are discussed and results are presented to demonstrate the effectiveness of the method. In addition to average jet energy corrections, we show that the jet shape can be corrected for the effects of pile-up, by up to 40% near the edge of the jet. The resulting uncertainty due to pile-up after these corrections is approximately 100 MeV for each additional primary vertex, which is a factor of 5 improvement over the the measured bias prior to the correction.