Measurement of the Z boson cross-section in - Harvard University ...

Chapter 4: Data Collection and Event Reconstruction 97
the muon spectrometer (MS), but the basic strategy is to convert ADC/TDC counts
into energy, time and/or distance estimates. The reconstruction software is part
of the ATLAS offline software framework, known as Athena. The raw data input
to the reconstruction chain is in the so-called bytestream format. The output of
reconstruction are Event Summary Data (ESD) and Analysis Object Data (AOD)
files.
The ESD contains the detailed output of reconstruction, including sufficient in-
formation to enable jet calibration, track re-fitting etc. (discussed below). It has
been designed to allow quick tuning of reconstruction algorithms and extraction of
calibration constants. The AOD contains a summary of the reconstructed event, in-
cluding all physics objects in the event as well as event-level metadata 1 . AODs can
be produced from ESDs. Our analysis used collections of variables extracted from
ESDs or AODs, known as D3PDs, that allow efficient, CPU-economic access to data.
4.2.1 Reconstruction in the Inner Detector
Inner detector reconstruction includes the reconstruction of tracks, vertices, the
beamline, and electron bremsstrahlung recovery. Track reconstruction in the inner
detector has three main components: the primary inside-out reconstruction, the sub-
sequent outside-in reconstruction, and a final TRT-only reconstruction. The various
steps involved in each will be briefly described below.
1 Event metadata consists of such information as the run and luminosity block the event belongs
to, the bunch crossing which produced it etc.