Abstract
The ATLAS experiment records data from the proton-proton collisions produced by the Large Hadron Collider (LHC). The Tile Calorimeter is the hadronic sampling calorimeter of ATLAS in the region uηu < 1.7. It uses iron absorbers and scintillators as active material. The LHC will provide collisions every 25 ns, putting very strong requirements on the energy measurement in presence of energy deposits from different collisions in the same read out window and physical calorimeter channel (pile-up). In 2011 the LHC is running with filled bunches at 50 ns spacing and at intensities which yield up to about 8 proton-proton collisions per bunch crossing. We present a quality factor that can be computed online for each collision and for each calorimeter channel within the 10 μs latency of the ATLAS first level trigger (L1 trigger), and could allow to identify calorimeter channels presenting pile-up. In presence of a poor quality factor the data from the corresponding channel is read out with additional information to allow for an offline dedicated treatment of the signals to account for pile-up.
Highlights
T HE Large Hadron Collider (LHC), currently under operation at CERN, with its unprecedented high energy and luminosity extends the frontier of particle physics
The LHC will operate with proton bunches crossing every 25 ns, in 2011 it has operated with 50 ns bunch spacing and with an expected average number of 8 proton-proton collisions per bunch crossing
The quality factor distribution is computed in data using an integrated luminosity of 60 nb−1 taken in March 2011 at a period where the LHC was operating with only 2 bunches per beam, separated by at least 2.5 μs, ensuring the absence of out-of-time pile-up
Summary
T HE Large Hadron Collider (LHC), currently under operation at CERN, with its unprecedented high energy and luminosity extends the frontier of particle physics. The ATLAS experiment needs to be sensitive to a large number of possible decay channels and so must provide an excellent particle identification and high resolution measurements of energies, momenta and directions for the outgoing particles in the proton-proton collisions. TileCal provides vital information for the first level of trigger (L1-trigger), participates in the measurement of the missing energy due to non-interacting particles and to the identification of electrons and photons. It uses steel as an absorber and scintillating plastic tiles as an active material. A numerical model has been developed to simulate the TileCal pulse shapes and quality factors with and without outof-time pile-up. The numerical model allows to predict quality factor distributions permitting the optimization of the quality factor online selection criteria, under the constraints of available bandwidth while keeping a reliable out-of-time pile-up detection
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