C. Wiglesworth

Collision experiments at the Large Hadron Collider suffer from the problem of pile-up, which is the read-out of multiple simultaneous background proton-proton collisions per beam-crossing. We introduce a pile-up mitigation technique based on wavelet decomposition. Pile-up is treated as a form of white noise, which can be removed by filtering beam-crossing events in the wavelet domain. The particle-level performance of the method is evaluated using a sample of simulated proton-proton collision events that contain Z bosons decaying to a pair of neutrinos, overlaid with pile-up. In the wavelet representation, the pile-up noise level is found to grow with the square root of the number of background proton-proton collisions.

Recent charge collection measurements after severe hadron irradiation have proved that n-side readout segmented planar silicon detectors can successfully operate up to the doses anticipated for the innermost layers of the upgraded experiments in the future super LHC (sLHC) at CERN. The charge collected by the irradiated sensors is sufficient to guarantee a signal over noise (S/N) ratio above 10 even for the pixel layers located at the smallest radial distance from the beam line (less than 4 cm away). The signal depends on the applied bias and voltages as high as 1000V could be required to satisfy the minimum signal height for the most exposed detectors. The radiation at the doses of the pixel layers in the sLHC also cause an important increase of the reverse current The high bias voltages and reverse currents cause significant power dissipation and adequate cooling needs to be applied to limit the current well below the thermal-runaway level.

The search for the Standard Model (SM) Higgs boson is one of the main objectives of the Large Hadron Collider (LHC). The decay mode leading to a four lepton (electron/muon) final state provides an experimentally clean signature and contributes significantly to the discovery potential. The analysis strategy for selecting signal and rejecting backgrounds is described. The sensitivity of the ATLAS detector to a SM Higgs boson in the four lepton final state and in a combination of channels is presented for a range of masses, from 120 GeV to 600 GeV.

The high gradients potentially achievable in distributed-coupling C-band photoinjectors make them attractive for many high brightness applications. Here we discuss optimization results for a 1.6 cell C-band photoinjector with a 240 MV/m peak field at the cathode that delivers a 250 pC electron bunch charge. We use a Multi-Objective Genetic Algorithm (MOGA), obtaining a Pareto front of emittance vs. bunch length. We also perform MOGA optimizations including an aperture to retain only a bright beam core. We find this reduces the emittance of the final beam by more than factor of 2 in some cases. For example, we find that at a root mean square bunch length of 1.6 ps, the use of an aperture improves the transverse emittance from 120 nm to 58 nm assuming negligible photocathode intrinsic emittance. The sacrificial charge at the periphery of the electron beam removed by the aperture linearizes the final slice phase space inside of the remaining beam core. The results obtained surpass the experimental state-of-the-art for beamlines with similar bunch charge.