Dag Toppe Larsen

Particle-Yield Modification in Jetlike Azimuthal Dihadron Correlations in Pb-Pb Collisions at root S-NN=2.76 TeV

The yield of charged particles associated with high-p(t) trigger particles (8<p(t)<15 GeV/c) is measured with the ALICE detector in Pb-Pb collisions at √s(NN)=2.76 TeV relative to proton-proton collisions at the same energy. The conditional per-trigger yields are extracted from the narrow jetlike correlation peaks in azimuthal dihadron correlations. In the 5% most central collisions, we observe that the yield of associated charged particles with transverse momenta p(t)>3 GeV/c on the away side drops to about 60% of that observed in pp collisions, while on the near side a moderate enhancement of 20%-30% is found.

Online data compression in the ALICE O2 facility

The ALICE Collaboration and the ALICE O2 project have carried out detailed studies for a new online computing facility planned to be deployed for Run 3 of the Large Hadron Collider (LHC) at CERN. Some of the main aspects of the data handling concept are partial reconstruction of raw data organized in so called time frames, and based on that information reduction of the data rate without significant loss in the physics information. A production solution for data compression has been in operation for the ALICE Time Projection Chamber (TPC) in the ALICE High Level Trigger online system since 2011. The solution is based on reconstruction of space points from raw data. These so called clusters are the input for reconstruction of particle trajectories. Clusters are stored instead of raw data after a transformation of required parameters into an optimized format and subsequent lossless data compression techniques. With this approach, a reduction of 4.4 has been achieved on average. For Run 3, not only a significantly higher reduction is required but also improvements in the implementation of the actual algorithms. The innermost operations of the processing loop effectively need to be called up to O(1011)/s to cope with the data rate. This can only be achieved in a parallel scheme and makes these operations candidates for optimization. The potential of template programming and static dispatch in a polymorphic implementation has been studied as an alternative to the commonly used dynamic dispatch at runtime. In this contribution we report on the development of a specific programming technique to efficiently combine compile time and runtime domains and present results for the speedup of the algorithm.

pi(0) and eta reconstruction from photon conversions in ALICE for first p-p collisions at the LHC

Measurements of π0 and η inclusive spectra provide reference data for upcoming heavy ion runs, as well as a check on the applicability of perturbative QCD calculations at LHC energies. The high-resolution central tracking system of ALICE can be used to reconstruct π0 and η through photon conversions, as an alternative to direct measurement in the ALICE Calorimeters. Knowledge of the ALICE material budget is crucial for the extraction of the absolute yield from the conversion technique. The statistics availible from this technique are comparable to that of the photon spectrometer (PHOS), and the reconstruction method can also be applied for Pb-Pb collisions. Moreover, the implementation of a photon conversion trigger in the High Level Trigger (HLT) framework gives the possibility of identifying π0 and η candidates online, and increasing the statistics at higher momentum. The status of the π0 meson reconstruction from photon conversions from p-p collisions at = 900 GeV and = 7 TeV is presented in this article.

DCS Communication Software for the ALICE TPC Front-End Electronics

The ALICE Time Projection Chamber (TPC) is read out by 4356 Front-End Cards serving roughly 560000 channels. Each channel has to be configured and monitored individually. As one part of the overall controlling of the detector this task is covered by the Detector Control System (DCS). Since fault tolerance, error correction and system stability in general are major concerns, a system consisting of independently running layers has been designed. The functionality layers are running on a large number of nodes and sub-nodes. The low-level node controlling the Front-End Electronics is an embedded computer system, the DCS board, which provides the opportunity to run a light-weight Linux system on the card. The board interfaces to the front-end electronics via a dedicated hardware interface and connects to the higher DCS-layers via the DIM communication framework over Ethernet. This article presents the structure of the communication software and the application of the DCS board.