Wenzhao Li

Studies for a common selection software environment in ATLAS: from the level-2 trigger to the offline reconstruction

The ATLAS High Level Triggers (HLT) primary function of event selection will be accomplished with a Level-2 trigger farm and an event filter (EF) farm, both running software components developed in the ATLAS offline reconstruction framework. While this approach provides a unified software framework for event selection, it poses strict requirements on offline components critical for the Level-2 trigger. A Level-2 decision in ATLAS must typically be accomplished within 10 ms and with multiple event processing in concurrent threads. To address these constraints, prototypes have been developed that incorporate elements of the ATLAS data flow, high level trigger, and offline framework software. To realize a homogeneous software environment for offline components in the HLT, the Level-2 Steering Controller was developed. With electron/gamma- and muon-selection slices it has been shown that the required performance can be reached, if the offline components used are carefully designed and optimized for the application in the HLT.

Transverse Wobbling in

A pair of transverse wobbling bands is observed in the nucleus ^{135}Pr. The wobbling is characterized by ΔI=1, E2 transitions between the bands, and a decrease in the wobbling energy confirms its transverse nature. Additionally, a transition from transverse wobbling to a three-quasiparticle band comprised of strong magnetic dipole transitions is observed. These observations conform well to results from calculations with the tilted axis cranking model and the quasiparticle rotor model.

^{135}

The ATLAS high-level trigger (HLT) system provides software-based event selection after the initial LVL1 hardware trigger. It is composed of two stages, the LVL2 trigger and the event filter (EF). The LVL2 trigger performs event selection with optimized algorithms using selected data guided by Region of Interest pointers provided by the LVL1 trigger. Those events selected by LVL2 are built into complete events, which are passed to the EF for a further stage of event selection and classification using off-line algorithms. Events surviving the EF selection are passed for off-line storage. The two stages of HLT are implemented on processor farms. The concept of distributing the selection process between LVL2 and EF is a key element in the architecture, which allows it to be flexible to changes (luminosity, detector knowledge, background conditions, etc.) Although there are some differences in the requirements between these subsystems there are many commonalities. An overview of the dataflow (event selection) and supervision (control, configuration, monitoring) activities in the HLT is given, highlighting where commonalities between the two subsystems can be exploited and indicating where requirements dictate that implementations differ. An HLT prototype system has been built at CERN. Functional testing is being carried out in order to validate the HLT architecture.

Pr

Presented are the main design features and performance results of the cathode strip chambers (CSCs) for the CMS Endcap Muon System. The six-plane structure of these chambers yields a spatial resolution of about 80 /spl mu/m, essentially uniform and independent of the strip width (up to 16 mm, which is unusually wide for the cathode-to-anode wire distance of 5 mm). In addition, the net spatial resolution of about one-tenth of the strip width at the hardware trigger level (300ns) is obtained using a simple network of comparators. The time resolution achieved at the trigger level is /spl sim/4ns (RMS) that allows unambiguous tagging of bunch crossing occurring every 25 ns. Aging tests, including those obtained with a recirculating gas system, showed only minor aging effects. The aging studies were performed with large-scale chambers; 700 m of wire were irradiated for a dose up to 0.4 C/cm of the total accumulated charge.