D. Cavalli

Physics potential and experimental challenges of the LHC luminosity upgrade

Abstract.We discuss the physics potential and the experimental challenges of an upgraded LHC running at an instantaneous luminosity of 1035 cm-2s-1. The detector R&D needed to operate ATLAS and CMS in a very high radiation environment and the expected detector performance are discussed. A few examples of the increased physics potential are given, ranging from precise measurements within the Standard Model (in particular in the Higgs sector) to the discovery reach for several New Physics processes.

MINIMAL SUPERSYMMETRIC STANDARD MODEL HIGGS RATES AND BACKGROUNDS IN ATLAS

This study presents an overview of the potential of the ATLAS detector at LHC for the observation of the Higgs boson of the minimal supersymmetric Standard Model (MSSM). The expected rates, backgrounds and significances are discussed channel by channel using realistic assumptions for the detector performance. As final results, the ranges of the MSSM parameter space projected on the (mA, tanβ) and (mh, tanβ) planes, for which the expected significances for the discovery of the different channels exceed a 5σ value, are shown for the ATLAS detector alone and for combined results from the ATLAS and CMS detectors. It is concluded that the combined potential of the two LHC detectors should fully cover the Higgs sector of the MSSM parameter space. The sensitivity of the results to the upper limit of the allowed mass for the lightest Higgs boson is extensively discussed. The direct impact of the SUSY particle sector on such searches is neglected in this paper.

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.

A lead-liquid scintillator electromagnetic calorimeter for direct photon physics

Abstract A fine-grained sampling electromagnetic calorimeter using liquid scintillator contained in teflon tubes, its associated electronics and reconstruction programs, as used in an experiment on direct photons at CERN, are described. The performance of the system based on three years of operation is discussed.

A 1152 channel timing system for an electromagnetic calorimeter readout

Abstract A 1152 channel timing system used with a large electromagnetic calorimeter is described. Analysis of the timing information from the vertical and horizontal elements of the calorimeter yielded values for the position coordinates of the showers. This information was used to resolve ambiguities in the pattern recognition arising from multiple showers. A resolution of better than 0.25 ns for all channels was achieved. The calibration methods employed to maintain this resolution over several years are discussed.

High transverse momentum π0 production by π− and π+ on protons at 280 GeV/c

The inclusive cross sections for π0 production by π− and π+ on protons have been measured with a beam momentum of 280 GeV/c using a fine grained electromagnetic calorimeter and the CERN Omega spectrometer. The transverse momentum and FeynmanxF ranges covered are 4.0<pT<7.0 GeV/c and −0.45<xF<0.6 respectively. The data are compared with leading order QCD calculations.

Design, deployment and functional tests of the online event filter for the ATLAS experiment at LHC

The Event Filter (EF) selection stage is a fundamental component of the ATLAS Trigger and Data Acquisition architecture. Its primary function is the reduction of data flow and rate to values acceptable by the mass storage operations and by the subsequent offline data reconstruction and analysis steps. The computing instrument of the EF is organized as a set of independent subfarms, each connected to one output of the Event Builder (EB) switch fabric. Each subfarm comprises a number of processors analyzing several complete events in parallel. This paper describes the design of the ATLAS EF system, its deployment in the 2004 ATLAS combined test beam together with some examples of integrating selection and monitoring algorithms. Since the processing algorithms are not explicitly designed for EF but are adapted from the offline ones, special emphasis is reserved to system reliability and data security, in particular for the case of failures in the processing algorithms. Other key design elements have been system modularity and scalability. The EF shall be able to follow technology evolution and should allow for using additional processing resources possibly remotely located

Portable Gathering System for Monitoring and Online Calibration at ATLAS.

During the runtime of any experiment, a central monitoring system that detects problems as soon as they appear has an essential role. In a large experiment, like ATLAS, the online data acquisition system is distributed across the nodes of large farms, each of them running several processes that analyse a fraction of the events. In this architecture, it is necessary to have a central process that collects all the monitoring data from the different nodes, produces full statistics histograms and analyses them. In this paper we present the design of such a system, called the gatherer. It allows to collect any monitoring object, such as histograms, from the farm nodes, from any process in the

Study of the performance of a large sample of Philips photomultipliers type XP2972

Abstract The gain of the Philips XP2972 phototube was measured as a function of time and anode current using 3456 tubes in conditions simulating the experimental situation at the CERN SPS. After an initial ageing period of 35 h, the mean gain variation was measured to be 0.7% with an rms of 0.5% over 12 h at constant anode current ( I a =1.6 μ A). At an approximately constant gain of 2.2×10 5 , the majority (88%) of the tubes show an increase in gain with an average of 1.6% and an rms of 1.1% when the anode current rises from about 10 nA to 1.6 μA. These characteristics were used to select and distribute the tubes on the electromagnetic calorimeter of the CERN WA70 experiment. Short term instability and photocathode homogeneity were studied on a reduced sample.

High pT trigger electronics for a large orthogonal readout electromagnetic calorimeter

Abstract A trigger system has been designed and built to select events containing high p T electromagnetic showers detected in a large calorimeter with orthogonal readout. The electronics include analog adders with up to 123 inputs, pulse shapers with 20 ns integration time, 100 MHz flash ADCs and ECL loop-up tables. The total number of input channels is 3072 and the trigger decision is made in about 120 ns.