On the role of composition entropies in the statistical mechanics of polydisperse systems

Polydisperse systems are commonly encountered when dealing with soft matter in general or any non-simple fluid. Yet their treatment within the framework of statistical thermodynamics is a delicate task as the latter has been essentially devised for simple—non-fully polydisperse—systems. In this paper, we address the issue of defining a non-ambiguous combinatorial entropy for these systems. We do so by focusing on the general property of extensivity of the thermodynamic potentials and discussing a specific mixing experiment. This leads us to introduce the new concept of composition entropy for single phase systems that we do not assimilate to a mixing entropy. We then show that they do not contribute to the thermodynamics of the system at a fixed composition and prescribe to subtract ln N! from the free energy characterizing a system however polydisperse it can be. We then re-derive general expressions for the mixing entropy between any two polydisperse systems and interpret them in term of distances between probability distributions, showing that one of these metrics relates naturally to a recent extension of Landauer's principle. We then propose limiting expressions for the mixing entropy in the case of mixing with equal proportions in the original compositions and finally address the challenging problem of chemical reactions

Implementation and Performance of the High-Level Trigger electron and photon selection for the ATLAS experiment at the LHC

The ATLAS three-tier trigger system faces the challenge to reduce the incoming rate of 40 MHz to â¼ 200 Hz. It consists of hardware based Level-1, and a software based High-Level Trigger (HLT). In this paper an overview of the selection algorithms for electrons and photons will be given as well as the expected performance. The electron and photon trigger menu and the strategy for the initial phase of LHC exploitation

The ATLAS trigger - high-level trigger commissioning and operation during early data taking

The ATLAS experiment is one of the two general-purpose experiments due to start operation soon at the Large Hadron Collider (LHC). The LHC will collide protons at a centre of mass energy of 14~TeV, with a bunch-crossing rate of 40~MHz. The ATLAS three-level trigger will reduce this input rate to match the foreseen offline storage capability of 100-200~Hz. This paper gives an overview of the ATLAS High Level Trigger focusing on the system design and its innovative features. We then present the ATLAS trigger strategy for the initial phase of LHC exploitation. Finally, we report on the valuable experience acquired through in-situ commissioning of the system where simulated events were used to exercise the trigger chain. In particular we show critical quantities such as event processing times, measured in a large-scale HLT farm using a complex trigger menu

The ATLAS Trigger/DAQ Authorlist, version 1.0

This is a reference document giving the ATLAS Trigger/DAQ author list, version 1.0 of 20 Nov 2008

The ATLAS Trigger/DAQ Authorlist, version 3.0

This is the ATLAS Trigger/DAQ Authorlist, version 3.0, 11 September 200

The ATLAS Trigger/DAQ Authorlist, version 2.0

This is the ATLAS Trigger/DAQ Authorlist, version 2.0, 31 July 200

The ATLAS Trigger/DAQ Authorlist, version 3.1

This is the ATLAS Trigger/DAQ Authorlist, version 3.1, 17 September 200

Software Validation Infrastructure for the ATLAS Trigger

The ATLAS trigger system is responsible for selecting the interesting collision events delivered by the Large Hadron Collider (LHC). The ATLAS trigger will need to achieve a ~10^-7 rejection factor against random proton-proton collisions, and still be able to efficiently select interesting events. After a first processing level based on hardware, the final event selection is based on custom software running on two CPU farms, containing around two thousand multi-core machines. This is known as the high-level trigger. Running the trigger online during long periods demands very high quality software. It must be fast, performant, and essentially bug-free. With more than 100 contributors and around 250 different packages, a thorough validation of the HLT software is essential. This relies on a variety of unit and integration tests as well as on software metrics, and uses both in-house and open source software. This presentation presents the existing infrastructure used for validating the high-level trigger software, as well as plans for its future development

Software Validation Infrastructure for the ATLAS High-Level Trigger

The ATLAS trigger will need to achieve a 10^−7 rejection factor against proton-proton collisions, and still be able to efficiently select interesting events. After a first hardware-implemented processing level, the final event selection is done by the high-level trigger (HLT), implemented on software. With more than 100 contributors and around 250 different packages, a thorough validation of the HLT software is essential. This paper describes the existing infrastructure used for validating the HLT software