The ALICE Level 0 Pixel Trigger Driver Layer

The ALICE Silicon Pixel Detector (SPD) comprises the two innermost layers of the ALICE inner tracker system. The SPD contains 120 detector modules each including 10 readout chips. Each of these pixel chips generates a digital Fast-OR output signal indicating the presence of at least one pixel hit in its pixel matrix. The Pixel Trigger (PIT) System has been implemented to process the 1200 Fast-Or signals from the SPD and provides an input signal to the ALICE Central Trigger Processor (CTP) for the fastest (Level 0) trigger decision within a latency of 800 ns. The PIT processor interfaces with several ALICE systems: it receives input data from the SPD, it accepts configuration commands from the CTP and sends status information to the Alice Experimental Control System (ECS). The PIT control system required an accurate design of hardware and software solutions to implement coordinated operation of the PIT and the ALICE systems to which it interfaces to. We present here the design, the implementation and the first operational experience of the PIT Control and Calibration system. The hardware configuration and control are implemented via the ALICE Detector Data Link, on top of which a custom control system has been implemented. A driver layer has been realized under stringent requirements of robustness and reusability. It qualifies as a general purpose hardware driver for electronic systems equipped with the ALICE DDL front end board (SIU). Various testing and calibration procedures need to be performed on the SPD and the PIT systems in order to provide an optimized trigger signal to the CTP. These include methods to compensate all signals propagation delays and automatic SPD DAC scans to tune the detector response. The PIT control system has been tailored to implement automatically most of the former procedures, requiring coordinated and extensive information exchange between the interfacing systems.CER

Implementation and experience with luminosity levelling with offset beam

The practice of luminosity levelling with an offset beam has been used as a routine operation in the LHC since 2011. This paper will describe how it has been implemented and what has been the operational experience with the system.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201

Operational Experience with the ALICE Pixel detector

The Silicon Pixel Detector (SPD) constitutes the two innermost layers of the Inner Tracking System of the ALICE experiment and it is the closest detector to the interaction point. As a vertex detector, it has the unique feature of generating a trigger signal that contributes to the L0 trigger of the ALICE experiment. The SPD started collecting data since the very first pp collisions at LHC in 2009 and since then it has taken part in all pp, Pb-Pb and p-Pb data taking campaigns. This contribution will present the main features of the SPD, the detector performance and the operational experience, including calibration and optimization activities from Run 1 to Run 2

Upgrade of the Inner Tracking System of ALICE

The upgrade of the Inner Tracking System (ITS) of ALICE is planned for the second long shutdown of the LHC in 2019-2020. The ALICE physics program after the shutdown requires the ITS to have improved tracking capabilities and improved impact parameter resolution at very low transverse momentum, as well as a substantial increase in the readout rate. To fulfill these requirements the current ITS will be replaced by seven layers of Monolithic Active Pixel Sensors. The new detector will be moved as close as 23 mm to the interaction point and will have a significantly reduced material budget. Several prototypes of the sensor have been developed to test different aspects of the sensor design including prototypes with analog and digital readout, as well as small and final-size sensors. These prototypes have been thoroughly characterized both in laboratory tests and at test beam facilities including studies on the radiation hardness of the sensors. This contribution gives an overview of the current status of the research and development with a focus on the pixel sensors and the characterization of the latest prototypes.Comment: 10 pages, 9 figures, proceedings of VERTEX 2015, 1-5 June 2015, Santa Fe, New Mexico, US

Information Causality, the Tsirelson Bound, and the 'Being-Thus' of Things

The principle of `information causality' can be used to derive an upper bound---known as the `Tsirelson bound'---on the strength of quantum mechanical correlations, and has been conjectured to be a foundational principle of nature. To date, however, it has not been sufficiently motivated to play such a foundational role. The motivations that have so far been given are, as I argue, either unsatisfactorily vague or appeal to little if anything more than intuition. Thus in this paper I consider whether some way might be found to successfully motivate the principle. And I propose that a compelling way of so doing is to understand it as a generalisation of Einstein's principle of the mutually independent existence---the `being-thus'---of spatially distant things. In particular I first describe an argument, due to Demopoulos, to the effect that the so-called `no-signalling' condition can be viewed as a generalisation of Einstein's principle that is appropriate for an irreducibly statistical theory such as quantum mechanics. I then argue that a compelling way to motivate information causality is to in turn consider it as a further generalisation of the Einsteinian principle that is appropriate for a theory of communication. I describe, however, some important conceptual obstacles that must yet be overcome if the project of establishing information causality as a foundational principle of nature is to succeed.Comment: '*' footnote added to page 1; 24 pages, 1 figure; Forthcoming in Studies in History and Philosophy of Modern Physic

The Virtual Monte Carlo

The concept of Virtual Monte Carlo (VMC) has been developed by the ALICE Software Project to allow different Monte Carlo simulation programs to run without changing the user code, such as the geometry definition, the detector response simulation or input and output formats. Recently, the VMC classes have been integrated into the ROOT framework, and the other relevant packages have been separated from the AliRoot framework and can be used individually by any other HEP project. The general concept of the VMC and its set of base classes provided in ROOT will be presented. Existing implementations for Geant3, Geant4 and FLUKA and simple examples of usage will be described.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 8 pages, LaTeX, 6 eps figures. PSN THJT006. See http://root.cern.ch/root/vmc/VirtualMC.htm