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The ATLAS beam pick-up based timing system
Stockholm University, Faculty of Science, Department of Physics. (Elementarpartikelfysik)
European Organization for Nuclear Research, 1211 Genève, Switzerland.
2010 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, Vol. 623, no 1, 558-560 p.Article in journal (Refereed) Published
Abstract [en]

The ATLAS BPTX stations are composed of electrostatic button pick-up detectors, located 175 m away along the beam pipe on both sides of ATLAS. The pick-ups are installed as a part of the LHC beam instrumentation and used by ATLAS for timing purposes.

The usage of the BPTX signals in ATLAS is twofold: they are used both in the trigger system and for LHC beam monitoring. The BPTX signals are discriminated with a constant-fraction discriminator to provide a Level-1 trigger when a bunch passes through ATLAS. Furthermore, the BPTX detectors are used by a stand-alone monitoring system for the LHC bunches and timing signals. The BPTX monitoring system measures the phase between collisions and clock with a precision better than 100 ps in order to guarantee a stable phase relationship for optimal signal sampling in the sub-detector front-end electronics. In addition to monitoring this phase, the properties of the individual bunches are measured and the structure of the beams is determined.

On September 10, 2008, the first LHC beams reached the ATLAS experiment. During this period with beam, the ATLAS BPTX system was used extensively to time in the read-out of the sub-detectors. In this paper, we present the performance of the BPTX system and its measurements of the first LHC beams.

Place, publisher, year, edition, pages
Elsevier , 2010. Vol. 623, no 1, 558-560 p.
Keyword [en]
ATLAS, Beam monitoring, Level-1 trigger, BPTX, LHC, LHC timing signals
National Category
Subatomic Physics
URN: urn:nbn:se:su:diva-63066DOI: 10.1016/j.nima.2010.03.069OAI: diva2:446616
Available from: 2011-10-07 Created: 2011-10-07 Last updated: 2011-10-10Bibliographically approved
In thesis
1. Searches for exotic stable massive particles with the ATLAS experiment
Open this publication in new window or tab >>Searches for exotic stable massive particles with the ATLAS experiment
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents two signature-based searches for exotic long-lived particles using experimental data collected by the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. At the LHC, proton-proton collisions take place at the world-record center-of-mass energy of 7 TeV and luminosities of up to  3×1033 cm-2s-1 . New physics has long been anticipated at the LHC and in this thesis two searches for hitherto unobserved particles are presented.

Long-lived heavy hadrons have been predicted by models of supersymmetry, and these were the target of the first physics analysis. Using measurements of timing and energy loss, a search for so-called R-hadrons was performed. No excess was observed in the data, and new lower limits were established on the masses of meta-stable supersymmetric particles with color charge: mgluino > 562-586 GeV (depending on choice of scattering model), mstop > 309 GeV and msbottom > 294 GeV. These constraints are the most stringent limits published to date.

In addition, a ``blue-sky'' search was made for objects possessing high electric charge. Ionization energy loss measurements were combined with variables describing the shape of electromagnetic showers to separate the sought signal from background processes. No event in the experimental data passed the selection and the results are in agreement with a background-only hypothesis. Upper limits between 1-12 pb were computed for the production cross sections of particles with electric charge 6e ≤ |q| ≤ 17e and mass 200 ≤ m ≤ 1000 GeV. This is the first dedicated search for such particles at the LHC.

Finally, a system designed to monitor the LHC beams and timing signals based on beam pick-up detectors is described together with results from early LHC operation.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2011. 185 p.
ATLAS, ATLAS experiment, supersymmetry, squark, gluino, stable massive particles, long-lived particles, physics analysis, search analysis, LHC, Large Hadron Collider
National Category
Subatomic Physics
Research subject
urn:nbn:se:su:diva-63068 (URN)978-91-7447-341-4 (ISBN)
Public defence
2011-11-04, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Available from: 2011-10-13 Created: 2011-10-07 Last updated: 2011-10-10Bibliographically approved

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Ohm, Christian
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