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Searches for Massive Highly Ionising Particles at the ATLAS Experiment and in Polar Volcanic Rocks, and Performance Studies of the First Level ATLAS Trigger System
Stockholm University, Faculty of Science, Department of Physics. (Elementary particle physics)
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Standard Model (SM) of particle physics describes the elementary particles and their interactions. Despite passing a number of high precision falsification tests, it is argued that the SM suffers from a number of shortcomings. Many Beyond the Standard Model (BSM) theories have therefore been postulated. Exotic highly ionising particles such as magnetic monopoles and Highly Electrically Charged Objects (HECOs), with masses at or above the TeV-scale, are predicted in many of these theories. Monopoles arise naturally in grand unification theories. Proposed candidates for HECOs are Q-balls, strangelets and micro-black hole remnants.

The Large Hadron Collider (LHC) at CERN is the world's largest and most powerful particle accelerator, colliding protons at centre-of-mass energies up to 13 TeV. One of the main purposes of the LHC is to search for particles beyond the SM. The research presented in this thesis comprises a search for magnetic monopoles and HECOs at one of the largest of the LHC detectors, the ATLAS detector. In addition, studies were made on the performance of the ATLAS trigger system, which is responsible for making the initial online selection of interesting proton-proton events.

The search for monopoles and HECOs at ATLAS was conducted using a customized trigger and selection variables optimized for the non-standard particle signature in ATLAS. The dataset corresponds to an integrated luminosity of 7.0 fb^{-1} and the centre-of-mass energy was 8 TeV. No events were observed and upper limits on production cross-sections were set for monopoles and HECOs of mass 200-2500 GeV and charge in the range $0.5-2.0$ g_D, where g_D is the Dirac charge, and 10 - 60 e, respectively.

Magnetic monopoles were also sought in polar volcanic rock using a SQUID magnetometer at ETH, Zürich. No candidates were found leading to limits on the monopole density in polar igneous rocks of 9.8 * 10^{-5}/gram.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2016. , 259 p.
Keyword [en]
Magnetiska monopoler, Trigger
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-127981ISBN: 978-91-7649-293-2 (print)OAI: oai:DiVA.org:su-127981DiVA: diva2:912039
Public defence
2016-05-04, sal FP41, AlbaNova universitetscentrum, Roslagstullsbacken 33, Stockholm, 13:00 (English)
Opponent
Supervisors
Available from: 2016-04-11 Created: 2016-03-15 Last updated: 2017-02-17Bibliographically approved
List of papers
1. The ATLAS transverse-momentum trigger performance at the LHC in 2011
Open this publication in new window or tab >>The ATLAS transverse-momentum trigger performance at the LHC in 2011
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The transverse momentum triggers of the ATLAS experiment at the CERN Large Hadron Collider are designed to select collision events with non-interacting particles passing through the detector and events with a large amount of outgoing momentum transverse to the beam axis. These triggers use global sums over the full calorimeter so are sensitive to measurement fluctuations and systematic changes anywhere in the detector. During the 2011 data-taking period, the LHC beam conditions for proton-proton collisions went through considerable evolution, starting with an average number of interactions per bunch crossing in a run, ⟨μ⟩, of about 3, increasing to typical values of 7 to 15, and even including one run with ⟨μ⟩ of about 30. These changes were accompanied by changes in the bunch structure, including the number of filled bunches, how these were spaced, and the intensity of individual bunches. An increase in μ results in an increase of both the average energy deposit in the calorimeter and the energy-measurement fluctuations. Changes in beam conditions in turn necessitated changes in the calorimeter noise-suppression schemes used at various trigger levels. Trans- verse momentum distributions and trigger rates were impacted by all of these changes. This note contains a description of the transverse momentum triggers, the challenges faced in the 2011 data-taking period, the strategies used to deal with changes in the beam and detector, and characterization of the trigger performance in 2011. Even under these conditions, the trigger behavior was close to what was expected and allowed robust collection of data used for physics studies. 

Place, publisher, year, edition, pages
Geneva: CERN, 2014
Keyword
Trigger, transverse-momentum, ATLAS
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-127987 (URN)
Conference
None, ATLAS publication type
Note

ATLAS Note. ATLAS-CONF-2014-002.

Available from: 2016-03-15 Created: 2016-03-15 Last updated: 2016-03-30Bibliographically approved
2. Search for Magnetic Monopoles in root s=7 TeV pp Collisions with the ATLAS Detector
Open this publication in new window or tab >>Search for Magnetic Monopoles in root s=7 TeV pp Collisions with the ATLAS Detector
Show others...
2012 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 109, no 26, 261803Article in journal (Refereed) Published
Abstract [en]

This Letter presents a search for magnetic monopoles with the ATLAS detector at the CERN Large Hadron Collider using an integrated luminosity of 2.0 fb(-1) of pp collisions recorded at a center-of-mass energy root s = 7 TeV. No event is found in the signal region, leading to an upper limit on the production cross section at 95% confidence level of 1.6/epsilon fb for Dirac magnetic monopoles with the minimum unit magnetic charge and with mass between 200 GeV and 1500 GeV, where epsilon is the monopole reconstruction efficiency. The efficiency epsilon is high and uniform in the fiducial region given by pseudorapidity vertical bar eta vertical bar < 1: 37 and transverse kinetic energy 600-700<E-kin sin theta< 1400 GeV. The minimum value of 700 GeV is for monopoles of mass 200 GeV, whereas the minimum value of 600 GeV is applicable for higher mass monopoles. Therefore, the upper limit on the production cross section at 95% confidence level is 2 fb in this fiducial region. Assuming the kinematic distributions from Drell-Yan pair production of spin-1= 2 Dirac magnetic monopoles, the efficiency is in the range 1%-10%, leading to an upper limit on the cross section at 95% confidence level that varies from 145 fb to 16 fb for monopoles with mass between 200 GeV and 1200 GeV. This limit is weaker than the fiducial limit because most of these monopoles lie outside the fiducial region. DOI: 10.1103/PhysRevLett.109.261803

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-87665 (URN)10.1103/PhysRevLett.109.261803 (DOI)000312932800005 ()
Note

AuthorCount:2876;

Available from: 2013-02-18 Created: 2013-02-14 Last updated: 2017-12-06Bibliographically approved
3. Search for Magnetic Monopoles in Polar Volcanic Rocks
Open this publication in new window or tab >>Search for Magnetic Monopoles in Polar Volcanic Rocks
Show others...
2013 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 110, no 12, 121803Article in journal (Refereed) Published
Abstract [en]

For a broad range of values of magnetic monopole mass and charge, the abundance of monopoles trapped inside Earth would be expected to be enhanced in the mantle beneath the geomagnetic poles. A search for magnetic monopoles was conducted using the signature of an induced persistent current following the passage of igneous rock samples through a SQUID-based magnetometer. A total of 24.6 kg of rocks from various selected sites, among which 23.4 kg are mantle-derived rocks from the Arctic and Antarctic areas, was analyzed. No monopoles were found, and a 90% confidence level upper limit of 9.8 x 10(-5)/g is set on the monopole density in the search samples.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-89798 (URN)10.1103/PhysRevLett.110.121803 (DOI)000316682600002 ()
Note

AuthorCount:9;

Available from: 2013-05-10 Created: 2013-05-08 Last updated: 2017-12-06Bibliographically approved

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