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Katarina Bendtz


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Besöksadress Frescati hagväg 14
Rum 348
Postadress Psykologiska institutionen 106 91 Stockholm

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I urval från Stockholms universitets publikationsdatabas
  • 2016. Yiming Abulaiti (et al.). Physical Review D 93 (5)

    A search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 7.0 fb(-1). A customized trigger significantly increases the sensitivity, permitting a search for such particles with charges and energies beyond what was previously accessible. No events were found in the signal region, leading to production cross section upper limits in the mass range 200-2500 GeV for magnetic monopoles with magnetic charge in the range 0.5g(D) < vertical bar g vertical bar < 2.0g(D), where g(D) is the Dirac charge, and for stable particles with electric charge in the range 10 < vertical bar z vertical bar < 60. Model-dependent limits are presented in given pair-production scenarios, and model-independent limits are presented in fiducial regions of particle energy and pseudorapidity.

  • 2013. Katarina Bendtz (et al.). Physical Review Letters 110 (12)

    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.

  • 2014. Collaboration ATLAS.

    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. 

  • 2016. Katarina Bendtz, David Milstead, Kenneth Österberg.

    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.

  • 2016. B. Acharya (et al.). Journal of High Energy Physics (JHEP) (8)

    The MoEDAL experiment is designed to search for magnetic monopoles and other highly-ionising particles produced in high-energy collisions at the LHC. The largely passive MoEDAL detector, deployed at Interaction Point 8 on the LHC ring, relies on two dedicated direct detection techniques. The first technique is based on stacks of nuclear-track detectors with surface area similar to 18 m(2), sensitive to particle ionisation exceeding a high threshold. These detectors are analysed offline by optical scanning microscopes. The second technique is based on the trapping of charged particles in an array of roughly 800 kg of aluminium samples. These samples are monitored offline for the presence of trapped magnetic charge at a remote superconducting magnetometer facility. We present here the results of a search for magnetic monopoles using a 160 kg prototype MoEDAL trapping detector exposed to 8TeV proton-proton collisions at the LHC, for an integrated luminosity of 0.75 fb(-1). No magnetic charge exceeding 0.5g(D) (where g(D) is the Dirac magnetic charge) is measured in any of the exposed samples, allowing limits to be placed on monopole production in the mass range 100 GeV <= m <= 3500 GeV. Model-independent cross-section limits are presented in fiducial regions of monopole energy and direction for 1g(D) <= vertical bar g vertical bar <= 6g(D), and model-dependent cross-section limits are obtained for Drell-Yan pair production of spin-1/2 and spin-0 monopoles for 1g(D) <= vertical bar g vertical bar <= 4g(D). Under the assumption of Drell-Yan cross sections, mass limits are derived for vertical bar g vertical bar = 2g(D) and vertical bar g vertical bar = 3g(D) for the first time at the LHC, surpassing the results from previous collider experiments.

  • 2013. Barbro Åsman (et al.). Physics Letters B 719 (4-5), 280-298

    Many extensions of the Standard Model posit the existence of heavy particles with long lifetimes. In this Letter, results are presented of a search for events containing one or more such particles, which decay at a significant distance from their production point, using a final state containing charged hadrons and an associated muon. This analysis uses a data sample of proton-proton collisions at root s = 7 TeV corresponding to an integrated luminosity of 4.4 fb(-1) collected in 2011 by the ATLAS detector operating at the Large Hadron Collider. Results are interpreted in the context of R-parity violating supersymmetric scenarios. No events in the signal region are observed and limits are set on the production cross section for pair production of supersymmetric particles, multiplied by the square of the branching fraction for a neutralino to decay to charged hadrons and a muon, based on the scenario where both of the produced supersymmetric particles give rise to neutralinos that decay in this way. However, since the search strategy is based on triggering on and reconstructing the decay products of individual long-lived particles, irrespective of the rest of the event, these limits can easily be reinterpreted in scenarios with different numbers of long-lived particles per event. The limits are presented as a function of neutralino lifetime, and for a range of squark and neutralino masses.

Visa alla publikationer av Katarina Bendtz vid Stockholms universitet

Senast uppdaterad: 20 februari 2018

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