Previous events in 2020

Master thesis defense by Christian Michelsen

17 January 2020 kl. 15:00

Title: A Physicist’s Approach To Machine learning – Understanding The Basic Bricks

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PhD defense by Vojtech Pacik

12 February 2020 kl. 11:00

Title: Measurement of anisotropic flow using the ALICE experiment at CERN-LHC


The primary goal of ultra-relativistic heavy-ion physics is the study of the created strongly- interacting quark-gluon plasma (sQGP).Measurements of the azimuthal anisotropy of created particles, quantified by anisotropic flow vn coefficients, compared to hydrodynamic calculations, can be used to investigate this unique state of nuclear matter and its properties.

Due to the absence of the QGP-like medium, small collision systems have been considered as a baseline for the heavy-ion measurements. However, high-multiplicity pp and p-Pb collisions have revealed similar collective behaviour traditionally associated with the expanding medium.The origin of such features is not yet understood and is a focus point of the present work.

This work presents the analysis of azimuthal correlations of inclusive charged hadrons and identified particles in Pb-Pb and p-Pb collisions at centre-of-mass energy of 5.02 TeV recorded by ALICE detector at the Large Hadron Collider. Besides the vn measurement obtained for the first time using the 4-particle cumulants, more advanced observables such as flow fluctuations and non-linear flow response are studied in Pb-Pb collisions. The presented results exhibit an explicit mass ordering consistent with radial expansion with universal velocity, as described by hydrodynamical calculations based on the iEBE-VISHNU model for low pT < 3 GeV/c, and baryon/meson grouping at intermediate pT region.

Non-flow correlations, arising from jet fragmentation and resonance decays, present a challenge as they generally dominate in small collision systems. In order to reduce such contamination, a pseudo-rapidity separation between correlated particles is applied as well as subtraction of remaining non-flow estimate based on a measurement of minimum-bias pp collisions at centre-of-mass energy of 13 TeV. Motivated by Pb-Pb measurements, an initial attempt for extracting v2 using the 4-particle cumulant is made.The mass-related features observed in Pb-Pb collisions are also apparent in non-flow subtracted p-Pb measurement.

Overall, these differential measurements of vn coefficients present challenges for theoretical calculations further constraining the medium properties as well as initial conditions of the collision. In addition to the inclusive particles, the measurements using identified hadrons provide unique insights into particle production mechanisms. The results presented here mark a starting point for potential future development in investigating the obscure origin of the collectivity by analysing high-multiplicity pp collisions.

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Seminar by Prof. Torsten Åkesson

20 February 2020 kl. 12:00

Title: Search for Light Dark Matter using a Primary Electron Beam
The constituents of dark matter are still unknown, and the viable possibilities span a very large mass range. Specific scenarios for the origin of dark matter sharpen the focus on a narrower range of masses: the natural scenario where dark matter originates from thermal contact with familiar matter in the early Universe requires the DM mass to lie within about an MeV to 100 TeV. Considerable experimental attention has been given to exploring Weakly Interacting Massive Particles in the upper end ...
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Master thesis defense by Loui Nørgaard Wentzel

21 February 2020 kl. 15:00

Using Machine Learning on electron identification and energy regression in the forward region in ATLAS Read more