Refine
Has Fulltext
- yes (2)
Is part of the Bibliography
- yes (2)
Year of publication
- 2014 (2) (remove)
Document Type
- Doctoral Thesis (2)
Language
- English (2)
Keywords
- ATLAS <Teilchendetektor> (1)
- Exotics (1)
- Gamma-Burst (1)
- Leptoquark (1)
- Neutrino (1)
- Particle Physics (1)
- astroparticle (1)
- cosmic ray (1)
- gamma-ray burst (1)
- grb (1)
It is natural to consider the possibility that the most energetic particles detected (> 10^18 eV), ultra-high-energy cosmic rays (UHECRs), are originated at the most luminous transient events observed (> 10^52 erg s^-1), gamma-ray bursts (GRBs). As a result of the interaction of highly-accelerated, magnetically-confined protons and ions with the photon field inside the burst, both neutrons and UHE neutrinos are expected to be created: the former escape the source and beta-decay into protons which propagate to Earth, where they are detected as UHECRs, while the latter, if detected, would constitute the smoking gun of hadronic acceleration in the sources.
Recently, km-scale neutrino telescopes such as IceCube have finally reached the sensitivities required to probe the neutrino predictions of some of the existing GRB models. On that account, we present here a revised, self-consistent model of joint UHE proton and neutrino production at GRBs that includes a state-of-the-art, improved numerical calculation of the neutrino flux (NeuCosmA); that uses a generalised UHECR emission model where some of the protons in the sources are able to "leak out" of their magnetic confinement before having interacted; and that takes into account the energy losses of the protons during their propagation to Earth. We use our predictions to take a close look at the cosmic ray-neutrino connection and find that the current UHECR observations by giant air shower detectors, together with the upper bounds on the flux of neutrinos from GRBs, are already sufficient to put tension on several possibilities of particle emission and propagation, and to point us towards some requirements that should be fulfilled by GRBs if they are to be the sources of the UHECRs. We further refine our analysis by studying a dynamical burst model, where we find that the different particle species originate at distinct stages of the expanding GRB, each under particular conditions. Finally, we consider a possibility of new physics: the effect of neutrino decay in the flux of UHE neutrinos from GRBs. On the whole, our results demonstrate that self-consistent models of particle production are now integral to the advancement of the field, given that the full picture of the UHE Universe will only emerge as a result of looking at the multi-messenger sky, i.e., at gamma-rays, cosmic rays, and neutrinos simultaneously.
Leptoquarks are hypothetical particles that attempt to explain the coincidental similarities between leptons and quarks included in SM. Their exact properties vary between different theoretical models, and there are no strong theoretical constraints on their possible mass values. They can possibly be produced from particle
collisions, and there have already been searching efforts at previous collider experiments. Their presence have yet been observed, and this fact has been translated into lower bound exclusions on their possible mass values. The Large Hadron Collider (LHC) being the most recently constructed particle collider with the highest collision energies ever achieved experimentally, provides a new platform to continue the search for Leptoquarks at even higher mass ranges.
This thesis describes a search for pair-produced second-generation Leptoquarks using 20.3 fb−1 of data recorded by the ATLAS detector of LHC at √s = 8 TeV. Events with two oppositely charged muons and two or more jets in the final state were used. Candidate leptoquark events were selected with the help of four observables: the di-muon invariant mass (Mμμ ), the sum of the pT of the two muons
(LT ), the sum of the pT of the two leading jets (HT ) and the average Leptoquark mass (MLQ ). Monte Carlo simulations of SM background processes have shown
to be in good agreement with data, both in the region constructed using selection requirements for candiate leptoquark events and in the designated control regions.
Since no significant excess of events was observed in data, a exclusion limit was set as a function of the Leptoquark mass.