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Carlos Arg\\\"uelles Delgado
Publication date
2017
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English
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Lorentz symmetry is a fundamental space-time symmetry underlying the Standard Model of particle physics and gravity. However, unified theories, such as string theory, allow for violation of this symmetry. Thus, the discovery of Lorentz symmetry violation could be the first hint of these theories. Here, we use high-energy atmospheric neutrinos observed at the IceCube Neutrino Observatory to search for anomalous neutrino oscillations as signals of Lorentz violation. The large range of neutrino energies and propagation baselines, together with high statistics, let us perform the most precise test of space-time symmetry in the neutrino sector to date. We find no evidence for Lorentz violation. This allows us to constrain the size of the dimension-four operator in the Standard-Model Extension for Lorentz violation to the $10^{-28}$ level and to set limits on higher dimensional operators of that theory. These are among the most stringent limits on Lorentz violation across all fields of physics.
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As atmospheric neutrinos propagate through the Earth, vacuum-like oscillations are modified by Standard-Model neutral- and charged-current interactions with electrons. Theories beyond the Standard Model introduce heavy, TeV-scale bosons that can produce nonstandard neutrino interactions. These additional interactions may modify the Standard Model matter effect producing a measurable deviation from the prediction for atmospheric neutrino oscillations. The result described in this paper constrains nonstandard interaction parameters, building upon a previous analysis of atmospheric muon-neutrino disappearance with three years of IceCube-DeepCore data. The best fit for the muon to tau flavor changing term is $epsilon_{mu tau}=-0.0005$, with a 90% C.L. allowed range of $-0.0067 <epsilon_{mu tau}< 0.0081$. This result is more restrictive than recent limits from other experiments for $epsilon_{mu tau}$. Furthermore, our result is complementary to a recent constraint on $epsilon_{mu tau}$ using another publicly available IceCube high-energy event selection. Together, they constitute the worlds best limits on nonstandard interactions in the $mu-tau$ sector.
The status of Lorentz- and CPT-violation searches using measurements of the anomalous magnetic moment of the muon is reviewed. Results from muon g-2 experiments have set the majority of the most stringent limits on Standard- Model Extension Lorentz and CPT violation in the muon sector. These limits are consistent with calculations of the level of Standard-Model Extension effects required to account for the current 3.7{sigma} experiment-theory discrepancy in the muons g-2. The prospects for the new Muon g-2 Experiment at Fermilab to improve upon these searches is presented.
Although they are best known for studying astrophysical neutrinos, neutrino telescopes like IceCube can study neutrino interactions, at energies far above those that are accessible at accelerators. In this writeup, I present two IceCube analyses of neutrino interactions at energies far above 1 TeV. The first measures neutrino absorption in the Earth, and, from that determines the neutrino-nucleon cross-section at energies between 6.3 and 980 TeV. We find that the cross-sections is 1.30 $^{+0.21}_{-0.19}$ (stat.) $^{+0.39}_{-0.43}$ (syst.) times the Standard Model cross-section. We also present a measurement of neutrino inelasticity, using $ u_mu$ charged-current interactions that occur within IceCube. We have measured the average inelasticity at energies from 1 TeV to above 100 TeV, and found that it is in agreement with the Standard Model expectations. We have also performed a series of fits to this track sample and a matching cascade sample, to probe aspects of the astrophysical neutrino flux, particularly the flavor ratio.
Neutrino oscillation physics has entered a new precision era, which poses major challenges to the level of control and diagnostics of the neutrino beams. In this paper, we review the design of high-precision beams, their current limitations, and the latest techniques envisaged to overcome such limits. We put emphasis on monitored neutrino beams and advanced diagnostics to determine the flux and flavor of the neutrinos produced at the source at the per-cent level. We also discuss ab-initio measurements of the neutrino energy -- i.e. measurements performed without relying on the event reconstruction at the neutrino detector -- to remove any flux-induced bias in the determination of the cross sections.
Experimental tests of Lorentz symmetry in systems of all types are critical for ensuring that the basic assumptions of physics are well-founded. Data from all phases of the Sudbury Neutrino Observatory, a kiloton-scale heavy water Cherenkov detector, are analyzed for possible violations of Lorentz symmetry in the neutrino sector. Such violations would appear as one of eight possible signal types in the detector: six seasonal variations in the solar electron neutrino survival probability differing in energy and time dependence, and two shape changes to the oscillated solar neutrino energy spectrum. No evidence for such signals is observed, and limits on the size of such effects are established in the framework of the Standard Model Extension, including 40 limits on perviously unconstrained operators and improved limits on 15 additional operators. This makes limits on all minimal, Dirac-type Lorentz violating operators in the neutrino sector available for the first time.
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