25 research outputs found

    Causation does not explain contextuality

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    Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-go theorems that show quantum correlations cannot be explained by non-contextual ontological models, where physical properties are assumed to exist prior to and independently of the act of measurement. However, all such contextuality proofs assume a traditional notion of causal structure, where causal influence flows from past to future according to ordinary dynamical laws. This leaves open the question of whether the apparent contextuality of quantum mechanics is simply the signature of some exotic causal structure, where the future might affect the past or distant systems might get correlated due to non-local constraints. Here we show that quantum predictions require a deeper form of contextuality: even allowing for arbitrary causal structure, no model can explain quantum correlations from non-contextual ontological properties of the world, be they initial states, dynamical laws, or global constraints.Comment: 18+8 pages, 3 figure

    From the sublime to the ridiculous: top physics and minimum bias events in the ATLAS detector at the LHC

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    This thesis is comprised of two separate physics themes, both of which involve the ATLAS detector situated at the LHC at CERN. The first constituent is a study of the top quark signal in the fully-leptonic channel for proton-proton collisions at a centre-of-mass energy of 10 TeV. Here an event counting analysis is performed based on Monte Carlo simulation. This is supplemented by a study into one of the sources of systematic error. The second component is forward-backward correlations in minimum bias events. For this, there is a Monte Carlo hadron-level comparison of the correlation for 900 GeV centre-of-mass collisions, followed by a comparison of Monte Carlo predictions to data for 900 GeV and 7 TeV collisions. Top Physics A measurement of the fully-leptonic ttbar cross-section in the three decay channels ee, mumu, and emu is performed on ATLAS produced fully simulated pseudo-event data-samples. Selection rates for signal and background events consistent with ATLAS results are found along with the kinematic distributions of selected events. A calculation of the non-hadronic ttbar cross-section, based on the measured cross-sections, will then return the theoretical value of 217:06pb used to generate the original samples, showing the closure of the pseudo-analysis process. A more detailed study is made of the systematic uncertainty arising from variations in the initial (ISR) and final (FSR) state showering models, based on the Pythia event generator. A fast simulation of the ATLAS detector is used with similar object and event selection to the fully simulated case. The effect of ISR variations on the signal is found to be negligible as it is washed out in the subsequent decays of the ttbar system. However, the effect of FSR is found to cause 5% uncertainty in the selected signal events. In addition, in the main background of each of the selection channels the effect of FSR is found to produce variations of up to 30% in well populated channels. The variations in signal and background measurements will then be used to calculate a new estimate of the systematics on the measured ttbar cross-section for each channel. Minimum Bias A detailed study of the forward-backward (FB) correlation and event shapes of a selection of Pythia tunes for pp collisions with CoM = 900 GeV is performed. This includes an investigation into the sources of particle production in generated minimum bias events as well as the component sub-processes in generated minimum bias events. The tunes are found to be practically degenerate (within 10 - 20% variation) for the 'standard' distributions. The inclusion of a new observable, namely the forward-backward correlation, to the standard set is recommended. The study finds that the FB-correlation and its pT and dependent variations are able to discern differences between the selected tunes to a greater degree than the usual inclusive distributions. Further, the FB-correlation is found to be sensitive to the particle production processes within the tunes, an invaluable property for the purposes of generator tuning. A measurement of the forward-backward correlation for pp collision of CoM = 900 GeV and 7 TeV at the LHC using the ATLAS detector is made. The measured correlation is compared to the predicted correlation of several ATLAS centrally produced generator tunes. A correction procedure is developed and validated on the generator samples to correct the generated correlation to the hadron-level correlation. This is then applied to the measured correlation and a comparison of corrected data to the hadron-level predictions of the generated tunes made. The corrected correlations at the two collision energies are compared as well as the calculation of a global correlation at both energies. The measured and corrected correlations are found to lie above the predicted distributions at both energies and across the eta-range. Further investigation of measured correlation using augmented FB-correlations is recommended

    Quantum Mechanics: Statistical Balance Prompts Caution in Assessing Conceptual Implications

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    Throughout quantum mechanics there is statistical balance, in the collective response of an ensemble of systems to differing measurement types. Statistical balance is a core feature of quantum mechanics, underlying quantum mechanical states, and not yet explained. The concept of “statistical balance” is here explored, comparing its meaning since 2019 with its original meaning in 2001. Statistical balance now refers to a feature of contexts in which: (a) there is a prescribed probability other than 0 or 1 for the collective response of an ensemble to one measurement type; and (b) the collective response of the same ensemble to another measurement type demonstrates that no well-defined value can be attributed, for the property relevant to the original measurement type, to individual members of the ensemble. In some unexplained way, the outcomes of single runs of a measurement of the original type “balance” each other to give an overall result in line with the prescribed probability. Unexplained statistical balance prompts caution in assessing the conceptual implications of entanglement, measurement, uncertainty, and two-slit and Bell-type analyses. Physicists have a responsibility to the wider population to be conceptually precise about quantum mechanics, and to make clear that many possible conceptual implications are uncertain

    From the sublime to the ridiculous : top physics and minimum bias events in the ATLAS detector at the LHC

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    This thesis is comprised of two separate physics themes, both of which involve the ATLAS detector situated at the LHC at CERN. The first constituent is a study of the top quark signal in the fully-leptonic channel for proton-proton collisions at a centre-of-mass energy of 10 TeV. Here an event counting analysis is performed based on Monte Carlo simulation. This is supplemented by a study into one of the sources of systematic error. The second component is forward-backward correlations in minimum bias events. For this, there is a Monte Carlo hadron-level comparison of the correlation for 900 GeV centre-of-mass collisions, followed by a comparison of Monte Carlo predictions to data for 900 GeV and 7 TeV collisions. Top Physics A measurement of the fully-leptonic ttbar cross-section in the three decay channels ee, mumu, and emu is performed on ATLAS produced fully simulated pseudo-event data-samples. Selection rates for signal and background events consistent with ATLAS results are found along with the kinematic distributions of selected events. A calculation of the non-hadronic ttbar cross-section, based on the measured cross-sections, will then return the theoretical value of 217:06pb used to generate the original samples, showing the closure of the pseudo-analysis process. A more detailed study is made of the systematic uncertainty arising from variations in the initial (ISR) and final (FSR) state showering models, based on the Pythia event generator. A fast simulation of the ATLAS detector is used with similar object and event selection to the fully simulated case. The effect of ISR variations on the signal is found to be negligible as it is washed out in the subsequent decays of the ttbar system. However, the effect of FSR is found to cause 5% uncertainty in the selected signal events. In addition, in the main background of each of the selection channels the effect of FSR is found to produce variations of up to 30% in well populated channels. The variations in signal and background measurements will then be used to calculate a new estimate of the systematics on the measured ttbar cross-section for each channel. Minimum Bias A detailed study of the forward-backward (FB) correlation and event shapes of a selection of Pythia tunes for pp collisions with CoM = 900 GeV is performed. This includes an investigation into the sources of particle production in generated minimum bias events as well as the component sub-processes in generated minimum bias events. The tunes are found to be practically degenerate (within 10 - 20% variation) for the 'standard' distributions. The inclusion of a new observable, namely the forward-backward correlation, to the standard set is recommended. The study finds that the FB-correlation and its pT and dependent variations are able to discern differences between the selected tunes to a greater degree than the usual inclusive distributions. Further, the FB-correlation is found to be sensitive to the particle production processes within the tunes, an invaluable property for the purposes of generator tuning. A measurement of the forward-backward correlation for pp collision of CoM = 900 GeV and 7 TeV at the LHC using the ATLAS detector is made. The measured correlation is compared to the predicted correlation of several ATLAS centrally produced generator tunes. A correction procedure is developed and validated on the generator samples to correct the generated correlation to the hadron-level correlation. This is then applied to the measured correlation and a comparison of corrected data to the hadron-level predictions of the generated tunes made. The corrected correlations at the two collision energies are compared as well as the calculation of a global correlation at both energies. The measured and corrected correlations are found to lie above the predicted distributions at both energies and across the eta-range. Further investigation of measured correlation using augmented FB-correlations is recommended.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

    Quantum correlations: a window into fundamental physics

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    The past century has seen many of nature's secrets unravelled by the immensely successful theories of particle physics and general relativity, frameworks in which the world is described as a collection of many quantum fields, lying on a background classical spacetime. High-energy signals, originating naturally from the cosmos, or artificially from particle accelerators, held many empirical clues in support of these descriptions. In recent years, the formidable advances in quantum control have brought to light a model-agnostic conception of physics, once thought to be merely philosophical, as an alternative path of fundamental investigations. This modern information theoretic framework, eschews any description of nature beyond the correlations between measurements predicted by quantum theory. In this thesis, three questions of fundamental physics are studied from the perspective of quantum information and quantum control.Open Acces

    The Hidden Geometry of Particle Collisions

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    We establish that many fundamental concepts and techniques in quantum field theory and collider physics can be naturally understood and unified through a simple new geometric language. The idea is to equip the space of collider events with a metric, from which other geometric objects can be rigorously defined. Our analysis is based on the energy mover's distance, which quantifies the "work" required to rearrange one event into another. This metric, which operates purely at the level of observable energy flow information, allows for a clarified definition of infrared and collinear safety and related concepts. A number of well-known collider observables can be exactly cast as the minimum distance between an event and various manifolds in this space. Jet definitions, such as exclusive cone and sequential recombination algorithms, can be directly derived by finding the closest few-particle approximation to the event. Several area- and constituent-based pileup mitigation strategies are naturally expressed in this formalism as well. Finally, we lift our reasoning to develop a precise distance between theories, which are treated as collections of events weighted by cross sections. In all of these various cases, a better understanding of existing methods in our geometric language suggests interesting new ideas and generalizations.Comment: 56 pages, 11 figures, 5 tables; v2: minor changes and updated references; v3: updated to match JHEP versio
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