Theses oportunities 

DOMAINS:

• Technologies associated to the Portuguese participation at CERN and their transfer to society
• Particle and Astroparticle Physics and associated scientific domains

Technologies associated to the Portuguese participation at CERN and their transfer to society

• Development of a high voltage system for the ATLAS Tilecal calorimeter and performance tests with high energy particles

  DOMAIN: Technologies associated to the Portuguese participation at CERN and their transfer to society

  
  

  SUPERVISOR: Guiomar Evans

  CO-SUPERVISOR: Agostinho Gomes
  

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade de Lisboa
  

  
  

  ABSTRACT

  This thesis proposal focus on the development, implementation and integration of a high voltage (HV) system to be used in the Tilecal calorimeter for the operation in the future High Luminosity LHC (HL-LHC) environment (upgrade Phase II). Tilecal, the ATLAS hadron calorimeter in the barrel region is a key sub-detector used for the measurement of jets energy, missing transverse energy, identification of muons with low transverse momentum and for other physics' tasks. All the Tilecal electronics is being upgraded for the HL-LHC operation. The current HV system is based on a HV distributor system located in the detector that receives a single HV per module as input and regulates the individual voltages to be applied locally to each photomultiplier tube (PMT). This concept has been in use in the Tilecal, and it has the important advantage of not requiring (a large number of) 100-150 m long cables from the HV regulator to the PMTs. In the upgrade, the HV system will be replaced since it has two drawbacks: the radiation damage and the impossibility of replacement of boards if a problem occurs since access is difficult and is possible only at the LHC shutdowns. The new HV system for the upgrade Phase II is a remote one. The HV boards will fit in crates that provide low voltage and that are located outside the ATLAS main cavern. They use standard electronics components since they are not located in the areas exposed to radiation inside the detector but this solution has the drawback of requiring a large number of long cables. A new control and monitoring system is being developed. The HV regulation and the respective control system designs are being finalized and the prototypes will be tested in the calorimeter environment in setups similar to the one of the ATLAS detector, using beams of high energy pions, electrons and muons at CERN and likely also in a special module that will operate in the ATLAS detector. These tests will allow to access the performance of the new Tilecal electronics that is being developed for the HL-LHC. Linearity, stability and noise of the developed system will be measured in the tests with beams of high energy particles and whenever possible in the ATLAS detector during the LHC Run 3 that will start in 2021. A special prototype called demonstrator featuring the new electronics for Phase II will be produced and it is expected to be inserted in the ATLAS detector for regular operation during LHC operation in Run3. This full integration in ATLAS will allow to test the system in the normal conditions of operation before the Phase II upgrade takes place and will give useful information about the performance for the future operation in Phase II.

• Development of fast parallel trigger algorithms for the ATLAS experiment at CERN

  DOMAIN: Technologies associated to the Portuguese participation at CERN and their transfer to society

  SUPERVISOR: Patricia Conde Muino

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade de Lisboa
  

  
  

  ABSTRACT

  The LHC is the highest energy particle accelerator ever built. The gigantic ATLAS experiment records proton and ion collisions produced by the LHC to study the most fundamental matter particles and the forces between them. At the nominal rate of the LHC, the proton bunches cross 40 million times per second, producing up to 40 collisions per bunch crossing. This event rate is processed in real time by the ATLAS Trigger and data acquisition system, that analyse the results of the collisions, as registered by the 10^8 electronic channels of the detector to select a maximum rate of about 1000 events/second for further offline storage and analysis. In 2025-26, the LHC will be upgraded to increase the LHC collision rate up to a factor 7, to allow acquiring a huge amount of data and pushing the limits of our understanding of Nature. The collision rate and data volume after the LHC upgrade will impose extreme demands on the ATLAS trigger system. The estimated increase in trigger rates and event size lead to larger data volume and much longer event reconstruction times, that are not matched by the slower expected growth in computing power at fixed cost. This requires a change in paradigm, increasing parallelism in computer architecture, using concurrency and multithreading and/or hardware accelerators, such as GPUs or FPGAs for handling suitable algorithmic code. The objective of this thesis program is develop novel calorimeter clustering and jet reconstruction algorithms using accelerators such as FPGAs or GPUs, for the Phase II Upgrade of the ATLAS Trigger system. The student will work in close collaboration with researchers from LIP computing center and particle physics groups, as well as with colleagues from CERN and other institutions involved in the ATLAS experiment. This work will be developed in an international environment. The student will contribute to the improvement of the jet trigger system of the ATLAS experiment at CERN. Presentations at ATLAS Collaboration meetings are expected, either by video-conferencing or at CERN.

• Seeds for the Next Frontier Detectors: Lessons from the TileCal/ATLAS Operation and R&D on Emergent Scintillating Materials
  

  DOMAIN: Technologies associated to the Portuguese participation at CERN and their transfer to society

  
  

  SUPERVISOR: Rute Pedro

  CO-SUPERVISOR: Amelia Maio

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas

  DEGREE INSTITUTION: Universidade de Lisboa

  
  

  ABSTRACT

  Currently, the field of Particle Physics is planning the next generation experiments with options for CERN-based accelerators, namely the FCC cicular collider, under consideration by the update of the European Strategy for collider HEP. *On the other hand*, the main technological challenges in the R&D for the future detectors are already identified and are input for the decision. Calorimeters are indispensable instruments to measure the energy of the collision products. For sampling hadronic calorimeters, choices relying on organic scintillators and wavelength-shifting (WLS) fibres read by photodetectors are successfull due to the low cost and are strong options for the future. Their operation under the expected harsher radiation conditions must meet crucial requirements of high light yield, fast response and radiation hardness. Although recent developments in organic scintillators/WLS indicate a breakthrough on light emission and time response, these emergent materials are lacking in R&D to scrutinise their radiation tolerance. This proposal includes R&D on the new organic scintillators/WLS, with the characterization of the light yield, attenuation length and resistance to ionising radiation. The work will be carried on at the LIP Laboratory of Optics and Scintillating Materials (LoMAC) and collaboration with national and CERN partners is expected. This research exploits also the current operation of the ATLAS Tile hadronic calorimeter to model the radiation damage of scintillators and WLS fibres using calibration data acquired in the real experimental environment. Several factors contribute to the total light output of scintillator+WLS fibre calorimeters, such as fibre length, scintillator plate/tile sizes, dose, dose rate and others. The plan will explore how these factors correlate with the light yield degradation using regression techniques based on modern machine learning and build tools to optimise the design of future detectors. 
  

  
  

Particle and Astroparticle Physics and associated scientific domains

• Expecting the unexpected: going beyond the standard searches for vector-like quarks at the ATLAS experiment at CERN
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Nuno Castro

  CO-SUPERVISOR: Miguel Crispim Romão
  

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade do Minho
  

  
  

  ABSTRACT
  

  A cornerstone of the Standard Model (SM) of Particle Physics is the formulation of the electroweak interactions as arising from a spontaneously broken gauge symmetry. Experiments over the past four decades have confirmed this hypothesis with precision, most notably the LEP and SLC collider programs. The ATLAS and CMS collaborations reported in 2012 observations of a new particle produced at the CERN Large Hadron Collider (LHC) possessing properties so far consistent with those predicted for the SM Higgs boson. It should be noted, nonetheless, that the exact nature of the symmetry-breaking mechanism is not yet determined. Furthermore, regardless of the many experimental validations of the SM, it is known that it cannot be regarded as a final theory, given the many problems it fails to solve, namely the hierarchy problem, the lack of a dark matter candidate, matter-antimatter asymmetry, and others. Attempting to solve these problems, many beyond the SM theories were built. Vector-like quarks (VLQ) are featured in some of these models, as spin 1/2 fermions, color triplets with the same left and right quantum numbers, mixing with SM quarks. Both the ATLAS and CMS experiments have developed a comprehensive search program for vector-like quarks. Nonetheless, and despite a significant effort to present general results, most of these analysis made important assumptions on the production and decay modes of the vector-like quarks and thus missing possible alternative signatures, which can have strong phenomenological motivations. The current proposal foresees the development and implementation of a search for vector-like quarks which can be produced in pairs via a heavy gluon or decay into new scalars. Given the multitude of final states that vector-like quark production can have, the search strategy will rely on the use of deep learning. A complete experimental analysis, considering a detailed study of the modelling of backgrounds and sources of uncertainties will be developed. The phenomenological consequences of the experimental results will be also be studied, in close collaboration with the Phenomenology group at LIP. The current proposal will be integrated in the Portuguese ATLAS team and collaboration with several international groups is foreseen.

  
  

• Heavy Flavour Jets Production in Heavy Ion Collisions at the High Luminosity LHC with the ATLAS Detector
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Helena Santos

  CO-SUPERVISOR: Patricia Conde Muino
  

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade de Lisboa
  

  
  

  ABSTRACT

  Context: Ultrarelativistic nucleus-nucleus collisions at the Large Hadron Collider (LHC) provide an unique opportunity to recreate the Quark Gluon Plasma (QGP) in the laboratory energy frontier. This plasma of quarks and gluons, which is known to behave as a nearly perfect liquid, was the prevailing state of the Universe shortly after the Big Bang. The capabilities of ATLAS, namely large acceptance and high granularity calorimeters, afford excellent handles for QGP studies. The ATLAS experiment is strongly committed with the HI program of LHC and great expectations on the capabilities of the Upgrade to bring deeply understanding on the nature of the QGP are raised. A major goal of the Heavy Ion Program of the LHC is the understanding of the effects of the QGP on jets, namely the study of the nature of the energy loss suffered by the quarks and gluons while crossing the QGP. The bottom quark, in particular, constitutes an excellent probe. Due to its large virtuality, Q, it has a formation time,∆t ≈1/Q ≈ 0.1 fm/c, much smaller than the formation time of the QGP at the LHC (≈10 fm/c). The understanding of the nature of the energy loss (either collisional or gluon radiative), by its turn, is crucial to infer the properties of the QGP. The HI ATLAS/LIP group is contributing with important developments preceding the b-jet physics analysis, namely on b-jet reconstruction, b- tagging and b-jet triggers in HI collisions. 

  
  

  Objectives: The goal of the proposed thesis is the prospective study of the Heavy Flavour jets production in the HL-LHC phase (expected to start in 2027) benefiting from the 1 order of magnitude increased luminosity foreseen for the Pb+Pb runs. The most important ATLAS upgraded components for the proposed project are the calorimeters front-end electronics and the new tracker detector. Currently jets are reconstructed using the transverse energy of calorimeter towers (piled cells) as input signals, after subtracting the QCD underlying event. The new readout electronics of the calorimeters will provide support for a more sophisticated detector signal processing. The remaining part of jet reconstruction regards the identification of the b-jets, i.e. b-tagging. This technique aims the highest possible efficiency for tagging b-jets, with the largest possible rejection of light jets. In ATLAS the most used techniques take advantage of the relatively long lifetime of hadrons containing bottom quarks (ctau 450 mm), as well as of the hard fragmentation and the high mass of these hadrons. These properties lead to tracks in the ITk with large impact parameters (i.e., transverse and longitudinal distances of closest approach of the track to the primary and secondary vertices), on contrary to the tracks from light jets. Such a feature allows to disentangle heavy flavour jets from light jets, but it requires excellent impact parameter resolution. This is ensured by the ITk. Machine learning techniques using the properties of both the impact parameters and the secondary vertices have proven to increase significantly the b-tagging performance in pp collisions and the development in Pb+Pb is ongoing. Analysis of data taken in Run 2 and Run 3 of LHC will provide not only results on Heavy Flavour jets in HI collisions per se, but will also contribute preciously to the validation of the prospective study in the HL-LHC. 

  
  

  Requirements: This is an experimental PhD program. The work will be developed at LIP - Laboratorio de Instrumentacao e Fisica Experimental de Particulas. The student should have solid computing skills, namely in C++ programming. Furthermore, she/he will concurrently participate in the technical activities in which the ATLAS/LIP group is involved, namely in the Tile calorimeter and/or in Trigger systems.

  
  

• Heavy Flavour Jets Production in Heavy Ion Collisions in Run 3 of the LHC with the ATLAS Detector
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Helena Santos

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade de Lisboa
  

  
  

  ABSTRACT

  Context: Ultrarelativistic nucleus-nucleus collisions at the Large Hadron Collider (LHC) provide an unique opportunity to recreate the Quark Gluon Plasma (QGP) in the laboratory energy frontier. This plasma of quarks and gluons, which is known to behave as a nearly perfect liquid, was the prevailing state of the Universe shortly after the Big Bang. The capabilities of ATLAS, namely large acceptance and high granularity calorimeters, afford excellent handles for QGP studies. A major goal of the Heavy Ion Program of the LHC is the understanding of the effects of the QGP on jets, namely the study of the nature of the energy loss suffered by the quarks and gluons while crossing the QGP. The bottom quark, in particular, constitutes an excellent probe. Due to its large virtuality, Q, it has a formation time,∆t ≈1/Q ≈ 0.1 fm/c, much smaller than the formation time of the QGP at the LHC (≈10 fm/c). The understanding of the nature of the energy loss (either collisional or gluon radiative), by its turn, is crucial to infer the properties of the QGP. The HI ATLAS/LIP group is contributing with important developments preceding the b-jet physics analysis, namely on b-jet reconstruction, b-tagging and b-jet triggers in HI collisions. 

  
  

  Objectives: The student will participate in Pb+Pb data acquisition at CERN already during Run 3 (expected for the Falls of 2021-22-23-24) and will analyse the data. The analysis will explore strategies, namely machine learning techniques, to separate the b-quarks jets from light jets (mostly u- and d-quarks) and further separation of b-quarks jets originating directly from the hard process from those arising from gluon splitting with the aim of devising novel experimental observables sensitive to the different energy loss of quarks and gluons. 

  
  

  Requirements: This is an experimental PhD program. The work will be developed at LIP - Laboratorio de Instrumentacao e Fisica Experimental de Particulas. The student should have solid computing skills, namely in C++ programming. Furthermore, she/he will concurrently participate in the technical activities in which the ATLAS/LIP group is involved, namely in the Tile calorimeter and/or in Trigger systems.

• Measurement of top quark rare decay t->sW at ATLAS

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Filipe Veloso

  CO-SUPERVISOR: Ricardo Gonçalo
  

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas
  

  DEGREE INSTITUTION: Universidade de Coimbra
  

  
  

  ABSTRACT

  The top quark is the heaviest elementary particle known, with a mass close to the electroweak symmetry breaking, and it can provide clues about the symmetry breaking and the Higgs mechanisms. It is thus an excellent object to test the Standard Model of Particle Physics (SM). There is an important effort to study the top quark properties, like its mass, production cross-sections, electric charge, spin, decay asymmetries, rare decays, etc... Deviations from SM predictions of the production and decay properties of the top quark provide model-independent tests for physics beyond the SM. According to the SM, the top quark decays nearly 100% of the time to a W boson and a b quark. The Cabbibo-Kobayashi-Maskawa (CKM) quark mixing matrix is related to the rates of the Flavour Changing Charged Current (FCCC) decay modes. Some of the elements, e.g. Vts, were not yet directly measured but are determined from the unitarity conditions of the matrix. A direct measurement of these elements put strict conditions on the assumptions behind the matrix properties, as the existence of only three families on the SM. This research program will be developed within the Portuguese ATLAS group. It aims to measure the decay rate of the top quark into a W boson plus a s-quark with LHC data collected by the ATLAS detector using computational tools such as machine learning techniques. This result will then be used to measure the amplitude of the CKM element Vts. In addition the student will participate in the maintenance and operation of the ATLAS detector, namely in the calibration of the TileCal hadronic calorimeter. Short periods at CERN may also be required in order to collaborate in working meetings and/or shifts.

  
  

• Probing the Electroweak Vacum with di-Higgs production at the ATLAS experimente at CERN
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Ricardo Gonçalo

  CO-SUPERVISOR: Konstantinos Nikolopoulos
  

  CO-SUPERVISOR: Filipe Veloso

  HOST INSTITUTION: LIP
  

  DEGREE INSTITUTION: Universidade de Coimbra

  ABROAD-INSTITUTION: University of Birmingham

  
  

  ABSTRACT

  Since its discovery, the Higgs boson became a prime tool to search for physics beyond the Standard Model (SM). At the current level of precision, the Higgs boson is compatible with SM expectations. A number of open questions suggest the existence of new physics, that could be unveiled as we explore the LHC data. A wealth of experimental results from the ATLAS and CMS experiments, probe the region around the minimum of the Higgs potential, or vacuum. But the shape of this potential is not constrained experimentally. This shape is intimately connected to the breaking of the electroweak gauge symmetry, which resulted in the fundamental forces we experience today. To experimentally constrain this shape we must measure the Higgs boson self-coupling, which is accessible at the LHC through the simultaneous production of two Higgs bosons. The selected student will join the Portuguese ATLAS team, working in close collaboration with theorists and integrated into our international collaboration. He or she will be able to contribute to enhancing our current knowledge in this important area, which will become one of the most important measurements of LHC experiments. The student will also employ the latest theory developments and the most recent advances in reconstruction techniques: from boosted object identification to machine learning. Part of this research will be done at the University of Birmingham, in the United Kingdom, in co-supervision with a colleague from the ATLAS collaboration. The successful student will be able to participate in the operation of the ATLAS experiment during the LHC Run 3 to start in 2021, and travel to CERN will be required. 

  
  

• Search for New Physics in the associated production channel of a Higgs and a W boson at ATLAS
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Patricia Conde Muino

  CO-SUPERVISOR: Rui Santos

  CO-SUPERVISOR: Valerio Dao

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas

  DEGREE INSTITUTION: Universidade de Lisboa

  ABROAD-INSTITUTION: CERN

  
  

  ABSTRACT

  Since the discovery of the Higgs boson, the precise measurement of its properties has become a fundamental part of the ATLAS Physics programme. The recent announcement of the observation of the Higgs decay to b-quarks and the associated production of the Higgs with top quarks, done by the ATLAS and CMS collaborations at CERN, probe directly the coupling of the Higgs to quarks and constituted an important step forward in the understanding of the Higgs mechanism. As the LHC continues to take data and more luminosity is accumulated, more precise measurements of the Higgs boson properties are possible, opening the door to search for new physics in the Higgs sector. Along this line of research, the study of the high transverse momentum (high-pT) Higgs production, in the associated production channel with a W boson, is sensitive to new physics in the hWW vertex and constitutes one of the measurements to be done in the near future by the ATLAS collaboration. The main objective of this research project is to search for anomalous Spin and CP components of the interaction vertex between the Higgs and the W bosons. The measurement will be done in the associated production channel of the Higgs with a W, when the W decays to leptons (𝓵𝜈) and the Higgs decays to b-quark pairs. Being affected by different systematics and kinematic constraints with respect to the h→WW decay, this channel allows probing the spin and CP properties of the hWW vertex in a complementary way to the studies done so far. The work plan foresees the identification of the most sensitive observables for anomalous couplings, followed by the analysis of the full Run-2 ATLAS dataset. The results will be interpreted in the framework of the Effective Field Theory (EFT) approach. At the same time the results will be interpreted in terms of extensions of the Standard Model with extra sources of CP-violation. The student will be part of the ATLAS team participating in this analysis. The work will be developed in an international collaboration and the results obtained will be presented at CERN. The student is expected to contribute in addition to the data taking and detector operation activities, both at CERN and at LIP. This PhD grant foresees a two-year stay at CERN to develop the proposed research project. 

  
  

• Search for new physics with forward proton detectors at ATLAS

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Patricia Conde Muino

  CO-SUPERVISOR: Nuno Castro

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas

  DEGREE INSTITUTION: Universidade de Lisboa

  
  

  ABSTRACT

  The non-abelian structure of the gauge theory in the SM implies the existence of triple and quartic gauge boson couplings (TGC and QGC, respectively) fully constrained by the gauge symmetry. The measurement QGC provide a window into the Electroweak symmetry breaking mechanism, given the fact that the longitudinal modes of the W and Z bosons are Goldstone bosons. Deviations from the SM predictions can appear due to interchange of new particles, integrated out in the effective interaction, in new physics theories. Models with a new heavy scalar singlet interacting with the Higgs sector can modify the quartic gauge boson couplings but not the triple ones. It is, therefore, essential to probe this missing part of the SM, measuring both the TGC and QGC.

    The ATLAS sensitivity to anomalous couplings in the γγWW, γγγγ and γγZZ vertices can be improved two orders of magnitude by using the ATLAS Forward Proton tagging detectors (AFP) [1]. AFP effectively converts the LHC into a photon-photon collider: the two scattered protons emit two photons that annihilate to produce a pair of vector bosons (two W’s, for instance). The protons, that stay intact after the interaction, are scattered through very small angles and they are detected at the AFP stations. Since there is no underlying event, the two vector bosons are the only particles produced centrally. If they decay to leptons they can be easily triggered and identified. The invariant mass of the vector boson pair can be measured precisely by determining the proton energy loss with the AFP detectors, even in the case of neutrinos in the final state. The presence of anomalous quartic gauge boson couplings could be observed as an increase in the number of detected vector boson pairs with large invariant masses. This project proposes the search for anomalous couplings of the type γγWW using the AFP detectors. The same final state can be used to search for dark matter in photon-induced processes, using also the capability of the forward proton tagging detectors [2]. The search for dark matter is challenged due to the low transverse momentum of the leptons produced. An adequate strategy for triggering this kind of processes is therefore needed. It implies the combination of proton tagging information with muon/electron triggers reconstructed with the ATLAS central detectors, already at the first level trigger and probably making use of the topological trigger processors. The development and optimisation of such a trigger strategy is also an objective of this project. The student is will develop the work in the framework of the ATLAS international collaboration. S/he is expected to contribute to the ATLAS data taking activities and also the commissioning and performance studies of the AFP detector, fundamental for the success of this project. Frequent presentations of the results achieved are expected, either in collaboration meetings at CERN or by videoconference. 7.- References [1] E. Chapon, C. Royon, and O. Kepka, Anomalous quartic WWγγ, ZZγγ, and trilinear WWγ couplings in two-photon processes at high luminosity at the LHC, Phys.Rev. D81 (2010) 074003, arXiv:0912.5161 [hep-ph]. [2] L.A. Harland-Lang, V.A. Khoze, M.G. Ryskin and M. Tasevsky, LHC Searches for Dark Matter in Compressed Mass Scenarios: Challenges in the Forward Proton Mode, arXiv:1812.04886 [hep-ph]. 

  
  

• Signals from Beyond: Search for Anomalies in the LHC Data with the ATLAS Experiment at CERN
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Rute Pedro

  CO-SUPERVISOR: Nuno Castro

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas

  DEGREE INSTITUTION: Universidade do Minho

  
  

  ABSTRACT

  The Standard Model (SM) of Particle Physics is notably descriptive and predicted new particles well in advance, from which the Higgs boson discovered at CERN's Large Hadron Collider (LHC) is a remarkable recent case. However, there is paramount evidence for the need of beyond-Standard Model (BSM) physics, namely to provide dark matter candidates, explain the matter/dark-matter asymmetry, address the hierarchy problem and others. The LHC has a rich program on searches for New Physics (NP) but clues from new particles or interactions have not yet been located. Typical searches are guided by specific BSM candidates and would benefit from a complementary model-independent strategy, augmenting the scope of searches to signs of NP not even framed by theory. This proposal is to perform a novel generic search for NP within the ATLAS/LHC experiment using anomaly detection (AD) techniques based on generative Deep Learning (DL). The DL model will learn SM physics from simulated data and then look for anomalous non-SM like events in the real collision data. Detector effect anomalies can mislead the NP detection and a detailed study of this background will be considered to construct a high fidelity AD. Moreover, the impact of sources of theoretical and experimental uncertainties on the AD performance will be assessed. Benchmark NP signals will be used as tests throughout the AD development. The project will be integrated into the ATLAS Portuguese group, and collaboration with several international groups is foreseen. Synergies with the LIP Competence Centre for Simulation and Big Data and with the LIP Phenomenology group will be explored, namely to investigate approaches for experimental result interpretability and recasting into theory exclusion limits.  

  
  

• The Heavy Weights: Measuring Higgs and Top-Quark Associated Production at the ATLAS LHC Experiment to Probe Beyond the Standard Model
  

  DOMAIN: Particle and Astroparticle Physics and associated scientific domains

  
  

  SUPERVISOR: Ricardo Gonçalo

  CO-SUPERVISOR: Yvonne Peters

  HOST INSTITUTION: Laboratório de Instrumentação e Física Experimental de Partículas

  DEGREE INSTITUTION: Universidade de Coimbra

  ABROAD-INSTITUTION: University of Manchester

  
  

  ABSTRACT

  After an intense search, the associated production of the Higgs boson with a top quark pair was finally observed in 2018. This production channel provides the best way to directly measure the coupling between Higgs and top, the heaviest fundamental particles in the Standard Model (SM). But it also provides a way to look beyond the SM, in particular to search for signs of a non-standard Higgs boson, leading to CP-violation in the Higgs sector. Such a component is well justified in scenarios like the two-Higgs doublet model, and finding it would constitute a major discovery. In particular, it could lead to understanding why there is a huge asymmetry between matter and antimatter in the Universe. In this leading edge research, the selected student will analyze data collected by the ATLAS experiment during the LHC Run 3, to start in 2021. He or she will have the opportunity to participate in the operation of the experiment at CERN. The student will integrate the Portuguese ATLAS team and will use recent techniques developed in our group to enhance the experimental sensitivity of the analysis. He or she will be co-supervised by a colleague from the University of Manchester, where the student will spend part of the time of the PhD, as foreseen in the grant. Besides the Manchester group, the student would work in a vibrant international team within the ATLAS collaboration.