Vacancies

Here we list possible job opportunities within my group, as well as available bachelor and master projects. Prospective candidates are encouraged to contact me at j.rojo@vu.nl.


PhD position in hadronic structure and high-energy neutrino interactions

The Theory group of Nikhef, the national institute for subatomic physics in The Netherlands, is looking for a PhD candidate in the topic of hadronic structure and high-energy neutrino interactions.

The position. The Nikhef Theory group has an active research program aiming to scrutinise the quark and gluon structure of protons and nuclei as well as novel phenomena within Quantum Chromodynamics (QCD). This program develops itself at the boundary between theory and experiment and relies on cutting-edge statistical techniques and machine learning tools. The successful candidate will be embedded within the NNPDF Collaboration and develop novel research lines on hadronic structure, perturbative QCD, LHC phenomenology, and high-energy neutrino interactions, including the connection between particle and astroparticle physics.

As part of this PhD project, the successful candidate will carry out feasibility studies of the scientific potential for QCD, hadronic structure, and astroparticle physics at the proposed Forward Physics Facility (FPF). At the FPF, high-energy neutrinos produced in the forward region in proton-proton collisions at the LHC would offer an unprecedented probe of extreme QCD phenomena, the quark and gluon substructure of protons, and of properties of the neutrino sector in regions currently unexplored.

Requirements. Excellent software and programming skills, in particular in C++ and Python, are specially encouraged. Prior expertise in Quantum Chromodynamics, hadron structure, and/or neutrino physics is welcome. Applicants should have a MSc degree in theoretical or experimental particle physics (or a closely related topic) by the time they start their appointment at Nikhef.

Offer. The candidate will be employed by the Vrije Universiteit Amsterdam, one of the partners of the Nikhef consortium. The (astro-)particle physics section of the VU Amsterdam is fully embedded within the Nikhef partnership. He/she will receive a 1 year contract, which upon satisfactory performance will be extended up to a total of four years. The gross monthly starting salary will be EUR2541, increasing to EUR3247 in the fourth year. A favourable tax agreement, the 30% ruling, may apply to non-Dutch applicants. Additionally, the Vrije Universiteit Amsterdam offers excellent fringe benefits and various schemes and regulations to promote a good work/life balance, such as a maximum of 41 days of annual leave based on full-time employment, 8% holiday allowance and 8.3% end-of-year bonus, contribution to commuting expenses, and an optional model for designing a personalized benefits package

Application. Qualified applicants are encouraged to inquire about this position by sending a cover letter, a detailed CV, an updated transcript with their grades, and the names of two possible referees to dr. Juan Rojo. There is no deadline for this position, and review of applications will start immediately and continue until the position has been filled.

Nikhef is the national institute for subatomic physics in The Netherlands. At Nikhef, approximately 175 physicists and 75 technical staff members work together in an open and international scientific environment. Together, they perform theoretical and experimental research in the fields of particle and astroparticle physics. The Nikhef institute is a collaboration between six major Dutch universities, including the Vrije Universiteit Amsterdam, and the Dutch Foundation for Scientific Research (NWO). The Nikhef Theory group is composed by 10 staff members and around 10 postdocs and 15 PhD students. The group has a strong expertise in effective field theories, higher order calculations in quantum chromodynamics, machine learning in particle physics, proton structure determinations, flavor and beyond the standard model physics, and cosmology among others. The group also has strong connections with other national and international groups in theoretical high energy physics, as well as frequent interactions with the experimental groups at Nikhef.


Master projects UvA/VU Physics & Astronomy 2022-2023

More information on available MSc projects in my group here.

Effective Field Theories of Particle Physics from low- to high-energies

Known elementary matter particles exhibit a surprising three-fold structure. The particles belonging to each of these three “generations” seem to display a remarkable pattern of identical properties, yet have vastly different masses. This puzzling pattern is unexplained. Equally unexplained is the bewildering imbalance between matter and anti-matter observed in the universe, despite minimal differences in the properties of particles and anti-particles. These two mystifying phenomena may originate from a deeper, still unknown, fundamental structure characterised by novel types of particles and interactions, whose unveiling would revolutionise our understanding of nature. Until recently, it was widely assumed that matter particles from each of the three generations interact with the same (“universal”) strength. This hypothesis is being challenged by new measurements at the Large Hadron Collider (LHC) at CERN, which hint towards non-universal interactions. If confirmed, these measurements will be the first signs of new particles and interactions in high-energy colliders. These exciting findings indicate the urgent need to explore such phenomena in depth. The ultimate goal of particle physics is uncovering a fundamental theory which allows the coherent interpretation of phenomena taking place at all energy and distance scales. In this project, the students will exploit the Effective Field Theory (EFT) formalism, which allows the theoretical interpretation of particle physics data in terms of new fundamental quantum interactions which relate seemingly disconnected processes. Specifically, the goal is to connect measurements from ATLAS and LHCb among them and to jointly interpret this information with that provided by other experiments, from CMS and Belle-II to very low-energy probes such as the anomalous magnetic moment of the muon or electric dipole moments of the electron and neutron.

This project will be based on theoretical calculations in particle physics, numerical simulations in Python, analysis of existing data from the LHC and other experiments, as well as formal developments in understanding the operator structure of effective field theories. This project accommodates several students, who would work together in developing the main formalism while each of them focuses on a specific sub-project. Depending on the student profile, sub-projects with a strong computational and/or machine learning component are also possible.

Subproject #1: SMEFT & Flavour symmetries. While the power of the Standard Model EFT (named SMEFT) framework is its generality and lack of assumptions, the number of operators is somewhat daunting. A popular way to trim the number of operators is to assume flavour symmetries that relate operators with different quark and lepton flavours. In this project you will investigate the theoretical basis for commonly-used flavour symmetries and what they imply for the connection between high-energy observables involving third-generation particles (top and bottom quarks and tau leptons) and low-energy precision tests involving first- and second-generation particles.

Subproject #2: SMEFT & magnetic moment of the muon. The magnetic moment of the muon appears to differ from the Standard Model expectations by a large amount, well beyond the known experimental and theoretical uncertainties. Recent experiments have only strengthened the significance of this anomaly. In this project, the students will investigate the feasibility of implementing the measurement of the magnetic moment of the muon into a global SMEFT analysis, by exploiting recently provided calculations. Special attention will be devoted to the flavour assumptions required to consistently match this measurement with the LHC data. The SMEFiT analysis framework will be used to connect the g-2 data with high-energy LHC measurements.

References: arXiv:2105.00006https://arxiv.org/abs/1901.05965 , https://arxiv.org/abs/1906.05296 ,  https://arxiv.org/abs/1908.05588,  https://arxiv.org/abs/1905.05215

High-energy neutrino-nucleon interactions at the Forward Physics Facility

High-energy collisions at the High-Luminosity Large Hadron Collider (HL-LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing experiments. The proposed Forward Physics Facility (FPF) to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). High statistics neutrino detection will provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. The FPF has the promising potential to probe our understanding of the strong interactions as well as of proton and nuclear structure, providing access to both the very low-x and the very high-x regions of the colliding protons. The former regime is sensitive to novel QCD production mechanisms, such as BFKL effects and non-linear dynamics, as well as the gluon parton distribution function (PDF) down to x=1e-7, well beyond the coverage of other experiments and providing key inputs for astroparticle physics. In addition, the FPF acts as a neutrino-induced deep-inelastic scattering (DIS) experiment with TeV-scale neutrino beams. The resulting measurements of neutrino DIS structure functions represent a valuable handle on the partonic structure of nucleons and nuclei, particularly their quark flavour separation, that is fully complementary to the charged-lepton DIS measurements expected at the upcoming Electron-Ion Collider (EIC).

In this project, the student(s) will carry out updated predictions for the neutrino fluxes expected at the FPF, assess the precision with which neutrino cross-sections will be measured, and quantify their impact on proton and nuclear structure by means of machine learning tools and state-of-the-art calculations in perturbative Quantum Chromodynamics.

References: arXiv:2109.10905, arXiv:2201.12363 , arXiv:2109.02653

Probing the origin of the proton spin with machine learning

At energy-frontier facilities such as the Large Hadron Collider (LHC), scientists study the laws of Nature in their quest for novel phenomena both within and beyond the Standard Model of particle physics. An in-depth understanding of the quark and gluon substructure of protons and heavy nuclei is crucial to address pressing questions from the nature of the Higgs boson to the origin of cosmic neutrinos. The key to address some of these questions is by carrying out an universal analysis of nucleon structure from the simultaneous determination of the momentum and spin distributions of quarks and gluons and their fragmentation into hadrons. This effort requires combining an extensive experimental dataset and cutting-edge theory calculations within a machine learning framework where neural networks parametrise the underlying physical laws while minimizing ad-hoc model assumptions.

In this project, the student(s) will carry out a new global analysis of the spin structure of the proton by means of machine learning tools and state-of-the-art calculations in perturbative Quantum Chromodynamics, and integrate it within the corresponding global NNPDF analyses of unpolarised proton and nuclear structure in the framework of a combined integrated global analysis of non-perturbative QCD.

References: arXiv:2201.12363 , arXiv:2109.02653

Bachelor projects UvA/VU Physics & Astronomy for spring 2022

Effective Field Theories of Particle Physics from low- to high-energies

Known elementary matter particles exhibit a surprising three-fold structure. The particles belonging to each of these three “generations” seem to display a remarkable pattern of identical properties, yet have vastly different masses. This puzzling pattern is unexplained. Equally unexplained is the bewildering imbalance between matter and anti-matter observed in the universe, despite minimal differences in the properties of particles and anti-particles. These two mystifying phenomena may originate from a deeper, still unknown, fundamental structure characterised by novel types of particles and interactions, whose unveiling would revolutionise our understanding of nature. Until recently, it was widely assumed that matter particles from each of the three generations interact with the same (“universal”) strength. This hypothesis is being challenged by new measurements at the Large Hadron Collider (LHC) at CERN, which hint towards non-universal interactions. If confirmed, these measurements will be the first signs of new particles and interactions in high-energy colliders. These exciting findings indicate the urgent need to explore such phenomena in depth. The ultimate goal of particle physics is uncovering a fundamental theory which allows the coherent interpretation of phenomena taking place at all energy and distance scales. In this project, the students will exploit the Effective Field Theory (EFT) formalism, which allows the theoretical interpretation of particle physics data in terms of new fundamental quantum interactions which relate seemingly disconnected processes. Specifically, the goal is to connect measurements from ATLAS and LHCb among them and to jointly interpret this information with that provided by other experiments, from CMS and Belle-II to very low-energy probes such as the anomalous magnetic moment of the muon or electric dipole moments of the electron and neutron.

Methodology and workplan. This project will be based on theoretical calculations in particle physics, numerical simulations in Python, analysis of existing data from the LHC and other experiments, as well as formal developments in understanding the operator structure of effective field theories.. This project accommodates several students, who would work together in developing the main formalism while each of them focuses on a specific sub-project. The maximum capacity of this project is 5 students.. Depending on the student profile, sub-projects with a strong computational / machine learning component are also possible. During the first four weeks of the project, students will learn the required background material on effective field theories, following the guidelines from the supervisors. Afterwards, they will focus on different sub-projects, each covering a different aspect of the same global EFT program.

Required knowledge: Quantum Mechanics 2, Particle Physics 1 (required), Advanced Quantum Mechanics, Particle Physics 2, Machine Learning (optional)

Subproject #1: SMEFT & Flavour symmetries. While the power of the Standard Model EFT (named SMEFT) framework is its generality and lack of assumptions, the number of operators is somewhat daunting. A popular way to trim the number of operators is to assume flavour symmetries that relate operators with different quark and lepton flavours. In this project you will investigate the theoretical basis for commonly-used flavour symmetries and what they imply for the connection between high-energy observables involving third-generation particles (top and bottom quarks and tau leptons) and low-energy precision tests involving first- and second-generation particles.

Subproject #2: SMEFT & magnetic moment of the muon. The magnetic moment of the muon appears to differ from the Standard Model expectations by a large amount, well beyond the known experimental and theoretical uncertainties. Recent experiments have only strengthened the significance of this anomaly. In this project, the students will investigate the feasibility of implementing the measurement of the magnetic moment of the muon into a global SMEFT analysis, by exploiting recently provided calculations. Special attention will be devoted to the flavour assumptions required to consistently match this measurement with the LHC data, also at the light of the connection with Subproject #1. The SMEFiT analysis framework will be used to connect the g-2 data with high-energy LHC measurements.

Subproject #3: CP Violation and low-energy precision experiments. Most analyses of LHC data are performed under the assumption that CP symmetry (charge conjugation + parity, essentially the symmetry between particles and anti-particles) is conserved. More recent analyses attempt to also measure possible new sources of CP violation in SMEFT operators in the Higgs and top sector.

Subproject #3a: CP Violation and low-energy precision experiments. Low-energy precision experiments can also set stringent constraints on new mechanisms of CP violation. In this project you will try to combine high- and low-energy data to put CP symmetry to the test.

Subproject #3b: CP Violation and flavour physics experiments. Besides low-energy precision experiments, also B-meson decays are excellent probes of CP violation. Unlike most low-energy experiments, this allows us to probe CP violation in the third generation. In this project you will link constraints on CP violation at high-energy to those from B meson decays.

Subproject #4: SMEFT & optimal observables. In full generality, the number of operators in SMEFT spans a very large parameter space. These parameters are constrained by experimental inputs from ATLAS and CMS, depending on the precise parameters these constraints may be more or less stringent. In order to fully exploit the whole parameters space in SMEFT, it is necessary to devise statistically optimal observables that have a large constraining power. In this project, we will define such observables. This project has a strong computational / machine learning component and may involve simulations based on tools such as MadGraph and Pythia8.

Juan Rojo (VU Amsterdam & Nikhef): j.rojo at vu.nl, Keri Vos (UM & Nikhef): k.vos at maastrichtuniversity.nl, Jordy de Vries (UvA & Nikhef): j.devries4 at uva.nl