Research

Protons and neutrons make up the vast majority of all visible matter in the universe. Their structure and interactions are governed by the physics of the strong force and its gauge theory: quantum chromodynamics (QCD). I am fascinated by the complexity QCD, its features and emergent phenomena. The emergence of nucleons, and hadrons in general, from a strongly interacting system of quarks and gluons is one of the fundamental question of modern nuclear physics. My research focuses on the following open questions:

  • What is the gluonic structure of the proton?
  • How does the mass of the proton emerge from its gluonic structure?
  • Does the presence of a nuclear potential modify the proton ground state?
  • Why does a quark, when removed from a proton, dress itself into a jet of new hadrons?

As an experimental physicist, I design, conduct and analyze experiments to come closer to a more full understanding of the strong force, and the nature of complex, strongly interacting systems in general. My expertise lies with exclusive channels through electron-proton scattering, such as deeply-virtual meson production (DVMP) and deeply-virtual Compton scattering (DVCS), as well as semi-inclusive deep inelastic scattering (SIDIS).

Projects

  • The J/ψ-007 experiment: a search for the LHCb charmed pentaquark

    The LHCb experiment found very strong evidence for a charmed pentaquark. With the J/ψ-007 experiment we will use a high-intensity photon beam to investigate if this is really a new five-quark state.

    The LHCb Collaboration at CERN announced the discovery of two J/ψ − p resonances consistent with charmed-pentaquark (Pc) states in 2015. This discovery has spurred a new excitement in the high-energy and nuclear physics communities, generating almost 600 publications in the three years since the original press release.

    The true nature of these Pc states is still unclear. Even the exact spin-parity assignments cannot be fully constrained by the existing data on J/ψ photo-production. Are these J/ψ − p resonances truly new states, in the form of a true five-quark state, or some form of molecular binding between the J/ψ and the nucleon? Or is this observation a remarkable consequence of kinematic enhancement through final-state interactions?

    In 2016, I designed an 11-day experiment that uses the Hall C spectrometers in Jefferson Lab to investigate the true nature of these states in photo-production, by using a copper radiator. I successfully defended this experiment to the Jefferson Lab Program Advisory Committee (PAC), who awarded a “high-impact” label in addition to the highest possible rating.

    In only 11 days, this experiment will provide an answer about the true nature of what was observed by the LHCb collaboration, as well as greatly expand our knowledge of the absolute J/ψ cross section near-threshold.  For more information, I refer to the updated proposal, as well as my presentation to the PAC. The J/ψ-007 experiment is scheduled to run in February 2019.

  • Exclusive J/ψ production near threshold at SoLID

    With the J/ψ experiment at SoLID we will be able to study the threshold region with unprecedented luminosity. This will allow us to address questions regarding the dynamic origin of the proton mass, and provide access to a possible attractive QCD Van der Waals force.

    Protons and neutrons are responsible for 99% of the mass of the visible universe. Modern calculations indicate that the proton mass is dynamical in origin and almost entirely unaffected by the value of the quark mass [Cloet, et al. (2015), Bhagwat et. al (2003)]. In other words: the Higgs mechanism is largely irrelevant for ‘normal’ matter. The origin of the nucleon’s mass is a hot topic in nuclear science, highlighted in the 2015 Long Range Plan for Nuclear Science: “The vast majority […] is due to quantum fluctuations of quark-antiquark pairs, the gluons and the energy associated with quarks moving around close to the speed of light”. The proton mass is intimately related to the trace anomaly of the QCD energy-momentum tensor, accessible through the photo-production cross section for quarkonium, e.g. J/ψ, near threshold [Kharzeev (1995), Ji (1995)].

    The J/ψ-nucleon interaction near threshold is predicted to include an attractive color Van der Waals force, which has never been observed [Gryniuk and Vanderhaeghen (2016)]. Such an attractive force would allow for boundJ/ψ-nucleon states, a potential explanation for the LHCb pentaquark. The future experiment E12-12-006 with the SoLID detector in Hall A at JLab is dedicated to study J/ψ production near threshold. Due to energy reach and unprecedented luminosity, this experiment will provide a unique new probe into the strong interaction and a deeper understanding of the dynamic origin of mass in QCD. I co-authored a comprehensive review on this topic.

    The SoLID detector will be part of the second phase of the 12GeV program at Jefferson Lab. We are currently in early stages of (pre-) R&D, and tentatively expect the experiment to start within the next decade. The luminosity conditions at SoLID will be unprecedented for this type of experiment, bringing new challenges to the detector and trigger design. I have coordinated an effort to build a prototype for the SoLID light-gas Cherenkov detector (LGC), with the first preliminary tests to be conducted parasitically in Hall C at JLab.

  • Exclusive J/ψ and Y production at an EIC

    The electron ion collider will be the ultimate machine to study the gluonic origin of the proton through exclusive J/ψ and Υ production. It will also provide a natural continuation of the threshold quarkonium program at SoLID through near-threshold Υ production.

    What does the matter distribution of the proton really look like? The ‘shape’ of the proton is currently understood in terms of its electromagnetic form factor and related charge radius. We do not yet know how the gluons play into this: do they behave as a set of springs at the center, or do they reach far beyond the traditional proton radius?

    The white-paper for the EIC argues to use elastic J/ψ electro-production at higher center-of- mass energies to constrain the gluon distribution in 3 dimensions. I propose to apply the same procedure with elastic Υ electro-production. Due to the much larger mass of the b-quark, higher order corrections for the Υ will be strongly suppressed compared to the J/ψ, yielding a more precise probe. A comparison of both measurement will provide strong evidence for the validity of the universality of the extracted gluon distribution. More info can be found here.

    Beyond nucleon imaging, quarkonium production at the EIC can also be used to study the gluonic structure of nuclei, as well as nucleons in a nuclear medium. The comprehensive imaging only possible at the EIC will shed light topics such as modifications to the proton ground state in a nuclear medium, or the possible existence of six-quark states inside of a nucleus.

    Furthermore, the EIC has a wide energy reach, including near-threshold Υ production. This will provide for a natural continuation of the near-threshold program at JLab12 through an independent channel, trading statistical precision for lower theoretical uncertainty. Topics include the search for a bottom-pentaquark and a universality test for the SoLID J/ψ program.

  • Hadronization in SIDIS and the applicability of factorization

    What are the features of harmonization and factorization at intermediate energies? How can we improve our understanding of TMDs at these energies? And what can this teach us about confinement in QCD?

    For my thesis research, I extracted pion and kaon multiplicities in SIDIS at the HERMES experiment. My results have been used to study both nucleon structure and the fragmentation process in a 3D transverse-momentum dependent (TMD) fashion. During this research, I was struck by the fact that TMD factorization appears to be holding at intermediate energies, far below the energetic regime required by the factorization theorem for SIDIS. Due to my interest in this area of study, I intend to join the CSV experiment in Hall C, which is an effort from the ANL medium-energy group. This experiment will provide for the necessary high- precision measurements that can be used locate potential issues with factorization at intermediate energies. This experiment will follow immediately after my J/ψ experiment in Spring 2019.

    In a similar vein, I am part of a collaboration between experts from theoretical and experimental nuclear (NP) as well as high-energy physics (HEP). We study the topic of hadronization by connecting the Monte Carlo- based approach from HEP, through the Lund string model in Pythia8, with recent developments in TMDs. This connection between Pythia8 and TMDs can then be used to access the phenomenology of factorization at intermediate energies, while a TMD-improved version of Pythia8 can boost the potential to discover physics beyond the Standard Model at the LHC.