Browsing by Author "Mehen, Thomas C"

In this thesis I discuss an alternative approach for investigating quarkonium production in hadron colliders. I present a complete framework for developing observables for studies of charmonium states produced within a jet. My work is based on the use of effective field theories of quantum chromodynamics that allow for the approximate factorization of jet cross sections in perturbative calculable terms and universal non-perturbative functions that are extracted from data. Particularly in this thesis I explore the factorization approach of non-relativistic quantum chromodynamics and soft-collinear effective theory. The fragmenting jet functions play central role in factorization theorems for cross sections for identified hadrons within jets. This cross sections can depend on the hadron-jet energy ratio and possibly on other jet observables. I expand this concept to jet-shape observables known as angularities and introduce the transverse momentum dependent fragmenting jet functions. Applications of these advanced methods to J/ψ production from gluon fragmentation in electron-positron annihilation are presented and I develop the tools for expanding this work in hadron colliders. Additionally, I compare predictions for J/ψ production in jets, based on the framework of fragmenting jet functions, against recent experimental data from the LHCb collaboration.

In this thesis, we study effective field theories for doubly heavy baryons and lattice QCD. We construct a chiral Lagrangian for doubly heavy baryons and heavy mesons that is invariant under heavy quark-diquark symmetry at leading order and includes the leading O(1/m_Q ) symmetry violating operators. The theory is used to predict the electromagnetic decay width of the J = 3/2 member of the ground state doubly heavy baryon doublet. Numerical estimates are provided for doubly charm baryons. We also calculate chiral corrections to doubly heavy baryon masses and strong decay widths of low lying excited doubly heavy baryons. We derive the couplings of heavy diquarks to weak currents in the limit of heavy quark-diquark symmetry, and construct the chiral Lagrangian for doubly heavy baryons coupled to weak currents. Chiral corrections to doubly heavy baryon zero-recoil semileptonic decay for both unquenched and partially quenched QCD are calculated. This theory is used to derive chiral extrapolation formulae for measurements of the doubly heavy baryon zero-recoil semileptonic decay form factors in lattice QCD simulations. Additionally, we study the pion physics on lattice using chiral perturbation theory. For finite volume field theories with discrete translational invariance, conserved currents can obtain additional corrections from infrared effects. We demonstrate this for pions using chiral perturbation theory coupled to electromagnetism in a periodic box. Gauge invariant single particle effective theories are constructed to explain these results. We use chiral perturbation theory to study the extraction of pion electromagnetic polarizabilities from lattice QCD. Chiral extrapolation formulae are derived for partially quenched and quenched QCD simulations. We determine finite volume corrections to the Compton scattering tensor of pions.

Quantum chromodynamics (QCD), the theory of quarks and gluons, is known to be

the correct description of strong nuclear interactions. At high energy and momenta,

one can use QCD directly to compute quantities of physical interest related to the

strong force. At low energies and momenta, one should use a different description in

terms of the degrees of freedom relevant at that scale. Two approaches to achieve

this end are effective field theories and gauge/gravity dualities. The former involves

a field theory more or less like QCD itself, but with states which are composites

of quarks and gluons. Then a perturbative expansion is made not in terms of the

gauge coupling but instead in terms of the momentum of the fields. This approach

dates back to the 1970s and is on firm theoretical footing. Gauge/gravity dualities

are a newer and less understood technique, which relates the physics of the strong

interactions to a different but likely equivalent theory in a higher dimensional space-

time, where the quantity of interest can be computed more readily. We employ

both effective field theories and gauge/gravity dualities to study the physics of ex-

otic quarkonium states, that is bound states containing a heavy quark-antiquark pair

which nevertheless cannot be be understood working only with the standard quark

model of hadrons. Candidates for such states, long speculated to exist, have recently

been observed at particle colliders, so that the theory of exotic quarkonium is now

of great experimental importance.

While bound states of heavy quarks $Q\bar{Q}$ called quarkonia have been studied for nearly a half-century, their production is still not well understood. We examine how techniques from Effective Field Theories (EFTs) of the strong force can be used to probe the production of the $J/\psi(c\bar{c})$. The focus will be to study how quarkonia are produced in jets, highly-collimated sprays of hadrons ubiquitous at particle colliders. We review the study of quarkonium production using Non-relativistic QCD (NRQCD) and the study of jet substructure observables using the Soft-Collinear Effective Theory (SCET). The concept of Fragmenting Jet Functions (FJF), which describe a hadron's energy distribution inside a jet of measured substructure, is extended to jets where the angularity is measured or where the transverse momenta of a hadron relative to the jet axis is measured. Predictions of the energy distribution of $J/\psi$ in jets at the LHC using FJFs are compared with the latest LHCb data using various extractions of the non-perturbative NRQCD long-distance-matrix-elements (LDMEs) in the literature. These distributions are also calculated using a modification of the Pythia Monte Carlo, which is shown to have an unphysical model of quarkonium production and gives results consistent with our FJF calculations. Our predictions of the energy of $J/\psi$ produced in jets fit the data much better than default Monte Carlo results. We also demonstrate that LDMEs extracted from high transverse momentum data do a better job at predicting the LHCb measurements.

We describe the application of effective field theories for quantum chromodynamics (QCD) to two bound states involving heavy quarks: the $T_{cc}^+$ exotic meson and the $J/\psi$. We study the decay of the $T_{cc}^+$ in an effective theory for hadronic molecules, and find agreement with experiment. We also use the nonrelativistic QCD (NRQCD) factorization formalism to derive the leading-order transverse momentum dependent fragmentation functions (FFs) for quarks and gluons fragmenting to $J/\psi$. We then make use of these TMD FFs to compare the $J/\psi$ production mechanisms of light quark fragmentation and photon-gluon fusion, where the conclusions we draw can motivate future experiments at the Electron Ion Collider, shedding light on the inner structure of nucleons and testing ideas from NRQCD factorization. These results showcase the utility of effective field theories in explaining experiments and testing key concepts in nuclear/particle physics.