High Energy Physics Phenomenology

We investigate features of the deconfinement phase transition in anSU(Nc)gauge theory as revealed by fluctuations of the order parameter. The tool of choice is an effective model built from one-loop expressions of the field determinants of gluon and ghost, in the presence of a Polyakov loop background field. We show that the curvature masses associated with the Cartan angles, which serve as a proxy to study theA0-gluon screening mass, show a characteristic dip in the vicinity of the transition temperature. The strength of the observables, which reflects a competition between the confining and the deconfining forces, is sensitive to assumptions of dynamics, thus provides an interesting link between theZ(Nc)vacuum structure and the properties of gluon and ghost propagators.

We derive simple relations which express 2D light front force distributions in terms of 3D Breit frame pressure and shear force distributions. Mathematically the relations correspond to invertible Abel transformation and they establish one-to-one mathematical equivalence of 3D Breit frame force distributions and 2D light front ones.Any knowledge (model calculation, experimental measurement, etc.) about pressure and shear force distributions in Breit frame can be unambiguously transformed into light front force distributions with the help of Abel transformation. It is important that the transformation ensures 2D stability conditions if the 3D stability conditions are satisfied.As an illustration of how the relations work, we calculated the light front force distributions for a large nucleus as a liquid drop, and for largeNcnucleon as a chiral soliton.

In this work, we find the light front densities for momentum and forces, including pressure and shear forces, within hadrons. This is achieved by deriving relativistically correct expressions relating these densities to the gravitational form factorsA(t)andD(t)associated with the energy momentum tensor. The derivation begins from the fundamental definition of density in a quantum field theory, namely the expectation value of a local operator within a spatially-localized state. We find that it is necessary to use the light front formalism to define a density that corresponds to internal hadron structure. When using the instant form formalism, it is impossible to remove the spatial extent of the hadron wave function from any density, and -- even within instant form dynamics -- one does not obtain a Breit frame Fourier transform for a properly defined density. Within the front formalism, we derive new expressions for various mechanical properties of hadrons, including the mechanical radius, as well as for stability conditions. The multipole ansatz for the form factors is used as an example to illustrate all of these findings.

In the semileptonic decays of heavy mesons and baryons the lepton-mass dependence factors out in the quadraticcos2θcoefficient of the differentialcosθdistribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor and restricting the phase space integration to the?lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three(e,μ,?)modes in a given semileptonic decay process. We discuss how the identity is spoiled by New Physics effects. We discuss semileptonic heavy meson decays such asB¯0??D(??+????ν¯??andB??c?�J/?(ηc)????ν¯??, and semileptonic heavy baryon decays such as?b???c????ν¯??for each??e,μ,?.

I examine the regime of forward scattering of an energetic particle in a Plasma medium in thermal equilibrium. Treating the particle as an open quantum system interacting with a bath, I look at the time evolution of the reduced density matrix of the system. The kinematic and dynamical time scales that emerge can exist in several possible hierarchies which can lead to different EFT formulations. I show that in certain hierarchies, it becomes necessary to account for arbitrary number of coherent exchanges between the system and the bath going beyond the independent scattering paradigm. Analytic results are obtained in certain limits and the formalism is applied for the measurement of transverse momentum broadening of a quark in a Quark Gluon Plasma medium.

We introduce a novel strategy for machine-learning-based fast simulators, which is the first that can be trained in an unsupervised manner using observed data samples to learn a predictive model of detector response and other difficult-to-model transformations. Across the physical sciences, a barrier to interpreting observed data is the lack of knowledge of a detector's imperfect resolution, which transforms and obscures the unobserved latent data. Modeling this detector response is an essential step for statistical inference, but closed-form models are often unavailable or intractable, requiring the use of computationally expensive, ad-hoc numerical simulations. Using particle physics detectors as an illustrative example, we describe a novel strategy for a fast, predictive simulator called Optimal Transport based Unfolding and Simulation (OTUS), which uses a probabilistic autoencoder to learn this transformation directly from observed data, rather than from existing simulations. Unusually, the probabilistic autoencoder's latent space is physically meaningful, such that the decoder becomes a fast, predictive simulator for a new latent sample, and has the potential to replace Monte Carlo simulators. We provide proof-of-principle results forZ-boson and top-quark decays, but stress that our approach can be widely applied to other physical science fields.

We consider the production of four charged leptons in hadron collisions and compute the next-to-leading order (NLO) QCD corrections to the loop-induced gluon fusion contribution by consistently accounting for the Higgs boson signal, its corresponding background and their interference. The contribution from heavy-quark loops is exactly included in the calculation except for the two-loopgg?�ZZ????continuum diagrams, for which the unknown heavy-quark effects are approximated through a reweighting procedure. Our calculation is combined with the next-to-next-to-leading order QCD and NLO electroweak corrections to theqq¯????process, including all partonic channels and consistently accounting for spin correlations and off-shell effects. The computation is implemented in the MATRIX framework and allows us to separately study the Higgs boson signal, the background and the interference contributions, whose knowledge can be used to constrain the Higgs boson width through off-shell measurements. Our state-of-the-art predictions for the invariant-mass distribution of the four leptons are in good agreement with recent ATLAS data.

We present a calculation of the next-to-leading order (NLO) QCD corrections to gluon-induced electroweak gauge boson pair production,gg?�ZZandgg??W+W??, matched to the PYTHIA8 parton shower in the POWHEG approach. The calculation consistently incorporates the continuum background, the Higgs-mediatedgg??H???�VVprocess, and their interference. We consider leptonic decay modes of the massive vector bosons and retain offshell and non-resonant contributions. The processes considered are loop-induced at leading order and thus contain two-loop virtual contributions as well as loop-squared real contributions. Parton-shower effects are found to be marginal in inclusive observables and quite sizeable in observables that are exclusive in additional jet radiation. The Monte Carlo generator presented here allows for realistic experimental effects to be incorporated in state-of-the-art precision analyses of diboson production and of the Higgs boson in the offshell regime.

We calculate the collinear anomalous dimensions in massless four-loop QCD andN=4supersymmetric Yang-Mills theory from the infrared poles of vertex form factors. We give very precise numerical approximations and a conjecture for the complete analytic results in both models we consider.

In the paper, we calculate the fragmentation functions for a quark to fragment into a spin-singlet quarkonium, where the flavor of the initial quark is different from that of the constituent quark in the quarkonium. The ultraviolet divergences in the phase space integral are removed through the operator renormalization under the modified minimal subtraction scheme. The fragmentation functionDq??ηQ(z,μF)is expressed as a two-dimensional integral. Numerical results for the fragmentation functions of a light quark or a bottom quark to fragment into theηcare presented. As an application of those fragmentation functions, we study the processesZ??ηc+qq¯g(q=u,d,s)andZ??ηc+bb¯gunder the fragmentation and the direct nonrelativistic QCD approaches.