Search results for "QUARK"

Review of proton and nuclear shape fluctuations at high energy

2020

Determining the inner structure of protons and nuclei in terms of their fundamental constituents has been one of the main tasks of high energy nuclear and particle physics experiments. This quest started as a mapping of the (average) parton densities as a function of longitudinal momentum fraction and resolution scale. Recently, the field has progressed to more differential imaging, where one important development is the description of the event-by-event quantum fluctuations in the wave function of the colliding hadron. In this Review, recent developments on the extraction of proton and nuclear transverse geometry with event-by-event fluctuations from collider experiments at high energy is …

Estudio unificado del espectro y propiedades de mesones pesados para energı́as por debajo y por encima de umbrales mesón-mesón

2022

Asymptotic freedom and color confinement are undoubtedly the most remarkable aspects of quantum chromodynamics (QCD). Indeed, it is because of these features that QCD is universally accepted as the quantum field theory of strong interactions. On the one hand, asymptotic freedom, meaning that the theory approaches a noninteracting one in the high energy limit, allows for a perturbative treatment, so that the QCD Lagrangian can be used to derive analytical expressions describing high-energy processes. On the other hand, color confinement, implying that all observable states are color-neutral, is a purely nonperturbative phenomenon, which prevents an analytical calculation of the low-energy in…

Approach to equilibrium of a quarkonium in a quark-gluon plasma

2018

We derive equations of motion for the reduced density matrix of a heavy quarkonium in contact with a quark-gluon plasma in thermal equilibrium. These equations allow in particular a proper treatment of the regime when the temperature of the plasma is comparable to the binding energy of the quarkonium. These equations are used to study how the quarkonium approaches equilibrium with the plasma, and we discuss the corresponding entropy increase, or free energy decrease, depending on the temperature regime. The effect of collisions can be accounted for by the generalization of the imaginary potential introduced in previous studies, and from which collision rates are derived. An important outcom…

Creation of quark-gluon plasma droplets with three distinct geometries

2019

Experimental studies of the collisions of heavy nuclei at relativistic energies have established the properties of the quark–gluon plasma (QGP), a state of hot, dense nuclear matter in which quarks and gluons are not bound into hadrons1,2,3,4. In this state, matter behaves as a nearly inviscid fluid5 that efficiently translates initial spatial anisotropies into correlated momentum anisotropies among the particles produced, creating a common velocity field pattern known as collective flow. In recent years, comparable momentum anisotropies have been measured in small-system proton–proton (p+p) and proton–nucleus (p+A) collisions, despite expectations that the volume and lifetime of the medium…

Highly occupied gauge theories in 2 + 1 dimensions : a self-similar attractor

2019

Motivated by the boost-invariant Glasma state in the initial stages in heavy-ion collisions, we perform classical-statistical simulations of SU(2) gauge theory in 2+1 dimensional space-time both with and without a scalar field in the adjoint representation. We show that irrespective of the details of the initial condition, the far-from-equilibrium evolution of these highly occupied systems approaches a unique universal attractor at high momenta that is the same for the gauge and scalar sectors. We extract the scaling exponents and the form of the distribution function close to this non-thermal fixed point. We find that the dynamics are governed by an energy cascade to higher momenta with sc…

Minijet initial state of heavy-ion collisions from next-to-leading order perturbative QCD

2014

Measurements of the groomed jet radius and momentum splitting fraction with the soft drop and dynamical grooming algorithms in pp collisions at √s = …

2023

This article presents measurements of the groomed jet radius and momentum splitting fraction in pp collisions at √ s = 5.02 TeV with the ALICE detector at the Large Hadron Collider. Inclusive charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm for transverse momentum 60< 80 GeV/c. We report results using two different grooming algorithms: soft drop and, for the first time, dynamical grooming. For each grooming algorithm, a variety of grooming settings are used in order to explore the impact of collinear radiation on these jet substructure observables. These results are compared to perturbative calculations that include resummation of large logarithms at all or…

Measurement of inclusive and leading subjet fragmentation in pp and Pb–Pb collisions at √sNN = 5.02 TeV

2023

This article presents new measurements of the fragmentation properties of jets in both proton–proton (pp) and heavy-ion collisions with the ALICE experiment at the Large Hadron Collider (LHC). We report distributions of the fraction zr of transverse momentum carried by subjets of radius r within jets of radius R. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with jet radius R = 0.4, and subjets are reconstructed by reclustering the jet constituents using the anti-kT algorithm with radii r = 0.1 and r = 0.2. In proton–proton collisions, we measure both the inclusive and leading subjet distributions. We compare these measurements to perturbative calculatio…

Dielectron production at midrapidity at low transverse momentum in peripheral and semi-peripheral Pb–Pb collisions at √sNN = 5.02 TeV

2023

Underlying-event properties in pp and p–Pb collisions at √sNN = 5.02 TeV

2023

We report about the properties of the underlying event measured with ALICE at the LHC in pp and p–Pb collisions at √sNN = 5.02 TeV. The event activity, quantified by charged-particle number and summed-pT densities, is measured as a function of the leading-particle transverse momentum (ptrigT). These quantities are studied in three azimuthal-angle regions relative to the leading particle in the event: toward, away, and transverse. Results are presented for three different pT thresholds (0.15, 0.5 and 1 GeV/c) at mid-pseudorapidity (|η| 10 GeV/c, whereas for lower ptrigT values the event activity is slightly higher in p–Pb than in pp collisions. The measurements are compared with predictions …