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Register a new userFrom hydro to jet quenching, coalescence and hadron cascade: a coupled approach to solving the $R_{AA}otimes v_2$ puzzle
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Hydrodynamics and jet quenching are responsible for the elliptic flow $v_2$ at low transverse momentum $p_T$ and hadron suppression and $v_2$ at high $p_T$, respectively, in high-energy heavy-ion collisions. A consistent description of the hadron suppression factor $R_{AA}$ and $v_2$, especially at intermediate $p_T$, however, remains a challenge. We solve this long-standing $R_{AA}otimes v_2$ puzzle by describing hadron production from low to intermediate and high $p_T$ within the coupled linear Boltzmann transport-hydro model that combines concurrent jet transport and medium hydro evolution with quark coalescence in the hadronization and hadron casacde in the final evolution of the system. We illustrate that quark coalescence and hadron cascade are the keys to solving the puzzle. They also lead to a splitting of $v_2$ for pions, kaons and protons in the intermediate $p_T$ region. We demonstrate for the first time that experimental data on $R_{AA}$, $v_2$ and their hadron flavor dependence from low to intermediate and high $p_T$ in high-energy heavy-ion collisions can be understood within this coupled framework.
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High $p_T > 10$ GeV elliptic flow, which is experimentally measured via the correlation between soft and hard hadrons, receives competing contributions from event-by-event fluctuations of the low $p_T$ elliptic flow and event plane angle fluctuations in the soft sector. In this paper, a proper account of these event-by-event fluctuations in the soft sector, modeled via viscous hydrodynamics, is combined with a jet energy loss model to reveal that the positive contribution from low $p_T$ $v_2$ fluctuations overwhelms the negative contributions from event plane fluctuations. This leads to an enhancement of high $p_T > 10$ GeV elliptic flow in comparison to previous calculations and provides a natural solution to the decade long high $p_T$ $R_{AA} otimes v_2$ puzzle. We also present the first theoretical calculation of high $p_T$ $v_3$, which is shown to be compatible with current LHC data. Furthermore, we discuss how short wavelength jet-medium physics can be deconvoluted from the physics of soft, bulk event-by-event flow observables using event shape engineering techniques.
The observed inclusive jet suppression in heavy-ion collisions at LHC has a very weak $p_{T}$ dependence over a large range of $p_{T}$ = 50-1000 GeV and is almost independent of the colliding energy, though the initial energy density of the bulk medium has increased from $sqrt{s}$ = 2.76 to 5.02 TeV by about 20%. This interesting phenomenon is investigated in the linear Boltzmann transport (LBT) model for jet propagation in an event-by-event 3+1D hydro background. We show that the $p_{T}$ dependence of jet $R_{AA}$ is determined by the initial spectrum in $p+p$ collisions and $ p_{T} $ dependence of jet energy loss. Furthermore, jet energy loss distributions for inclusive jet and $ gamma-$jet at both LHC energies are extracted directly from experimental data through the state-of-art Bayesian analysis. The averaged jet energy loss has a weak $p_{T}$ dependence and the scaled jet energy loss distributions have a large width, both of which are consistent with the LBT simulations and indicate that jet quenching is caused by only a few out-of-cone jet medium scatterings.
We compute the inclusive jet spectrum in the presence of a dense QCD medium by going beyond the single parton energy loss approximation. We show that higher-order corrections are important yielding large logarithmic contributions that must be resummed to all orders. This reflects the fact that jet quenching is sensitive to fluctuations of the jet substructure.
We calculate higher-order corrections to the quenching factor of heavy-quark jets due to hard, in-medium splittings in the framework of the BDMPS-Z formalism. These corrections turn out to be sensitive to a single mass-scale $m_ast = (hat q L)^{1/2}$, where $hat q$ is the medium transport coefficient and $L$ the path length, and allow to draw a distinction between the way light, with $m < m_ast$ (in contrast to massless $m=0$), and genuinely heavy, with $m > m_ast$, quark jets are quenched in the medium. We show that the corrections to the quenching factor at high energies are double-logarithmic and qualitatively of the same order as for the massless quark jet.
We present a review of the description of hadron properties along an invariant mass operator in the point form of Poincare-invariant relativistic dynamics. The quark-quark interaction is furnished by a linear confinement, consistent with the QCD string tension, and a hyperfine interaction derived from Goldstone-boson exchange. The main advantage of the point-form approach is the possibility of calculating manifestly covariant observables, since the generators of Lorentz transformations remain interaction-free. We discuss the static properties of the mass-operator eigenstates, such as the invariant mass spectra of light- and heavy-flavor baryons, the characteristics of the eigenstates in terms of their spin, flavor, and spatial dependences as well as their classification into spin-flavor multiplets. Regarding dynamical observables we address the electroweak structures of the nucleon and hyperon ground states, including their electric radii, magnetic moments as well as axial charges, and in addition a recently derived microscopic description of the $pi NN$ as well as $pi NDelta$ interaction vertices. Except for hadronic resonance decays, which are not addressed here due to space limitations, all of these observables are obtained in good agreement with existing phenomenology. Relativistic (boost) effects are generally sizable. We conclude that low-energy hadrons can be well described by an effective theory with a finite number of degrees of freedom, as long as the symmetries of low-energy quantum chromodynamics (spontaneously broken chiral symmetry) as well as special relativity (Poincare invariance) are properly taken into account. The latter requirement is particularly well and efficiently met in the point-form approach.
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