ALICE measures the radial jet-energy flow observable Δp_T in Pb-Pb (5.02 TeV) and pp (13 TeV) collisions and reports narrowing of the energy distribution in heavy-ion collisions at 3.5-4.5σ significance.
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Heavy Ion Collisions: The Big Picture, and the Big Questions
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abstract
Heavy ion collisions quickly form a droplet of quark-gluon plasma (QGP) with a remarkably small viscosity. We give an accessible introduction to how to study this smallest and hottest droplet of liquid made on earth and why it is so interesting. The physics of heavy ions ranges from highly energetic quarks and gluons described by perturbative QCD to a bath of strongly interacting gluons at lower energy scales. These gluons quickly thermalize and form QGP, while the energetic partons traverse this plasma and end in a shower of particles called jets. Analyzing the final particles in a variety of different ways allows us to study the properties of QGP and the complex dynamics of multi-scale processes in QCD which govern its formation and evolution, providing what is perhaps the simplest form of complex quantum matter that we know of. Much remains to be understood, and throughout the review big open questions will be encountered.
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First measurement of dNch/dη in OO collisions at 5.36 TeV yields midrapidity densities of 41.8 overall and 135 in central events, consistent with PbPb per participant but showing deviations from simple scaling.
New parton-shower algorithm that exactly reproduces linearized EKT dynamics for jet thermalization including recoils, holes, quantum statistics and merging.
The mid-rapidity curvature of Δv₁^even(p − p̄) is proposed as a robust discriminator of initial-state baryon rapidity profiles motivated by double-junction stopping.
Neutral-pion nuclear modification factors in OO collisions exhibit suppression at 4.9 sigma after subtracting cold-nuclear-matter effects via pO data, consistent with parton energy loss models.
A nonflow subtraction framework for m-particle cumulants is developed and tested in HIJING simulations for O+O and d+Au collisions.
In large-Nc and harmonic oscillator limits, medium-induced splittings are computed analytically double-differential in z and θ, with an improved semi-hard approximation validated for high-energy partons.
First measurement of the nuclear modification factor R_AA in OO collisions at 5.36 TeV shows suppression with a minimum of 0.69 at p_T around 6 GeV, favoring models with parton energy loss.
First measurements of v_n (n=2-4) in 5.36 TeV O+O and Ne+Ne collisions show enhanced v2 in central neon collisions consistent with prolate nuclear deformation.
Introduces a new thermodynamic state function enabling computation of high-order temperature fluctuations in hot QCD matter from heavy-ion collision data, predicting strong suppression and negative skewness in the QGP phase.
Principal component analysis of spectral fluctuations in heavy-ion collisions yields thermal and geometric normal modes that explain 99.5% of variance and account for measured flow observables v0(pT) and v02(pT).
Numerical solution of differential equations for the full in-medium gluon emission spectrum from a QCD antenna with realistic scattering models.
Track functions exhibit model-dependent modifications to higher moments in heavy-ion jets, with RG flows qualitatively preserved, enabling discrimination between jet quenching pictures.
ATLAS observes increasing dijet imbalance with centrality in O+O and Ne+Ne collisions at 5.36 TeV, consistent with medium-induced energy loss in small systems.
Bayesian global fit to Xe-Xe and Pb-Pb LHC data infers nearly maximal triaxiality for the 129Xe ground state and extracts two- and three-particle correlations.
A data-driven method is introduced to quantify contamination effects from light-ion beam transmutation using time-dependent control regions and a simple illustrative model.
Energy-energy correlators in heavy-ion collisions exhibit classical hydrodynamic scaling from collective flow at large angles within the small-angle regime, collective modes at smaller angles, and light-ray OPE at even smaller angles.
STAR reports 20% suppression of recoiling hadrons and jets in high-event-activity O+O collisions at 200 GeV, with a measured 0.7 GeV/c pT shift for large-radius jets, providing evidence for jet quenching in small systems.
In a rigidly rotating free Fermi gas, the relativistic Barnett effect produces different Fermi energies for spin-up and spin-down fermions, leading to a moment of inertia that scales as 1/T at high temperature, analogous to the Curie law.
New measurements of isolated, non-isolated, and inclusive J/ψ yields, nuclear modification factors, and fractions up to 60 GeV in pp and Pb+Pb collisions at 5.02 TeV.
Archived ALEPH data analysis finds ridge-like modulations and sign-changing v2 proxy in two-particle correlations for multiplicity above 30-50 in e+e- collisions with W+W- contribution, deviating from Monte Carlo predictions.
ATLAS measures charged-particle pseudorapidity density and mean transverse momentum in O+O and Ne+Ne collisions at 5.36 TeV as a function of centrality and eta.
ATLAS reports significant suppression (I_AA < 1) of photon-tagged two-jet yields in Pb+Pb versus pp collisions at 5.02 TeV across three observables, compared to JEWEL, JETSCAPE, and LBT models.
Proposes EIC jet-pion-electron measurements to detect and quantify short-range quark pair correlations in protons, expecting ud pairs to dominate due to diquark attraction.
citing papers explorer
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Full energy fraction and angular dependence of medium-induced splittings in the large-$N_c$ limit
In large-Nc and harmonic oscillator limits, medium-induced splittings are computed analytically double-differential in z and θ, with an improved semi-hard approximation validated for high-energy partons.
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Gluon radiation from a QCD antenna with realistic parton-medium interactions
Numerical solution of differential equations for the full in-medium gluon emission spectrum from a QCD antenna with realistic scattering models.
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Mapping jet substructure in heavy-ion collisions with track functions
Track functions exhibit model-dependent modifications to higher moments in heavy-ion jets, with RG flows qualitatively preserved, enabling discrimination between jet quenching pictures.
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Hydrodynamics and Energy Correlators
Energy-energy correlators in heavy-ion collisions exhibit classical hydrodynamic scaling from collective flow at large angles within the small-angle regime, collective modes at smaller angles, and light-ray OPE at even smaller angles.
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Short-Range Correlations Between Partons in a Proton
Proposes EIC jet-pion-electron measurements to detect and quantify short-range quark pair correlations in protons, expecting ud pairs to dominate due to diquark attraction.
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Bayesian inference constraints on jet quenching across centrality, beam energy, and observable classes in LHC heavy-ion collisions
Bayesian posteriors from JETSCAPE jet-quenching model are largely compatible across centrality but exhibit shifts across beam energy and observable class, with varying ability to predict complementary datasets.
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FRG analysis of dense two-color QCD within the linear sigma model
FRG analysis in the linear sigma model for QC2D shows enhanced meson U(1)_A anomaly couplings with increasing mu_q but suppressed topological susceptibility following chiral restoration at high density or temperature.
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Minimal superfluid vortices in chiral perturbation theory
Leading order chiral perturbation theory yields the minimal energy condition for vortex nucleation in the pion condensed phase, with vortices carrying quantized angular momentum and self-confining pions.
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Magnetized bottom-up thermalization in heavy-ion collisions
Strong magnetic fields may accelerate early quark production via gluon decay in the bottom-up scenario when |eB| approaches Q_s^2, modifying pre-equilibrium chemical composition.
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Thermodynamics of the Isospectral family of holographic vector mesons
Isospectral transformations in softwall AdS/QCD allow tuning the rho meson's decay constant to its experimental value of 226 MeV, producing a predicted melting temperature of 157 MeV from spectral function computations at finite temperature and chemical potential.
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Nonequilibrium coherent effects at finite chemical potential
Finite chemical potential splits particle and antiparticle phases in the homogeneous solution of the statistical propagator, yielding a transient interference pattern erased by damping.
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Light-Ion Collisions: Bridging Small and Large QCD Systems
Light-ion collisions at the LHC provide evidence of quark-gluon plasma formation in small systems, bridging proton-proton and heavy-ion regimes.
- Quantum simulating multi-particle processes in high energy nuclear physics: dijet production and color (de)coherence