Extracting jet transport coefficient from jet quenching at RHIC and LHC (1312.5003v2)

Abstract: Within five different approaches to parton propagation and energy loss in dense matter, a phenomenological study of experimental data on suppression of large $p_T$ single inclusive hadrons in heavy-ion collisions at both RHIC and LHC was carried out. The evolution of bulk medium used in the study for parton propagation was given by 2+1D or 3+1D hydrodynamic models which are also constrained by experimental data on bulk hadron spectra. Values for the jet transport parameter $\hat q$ at the center of the most central heavy-ion collisions are extracted or calculated within each model, with parameters for the medium properties that are constrained by experimental data on the hadron suppression factor $R_{AA}$. For a quark with initial energy of 10 GeV we find that $\hat q\approx 1.2 \pm 0.3$ GeV$^2$/fm at an initial time $\tau_0=0.6$ fm/$c$ in Au+Au collisions at $\sqrt{s}=200$ GeV/n and $\hat q\approx 1.9 \pm 0.7 $ GeV$^2$/fm in Pb+Pb collisions at $\sqrt{s}=2.76 $ TeV/n. Compared to earlier studies, these represent significant convergence on values of the extracted jet transport parameter, reflecting recent advances in theory and the availability of new experiment data from the LHC.

• The paper extracts the jet transport coefficient from RHIC and LHC jet quenching data using multiple theoretical frameworks.
• It employs five distinct models to analyze parton energy loss and scattering mechanisms in the quark-gluon plasma.
• The convergence of extracted coefficient values highlights improved insights into medium properties and jet-medium interactions.

Extracting Jet Transport Coefficient from Jet Quenching at RHIC and LHC

The paper presents a detailed analysis of jet quenching phenomena in high-energy heavy-ion collisions conducted at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The central focus is to extract the jet transport coefficient, $\hat{q}$, a critical parameter that characterizes the interaction strength of jets with the dense medium, often referred to as quark-gluon plasma (QGP), created in these collisions.

Methodology and Approaches

The paper employs five distinct theoretical frameworks for modeling parton propagation and energy loss: GLV-CUJET, Higher-Twist (HT) models (including HT-M and HT-BW), MARTINI, and McGill-AMY. These frameworks differ primarily in the treatment of multiple scattering and parton-medium interactions, offering a comprehensive ecosystem of toolkits for understanding the jet-medium interaction.

• GLV-CUJET Model: This model describes multiple scatterings using a potential model for the medium, exploring scenarios with both static and dynamically screened interactions, and includes high-order opacity corrections.
• Higher-Twist Models (HT-M and HT-BW): These models focus on medium-modified quark fragmentation functions where the jet transport coefficient emerges as the principal parameter influencing energy loss. HT-M extends the evaluation to incorporate multiple scatterings through evolved effective QCD fragmentation functions.
• MARTINI and McGill-AMY Models: Leveraging hard-thermal-loop (HTL) framework interactions, these models integrate both elastic and radiative jet energy losses, modeled by solving rate equations for parton distribution functions within the medium. Hydrodynamic models provide the bulk medium evolution that serves as input for these calculations.

Results

Across these models, values for the jet transport coefficient $\hat{q}$ are extracted by fitting to suppression factors of large $p_T$ single inclusive hadron spectra, quantified by the nuclear modification factor $R_{AA}$ at RHIC and LHC. Significant convergence in the extracted values of $\hat{q}$ is observed compared to earlier studies, highlighting recent advances in theoretical and experimental inputs.

• For RHIC, $\hat{q} \approx 1.2 \pm 0.3$ GeV$^2$/fm at an initial time $\tau_0 = 0.6$ fm/$c$.
• For LHC, $\hat{q} \approx 1.9 \pm 0.7$ GeV$^2$/fm, demonstrating an increased interaction strength in the denser medium at higher collision energies.

Implications and Future Directions

The findings have significant implications for understanding the microphysical properties of the QGP. The convergence in $\hat{q}$ values underscores the utility of multiple modeling approaches to arrive at a more unified depiction of jet-medium interactions. These results suggest that the medium created in these high-energy collisions possesses considerable density and partonic interaction strength.

Future research can extend these methodologies to explore jet modification profiles, dihadron, or $\gamma$-jet correlations and to assess azimuthal asymmetries of jets. Additionally, advancements in lattice QCD and non-perturbative techniques may offer further insights into the parametric landscapes of the QCD medium, potentially refining constraints on $\hat{q}$. Furthermore, upcoming data from RHIC and LHC, particularly at varying energies, will be critical for validating these models and refining our understanding of medium properties and transport phenomena.

In summary, this paper sharpens the focus on extracting intrinsic medium properties and reaffirms the need for cross-validating theoretical models with data-rich environments to deepen our understanding of QGP behavior and jet-medium interactions.