Energy and scale dependence of $$\hat{q}$$ and the “JET puzzle”
Here, we present an attempt to probe the underlying structure of the quark-gluon plasma (QGP) at high resolution, based on the extracted jet transport coefficient $$\hat{q}$$. We argue that the exchanged momentum $$\textit{k}$$ between the hard parton and the medium varies over a range of scales, and for $$\textit{k}$$ ≥ 1 GeV, $$\hat{q}$$ can be expressed in terms of a parton distribution function (PDF). Because the mass of a QGP constituent is unknown, we define a scaling variable $$x_N$$ to represent the ratio of the parton momentum to the momentum of a self-contained section of the plasma which has a mass of 1 GeV. This scaling variable is used to parametrize the QGP-PDF. Calculations based on this reconstructed $$\hat{q}$$ are compared to data sensitive to the hardcore of jets, i.e., the single hadron suppression in terms of the nuclear modification factor $$R_{ A A}$$ and the azimuthal anisotropy parameter $$v_2$$ as a function of transverse momentum $$p_T$$, centrality, and energy of the collision. It is demonstrated that the scale evolution of the QGP-PDF is responsible for the reduction in the normalization of $$\hat{q}$$ between fits to the Relativistic Heavy-Ion Collider and the Large Hadron Collider data; a puzzle, first discovered by the JET Collaboration.
- Research Organization:
- Wayne State Univ., Detroit, MI (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC); National Science Foundation (NSF)
- Grant/Contract Number:
- SC0013460; PHY-1207918; ACI-1550300
- OSTI ID:
- 1802489
- Alternate ID(s):
- OSTI ID: 1604503
- Journal Information:
- Physical Review C, Vol. 101, Issue 3; ISSN 2469-9985
- Publisher:
- American Physical Society (APS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
Similar Records
Solving the puzzle with x and scale dependence
QLBT: a linear Boltzmann transport model for heavy quarks in a quark-gluon plasma of quasi-particles