Speaker
Jiechen Xu
(Columbia University)
Description
We present a $\chi^2/d.o.f.$ analysis of RHIC and LHC $R_{AA}$ ($p_T>10$ GeV/c) and $v_2$ ($p_T>10$ GeV/c) data using the new open C++ source CUJET2.0 code [1] developed as a component of the DOE JET collaboration project. The code evaluates jet path integral involving running coupling DGLV induced radiated gluon energy loss rates as well as elastic energy loss for jets propagating though viscous hydrodynamics VISH 2+1D expanding thermal fields $T(x,y,t)$ constrained by fits to bulk low $p_T$ observables. We compare numerical results as a function of our main control parameter, $\alpha_{max}$, an assumed upper bound on the vacuum running coupling in the infrared. A $\chi^2/d.o.f.$ analysis shows that $R^\pi_{AA}$ data from RHIC and LHC are consistent with CUJET2.0 at the $\chi^2/d.o.f.< 2$ level for $\alpha_{max}=0.22-0.27$. The corresponding $\hat{q}(E_{jet}, T)/T^3$ effective jet transport coefficient field of this model is evaluated and compared to other (HT-BW, HT-M, MARTINI, McGill-AMY) JET collaboration models [2]. We focus here on the main current jet quenching puzzle (not discussed in [2]) the underestimation of jet elliptic asymmetry, $v_2(p_T)$ at both RHIC and LHC by CUJET and most other pQCD based tomographic models. We show that relaxing the assumption that $\alpha_{max}$ is independent of the local T field can reduce the $v_2$ discrepancy between CUJET and data to the $\chi^2_{v_2}/d.o.f.< 2$ level by allowing as small as $10\%$ variations of the path averaged $\alpha_{max}(T(z))$ along in and out paths. We speculate about origin of such variations and propose additional future tests to help elucidate the "tricky azimuthal dependence" of jet quenching seen at RHIC and LHC.
References
[1] Jiechen Xu, Alessandro Buzzatti, Miklos Gyulassy, "Azimuthal Jet Flavor Tomography with CUJET2.0 of Nuclear Collisions at RHIC and LHC", arXiv:1402.2956.
[2] The JET Collaboration, "Extracting jet transport coefficient from jet quenching at RHIC and LHC", arXiv:1312.5003.
Primary author
Jiechen Xu
(Columbia University)
Co-authors
Dr
Alessandro Buzzatti
(Columbia University, LBNL)
Prof.
Miklos Gyulassy
(Columbia University, LBNL, Wigner RCP)
