PoS - Proceedings of Science
Volume 355 - 13th International Workshop in High pT Physics in the RHIC and LHC Era (High-pT2019) - Main session
Measurements and Calculations of $\hat{q}L$ via transverse momentum broadening in RHI collisions using di-hadron correlations
M. Tannenbaum
Full text: pdf
Pre-published on: August 27, 2019
Published on: March 27, 2020
Abstract
The renewed interest in analyzing RHIC data on di-hadron correlations as probes of final state transverse momentum broadening as shown at Quark Matter 2018~\cite{MiklosQM2018} by theoretical calculations~\cite{ChenCCNUPLB773} compared to experimental measurements~\cite{PXppg074, STARPLB760} led me to review the quoted theoretical calculations and experimental measurements because the theoretical calculation~\cite{ChenCCNUPLB773} does not show the correct errors of the PHENIX measurements~\cite{PXppg074,PXppg083} as published. The above references were checked and fits were performed to the published measurements with the correct errors~\cite{PXppg074,PXppg083} to determine $\hat{q}L$ from the measured azimuthal broadening to compare with the theoretical calculation~\cite{ChenCCNUPLB773}. The new fits with the correct errors give values of <${\hat{q}L}$> on the order of
$-1\pm 1$ GeV$^2$, clearly inconsistent with the value of $\hat{q}L=13$ GeV$^2$ claimed in the theoretical calculations~\cite{ChenCCNUPLB773}. One STAR measurement~\cite{STARPLB760}, that I had previously analyzed~\cite{MJTPLB771}, quoted in Ref.~\cite{ChenCCNUPLB773} gave a value of $<{\hat{q}L}>=0.86\pm 0.87$ GeV$^2$ also inconsistent with the theoretical claim~\cite{ChenCCNUPLB773}. As a check I calculated the values of $\hat{q}L$ from a more recent PHENIX measurement with superior errors~\cite{ppg106}. The values of $\hat{q}L$ from these measurements also had the interesting effect of being consistent with zero for larger values of associated $p_{Ta}\geq 3$ GeV/c. This effect is well known from all previous measurements of the ratio of the $p_{Ta}$ distributions in Au+Au to p+p for a given trigger $p_{Tt}$ called $I_{AA}$~\cite{STARPLB760,ppg106,ALICEPLB763} which remain constant for $p_{Ta}\geq 3$ GeV/c. One possible explanation is that for $p_{Ta}\geq 3$ GeV/c, which is at a fraction $\approx 1$\% of the $x_E\approx p_{Ta}/p_{Tt}$ distribution, these hard fragments are distributed narrowly around the jet axis so that they are not strongly affected by the medium~\cite{YacineIJMPA}. Hence, di-jets rather than di-hadrons at RHIC are proposed as an improved azimuthal broadening measurement to determine $\hat{q}L$ and possibly $\hat{q}$.
DOI: https://doi.org/10.22323/1.355.0021
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