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Register a new userMeasurement of $hat{q}$ in Relativistic Heavy Ion Collisions using di-hadron correlations
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M. J. Tannenbaum
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The azimuthal width of the di-hadron correlations in p$+$p collisons, beyond the fragmentation transverse momentum, $j_T$, is dominated by $k_T$, the so-called intrinsic transverse momentum of a parton in a nucleon, which can be measured. The predicted azimuthal broadening in A$+$A collisions should produce a larger $k_T$ than in p$+$p collisions. The present work introduces the observation that the $k_T$ measured in p$+$p collisions for di-hadrons with $p_{Tt}$ and $p_{Ta}$ must be reduced to compensate for the energy loss of both the trigger and away parent partons when comparing to the $k_T$ measured with the same di-hadron $p_{Tt}$ and $p_{Ta}$ in Au$+$Au collisions. This idea is applied to a recent STAR di-hadron measurement, with result $langle{hat{q}L}rangle=2.1pm 0.6$ GeV$^2$. This is more precise but in agreement with a theoretical calulation of $langle{hat{q}L}rangle=14^{+42}_{-14}$ GeV$^2$ using the same data. Assuming a length $langle{L}rangleapprox 7$ fm for central Au$+$Au collisions the present result gives $hat{q}=0.30pm 0.09$ GeV$^2$/fm, in fair agreement with the JET collaboration result of $hat{q}approx 1.2pm 0.3$ GeV$^2$/fm at initial time $tau_0=0.6$ fm/c in Au+Au collisions at $sqrt{s_{NN}}=200$ GeV.
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In the BDMPSZ model, the energy loss of an outgoing parton in a medium $-dE/dx$ is the transport coefficient $hat{q}$ times $L$ the length traveled. This results in jet quenching, which is well established. However BDMPSZ also predicts an azimuthal broadening of di-jets also proportional to $hat{q}L$ which has so far not been observed. The broadening should produce a larger $k_T$ in A$+$A than in p$+$p collisions. This presentation introduces the observation that the $k_T$ measured in p$+$p collisions for di-hadrons with $p_{Tt}$ and $p_{Ta}$ must be reduced to compensate for the energy loss of both the trigger and away parent partons when comparing to the $k_T$ measured with the same di-hadron $p_{Tt}$ and $p_{Ta}$ in A$+$A collisions. This idea is applied to a recent STAR di-hadron measurement in Au$+$Au at $sqrt{s_{NN}}$=200 GeV, [Phys. Lett. B760 (2016) 689], with result $<{hat{q}L}>=2.1pm 0.6$ GeV$^2$. This is more precise but in agreement with a theoretical calculation of $<{hat{q}L}>=14^{+42}_{-14}$ GeV$^2$ using the same data. Assuming a length $<{L}>approx 7$ fm for central Au$+$Au collisions the present result gives $hat{q}approx 0.30pm 0.09$ GeV$^2$/fm, in fair agreement with the JET collaboration result from single hadron suppression of $hat{q}approx 1.2pm 0.3$ GeV$^2$/fm at an initial time $tau_0=0.6$ fm/c in Au$+$Au collisions at $sqrt{s_{NN}}=200$ GeV. There are several interesting details to be discussed: for a given $p_{Tt}$ the $<{hat{q}L}>$ seems to decrease then vanish with increasing $p_{Ta}$; the di-jet spends a much longer time in the medium ($approx 7$ fm/c) then $tau_0=0.6$ fm/c which likely affects the value of $hat{q}$ that would be observed.
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[1] by theoretical calculations[6] compared to experimental measurements[4,5] led me to review the quoted theoretical calculations and experimental measurements because the theoretical calculation[6] does not show the PHENIX measurements[4] as published. The above references were checked and fits were performed to the published measurements[4,7] to determine $hat{q}L$ from the measured azimuthal broadening to compare with the theoretical calculation[6]. The new results will be presented in addition to some corrections to the previous work[3]. The measured values of $hat{q}L$ show the interesting effect of being consistent with zero for larger values of associated $p_{Ta}geq3$ GeV/c which is shown to be related to well known measurements of the ratio of the Au+Au to p+p associated $p_{Ta}$ distributions for a given trigger $p_{Tt}$ called $I_{AA}$[23,25]. Di-jets rather than di-hadrons are proposed as an improved azimuthal broadening measurement to determine $hat{q}L$ and possibly $hat{q}$.
Results from Relativistic Heavy Ion Collider Physics in 2018 and plans for the future at Brookhaven National Laboratory are presented.
We develop for charmed hadron production in relativistic heavy-ion collisions a comprehensive coalescence model that includes an extensive set of $s$ and $p$-wave hadronic states as well as the strict energy-momentum conservation, which ensures the boost invariance of the coalescence probability and the thermal limit of the produced hadron spectrum. By combining our hadronization scheme with an advanced Langevin-hydrodynamics model that incorporates both elastic and inelastic energy loss of heavy quarks inside the dynamical quark-gluon plasma, we obtain a successful description of the $p_mathrm{T}$-integrated and differential $Lambda_c/D^0$ and $D_s/D^0$ ratios measured at RHIC and the LHC. We find that including the effect of radial flow of the medium is essential for describing the enhanced $Lambda_c/D^0$ ratio observed in relativistic heavy-ion collisions. We also find that the puzzling larger $Lambda_c/D^0$ ratio observed in Au+Au collisions at RHIC than in Pb+Pb collisions at the LHC is due to the interplay between the effects of the QGP radial flow and the charm quark transverse momentum spectrum at hadronization. Our study further suggests that charmed hadrons have larger sizes in medium than in vacuum.
We review hadron production in heavy ion collisions with emphasis on pion and kaon production at energies below 2 AGeV and on partonic collectivity at RHIC energies.
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