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تسجيل مستخدم جديدImproved Comparison of Measurements and Calculations of $hat{q}L$ via transverse momentum broadening in Relativistic Heavy Ion Collisions using di-hadron correlations
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M. J. Tannenbaum
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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 $hat{q}$.
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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 predict
ed 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.
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 b
roadening 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.
Results from Relativistic Heavy Ion Collider Physics in 2018 and plans for the future at Brookhaven National Laboratory are presented.
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