We compare the jet-path length and beam-energy dependence of the pion nuclear modification factor and a parton-jet nuclear modification factor at RHIC and LHC. We contrast predictions based on a ...linear pQCD and a highly non-linear hybrid-AdS holographic model of jet-energy loss. We find that both models require a reduction of the jet-medium coupling from RHIC to LHC to account for the measured pion nuclear modification factor. In case of the parton-jet nuclear modification factor, however, which serves as a lower bound for the LO jet nuclear modification factor of reconstructed jets, the extracted data can be characterized without a reduced jet-medium coupling at LHC energies. We conclude that while reconstructed jets are sensitive to both quarks and gluons and thus provide more information than the pion nuclear modification factor, their information regarding the jet-medium coupling is limited due to the superimposition with NLO and medium effects. Hence, a detailed description of the underlying physics requires both the leading hadron and the reconstructed jet nuclear modification factor. Unfortunately, the results for both the pion and the parton-jet nuclear modification factor are insensitive to the jet-path dependence of the models considered.
Recent data on the high-pT pion nuclear modification factor, \(R_{AA}(p_T)\), and its elliptic azimuthal asymmetry, \(v_2(p_T)\), from RHIC/BNL and LHC/CERN are analyzed in terms of a wide class of ...jet-energy loss models coupled to different (2+1)d transverse plus Bjorken expanding hydrodynamic fields. We test the consistency of each model by demanding a simultaneous account of the azimuthal, the transverse momentum, and the centrality dependence of the data at both 0.2 and 2.76 ATeV energies. We find a rather broad class of jet-energy independent energy-loss models \(dE/dx= \kappa(T) x^z T^{2+z} \zeta_q\) that, when coupled to bulk constrained temperature fields T(x,t), can account for the current data at the \(\chi^2<2\) level with different temperature-dependent jet-medium couplings and path-length dependence exponents \(0\le z \le 2\). We test the sensitivity of predictions to different skewed energy-loss fluctuations via a convenient scaling factor distributed in a finite range \(0< \zeta_q < 2+q\) with unit mean. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling as well as a near-\(T_c\) dominated, pQCD-inspired energy-loss scenario are shown to be inconsistent with the LHC data, once the parameters are constrained by fitting to RHIC results, we find several new solutions with a temperature-dependent jet-medium coupling. We conclude that the current level of statistical and systematic uncertainties of the measured data does not allow a constraint on the path-length exponent z to a range narrower than 0-2.
Results based on a generic jet-energy loss model that interpolates between running coupling pQCD-based and AdS/CFT-inspired holographic prescriptions are compared to recent data on the high-p_T pion ...nuclear modification factor and the high-p_T elliptic flow in nuclear collisions at RHIC and LHC. The jet-energy loss model is coupled to various (2+1)d (viscous hydrodynamic) fields. The impact of energy-loss fluctuations is discussed. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling is shown to be inconsistent with the LHC data, we find a rather broad class of jet-energy independent energy-loss models \(dE/dx= \kappa(T) x^z T^{2+z}\) that can account for the current data with different temperature-dependent jet-medium couplings \(\kappa(T)\) and path-length dependence exponents of \(0\le z \le 2\).
The double-peak structure observed in soft-hard dihadron correlations was recently studied intensively in order to learn more about the jet-induced medium excitation in ultrarelativistic heavy-ion ...collisions. Experimental data shows that the double-peak structure obtained for soft trigger particles coalesces into one peak for harder trigger particles. We demonstrate that this effect occurs when averaging over many jet events in a transversally expanding background, while a hot spot scenario always leads to two distinct peaks. This suggests to study soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets at RHIC and LHC in order to really disentangle medium effects from jets.
A generic jet-energy loss model that is coupled to state-of-the-art hydrodynamic fields and interpolates between a wide class of running coupling pQCD-based and AdS/CFT-inspired models is compared to ...recent data on the azimuthal and transverse momentum dependence of high-pT pion nuclear modification factors and high-pT elliptic flow measured at RHIC and LHC. We find that RHIC data are surprisingly consistent with various scenarios considered. However, extrapolations to LHC energies favor running coupling pQCD-based models of jet-energy loss. While conformal holographic models are shown to be inconsistent with data, recent non-conformal generalizations of AdS holography may provide an alternative description.
This thesis investigates the jet-medium interactions in a Quark-Gluon Plasma using a hydrodynamical model. It deals with the creation of Mach cones which are supposed to exhibit a characteristic ...structure in the measured angular particle distributions allowing for direct conclusions about the Equation of State and in particular about the speed of sound of the medium. Several different scenarios of jet energy loss are examined and different mechanisms of energy and momentum loss are analyzed, ranging from weak interactions (based on calculations from perturbative Quantum Chromodynamics, pQCD) to strong interactions (formulated using the Anti-de-Sitter/Conformal Field Theory Correspondence, AdS/CFT). Though they result in different angular particle correlations which could in principle allow to distinguish the underlying processes, it is shown that the characteristic structure observed in experimental data can be obtained due to the different contributions of several possible jet trajectories through an expanding medium. Such a structure cannot directly be connected to the Equation of State. In this context, the impact of a strong flow created behind the jet (the diffusion wake) is examined which is common to almost all jet deposition scenarios. Besides that, the transport equations for dissipative hydrodynamics are discussed which are fundamental for any numerical computation of viscous effects in a Quark-Gluon Plasma.
Recent data on the azimuthal and transverse momentum dependence of high-pT>10 GeV pion nuclear modification factors in nuclear collisions at RHIC/BNL and LHC/CERN are analyzed in terms of a wide ...class of jet-energy loss models and a variety of transverse expanding collective flow backgrounds. RHIC data at 200 AGeV are found to be surprisingly consistent with rather different dE/dx models when coupled to recent 2+1D minimally viscous QGP flow field predictions. However, extrapolations to LHC, with parameters fixed at RHIC, favor running coupling QCD based energy-loss models over fixed coupling QCD, conformal AdS holography, or Tc-dominated jet-energy loss models that tend to overpredict jet quenching at the LHC.
The nuclear modification factor R_{AA} measured in Pb+Pb collisions at the Large Hadron Collider (LHC) suggests that the jet-medium coupling in a Quark-Gluon Plasma at LHC energies is reduced as ...compared to energies reached at the Relativistic Heavy Ion Collider (RHIC). We estimate the reduction factor using a simple generic energy-loss model and find that the jet-medium coupling at the LHC is approximately 10% smaller than at RHIC. Moreover, we examine different jet-energy loss prescriptions with \(dE/dx\sim E^a\) and show that the measured momentum dependence of the nuclear modification factor at the LHC rules out any model with \(E^{a>1/3}\).
An increasing number of ethnic minorities are expected to enter the United States workforce based on projected demographic changes. This includes American Indian Alaskan Native (AI AN) nurses. ...Sociocultural influences on sleep disturbances, sleepiness, and other aspects related to shift-work tolerance are of unrecognized importance. More minority nurses are needed to provide culturally congruent care; however, AI AN nurses represent less than 1% of nurses located throughout the American workforce. This article aims to verify the feasibility of Internet data collection (Web-based survey) methods and instrument stability as the first part of a two-phase study comparing individual differences and shift-work-related sleep disturbances between AI AN and White non-Hispanic (WNH) nurses. In the first phase, an Internet survey was used to reach a cross-section of AI AN and WNH nurses. The on-line survey was composed of accepted shift-work-related instruments. Items estimating sleep disturbances, sociocultural choices, time awareness, polychronicity, morningness eveningness, ethnic identity, and demographic questions were asked. The survey was linked to a series of Web pages describing the study purpose, inclusion and exclusion criteria, consent form, Web survey, and the second phase of the study in which subjects were invited to participate in actigraphy measurements. The survey was pilot-tested for error codes, item confusion, length, and completion time. Forced-answer questions were added asking ethnicity, age group, license type, state where licensed, and legal name on nursing license before accessing the survey. Data were saved periodically, cued by the word "continue." The database was located on a secure server and password protected. Nurses were recruited using published articles and printed advertisements, hospital e-mail systems, national nursing organization Web sites (minoritynurse.com; NANAINA.org), nursing Web site discussion groups, snow-balling, and word of mouth. The site was accessed 656 times with the Internet survey being completed by 138 WNH and 56 AI AN nurses meeting the inclusion criteria. Except for the polychronicity measure (PAI3), instruments measuring time awareness, chronotype, and situational sleepiness achieved acceptable reliability coefficients with Internet data collection. Using pull-down menus would improve questions asking specific times. Internet data collection with different ethnic groups is possible; however, accessing the target population may be difficult. Despite extensive recruitment efforts, few AI AN nurses participated. Computer literacy and failing to relate to the study's purpose may have limited the interest of the AI AN nurses. It is possible to recruit nurse shift workers and collect individual difference and sleep disturbance data through the Internet; however, the researcher must remain vigilant throughout the process.
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