Tue·Mar 13, 2018Tuesday·March 13, 2018

1. 01*

   Correlation Measurements Between Flow Harmonics in Au+Au Collisions at RHIC

   STAR Collaboration: J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · M. M. Aggarwal · Z. Ahammed · N. N. Ajitanand · I. Alekseev · D. M. Anderson · R. Aoyama · A. Aparin and 337 other authors

   Flow harmonics ($v_n$) in the Fourier expansion of the azimuthal distribution of particles are widely used to quantify the anisotropy in particle emission in high-energy heavy-ion collisions. The symmetric cumulants, $SC(m,n)$, are used to measure the correlations between different orders of flow harmonics. These correlations are used to constrain the initial conditions and the transport properties of the medium in theoretical models. In this Letter, we present the first measurements of the four-particle symmetric cumulants in Au+Au collisions at $\sqrt{s_{NN}}$ = 39 and 200 GeV from data collected by the STAR experiment at RHIC. We observe that $v_2$ and $v_3$ are anti-correlated in all centrality intervals with similar correlation strengths from 39 GeV Au+Au to 2.76 TeV Pb+Pb (measured by the ALICE experiment). The $v_2$-$v_4$ correlation seems to be stronger at 39 GeV than at higher collision energies. The initial-stage anti-correlations between second and third order eccentricities are sufficient to describe the measured correlations between $v_2$ and $v_3$. The best description of $v_2$-$v_4$ correlations at $\sqrt{s_{NN}}$ = 200 GeV is obtained with inclusion of the system's nonlinear response to initial eccentricities accompanied by the viscous effect with $\eta /s$ $>$ 0.08. Theoretical calculations using different initial conditions, equations of state and viscous coefficients need to be further explored to extract $\eta /s$ of the medium created at RHIC.

   nucl-exhep-exPLB(2018)·48 citations
2. 02*

   Nucleon Quark Distribution Functions from the Dyson-Schwinger Equations

   Kyle D. Bednar🇺🇸 · Ian C. Cloët🇺🇸 · Peter C. Tandy🇺🇸

   We present results for the nucleon's leading-twist spin-independent valence parton distribution functions obtained from a theoretical framework based on the Dyson-Schwinger equations (DSEs) of QCD that previously gave an excellent description of nucleon electromagnetic form factors. We employ the rainbow-ladder truncation of the DSEs and utilize nucleon bound state amplitudes from the Poincaré-covariant Faddeev equation, where the dominant scalar and axial-vector quark-quark correlations are included. This DSE framework is used to numerically evaluate the first 20 moments of the valence $u$ and $d$ quark distribution functions, from which the $x$-dependence of the distributions is found to be well constrained. We find good agreement with empirical parameterizations of experimental data and make the prediction that the $d/u$ ratio in the $x\to 1$ limit, invariant under scale evolution, takes the value $d/u\to 0.087\pm 0.010$. We find that this ratio is rather sensitive to the strength of axial-vector diquark correlations. However, contrary to a naive expectation, our result for the $d/u$ ratio in the $x\to 1$ limit does not vanish when only scalar diquark correlations are present, although it is an order of magnitude smaller than our $d/u$ result that also includes axial-vector diquarks. The valence quark distribution results are set in a broader context via a simple pion cloud model estimate of sea-quark light-cone momenta and gluon light-cone momentum.

   ↳ nucl-thhep-phnucl-exPLB(2018)·21 citations
3. 03*

   Extraction of Heavy-Flavor Transport Coefficients in QCD Matter

   R. Rapp🇺🇸 · P.B. Gossiaux🇫🇷 · A. Andronic🇩🇪 · R.Averbeck🇩🇪 · S.Masciocchi🇩🇪 · A. Beraudo🇮🇹 · E. Bratkovskaya🇩🇪 · P. Braun-Munzinger🇩🇪 · S. Cao🇺🇸 · A. Dainese🇮🇹 · S.K. Das🇮🇹 · M. Djordjevic🇷🇸 and 19 other authors

   We report on broadly based systematic investigations of the modeling components for open heavy-flavor diffusion and energy loss in strongly interacting matter in their application to heavy-flavor observables in high-energy heavy-ion collisions, conducted within an EMMI Rapid Reaction Task Force framework. Initial spectra including cold-nuclear-matter effects, a wide variety of space-time evolution models, heavy-flavor transport coefficients, and hadronization mechanisms are scrutinized in an effort to quantify pertinent uncertainties in the calculations of nuclear modification factors and elliptic flow of open heavy-flavor particles in nuclear collisions. We develop procedures for error assessments and criteria for common model components to improve quantitative estimates for the (low-momentum) heavy-flavor diffusion coefficient as a long-wavelength characteristic of QCD matter as a function of temperature, and for energy loss coefficients of high-momentum heavy-flavor particles.

   ↳ nucl-thhep-phnucl-exNPA(2018)·313 citations
4. 04*

   Lattice Calculation of Parton Distribution Function from LaMET at Physical Pion Mass with Large Nucleon Momentum

   Jiunn-Wei Chen🇹🇼 · Luchang Jin🇺🇸 · Huey-Wen Lin🇺🇸 · Yu-Sheng Liu🇨🇳 · Yi-Bo Yang🇺🇸 · Jian-Hui Zhang🇩🇪 · Yong Zhao🇺🇸

   We present a lattice-QCD calculation of the unpolarized isovector parton distribution function (PDF) using ensembles at the physical pion mass with large proton boost momenta $P_z\in \{2.2,2.6,3.0\}$~GeV within the framework of large-momentum effective theory (LaMET). In contrast to our previous physical-pion PDF result, we increase the statistics significantly, double the boost momentum, increase the investment in excited-state contamination systematics, and switch to ${\gamma }_t$ operator to avoid mixing with scalar matrix elements. We use four source-sink separations in our analysis to control the systematics associated with excited-state contamination. The one-loop LaMET matching corresponding to the new operator is calculated and applied to our lattice data. We detail the systematics that affect PDF calculations, providing guidelines to improve the precision of future lattice PDF calculations. We find our final parton distribution to be in reasonable agreement with the PDF provided by the latest phenomenological analysis.

   ↳ hep-lathep-exhep-phnucl-ex+1110 citations
5. 05*

   Three-dimensional Imaging for Large LArTPCs

   Xin Qian🇺🇸 · Chao Zhang🇺🇸 · Brett Viren🇺🇸 · Milind Diwan🇺🇸

   High-performance event reconstruction is critical for current and future massive liquid argon time projection chambers (LArTPCs) to realize their full scientific potential. LArTPCs with readout using wire planes provide a limited number of 2D projections. In general, without a pixel-type readout it is challenging to achieve unambiguous 3D event reconstruction. As a remedy, we present a novel 3D imaging method, Wire-Cell, which incorporates the charge and sparsity information in addition to the time and geometry through simple and robust mathematics. The resulting 3D image of ionization density provides an excellent starting point for further reconstruction and enables the true power of 3D tracking calorimetry in LArTPCs.

   ↳ physics.ins-dethep-exnucl-exJINST(2018)·67 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.