Wed·Apr 27, 2016Wednesday·April 27, 2016

1. 01*

   Photoproduction of the $f_1(1285)$ Meson

   R. Dickson · R. A. Schumacher (CLAS Collaboration)

   The $f_1(1285)$ meson with mass $1281.0\pm 0.8$ MeV/$c^2$ and width $18.4\pm 1.4$ MeV (FWHM) was measured for the first time in photoproduction from a proton target using CLAS at Jefferson Lab. Differential cross sections were obtained via the $\eta {\pi }^{+}{\pi }^{-}$, $K^{+}{\bar{K}}^0{\pi }^{-}$, and $K^{-}{K}^0{\pi }^{+}$ decay channels from threshold up to a center-of-mass energy of 2.8 GeV. The mass, width, and an amplitude analysis of the $\eta {\pi }^{+}{\pi }^{-}$ final-state Dalitz distribution are consistent with the axial-vector $J^P=1^{+}$ $f_1(1285)$ identity, rather than the pseudoscalar $0^{-}$ $\eta (1295)$. The production mechanism is more consistent with $s$-channel decay of a high-mass $N^{\ast }$ state, and not with $t$-channel meson exchange. Decays to $\eta \pi \pi$ go dominantly via the intermediate $a_0^{\pm }(980){\pi }^{\mp }$ states, with the branching ratio $\Gamma (a_0\pi \text{ (no}\bar{K}K\text{)})/\Gamma (\eta \pi \pi \text{(all)})=0.74\pm 0.09$. The branching ratios $\Gamma (K\bar{K}\pi )/\Gamma (\eta \pi \pi )=0.216\pm 0.033$ and $\Gamma (\gamma {\rho }^0)/\Gamma (\eta \pi \pi )=0.047\pm 0.018$ were also obtained. The first is in agreement with previous data for the $f_1(1285)$, while the latter is lower than the world average.

   nucl-exhep-exPRC(2016)·45 citations
2. 02*

   Triangular flow of negative pions emitted in PbAu collisions at $\sqrt{s_{NN}}=$ 17.3 GeV

   Jovan Milosevic (for the CERES/NA45 Collaboration)

   Differential triangular flow, $v_3(p_T)$, of negative pions is measured at $\sqrt{s_{NN}}$= 17.3 GeV around midrapidity by the CERES/NA45 experiment at CERN in central PbAu collisions in the range 0-30\% with a mean centrality of 5.5\%. This is the first measurement as a function of transverse momentum of the triangular flow at SPS energies. The $p_T$ range extends from about 0.05 GeV/c to more than 2 GeV/c. The triangular flow magnitude, corrected for the HBT effects, is smaller by a factor of about 2 than the one measured by the PHENIX experiment at RHIC and the ALICE experiment at the LHC. Within the analyzed range of central collisions no significant centrality dependence is observed. The data are found to be well described by a viscous hydrodynamic calculation combined with an UrQMD cascade model for the late stages.

   nucl-exNPA(2017)·4 citations
3. 03*

   Correlated event-by-event fluctuations of flow harmonics in Pb-Pb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=2.76$ TeV

   ALICE Collaboration

   We report the measurements of correlations between event-by-event fluctuations of amplitudes of anisotropic flow harmonics in nucleus-nucleus collisions, obtained for the first time using a new analysis method based on multiparticle cumulants in mixed harmonics. This novel method is robust against systematic biases originating from non-flow effects and by construction any dependence on symmetry planes is eliminated. We demonstrate that correlations of flow harmonics exhibit a better sensitivity to medium properties than the individual flow harmonics. The new measurements are performed in Pb-Pb collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{{}_{\mathrm{NN}}}}=2.76$ TeV by the ALICE experiment at the Large Hadron Collider (LHC). The centrality dependence of correlation between event-by-event fluctuations of the elliptic, $v_2$, and quadrangular, $v_4$, flow harmonics, as well as of anti-correlation between $v_2$ and triangular, $v_3$, flow harmonics are presented. The results cover two different regimes of the initial state configurations: geometry-dominated (in mid-central collisions) and fluctuation-dominated (in the most central collisions). Comparisons are made to predictions from MC-Glauber, viscous hydrodynamics, AMPT and HIJING models. Together with the existing measurements of individual flow harmonics the presented results provide further constraints on initial conditions and the transport properties of the system produced in heavy-ion collisions.

   nucl-exPRL(2016)·249 citations
4. 04*

   Origin of the mass splitting of azimuthal anisotropies in a multi-phase transport model

   Hanlin Li🇨🇳 · Liang He🇺🇸 · Zi-Wei Lin🇺🇸 · Denes Molnar🇺🇸 · Fuqiang Wang🇺🇸 · Wei Xie🇺🇸

   Both hydrodynamics-based models and a multi-phase transport (AMPT) model can reproduce the mass splitting of azimuthal anisotropy ($v_n$) at low transverse momentum ($p_{\perp }$) as observed in heavy ion collisions. In the AMPT model, however, $v_n$ is mainly generated by the parton escape mechanism, not by the hydrodynamic flow. In this study we provide detailed results on the mass splitting of $v_n$ in this transport model, including $v_2$ and $v_3$ of various hadron species in d+Au and Au+Au collisions at the Relativistic Heavy Ion Collider and p+Pb collisions at the Large Hadron Collider. We show that the mass splitting of hadron $v_2$ and $v_3$ in AMPT first arises from the kinematics in the quark coalescence hadronization process, and then, more dominantly, comes from hadronic rescatterings, even though the contribution from the latter to the overall charged hadron $v_n$ is small. We further show that there is no qualitative difference between heavy ion collisions and small-system collisions or between elliptic ($v_2$) and triangular ($v_3$) anisotropies. Our studies thus demonstrate that the mass splitting of $v_2$ and $v_3$ at low-$p_{\perp }$ is not a unique signature of hydrodynamic collective flow but can be the interplay of several physics effects.

   ↳ nucl-thnucl-exPRC(2017)·34 citations
5. 05*

   Protophobic Fifth Force Interpretation of the Observed Anomaly in ${}^8$Be Nuclear Transitions

   Jonathan L. Feng🇺🇸 · Bartosz Fornal🇺🇸 · Iftah Galon🇺🇸 · Susan Gardner🇺🇸 · Jordan Smolinsky🇺🇸 · Tim M. P. Tait🇺🇸 · Philip Tanedo🇺🇸

   Recently a 6.8$\sigma$ anomaly has been reported in the opening angle and invariant mass distributions of $e^{+}{e}^{-}$ pairs produced in ${}^8\text{Be}$ nuclear transitions. The data are explained by a 17 MeV vector gauge boson $X$ that is produced in the decay of an excited state to the ground state, ${}^8{\text{Be}}^{\ast }\to {}^8\text{Be}X$, and then decays through $X\to e^{+}{e}^{-}$. The $X$ boson mediates a fifth force with a characteristic range of 12 fm and has milli-charged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic $X$ boson may also alleviate the current 3.6$\sigma$ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2016)·301 citations
6. 06*

   Distribution amplitudes of radially-excited pi- and K-mesons

   Bo-Lin Li🇨🇳 · Lei Chang🇨🇳 · Fei Gao🇨🇳 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪 · Hong-Shi Zong🇨🇳

   A symmetry-preserving truncation of the two-body bound-state problem in relativistic quantum field theory is used to compute the leading-twist parton distribution amplitudes (PDAs) for the first radial excitations of the $\pi$- and $K$-mesons. In common with ground states in these channels, the PDAs are found to be dilated with respect to the relevant conformal-limit form and skewed toward the heavier valence-quark in asymmetric systems. In addition, the PDAs of radially-excited pseudoscalar mesons are not positive definite, owing to the fact that dynamical chiral symmetry breaking (DCSB) forces the leptonic decay constant of such states to vanish in the chiral limit. These results highlight that DCSB is expressed visibly in every pseudoscalar meson constituted from light-quarks. Hence, so long as its impact is empirically evident in the pseudoscalar members of a given spectrum level, it is unlikely that chiral symmetry is restored in any of the hadrons that populate this level.

   ↳ nucl-thhep-lathep-phnucl-exPRD(2016)·45 citations
7. 07*

   Wounded quarks in A+A, p+A, and p+p collisions

   Piotr Bozek🇵🇱 · Wojciech Broniowski🇵🇱 · Maciej Rybczynski🇵🇱

   We explore predictions of the wounded quark model for particle production and properties of the initial state formed in ultrarelativistic heavy-ion collisions. The approach is applied uniformly to A+A collisions in a wide collision energy range, as well as for p+A and p+p collisions at the CERN Large Hadron Collider (LHC). We find that generically the predictions from wounded quarks for such features as eccentricities or initial sizes are close (within 15\%) to predictions of the wounded nucleon model with an amended binary component. A larger difference is found for the size in p+Pb system, where the wounded quark model yields a smaller (more compact) initial fireball than the standard wounded nucleon model. The inclusion of subnucleonic degrees of freedom allows us to analyze p+p collisions in an analogous way, with predictions that can be used in further collective evolution. The approximate linear dependence of particle production in A+A collisions on the number of wounded quarks, as found in previous studies, makes the approach based on wounded quarks natural. Importantly, at the LHC energies we find approximate uniformity in particle production from wounded quarks, where at a given collision energy per nucleon pair similar production of initial entropy per source is needed to explain the particle production from p+p collisions up to A+A collisions. We also discuss the sensitivity of the wounded quark model predictions to distribution of quarks in nucleons, distribution of nucleons in nuclei, and to the quark-quark inelasticity profile in the impact parameter. In our procedure, the quark-quark inelasticity profile is chosen in such a way that the experiment-based parametrization of the proton-proton inelasticity profile is properly reproduced. The parameters of the overlaid multiplicity distribution is fixed from p+p and p+Pb data.

   ↳ nucl-thnucl-exPRC(2016)·79 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.