Thu·Aug 24, 2017Thursday·August 24, 2017

1. 01*

   Measurements of azimuthal anisotropy and charged-particle multiplicity in $d$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=$200, 62.4, 39, and 19.6 GeV

   C. Aidala🇺🇸 · Y. Akiba🇯🇵 · M. Alfred🇺🇸 · K. Aoki🇯🇵 · N. Apadula🇺🇸 · C. Ayuso🇺🇸 · V. Babintsev🇷🇺 · A. Bagoly🇭🇺 · K.N. Barish🇺🇸 · S. Bathe🇺🇸 · A. Bazilevsky🇺🇸 · R. Belmont🇺🇸 and 234 other authors

   We present measurements of the elliptic flow, $v_2$, as a function of transverse momentum ($p_T$), pseudorapidity ($\eta$), and centrality in $d$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=$200, 62.4, 39, and 19.6 GeV. The beam-energy scan of $d$$+$Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero $v_2$ signal at all four collision energies, which, at midrapidity and low $p_T$, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the {\sc ampt} Monte Carlo generator) show good agreement with the data at midrapidity to forward ($d$-going) rapidities and low $p_T$. At backward (Au-going) rapidities and $p_T>1.5$ GeV/$c$, the data diverges from {\sc ampt} calculations of $v_2$ relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity ($d{N}_{\mathrm{ch}}/d\eta$) as a function of $\eta$ in central $d$$+$Au collisions at the same energies. We find that in $d$$+$Au collisions at $\sqrt{s_{{}_{NN}}}=$200 GeV the $v_2$ scales with $d{N}_{\mathrm{ch}}/d\eta$ over all $\eta$ in the PHENIX acceptance. At $\sqrt{s_{{}_{NN}}}=$62.4, and 39 GeV, $v_2$ scales with $d{N}_{\mathrm{ch}}/d\eta$ at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the $d{N}_{\mathrm{ch}}/d\eta$ scaling may be a further indication of nonflow effects dominating at backward rapidity.

   nucl-exPRC(2017)·70 citations
2. 02*

   Principal-component analysis of two-particle azimuthal correlations in PbPb and pPb collisions at CMS

   CMS Collaboration

   For the first time a principle-component analysis is used to separate out different orthogonal modes of the two-particle correlation matrix from heavy ion collisions. The analysis uses data from sqrt(s[NN]) = 2.76 TeV PbPb and sqrt(s[NN]) = 5.02 TeV pPb collisions collected by the CMS experiment at the LHC. Two-particle azimuthal correlations have been extensively used to study hydrodynamic flow in heavy ion collisions. Recently it has been shown that the expected factorization of two-particle results into a product of the constituent single-particle anisotropies is broken. The new information provided by these modes may shed light on the breakdown of flow factorization in heavy ion collisions. The first two modes ("leading" and "subleading") of two-particle correlations are presented for elliptical and triangular anisotropies in PbPb and pPb collisions as a function of pt over a wide range of event activity. The leading mode is found to be essentially equivalent to the anisotropy harmonic previously extracted from two-particle correlation methods. The subleading mode represents a new experimental observable and is shown to account for a large fraction of the factorization breaking recently observed at high transverse momentum. The principle-component analysis technique has also been applied to multiplicity fluctuations. These also show a subleading mode. The connection of these new results to previous studies of factorization is discussed.

   nucl-exhep-exPRC(2017)·42 citations
3. 03*

   Disentangling the role of the $Y(4260)$ in $e^{+}{e}^{-}\to D^{\ast }{\bar{D}}^{\ast }$ and $D_s^{\ast }{\bar{D}}_s^{\ast }$ via line shape studies

   Si-Run Xue🇨🇳 · Hao-Jie Jing🇨🇳 · Feng-Kun Guo🇨🇳 · Qiang Zhao🇨🇳

   Whether the $Y(4260)$ can couple to open charm channels has been a crucial issue for understanding its nature. The available experimental data suggest that the cross section line shapes of exclusive processes in $e^{+}{e}^{-}$ annihilations have nontrivial structures around the mass region of the $Y(4260)$. As part of a series of studies of the $Y(4260)$ as mainly a $\bar{D}{D}_1(2420)+c.c.$ molecular state, we show that the partial widths of the $Y(4260)$ to the two-body open charm channels of $e^{+}{e}^{-}\to D^{\ast }{\bar{D}}^{\ast }$ and $D_s^{\ast }{\bar{D}}_s^{\ast }$ are much smaller than that to $\bar{D}{D}^{\ast }\pi +c.c.$. The line shapes measured by the Belle Collaboration for these two channels can be well described by the vector charmonium states $\psi (4040)$, $\psi (4160)$ and $\psi (4415)$ together with the $Y(4260)$. It turns out that the interference of the $Y(4260)$ with the other charmonia produces a dip around 4.22~GeV in the $e^{+}{e}^{-}\to D^{\ast }{\bar{D}}^{\ast }$ cross section line shape. The data also show an evidence for the strong coupling of the $Y(4260)$ to the $D{\bar{D}}_1(2420)$, in line with the expectation in the hadronic molecular scenario for the $Y(4260)$.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2018)·23 citations
4. 04*

   Azimuthal transverse single-spin asymmetries of inclusive jets and charged pions within jets from polarized-proton collisions at $\sqrt{s}=500$ GeV

   STAR Collaboration: 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🇷🇺 · D. Arkhipkin🇺🇸 and 338 other authors

   We report the first measurements of transverse single-spin asymmetries for inclusive jet and jet + ${\pi }^{\pm }$ production at midrapidity from transversely polarized proton-proton collisions at $\sqrt{s}=500$ GeV. The data were collected in 2011 with the STAR detector sampled from 23 pb${}^{-1}$ integrated luminosity with an average beam polarization of 53%. Asymmetries are reported for jets with transverse momenta $6<p_{T,jet}<55$ GeV/c and pseudorapidity $|\eta |<1$. Presented are measurements of the inclusive-jet azimuthal transverse single-spin asymmetry, sensitive to twist-3 initial-state quark-gluon correlators; the Collins asymmetry, sensitive to quark transversity coupled to the polarized Collins fragmentation function; and the first measurement of the "Collins-like" asymmetry, sensitive to linearly polarized gluons. Within the present statistical precision, inclusive-jet and Collins-like asymmetries are small, with the latter allowing the first experimental constraints on gluon linear polarization in a polarized proton. At higher values of jet transverse momenta, we observe the first non-zero Collins asymmetries in polarized-proton collisions, with a statistical significance of greater than $5\sigma$. The results span a range of x similar to results from SIDIS but at much higher $Q^2$. The Collins results enable tests of universality and factorization-breaking in the transverse momentum-dependent formulation of perturbative quantum chromodynamics.

   ↳ hep-exnucl-exPRD(2018)·57 citations
5. 05*

   Electric dipole strength and dipole polarizability in ${}^{48}$Ca within a fully self-consistent second random-phase approximation

   Danilo Gambacurta🇷🇴 · Marcella Grasso🇫🇷 · Olivier Vasseur🇫🇷

   The second random-phase-approximation model corrected by a subtraction procedure designed to cure double counting, instabilities, and ultraviolet divergences, is employed for the first time to analyze the dipole strength and polarizability in ${}^{48}$Ca. All the terms of the residual interaction are included, leading to a fully self-consistent scheme. Results are illustrated with two Skyrme parametrizations, SGII and SLy4. Those obtained with the SGII interaction are particularly satisfactory. In this case, the low-lying strength below the neutron threshold is extremely well reproduced and the giant dipole resonance is described in a very satisfactory way especially in its spreading and fragmentation. Spreading and fragmentation are produced in a natural way within such a theoretical model by the coupling of 1 particle-1 hole and 2 particle-2 hole configurations. Owing to this feature, we may provide for the electric polarizability as a function of the excitation energy a curve with a similar slope around the centroid energy of the giant resonance compared to the corresponding experimental results. This represents a considerable improvement with respect to previous theoretical predictions obtained with the random-phase approximation or with several ab-initio models. In such cases, the spreading width of the excitation cannot be reproduced and the polarizability as a function of the excitation energy displays a stiff increase around the predicted centroid energy of the giant resonance.

   ↳ nucl-thnucl-exPLB(2018)·32 citations
6. 06*

   Beam-Energy Dependence of Directed Flow of $\Lambda$, $\bar{\Lambda }$, $K^{\pm }$, $K_s^0$ and $\varphi$ in Au+Au Collisions

   STAR Collaboration: 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🇷🇺 · D. Arkhipkin🇺🇸 and 338 other authors

   Rapidity-odd directed flow measurements at midrapidity are presented for $\Lambda$, $\bar{\Lambda }$, $K^{\pm }$, $K_s^0$ and $\varphi$ at $\sqrt{s_{NN}}=$ 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV in Au+Au collisions recorded by the STAR detector at the Relativistic Heavy Ion Collider. These measurements greatly expand the scope of data available to constrain models with differing prescriptions for the equation of state of quantum chromodynamics. Results show good sensitivity for testing a picture where flow is assumed to be imposed before hadron formation and the observed particles are assumed to form via coalescence of constituent quarks. The pattern of departure from a coalescence-inspired sum-rule can be a valuable new tool for probing the collision dynamics.

   ↳ hep-exnucl-exPRL(2018)·145 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.