Bulletin of the American Physical Society
2017 Fall Meeting of the APS Division of Nuclear Physics
Volume 62, Number 11
Wednesday–Saturday, October 25–28, 2017; Pittsburgh, Pennsylvania
Session JJ: Mini-Symposium on How Small is the QGP? Collectivity in Small Systems I |
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Chair: Julia Velkovska, Vanderbilt University Room: City Center A |
Friday, October 27, 2017 10:30AM - 11:06AM |
JJ.00001: The physical origin of multi-particle correlations in small collision systems Invited Speaker: Bjoern Schenke Correlation measurements in collisions of relatively small systems like proton+proton and proton+heavy ion collisions, performed at the Large Hadron Collider (LHC) and the Relativistiv Heavy Ion Collider (RHIC), show strikingly similar features to those observed in heavy ion collisions. Both strong final state interactions, which do explain the data in heavy ion collisions quantitatively, and initial state correlations are found to generate signals that reproduce the experimental data at least qualitatively. I review the status of our understanding of correlation measurements in small collision systems, discussing both hydrodynamic and transport approaches to final state effects, as well as initial state calculations, predominantly performed in the color glass condensate framework. I will also mention recent progress in combining the two sources of correlations into one coherent framework. [Preview Abstract] |
Friday, October 27, 2017 11:06AM - 11:18AM |
JJ.00002: PHENIX results on anisotropic flow in d+Au collisions from 19.6 to 200 GeV Sylvia Morrow Results on elliptic flow in p+p and p/d/$^{3}$He+A have raised the question of how small a system can be while still exhibiting collective behavior. In 2016, RHIC operations included d+Au collisions at 200, 62.4, 39, and 19.6 GeV. In this talk we present results on elliptic and triangular flow at midrapidity as a function of transverse momentum and event multiplicity in d+Au collisions at various energies. We compare these results with several theoretical predictions in scenarios including pre-equilibrium flow, hydrodynamic flow, partonic scattering, and purely hadronic scattering in order to assess the role of each stage in the system evolution for producing collective effects in small systems. [Preview Abstract] |
Friday, October 27, 2017 11:18AM - 11:30AM |
JJ.00003: PHENIX results on identified particles spectra and anisotropic flow in p/d/$^{3}$He+Au collisions at 200 GeV Weizhuang Peng Recent results from small collision systems at RHIC and LHC indicate that many of the signatures of collective behavior observed in AA collisions are also present in small systems in high-multiplicity events. The PHENIX experiment has performed comprehensive studies of long-range particle correlations and anisotropic flow in collisions. Mass ordering has been observed in the pt distributions of the anisotropic flow coefficients vn. Such mass ordering is a key feature in the hydrodynamics description of the system evolution and arises from radial flow, where all particles move with a common flow velocity. However, the mass ordering is also seen in microscopic transport models such as AMPT. Information about the radial flow can be gained more directly from measurements of the transverse momentum distributions of identified hadrons. Identified particle spectra and anisotropic flow in p/d/$^{3}$He+Au collisions will be presented and compared to theoretical predictions. [Preview Abstract] |
Friday, October 27, 2017 11:30AM - 11:42AM |
JJ.00004: Latest results on collectivity in small systems at CMS Zhenyu Chen In recent years, a wealth of experimental evidence has suggested the presence of novel collectivity in smallest hadronic collision systems such as pp and pPb with high-multiplicity final states. The origin of the observed collectivity is under intense debate, i.e., whether a strongly coupled quark-gluon medium is formed there, similar to that in large heavy ion collisions. With new pp and pPb data collected during the LHC run 2, latest results at CMS on collectivity in small system will be presented, including multi-particle azimuthal correlations and identified particle correlations for light and heavy flavor species. These results will provide new insights in unraveling the nature of collectivity in small but dense QCD systems. [Preview Abstract] |
Friday, October 27, 2017 11:42AM - 11:54AM |
JJ.00005: Recent ATLAS measurements of azimuthal anisotropies in $pp$ and $p$+Pb collisions Soumya Mohapatra The azimuthal anisotropies of particle yields observed in relativistic heavy-ion collisions have been traditionally considered as a strong evidence of the formation on a deconfined quark-gluon plasma produced in these collisions. However multiple recent measurements from the ATLAS Collaboration in $pp$ and $p$+Pb systems show similar features as those observed in A+A collisions, indicating the possibility of the production of such a deconfined medium in smaller collision systems. This talk presents a comprehensive summary of these ATLAS measurements in $pp$ collisions at 2.76, 5.02 and 13 TeV and in $p$+Pb collisions at 5.02 and 8.16 TeV. It includes measurements of two-particle hadron-hadron and muon-hadron correlations in $\Delta\phi$ and $\Delta\eta$, with a template fitting procedure used to subtract the dijet contributions. Measurements of multi-particle cumulants $c_n\{2-8\}$ are also presented. The cumulant measurements confirm presence of collective phenomena in $p$+Pb collisions, but are biased by non-flow correlations and are not able to provide evidence for collectivity in $pp$ collisions. To address this, measurements from a new sub-event cumulant method that suppresses the contribution of non-flow effects are presented. [Preview Abstract] |
Friday, October 27, 2017 11:54AM - 12:06PM |
JJ.00006: Azimuthally-dependent femtoscopy in central p+Pb collisions at 5 TeV with ATLAS Brian Cole Hanbury Brown and Twiss (HBT) radii with respect to the 2nd-order event plane are measured in central p+Pb collisions at $\sqrt{s_\textrm{NN}} = 5.02$ TeV with the ATLAS detector at the LHC. A total integrated luminosity of 28 nb$^−1$ is sampled. The radii and their relative modulation are presented as a function of the magnitude of the flow vector $|q_2|$ measured at the side of the calorimeters that the Pb beam faces with pseudorapidity $\eta < −2.5$. Modulations of the transverse HBT radii are observed with the same orientation as in ion-ion collisions, in which they are attributed to hydrodynamic evolution from an elliptic initial geometry. This modulation is consistent with a hydrodynamic evolution of a short-lived medium. [Preview Abstract] |
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