Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session U12: Minisymposium on Initial State and Early Time Dynamics of Heavy Ion Collisions IIMini-Symposium
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Sponsoring Units: DNP Chair: Frank Guerts, Rice University Room: A222-223 |
Monday, April 16, 2018 3:30PM - 3:42PM |
U12.00001: Progress toward identifying BFKL effects in dijet processes Timothy Raben, Christophe Royon, Federico Deganutti, Augustin Sabio Vera, Gregorio Chachamis, David Gordo Gomez We present progress toward the theoretical understanding of BFKL effects in dijet processes in order to better isolate kinematical regimes relevant to experiments. BFKL effects have been notoriously difficult to clearly identify in processes involving two jets. The theoretically simplest example, Mueller-Navelet or inclusive dijets, has been shown to be well described via DGLAP evolution. We describe progress in identifying new observables that more strongly depend on BFKL effects that might show clear signatures at the LHC. The cleanest experimental example is that of Mueller-Tang jets. Here dijets are produced with a large rapidity gap resulting from single Pomeron exchange. Theoretically this requires a more complicated description, but recent progress in understanding the combination of the NLL kernel and the NLO impact factors have made a theoretical prediction possibly that is consistent with current results from the LHC [Preview Abstract] |
Monday, April 16, 2018 3:42PM - 3:54PM |
U12.00002: Analyzing jets emitted from Bose-Einstein condensates with insights from particle and nuclear physics. Miguel Arratia In this talk, I will propose an explanation for some of the features of the emission of jets of atoms from stimulated Bose-Einstein condensates, discovered recently by Clark et al. [1], by using analogies with particle physics [2]. I argue that the widening and depletion of the away-side peak in the measured angular correlation function is consistent with a dijet acoplanarity of a few degrees, similar to the case of parton-parton scattering with "intrinsic kT''. I will also show proposals for studies of collectivity in this jet phenomenon inspired in studies of the quark-gluon plasma.\\ \\$[1]$ L.W Clark, L.W Clark et al, ”Collective emission of matter-wave jets from driven BoseEinstein condensates”, Nature 551, 356359 \\ \\$[2]$ M. Arratia, On the jets emitted by driven Bose-Einstein condensates, https://arxiv.org/abs/1801.05515 [Preview Abstract] |
Monday, April 16, 2018 3:54PM - 4:06PM |
U12.00003: Measurement of Double-Differential Jet Cross Section in pp Collisions at $\sqrt{s}$ = 5 TeV with the CMS Detector Owen Baron, Ian Laflotte, Raghav Kunnawalkam Elayavalli, Sevil Salur, John Strologas Jets are highly collimated particle showers arising predominantly from hard parton scattering, such as in proton-proton collisions at the LHC. Jet measurements are a significant tool for exploring the strong coupling constant in different kinematic regions and for refining Parton Distribution Functions (PDFs). In addition, jets from proton-proton collisions are compared with those from heavy ion collisions in order to explore the differences between initial and final state effects of nuclear matter. Comparing the observed behavior of jets that have transversed the Quark-Gluon Plasma (QGP) to those from pp-collisions provides insight into the nature of this hot nuclear medium. We present preliminary results of the double-differential jet cross section from 5-TeV proton-proton collisions at the LHC using reconstructed anti-k$_{T}$ Particle Flow jets at $\sqrt{s}$ = 5 TeV center-of-mass energy recorded by the CMS detector. The cross sections are extended to low values of jet transverse momenta and cover a range of pseudorapidities. [Preview Abstract] |
Monday, April 16, 2018 4:06PM - 4:18PM |
U12.00004: Event-plane dependent away-side jet-like correlation shape in Au+Au collisions at 200 GeV from STAR Liang Zhang A strongly coupled quark gluon plasma (QGP) is created in relativistic heavy-ion collisions. Jets are a good probe of the energy loss properties of the QGP experienced by hard partons traversing the medium. The purpose of this analysis is to investigate the event plane (EP) dependence of jet energy loss. Measurements of jet-like correlations are complicated by the large underlying anisotropic flow background. In this analysis, we require a large recoil ($P_{x}$) within a given pseudo-rapidity ($\eta$) range from a high-$p_{T}$ trigger particle to enhance in-acceptance population of away-side jet. We subtract the flow background by taking the difference of the two-particle correlation in the close-region and far-region with respect to the $\eta$ region of $P_{x}$. The close- and far-region are symmetric about mid-rapidity. We analyze the correlation shape as a function of the trigger particle azimuthal angle relative to the EP, which is reconstructed from the beam-beam counters (BBCs) that are displaced by several units in $\eta$ from the mid-rapidity region. The large $\eta$ gap can effectively eliminate the correlation between trigger particles and EP. EP-dependent away-side jet-like correlation shapes and their implications for jet-medium interactions will be discussed. [Preview Abstract] |
Monday, April 16, 2018 4:18PM - 4:30PM |
U12.00005: Study of jet energy loss with jet-hadron correlations in pp and Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV with ALICE Raymond Ehlers High momentum jets produced in ultra-relativistic heavy ion collisions are sensitive probes of the properties of the quark-gluon plasma. Measurement of jet energy loss in jet-hadron correlations, in which a reconstructed jet is correlated with charged hadrons in the event, is a direct probe of interactions between the jet and the medium. The near-side of the correlation is sensitive to the modification of jet structure, while the away-side is sensitive to broadening and softening of the associated recoil jet due to jet quenching. Azimuthal jet-hadron correlations were measured for R=0.2 full (charged + neutral) jets reconstructed in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76$ TeV recorded by the ALICE collaboration at the LHC. To remove contributions from the Pb--Pb combinatorial background, jet constituents were required to pass a high energy (for EMCal clusters) and momentum (for charged tracks) threshold. Associated charged hadron yields and correlation widths were extracted from the correlation function for several associated hadron transverse momenta. In order to provide a baseline measurement, jet-hadron correlations were also measured in pp data embedded into Pb--Pb data. Model predictions are compared. The current status of the analysis will be presented. [Preview Abstract] |
Monday, April 16, 2018 4:30PM - 4:42PM |
U12.00006: Inclusive jet measurements in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ALICE James Mulligan The ALICE detector is designed to study the quark-gluon plasma created in ultrarelativistic heavy-ion collisions at the Large Hadron Collider. The quark-gluon plasma is the only known experimental system of deconfined quarks and gluons, and it may allow insight into a variety of open questions about the high temperature regime of QCD and the emergent behaviors of QCD. One major effort to probe the quark-gluon plasma is the study of high momentum jets produced in the initial hard scattering of a heavy-ion collision. The yield and structure of jets in heavy-ion collisions at different collision energies and kinematical ranges give information about the interaction of jets with the quark-gluon plasma, and in turn about the structure of the quark-gluon plasma itself. ALICE reconstructs jets with high-precision tracking of charged particles combined with calorimetric detection of neutral particles, achieving a unique kinematical range of jets down to low momenta. The status of a recent inclusive jet measurement over a variety of jet radii and momenta in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ALICE will be shown. [Preview Abstract] |
Monday, April 16, 2018 4:42PM - 4:54PM |
U12.00007: Photon - Hadron Correlations in Heavy Ion Collisions from PHENIX Tyler Danley Direct photon-jet pairs are produced in the initial hard scattering of an ion collision and the photon is not affected by the quark-gluon plasma, while the jet loses energy. This allows the direct photon to be an energy calibrator for the jet which can then be studied through photon-hadron pair correlations. Obtaining direct photons is challenging because of the myriad of background photons and typically a statistical subtraction method is used in A+A at RHIC. In addition to a statistical method, we have also developed a direct method to obtain isolated photons in A+A by using an isolation cut like those used in direct photon identification in p+p collisions. The isolation cut provides for a cleaner sample of direct photons, potentially reducing the systematic uncertainties on direct photon-hadron correlations when compared to the statistical subtraction sample but presents its own new challenges in the A+A high multiplicity environment. We present the status of centrality-dependent direct photon-hadron angular correlations and fragmentation functions in A+A collisions as well as results from recent high-statistics PHENIX datasets. [Preview Abstract] |
Monday, April 16, 2018 4:54PM - 5:06PM |
U12.00008: $\gamma$ and $\pi^0$-Hadron Correlations in Heavy Ion Collisions at the LHC with ALICE Michael Oliver In ultra-relativistic heavy ion collisions, direct photons from hard-scatters do not interact with the strongly interacting quark-gluon plasma, providing a clean probe into hard-scatter kinematics. Thus, correlations between direct photons and hadrons from an away-side jet are not subject to any trigger bias due to quenching of the trigger, allowing an unambiguous measurement of the modification of the away-side jet. A major background to these direct photon triggers are decay photons from high momentum neutral pions. The impact of correlations with these pions can be removed by measuring correlations with identified $\pi^{0}$'s at various transverse momenta, and using kinematics to convert these $\pi^0$-hadron correlations to $\gamma^{\text{decay}}$-hadron correlations to subtract these from inclusive $\gamma$-hadron correlations to find true $\gamma^{\text{direct}}$-hadron correlations. Using the ALICE Electromagnetic Calorimeter, we detect both the inclusive photon and $\pi^{0}$ triggers, and correlate them with charged hadrons detected using ALICE's Inner Tracking System and Time Projection Chamber to measure $\gamma^{\text{direct}}$-hadron correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}= 5.02$ TeV. Progress towards this measurement will be shown. [Preview Abstract] |
Monday, April 16, 2018 5:06PM - 5:18PM |
U12.00009: Studies of Jet-related Two-Particle Correlations in Small and Peripheral Heavy Ion Systems with PHENIX Abinash Pun The study of high pT 2-particle correlation observables in small systems like $d+Au$ is considered to be useful to isolate cold-nuclear matter effects. Comparison of the correlations in small systems to that in Au+Au can help to identify effects from the final-state interactions in the quark gluon plasma, QGP, created in $Au+Au$. The quantity, $R_I$, the double ratio of near- to away-side per-trigger yields divided by the same in the $p+p$ reference, can cancel out the systematics to the level where very small suppressions or enhancements could be observable. Since these types of signals could be qualitatively similar to energy-loss jet modification due to presence of hot QGP seen in $Au+Au$, we investigate possible cold nuclear effects, systematics, and backgrounds for an existing PHENIX preliminary result for RI in the $d+Au$ system. Also, we present the status and possibilities of making the RI measurement in other small systems, such as $p+Au$, and $^{3}$$He+Au$ and also in peripheral $Au+Au$ for reference. [Preview Abstract] |
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