Mon·Jan 1, 2018Monday·January 1, 2018

1. 01*

   Directed flow in Au+Au collisions from the RHIC Beam Energy Scan at the STAR experiment

   Subhash Singha (for the STAR Collaboration)🇺🇸

   We report results of $v_1(y)$ and $d{v}_1/dy$ near mid-rapidity for ${\pi }^{\pm }$, $K^{\pm }$, $K_s^0$, $p$, $\overline{p}$, $\Lambda$, $\overline{\Lambda }$ and $\varphi$ from Beam Energy Scan Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7 - 200 GeV using the STAR detector at RHIC. The $d{v}_1/dy$ of ${\pi }^{\pm }$, $K^{\pm }$ and $K_s^0$ mesons remains negative over all beam energies. The $d{v}_1/dy$ of $p$ and $\Lambda$ baryons shows a sign change around 10 - 15 GeV, while net baryons (net p and net $\Lambda$) indicate a double sign change. The $d{v}_1/dy$ of $\overline{p}$, $\overline{\Lambda }$ and $\varphi$ show a similar trend for $\sqrt{s_{NN}}>$ 14.5 GeV. For the first time, $v_1$ measurements are used to test a quark coalescence hypothesis. Many measurements are found to be consistent with the particles being formed via coalescence of constituent quarks. The observed deviations from that consistency offer a new approach for probing the collision process at the quark level.

   nucl-exhep-exnucl-thPoS(2018)·0 citations
2. 02*

   Nuclear modification of leading hadrons and jets within a virtuality ordered parton shower

   Shanshan Cao🇺🇸 · Abhijit Majumder🇺🇸

   The event generator based on the higher-twist energy loss formalism -- Modular All Twist Transverse-scattering Elastic-drag and Radiation (MATTER) -- is further developed and coupled to a hydrodynamic model for studying jet modification in relativistic nuclear collisions. The probability of parton splitting is calculated using the Sudakov form factor that is constructed by a combination of vacuum and medium-induced splitting functions; and the full parton showers are simulated, including both energy-momentum and space-time evolutions of all jet partons. With the assumption that partons below a virtual scale of 1 GeV is absorbed by the medium, this framework is able to provide a reasonable description of the nuclear modification of both leading hadrons and jets at high transverse momentum at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider.

   ↳ nucl-thhep-phnucl-exPRC(2020)·84 citations
3. 03*

   Prospects for $\gamma \gamma \to$ Higgs observation in ultraperipheral ion collisions at the Future Circular Collider

   David d'Enterria🇨🇭 · Daniel E. Martins🇧🇷 · Patricia Rebello Teles🇧🇷

   We study the two-photon production of the Higgs boson, $\gamma \gamma \to \mathrm{H}$, at the Future Circular Collider (FCC) in ultraperipheral PbPb and pPb collisions at $\sqrt{s_{NN}}=39$ and 63 TeV. Signal and background events are generated with MADGRAPH 5, including $\gamma$ fluxes from the proton and lead ions in the equivalent photon approximation, yielding $\sigma (\gamma \gamma \to \mathrm{H})$ = 1.75 nb and 1.5 pb in PbPb and pPb collisions respectively. We analyse the H$\to b\bar{b}$ decay channel including realistic reconstruction efficiencies for the final-state $b$-jets, showered and hadronized with PYTHIA 8, as well as appropriate selection criteria to reduce the dominant exclusive $\gamma \gamma \to b\bar{b}$ continuum background. Observation of $\mathrm{PbPb}\stackrel{\gamma \gamma }{\to }(\mathrm{Pb})\mathrm{H}(\mathrm{Pb})$ is achievable in the first year with the expected PbPb integrated luminosities.

   ↳ hep-phhep-exnucl-exnucl-thCERN Proc.(2018)·4 citations
4. 04*

   Exclusive photoproduction of ${\pi }^0$ up to large values of Mandelstam variables $s,t$ and $u$ with CLAS

   M.C. Kunkel · 32 · 18 M.J. Amaryan · 32 · I.I. Strakovsky · 16 J. Ritman · 3 · 18 G.R. Goldstein · 43 K.P. Adhikari · 28 S Adhikari · 13 H. Avakian · 39 J. Ball and 160 other authors

   Exclusive photoproduction cross sections have been measured for the process $\gamma p\to p{\pi }^0(e^{+}{e}^{-}(\gamma ))$ with the Dalitz decay final state using tagged photon energies in the range of $E_{\gamma }=1.275-5.425$ GeV. The complete angular distribution of the final state ${\pi }^0$, for the entire photon energy range up to large values of $t$ and $u$, has been measured for the first time. The data obtained show that the cross section $d\sigma /dt$, at mid to large angles, decreases with energy as $s^{-6.89\pm 0.26}$. This is in agreement with the perturbative QCD quark counting rule prediction of $s^{-7}$. Paradoxically, the size of angular distribution of measured cross sections is greatly underestimated by the QCD based Generalized Parton Distribution mechanism at highest available invariant energy $s=11$ GeV${}^2$. At the same time, the Regge exchange based models for ${\pi }^0$ photoproduction are more consistent with experimental data.

   ↳ hep-exhep-phnucl-exnucl-thPRC(2018)·27 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.