Tue·Feb 19, 2019Tuesday·February 19, 2019

1. 01*

   Data-driven subtraction of anisotropic flows in jet-like correlation studies in heavy-ion collisions

   Liang Zhang🇨🇳 · Kun Jiang🇨🇳 · Cheng Li🇨🇳 · Feng Liu🇨🇳 · Fuqiang Wang🇺🇸

   Measurements of two-particle azimuthal angle correlations are a useful tool to study the distribution of jet energy loss, however, they are complicated because of the significant anisotropic flow background. We devise a data-driven method for subtracting anisotropic flow background in jet-like correlation analysis. We first require a large recoil momentum ($P_x$) within a given pseudo-rapidity ($\eta$) range from a high-transverse momentum particle to enhance in-acceptance population of away-side jet-like correlations. Then we take the difference of two-particle correlations in the close-region and far-region with respect to the $\eta$ region of $P_x$ to subtract the anisotropic flow background. We use a toy model which contains only anisotropic flow and PYTHIA8 which have jets to demonstrate the validity of our data-driven method. The results indicate that the data-driven method can subtract anisotropic flow effectively.

   nucl-exPRC(2019)·1 citation
2. 02*

   Event-plane dependent away-side jet-like correlation shape in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV from STAR

   Liang Zhang🇨🇳

   We employ a data-driven method to subtract the flow background of all harmonics by calculating the difference of the two-particle correlations between the close-region and far-region, determined depending on the pseudo-rapidity ($\eta$) distance from the region where an enhanced recoil transverse momentum ($P_x$) from a high-$p_T$ trigger particle is selected. We analyze the correlation shape as a function of the trigger particle azimuthal angle relative to the event-plane (EP) reconstructed from the beam-beam counters (BBCs) which are displaced by several units in $\eta$ from the mid-rapidity region. The large $\eta$ gap can effectively eliminate the auto-correlation between trigger particles and EP. We correct for the relatively large resolution effect from the BBC EP determination via an unfolding procedure. The width of unfolded away-side jet-like correlation increases with longer path-length, which is an indication of jet-medium interactions.

   nucl-exPoS(2019)·0 citations
3. 03*

   Comparing proton momentum distributions in $A=2$ and 3 nuclei via ${}^2$H ${}^3$H and ${}^3$He $(e,e^{\prime }p)$ measurements

   R. Cruz-Torres🇺🇸 · S. Li🇺🇸 · F. Hauenstein🇺🇸 · A. Schmidt🇺🇸 · D. Nguyen🇺🇸 · D. Abrams🇺🇸 · H. Albataineh🇺🇸 · S. Alsalmi🇺🇸 · D. Androic🇭🇷 · K. Aniol🇺🇸 · W. Armstrong🇺🇸 · J. Arrington🇺🇸 and 116 other authors

   We report the first measurement of the $(e,e^{\prime }p)$ reaction cross-section ratios for Helium-3 (${}^3$He), Tritium (${}^3$H), and Deuterium ($d$). The measurement covered a missing momentum range of $40\le p_{miss}\le 550$ MeV$/c$, at large momentum transfer ($⟨Q^2⟩\approx 1.9$ (GeV$/c$)${}^2$) and $x_B>1$, which minimized contributions from non quasi-elastic (QE) reaction mechanisms. The data is compared with plane-wave impulse approximation (PWIA) calculations using realistic spectral functions and momentum distributions. The measured and PWIA-calculated cross-section ratios for ${}^3$He$/d$ and ${}^3$H$/d$ extend to just above the typical nucleon Fermi-momentum ($k_F\approx 250$ MeV$/c$) and differ from each other by $\sim 20\%$, while for ${}^3$He/${}^3$H they agree within the measurement accuracy of about 3\%. At momenta above $k_F$, the measured ${}^3$He/${}^3$H ratios differ from the calculation by $20\%-50\%$. Final state interaction (FSI) calculations using the generalized Eikonal Approximation indicate that FSI should change the ${}^3$He/${}^3$H cross-section ratio for this measurement by less than 5\%. If these calculations are correct, then the differences at large missing momenta between the ${}^3$He/${}^3$H experimental and calculated ratios could be due to the underlying $NN$ interaction, and thus could provide new constraints on the previously loosely-constrained short-distance parts of the $NN$ interaction.

   nucl-exnucl-thPLB(2019)·28 citations
4. 04*

   States of the ${}^{12}$C Nucleus in the Toroidal Configuration

   Cheuk-Yin Wong🇺🇸 · Andrzej Staszczak🇵🇱

   The ${}^{12}$C nucleus with $N$=6 and $Z$=6 is a doubly closed-shell nucleus in a toroidal potential. In the description of the ground state and the Hoyle state of ${}^{12}$C in the resonating group method or the generator coordinate method, a superposition of the orientations of Wheeler's triangular cluster on the cluster plane would naturally generate an intrinsic toroidal density. A toroidal state also has a probability amplitude to overlap with a 3-alpha cluster, which is the dominant decay mode for the Hoyle state. For these reasons, we study a toroidal description of the states of ${}^{12}$C in the toroidal configuration both phenomenologically and microscopically. A toroidal ${}^{12}$C nucleus distinguishes itself by toroidal particle-hole multiplet excitations between one toroidal single-particle shell to another. From such a signature and experimental data, we find phenomenologically that the Hoyle state and many of its higher excited states may be tentatively attributed to those of the ${}^{12}$C nucleus in a toroidal configuration. We then study the ${}^{12}$C system from a microscopic mean-field approximation using variational wave functions. We find that the equidensity surfaces of the ${}^{12}$C ground state exhibit a dense toroidal core immersed in lower-density oblate spheroids in the surface region. Furthermore, there are prominent toroidal features of the equidensity surfaces for the state at the Hoyle excitation energy, at which previous cluster model calculations indicate the presence of a 3-alpha cluster state. A toroidal coexistence model therefore may emerge to suggest the possibility that the physical Hoyle state may have probability amplitudes to be in the toroidal configuration and the 3-alpha cluster configuration.

   ↳ nucl-thastro-ph.SRnucl-ex1 citation
5. 05*

   Ultra-peripheral-collision studies in the fixed-target mode with the proton and lead LHC beams

   N. Yamanaka🇫🇷 · C. Hadjidakis🇫🇷 · D. Kikola🇵🇱 · J.P. Lansberg🇫🇷 · L. Massacrier🇫🇷 · M.G. Echevarria🇮🇹 · A. Kusina🇵🇱 · I. Schienbein🇫🇷 · J. Seixas🇵🇹 · H.S. Shao🇫🇷 · A. Signori🇺🇸 · B. Trzeciak🇳🇱 and 21 other authors

   We address the physics case related to the studies of ultra-peripheral pH, pPb, PbH, and PbPb collisions in the fixed-target mode at the LHC. In particular, we discuss how one can measure the gluon generalized parton distribution E_g(x,xi,t) in exclusive J/psi photoproduction with a transversely polarized hydrogen target.

   ↳ hep-exhep-phnucl-exnucl-thPoS(2019)·1 citation

* 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.