Mon·Sep 28, 2020Monday·September 28, 2020

1. 01*

   Investigating Hard Splittings via Jet Substructure in pp and Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV with ALICE

   Raymond Ehlers · for the ALICE Collaboration

   Jets lose energy as they propagate through the Quark-Gluon Plasma, modifying their parton shower. Jet substructure, which provides access to the evolution of jet splittings, is expected to be sensitive to interactions between the medium and the jet, providing the opportunity to further constrain both jet and medium properties. By utilizing grooming techniques, we can focus on the most pertinent hard splittings. Of particular interest is the search for large transverse momentum kicks which may indicate the presence of point-like scatters within the Quark-Gluon Plasma. We explore the jet substructure of inclusive jets in pp and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, utilizing Soft Drop and other grooming methods, as well as the Lund Plane, in order to access the hardest jet splitting, with a particular focus on the hardest $k_{\mathrm{T}}$ splitting.

   nucl-exPoS(2021)·6 citations
2. 02*

   Experimental search for an exotic spin-spin-velocity-dependent interaction using an optically polarized vapor and a rare-earth iron garnet

   P.-H. Chu🇺🇸 · Y. J. Kim🇰🇷 · S. Newman · I. Savukov🇺🇸 · J. C. Long🇺🇸

   We report an experimental search for an exotic spin-spin-velocity-dependent interaction between polarized electrons of Rb atoms and polarized electrons of a solid-state mass, violating both the time-reversal and parity symmetries. This search targets a minute effective magnetic field induced by the interaction. A spin-exchange relaxation-free (SERF) magnetometer based on an optically polarized Rb vapor is the key element for both a source of polarized electrons and a high-sensitivity detector. A dysprosium iron garnet (DyIG) serves as the polarized mass, with an extremely small magnetization at the critical temperature around 240 K and a high spin density. To reduce the magnetization, one of major systematic effects, a home-built cooling system controls the mass temperature. To our knowledge, this is the first search for an exotic spin-dependent interaction using the compensated ferrimagnet DyIG as a polarized mass. The experiment set the most stringent limit on the electron-electron coupling strength in the centimeter interaction range, in particular $g_V^e{g}_V^e<10^4$ at $\lambda =2$ cm.

   nucl-exphysics.ins-det2 citations
3. 03*

   Diffusion Monte Carlo calculations of fully-heavy (multiquark) bound states

   M.C. Gordillo🇪🇸 · F. De Soto🇪🇸 · J. Segovia🇪🇸

   We use a diffusion Monte Carlo method to solve the many-body Schrödinger equation describing fully-heavy tetraquark systems. This approach allows to reduce the uncertainty of the numerical calculation at the percent level, accounts for multi-particle correlations in the physical observables, and avoids the usual quark-clustering assumed in other theoretical techniques applied to the same problem. The interaction between particles was modeled by the most general and accepted potential, i.e. a pairwise interaction including Coulomb, linear-confining and hyperfine spin-spin terms. This means that, in principle, our analysis should provide some rigorous statements about the mass location of the all-heavy tetraquark ground states, which is particularly timely due to the very recent observation made by the LHCb collaboration of some enhancements in the invariant mass spectra of $J/\psi$-pairs. Our main results are: (i) the $cc\bar{c}\bar{c}$, $cc\bar{b}\bar{b}$ ($bb\bar{c}\bar{c}$) and $bb\bar{b}\bar{b}$ lowest-lying states are located well above their corresponding meson-meson thresholds; (ii) the $J^{PC}=0^{++}$ $cc\bar{c}\bar{c}$ ground state with preferred quark-antiquark pair configurations is compatible with the enhancement(s) observed by the LHCb collaboration; (iii) our results for the $cc\bar{c}\bar{b}$ and $bb\bar{c}\bar{b}$ sectors seem to indicate that the $0^{+}$ and $1^{+}$ ground states are almost degenerate with the $2^{+}$ located around $100\text{MeV}$ above them; (iv) smaller mass splittings for the $cb\bar{c}\bar{b}$ system are predicted, with absolute mass values in reasonable agreement with other theoretical works; (v) the $1^{++}$ $cb\bar{c}\bar{b}$ tetraquark ground state lies at its lowest $S$-wave meson-meson threshold and it is compatible with a molecular configuration.

   ↳ hep-phhep-exhep-latnucl-ex+1PRD(2020)·101 citations
4. 04*

   Kinetic energy dissipation and fluctuations in strongly-damped heavy-ion collisions within the stochastic mean-field approach

   Sakir Ayik🇺🇸 · Kazuyuki Sekizawa🇯🇵

   Background: Microscopic mean-field approaches have been successful in describing the most probable reaction outcomes in low-energy heavy-ion reactions. However, those approaches are known to severely underestimate dispersions of observables around the average values that has limited their applicability. Recently it has been shown that a quantal transport approach based on the stochastic mean-field (SMF) theory significantly improves the description, while its application has been limited so far to fragment mass and charge dispersions. Purpose: In this work, we extend the quantal transport approach based on the SMF theory for relative kinetic energy dissipation and angular momentum transfer in low-energy heavy-ion reactions. Results: As the first application of the proposed formalism, we consider the radial linear momentum dispersion, neglecting the coupling between radial and angular momenta. We analyze the total kinetic energy (TKE) distribution of binary reaction products in the ${}^{136}$Xe+${}^{208}$Pb reaction at $E_{c.m.}=526$ MeV and compare with experimental data. From time evolution of single-particle orbitals in TDHF, the radial diffusion coefficient is computed on a microscopic basis, while a phenomenological treatment is introduced for the radial friction coefficient. By solving the quantal diffusion equation for the radial linear momentum, the dispersion of the radial linear momentum is obtained, from which one can construct the TKE distribution. We find that the calculations provide a good description of the TKE distribution for large values of energy losses, TKEL $\gtrsim$ 150 MeV. However, the calculations underestimate the TKE distribution for smaller energy losses. Further studies are needed to improve the technical details of calculations. (Shortened due to the word limit)

   ↳ nucl-thnucl-exPRC(2020)·15 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.