Wed·Sep 12, 2018Wednesday·September 12, 2018

1. 01*

   $J/\psi$ polarization in the CGC+NRQCD approach

   Yan-Qing Ma🇨🇳 · Tomasz Stebel🇵🇱 · Raju Venugopalan🇺🇸

   We compute the $J/\psi$ polarization observables ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$, ${\lambda }_{\theta \varphi }$ in a Color Glass Condensate (CGC) + nonrelativistic QCQ (NRQCD) formalism that includes contributions from both color singlet and color octet intermediate states. Our results are compared to low $p_T$ data on $J/\psi$ polarization from the LHCb and ALICE experiments on proton-proton collisions at center-of-mass energies of $\sqrt{s}=7$ TeV and 8 TeV. Our CGC+NRQCD computation provides a better description of data for $p_T\le 15$ GeV relative to extant next-to-leading (NLO) calculations within the collinear factorization framework. These results suggest that higher order computations in the CGC+NRQCD framework have the potential to greatly improve the accuracy of extracted values of the NRQCD universal long distance matrix elements.

   ↳ hep-phnucl-exnucl-thJHEP(2018)·47 citations
2. 02*

   Solar neutrinos with the JUNO experiment

   Giuseppe Salamanna🇮🇹

   The JUNO liquid scintillator-based experiment, construction of which is on-going in Jiangmen (China), will start operations in 2020 and will detect anti-neutrinos from nearby reactors; but also solar neutrinos via elastic scattering on electrons. Its physics goals are broad; its primary aim to measure the neutrino mass ordering demands to collect large statistics, which requires JUNO's 20 kt sensitive mass, and achieve an unprecedented energy resolution (3$\%/\sqrt{E}$). Thanks to these characteristics, JUNO is in a very good position to contribute to the solar neutrino studies in the line of previous experiments of similar technology. It will collect a large sample of neutrinos from ${}^7$Be and ${}^8$B. In particular, for ${}^7$Be the target energy resolution will provide a powerful tool to isolate the electron energy end point from backgrounds like ${}^{210}$Bi and ${}^{85}$Kr. At the same time, challenges will have to be faced mainly related to the reduction and estimation of the backgrounds. While a thorough LS purification campaign is being planned, the desired level of purification is less aggressive than e.g. in Borexino. Also, cosmogenic backgrounds such as cosmic ray muons traversing the relatively thin layer of ground above JUNO (700 m) and crossing the detector will need to be vetoed with dedicated techniques for the extraction of ${}^8$B. In my talk I reviewed JUNO's preliminary analysis strategy and challenges in the solar neutrino sector; and provided the current estimates of its solar neutrino and background yields, with related energy spectra, assuming two benchmark scenarios of scintillator radio-purity.

   ↳ physics.ins-dethep-exnucl-ex3 citations
3. 03*

   Energy dependent kinetic freeze-out temperature and transverse flow velocity in high energy collisions

   Li-Li Li🇨🇳 · Fu-Hu Liu🇨🇳

   Transverse momentum spectra of negative and positive pions produced at mid-(pseudo)rapidity in inelastic or non-single-diffractive proton-proton collisions and in central nucleus-nucleus collisions over an energy range from a few GeV to above 10 TeV are analyzed by a (two-component) blast-wave model with Boltzmann-Gibbs statistics and with Tsallis statistics respectively. The model results are in similarly well agreement with the experimental data measured by a few productive collaborations who work at the Heavy Ion Synchrotron (SIS), Super Proton Synchrotron (SPS), Relativistic Heavy Ion Collider (RHIC), and Large Hadron Collider (LHC), respectively. The energy dependent kinetic freeze-out temperature and transverse flow velocity are obtained and analyzed. Both the quantities have quick increase from the SIS to SPS, and slight increase or approximate invariability from the top RHIC to LHC. Around the energy bridge from the SPS to RHIC, the considered quantities in proton-proton collisions obtained by the blast-wave model with Boltzmann-Gibbs statistics show more complex energy dependent behavior comparing with the results in other three cases.

   ↳ hep-phhep-exnucl-exnucl-thEPJA(2018)·27 citations
4. 04*

   Production of Light Nuclei at Thermal Freezeout in Heavy-Ion Collisions

   Xinyuan Xu🇺🇸 · Ralf Rapp🇺🇸

   We revisit the problem of the production of light atomic nuclei in ultrarelativistic heavy-ion collisions. While their production systematics is well produced by hadro-chemical freezeout at temperatures near the QCD pseudo-critical temperature, their small binding energies of a few MeV per nucleon suggest that they cannot survive as bound states under these conditions. Here, we adopt the concept of effective chemical potentials in the hadronic evolution from chemical to thermal freezeout (at typically $T_{\mathrm{fo}}$$\simeq$100\,MeV), which, despite frequent elastic rescatterings in hadronic matter, conserves the effective numbers of particles which are stable under strong interactions, most notably pions, kaons and nucleons. It turns out that the large chemical potentials that build up for antibaryons result in thermal abundances of light nuclei and antinuclei, formed at thermal freezeout, which essentially agree with the ones evaluated at chemical freezeout. Together with their transverse-momentum spectra, which also indicate a kinetic freezeout near $T_{\mathrm{fo}}$, this provides a natural explanation for their production systematics without postulating their survival at high temperatures.

   ↳ nucl-thhep-phnucl-exEPJA(2019)·34 citations
5. 05*

   Polarization observables in $e^{+}{e}^{-}$ annihilation to a baryon-antibaryon pair

   Elisabetta Perotti🇸🇪 · Göran Fäldt🇸🇪 · Andrzej Kupść🇸🇪 · Stefan Leupold (Uppsala U.)🇸🇪 · Jiao Jiao Song (Shandong U. and Beijing, Inst. High Energy Phys.)🇨🇳

   Using the helicity formalism of Jacob and Wick we derive spin density matrices of baryon antibaryon pairs produced in $e^{+}{e}^{-}$ annihilation. We consider the production of pairs with spins $1/2+\overline{1/2}$, $1/2+\overline{3/2}$ (+c.c.) and $3/2+\overline{3/2}$. We provide modular expressions to include chains of weak hadronic two-body decays of the produced hyperons. The expressions are suitable for the analysis of high statistics data from $J/\psi$ and $\psi (2S)$ decays at $e^{+}{e}^{-}$ colliders, by fits to the fully differential angular distributions of the measured particles. We illustrate the method by examples, such as the inclusive measurement of the $e^{+}{e}^{-}\to \psi (2S)\to {\Omega }^{-}{\bar{\Omega }}^{+}$ process where one decay chain ${\Omega }^{-}\to \Lambda K^{-}$ followed by $\Lambda \to p{\pi }^{-}$ is considered. Finally we show that the inclusive angular distributions can be used to test spin assignment of the produced baryons.

   ↳ hep-phhep-exnucl-exPRD(2019)·118 citations
6. 06*

   First ultracold neutrons produced at TRIUMF

   S. Ahmed🇨🇦 · E. Altiere🇨🇦 · T. Andalib🇨🇦 · B. Bell🇨🇦 · C. P. Bidinosti🇨🇦 · E. Cudmore🇨🇦 · M. Das🇨🇦 · C. A. Davis🇨🇦 · B. Franke🇨🇦 · M. Gericke🇨🇦 · P. Giampa🇨🇦 · P. Gnyp🇨🇦 and 41 other authors

   We installed a source for ultracold neutrons at a new, dedicated spallation target at TRIUMF. The source was originally developed in Japan and uses a superfluid-helium converter cooled to 0.9K. During an extensive test campaign in November 2017, we extracted up to 325000 ultracold neutrons after a one-minute irradiation of the target, over three times more than previously achieved with this source. The corresponding ultracold-neutron density in the whole production and guide volume is 5.3cm${}^{-3}$. The storage lifetime of ultracold neutrons in the source was initially 37s and dropped to 24s during the eighteen days of operation. During continuous irradiation of the spallation target, we were able to detect a sustained ultracold-neutron rate of up to 1500s${}^{-1}$. Simulations of UCN production, UCN transport, temperature-dependent UCN yield, and temperature-dependent storage lifetime show excellent agreement with the experimental data and confirm that the ultracold-neutron-upscattering rate in superfluid helium is proportional to $T^7$.

   ↳ physics.ins-detnucl-exPRC(2019)·57 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.