Thu·Aug 5, 2021Thursday·August 5, 2021

1. 01*

   Production of light nuclei in small collision systems with ALICE

   Chiara Pinto (for the ALICE Collaboration)🇮🇹

   The energy densities reached in high-energy hadronic collisions at the LHC allow significant production of light (anti)nuclei. Their production yields have been measured as a function of $p_{\mathrm{T}}$ and charged-particle multiplicity in different collision systems and at different center-of-mass energies by ALICE. One of the most interesting results obtained from such a large variety of experimental data is that the dominant production mechanism of light (anti)nuclei seems to depend solely on the event charged-particle multiplicity. Evidence for this comes from the continuous evolution of the deuteron-to-proton and ${}^3$He-to-proton ratios with the event multiplicity across different collision systems and energies. The characterization of the light nuclei production mechanism is complemented by measurements of their production yields in jets and in the underlying event. In this paper, recent results on light nuclei production in small collision systems are shown and discussed in the context of the statistical hadronization and coalescence models. In addition, recent results on the deuteron production in jets and new preliminary results on its production in the underlying event measured in pp collisions at $\sqrt{s}=$ 13 TeV are discussed.

   nucl-exhep-exEPJ Web Conf.(2022)·0 citations
2. 02*

   Investigation of the background in coherent $J/\psi$ production at the EIC

   Wan Chang🇨🇳 · Elke-Caroline Aschenauer🇺🇸 · Mark D. Baker🇺🇸 · Alexander Jentsch🇺🇸 · Jeong-Hun Lee🇺🇸 · Zhoudunming Tu🇺🇸 · Zhongbao Yin🇨🇳 · Liang Zheng🇨🇳

   Understanding various fundamental properties of nucleons and nuclei are among the most important scientific goals at the upcoming Electron-Ion Collider (EIC). With the unprecedented opportunity provided by the next-generation machine, the EIC might provide definitive answers to many standing puzzles and open questions in modern nuclear physics. Here we investigate one of the golden measurements proposed at the EIC, which is to obtain the spatial gluon density distribution within a lead ($Pb$) nucleus. The proposed experimental process is the exclusive $J/\psi$ vector-meson production off the $Pb$ nucleus - $e+Pb\to e^{\prime }+J/\psi +P{b}^{\prime }$. The Fourier transformation of the momentum transfer $|t|$ distribution of the coherent diffraction is the transverse gluon spatial distribution. In order to measure it, the experiment has to overcome an overwhelmingly large background arising from the incoherent diffractive production, where the nucleus $P{b}^{\prime }$ mostly breaks up into fragments of particles in the far-forward direction close to the hadron-going beam rapidity. In this paper, we systematically study the rejection of incoherent $J/\psi$ production by vetoing products from these nuclear breakups - protons, neutrons, and photons, which is based on the BeAGLE event generator and the most up-to-date EIC Far-forward Interaction Region design. The achieved vetoing efficiency, the ratio between the number of vetoed events and total incoherent events, ranges from about 80% - 99% depending on $|t|$, which can resolve at least the first minimum of the coherent diffractive distribution based on the Sar$t$re model. Experimental and accelerator machine challenges as well as potential improvements are discussed.

   nucl-exhep-exhep-phnucl-thPRD(2021)·28 citations
3. 03*

   Inclusive J/$\psi$ production at midrapidity in pp collisions at $\sqrt{s}=13$ TeV

   ALICE Collaboration

   We report on the inclusive J/$\psi$ production cross section measured at the CERN Large Hadron Collider in proton-proton collisions at a centre-of-mass energy $\sqrt{s}=13$ TeV. The J/$\psi$ mesons are reconstructed in the ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ decay channel and the measurements are performed at midrapidity ($|y|<0.9$) in the transverse-momentum interval $0<p_{\mathrm{T}}<40$ GeV/$c$, using a minimum-bias data sample corresponding to an integrated luminosity $L_{\text{int}}=32.2{\text{nb}}^{-1}$ and an Electromagnetic Calorimeter triggered data sample with $L_{\text{int}}=8.3{\mathrm{pb}}^{-1}$. The $p_{\mathrm{T}}$-integrated J/$\psi$ production cross section at midrapidity, computed using the minimum-bias data sample, is $\text{d}\sigma /\text{d}y{|}_{y=0}=8.97\pm 0.24(\text{stat})\pm 0.48(\text{syst})\pm 0.15(\text{lumi})\mu \text{b}$. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and $p_{\mathrm{T}}$-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models.

   nucl-exhep-exEPJC(2021)·35 citations
4. 04*

   Estimation of radiative half-life of ${}^{229m}$Th by half-life measurement of other nuclear excited states in ${}^{229}$Th

   Y. Shigekawa · A. Yamaguchi🇬🇧 · K. Suzuki · H. Haba🇯🇵 · T. Hiraki · H. Kikunaga · T. Masuda · S. Nishimura🇯🇵 · N. Sasao🇯🇵 · A. Yoshimi🇯🇵 · K. Yoshimura

   We perform coincidence measurements between $\alpha$ particles and $\gamma$ rays from a ${}^{233}$U source to determine the half-lives of the excited state in a ${}^{229}$Th nucleus. We first prove that the half-lives of 42.43- and 164.53-keV states are consistent with literature values, whereas that of the 97.14-keV state (93(7) ps) deviates from a previously measured value (147(12) ps). The half-lives of 71.83- and 163.25-keV states are determined for the first time. Based on the obtained half-lives and the Alaga rule, we estimate the radiative half-life of the low-energy isomeric state (${}^{229m}$Th) to be $5.0(11)\times 10^3$ s, which is one of the key parameters for the frequency standard based on ${}^{229}$Th.

   nucl-exphysics.atom-phPRC(2021)·12 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.