Tue·Sep 14, 2021Tuesday·September 14, 2021

1. 01*

   ${\mathrm{\Lambda }}_{\mathrm{c}}^{+}$ production cross section in pp and p--Pb collisions down to $p_{\mathrm{T}}$ = 0 at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV measured with ALICE

   Annalena Sophie Kalteyer (for the ALICE Collaboration)🇩🇪

   The open heavy-flavour hadron measurements in proton--proton and proton--lead collisions give insight into the charm production and hadronization mechanisms. In this contribution, the latest measurements of the production cross section of prompt ${\Lambda }_{\mathrm{c}}^{+}$ and its charge conjugate performed with the ALICE detector at midrapidity in pp, and the new measurement of ${\Lambda }_{\mathrm{c}}^{+}\to \mathrm{p}{\mathrm{K}}_{\mathrm{S}}^0$ performed down to $p_{\mathrm{T}}=0$ in p--Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV are presented. We also present the first ALICE measurement of the baryon-to-meson ratio ${\Lambda }_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ and the ${\Lambda }_{\mathrm{c}}^{+}$ nuclear modification factor $R_{\mathrm{pPb}}$ down to $p_{\mathrm{T}}$ = 0 in p--Pb collisions. The ${\Lambda }_{\mathrm{c}}^{+}/{\mathrm{D}}^0$ ratio at midrapidity at the LHC is significantly higher than the one in ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ collisions, suggesting that the fragmentation of charm is not universal across different collision systems. The results are compared with theoretical calculations.

   nucl-exhep-exPoS(2021)·0 citations
2. 02*

   Remeasuring the anomalously enhanced $B(E2;2^{+}\to 1^{+})$ in ${}^8\mathrm{Li}$

   S. L. Henderson · T. Ahn🇺🇸 · P. J. Fasano🇺🇸 · A. E. McCoy🇨🇦 · S. Aguilar · D. T. Blankstein · L. Caves · A. C. Dombos🇺🇸 · R. K. Grzywacz🇺🇸 · K. L. Jones · S. Jin🇨🇳 · R. Kelmar and 5 other authors

   The large reported $E2$ strength between the $2^{+}$ ground state and $1^{+}$ first excited state of $\text{isotope}[8]Li$, $B(E2;2^{+}\to 1^{+})=55(15)e^2{\text{fm}}^4$, presents a puzzle. Unlike in neighboring $A=7\text{–}9$ isotopes, where enhanced $E2$ strengths may be understood to arise from deformation as rotational in-band transitions, the $2^{+}\to 1^{+}$ transition in ${}^8$Li cannot be understood in any simple way as a rotational in-band transition. Moreover, the reported strength exceeds \textit{ab initio} predictions by an order of magnitude. In light of this discrepancy, we revisited the Coulomb excitation measurement of this strength, now using particle-$\gamma$ coincidences, yielding a revised $B(E2;2^{+}\to 1^{+})$ of $19{(}_{-6}^{+7})(2)$~e${}^2$fm${}^4$. We explore how this value compares to what might be expected in the limits of rotational models. While the present value is about a factor of three smaller than previously reported, it remains anomalously enhanced.

   nucl-exnucl-thPRC(2024)·4 citations
3. 03*

   Search for rare alpha and double beta decays of Yb isotopes to excited levels of daughter nuclei

   M. Laubenstein🇮🇹 · B. Lehnert🇺🇸 · S. S. Nagorny🇨🇦 · S. Schönert🇩🇪

   A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra-low background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb${}_2$(C${}_2$O${}_4$)${}_3$ powder sample was measured for 11.3~d with a total Yb exposure of 1.25 kg$\times$d. Half-life limits for $\alpha$-decay modes of ${}^{168}$Yb, ${}^{170}$Yb, ${}^{171}$Yb, ${}^{172}$Yb, ${}^{173}$Yb, ${}^{174}$Yb and ${}^{176}$Yb into the first excited states have been obtained between $6\times 10^{14}$ yr and $2\times 10^{16}$ yr. These are the first experimental constraints of these decay modes. Double electron capture of ${}^{168}$Yb and double beta decay of ${}^{176}$Yb into the first excited 2${}^{+}$ and 0${}^{+}$ states could be excluded with limits between $1\times 10^{14}$ yr to $8\times 10^{16}$ yr. This improves the experimental information on some of the decay modes compared to previous constraints.

   nucl-exEPJC(2022)·4 citations
4. 04*

   Off-of-equilibrium effects on Kurtosis Along Strangeness-Neutral Trajectories

   Travis Dore🇺🇸 · Jamie Karthein🇺🇸 · Debora Mroczek🇺🇸 · Paolo Parotto🇩🇪 · Jacquelyn Noronha-Hostler🇺🇸 · Claudia Ratti🇺🇸

   The Beam Energy Scan program at the Relativistic Heavy Ion Collider (RHIC) is searching for the QCD critical point. The main signal for the critical point is the kurtosis of the distribution of proton yields obtained on an event-by-event basis where one expects a peak at the critical point. However, its exact behavior is still an open question due to out-of-equilibrium effects and uncertainty in the equation of state. Here we use a simplistic hydrodynamic model that enforces strangeness-neutrality, selecting trajectories that pass close to the critical point. We vary the initial conditions to estimate the effect of out-of-equilibrium hydrodynamics on the kurtosis signal.

   ↳ nucl-thhep-phnucl-exEPJ Web Conf.(2022)·4 citations
5. 05*

   Apparent strangeness enhancement from multiplicity selection in high energy proton-proton collisions

   Constantin Loizides (ORNL)🇺🇸 · Andreas Morsch (CERN)🇨🇭

   The increase of strange-particle yields relative to pions versus charged-particle multiplicity in proton-proton (pp) collisions at the LHC is usually described by microscopic or hydrodynamical models as a result of the increasing density of produced partons or strings and their interactions. Instead, we consider the multiple partonic interaction (MPI) picture originally developed in the context of the PYTHIA event generator. We find that strangeness enhancement in PYTHIA is hidden by a large excess of low-$p_{\mathrm{T}}$ multi-strange baryons, which mainly results from the hadronization of $u$-quark, $d$-quark and gluon ($udg$) strings. Strange baryons produced in strings formed from parton showers initiated by strange quarks ($s$-fragmentation), however, describe well the spectral shapes of $\Xi$ and $\Omega$ baryons and their multiplicity dependence. Since the total particle yield contains contributions from soft and hard particle production, which cannot be experimentally separated, we argue that the correct description of the $p_{\mathrm{T}}$-spectra is a minimum requirement for meaningful comparisons of multiplicity dependent yield measurements to MPI based calculations. We demonstrate that the $s$-fragmentation component describes the increase of average $p_{\mathrm{T}}$ and yields with multiplicity seen in the data, including the approximate multiplicity scaling for different collision energies. When restricted to processes that reproduce the measured $p_{\mathrm{T}}$-spectra, the MPI framework exhibits a smooth evolution from strictly proportional multiplicity scaling ($K_{\mathrm{S}}^0$, $\Lambda$, where the $udg$-hadronization component dominates) to linearity ($s$-fragmentation) and on to increasingly non-linear behavior ($c$-, $b$-quark and high-$p_{\mathrm{T}}$ jet fragmentation), hence providing a unified approach for particle production in pp collisions.

   ↳ hep-phhep-exnucl-ex9 citations
6. 06*

   Transverse momentum analysis of collective motion in relativistic nuclear collisions

   P. Danielewicz🇺🇸 · G. Odyniec (LBL)🇺🇸

   Novel transverse-momentum technique is used to analyse charged-particle exclusive data for collective motion in the Ar+KCl reaction at 1.8 GeV/nucl. Previous analysis of this reaction, employing the standard sphericity tensor, revealed no significant effect. In the present analysis, collective effects are observed, and they are substantially stronger than in the Cugnon cascade model, but weaker than in the hydrodynamical model.

   ↳ nucl-thnucl-exPLB(1985)·504 citations
7. 07*

   Redesigning the Jefferson Lab Hall A Beam Line for High Precision Parity Experiments

   Jay Benesch🇺🇸 · Yves Roblin🇺🇸

   The Continuous Electron Beam Accelerator Facility (CEBAF) was built with a thermionic electron source and the three original experimental hall lines reflected this. A few years after beam delivery began a parity violation experiment was approved and two polarimeters were installed in the Hall A beam line without consultation with the accelerator physics group. The beam raster system was placed after the new Compton polarimeter, before one accelerator quadrupole and four quadrupoles in the new Moller polarimeter. It was very difficult to meet experimental requirements on envelope functions and raster shape with this arrangement so a member of the accelerator physics group had a sixth quadrupole installed downstream of the Moller polarimeter. All of the parity experiments in Hall A have been run with this still-unsatisfactory configuration. The MOLLER experiment is predicated on achieving a 2% error on a 32 ppb asymmetry. Beam line changes are required to meet the systematic error budget. This paper documents the existing beam line, an interim change which can be accomplished during a annual maintenance down, and the final configuration for MOLLER and subsequent experiments.

   ↳ physics.acc-phnucl-exphysics.ins-detJINST(2021)·2 citations
8. 08*

   Quenching of Gamow-Teller strengths and two particle -- two hole configurations

   Danilo Gambacurta🇮🇹 · Marcella Grasso🇫🇷

   We apply the charge-exchange subtracted second random-phase approximation (SSRPA), based on Skyrme functionals, to investigate Gamow-Teller resonances in several closed-shell and closed-subshell nuclei, located in different regions of the nuclear chart. After having discussed the SSRPA findings obtained within different approximation schemes in ${}^{48}$Ca, we compare our results with {\it{ab-initio}} coupled-cluster predictions available for C and O isotopes, where two-body currents are included. Our integrated strenghts, obtained by using one-body transition operators, are lower compared to the corresponding {\it{ab-initio}} results. This indicates that, within our model, quenching effects are mainly driven by the inclusion of two particle - two hole configurations and that the role of a two-body contribution in the transition operator is less important than in the coupled-cluster approach. By analyzing heavier nuclei, ${}^{90}$ Zr and ${}^{132}$Sn, we confirm the same conclusions that we have recently drawn for ${}^{48}$Ca: the inclusion of two particle - two hole configurations is very effective in our model for providing strengths which are significantly more quenched than in other theoretical models and, thus, in better agreement with the experimental measurements. This occurs because two particle - two hole configurations have a density which strongly increases with the excitation energy. Their inclusion thus pushes a significant amount of the strength to higher energies, compared to what happens in other theoretical models, reducing in this way the cumulative sum of the strength up to excitation energies around 20-30 MeV.

   ↳ nucl-thnucl-exPRC(2022)·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.