Wed·Sep 22, 2021Wednesday·September 22, 2021

1. 01*

   Differential measurements of jet substructure and partonic energy loss in Au$+$Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

   STAR Collaboration: M. S. Abdallah · B. E. Aboona · J. Adam · L. Adamczyk · J. R. Adams · J. K. Adkins · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · I. Alekseev · D. M. Anderson and 384 other authors

   The STAR collaboration presents jet substructure measurements related to both the momentum fraction and the opening angle within jets in \pp and \AuAu collisions at \sqrtsn $=200$ GeV. The substructure observables include SoftDrop groomed momentum fraction (\zg), groomed jet radius (\rg), and subjet momentum fraction (\zsj) and opening angle (\tsj). The latter observable is introduced for the first time. Fully corrected subjet measurements are presented for \pp collisions and are compared to leading order Monte Carlo models. The subjet \tsj~distributions reflect the jets leading opening angle and are utilized as a proxy for the resolution scale of the medium in \AuAu collisions. We compare data from \AuAu collisions to those from \pp which are embedded in minimum-bias \AuAu events in order to include the effects of detector smearing and the heavy-ion collision underlying event. The subjet observables are shown to be more robust to the background than \zg~and \rg. We observe no significant modifications of the subjet observables within the two highest-energy, back-to-back jets, resulting in a distribution of opening angles and the splittings that are vacuum-like. We also report measurements of the differential di-jet momentum imbalance ($A_{\mathrm{J}}$) for jets of varying \tsj. We find no qualitative differences in energy loss signatures for varying angular scales in the range $0.1<$ \tsj $<0.3$, leading to the possible interpretation that energy loss in this population of high momentum di-jet pairs, is due to soft medium-induced gluon radiation from a single color-charge as it traverses the medium.

   nucl-exhep-exPRC(2022)·43 citations
2. 02*

   System Size and Flavour Dependence of Chemical Freeze-out Temperatures in ALICE Data from pp, pPb and PbPb Collisions at LHC Energies

   Fernando Antonio Flor🇺🇸 · Gabrielle Olinger🇺🇸 · René Bellwied🇺🇸

   We present the system size and flavour dependence of the chemical freeze-out temperature ($T_{\mathrm{ch}}$) at vanishing baryo-chemical potential calculated via thermal fits to experimental yields for several multiplicity classes in pp, pPb and PbPb collisions measured by ALICE. Using the Thermal-FIST Hadron Resonance Gas model package, we compare the quality of fits across various treatments of strangeness conservation under different freeze-out conditions as a function of the charged particle multiplicity density $⟨d{N}_{\mathrm{ch}}/d\eta ⟩$. Additionally, we examine how the anti-hadron to pion yield ratios of light and strange baryons, as well as the $\varphi$ meson, evolve within a flavour-dependent model. Through a unique two-temperature chemical freeze-out approach, we show that flavour dependence of $T_{\mathrm{ch}}$ in a Strangeness Canonical Ensemble leads to a natural explanation of strangeness enhancement from small to large systems at LHC energies without requiring any non-equilibrium particle production at small $⟨d{N}_{\mathrm{ch}}/d\eta ⟩$.

   nucl-exhep-exhep-phnucl-thPLB(2022)·23 citations
3. 03*

   Measurement of charged-pion production in deep-inelastic scattering off nuclei with the CLAS detector

   S. Moran🇨🇱 · R. Dupre🇫🇷 · H. Hakobyan🇨🇱 · M. Arratia🇺🇸 · W. K. Brooks🇨🇱 · A. Borquez🇨🇱 · A. El Alaoui🇨🇱 · L. El Fassi🇺🇸 · K. Hafidi🇺🇸 · R. Mendez🇨🇱 · T. Mineeva🇨🇱 · S. J. Paul🇺🇸 and 132 other authors

   Background: Energetic quarks in nuclear DIS propagate through the nuclear medium. Processes that are believed to occur inside nuclei include quark energy loss through medium-stimulated gluon bremsstrahlung and intra-nuclear interactions of forming hadrons. More data are required to gain a more complete understanding of these effects. Purpose: To test the theoretical models of parton transport and hadron formation, we compared their predictions for the nuclear and kinematic dependence of pion production in nuclei. Methods: We have measured charged-pion production in semi-inclusive DIS off D, C, Fe, and Pb using the CLAS detector and the CEBAF 5.014 GeV electron beam. We report results on the nuclear-to-deuterium multiplicity ratio for ${\pi }^{+}$ and ${\pi }^{-}$ as a function of energy transfer, four-momentum transfer, and pion energy fraction or transverse momentum - the first three-dimensional study of its kind. Results: The ${\pi }^{+}$ multiplicity ratio is found to depend strongly on the pion fractional energy $z$, and reaches minimum values of $0.67\pm 0.03$, $0.43\pm 0.02$, and $0.27\pm 0.01$ for the C, Fe, and Pb targets, respectively. The $z$ dependences of the multiplicity ratios for ${\pi }^{+}$ and ${\pi }^{-}$ are equal within uncertainties for C and Fe targets but show differences at the level of 10$\%$ for the Pb-target data. The results are qualitatively described by the GiBUU transport model, as well as with a model based on hadron absorption, but are in tension with calculations based on nuclear fragmentation functions. Conclusions: These precise results will strongly constrain the kinematic and flavor dependence of nuclear effects in hadron production, probing an unexplored kinematic region. They will help to reveal how the nucleus reacts to a fast quark, thereby shedding light on its color structure, transport properties, and on the mechanisms of the hadronization process.

   nucl-exhep-exPRC(2022)·29 citations
4. 04*

   Warning: The mini gamma-ray-bursts in planning hadron colliders beyond the LHC energies

   Wei Zhu🇨🇳 · Zhiyi Cui🇨🇳 · Jianhong Ruan🇨🇳

   Gluons may converge to a stable state at a critical momentum in nucleon. This gluon condensation will greatly increase the proton-proton cross section provided that the collision energies exceed the gluon condensation threshold. Based on the analyses of cosmic gamma-ray spectra, we find that the $p-Pb$ and $Pb-Pb$ collisions at the LHC are close to the energy region of the gluon condensation effect. We warn that for the next generation of hadron colliders increasing the collision energies, the extremely strong gamma-rays will be emitted in a narrow space of the accelerator due to the gluon condensation effect. Such artificial mini gamma-ray-bursts in the laboratory may damage the detectors.

   ↳ hep-phastro-ph.HEhep-exnucl-ex0 citations
5. 05*

   $\alpha$-clustering effect on flows of direct photons in heavy-ion collisions

   Chen-Zhong Shi · Yu-Gang Ma🇨🇳

   In this work, we reconstruct the $\gamma$-photon energy spectrum which is in good agreement with the experimental data of ${}^{86}$Kr + ${}^{12}$C at $E/A$ = 44 MeV in the framework of our modified EQMD model. The directed flow and elliptic flow of free protons and direct photons have been investigated by taking $\alpha$-clustering structure of ${}^{12}$C into account. Comparing with the free proton, the direct photon flows give a clearer information about early stage of nuclear reaction. Difference of collective flows between different configurations of ${}^{12}$C is observed in this work. This indicates that collective flows of direct photons are sensitive to the initial configuration, therefore the $\gamma$ bremsstrahlung process might be taken as an alternative probe to investigate $\alpha$-clustering structure in light nucleus from heavy ion collisions at Fermi-energy region.

   ↳ nucl-thnucl-exNucl.Sci.Tech.(2021)·48 citations
6. 06*

   Lambda polarization in ${}^{108}$Ag +${}^{108}$Ag and ${}^{197}$Au +${}^{197}$Au collisions around a few GeV

   Xian-Gai Deng🇨🇳 · Xu-Guang Huang🇨🇳 · Yu-Gang Ma🇨🇳

   Within the framework of Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model, we extract the global spin polarization of $\Lambda$ hyperon in ${}^{108}$Ag + ${}^{108}$Ag and ${}^{197}$Au + ${}^{197}$Au collisions at $\sqrt{s_{\mathrm{NN}}}=2.42-62.4$ GeV. We use two different approaches to calculate the $\Lambda$ polarization $P_y$: approach I is based on equilibrium assumption so that $P_y$ is determined by thermal vorticity and approach II assumes a proportional relation between $P_y$ and the system's angular momentum in $\Lambda$'s rest frame. We find that both approaches can describe the experimental data at low energies around a few GeV but only approach I describes well also higher-energy data. This suggests that at higher energies the relativistic effect plays an important role. After taking into such effect properly, the relativity-improved approach II can describe the higher-energy data as well.

   ↳ nucl-thhep-phnucl-exPLB(2022)·48 citations
7. 07*

   Persistence of cluster structure in the ground state of ${}^{11}$B

   Naoyuki Itagaki🇯🇵 · Tomoya Naito🇯🇵 · Yuichi Hirata🇯🇵

   The persistence of $\alpha +\alpha +t$ cluster configuration in the ground state of ${}^{11}$B is discussed. The $\alpha$ particles emitted from excited states of ${}^{12}$C could be utilized for cancer treatment, where the cluster states are created by a clinical proton beam on the ${}^{11}$B target. Although the cross section has been already available, for the nuclear structure side, whether the ground state of ${}^{11}$B contains the seeds of the cluster states is a crucial question, since the cluster structure may be washed out by the spin-orbit interaction, which has been known as a driving force to break the $\alpha$ clusters. For this purpose, in addition to the basis states with cluster configurations, we include their breaking effects by employing the antisymmetrized quasi cluster model (AQCM). The inclusion of the breaking effect of $\alpha +\alpha +t$ cluster structure is found to contribute to the lowering of the ground-state energy by about 2 MeV. Assuming the typical three-$\alpha$ cluster state of ${}^{12}$C as an equilateral triangular configuration with the relative distances of $\approx 4$ fm, the ground state of ${}^{11}$B is found to have a certain squared overlap with such state when a proton approaches. The third $3/2^{-}$ state has been suggested as a cluster state both theoretically and experimentally, and we confirmed the well-developed clustering.

   ↳ nucl-thnucl-exPRC(2022)·4 citations
8. 08*

   Quantum gravitational states of ultracold neutrons as a tool for probing of beyond-Riemann gravity

   A. N. Ivanov🇦🇹 · M. Wellenzohn🇦🇹 · H. Abele🇦🇹

   We analyze a possibility to probe beyond-Riemann gravity (BRG) contributions, introduced by Kostelecky and Li (see Phys. Rev. D 103, 024059 (2021) and Phys. Rev. D 104, 044054 (2021)) on the basis of the Effective Field Theory (EFT) by Kostelecky Phys. Rev. D 69, 105009 (2004). We carry out such an analysis by calculating the BRG contributions to the transition frequencies of the quantum gravitational states of ultracold neutrons (UCNs). These states are being used for a test of interactions beyond the Standard Model (SM) and General Relativity (GR) in the qBOUNCE experiments. We improve by order of magnitude some constraints obtained by Kostelecky and Li (2106.11293 [gr-qc]).

   ↳ gr-qchep-phhep-thnucl-exPLB(2021)·23 citations
9. 09*

   Higher-Order Kinematical Effects in Deeply Virtual Compton Scattering

   Yuxun Guo🇺🇸 · Xiangdong Ji🇺🇸 · Kyle Shiells🇺🇸

   We study the deeply virtual Compton scattering cross-section in twist-two generalized parton distribution (GPD) approximation, and show that different choices of light-cone vectors and gauges for the final photon polarization will lead to different higher-order kinematical corrections to the cross-section formula. The choice of light-cone vectors affects kinematic corrections at the twist-three level, accounting for the differences between the cross-section formulas in the literature. On the other hand, kinematical corrections from higher-twist GPDs should eliminate the light-cone dependence at twist three. Those light-cone dependencies are studied systematically at JLab 12 GeV and future EIC kinematics. They serve as the intrinsic systematic uncertainties in extracting the Compton form factors through the cross-section formula. More importantly, they are also necessary for understanding cross-section measurements with higher-twist precision and to reconstruct higher-order Compton form factors.

   ↳ hep-phnucl-exnucl-thJHEP(2021)·26 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.