Fri·Sep 1, 2023Friday·September 1, 2023

1. 01*

   Search for a neutron dark decay in ${}^6$He

   M. Le Joubioux · H. Savajols · W. Mittig · X. Fléchard · L. Hayen · Yu. E. Penionzhkevich · D. Ackermann · C. Borcea · L. Caceres · P. Delahaye · F. Didierjean · S. Franchoo and 15 other authors

   Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of ${}^6$He into ${}^4$He $+$ $n$ + $\chi$ provides an exceptionally clean detection signature when combined with a high efficiency neutron detector. Using a high-intensity ${}^6$He${}^{+}$ beam at GANIL, a search for a coincident neutron signal resulted in an upper limit on a dark decay branching ratio of Br${}_{\chi }\le 4.0\times 10^{-10}$ (95\% C.L.). Using the dark neutron decay model proposed originally by Fornal and Grinstein, we translate this into an upper bound on a dark neutron branching ratio of $\mathcal{O}(10^{-5})$, improving over global constraints by one to several orders of magnitude depending on $m_{\chi }$.

   nucl-exPRL(2024)·10 citations
2. 02*

   Measurements of long-range two-particle correlation over a wide pseudorapidity range in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   Correlations in azimuthal angle extending over a long range in pseudorapidity between particles, usually called the "ridge" phenomenon, were discovered in heavy-ion collisions, and later found in pp and p$-$Pb collisions. In large systems, they are thought to arise from the expansion (collective flow) of the produced particles. Extending these measurements over a wider range in pseudorapidity and final-state particle multiplicity is important to understand better the origin of these long-range correlations in small-collision systems. In this Letter, measurements of the long-range correlations in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV are extended to a pseudorapidity gap of $\Delta \eta \sim 8$ between particles using the ALICE, forward multiplicity detectors. After suppressing non-flow correlations, e.g., from jet and resonance decays, the ridge structure is observed to persist up to a very large gap of $\Delta \eta \sim 8$ for the first time in p$-$Pb collisions. This shows that the collective flow-like correlations extend over an extensive pseudorapidity range also in small-collision systems such as p$-$Pb collisions. The pseudorapidity dependence of the second-order anisotropic flow coefficient, $v_2(\eta )$, is extracted from the long-range correlations. The $v_2(\eta )$ results are presented for a wide pseudorapidity range of $-3.1<\eta <4.8$ in various centrality classes in p$-$Pb collisions. To gain a comprehensive understanding of the source of anisotropic flow in small-collision systems, the $v_2(\eta )$ measurements are compared to hydrodynamic and transport model calculations. The comparison suggests that the final-state interactions play a dominant role in developing the anisotropic flow in small-collision systems.

   nucl-exhep-exJHEP(2024)·15 citations
3. 03*

   Multiplicity and event-scale dependent flow and jet fragmentation in pp collisions at $\sqrt{s}$ = 13 TeV and in p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   Long- and short-range correlations for pairs of charged particles are studied via two-particle angular correlations in pp collisions at $\sqrt{s}=13$ TeV and p$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV. The correlation functions are measured as a function of relative azimuthal angle $\Delta \phi$ and pseudorapidity separation $\Delta \eta$ for pairs of primary charged particles within the pseudorapidity interval $|\eta |<0.9$ and the transverse-momentum interval $1<p_{\mathrm{T}}<4$ GeV/$c$. Flow coefficients are extracted for the long-range correlations ($1.6<|\Delta \eta |<1.8$) in various high-multiplicity event classes using the low-multiplicity template fit method. The method is used to subtract the enhanced yield of away-side jet fragments in high-multiplicity events. These results show decreasing flow signals toward lower multiplicity events. Furthermore, the flow coefficients for events with hard probes, such as jets or leading particles, do not exhibit any significant changes compared to those obtained from high-multiplicity events without any specific event selection criteria. The results are compared with hydrodynamic-model calculations, and it is found that a better understanding of the initial conditions is necessary to describe the results, particularly for low-multiplicity events.

   nucl-exhep-exJHEP(2024)·21 citations
4. 04*

   Azimuthal angle correlations of muons produced via heavy-flavor decays in 5.02 TeV Pb+Pb and $pp$ collisions with the ATLAS detector

   ATLAS Collaboration

   Angular correlations between heavy-quarks provide a unique probe of the quark-gluon plasma created in ultra-relativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy-quarks produced in 5.02 TeV Pb+Pb and $pp$ collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying $p_{\mathrm{T}}^{\mu }>4$ GeV and $|{\eta }^{\mu }|<2.4$, respectively. The distributions of azimuthal angle separation, $\Delta \varphi$, for muon pairs having pseudorapidity separation $|\Delta \eta |>0.8$, are measured in different Pb+Pb centrality intervals and compared to the same distribution measured in $pp$ collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all $\Delta \varphi$ distributions at $\Delta \varphi \sim \pi$, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the $\Delta \varphi$ distributions, are found to not vary significantly as a function of Pb+Pb collision centrality and are similar for $pp$ and Pb+Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma.

   nucl-exhep-exPRL(2024)·9 citations
5. 05*

   Measurements of ${\pi }^{\pm }$, $K^{\pm }$, $p$ and $\bar{p}$ spectra in ${}^{40}$Ar+${}^{45}$Sc collisions at 13$A$ to 150$A$ GeV/$c$

   NA61/SHINE Collaboration: H. Adhikary🇵🇱 · P. Adrich🇵🇱 · K.K. Allison🇺🇸 · N. Amin🇩🇪 · E.V. Andronov · T. Antićić🇭🇷 · I.-C. Arsene🇳🇴 · M. Bajda🇵🇱 · Y. Balkova🇵🇱 · M. Baszczyk🇵🇱 · D. Battaglia🇺🇸 · A. Bazgir🇵🇱 and 142 other authors

   The NA61/SHINE experiment at the CERN Super Proton Synchrotron studies the onset of deconfinement in strongly interacting matter through a beam energy scan of particle production in collisions of nuclei of varied sizes. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of ${\pi }^{\pm }$, $K^{\pm }$, $p$ and $\bar{p}$ produced in ${}^{40}$Ar+${}^{45}$Sc collisions at beam momenta of 13$A$, 19$A$, 30$A$, 40$A$, 75$A$ and 150$A$~\GeVc. The analysis uses the 10\% most central collisions, where the observed forward energy defines centrality. The energy dependence of the $K^{\pm }$/${\pi }^{\pm }$ ratios as well as of inverse slope parameters of the $K^{\pm }$ transverse mass distributions are placed in between those found in inelastic $p$+$p$ and central Pb+Pb collisions. The results obtained here establish a system-size dependence of hadron production properties that so far cannot be explained either within statistical or dynamical models.

   nucl-exhep-exEPJC(2024)·45 citations
6. 06*

   Dielectron production in central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The first measurement of the e${}^{+}$e${}^{-}$ pair production at midrapidity and low invariant mass in central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at the LHC is presented. The yield of e${}^{+}$e${}^{-}$ pairs is compared with a cocktail of expected hadronic decay contributions in the invariant mass ($m_{\mathrm{ee}}$) and pair transverse momentum ($p_{\mathrm{T},\mathrm{ee}}$) ranges $m_{\mathrm{ee}}<3.5$ GeV$/c^2$ and $p_{\mathrm{T},\mathrm{ee}}<8$ GeV$/c$. For $0.18<m_{\mathrm{ee}}<0.5$ GeV$/c^2$ the ratio of data to the cocktail of hadronic contributions amounts to $1.40\pm 0.11(stat.)\pm 0.23(syst.)\pm 0.16(\mathrm{cocktail})$ and $1.42\pm 0.11(stat.)\pm 0.23(syst.{)}_{-0.29}^{+0.24}(\mathrm{cocktail})$, including or not including medium effects in the estimation of the heavy-flavor background, respectively. It is consistent with predictions from two different models for an additional contribution of thermal e${}^{+}$e${}^{-}$ pairs from the hadronic and partonic phases. In the intermediate-mass range ($1.2<m_{\mathrm{ee}}<2.6$ GeV$/c^2$), the pair transverse impact parameter of the e${}^{+}$e${}^{-}$ pairs (DCA${}_{\mathrm{ee}}$) is used for the first time in Pb$-$Pb collisions to separate displaced dielectrons from heavy-flavor hadron decays from a possible (thermal) contribution produced at the interaction point. The data are consistent with a suppression of e${}^{+}$e${}^{-}$ pairs from $\mathrm{c}\overline{\mathrm{c}}$ and an additional prompt component. Finally, the first direct-photon measurement in the 10\% most central Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported via the study of virtual direct photons in the transverse momentum range $1<p_{\mathrm{T}}<5$ GeV$/c$. A model including prompt photons, as well as photons from the pre-equilibrium and fluid-dynamic phases, can reproduce the result, while being at the upper edge of the data uncertainties.

   nucl-exhep-exPRC(2025)·35 citations
7. 07*

   Measurements of longitudinal flow decorrelations in $pp$ and Xe+Xe collisions with the ATLAS detector

   ATLAS Collaboration

   Measurements of longitudinal flow decorrelations in 13 TeV $pp$ and 5.44 TeV Xe+Xe collisions with the ATLAS detector are presented. The measurements are performed using the two-particle correlation method, combining charged-particle tracks within $|\eta |<2.5$ with either calorimeter energy clusters or towers within $4.0<|\eta |<4.9$. A template-based subtraction procedure is used to remove non-flow effects in both the $pp$ and the Xe+Xe analyses. The dependence of the longitudinal flow decorrelations on the pseudorapidity separation between the particles is characterized via the slope parameter $F_n$ for the elliptic ($n=2$) and triangular ($n=3$) harmonic moments. The results are reported as a function of charged-particle multiplicity for the $pp$ and Xe+Xe collision systems. Comparing the data to a color string-based model of the initial geometry indicates that in $pp$ and peripheral Xe+Xe collisions, sub-nucleonic structure and fluctuations in longitudinal energy deposition are needed to describe the data.

   nucl-exhep-ex11 citations
8. 08*

   Upper Limit on the Chiral Magnetic Effect in Isobar Collisions at the Relativistic Heavy-Ion Collider

   STAR Collaboration: M. I. Abdulhamid · B. E. Aboona · J. Adam · J. R. Adams · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · A. Aitbaev · I. Alekseev · E. Alpatov · A. Aparin and 345 other authors

   The chiral magnetic effect (CME) is a phenomenon that arises from the QCD anomaly in the presence of an external magnetic field. The experimental search for its evidence has been one of the key goals of the physics program of the Relativistic Heavy-Ion Collider. The STAR collaboration has previously presented the results of a blind analysis of isobar collisions (${}_{44}^{96}\text{Ru}+{}_{44}^{96}\text{Ru}$, ${}_{40}^{96}\text{Zr}+{}_{40}^{96}\text{Zr}$) in the search for the CME. The isobar ratio ($Y$) of CME-sensitive observable, charge separation scaled by elliptic anisotropy, is close to but systematically larger than the inverse multiplicity ratio, the naive background baseline. This indicates the potential existence of a CME signal and the presence of remaining nonflow background due to two- and three-particle correlations, which are different between the isobars. In this post-blind analysis, we estimate the contributions from those nonflow correlations as a background baseline to $Y$, utilizing the isobar data as well as Heavy Ion Jet Interaction Generator simulations. This baseline is found consistent with the isobar ratio measurement, and an upper limit of 10% at 95% confidence level is extracted for the CME fraction in the charge separation measurement in isobar collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV.

   nucl-exnucl-thPRResearch(2024)·26 citations
9. 09*

   Measurement of the centrality dependence of the dijet yield in $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}$ = 8.16 TeV with the ATLAS detector

   The ATLAS Collaboration

   The measurement of hard scatterings in proton-nucleus collisions has resulted in a greater understanding of both the proton and nuclear structure. ATLAS measured the centrality dependence of the dijet yield using 165 nb${}^{-1}$ of $p$+Pb data collected at $\sqrt{s_{{}_{\text{NN}}}}$ = 8.16 TeV in 2016. The event centrality, which reflects the $p$+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, $R_{\mathrm{CP}}$, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The $R_{\mathrm{CP}}$ shows a scaling with the Bjorken-$x$ of the parton originating from the proton, $x_p$, while no such trend is observed as a function of $x_{\mathrm{Pb}}$. This analysis provides unique input to understanding the role of small proton spatial configurations in $p$+Pb collisions by covering parton momentum fractions from the valence region down to $x_p\sim 10^{-3}$ and $x_{\mathrm{Pb}}\sim 4\cdot 10^{-4}$.

   nucl-exhep-exPRL(2024)·19 citations
10. 10*

    Influence of the symmetry energy on the nuclear binding energies and the neutron drip line position

    Ante Ravlić🇺🇸 · Esra Yüksel🇹🇷 · Tamara Nikšić🇭🇷 · Nils Paar🇭🇷

    A clear connection can be established between properties of nuclear matter and finite-nuclei observables, such as the correlation between the slope of the symmetry energy and dipole polarizability, or between compressibility and the isoscalar monopole giant resonance excitation energy. Establishing a connection between realistic atomic nuclei and an idealized infinite nuclear matter leads to a better understanding of underlying physical mechanisms that govern nuclear dynamics. In this work, we aim to study the dependence of the binding energies and related quantities (e.g. location of drip lines, the total number of bound even-even nuclei) on the symmetry energy $S_2(\rho )$. The properties of finite nuclei are calculated by employing the relativistic Hartree-Bogoliubov (RHB) model, assuming even-even axial and reflection symmetric nuclei. Calculations are performed by employing two families of relativistic energy density functionals (EDFs), based on different effective Lagrangians, constrained to a specific symmetry energy at saturation density $J$ within the interval of $30$--$36$ MeV. Nuclear binding energies and related quantities of bound nuclei are calculated between $8\le Z\le 104$ from the two-proton to the two-neutron drip line. As the neutron drip line is approached, the interactions with stiffer $J$ tend to predict more bound nuclei, resulting in a systematic shift of the two-neutron drip line towards more neutron-rich nuclei. Consequentially, a correlation between the number of bound nuclei $N_{nucl}$ and $S_2(\rho )$ is established for a set of functionals constrained using the similar optimization procedures. The direction of the relationship between the number of bound nuclei and symmetry energy highly depends on the density under consideration.

    ↳ nucl-thnucl-exPRC(2023)·9 citations
11. 11*

    Effect of initial-state geometric configurations on the nuclear liquid-gas phase transition

    Y. T. Cao · X. G. Deng🇨🇳 · Y. G. Ma🇨🇳

    Within the framework of an extended quantum molecular dynamics model, we simulated ${}^{40}$Ca + ${}^{16}$O collisions at beam energies ranging from 60 to 150 MeV/nucleon for ${}^{16}$O with different $\alpha$-cluster configurations. Results imply that different $\alpha$-cluster configurations lead to different yields of deuteron, triton, ${}^3$He and ${}^4$He, but not for proton and neutron. We discuss the effect of geometric fluctuations which are presented by double ratios of light nuclei, namely ${\mathcal{O}}_{\text{p-d-t}}$ and ${\mathcal{O}}_{\text{p-d-He}}$. It is found that magnitude hierarchy of geometric fluctuations is chain, kite, square and tetrahedron structure of ${}^{16}$O. ${\mathcal{O}}_{\text{p-d-t}}$ has maximum value around 80 -- 100 MeV/nucleon which could be related to liquid-gas phase transition, that is consistent with results from the charge distribution of the heaviest fragments in the collisions.

    ↳ nucl-thnucl-exPRC(2023)·14 citations
12. 12*

    Studying strangeness and baryon production mechanisms through angular correlations between charged $\Xi$ baryons and identified hadrons in pp collisions at $\sqrt{s}$ = 13 TeV

    ALICE Collaboration

    The angular correlations between charged $\Xi$ baryons and associated identified hadrons (pions, kaons, protons, $\Lambda$ baryons, and $\Xi$ baryons) are measured in pp collisions at $\sqrt{s}=13$ TeV with the ALICE detector to give insight into the particle production mechanisms and balancing of quantum numbers on the microscopic level. In particular, the distribution of strangeness is investigated in the correlations between the doubly-strange $\Xi$ baryon and mesons and baryons that contain a single strange quark, K and $\Lambda$. As a reference, the results are compared to $\Xi \pi$ and $\Xi \mathrm{p}$ correlations, where the associated mesons and baryons do not contain a strange valence quark. These measurements are expected to be sensitive to whether strangeness is produced through string breaking or in a thermal production scenario. Furthermore, the multiplicity dependence of the correlation functions is measured to look for the turn-on of additional particle production mechanisms with event activity. The results are compared to predictions from the string-breaking model PYTHIA 8, including tunes with baryon junctions and rope hadronisation enabled, the cluster hadronisation model HERWIG 7, and the core-corona model EPOS-LHC. While some aspects of the experimental data are described quantitatively or qualitatively by the Monte Carlo models, no model can match all features of the data. These results provide stringent constraints on the strangeness and baryon number production mechanisms in pp collisions.

    ↳ hep-exnucl-exJHEP(2024)·17 citations
13. 13*

    Lattice QCD Calculation of Electroweak Box Contributions to Superallowed Nuclear and Neutron Beta Decays

    Peng-Xiang Ma🇨🇳 · Xu Feng🇨🇳 · Mikhail Gorchtein🇩🇪 · Lu-Chang Jin🇺🇸 · Keh-Fei Liu🇺🇸 · Chien-Yeah Seng🇺🇸 · Bi-Geng Wang🇺🇸 · Zhao-Long Zhang🇨🇳

    We present the first lattice QCD calculation of the universal axial $\gamma W$-box contribution ${\square }_{\gamma W}^{VA}$ to both superallowed nuclear and neutron beta decays. This contribution emerges as a significant component within the theoretical uncertainties surrounding the extraction of $|V_{ud}|$ from superallowed decays. Our calculation is conducted using two domain wall fermion ensembles at the physical pion mass. To construct the nucleon 4-point correlation functions, we employ the random sparsening field technique. Furthermore, we incorporate long-distance contributions to the hadronic function using the infinite-volume reconstruction method. Upon performing the continuum extrapolation, we arrive at ${\square }_{\gamma W}^{VA}=3.65(8{)}_{\mathrm{lat}}(1{)}_{\mathrm{PT}}\times 10^{-3}$. Consequently, this yields a slightly higher value of $|V_{ud}|=0.97386(11{)}_{exp.}(9{)}_{\mathrm{RC}}(27{)}_{\mathrm{NS}}$, reducing the previous $2.1\sigma$ tension with the CKM unitarity to $1.8\sigma$. Additionally, we calculate the vector $\gamma W$-box contribution to the axial charge $g_A$, denoted as ${\square }_{\gamma W}^{VV}$, and explore its potential implications.

    ↳ hep-lathep-phnucl-exPRL(2024)·51 citations
14. 14*

    Neutron Star vs Quark Star in the Multimessenger Era

    Zheng Cao🇨🇳 · Lie-Wen Chen🇨🇳

    Neutron stars (NSs) which could contain exotic degrees of freedom in the core and the self-bound quark stars (QSs) made purely of absolutely stable deconfined quark matter are still two main candidates for the compact objects observed in pulsars and gravitational wave (GW) events in binary star mergers. We perform a Bayesian model-agnostic inference of the properties of NSs and QSs by combining multi-messenger data of GW170817, GW190425, PSR J0030+0451, PSR J0740+6620, PSR J1614-2230, PSR J0348+0432 as well as ab initio calculations from perturbative quantum chromodynamics and chiral effective field theory. We find the NS scenario is strongly favored against the QS scenario with a Bayes factor of NS over QS ${\mathcal{B}}_{\text{QS}}^{\text{NS}}=11.5$. In addition, the peak of the squared sound velocity $c_s^2\sim 0.5c^2$ around $3.5$ times nuclear saturation density $n_0$ observed in the NS case disappears in the QS case which suggests that the $c_s^2$ first increases and then saturates at $c_s^2\sim 0.5c^2$ above $\sim 4n_0$. The sound velocity and trace anomaly are found to approach the conformal limit in the core of heavy NSs with mass $M\gtrsim 2M_{\odot }$, but not in the core of QSs.

    ↳ astro-ph.HEhep-phnucl-exnucl-th14 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.