Thu·May 13, 2021Thursday·May 13, 2021

1. 01*

   Experimental evidence for an attractive p-$\varphi$ interaction

   ALICE Collaboration

   This Letter presents the first experimental evidence of the attractive strong interaction between a proton and a $\varphi$ meson. The result is obtained from two-particle correlations of combined p-$\varphi \oplus \overline{\mathrm{p}}$-$\varphi$ pairs measured in high-multiplicity pp collisions at $\sqrt{s}=13$ TeV by the ALICE collaboration. The spin-averaged scattering length and effective range of the p-$\varphi$ interaction are extracted from the fully corrected correlation function employing the Lednický-Lyuboshits approach. In particular, the imaginary part of the scattering length vanishes within uncertainties, indicating that inelastic processes do not play a prominent role for the p-$\varphi$ interaction. These data demonstrate that the interaction is dominated by elastic p-$\varphi$ scattering. Furthermore, an analysis employing phenomenological Gaussian- and Yukawa-type potentials is conducted. Under the assumption of the latter, the N-$\varphi$ coupling constant is found to be $g_{\mathrm{N}-\varphi }=0.14\pm 0.03(stat.)\pm 0.02(syst.)$. This work provides valuable experimental input to accomplish a self-consistent description of the N-$\varphi$ interaction, which is particularly relevant for the more fundamental studies on partial restoration of chiral symmetry in nuclear medium.

   nucl-exhep-exPRL(2021)·132 citations
2. 02*

   Measurement of the production cross section of prompt ${\Xi }_{\mathrm{c}}^0$ baryons at midrapidity in pp collisions at $\sqrt{s}$ = 5.02 TeV

   ALICE Collaboration

   The transverse momentum ($p_{\mathrm{T}}$) differential cross section of the charm-strange baryon ${\Xi }_{\mathrm{c}}^0$ is measured at midrapidity ($|y|<$ 0.5) via its semileptonic decay into ${\mathrm{e}}^{+}{\Xi }^{-}{\nu }_{\mathrm{e}}$ in pp collisions at $\sqrt{s}$ = 5.02 TeV with the ALICE detector at the LHC. The ratio of the $p_{\mathrm{T}}$-differential ${\Xi }_{\mathrm{c}}^0$-baryon and ${\mathrm{D}}^0$-meson production cross sections is also reported. The measurements are compared with simulations with different tunes of the PYTHIA 8 event generator, with predictions from a statistical hadronisation model (SHM) with a largely augmented set of charm-baryon states beyond the current lists of the Particle Data Group, and with models including hadronisation via quark coalescence. The $p_{\mathrm{T}}$-integrated cross section of prompt ${\Xi }_{\mathrm{c}}^0$-baryon production at midrapidity is also reported, which is used to calculate the baryon-to-meson ratio ${\Xi }_{\mathrm{c}}^0/{\mathrm{D}}^0=0.20\pm 0.04{(stat.)}_{-0.07}^{+0.08}(syst.)$. These results provide an additional indication of a modification of the charm fragmentation from ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ and ${\mathrm{e}}^{-}\mathrm{p}$ collisions to pp collisions.

   nucl-exhep-exJHEP(2021)·75 citations
3. 03*

   Kaon-proton strong interaction at low relative momentum via femtoscopy in Pb-Pb collisions at the LHC

   ALICE Collaboration

   In quantum scattering processes between two particles, aspects characterizing the strong and Coulomb forces can be observed in kinematic distributions of the particle pairs. The sensitivity to the interaction potential reaches a maximum at low relative momentum and vanishing distance between the two particles. Ultrarelativistic heavy-ion collisions at the LHC provide an abundant source of many hadron species and can be employed as a measurement method of scattering parameters that is complementary to scattering experiments. This study confirms that momentum correlations of particles produced in Pb-Pb collisions at the LHC provide an accurate measurement of kaon-proton scattering parameters at low relative momentum, allowing precise access to the $K^{-}p\to K^{-}p$ process. This work also validates the femtoscopic measurement in ultrarelativistic heavy-ion collisions as an alternative to scattering experiments and a complementary tool to the study of exotic atoms with comparable precision. In this work, the first femtoscopic measurement of momentum correlations of $K^{-}p(K^{+}\overline{p})$ and $K^{+}p(K^{-}\overline{p})$ pairs in Pb-Pb collisions at centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV registered by the ALICE experiment is reported. The components of the $K^{-}p$ complex scattering length are extracted and found to be $\Re f_0=-0.91\pm 0.03$(stat)${}_{-0.03}^{+0.17}$(syst) and $\Im f_0=0.92\pm 0.05$(stat)${}_{-0.33}^{+0.12}$(syst). The results are compared with chiral effective field theory predictions as well as with existing data from dedicated scattering and exotic kaonic atom experiments.

   nucl-exhep-exPLB(2021)·48 citations
4. 04*

   Charged-particle multiplicity fluctuations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   Measurements of event-by-event fluctuations of charged-particle multiplicities in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV using the ALICE detector at the CERN Large Hadron Collider (LHC) are presented in the pseudorapidity range $|\eta |<0.8$ and transverse momentum $0.2<p_{\mathrm{T}}<2.0$ GeV/$c$. The amplitude of the fluctuations is expressed in terms of the variance normalized by the mean of the multiplicity distribution. The $\eta$ and $p_{\mathrm{T}}$ dependences of the fluctuations and their evolution with respect to collision centrality are investigated. The multiplicity fluctuations tend to decrease from peripheral to central collisions. The results are compared to those obtained from HIJING and AMPT Monte Carlo event generators as well as to experimental data at lower collision energies. Additionally, the measured multiplicity fluctuations are discussed in the context of the isothermal compressibility of the high-density strongly-interacting system formed in central Pb-Pb collisions.

   nucl-exhep-exEPJC(2021)·10 citations
5. 05*

   Measurement of K${}^{\ast }$(892)${}^{\pm }$ production in inelastic pp collisions at the LHC

   ALICE Collaboration

   The first results on K${}^{\ast }$(892)${}^{\pm }$ resonance production in inelastic pp collisions at LHC energies of $\sqrt{s}=5.02$, 8, and 13 TeV are presented. The K${}^{\ast }$(892)${}^{\pm }$ has been reconstructed via its hadronic decay channel K${}^{\ast }$(892)${}^{\pm }$ $\to$ ${\mathrm{K}}_{\mathrm{S}}^0$ $+{\pi }^{\pm }$ with the ALICE detector. Measurements of transverse momentum distributions, $p_{\mathrm{T}}$-integrated yields, and mean transverse momenta for charged K${}^{\ast }$(892) are found to be consistent with previous ALICE measurements for neutral K${}^{\ast }$(892) within uncertainties. For $p_{\mathrm{T}}>1$ GeV/$c$ the K${}^{\ast }$(892)${}^{\pm }$ transverse momentum spectra become harder with increasing centre-of-mass energy from 5.02 to 13 TeV, similar to what previously observed for charged kaons and pions. For $p_{\mathrm{T}}<1$ GeV/$c$ the K${}^{\ast }$(892)${}^{\pm }$ yield does not evolve significantly and the abundance of K${}^{\ast }$(892)${}^{\pm }$ relative to K is rather independent of the collision energy. The transverse momentum spectra, measured for K${}^{\ast }$(892)${}^{\pm }$ at midrapidity in the interval $0<p_{\mathrm{T}}<15$ GeV/$c$, are not well described by predictions of different versions of PYTHIA 6, PYTHIA 8 and EPOS-LHC event generators. These generators reproduce the measured $p_{\mathrm{T}}$-integrated K${}^{\ast \pm }$/K ratios and describe well the momentum dependence for $p_{\mathrm{T}}<2$ GeV/$c$.

   nucl-exhep-exPLB(2022)·17 citations
6. 06*

   Density matrix renormalization group description of the island of inversion isotopes ${}^{28-33}$F

   K. Fossez🇺🇸 · J. Rotureau🇸🇪

   Recent experiments have confirmed that the neutron-rich isotopes ${}^{28,29}$F belong to the so-called island of inversion (IOI), a region of the nuclear chart around $Z=10$ and $N=20$ where nuclear structure deviates from the standard shell model predictions due to deformation and continuum effects. However, while the general principles leading to the IOI are relatively well understood, the details of the low-lying structure of the exotic fluorine isotopes ${}^{28-33}$F are basically unknown. In this work, we perform large-scale shell model calculations including continuum states to investigate the properties of the neutron-rich isotopes ${}^{25-33}$F, using a core of ${}^{24}$O and an effective two-body interaction with only three adjustable parameters. We adjust the core potential and interaction on experimentally confirmed states in ${}^{25,26}$O and ${}^{25-27}$F and solve the many-body problem using the density matrix renormalization group method for open quantum systems in a $sd$-$fp$ model space. We obtain the first detailed spectroscopy of ${}^{25-33}$F in the continuum and show how the interplay between continuum effects and deformation explains the recent data on ${}^{28,29}$F, and produces an inversion of the ${5/2}^{+}$ and ${1/2}^{+}$ states in ${}^{29,31,33}$F. Several deformed one- and two-neutron halo states are predicted in ${}^{29,31}$F, and we predict the ground state of ${}^{30}$F to have a structure similar to that of the first ${5/2}^{+}$ state of ${}^{29}$F. We also suggest several experimental studies to constraint models and test the present predictions. The complex structure of neutron-rich fluorine isotopes offers a trove of information about the formation of the southern shore of the IOI through a subtle interplay of deformation and continuum couplings driven by the occupation of the quasi-degenerate neutron shells $0d_{3/2}$ and $1p_{3/2}$.

   ↳ nucl-thnucl-exPRC(2022)·23 citations
7. 07*

   Probing nuclear quadrupole deformation from correlation of elliptic flow and transverse momentum in heavy ion collisions

   Jiangyong Jia🇺🇸 · Shengli Huang🇺🇸 · Chunjian Zhang🇺🇸

   In heavy ion collisions, elliptic flow $v_2$ and radial flow, characterized by event-wise average transverse momentum $[p_{\mathrm{T}}]$, are related to the shape and size of the overlap region, which are sensitive to the shape of colliding atomic nuclei. The Pearson correlation coefficient between $v_2$ and $[p_{\mathrm{T}}]$, ${\rho }_2$, was found to be particularly sensitive to the quadrupole deformation parameter $\beta$ that is traditionally measured in low energy experiments. Built on earlier insight that the prolate deformation $\beta >0$ reduces the ${\rho }_2$ in ultra-central collisions (UCC), we show that the prolate deformation $\beta <0$ enhances the value of ${\rho }_2$. As $\beta >0$ and $\beta <0$ are the two extremes of triaxiality, the strength and sign of $v_2^2-[p_{\mathrm{T}}]$ correlation can be used to provide valuable information on the triaxiality of the nucleus. Our study provide further arguments for using the hydrodynamic flow as a precision tool to directly image the deformation of the atomic nuclei at extremely short time scale ($<10^{-24}$s).

   ↳ nucl-thhep-phnucl-exphysics.atom-phPRC(2022)·57 citations
8. 08*

   Is the Chiral Magnetic Effect fast enough?

   Jewel K. Ghosh🇧🇩 · Sebastian Grieninger🇪🇸 · Karl Landsteiner🇪🇸 · Sergio Morales-Tejera🇪🇸

   It depends: While we find within holography that the lifetime of the magnetic field for collider energies like the ones achieved at RHIC is long enough to build up the chiral magnetic current, the lifetime of the magnetic field at LHC seems to be too short. We study the real time evolution of the chiral magnetic effect out-of-equilibrium in strongly coupled holographic gauge theories. We consider the backreaction of the magnetic field onto the geometry and monitor pressure and chiral magnetic current. Our findings show that generically at small magnetic field the pressure builds up faster than the chiral magnetic current whereas at strong magnetic field the opposite is true. At large charge we also find that equilibration is delayed significantly due to long lived oscillations. We also match the parameters of our model to QCD parameters and draw lessons of possible relevance to the realization of the chiral magnetic effect in heavy ion collisions. In particular, we find an equilibration time of about $\sim 0.35$ fm/c in presence of the chiral anomaly for plasma temperatures of order $T\sim 300-400$ MeV.

   ↳ hep-phcond-mat.str-elhep-thnucl-ex+1PRD(2021)·26 citations
9. 09*

   HeCTOr: the ${}^3$He Cryogenic Target of Orsay for direct nuclear reactions with radioactive beams

   F. Galtarossa🇫🇷 · M. Pierens🇫🇷 · M. Assié🇫🇷 · V. Delpech🇫🇷 · F. Galet🇫🇷 · H. Saugnac🇫🇷 · D. Brugnara🇮🇹 · D. Ramos🇫🇷 · D. Beaumel🇫🇷 · P. Blache🇫🇷 · M. Chabot🇫🇷 · F. Chatelet🇫🇷 and 9 other authors

   Direct nuclear reactions with radioactive ion beams represent an extremely powerful tool to extend the study of fundamental nuclear properties far from stability. These measurements require pure and dense targets to cope with the low beam intensities. The ${}^3$He cryogenic target HeCTOr has been designed to perform direct nuclear reactions in inverse kinematics. The high density of ${}^3$He scattering centers, of the order of 10${}^{20}$ atoms/cm${}^2$, makes it particularly suited for experiments where low-intensity radioactive beams are involved. The target was employed in a first in-beam experiment, where it was coupled to state-of-the-art gamma-ray and particle detectors. It showed excellent stability in gas temperature and density over time. Relevant experimental quantities, such as total target thickness, energy resolution and gamma-ray absorption, were determined through dedicated Geant4 simulations and found to be in good agreement with experimental data.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·7 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.