Fri·Nov 1, 2019Friday·November 1, 2019

1. 01*

   Invariant-mass spectroscopy of ${}^{14}$O excited states

   R.J. Charity🇺🇸 · K.W. Brown🇺🇸 · J. Okolowicz🇵🇱 · M. Ploszajczak🇫🇷 · J.E. Elson🇺🇸 · W. Reviol🇺🇸 · L.G. Sobotka🇺🇸 · W.W. Buhro🇺🇸 · Z. Chajecki🇺🇸 · W.G. Lynch🇺🇸 · J. Manfredi🇺🇸 · R. Shane🇺🇸 and 6 other authors

   Excited states in ${}^{14}$O have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast ${}^{15}$O beam and the invariant-mass technique was employed to isolate the 1$p$ and 2$p$ decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the Shell Model Embedded in the Continuum that treats bound and scattering states in a unified model. By comparing energies, widths and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2${}^{+}$ state that we find is in near degeneracy with the third 0${}^{+}$ state. An interesting case of sequential 2$p$ decay through a pair of degenerate ${}^{13}$N excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons.

   nucl-exnucl-thPRC(2019)·19 citations
2. 02*

   A Precision Measurement of the Neutron Scattering Length of He-4 Using Neutron Interferometry

   R. Haun🇺🇸 · F. E. Wietfeldt🇺🇸 · M. Arif · M. G. Huber🇨🇦 · T. C. Black · B. Heacock🇺🇸 · D. A. Pushin🇨🇦 · C. B. Shahi

   We report a 0.08 % measurement of the bound neutron scattering length of ${}^4$He using neutron interferometry. The result is $b=(3.0982\pm 0.0021\text{mbox}[stat]\pm 0.0014\text{mbox}[sys])\text{mbox}fm$. The corresponding free atomic scattering length is $a=(2.4746\pm 0.0017\text{mbox}[stat]\pm 0.0011\text{mbox}[sys])\text{mbox}fm$. With this result the world average becomes $b=(3.0993\pm 0.0025)$ fm, a 2 % downward shift and a reduction in uncertainty by more than a factor of six. Our result is in disagreement with a previous neutron interferometric measurement but is in good agreement with earlier measurements using neutron transmission.

   nucl-exPRL(2020)·13 citations
3. 03*

   Internal Consistency of Neutron Coherent Scattering Length Measurements from Neutron Interferometry and from Neutron Gravity Reflectometry for Exotic Yukawa Analyses

   W. M. Snow🇺🇸 · J. Apanavicius🇺🇸 · K. A. Dickerson🇺🇸 · J. S. Devaney🇺🇸 · H. Drabek🇺🇸 · A. Reid🇺🇸 · B. Shen🇺🇸 · J. Woo🇺🇸 · C. Haddock🇺🇸 · E. Alexeev🇺🇸 · M. Peters🇺🇸

   Many theories beyond the Standard Model postulate short-range modifications to gravity which produce deviations of Newton's gravitational potential from a strict $1/r$ dependence. It is common to analyze experiments searching for these modifications using a potential of the form $V^{\prime }(r)=-\frac{GMm}{r}[1+\alpha \exp (-r/\lambda )]$. The best present constraints on $\alpha$ for $\lambda <100$\,nm come from neutron scattering and often employ comparisons of different measurements of the coherent neutron scattering amplitudes $b$. We analyze the internal consistency of existing data from two different types of measurements of low energy neutron scattering amplitudes: neutron interferometry, which involves squared momentum transfers $q^2=0$, and neutron gravity reflectometry, which involves squared momentum transfers $q^2=8m{V}_{opt}$ where $m$ is the neutron mass and $V_{opt}$ is the neutron optical potential of the medium. We show that the fractional difference $\frac{\Delta b}{|b|}$ averaged over the 7 elements where high precision data exists on the same material from both measurement methods is $[2.2\pm 1.4]\times 10^{-4}$. We also show that $\frac{\Delta b}{|b|}$ for this data is insensitive both to exotic Yukawa interactions and also to the electromagnetic neutron-atom interactions proportional to the neutron-electron scattering length $b_{ne}$ and the neutron polarizability scattering amplitude $b_{pol}$. This result will be useful in any future global analyses of neutron scattering data to determine $b_{ne}$ and bound $\alpha$ and $\lambda$. We also discuss how various neutron interferometric and scattering techniques with cold and ultracold neutrons can be used to improve the precision of $b$ measurements and make some specific proposals.

   nucl-exhep-exPRD(2020)·8 citations
4. 04*

   Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators $G_2^{\mathrm{CI}}$ and $G_2^{\mathrm{CD}}$ in Pb--Pb collisions at $\sqrt{s_{\text{NN}}}=2.76\text{TeVe}$ by the ALICE collaboration. The two-particle transverse momentum correlator $G_2$ was introduced as a measure of the momentum current transfer between neighbouring system cells. The correlators are measured as a function of pair separation in pseudorapidity ($\Delta \eta$) and azimuth ($\Delta \phi$) and as a function of collision centrality. From peripheral to central collisions, the correlator $G_2^{\mathrm{CI}}$ exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, $G_2^{\mathrm{CD}}$ exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density $\eta /s$ of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of $\eta /s$ and is in qualitative agreement with values obtained from anisotropic flow measurements.

   nucl-exhep-exPLB(2020)·26 citations
5. 05*

   Global baryon number conservation encoded in net-proton fluctuations measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   Experimental results are presented on event-by-event net-proton fluctuation measurements in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV, recorded by the ALICE detector at the CERN LHC. These measurements have as their ultimate goal an experimental test of Lattice QCD (LQCD) predictions on second and higher order cumulants of net-baryon distributions to search for critical behavior near the QCD phase boundary. Before confronting them with LQCD predictions, account has to be taken of correlations stemming from baryon number conservation as well as fluctuations of participating nucleons. Both effects influence the experimental measurements and are usually not considered in theoretical calculations. For the first time, it is shown that event-by-event baryon number conservation leads to subtle long-range correlations arising from very early interactions in the collisions.

   nucl-exhep-exPLB(2020)·96 citations
6. 06*

   Multiplicity dependence of K*(892)${}^0$ and $\varphi$(1020) production in pp collisions at $\sqrt{s}$ = 13 TeV

   ALICE Collaboration

   Measurements of identified hadrons as a function of the charged-particle multiplicity in pp collisions enable a search for the onset of collective effects in small collision systems. With such measurements, it is possible to study the mechanisms that determine the shapes of hadron transverse momentum ($p_{\mathrm{T}}$) spectra, to search for possible modifications of the yields of short-lived hadronic resonances due to scattering effects in the hadron-gas phase, and to investigate different explanations for the multiplicity evolution of strangeness production provided by phenomenological models. In this paper, these topics are addressed through measurements of the ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ mesons at midrapidity in pp collisions at $\sqrt{s}$ = 13 TeV as a function of the charged-particle multiplicity. The results include the $p_{\mathrm{T}}$ spectra, $p_{\mathrm{T}}$-integrated yields, mean transverse momenta, and the ratios of the yields of these resonances to those of longer-lived hadrons. Comparisons with results from other collision systems and energies, as well as predictions from phenomenological models, are also discussed.

   nucl-exhep-exPLB(2020)·96 citations
7. 07*

   Jet-hadron correlations measured relative to the second order event plane in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   The Quark Gluon Plasma (QGP) produced in ultra relativistic heavy-ion collisions at the Large Hadron Collider (LHC) can be studied by measuring the modifications of jets formed by hard scattered partons which interact with the medium. We studied these modifications via angular correlations of jets with charged hadrons for jets with momenta 20 < $p_{\mathrm{T}}^{\mathrm{jet}}$ < 40 GeV/$c$ as a function of the associated particle momentum. The reaction plane fit (RPF) method is used in this analysis to remove the flow modulated background. The analysis of angular correlations for different orientations of the jet relative to the second order event plane allows for the study of the path length dependence of medium modifications to jets. We present the dependence of azimuthal angular correlations of charged hadrons with respect to the angle of the axis of a reconstructed jet relative to the event plane in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV. The dependence of particle yields associated with jets on the angle of the jet with respect to the event plane is presented. Correlations at different angles relative to the event plane are compared through ratios and differences of the yield. No dependence of the results on the angle of the jet with respect to the event plane is observed within uncertainties, which is consistent with no significant path length dependence of the medium modifications for this observable.

   nucl-exhep-exPRC(2020)·14 citations
8. 08*

   Measurement of electrons from heavy-flavour hadron decays as a function of multiplicity in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The multiplicity dependence of electron production from heavy-flavour hadron decays as a function of transverse momentum was measured in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV using the ALICE detector at the LHC. The measurement was performed in the centre-of-mass rapidity interval $-1.07<y_{\mathrm{cms}}<0.14$ and transverse momentum interval 2 $<p_{\mathrm{T}}<$ 16 GeV/$c$. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the $p_{\mathrm{T}}$ spectra measured for different multiplicity classes with those measured in pp collisions ($Q_{\mathrm{pPb}}$) and in peripheral p-Pb collisions ($Q_{\mathrm{CP}}$). The $Q_{\mathrm{pPb}}$ results obtained are consistent with unity within uncertainties in the measured $p_{\mathrm{T}}$ interval and event classes. This indicates that heavy-flavour decay electron production is consistent with binary scaling and independent of the geometry of the collision system. Additionally, the results suggest that cold nuclear matter effects are negligible within uncertainties, in the production of heavy-flavour decay electrons at midrapidity in p-Pb collisions.

   nucl-exhep-exJHEP(2020)·14 citations
9. 09*

   Underlying Event properties in pp collisions at $\sqrt{s}$ = 13 TeV

   ALICE Collaboration

   This article reports measurements characterizing the Underlying Event (UE) associated with hard scatterings at midrapidity in pp collisions at $\sqrt{s}=13$ TeV. The hard scatterings are identified by the leading particle, the charged particle with the highest transverse momentum ($p_{\mathrm{T}}^{\mathrm{leading}}$) in the event. Charged-particle number and summed transverse-momentum densities are measured in different azimuthal regions defined with respect to the leading particle direction: Toward, Transverse, and Away. The Toward and Away regions contain the fragmentation products of the hard scatterings in addition to the UE contribution, whereas particles in the Transverse region are expected to originate predominantly from the UE. The study is performed as a function of $p_{\mathrm{T}}^{\mathrm{leading}}$ with three different $p_{\mathrm{T}}$ thresholds for the associated particles, $p_{\mathrm{T}}^{\min }>$ 0.15, 0.5, and 1.0 GeV/$c$. The charged-particle density in the Transverse region rises steeply for low values of $p_{\mathrm{T}}^{\mathrm{leading}}$ and reaches a plateau. The results confirm the trend that the charged-particle density in the Transverse region shows a stronger increase with $\sqrt{s}$ than the inclusive charged-particle density at midrapidity. The UE activity is increased by approximately 20% when going from 7 to 13 TeV. The plateau in the Transverse region ($5<p_{\mathrm{T}}^{\mathrm{leading}}<40$ GeV/$c$ ) is further characterized by the probability distribution of its charged-particle multiplicity normalized to its average value (relative transverse activity, $R_T$) and the mean transverse momentum as a function of $R_T$. Experimental results are compared to model calculations using PYTHIA 8 and EPOS LHC. The overall agreement between models and data is within 30%. These measurements provide new insights on the interplay between hard scatterings and the associated UE in pp collisions.

   nucl-exhep-exJHEP(2020)·54 citations
10. 10*

    Production of (anti-)${}^3$He and (anti-)${}^3$H in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

    ALICE Collaboration

    The transverse momentum ($p_{\mathrm{T}}$) differential yields of (anti-)${}^3$He and (anti-)${}^3$H measured in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE at the Large Hadron Collider (LHC) are presented. The ratios of the $p_{\mathrm{T}}$-integrated yields of (anti-)${}^3$He and (anti-)${}^3$H to the proton yields are reported, as well as the $p_{\mathrm{T}}$ dependence of the coalescence parameters $B_3$ for (anti-)${}^3$He and (anti-)${}^3$H. For (anti-)${}^3$He, the results obtained in four classes of the mean charged-particle multiplicity density are also discussed. These results are compared to predictions from a canonical statistical hadronization model and coalescence approaches. An upper limit on the total yield of ${}^4\overline{\mathrm{He}}$ is determined.

    nucl-exhep-exPRC(2020)·66 citations
11. 11*

    Azimuthal correlations of prompt D mesons with charged particles in pp and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

    ALICE Collaboration

    The measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at $\sqrt{s}$ = 5.02 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with the ALICE detector at the LHC is reported. The D${}^0$, D${}^{+}$, and D${}^{\ast +}$ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval 3 < $p_{\mathrm{T}}$ < 24 GeV/c and correlated with charged particles having $p_{\mathrm{T}}$ > 0.3 GeV/c and pseudorapidity $|\eta |<$ 0.8. The properties of the correlation peaks appearing in the near- and away-side regions (for $\Delta \phi \approx$ 0 and $\Delta \phi \approx \pi$, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p-Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators.

    nucl-exhep-exEPJC(2020)·44 citations
12. 12*

    Centrality and transverse momentum dependence of inclusive J/$\psi$ production at midrapidity in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

    ALICE Collaboration

    The inclusive J/$\psi$ meson production in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV at midrapidity ($|y|$ < 0.9) is reported by the ALICE Collaboration. The measurements are performed in the dielectron decay channel, as a function of event centrality and J/$\psi$ transverse momentum $p_{\mathrm{T}}$, down to $p_{\mathrm{T}}$ = 0 GeV/$c$. The J/$\psi$ mean transverse momentum $⟨p_{\mathrm{T}}⟩$ and $r_{\mathrm{AA}}$ ratio, defined as $⟨p_{\mathrm{T}}^2{⟩}_{\mathrm{PbPb}}/⟨p_{\mathrm{T}}^2{⟩}_{\mathrm{pp}}$, are evaluated. Both observables show a centrality dependence decreasing towards central (head-on) collisions. The J/$\psi$ nuclear modification factor $R_{\mathrm{AA}}$ exhibits a strong $p_{\mathrm{T}}$ dependence with a large suppression at high $p_{\mathrm{T}}$ and an increase to unity for decreasing $p_{\mathrm{T}}$. When integrating over the measured momentum range $p_{\mathrm{T}}$ < 10 GeV/$c$, the J/$\psi$ $R_{\mathrm{AA}}$ shows a weak centrality dependence. Each measurement is compared with results at lower center-of-mass energies and with ALICE measurements at forward rapidity, as well as to theory calculations. All reported features of the J/$\psi$ production at low $p_{\mathrm{T}}$ are consistent with a dominant contribution to the J/$\psi$ yield originating from charm quark (re)combination.

    nucl-exhep-exPLB(2020)·86 citations
13. 13*

    ${\rm Y}$ production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV

    ALICE Collaboration

    ${\rm Y}$ production in p-Pb interactions is studied at the centre-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\mathrm{NN}}}$ = 8.16 TeV with the ALICE detector at the CERN LHC. The measurement is performed reconstructing bottomonium resonances via their dimuon decay channel, in the centre-of-mass rapidity intervals $2.03<y_{\mathrm{cms}}<3.53$ and $-4.46<y_{\mathrm{cms}}<-2.96$, down to zero transverse momentum. In this work, results on the inclusive ${\rm Y}(1\mathrm{S})$ production cross section as a function of rapidity and transverse momentum are presented. The corresponding nuclear modification factor shows a suppression of the ${\rm Y}(1\mathrm{S})$ yields with respect to pp collisions, both at forward and backward rapidity. This suppression is stronger in the low transverse momentum region and shows no significant dependence on the centrality of the interactions. Furthermore, the ${\rm Y}(2\mathrm{S})$ nuclear modification factor is also evaluated, suggesting a suppression similar to that of the ${\rm Y}(1\mathrm{S})$. A first measurement of the ${\rm Y}(3\mathrm{S})$ has also been performed. Finally, results are compared with previous measurements performed by ALICE in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV and with theoretical calculations.

    nucl-exhep-exPLB(2020)·49 citations
14. 14*

    Probing the effects of strong electromagnetic fields with charge-dependent directed flow in Pb-Pb collisions at the LHC

    ALICE Collaboration

    The first measurement at the LHC of charge-dependent directed flow ($v_1$) relative to the spectator plane is presented for Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV. Results are reported for charged hadrons and ${\mathrm{D}}^0$ mesons for the transverse momentum intervals $p_{\mathrm{T}}>0.2$ GeV/$c$ and $3<p_{\mathrm{T}}<$ 6 GeV/$c$ in the 5-40% and 10-40% centrality classes, respectively. The difference between the positively and negatively charged hadron $v_1$ has a positive slope as a function of pseudorapidity $\eta$, $\mathrm{d}\Delta v_1/\mathrm{d}\eta =$[1.68 $\pm$ 0.49 (stat.) $\pm$ 0.41 (syst.)] $\times 10^{-4}$. The same measurement for ${\mathrm{D}}^0$ and $\bar{\mathrm{D}}{}^0$ mesons yields a positive value $\mathrm{d}\Delta v_1/\mathrm{d}\eta$= [4.9 $\pm$ 1.7 (stat.) $\pm$ 0.6 (syst.)]$\times 10^{-1}$, which is about three orders of magnitude larger than the one of the charged hadrons. These measurements can provide new insights into the effects of the strong electromagnetic field and the initial tilt of matter created in non-central heavy-ion collisions on the dynamics of light (u, d, and s) and heavy (c) quarks. The large difference between the observed $\Delta v_1$ of charged hadrons and ${\mathrm{D}}^0$ mesons may reflect different sensitivity of the charm and light quarks to the early time dynamics of a heavy-ion collision. These observations challenge some of the recent theoretical calculations, which predicted a negative and an order of magnitude smaller value of $\mathrm{d}\Delta v_1/\mathrm{d}\eta$ for both light-flavour and charmed hadrons.

    nucl-exhep-exPRL(2020)·135 citations
15. 15*

    Investigation of the p-${\Sigma }^0$ interaction via femtoscopy in pp collisions

    ALICE Collaboration

    This Letter presents the first direct investigation of the p-${\Sigma }^0$ interaction, using the femtoscopy technique in high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV measured by the ALICE detector. The ${\Sigma }^0$ is reconstructed via the decay channel to $\Lambda \gamma$, and the subsequent decay of $\Lambda$ to p${\pi }^{-}$. The photon is detected via the conversion in material to e${}^{+}$e${}^{-}$ pairs exploiting the unique capability of the ALICE detector to measure electrons at low transverse momenta. The measured p-${\Sigma }^0$ correlation indicates a shallow strong interaction. The comparison of the data to several theoretical predictions obtained employing the $CorrelationAnalysisToolusingtheSchr\ddot{o}dingerEquation$ (CATS) and the Lednický-Lyuboshits approach shows that the current experimental precision does not yet allow to discriminate between different models, as it is the case for the available scattering and hypernuclei data. Nevertheless, the p-${\Sigma }^0$ correlation function is found to be sensitive to the strong interaction, and driven by the interplay of the different spin and isospin channels. This pioneering study demonstrates the feasibility of a femtoscopic measurement in the p-${\Sigma }^0$ channel and with the expected larger data samples in LHC Run 3 and Run 4, the p-${\Sigma }^0$ interaction will be constrained with high precision.

    nucl-exhep-exPLB(2020)·122 citations
16. 16*

    Evidence of spin-orbital angular momentum interactions in relativistic heavy-ion collisions

    ALICE Collaboration

    The first evidence of spin alignment of vector mesons ($K^{\ast 0}$ and $\varphi$) in heavy-ion collisions at the Large Hadron Collider (LHC) is reported. The spin density matrix element ${\rho }_{00}$ is measured at midrapidity ($|y|<$ 0.5) in Pb-Pb collisions at a center-of-mass energy ($\sqrt{s_{\mathrm{NN}}}$) of 2.76 TeV with the ALICE detector. ${\rho }_{00}$ values are found to be less than 1/3 (1/3 implies no spin alignment) at low transverse momentum ($p_{\mathrm{T}}<$ 2 GeV/$c$) for $K^{\ast 0}$ and $\varphi$ at a level of 3$\sigma$ and 2$\sigma$, respectively. No significant spin alignment is observed for the $K_S^0$ meson (spin = 0) in Pb-Pb collisions and for the vector mesons in $pp$ collisions. The measured spin alignment is unexpectedly large but qualitatively consistent with the expectation from models which attribute it to a polarization of quarks in the presence of angular momentum in heavy-ion collisions and a subsequent hadronization by the process of recombination.

    nucl-exhep-exPRL(2020)·269 citations
17. 17*

    ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ production at midrapidity in pp collisions at $\sqrt{s}$ = 8 TeV

    ALICE Collaboration

    The production of ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ in pp collisions at $\sqrt{s}$ = 8 TeV was measured using Run 1 data collected by the ALICE collaboration at the LHC. The $p_{\mathrm{T}}$-differential yields d${}^{2}N$/d$y$d$p_{\mathrm{T}}$ in the range $0<p_{\mathrm{T}}<20$ GeV/$c$ for ${\mathrm{K}}^{\ast 0}$ and $0.4<p_{\mathrm{T}}<16$ GeV/$c$ for $\varphi$ have been measured at midrapidity, $|y|<0.5$. Moreover, improved measurements of the ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ at $\sqrt{s}=7$TeV are presented. The collision energy dependence of $p_{\mathrm{T}}$ distributions, $p_{\mathrm{T}}$-integrated yields and particle ratios in inelastic pp collisions are examined. The results are also compared with different collision systems. The values of the particle ratios are found to be similar to those measured at other LHC energies. In pp collisions a hardening of the particle spectra is observed with increasing energy, but at the same time it is also observed that the relative particle abundances are independent of the collision energy. The $p_{\mathrm{T}}$-differential yields of ${\mathrm{K}}^{\ast 0}$ and $\varphi$ in pp collisions at $\sqrt{s}=8$ TeV are compared with the expectations of different Monte Carlo event generators.

    nucl-exhep-exPRC(2020)·36 citations
18. 18*

    Evidence of rescattering effect in Pb-Pb collisions at the LHC through production of ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ mesons

    ALICE Collaboration

    Measurements of ${\mathrm{K}}^{\ast }(892{)}^0$ and $\varphi (1020)$ resonance production in Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity ($|y|$ $<$ 0.5) via their hadronic decay channels and the transverse momentum ($p_{\mathrm{T}}$) distributions are obtained for various collision centrality classes up to $p_{\mathrm{T}}$ $=$ 20 GeV$/c$. The $p_{\mathrm{T}}$-integrated yield ratio ${\mathrm{K}}^{\ast }(892{)}^0$$/$K in Pb-Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the $\varphi (1020)$$/$K ratio does not show any suppression. Furthermore, the measured ${\mathrm{K}}^{\ast }(892{)}^0$$/$K ratio in central Pb-Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the $\varphi (1020)$$/$K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of ${\mathrm{K}}^{\ast }(892{)}^0$ decay products in the hadronic phase of the collisions. The ${\mathrm{K}}^{\ast }(892{)}^0$$/$K yield ratios in Pb-Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be $\sim$ 4-7 fm$/c$ for central collisions. The $p_{\mathrm{T}}$-differential ratios of ${\mathrm{K}}^{\ast }(892{)}^0$$/$K, $\varphi (1020)$$/$K, ${\mathrm{K}}^{\ast }(892{)}^0$$/\pi$, $\varphi (1020)$$/\pi$, $p/$${\mathrm{K}}^{\ast }(892{)}^0$ and $p/$$\varphi (1020)$ are also presented for Pb-Pb and pp collisions at $\sqrt{s_{\mathrm{NN}}}$ $=$ 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-$p_{\mathrm{T}}$ phenomenon.

    nucl-exhep-exPLB(2020)·145 citations
19. 19*

    Parity-Violating Inelastic Electron-Proton Scattering at Low $Q^2$ Above the Resonance Region

    QWeak Collaboration: D. Androic🇭🇷 · D.S. Armstrong🇺🇸 · A. Asaturyan🇦🇲 · K. Bartlett🇺🇸 · R.S. Beminiwattha🇺🇸 · J. Benesch🇺🇸 · F. Benmokhtar🇺🇸 · J. Birchall🇨🇦 · R.D. Carlini🇺🇸 · J.C. Cornejo🇺🇸 · M.M. Dalton🇺🇸 · C.A. Davis🇨🇦 and 64 other authors

    We report the measurement of the parity-violating asymmetry for the inelastic scattering of electrons from the proton, at $Q^2=0.082$ GeV${}^2$ and $W=2.23$ GeV, above the resonance region. The result $A_{\mathrm{Inel}}=-13.5\pm 2.0(\mathrm{stat})\pm 3.9(\mathrm{syst})$~ppm agrees with theoretical calculations, and helps to validate the modeling of the $\gamma Z$ interference structure functions $F_1^{\gamma Z}$ and $F_2^{\gamma Z}$ used in those calculations, which are also used for determination of the two-boson exchange box diagram (${\square }_{\gamma Z}$) contribution to parity-violating elastic scattering measurements. A positive parity-violating asymmetry for inclusive ${\pi }^{-}$ production was observed, as well as positive beam-normal single-spin asymmetry for scattered electrons and a negative beam-normal single-spin asymmetry for inclusive ${\pi }^{-}$ production.

    nucl-exhep-phPRC(2020)·8 citations
20. 20*

    First measurement of ${\Lambda }_c$ baryon production in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV

    STAR Collaboration: J. Adam🇺🇸 · L. Adamczyk🇵🇱 · J. R. Adams🇺🇸 · J. K. Adkins🇺🇸 · G. Agakishiev🇷🇺 · M. M. Aggarwal🇮🇳 · Z. Ahammed🇮🇳 · I. Alekseev🇷🇺 · D. M. Anderson🇺🇸 · A. Aparin🇷🇺 · E. C. Aschenauer🇺🇸 · M. U. Ashraf🇨🇳 and 344 other authors

    We report on the first measurement of the charmed baryon ${\Lambda }_c^{\pm }$ production at midrapidity ($|y|$ $<$ 1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The ${\Lambda }_c$/$D^0$ (denoting (${\Lambda }_c^{+}+{\Lambda }_c^{-}$)/($D^0+\overline{D^0}$)) yield ratio is measured to be 1.08 $\pm$ 0.16 (stat.) $\pm$ 0.26 (sys.) in the 0--20% most central Au+Au collisions for the transverse momentum ($p_T$) range 3 $<$ $p_T$ $<$ 6 GeV/$c$. This is significantly larger than the PYTHIA model calculations for $p+p$ collisions. The measured ${\Lambda }_c$/$D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured ${\Lambda }_c$/$D^0$ ratio.

    nucl-exhep-exPRL(2020)·117 citations
21. 21*

    Indirect methods in nuclear astrophysics with relativistic radioactive beams

    Thomas Aumann🇩🇪 · Carlos A. Bertulani🇺🇸

    Reactions with radioactive nuclear beams at relativistic energies have opened new doors to clarify the mechanisms of stellar evolution and cataclysmic events involving stars and during the big bang epoch. Numerous nuclear reactions of astrophysical interest cannot be assessed directly in laboratory experiments. Ironically, some of the information needed to describe such reactions, at extremely low energies (e.g., keVs), can only be studied on Earth by using relativistic collisions between heavy ions at GeV energies. In this contribution, we make a short review of experiments with relativistic radioactive beams and of the theoretical methods needed to understand the physics of stars, adding to the knowledge inferred from astronomical observations. We continue by introducing a more detailed description of how the use of relativistic radioactive beams can help to solve astrophysical puzzles and several successful experimental methods. State-of-the-art theories are discussed at some length with the purpose of helping us understand the experimental results reported. The review is not complete and we have focused most of it to traditional methods aiming at the determination of the equation of state of symmetric and asymmetric nuclear matter and the role of the symmetry energy. Whenever possible, under the limitations of our present understanding of experimental data and theory, we try to pinpoint the information still missing to further understand how stars evolve, explode, and how their internal structure might be.

    ↳ nucl-thastro-ph.SRnucl-exPPNP(2020)·22 citations
22. 22*

    Prospects of Event Shape Sorting

    Boris Tomasik🇸🇰 · Jakub Cimerman🇨🇿

    Event Shape Sorting is a novel method which is devised to organise a sample of collision events in such a way, that events with similar final state distribution of hadrons end up sorted close to each other. Such events are likely to have evolved similarly. Thus the method allows to focus at finer features of the collision evolution because it would allow for averages over similar events that do not wash away these features. The algorithm is shortly explained. We also point out the distinction of Event Shape Sorting from the well established technique of Event Shape Engineering.

    ↳ nucl-thnucl-exPhys.Part.Nucl.(2020)·0 citations
23. 23*

    Probing QCD critical fluctuations from the yield ratio of strange hadrons in relativistic heavy-ion collisions

    Tianhao Shao🇨🇳 · Jinhui Chen🇨🇳 · Che Ming Ko🇺🇸 · Kai-Jia Sun🇺🇸

    By analyzing the available data on strange hadrons in central Pb+Pb collisions from the NA49 Collaboration at the Super Proton Synchrotron (SPS) and in central Au+Au collisions from the STAR Collaboration at the Relativistic Heavy-Ion Collider (RHIC) in a wide collision energy range from $\sqrt{s_{\mathrm{NN}}}$ = 6.3 GeV to 200 GeV, we find a possible non-monotonic behavior in the ratio \mathcal{O}_\text{K-\Xi$-$\phi$-$\Lambda}= $\frac{N(K^{+})N({\Xi }^{-})}{N(\varphi )N(\Lambda )}$ of $K^{+}$, ${\Xi }^{-}$, $\varphi$, and $\Lambda$ yields as a function of $\sqrt{s_{\mathrm{NN}}}$. Based on the quark coalescence model, which can take into account the effect of quark density fluctuations on hadron production, a possible non-monotonic behavior in the dependence of the strange quark density fluctuation on $\sqrt{s_{NN}}$ is obtained. This is in contrast to the coalescence model that does not include quark density fluctuations and also to the statistical hadronization model as both fail to describe even qualitatively the collision energy dependence of the ratio \mathcal{O}_\text{K-\Xi$-$\phi$-$\Lambda}. Our findings thus suggest that the signal and location of a possible critical endpoint in the QCD phase diagram, which is expected to result in large quark density fluctuations, can be found in the on-going Bean Energy Scan program at RHIC.

    ↳ hep-phnucl-exnucl-thPLB(2020)·15 citations
24. 24*

    Measurement of $J/\psi$ at forward and backward rapidity in $p$+$p$, $p$$+A$l, $p$$+A$u, and ${}^3$He+Au collisions at $\sqrt{s_{{}_{NN}}}=200\mathrm{GeV}$

    U.A. Acharya · A. Adare · C. Aidala · N.N. Ajitanand · Y. Akiba · M. Alfred · V. Andrieux · N. Apadula · H. Asano · B. Azmoun · V. Babintsev · M. Bai and 351 other authors

    Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of $J/\psi$ measurements at forward and backward rapidity in various small collision systems, $p$$+$$p$, $p$$+$Al, $p$$+$Au and ${}^3$He$+$Au, at $\sqrt{s_{{}_{NN}}}$=200 GeV. The results are presented in the form of the observable $R_{AB}$, the nuclear modification factor, a measure of the ratio of the $J/\psi$ invariant yield compared to the scaled yield in $p$$+$$p$ collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on $J/\psi$ production with different projectile sizes $p$ and ${}^3$He, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for $p$$+$Au and ${}^3$He$+$Au. However, for 0%--20% central collisions at backward rapidity, the modification for ${}^3$He$+$Au is found to be smaller than that for $p$$+$Au, with a mean fit to the ratio of $0.89\pm 0.03$(stat)$\pm 0.08$(syst), possibly indicating final state effects due to the larger projectile size.

    ↳ hep-exnucl-exPRC(2020)·41 citations
25. 25*

    Blast-wave description of ${\rm Y}$ elliptic flow at energies available at the CERN Large Hadron Collider

    Klaus Reygers🇩🇪 · Alexander Schmah🇩🇪 · Anastasia Berdnikova🇷🇺 · Xu Sun🇺🇸

    A simultaneous blast-wave fit to particle yields and elliptic flow ($v_2$) measured as a function of transverse momentum in Pb-Pb collisions at LHC energies is presented. A compact formula for the calculation of $v_2(p_T)$ for an elliptic freeze-out surface is used which follows from the Cooper-Frye ansatz without further assumptions. Over the full available $p_T$ range, the ${\rm Y}$ elliptic flow data is described by the prediction based on the fit to lighter particles. This prediction shows that, due to the large ${\rm Y}$ mass, a sizable elliptic flow is only expected at transverse momenta above 10 GeV/$c$.

    ↳ hep-phnucl-exnucl-thPRC(2020)·23 citations
26. 26*

    Searching for three-nucleon short-range correlations

    Misak M. Sargsian🇺🇸 · Donal B. Day🇺🇸 · Leonid L. Frankfurt🇮🇱 · Mark I. Strikman🇺🇸

    Three nucleon short range correlations~(SRCs) are one of the most elusive structures in nuclei. Their observation and the subsequent study of their internal makeup will have a significant impact on our understanding of the dynamics of super-dense nuclear matter which exists at the cores of neutron stars. We discuss the kinematic conditions and observables that are most favorable for probing 3N-SRCs in inclusive electro-nuclear processes and make a prediction for a quadratic dependence of the probabilities of finding a nucleon in 2N- and 3N- SRCs. We demonstrate that this prediction is consistent with the limited high energy experimental data available, suggesting that we have observed, for the first time, 3N-SRCs in electro-nuclear processes. Our analysis enables us to extract $a_3(A,Z)$, the probability of finding 3N-SRCs in nuclei relative to the A=3 system.

    ↳ nucl-thhep-phnucl-exPRC(2019)·16 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.