Mon·May 25, 2020Monday·May 25, 2020

1. 01*

   Observation of T=3/2 Isobaric Analog States in 9Be using p+8Li resonance scattering

   C. Hunt🇺🇸 · G.V. Rogachev🇺🇸 · S. Almaraz-Calderon · A. Aprahamian🇺🇸 · M. Avila🇨🇱 · L.T. Baby🇺🇸 · B. Bucher🇺🇸 · V.Z. Goldberg🇺🇸 · E.D. Johnson · K.W. Kemper🇺🇸 · A.N. Kuchera🇺🇸 · W.P. Tan🇺🇸 · I. Wiedenhover🇺🇸

   Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance. Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target. Method: The excitation function for p+8Li resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating T=3/2 isobaric analog states (IAS) in 9Be. Results: A good fit of the 8Li(p,p)8Li resonance elastic scattering excitation function was obtained using previously tentatively known 5/2- T=3/2 state at 18.65 MeV in 9Be and a new broad T=3/2 s-wave state - the 5/2+ at 18.5 MeV. These results fit the expected iso-mirror properties for the T=3/2 A=9 iso-quartet. Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited T=3/2 states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.

   nucl-exPRC(2020)·3 citations
2. 02*

   Production of light-flavor hadrons in pp collisions at $\sqrt{s}$ = 7 and $\sqrt{s}$ = 13 TeV

   ALICE Collaboration

   The production of ${\pi }^{\pm }$, ${\mathrm{K}}^{\pm }$, ${\mathrm{K}}_{\mathrm{S}}^0$, ${\mathrm{K}}^{\ast }(892{)}^0$, $\mathrm{p}$, $\varphi (1020)$, $\Lambda$, ${\Xi }^{-}$, ${\Omega }^{-}$, and their antiparticles was measured in inelastic proton-proton (pp) collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV at midrapidity ($|y|<0.5$) as a function of transverse momentum ($p_{\mathrm{T}}$) using the ALICE detector at the CERN LHC. Furthermore, the single-particle $p_{\mathrm{T}}$ distributions of ${\mathrm{K}}_{\mathrm{S}}^0$, $\Lambda$, and $\overline{\Lambda }$ in inelastic pp collisions at $\sqrt{s}$ = 7 TeV are reported here for the first time. The $p_{\mathrm{T}}$ distributions are studied at midrapidity within the transverse momentum range $0\le p_{\mathrm{T}}\le 20$ GeV/$c$, depending on the particle species. The $p_{\mathrm{T}}$ spectra, integrated yields, and particle yield ratios are discussed as a function of collision energy and compared with measurements at lower $\sqrt{s}$ and with results from various general-purpose QCD-inspired Monte Carlo models. A hardening of the spectra at high $p_{\mathrm{T}}$ with increasing collision energy is observed, which is similar for all particle species under study. The transverse mass and $x_{\mathrm{T}}\equiv 2p_{\mathrm{T}}/\sqrt{s}$ scaling properties of hadron production are also studied. As the collision energy increases from $\sqrt{s}$ = 7 to 13 TeV, the yields of non- and single-strange hadrons normalized to the pion yields remain approximately constant as a function of $\sqrt{s}$, while ratios for multi-strange hadrons indicate enhancements. The $p_{\mathrm{T}}$-differential cross sections of ${\pi }^{\pm }$, ${\mathrm{K}}^{\pm }$ and $\mathrm{p}$ ($\overline{\mathrm{p}}$) are compared with next-to-leading order perturbative QCD calculations, which are found to overestimate the cross sections for ${\pi }^{\pm }$ and $\mathrm{p}$ ($\overline{\mathrm{p}}$) at high $p_{\mathrm{T}}$.

   nucl-exhep-exEPJC(2021)·127 citations
3. 03*

   Measurement of the low-energy antideuteron inelastic cross section

   ALICE Collaboration

   In this Letter, we report the first measurement of the inelastic cross section for antideuteron-nucleus interactions at low particle momenta, covering a range of $0.3\le p<4$ GeV/$c$. The measurement is carried out using p-Pb collisions at a center-of-mass energy per nucleon-nucleon pair of $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV, recorded with the ALICE detector at the CERN LHC and utilizing the detector material as an absorber for antideuterons and antiprotons. The extracted raw primary antiparticle-to-particle ratios are compared to the results from detailed ALICE simulations based on the GEANT4 toolkit for the propagation of antiparticles through the detector material. The analysis of the raw primary (anti)proton spectra serves as a benchmark for this study, since their hadronic interaction cross sections are well constrained experimentally. The first measurement of the inelastic cross section for antideuteron-nucleus interactions averaged over the ALICE detector material with atomic mass numbers $⟨A⟩$ = 17.4 and 31.8 is obtained. The measured inelastic cross section points to a possible excess with respect to the Glauber model parameterization used in GEANT4 in the lowest momentum interval of $0.3\le p<0.47$ GeV/$c$ up to a factor 2.1. This result is relevant for the understanding of antimatter propagation and the contributions to antinuclei production from cosmic ray interactions within the interstellar medium. In addition, the momentum range covered by this measurement is of particular importance to evaluate signal predictions for indirect dark-matter searches.

   nucl-exhep-exPRL(2020)·50 citations
4. 04*

   Multiplicity dependence of J/$\psi$ production at midrapidity in pp collisions at $\sqrt{s}$ = 13 TeV

   ALICE Collaboration

   Measurements of the inclusive J/$\psi$ yield as a function of charged-particle pseudorapidity density $\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta$ in pp collisions at $\sqrt{s}$ = 13 TeV with ALICE at the LHC are reported. The J/$\psi$ meson yield is measured at midrapidity ($|y|<0.9$) in the dielectron channel, for events selected based on the charged-particle multiplicity at midrapidity ($|\eta |<1$) and at forward rapidity ($-3.7<\eta <-1.7$ and $2.8<\eta <5.1$); both observables are normalized to their corresponding averages in minimum bias events. The increase of the normalized J/$\psi$ yield with normalized $\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta$ is significantly stronger than linear and dependent on the transverse momentum. The data are compared to theoretical predictions, which describe the observed trends well, albeit not always quantitatively.

   nucl-exhep-exPLB(2020)·95 citations
5. 05*

   $\Lambda \mathrm{K}$ femtoscopy in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

   ALICE Collaboration

   The first measurements of the scattering parameters of $\Lambda$K pairs in all three charge combinations ($\Lambda$K${}^{+}$, $\Lambda$K${}^{-}$, and $\Lambda {\mathrm{K}}_{\mathrm{S}}^0$) are presented. The results are achieved through a femtoscopic analysis of $\Lambda$K correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV recorded by ALICE at the LHC. The femtoscopic correlations result from strong final-state interactions, and are fit with a parametrization allowing for both the characterization of the pair emission source and the measurement of the scattering parameters for the particle pairs. Extensive studies with the THERMINATOR 2 event generator provide a good description of the non-femtoscopic background, which results mainly from collective effects, with unprecedented precision. Furthermore, together with HIJING simulations, this model is used to account for contributions from residual correlations induced by feed-down from particle decays. The extracted scattering parameters indicate that the strong force is repulsive in the $\Lambda {\mathrm{K}}^{+}$ interaction and attractive in the $\Lambda {\mathrm{K}}^{-}$ interaction. The data hint that the and $\Lambda {\mathrm{K}}_{\mathrm{S}}^0$ interaction is attractive, however the uncertainty of the result does not permit such a decisive conclusion. The results suggest an effect arising either from different quark-antiquark interactions between the pairs ($\mathrm{s}\overline{\mathrm{s}}$ in $\Lambda$K${}^{+}$ and $\mathrm{u}\overline{\mathrm{u}}$ in $\Lambda$K${}^{-}$) or from different net strangeness for each system (S = 0 for $\Lambda$K${}^{+}$, and S = $-2$ for $\Lambda$K${}^{-}$). Finally, the $\Lambda$K systems exhibit source radii larger than expected from extrapolation from identical particle femtoscopic studies. This effect is interpreted as resulting from the separation in space-time of the single-particle $\Lambda$ and K source distributions.

   nucl-exhep-exPRC(2021)·38 citations
6. 06*

   Z-boson production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

   ALICE Collaboration

   Measurement of Z-boson production in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=8.16$ TeV and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity $-4<{\eta }_{\mu }<-2.5$ and transverse momentum $p_{\mathrm{T}}^{\mu }>20$ GeV/$c$ in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass $60<m^{\mu \mu }<120$ GeV$c^2$ and rapidity $2.5<y_{cms}^{\mu \mu }<4$. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward ($-4.46<y_{cms}^{\mu \mu }<-2.96$) and forward ($2.03<y_{cms}^{\mu \mu }<3.53$) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a $3.4\sigma$ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.

   nucl-exhep-exJHEP(2020)·48 citations
7. 07*

   First measurement of quarkonium polarization in nuclear collisions at the LHC

   ALICE Collaboration

   The polarization of inclusive J/$\psi$ and ${\rm Y}(1\mathrm{S})$ produced in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV at the LHC is measured with the ALICE detector. The study is carried out by reconstructing the quarkonium through its decay to muon pairs in the rapidity region $2.5<y<4$ and measuring the polar and azimuthal angular distributions of the muons. The polarization parameters ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$ and ${\lambda }_{\theta \varphi }$ are measured in the helicity and Collins-Soper reference frames, in the transverse momentum interval $2<p_{\mathrm{T}}<10$ GeV/$c$ and $p_{\mathrm{T}}<15$ GeV/$c$ for the J/$\psi$ and ${\rm Y}(1\mathrm{S})$, respectively. The polarization parameters for the J/$\psi$ are found to be compatible with zero, within a maximum of about two standard deviations at low $p_{\mathrm{T}}$, for both reference frames and over the whole $p_{\mathrm{T}}$ range. The values are compared with the corresponding results obtained for pp collisions at $\sqrt{s}=7$ and 8 TeV in a similar kinematic region by the ALICE and LHCb experiments. Although with much larger uncertainties, the polarization parameters for ${\rm Y}(1\mathrm{S})$ production in Pb-Pb collisions are also consistent with zero.

   nucl-exhep-exPLB(2021)·70 citations
8. 08*

   Elliptic flow of electrons from beauty-hadron decays in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

   ALICE Collaboration

   The elliptic flow of electrons from beauty hadron decays at midrapidity ($|y|$ $<$ 0.8) is measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with the ALICE detector at the LHC. The azimuthal distribution of the particles produced in the collisions can be parameterized with a Fourier expansion, in which the second harmonic coefficient represents the elliptic flow, $v_2$. The $v_2$ coefficient of electrons from beauty-hadron decays is measured for the first time in the transverse momentum ($p_{\mathrm{T}}$) range 1.3-6 GeV/$c$ in the centrality class 30-50%. The measurement of electrons from beauty-hadron decays exploits their larger mean proper decay length $c\tau \approx$ 500 $\mu$m compared to that of charm hadrons and most of the other background sources. The $v_2$ of electrons from beauty hadron decays at midrapidity is found to be positive with a significance of 3.75$\sigma$. The results provide insights on the degree of thermalization of beauty quarks in the medium. A model assuming full thermalization of beauty quarks is strongly disfavoured by the measurement at high $p_{\mathrm{T}}$, but is in agreement with the results at low $p_{\mathrm{T}}$. Transport models including substantial interactions of beauty quarks with an expanding strongly-interacting medium describe the measurement.

   nucl-exhep-exPRL(2021)·47 citations
9. 09*

   Transverse-momentum and event-shape dependence of D-meson flow harmonics in Pb-Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV

   ALICE Collaboration

   The elliptic and triangular flow coefficients $v_2$ and $v_3$ of prompt D${}^0$, D${}^{+}$, and D${}^{\ast +}$ mesons were measured at midrapidity ($|y|<0.8$) in Pb-Pb collisions at the centre-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=5.02$ TeV with the ALICE detector at the LHC. The D mesons were reconstructed via their hadronic decays in the transverse momentum interval $1<p_{\mathrm{T}}<36$ GeV/$c$ in central (0-10%) and semi-central (30-50%) collisions. Compared to pions, protons, and J/$\psi$ mesons, the average D-meson $v_n$ harmonics are compatible within uncertainties with a mass hierarchy for $p_{\mathrm{T}}\lesssim 3$ GeV/$c$, and are similar to those of charged pions for higher $p_{\mathrm{T}}$. The coupling of the charm quark to the light quarks in the underlying medium is further investigated with the application of the event-shape engineering (ESE) technique to the D-meson $v_2$ and $p_{\mathrm{T}}$-differential yields. The D-meson $v_2$ is correlated with average bulk elliptic flow in both central and semi-central collisions. Within the current precision, the ratios of per-event D-meson yields in the ESE-selected and unbiased samples are found to be compatible with unity. All the measurements are found to be reasonably well described by theoretical calculations including the effects of charm-quark transport and the recombination of charm quarks with light quarks in a hydrodynamically expanding medium.

   nucl-exhep-exPLB(2021)·119 citations
10. 10*

    Reactor neutrino applications and coherent elastic neutrino nucleus scattering

    Maitland Bowen🇺🇸 · Patrick Huber🇺🇸

    Potential applications of neutrino detection to nuclear security have been discussed since the 1970s. Recent years have seen great progress in detector technologies based on inverse beta decay, with the demonstration of ton-scale surface-level detectors capable of high quality neutrino spectrum measurements. At the same time coherent elastic neutrino nucleus scattering has been experimentally confirmed in 2017 with neutrinos from stopped pion decay and there is a number of experiments aimed at seeing this reaction with reactor neutrinos. The large cross section and threshold-less nature of this reaction make it plausible to consider it for applications to nuclear security and here, we present a first direct comparison of the two reaction modes.

    ↳ physics.ins-dethep-exhep-phnucl-ex+1PRD(2020)·32 citations
11. 11*

    Convergence of electric quadrupole rotational invariants from the nuclear shell model

    J. Henderson🇨🇦

    Nuclei exhibit both single-particle and collective degrees of freedom, with the latter often subdivided into vibrational and rotational motions. Experimentally identifying the relative roles of these collective modes is extremely challenging, particularly in the face of possible shape coexistence. Model-independent, invariant quantities describing the deformation of a nucleus in the intrinsic frame have long been known but their determination potentially requires a large quantity of experimental data to achieve convergence. Through comparison with the nuclear shell model, the question of convergence will be addressed. Shell-model calculations performed in the $sd$- and $pf$-shell model spaces are used to determine electric-quadrupole matrix elements for a multitude of low-lying states. Relative contributions to the rotationally invariant quantities from multiple states can therefore be determined. It is found that on average, the inclusion of four intermediate states results in the leading-order invariant, $⟨Q^2⟩$, converging to within 10% of its true value and the triaxiality term, $⟨\cos \left(3\delta \right)⟩$, converging to its true value, though some variance remains. Higher-order quantities relating to the softness of the nuclear shape are found to converge more slowly. The convergence of quadrupole rotationally invariant sum rules was quantified in the $sd$- and $pf$-shell model spaces and indicates the challenge inherent in a full determination of nuclear shape. The present study is limited to relatively small valence spaces. Larger spaces, such as the rare-earth region, potentially offer faster convergence.

    ↳ nucl-thnucl-exPRC(2020)·17 citations
12. 12*

    Heavy flavor dynamics across system size at the LHC

    Roland Katz🇫🇷 · Caio A. G. Prado🇨🇳 · Jacquelyn Noronha-Hostler🇺🇸 · Alexandre A. P. Suaide🇧🇷

    One of the fundamental signatures of the Quark Gluon Plasma has been the suppression of heavy flavor (specifically D mesons), which has been measured via the nuclear modification factor, $R_{AA}$ and azimuthal anisotropies, $v_n$, in large systems. However, multiple competing models can reproduce the same data for $R_{AA}$ to $v_n$. In this talk we break down the competing effects that conspire together to successfully reproduce $R_{AA}$ and $v_n$ in experimental data using Trento+v-USPhydro+DAB-MOD. Then using our best fit model we make predictions for $R_{AA}$ and $v_n$ across system size for ${}^{208}PbPb$, ${}^{129}XeXe$, ${}^{40}ArAr$, and ${}^{16}OO$ collisions. We find that 0--10\% centrality has a non-trivial interplay between the system size and eccentricities such that system size effects are masked in $v_2$ whereas in 30--50\% centrality the eccentricities are approximately constant across system size and, therefore, is a better centrality class to study D meson dynamics across system size.

    ↳ nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2020)·0 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.