We report on the observation of previously-unknown isotope ^21Al, the first unbound aluminum isotope located beyond the proton dripline. The ^21Al nucleus decays by one-proton (1p) emission, and its in-flight decays were detected by tracking trajectories of all decay products with micro-strip silicon detectors. The 1p-emission processes were studied by analyses of the measured angular correlations of decay products ^20Mg+p. The 1p-decay energies of ground and low-lying excited states of ^21Al, its mass excess and proton separation energy value S_p=-1.1(1) MeV were determined.

The root mean square radii of the proton density distribution in ^{16-24}O derived from measurements of charge changing cross sections with a carbon target at ∼900A  MeV together with the matter radii portray thick neutron skin for ^{22-24}O despite ^{22,24}O being doubly magic. Imprints of the shell closures at N=14 and 16 are reflected in local minima of their proton radii that provide evidence for the tensor interaction causing them. The radii agree with ab initio calculations employing the chiral NNLO_{sat} interaction, though skin thickness predictions are challenged. Shell model predictions agree well with the data.

The neutron-rich 213Pb isotope was produced in the fragmentation of a primary 1 GeV A 238U beam, separated in FRS in mass and atomic number, and then implanted for isomer decay γ-ray spectroscopy with the RISING setup at GSI. A newly observed isomer and its measured decay properties indicate that states in 213Pb are characterized by the seniority quantum number that counts the nucleons not in pairs coupled to angular momentum J=0. The conservation of seniority is a consequence of a geometric phase associated with particle-hole conjugation, which becomes observable in semi-magic nuclei where nucleons half-fill the valence shell. The γ-ray spectroscopic observables in 213Pb are thus found to be driven by two mechanisms, particle-hole conjugation and seniority conservation, which are intertwined through a Berry phase.

In a high-energy fragmentation experiment at GSI an I=π(6+) isomer and its γ-decay are identified in 102Sn, the two-neutron neighbour of the doubly-magic 100Sn. Its half-life is measured to be T=1/2367(11) ns. The possible existence of further isomers is discussed in the framework of large-scale shell model (LSSM) calculations including up to five particle-hole excitations of the 100Sn core. From the precise B(E2; 6+→4+) strength and the recently remeasured value for B(E2; 8+→6+) in the two-proton hole neighbour 98Cd effective E2 polarization charges for protons and neutrons were inferred including LSSM corrections within the full N=4 0ħω space. The results are discussed in comparison to predicted and empirically determined effective operators.

We plan to conduct an experimental search for eta'-mesic nuclei in order to investigate in-medium properties of the eta' meson. A 2.5 GeV proton beam is employed to produce eta'-mesic C-11 nuclei with the C-12(p,d)eta'circle times C-11 reaction. Simultaneous measurements of the forward ejected deuterons and decay protons from eta'-mesic nuclei will allow us to achieve high experimental sensitivity. The experiment will be performed at GSI by making full use of the fragment separator FRS and the WASA detector system. The plan of this proposed experiment is described.

We plan a semi-exclusive measurement of the 12 C( p,dp ) reaction to search for η’-mesic nuclei, aiming at investigating in-medium properties of the η′-meson. We employ a 2.5 GeV proton beam impinging on a carbon target to produce η′-mesic 11 C nuclei via the 12 C( p,d )η′⊗ 11 C reaction. Using coincidence measurements of the forward going deuterons, important for missing-mass spectroscopy, and decay protons emitted from the η′-mesic nuclei. for event selection will provide a high experimental sensitivity to observe η’-mesic nuclei. We will perform the measurements by combining the WASA detector system with the fragment separator FRS at GSI and also with the Super-FRS at FAIR in the future. The plan of the experiments and the present status are reported.

The production of $\rm{K}^{*}(\rm{892})^{0}$ and $\phi(1020)$ in pp collisions at $\sqrt{s}$ = 8 TeV were measured using Run 1 data collected by the ALICE collaboration at the LHC. The $p_{\rm{T}}$-differential yields d$^{\rm 2}N$/d$y$d$p_{\rm{T}}$ in the range 0 $<$ $p_{\rm{T}}$ $<$ 20 GeV/$c$ for $\rm{K}^{*0}$ and 0.4 $<$ $p_{\rm{T}}$ $<$ 16 GeV/$c$ for $\phi$ have been measured at midrapidity $|y|$ $<$ 0.5. Moreover, improved measurements of the $\rm{K}^{*}(892)^{0}$ and $\phi(1020)$ at $\sqrt{s}$ = 7 TeV are presented. The collision energy dependence of $p_{\rm{T}}$ distributions, $p_{\rm{T}}$-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 measured to be similar to those found 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 $p_{\rm{T}}$-differential yields of $\rm{K}^{*0}$ and $\phi$ in pp collisions at $\sqrt{s}$ = 8 TeV are compared with the expectations of different Monte Carlo event generators.

We plan to conduct an experimental search for η0-mesic nuclei in order to investigate in-medium properties of the η0 meson. A 2.5 GeV proton beam is employed to produce η0-mesic 11C nuclei with the 12C(p,d)η0⊗ 11C reaction. Simultaneous measurements of the forward ejected deuterons and decay protons from η0-mesic nuclei will allow us to achieve high experimental sensitivity. The experiment will be performed at GSI by making full use of the fragment separator FRS and the WASA detector system. The plan of this proposed experiment is described.

Measurements of K*(892)(0) and phi(1020) resonance production in Pb-Pb and pp collisions at root s(NN) = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (vertical bar y vertical bar < 0.5) via their hadronic decay channels and the transverse momentum (p(T)) distributions are obtained for various collision centrality classes up to p(T) = 20 GeV/c. The p(T)-integrated yield ratio K*(892)(0)/K in Pb-Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the phi(1020)/K ratio does not show any suppression. Furthermore, the measured K*(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 phi(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K*(892)(0) decay products in the hadronic phase of the collisions. The K*(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 similar to 4-7 fm/c for central collisions. The p(T)-differential ratios of K*(892)(0)/K, phi(1020)/K, K*(892)(0)/pi, phi(1020)/pi, p/K*(892)(0) and p/phi(1020) are also presented for Pb-Pb and pp collisions at root s(NN) = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-p(T) phenomenon. (C) 2020 The Author(s). Published by Elsevier B.V.

The global polarization of the Λ and Λ ¯ hyperons (PH) has been measured in Pb–Pb collisions at √ S NN = 2.76 TeV and 5.02 TeV in ALICE at the Large Hadron Collider (LHC). The hyperon global polarization is found to be consistent with zero at both collision energies. The local polarization of the Λ and Λ ¯ hyperons along the beam ( z ) direction, P z , has also been measured in Pb–Pb collisions at √ S NN = 5.02 TeV. The P z , measured as a function of the hyperon emission angle relative to the second harmonic symmetry plane, exhibits a second harmonic sine modulation, as expected due to elliptic flow. The measurements of global and local hyperon polarization are reported for different collision centralities and as a function of transverse momentum in semicentral collisions. These results show the first experimental evidence of a non-zero hyperon P z in Pb–Pb collisions at the LHC.

The inclusive J/ψ production in Pb–Pb collisions at the center-of-mass energy per nucleon pair $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV, measured with the ALICE detector at the CERN LHC, is reported. The J/ψ meson is reconstructed via the dimuon decay channel at forward rapidity (2.5 < y < 4) down to zero transverse momentum. The suppression of the J/ψ yield in Pb–Pb collisions with respect to binary-scaled pp collisions is quantified by the nuclear modification factor (RAA). The RAA at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV is presented and compared with previous measurements at $$ \sqrt{s_{\mathrm{NN}}} $$ = 2.76 TeV as a function of the centrality of the collision, and of the J/ψ transverse momentum and rapidity. The inclusive J/ψ RAA shows a suppression increasing toward higher transverse momentum, with a steeper dependence for central collisions. The modification of the J/ψ average transverse momentum and average squared transverse momentum is also studied. Comparisons with the results of models based on a transport equation and on statistical hadronization are carried out.

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 < ycms< 0.14 and transverse momentum interval 2 < pT< 16 GeV/c. The multiplicity dependence of the production of electrons from heavy-flavour hadron decays was studied by comparing the pT spectra measured for different multiplicity classes with those measured in pp collisions (QpPb) and in peripheral p-Pb collisions (Qcp). The QpPb results obtained are consistent with unity within uncertainties in the measured pT 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.

The ALICE collaboration at the CERN LHC reports novel measurements of jet substructure in pp collisions at $\sqrt{s}$= 7 TeV and central Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 2.76 TeV. Jet substructure of track-based jets is explored via iterative declustering and grooming techniques. We present the measurement of the momentum sharing of two-prong substructure exposed via grooming, the $z_{\rm{g}}$, and its dependence on the opening angle, in both pp and Pb-Pb collisions. We also present the first measurement of the distribution of the number of branches obtained in the iterative declustering of the jet, which is interpreted as the number of its hard splittings. In Pb-Pb collisions, we observe a suppression of symmetric splittings at large opening angles and an enhancement of splittings at small opening angles relative to pp collisions, with no significant modification of the number of splittings. The results are compared to predictions from various Monte Carlo event generators to test the role of important concepts in the evolution of the jet in the medium such as color coherence.

A measurement of the production of prompt Lambda(+)(C) baryons in Pb-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC is reported. The Lambda(+)(C) and (Lambda) over bar (-)(C) were reconstructed at midrapidity (vertical bar y vertical bar < 0.5) via the hadronic decay channel Lambda(+)(C) -> pK(S)(0) (and charge conjugate) in the transverse momentum and centrality intervals 6 < p(T) < 12 GeV/c and 0-80%. The Lambda(+)(C)/D-0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at root s = 7 TeV and in p-Pb collisions at root S-NN = 5.02 TeV. In particular, the values in p-Pb and Pb-Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common P-T interval covered by the measurements in the two collision systems. The Lambda(+)(C)/D-0 ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The Lambda(+)(C) nuclear modification factor, R-AA, is also presented. The measured values of the R-AA of Lambda(+)(C), D-S(+) and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (R-AA(D0) < R-AA(DS+) < R-AA(Lambda C+)), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium. (C) 2019 European Organization for Nuclear Research. Published by Elsevier B.V.

Charged-particle spectra at midrapidity are measured in Pb–Pb collisions at the centre-of-mass energy per nucleon–nucleon pair sNN=5.02 TeV and presented in centrality classes ranging from most central (0–5%) to most peripheral (95–100%) collisions. Possible medium effects are quantified using the nuclear modification factor (RAA) by comparing the measured spectra with those from proton–proton collisions, scaled by the number of independent nucleon–nucleon collisions obtained from a Glauber model. At large transverse momenta (8

The first measurement of dielectron (e(+)e(-)) production in central (0-10%) Pb-Pb collisions at root S-NN = 2.76 TeV at the LHC is presented. The dielectron invariant-mass spectrum is compared to the expected contributions from hadron decays in the invariant-mass range 0 < m(ee) < 3.5 GeV/c(2). The ratio of data and the cocktail of hadronic contributions without vacuum rho(0) is measured in the invariant-mass range 0.15 < m(ee) < 0.7 GeV/c(2), where an excess of dielectrons is observed in other experiments, and its value is 1.40 +/- 0.28 (stat.) +/- 0.08 (syst.) +/- 0.27 (cocktail). The dielectron spectrum measured in the invariant mass range 0 < m(ee) < 1 GeV/c(2) is consistent with the predictions from two theoretical model calculations that include thermal dielectron production from both partonic and hadronic phases with in-medium broadened rho(0) meson. The fraction of direct virtual photons over inclusive virtual photons is extracted for dielectron pairs with invariant mass 0.1 < m(ee) < 0.3 GeV/c(2) and in the transverse-momentum intervals 1 < p(T,ee) < 2 GeV/c and 2 < p(T,ee) < 4 GeV/c. The measured fraction of virtual direct photons is consistent with the measurement of real direct photons by ALICE and with the expectations from previous dielectron measurements at RHIC within the experimental uncertainties.

The most remote isotope from the proton dripline (by 4 atomic mass units) has been observed: ^{31}K. It is unbound with respect to three-proton (3p) emission, and its decays have been detected in flight by measuring the trajectories of all decay products using microstrip detectors. The 3p emission processes have been studied by the means of angular correlations of ^{28}S+3p and the respective decay vertices. The energies of the previously unknown ground and excited states of ^{31}K have been determined. This provides its 3p separation energy value S_{3p} of -4.6(2)  MeV. Upper half-life limits of 10 ps of the observed ^{31}K states have been derived from distributions of the measured decay vertices.

Measurements of inclusive and direct photon production at midrapidity in pp collisions at root s = 2.76 and 8 TeV are presented by the ALICE experiment at the LHC. The results are reported in transverse momentum ranges of 0.4 < p(T) < 10 GeV/c and 0.3 < p(T) < 16 GeV/c, respectively. Photons are detected with the electromagnetic calorimeter (EMCal) and via reconstruction of e(+) e(-) pairs from conversions in the ALICE detector material using the central tracking system. For the final measurement of the inclusive photon spectra the results are combined in the overlapping p(T), interval of both methods. Direct photon spectra, or their upper limits at 90% C.L. are extracted using the direct photon excess ratio R-gamma, which quantifies the ratio of inclusive photons over decay photons generated with a decay-photon simulation. An additional hybrid method, combining photons reconstructed from conversions with those identified in the EMCal, is used for the combination of the direct photon excess ratio R-gamma, as well as the extraction of direct photon spectra or their upper limits. While no significant signal of direct photons is seen over the full p(T), range, R-gamma, for p(T), > 7 GeV/c is at least one sigma above unity and consistent with expectations from next-to-leading order pQCD calculations.

The production yield of prompt D mesons and their elliptic flow coefficient v 2 were measured with the Event-Shape Engineering (ESE) technique applied to mid-central (10–30

We report on the first femtoscopic measurement of baryon pairs, such as p-p, p-Lambda, and Lambda-Lambda, measured by ALICE at the Large Hadron Collider (LHC) in proton-proton collisions at root s = 7 TeV. This study demonstrates the feasibility of such measurements in pp collisions at ultrarelativistic energies. The femtoscopy method is employed to constrain the hyperon-nucleon and hyperon-hyperon interactions, which are still rather poorly understood. A new method to evaluate the influence of residual correlations induced by the decays of resonances and experimental impurities is hereby presented. The p-p, p-Lambda, and Lambda-Lambda correlation functions were fitted simultaneously with the help of a new tool developed specifically for the femtoscopy analysis in small colliding systems: Correlation Analysis Tool using the Schrodinger equation (CATS). Within the assumption that in pp collisions the three particle pairs originate from a common source, its radius is found to be equal to r(0) = 1.125 +/- 0.018 (stat)(-0.035)(+0.058) (syst) fm. The sensitivity of the measured p-Lambda correlation is tested against different scattering parameters, which are defined by the interaction among the two particles, but the statistics is not sufficient yet to discriminate among different models. The measurement of the Lambda-Lambda correlation function constrains the phase space spanned by the effective range and scattering length of the strong interaction. Discrepancies between the measured scattering parameters and the resulting correlation functions at LHC and RHIC energies are discussed in the context of various models.