Featured Researches

Nuclear Experiment

A comprehensive analysis of differential cross sections and analyzing powers in the proton-deuteron break-up channel at 135 MeV

A selection of measured cross sections and vector analyzing powers, Ax and Ay, are presented for the pd break-up reaction. The data are taken with a polarized proton beam energy of 135 MeV using the Big Instrument for Nuclear-polarization Analysis (BINA) at KVI, the Netherlands. With this setup, Ax is extracted for the first time for a large range of energies as well as polar and azimuthal angles of the two outgoing protons. For most of the configurations, the results at small and large relative azimuthal angles differ in behavior when comparing experimental data with the theoretical calculations. We also performed a more global comparison of our data with theoretical calculations using a chi-square ( χ 2 ) analysis. The cross-section results show huge values of χ 2 /d.o.f.. The absolute values of χ 2 /d.o.f. for the components of vector analyzing powers, Ax and Ay, are smaller than the ones for the cross section, partly due to larger uncertainties for these observables. However, also for these observables no satisfactory agreement is found for all angular combinations. This implies that the present models of a three-nucleon force are not able to provide a satisfactory description of experimental data.

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Nuclear Experiment

A comprehensive study of analyzing powers in the proton-deuteron break-up channel at 135 MeV

A measurement of the analyzing powers for the 2 H ( p ⃗ ,pp)n break-up reaction was carried out at KVI exploiting a polarized-proton beam at an energy of 135 MeV. The scattering angles and energies of the final-state protons were measured using the Big Instrument for Nuclear-polarization Analysis (BINA) with a nearly 4π geometrical acceptance. In this work, we analyzed a large number of kinematical geometries including forward-forward configurations in which both the final-state particles scatter to small polar angles and backward-forward configurations in which one of the final-state particles scatters to large polar angles. The results are compared with Faddeev calculations based on modern nucleon-nucleon (NN) and three-nucleon (3N) potentials. Discrepancies between polarization data and theoretical predictions are observed for configurations corresponding to small relative azimuthal angles between the two final-state protons. These configurations show a large sensitivity to 3N force effects.

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Nuclear Experiment

A look into mirrors: A measurement of the β -asymmetry in 19 Ne decay and searches for new physics

High precision measurements of isospin T=1/2 decays in the neutron and nuclei provide strong model-independent constraints on extensions to the standard model of particle physics. A measurement of the β -asymmetry in 19 Ne decay between the initial nuclear spin and the direction of the emitted positron is presented which establishes this decay as the most precisely characterized nuclear mirror and fixes the Fermi-to-Gamow-Teller mixing ratio to ρ=1.6014(+21/−28 ) sys (8 ) stat . This is consistent with the previous, most precise measurement, produces a value of the CKM unitarity parameter V ud in agreement with the nuclear mirror, neutron and superallowed β -decay data sets, shows no evidence for second class currents, and can be effectively used with neutron decay data to place a limits on exotic tensor couplings.

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Nuclear Experiment

A method to test the coupling strength of the linear and nonlinear contributions to higher-order flow harmonics via Event Shape Engineering

A Multi-Phase Transport (AMPT) model is used to study the efficacy of shape-engineered events to delineate the degree of coupling between the linear and nonlinear contributions to the higher-order flow harmonics v 4 and v 5 . The study shows that the nonlinear contributions are strongly shape-dependent while the linear contributions are shape-independent, indicating little if any, coupling between the linear and nonlinear flow coefficients. The experimental verification of such patterns could be an invaluable tool for robust extraction of the linear and mode-coupled flow coefficients, especially for beam energies where the charged particle multiplicity and the event statistics precludes the use of current methods to establish the coupling strength.

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Nuclear Experiment

A search for a cosmologically-relevant boson in muon decay

Experiments looking for a lepton flavor-violating decay μ + → e + X 0 are reviewed in light of present-day germanium detector technology, with an eye on scenarios where a long-lived, slow-moving massive boson X 0 might have a cosmological impact. A broad swath of interesting, unexplored parameter space very close to the kinematic limit of the decay is found to be within the reach of a new proposed search. A number of possible roles for X 0 in past and present epochs can be investigated.

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Nuclear Experiment

A search for rare and induced nuclear decays in hafnium

A measurement of hafnium foil using a modified ultra-low-background high purity detector with optimized sample-to-detector geometry was performed at Laboratori Nazionale del Gran Sasso. Radiopurity of the stock Hf foil was studied in detail, in addition to an analysis of data collected over 310 days to search for rare processes that can occur in natural Hf isotopes. Firstly, limits on alpha decays of all natural Hf isotopes to the first excited state of the daughter nuclides were established in the range of 10 16 - 10 18 a (90% C.L.). Secondly, a search for modes of double electron capture and electron capture with positron emission in 174 Hf was performed, yielding half-life limits 10 16 - 10 18 a (90% C.L.). Lastly, novel dark matter-induced nuclear excitations in hafnium isotopes were investigated. For dark matter with 1 TeV/ c 2 mass, leading limits on the inelastic dark matter--nucleon cross section are set for mass splittings in the range 428 keV <δ< 473 keV.

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Nuclear Experiment

A sensitivity study of the primary correlators used to characterize chiral-magnetically-driven charge separation

A Multi-Phase Transport (AMPT) model is used to study the detection sensitivity of two of the primary correlators -- Δγ and R Ψ 2 -- employed to characterize charge separation induced by the Chiral Magnetic Effect (CME). The study, performed relative to several event planes for different input "CME signals", indicates a detection threshold for the fraction f CME =Δ γ CME /Δγ , which renders the Δγ -correlator insensitive to values of the Fourier dipole coefficient a 1 ≲2.5% , that is larger than the purported signal(signal difference) for ion-ion(isobaric) collisions. By contrast, the R Ψ 2 correlator indicates concave-shaped distributions with inverse widths ( σ −1 R Ψ 2 ) that are linearly proportional to a 1 , and independent of the character of the event plane used for their extraction. The sensitivity of the R Ψ 2 correlator to minimal CME-driven charge separation in the presence of realistic backgrounds, could aid better characterization of the CME in heavy-ion collisions.

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Nuclear Experiment

A stringent upper limit on the direct 3 α decay of the Hoyle State in 12 C

We investigate an implication of the most recent observation of a second J π = 2 + state in 12 C, which was measured using the 12 C( γ , α ) 8 Be (g.s.) reaction. In addition to the dissociation of 12 C to an α -particle and 8 Be in its ground state, a small fraction of events (2%) were identified as direct decays and decays to excited states in 8 Be. This allowed a limit on the direct 3 α partial decay width to be determined as Γ 3α <32(4) keV. Since this 2 + state is predicted by all theoretical models to be a collective excitation of the Hoyle state, the 3 α partial width of the Hoyle state is calculable from the ratio of 3 α decay penetrabilities of the Hoyle and 2 + states. This was calculated using the semi-classical WKB approach and we deduce a stringent upper limit for the direct decay branching ratio of the Hoyle state of Γ 3α Γ <5.7× 10 −6 , over an order of magnitude lower than previously reported. This result places the direct measurement of this rare decay mode beyond current experimental capabilities.

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Nuclear Experiment

A two-neutron halo is unveiled in 29 F

We report the measurement of reaction cross sections ( σ ex R ) of 27,29 F with a carbon target at RIKEN. The unexpectedly large σ ex R and derived matter radius identify 29 F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the 2 p 3/2 orbital, thereby vanishing the shell closure associated with the neutron number N=20 . The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of 27 F but are challenged for 29 F.

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Nuclear Experiment

Accessing tens-to-hundreds femtoseconds nuclear state lifetimes with low-energy binary heavy-ion reactions

A novel Monte Carlo technique has been developed to determine lifetimes of excited states in the tens-to-hundreds femtoseconds range. The method is applied to low-energy heavy-ion binary reactions populating nuclei with complex velocity distributions. Its relevance is demonstrated in connection with the 18 O(7.0 MeV/u) + 181 Ta experiment, performed at GANIL with the AGATA+VAMOS+PARIS setup, to study neutron-rich O, C, N, ... nuclei. Excited states in 17 O and 19 O, with known lifetimes, are used to validate the method over the ∼ 20-400 fs lifetime-sensitivity range. Emphasis is given to the unprecedented position resolution provided by γ -tracking arrays, which turns out to be essential for reaching the required accuracy in Doppler-shift correction, at the basis of the detailed analysis of γ -ray lineshape and resulting state lifetime determination. The technique is anticipated to be an important tool for lifetime investigations in exotic neutron-rich nuclei, produced with intense ISOL-type beams.

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