The LPCTrap experiment: measurement of the β–ν angular correlation in 6He using a transparent Paul trap

We report on the status of the LPCTrap experiment, devoted to measure the β–ν angular correlation in the pure Gamow–Teller decay of ⁶He. This measurement is motivated by the search for the presence of tensor type contributions to the weak interaction. The ⁶He ions are confined in a novel transparent Paul trap. The β particles and the recoil ions are detected in coincidence to deduce the angular correlation parameter. The commissioning run performed in 2005 has given the proof of principle of this experiment. Up to 10⁵ coincidences were recorded during a second run in 2006.     

Direct experimental limit on neutron-mirror-neutron oscillations

In case a mirror world with a copy of our ordinary particle spectrum would exist, the neutron n and its degenerate partner, the mirror neutron n', could potentially mix and undergo nn' oscillations. The interaction of an ordinary magnetic field with the ordinary neutron would lift the degeneracy between the mirror partners, diminish the n' amplitude in the n wave function and, thus, suppress its observability. We report an experimental comparison of ultracold neutron storage in a trap with and without superimposed magnetic field. No influence of the magnetic field is found and, assuming negligible mirror magnetic fields, a limit on the oscillation time taunn' > 103 s (95% C.L.) is derived.     

Precision measurements in nuclear beta decay

Precision measurements in nuclear beta decay provide sensitive means to determine the fundamental coupling of charged fermions to weak bosons and to test discrete symmetries in the weak interaction. The main motivation of such measurements is to find deviations from Standard Model predictions as possible indications of new physics. I focus here on two topics related to precision measurements in beta decay, namely: (i) the determination of the V _ud element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix from nuclear mirror transitions and (ii) selected measurements of time reversal violating correlations in nuclear and neutron decays. These topics complement those presented in other contributions to this conference.     

Using GPU parallelization to perform realistic simulations of the LPCTrap experiments

We performed classical molecular dynamics (MD) simulations in order to search the conditions for efficient sympathetic cooling of highly charged ions (HCIs) in a linear Paul trap. Small two-component ion Coulomb crystals consisting of laser-cooled ions and HCIs were characterized by the results of the MD simulations. We found that the spatial distribution is determined by not only the charge-to-mass ratio but also the space charge effect. Moreover, the simulation results suggest that the temperature of HCIs do not necessarily decrease with increasing the number of laser-cooled ions in the cases of linear ion crystals. We also determined the cooling limit of sympathetically cooled ¹⁶⁵Ho¹⁴⁺ ions in small linear ion Coulomb crystals. The present results show that sub-milli-Kelvin temperatures of at least 10 Ho¹⁴⁺ ions will be achieved by sympathetic cooling with a single laser-cooled Be⁺.     

Precision measurements with LPCTrap at GANIL

The experimental achievements and the results obtained so far with the LPCTrap device installed at GANIL are presented. The apparatus is dedicated to the study of the weak interaction at low energy by means of precise measurements of the β ? ν angular correlation parameter in nuclear β decays. So far, the data collected with three isotopes have enabled to determine, for the first time, the charge state distributions of the recoiling ions, induced by shakeoff process. The analysis is presently refined to deduce the correlation parameters, with the potential of improving both the constraint deduced at low energy on exotic tensor currents (⁶He¹⁺) and the precision on the V _{u d} element of the quark-mixing matrix (³⁵Ar¹⁺ and ¹⁹Ne¹⁺) deduced from the mirror transitions dataset.     

Proton-Induced Deuteron Breakup at E lab P = 65 MeV in Quasi-Free Scattering Configurations

The proton-deuteron breakup cross sections and analyzing powers A _y for three kinematically complete configurations in a quasi-free-scattering geometry have been measured at E ^lab _P = 65 MeV. The data are compared with predictions of rigorous Faddeev calculations using the Argonne AV14, Bonn-B, Nijmegen-78, and Paris potentials. A satisfactory agreement between theory and experimental data, both for cross sections and analyzing powers, has been found. Received January 16, 1995; accepted in final form March 13, 1995     

Geant4 Monte Carlo simulations for the LPCTrap setup

The LPCTrap setup at GANIL is fully operational since 2006. The first breakthrough was the detection of 100000 coincidences between the $ \beta$ particles and the recoil ions from the decay of ⁶He⁺ produced by the SPIRAL source. After preparation, the decaying nuclei are confined in a transparent Paul trap which is surrounded by a $ \beta$ -telescope made of a double-sided silicon strip detector followed by a scintillator, and by a micro-channel plate position-sensitive detector to record in coincidence the $ \beta$ particles and the recoil ions. Simulations of this system are needed in order to study possible systematic effects and extract with high accuracy the $ \beta$ - $ \nu$ angular-correlation coefficient. A code based on Geant4 is well suited for this purpose. In this contribution the results from the simulations compared with those from the experiment will be presented and discussed.     

|V<Subscript>ud</Subscript>| from T = 1/2 mirror transitions and the role of atom and ion traps

Precision correlation measurements in nuclear beta decay using atom and ion traps have made significant progress since the last ENAM2004 Conference. We review here the achievements and plans of different projects and discuss for each of them their potential to contribute to the determination of the V_ud element of the Cabibbo-Kobayashi-Maskawa quark mixing matrix. This matrix element has traditionally been determined from the analysis of data in nuclear superallowed 0⁺ \( \rightarrow\) 0⁺ transitions, neutron decay and pion beta decay but can also independently be determined from data in nuclear mirror transitions. This requires the measurement of correlation parameters in such decays to determine the Gamow-Teller to Fermi mixing ratio which, in most cases, dominates the error on the extracted value of | V _ud| .     

First Tests of a Linear Radiofrequency Quadrupole for the Cooling and Bunching of Radioactive Light Ions

A linear radiofrequency quadrupole has been built at the LPC-Caen for the manipulation of radioactive ions. The system was designed for the cooling and bunching of a continuous beam using the buffer gas cooling technique. The technique is being extended to its ultimate limit to apply it for the cooling of light ions using H₂ as buffer gas. The bunches are to be injected into a transparent Paul trap for further decay studies. The cooling and bunching section of the system has been successfully tested off-line with a source of stable ions. We describe here the specifications of the device and present the results of the first tests.

     

Temperature measurement of 6He?+? ions confined in a transparent Paul trap

The LPCTrap setup is a transparent Paul trap dedicated to the measurement of the ???C?? correlation coefficient a _?|? in the ?? decay of trapped radioactive nuclides. In a first experiment, the system has been used to record ??10⁵ coincidences between the ?? particles and recoiling ions emitted from the decay of ⁶He^?+? ions. The analysis of the collected data has already shown that the size of the ⁶He^?+? ion cloud confined in the Paul trap is a critical parameter, potentially limiting the accuracy on the a _?|? measurement. We report here the precise determination of the trapped ion cloud temperature and size. This was performed by extracting the trapped ions toward a position sensitive micro channel plate detector at different phases of the RF driving field. We find a temperature T _exp ?= 0.107(7) eV, consistent with the temperature values inferred using two other observables but 20% higher than the temperature T _sim ?= 0.09 eV predicted by realistic simulations of the ions interacting with the H₂ buffer gas.