1. WITCH - a first determination of the beta-neutrino angular correlation coefficient in 35 Ar decay S. Van Gorp, M. Breitenfeldt, V. De Leebeeck,T. Porobic, G. Soti, M. Tandecki, N. Severijns (K.U.Leuven, Belgium), P. Friedag, C. Weinheimer (Univ. Munster, Germany), M. Beck (Univ. Mainz, Germany), V. Kozlov, F. Glück (Univ. Karlsruhe, Germany), D. Zákoucký (NPI-Rez, Prague, Czech)

2. Data analysis: 3 (or 4) steps 2/13 1. reconstruct the experimentally obtained spectrum from the data 2. Simulate the experimentally obtained spectrum, taking into account the experimental conditions (3.) verify your simulations with experimental observations The observed beam spot The energy distribution of the ions in the trap Ratio  `s/ions from the PhD 4. Fit the two spectra to extract the  angular correlation coefficient a Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

3. Experimental conditions June 2011 ISOLDE target broke few days before the actual run. Replaced with used target. => low 35 Ar yield (5.10 5 compared to 2.10 7 in yieldbook) HV electrode could not be operated as intended. Not-optimal focus of the electrodes caused a loss off 40% Losses in the decay-trap -> A low statistics experiment (~2600 ions/trapload). losses in the decay-trap due to non-optimized voltages and timings. The red curve (better settings) shows a more constant behavior 3/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

4. Proof of recoil ions - Guassian bell shape indicates the observation of recoil ions - Position distribution shows the presence of recoil ions and missing counts along the Y- axis. 4/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

5. measurements 500 ms cooling in the cooler-trap. Afterwards capture in the decay-trap. Measurement with and without retardation voltages. Reconstruction via: - Subtraction - Regression analysis - Overshoot peak - Fitting the data 5/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

6. Normalization (1) : subtraction Difference of measurements with and without retardation voltage applied. (normalized via regression analysis). Correct the data for 35 Ar half-life and losses in the decay-trap. Scale factor f equals 3.540(3) 6/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

7. (less good) normalizations (2,3) Data set 2: normalization on the overshoot peak Data set 3: normalization via a fit function of the data 7/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

8. Simulations: Compare obtained spectra with simulated spectra. Therefore: 1. Simbuca simulates the ion cloud in the decay-trap. 2. Ion-cloud parameters are fed to a MC simulation program (SimWITCH). Comsol multiphysics program is used to extract electric fieldmaps given the electrode voltages Magnetic fieldmaps from the magnet manufacturer Buffergas collisions and excitations are handled by Simbuca 8/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

9. Simulations: Simbuca Due to limited time the traps were not properly optimized: Transfer time was not set ideally 32.5 us instead of 38.5 us. -mean energy of 4.5 eV (instead of 0.2 eV) -ions positions in the decay-trap is 15 mm lower than the center 9/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

10. Simulations: SimWITCH (1) Simulations for - All retardation voltages (0V, 150V, 250V, 350V, 600V) - All charge states (1 +,2 +,3 +,4 +,5 + ) 1 + : 75(1)% 2 + : 17.3(4)% 3 + : 5.7(2)% 4 + : 1.7(2)% 5 + : < 1 % Including the charge state distribution (as measured with LPC trap) we can extract %ions reaching the MCP depending on the retardation step and a -> Fit the data with a linear combination of a=1 and a=-1 to obtain the final result for the beta-neutrino angular correlation factor a. 10/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

11. Simulations: SimWITCH (2) Ions are not properly focused on the MCP, due to the lower HV settings applied. The applied voltages are not high enough to pull the ions of the magnetic field lines. - Ions are lost on SPDRIF01 electrode. - The higher the charge-state of the daughter ion the better the focus. Input spectra 1+1+ 2+2+ 11/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

12. Extracting a The preliminary result from the analysis yields a = 1.12 (33) stat c 2 / n = 0.64 SM value of a =0.09004(16). Not including actual experimental conditions yields a = 2.62 (42) !! => This stresses the importance of simulations!! a=-1 a=1 12/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

13. Conclusion and outlook Conclusion: - Seems to have solved unwanted ionization - Magnetic shield and RFQ allow much more testing time. - First determination of a on the decay of 35 Ar with the WITCH experiment. Outlook: - Experiment in October already increased the available statistics and solved the losses in the decay trap and in the spectrometer. - Count rate can be improved by: 10 (ISOLDE) * 50 (measurement time) * 2 (measurement cycle) * 2 (focussing electrode efficiency) * 4 (tuning in the B-field) = 8000 times more statistics -> sqrt(8000)=90 meaning that it is possible to reduce the statistical error to 0.5 % 13/13 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

14. Thank you for your attention. Acknowledgements

15. Simulation validity Due to the low amount of ions the position distribution is not comparable but the radial distribution is being used. 15/19 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012

16. Chamomile scheme: practical usage Function provided by Hamada and Iitaka [2]: Gravitational force ≈ Coulomb Force Conversion coefficient: Needed: - 64 bit linux - NVIDIA Graphics Card that supports CUDA - CUDA environment v3.x Not needed: - CUDA knowledge - … Simon Van Gorp - Scientific meeting - 16.02.2011 16/21 [2]: http://arxiv.org/abs/astro-ph/0703100, 2007http://arxiv.org/abs/astro-ph/0703100

17. GPU vs CPU GPU blows the CPU away. The effect becomes more visible with even more particles simulated. Simulating 4000 ions with a quadrupole excitation for 100ms with buffer gas. Takes 3 days with a GPU compared to 3-4 years with a CPU! GPU improvement factorCPU and GPU simulation time Simon Van Gorp - Scientific meeting - 16.02.2011 17/21

18. Simbuca overview Simbuca is a modular Penning Trap simulation package that can be applied to simulate: Charged particles (+/- /N charges) Under the influence of B and E fields With realistic buffer gas collisions Coulomb interaction included Can run on GPU and CPU http://sourceforge.net/projects/simbuca/ http://dx.doi.org/10.1016/j.nima.2010.11.032 Simon Van Gorp - Scientific meeting - 16.02.2011 18/21 Simulation of Ion Motion in a Penning trap with realistic BUffer gas collisions and Coulomb interaction using A Graphics Card.

19. Usage of the program WITCH Behavior of large ion clouds Mass separation of ions Smiletrap (Stockholm) Highly charged ions Cooling processes ISOLTRAP (CERN) In-trap decay Determine and understand the mass selectivity in a Penning trap ISOLTRAP(Greifswald) isobaric buncher, mass separation and negative mass effect CLIC (CERN) Simulate bunches of the beam Simon Van Gorp - Scientific meeting - 16.02.2011 19/21