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Search for physics beyond the standard electroweak model with the WITCH experiment. Simon Van Gorp 28 th of February 2011, Leuven. Promotor : Prof. Dr. Nathal Severijns. Outline. WITCH Motivation Overview Status 2007 Simbuca Graphics card Buffer gas routines An example
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Search for physics beyond the standard electroweak model with the WITCH experiment Simon Van Gorp 28th of February 2011, Leuven Promotor: Prof. Dr. NathalSeverijns
Outline • WITCH • Motivation • Overview • Status 2007 • Simbuca • Graphics card • Buffer gas routines • An example • June 2011 experiment • Data set • Reconstruction of the data • Simulations • results • Nonneutral plasmas • Boundary with one-particle regime • Penning trap excitations • One species • Multiple species • Conclusion Thesis defense
Physics motivation EXP [1]: |CS/CV| < 0.07 |CT/CA| < 0.09 =>Search for scalar (or Tensor) Interactions Low energy (couple 100 eV)! • Need for scattering free source Thesis defense [1]: Severijns, N., Beck, M., & Naviliat-Cuncic, O. (2006).Rev. Mod. Phys., 78(3), 991.
Overview ~7m Thesis defense
Experimental setup • Penning traps • Preparation trap • Helium buffer gas (10-3 - 10-4 mbar) • Possible excitations • Decay trap • scattering-free source • Energy determination with retardation spectrometer • Conversion of radial in axial energy Thesis defense
Time situation of the PhD • October 2007 • 35Cl contamination (ratio 25:1) • Charge exchange in REXTRAP (t1/2=70 ms) and WITCH (t1/2=8 ms) • Unwanted ionization effects (sudden discharges) => Upgrade campaign to tackle those issues (WITCH 2.0) • November 2009 • Still small ionization that was not noticed before was solved by installation of a wire Not covered in my thesis but in PhD thesis of Michael Tandecki • Our goal was in sight • Measure a • Prepare the tools for such the analysis of a Thesis defense
Simbuca • 104 – 106 ions / trap cycle stored up to a few seconds in the decay trap. • Simulation time scales with O(N2) • Tree codes O(N log(N)) • Scaled Coulomb approach • Novel approach by using the GPU instead of conventional CPU: Simbuca code • Complete simulations package • Different buffer gas routines and integrators • Importing realistic field maps Thesis defense
Integrators and buffer gas models • Integrators: • 4th and 5th order Runga Kutta with adaptive step size and error control. • 1st order (predictor corrector) Gear method. • Buffer gas models: • Langevin or polarizability model (= for all mases) • Ion Mobility based model ( ≈ for all mases) • HS1 SIMION model Simon Van Gorp – MPI Heidelberg –14.02.2012
Why a GPU? • GPU • -high parallelism • -very fast floating point calculations • -SIMD structure (pipelining!) • Stream processor • ≈ CPU • = Comparable with a factory assembly line with threads being the workers • Geforce 8800 GTX Simon Van Gorp Thesis defense 28th of February, 2011 9/x
Chamomile scheme • Calculating gravitational interactions on a Graphics Cardvia the Chamomile scheme from Hamada and Iitaka (in 2007). • Why a GPU? • -parallelism! • -only 20 float operations • -CUDA programming • language for GPU’s • i-particles piece available for each ‘assembly line’ • j-particles piece presents itself sequentially to each line • force is the output of each line [7]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/0703100, 2007 Simon Van Gorp Thesis defense 28th of February, 2011 10/x
Chamomile scheme: practical usage • Function provided by Hamada and Iitaka: • Gravitational force ≈ Coulomb Force • Conversion coefficient: • Needed: - 64 bit linux • - NVIDIA Graphics Card that supports CUDA • - CUDA environment v2.3 - 4.0 • Not needed: -CUDA knowledge • -… Simon Van Gorp Thesis defense 28th of February, 2011 11/x
GPU vs CPU • GPU blows the CPU away. The effect becomes more visible with even more • particles simulated. • Simulated is a quadrupole excitation for 100 ms with buffer gas. This takes 3 days • with a GPU compared to 3-4 years with a CPU! GPU improvement factor CPU and GPU simulation time Simon Van Gorp Thesis defense 28th of February, 2011 12/x
Simbuca: outlook and future • 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 • Piperade (Orsay and MPI Heidelberg) • Simulate mass separation of ion species Simon Van Gorp - Scientific meeting - 16.02.2011 13/21
Data analysis: 3 (or 4) steps • 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 b`s/ions from the PhD • 4.Fit the two spectra to extract the b-n angular correlation coefficient a Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Experimental conditions June 2011 • ISOLDE target broke few days before the actual run. Replaced with used target. => low 35Ar yield (5.105 compared to 2.107 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 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
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. Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
measurements • Reconstruction via: • Subtraction • Regression analysis • Overshoot peak • Fitting the data • 500 ms cooling in the cooler-trap. Afterwards capture in the decay-trap. • Measurement with and without retardation voltages. Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Normalization (1) : subtraction • Scale factor f equals 3.540(3) • Difference of measurements with and without retardation voltage applied. (normalized via regression analysis). • Correct the data for 35Ar half-life and losses in the decay-trap. Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
(less good) normalizations (2,3) • Data set 2: normalization on the overshoot peak • Data set 3: normalization via a fit function of the data Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Simulations: • Compare obtained spectra with simulated spectra. Therefore: • 1. Simbucasimulates the ion-cloud in the decay-trap. • 2. Ion-cloud parameters are fed to a MC simulation program (SimWITCH). • Comsolmultiphysics 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 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
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 Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
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. Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
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 pullthe ions of the • magnetic field lines. Input spectra 2+ 1+ • - Ions are lost on SPDRIF01 electrode. • - The higher the charge-state of the daughter ion the better the focus. Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Extracting a a=-1 a=1 • The preliminary result from the analysis yields a = 1.12 (33)statc2/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!! Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Conclusion and outlook • Conclusion: • - Seems to have solved unwanted ionization • - Magnetic shield and RFQ allow much more testing time. • - First determination of aon the decay of 35Ar 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 % Simon Van Gorp – WITCH collaboration meeting – 21 February 2012
Non-neutral plasmas: an outlook for WITCH • When trapping a large amount of ions, the cloud`s own electric field will create an E x B drift force for the ions with • Good agreement between calculated and fit value (factor 2). • Indications that around 104 ions the ion motion behaves like a nonneutral plasma Thesis defense
Boundary single particle & nonneutral plasma regime • Single ions regime: • Nonneutral plasma regime: When storing around 5000 and 20000 ions the ions behave like a nonneutral plasma (in good comparison with [x]) - Energy broadening due to Coulomb repulsion - Resistance to excitations due to electric field of the ion cloud Thesis defense [x]: Nikolaevet al. (2007). RCM, 21(22), 3527–3546
Single ion species trapped • Plot centered 133Cs ions vs. duration of the quadrupole excitation • Losses due to Coulomb effects • Resonant excitation frequency tends to be more positive (as in Ref. [x]) Thesis defense [x]: F. Ames et al. (2005). NIMA, 538, 17–32
Multiple ion species trapped • When multiple ion species are trapped a more negative frequency is favored [x] • Seems to depend on the N (not on n) • There is a large resistance to the applied excitation due to shielding of Ecloud • No C • C • ratio • 25% • to • 10% • Nx2 Thesis defense [x]: Herlert, A., et al. (2011). Hyperfine Interactions, 199, 211–220. 10.1007/s10751-011-0316-6.
Conclusion and Outlook • Conclusion • A versatile Penning trap simulation package is the first application that uses a GPU to calculate the Coulomb interaction between ions in the Penning trap. • First analysis and determination ofaon the decay of 35Ar with the WITCH experiment • Outlook • Simbuca will continue to be used by WITCH and other experiments. • Mass purification in Penning traps is a new field that is gaining interest • Investigate the properties of the non-neutral plasma in the WITCH Penning traps • New phase for WITCH, i.e. extensive investigation of systematic effects Thesis defense
Conclusion and outlook • Conclusion: • - Seems to have solved unwanted ionization • - Magnetic shield and RFQ allow much more testing time. • - First determination of aon the decay of 35Ar 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 % Simon Van Gorp – WITCH collaboration meeting – 21 February 2012