Search for physics beyond the Standard Electroweak model with the WITCH experiment Simon Van Gorp PhD defense 28th of February, Leuven Promotor: Prof. Dr. Nathal Severijns

Outline The WITCH experiment Motivation Status Overview Simbuca, a Penning trap simulation package Graphics card to calculate Coulomb interaction between the ions Usage by other groups First determination of a with the WITCH experiment Data set Reconstruction of the data Results Non-neutral plasma Boundary with single particle regime Energy distribution Mass selectivity due to presence of an ion plasma Summary and outlook Simon Van Gorp Thesis defense 28th of February, 2011 2/30

Physics motivation Experimental limits [1]: |CS/CV| < 0.07 |CT/CA| < 0.09 =>Search for Scalar (or Tensor) Interactions Prime candidate for WITCH is 35Ar Low energy (several 100 eV)! Need for scattering free source [1]: Severijns, N., Beck, M., & Naviliat-Cuncic, O. (2006).Rev. Mod. Phys., 78(3), 991 Simon Van Gorp Thesis defense 28th of February, 2011 3/30

Overview of the WITCH setup ~7m Simon Van Gorp Thesis defense 28th of February, 2011 4/30

Experimental setup Penning traps: Cooler trap (He buffer gas 10-3 – 10-4 mbar) excitations Decay trap Scattering free source Retardation spectrometer [2] to measure the energy Conversion of radial to axial energy [2]: Lobashev, V. & Spivak, P. (1985). NIM A 240(2), 305 – 310 Simon Van Gorp Thesis defense 28th of February, 2011 5/30

Time situation PhD October 2007 35Cl contamination in the ISOLDE beam (ratio 25:1) Charge-exchange in REXTRAP (t1/2=70 ms) and WITCH (t1/2=8 ms) Unwanted electric discharges November 2009 Still a remaining 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 The goal is in sight Measure a Prepare the tools for analysis of a Simon Van Gorp Thesis defense 28th of February, 2011 6/30

Outline The WITCH experiment Motivation Status Overview Simbuca, a Penning trap simulation package Graphics card to calculate Coulomb interaction between the ions Usage by other groups First determination of a with the WITCH experiment Data set Reconstruction of the data Results Non-neutral plasma Boundary with single particle regime Energy distribution Mass selectivity due to presence of an ion plasma Summary and outlook Simon Van Gorp Thesis defense 28th of February, 2011 7/30

Simbuca 104 – 106 ions / trap cycle stored up to a few seconds in the decay trap. Simulation time scales with O(N2) with N being the number of particles Tree codes O(N log(N)) Scaled Coulomb approach Novel approach by using a graphics card (GPU) instead of conventional CPU. Simbuca code was build around this idea [3] Complete, modular, simulation package Different buffer gas routines and integrators Importing realistic field maps Made available for free [4] [3]: Van Gorp et al. 2011) NIM A 638 192-200 [4]: http://sourceforge.net/projects/simbuca/ Simon Van Gorp Thesis defense 28th of February, 2011 8/30

Why a GPU? High parallelism due to parallel stream processors SIMD structure (pipelining!) Very fast floating point calculations CUDA programming language 8 x 16 stream processors ≈ each comparable to one CPU = Comparable with a factory assembly line with threads being the workers Geforce 8800 GTX Simon Van Gorp Thesis defense 28th of February, 2011 9/30

Chamomile scheme Calculating gravitational interactions on a Graphics Card via the Chamomile scheme from Hamada and Iitaka (in 2007) [5]. i-particles piece available for each ‘assembly line’ j-particles piece presents itself sequentially to each line force is the output of each line [5]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/0703100, 2007 Simon Van Gorp Thesis defense 28th of February, 2011 10/30

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 11/30

Simbuca: usage by other groups WITCH Behavior of large ion clouds Energy and position distribution Smiletrap (Stockholm) Highly charged ions Cooling processes ISOLTRAP (CERN) In-trap decay [6] Investigate the influence of Coulomb repulsion between ions in a Penning trap ISOLTRAP (Greifswald) isobaric buncher, mass separation and negative mass effect [7] CLIC accelerator (CERN) Simulate bunches of the beam Piperade (Orsay and MPI Heidelberg) Simulate mass separation of ion clouds [6]: A. Herlert, S. Van Gorp et al. Recoil-ion trapping for precision mass measurements, to be published [7]: Wolf, R et al. (2011). Hyperfine Interactions, 199, 115–122 Simon Van Gorp Thesis defense 28th of February, 2011 12/30

Outline The WITCH experiment Motivation Status Overview Simbuca, a Penning trap simulation package Graphics card to calculate Coulomb interaction between the ions Usage by other groups First determination of a with the WITCH experiment Data set Reconstruction of the data Results Non-neutral plasma Boundary with single particle regime Energy distribution Mass selectivity due to presence of an ion plasma Summary and outlook Simon Van Gorp Thesis defense 28th of February, 2011 13/30

Data analysis: 3 steps 1. reconstruct the experimentally obtained spectrum from the data 2. Simulate the experimentally obtained spectrum, taking into account the experimental conditions 3. Fit the two spectra to extract the b-n angular correlation coefficient a Simon Van Gorp Thesis defense 28th of February, 2011 14/30

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 yield book) HV electrode could not be operated as intended. Non-optimal focus of the electrodes caused a loss off 40% Losses in the decay-trap The red curve (better settings) shows a more constant behavior -> A low statistics experiment (~2600 ions/trap load). Simon Van Gorp Thesis defense 28th of February, 2011 15/30

Measurements Reconstruction via: Subtraction Regression analysis Overshoot peak Fitting the data 0.5 s in the cooler trap. Afterwards transfer to the decay-trap. Simon Van Gorp Thesis defense 28th of February, 2011 16/30

Normalization via regression analysis Scale factor f =3.540(3) Difference of measurements with and without retardation voltage applied. Correct the data for 35Ar half-life and losses in the decay-trap. Simon Van Gorp Thesis defense 28th of February, 2011 17/30

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 tracking simulation (SimWITCH). Comsol multiphysics program is used to extract electric field maps given the electrode voltages Magnetic field maps from the magnet manufacturer Buffer gas collisions and excitations are handled by Simbuca Simon Van Gorp Thesis defense 28th of February, 2011 18/30

Simulations: Simbuca Due to limited time the traps could not be fully optimized: The transfer time was set to 32.5 us instead of (ideal) 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 Thesis defense 28th of February, 2011 19/30

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 % As measured with LPC trap [8] -> 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. [8] C. Couratin et al. , to be published Simon Van Gorp Thesis defense 28th of February, 2011 20/30

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. 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 Thesis defense 28th of February, 2011 21/30

Extracting a a=-1 a=1 The preliminary result from the analysis yields a = 1.12 (33)stat c2/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 Thesis defense 28th of February, 2011 22/30

Error budget Systematic error estimated to be maximum 10% Possible improvements on the statistics: Possible to reduce the statistical error from 30 % to below 0.5 % Effect Improvement factor ISOLDE target eff. 10 Measurement time 50 Measurement cycle 2 Electrode focus eff. Tuning in B-field 4 Total: 8000 Simon Van Gorp Thesis defense 28th of February, 2011 23/30

Outline The WITCH experiment Motivation Status Overview Simbuca, a Penning trap simulation package Graphics card to calculate Coulomb interaction between the ions Usage by other groups First determination of a with the WITCH experiment Data set Reconstruction of the data Results Non-neutral plasma Boundary with single particle regime Energy distribution Mass selectivity due to presence of an ion plasma Summary and outlook Simon Van Gorp Thesis defense 28th of February, 2011 24/30

Non-neutral plasmas 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 Indications that around 104 ions the ion motion behaves like a non-neutral plasma Simon Van Gorp Thesis defense 28th of February, 2011 25/30

Boundary plasma regime single particle Single particle regime Non-neutral plasma regime non-neutral plasma When storing around 5000 and 20000 ions they start to behave as a non-neutral plasma (in good agreement with [9]) Energy broadening due to Coulomb repulsion Resistance to excitations due to electric field of the ion cloud Simon Van Gorp [9]: Nikolaev et al. (2007). RCM, 21(22), 3527–3546 Thesis defense 28th of February, 2011 26/30

Energy distribution due to Coulomb repulsion 1 accumulation 18 accumulations experiment Comparison between simulations and experiments Energy increase due to mutual Coulomb repulsion between the ions Large influence in any recoil energy distribution measurement simulations Simon Van Gorp Thesis defense 28th of February, 2011 27/30

Multiple ion species trapped 90% 85Rb 10% 87Rb 25 ms Dipole excitation -> de center all ions 75 ms Quadrupole excitation -> mass selective centering wc-10 Hz wc wc+10 Hz When multiple ion species are trapped a more negative excitation frequency is favored [10,11] There is a large resistance to the applied excitation due to shielding of Ecloud No Coulomb With #Particles x2 [10]: Herlert, A., et al. (2011). Hyp. Int., 199, 211–220 [11]: Mitchell, D. W. & Smith, R. D. (1995). Phys. Rev. E, 52, 4366–4386 Simon Van Gorp Thesis defense 28th of February, 2011 28/30

Summary and Outlook Summary The versatile Penning trap simulation package, Simbuca, is the first application that uses a GPU to calculate the Coulomb interaction between ions in the Penning trap. An ion cloud in a Penning trap of more than 104 ions behaves like a non-neutral plasma which has effect on the measured recoil energy distribution First analysis and determination of a on the decay of 35Ar with WITCH Statistical precision of 0.5% is possible Outlook Simbuca will continue to be used by WITCH and other experiments GPU simulations is a new field that is gaining interest Investigate the properties of the non-neutral plasma in the WITCH Penning traps New experiments in October and November were taken with enough statistics for a determination of a with a statistical precision below 5% => New phase for WITCH: i.e. extensive investigation of systematic effects Simon Van Gorp Thesis defense 28th of February, 2011 29/30

Thank you for your attention

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

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 - … [2]: http://arxiv.org/abs/astro-ph/0703100 , 2007 32/21 Simon Van Gorp - Scientific meeting - 16.02.2011

Simon Van Gorp - Scientific meeting - 16.02.2011 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 factor CPU and GPU simulation time 33/21 Simon Van Gorp - Scientific meeting - 16.02.2011

Simon Van Gorp - Scientific meeting - 16.02.2011 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 Simulation of Ion Motion in a Penning trap with realistic BUffer gas collisions and Coulomb interaction using A Graphics Card. 34/21 Simon Van Gorp - Scientific meeting - 16.02.2011

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.

Data analysis: 3 steps 1. reconstruct the experimentally obtained spectrum from the data 2. Simulate the experimentally obtained spectrum, taking into account the experimental conditions (3.) verify 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

(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

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]) Simon Van Gorp [x]: F. Ames et al. (2005). NIM A, 538, 17–32 Thesis defense