WITCH - a first determination of the beta-neutrino angular correlation 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. Gluck (Univ. Karlsruhe, Germany), D. Zakoucky (NPI-Rez, Prague, Czech), E. Liénard, X. Fléchard, C. Couratin, G. Ban (LPCC, Caen, France)

Overview 2/19 Motivation Experimental Setup WITCH status Measurement of a on 35 Ar Penning trap and MC Simulations Extracting a Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Motivation EXP: |C S /C V | < 0.07 |C T /C A | < 0.09 WITCH measures the beta-neutrino angular correlation coefficient, a. Which is extracted from the recoil energy of the nucleus after beta-decay. =>Search for scalar (or Tensor) Interactions Low energy (couple 100 eV)!  Need for scattering free source 3/19 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

mm Experimental Setup 4/19 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Retardation spectrometer 5/19 Energy conversion Ion reflected if Energy_ion < Energy_retardation retardation barrier is changed and #ions coming over the barrier are counted. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 traps

Isotope selection Simon Van Gorp – TCP Saariselkä /19 Interesting from a physics point of view Production ISOLDE ~ 10 6 / 10 7 particles per second Half-life: order of 1 s Stable daughter isotope Decay mode: b - (± 10 times more recoil ions than b + ) Due to shake-off the daughter ion can have a charge-state up to 5 + Minimal isobaric/isomeric contamination Simple decay scheme => 35 Ar

WITCH overview before run 2011 November 2009: Measurement on 35 Ar showed voltage dependent ionization June 2010: Measurement with 144 Eu, unfortunately a mixed cocktail beam from ISOLDE. Too low statistics to extract a recoil spectrum. Wire to reduce the secondary ionization proved to work. November 2010: Magnetic Shielding and RFQ operational. WITCH can work in parallel with REX-ISOLDE! -> Much more testing time: necessary for a precision experiment! would be even better at June 2011 Measuring a recoil spectrum on 35 Ar 7/19 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 June 2009 MondayTuesdayWednesdayThursdayFridaySaturdaySunday 1 – REX run Plan: det. MCP testing, sec. Ionization (Na22) 2 – REX run Plan: det. MCP testing, sec. Ionization (Na22) 3 – ISOLTRAP Plan: det. MCP testing, sec. Ionization (Na22) Simon n/a 4 – ISOLTRAP Plan: det. MCP testing, sec. Ionization (Na22) 5 – ISOLTRAP Plan: det. MCP testing, sec. Ionization (Na22) 6 – ISOLTRAP Plan: det. MCP testing, sec. Ionization (Na22) 7 – Belgian elections Plan: Back to CERN (with car) 8 Plan: tune REX beam into WITCH 9 Plan: tune REX beam into WITCH 10 Plan: tune REX beam into WITCH 11 – REX set-up Optional: baking & activation 12 – REX set-up Optional: baking & activation 13 Plan: tune REX beam into WITCH Optional: baking & activation 14 Plan: tune REX beam into WITCH Optional: baking & activation 15 – REX set-up Plan: baking & activation Brix? 16 – REX run Plan: baking & activation 17 – REX run Plan: baking & activation 18 – REX run Plan: baking & activation 19 – REX run Plan: baking & activation 20 – REX run Plan: baking & activation 21 – REX run Plan: cool and pumping down of the system 22 – REX run Plan: cool and pumping down of the system 23 – REX run Plan: cool and pumping down of the system 24 – REX run Plan: cool and pumping down of the system 25 Plan: tune REX beam into WITCH (with PDT) + trap tests 26 Plan: tune REX beam into WITCH (with PDT) + trap tests 27 Plan: tune REX beam into WITCH (with PDT) + trap tests 28 Plan: tune REX beam into WITCH (with PDT) + trap tests 29 Plan: tune REX beam into WITCH (with PDT) + trap tests 30 Plan: tune REX beam into WITCH (with PDT) + trap tests

35 Ar: unwanted ionization Ionization depends on the retardation barrier voltage. Nov 2009 run on 35 Ar 6 seconds spectrum Retardation voltage (0 -> 500V) from s 8/19 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Unwanted Penning Trap in WITCH Retardation barrier for ions = Potential well for e - trapped e - in the spectrometer ionize rest gas which is creating ionization. Installation of a wire in the spectrometer. If an e - hits this wire it will be picked up by the power supply and lost. -> Effective method to empty the unwanted Penning trap. 9/19 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt e e e e e e e e ionization secondary electron emission -

Solution: the spectrometer wire 10/19 Measurement on 144 Eu (June 2010) with the wire installed. No ionization observed. => Ready for a measurement on 35 Ar in 2011 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Experimental conditions 11/19 ISOLDE target broke few days before the actual run. Replaced with used target. => low 35 Ar yield ( compared to 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. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 losses in the decay-trap due to non-optimized voltages and timings. The red curve (better settings) shows a more constant behavior

measurements 12/ ms cooling in the cooler-trap. Afterwards capture in the decay-trap. Measurement with and without retardation voltages. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 Normalization on # ions in decay-trap = #ions in overshoot peak

normalization 13/19 Difference of measurements with and without retardation voltage applied. (normalized with #ions decay-trap). Correct the data for 35Ar half-life and losses in the decay-trap. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Simulations: 14/19 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 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Simulations: SimWITCH 15/19 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. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 Input spectra

Simulations to extract a 16/19 Simulations for - All retardation voltages (0V, 150V, 250V, 350V, 600V) - All charge states (1 +,2 +,3 +,4 +,5 + ) 1 + : 77% 2 + : 16% 3 + : 5% 4 +,5 + : 2% 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 - low-energy fundamental-interactions physics at – 4 okt 2011

Extracting a 17/19 The preliminary result from the analysis yields a = 0.80 (49) stat c 2 /N= 0.72 SM value of a =0.9004(16). Not including actual experimental conditions yields a = 5.98 (97) !! => This stresses the importance of simulations!! 7000 ions in spectrum. Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011 a=-1 a=1 a=0.80 (49)

Conclusion and outlook 18/19 Conclusion: - Seem to have solved unwanted ionization - Magnetic shield and RFQ allow much more testing time. - First determination of a on 35 Ar with the WITCH experiment. Outlook: - Upcoming experiment end October. - 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 - low-energy fundamental-interactions physics at – 4 okt 2011

Thank you for your attention. Acknowledgements

Backup slides Simon Van Gorp – TCP Saariselkä /24

g -> create e -  ionization collisions with gas molecules  secondary electrons and positive ions; secondary emission on cathode due to positive ion impact  more electrons  more ionization collisions  more secondary electrons and ions avalanche, self sustained discharge + + e e e e e e e e ionization secondary electron emission - - Unwanted discharges: Townsend discharge Townsend discharge (bad vacuum, with or without magnetic field) 21/21 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

trapped e - spend long time between cathode and anode  large pathlength  increased probability for discharge, even in good vacuum Penning Discharge (good vacuum, with magnetic field) + + e e e e e e e e ionization secondary electron emission - - Unwanted Penning Traps 22/21 Simon Van Gorp - low-energy fundamental-interactions physics at – 4 okt 2011

Additional proof for recoil ions Simon Van Gorp – TCP Saariselkä /24 Pulse height distribution of the ions is also registered. This is typically exponential for beta-particles and dark counts. And bell shaped for ions.

Simulations: Simbuca 24/24 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 - low-energy fundamental-interactions physics at – 4 okt 2011

Stable testing environment Simon Van Gorp – TCP Saariselkä /24 WITCH magnet interferes with Rex-runs Magnetic mu-metal shielding around part of the Rex-EBIS Possibility to run WITCH in parallel with a 3T magnetic field. WITCH ion source has low intensity and is continuous high intensity pulsed ISOLDE beam Small RFQ (15 cm) in combination with the ion source. RFQ can deliver bunches of 10^7 ions with 2.5 us time spread. Picture shielding

Simulation Motivation Data analysis by particle tracking routine to recreate a spectrum. A good understanding of the source of ions is needed. WITCH: ions per cycle -> Computer simulations are dominated by the Coulomb interaction calculation Solution: use a Graphics card to simulate Coulomb interactions. Development of the Simbuca simulation package Parameters to characterize Temperature (=Energy) # ions Position distribution Simon Van Gorp - Scientific meeting /21

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 /21 [2]: http://arxiv.org/abs/astro-ph/

The spectrometer wire Good correspondence between simulation and experimental data. The creation of the ionization can be stopped with installing a wire. We understand the ionization effect and More tests with a centered wire will be done Simon Van Gorp - Scientific meeting /21 Measurement on 144 Eu (June 2010) with the wire installed -> no ionization was seen

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 /21

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

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 /21

Quadrupole excitation Mass selective excitation on the frequency w c = q.B/m Continuous conversion between Magnetron and cyclotron radii. The cyclotron radius is cooled by Buffer gas collisions -> mass selective centering/cooling of ions The size of the final ion cloud one can reach is influenced by the Coulomb interaction Simon Van Gorp - Scientific meeting /21

Quadrupole excitation – movie Argon (150 ions ) and Chlorine (ions) mixture 1) 10ms w c excitation quadrupole excitation 2) 5ms w - dipole excitation 3) w c excitation quadrupole excitation Simon Van Gorp - Scientific meeting /21

frequency scans The effect of the Coulomb interaction is not yet understood All highly depended on mass, amplitudes, times of excitations… Simon Van Gorp - Scientific meeting /21 # particles / 100

Conclusion The WITCH experiment New traps installed We understand the small ionization trap in the spectrometer More tests with a (centered) wire will be done before the next beam time The Magnetic shielding works -> WITCH can work in parallel with REX-ISOLDE The Simbuca Code A big simulation-time gain to calculate Coulomb interactions on a GPU A new tool to investigate how large ion clouds are behaving and to explain observed frequency shifts Necessary for WITCH and being used by other groups Will be compared to experimental data in upcoming months Simon Van Gorp - Scientific meeting /21

Retardation spectrometer A potential barrier is applied and the #ions going over the barrier are counted with an MCP detector. This potential barrier is changed -> A spectrum is measured. Simon Van Gorp - Scientific meeting /21

WITCH History Simon Van Gorp - Scientific meeting first recoil spectrum measured 124 In First notice of discharges Electrodes could not be operated as intended 2007 physics run 35 Ar Discharges returned Stable 35 Cl + domination in the beam Trap-halflife of 35 Ar + was 8 ms Electrodes could not be operated as planned 2008 Technical improvements Vacuum upgrade All-metal buffer gas 37/24 spectrometer potential (V) 500V 0V

Discharges: example Simon Van Gorp - Scientific meeting  Huge increase in count rate  Can happen in couple of hours/minutes  Unexpected  Some discharges only happen in combination with a g source The energy barrier was set to +500 V in the first 3.4 seconds. After this the spectrometer switches to 0 V and it awaits the next cycle. 3 types of discharges 1)Townsend discharge (bad vacuum) 2)Vacuum breakdown (sharp electrodes) 3)Penning Discharge (combination of B and E field) 38/24

Coulomb interactions Simon Van Gorp – TCP Saariselkä Coulomb force scales with O(N 2 ) Tree methods (Barnes Hut, PM, P 3 M, PIC, FMM) reduces this to O(N log N) 39/12 Space is divided in nodes. Which are subdivided A node has the total charge and mass, and is located on the centre of mass. Approx. long range force by aggregating particles into one particle and use the force of this one particle Scaled Coulomb Force puts more weight to the charge of one ion to simulate more ions. Works well [1] [1]: D. Beck et al, Hyp. Int. 132, 2001

Why a GPU? Simon Van Gorp – TCP Saariselkä /12 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

Michaël Tandecki - Werkbespreking – 09/12/2009 Secondary ionization (2009) July 2009; measurement with same 60 Co as before (70% of the source strength, t 1/2 ~ 1925d)  Clear effect on background 20% higher when 450 V only 2.5 cps Much more decays are expected for 35 Ar 450V 0V spectrometer potential (V)

Michaël Tandecki - Werkbespreking – 09/12/2009 Charge exchange (with Ar) Situation in 2007: ‘Charge exchange half-life’ in REXTRAP; 75 ms in WITCH; 8 ms (= not enough to cool)

Michaël Tandecki - Werkbespreking – 09/12/2009 Charge exchange: improvements NEG pump He-57 gas bottle All-metal reducer Needle valve To turbo pump Full-range gauge All-metal angle valves

Michaël Tandecki - Werkbespreking – 09/12/2009 Most important issues with 35 Ar in 2007 Isobaric contamination from 35 Cl During the run: 25 times more Cl than Ar Charge exchange with buffer gas We couldn’t cool the ion cloud, because the ions were neutralized before being cooled Secondary ionization ‘Noise’/discharges showing up when switching the spectrometer

Simon Van Gorp - Scientific meeting Electropolishing the electrodes beforeafter 2 cm Most probably the reason why the huge discharge in the spectrometer is gone. Discharge with g -source gone! 45/24

Chamomile scheme Simon Van Gorp – TCP Saariselkä Calculating gravitational interactions on a Graphics Card via the Chamomile scheme from Hamada and Iitaka (in 2007). 46/12 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 [2]: T. Hamada and T. Iitaka, arXiv.org:astro-ph/ , 2007

Simon Van Gorp - Scientific meeting Improving the vacuum Vacuum system dry scroll pumps instead of rotary pumps extra valves in front of turbos for ‘vacuum safety’ Detector electropolishing of surrounding electrode Spectrometer redesign of some electrodes electropolishing of re-acceleration electrodes NEG foil around biggest retardation electrode Traps better Ti (>< Al) structure buffer gas system is ‘all-metal’ now NEG foil + resistive heater around the traps VBL teflon electrode connections gone installation of NEG coated chambers non-UHV compatible materials gone (Zn, …) HBL untouched

Michaël Tandecki - Werkbespreking – 09/12/2009 High voltage / re-acceleration

Michaël Tandecki - Werkbespreking – 09/12/2009 High voltage / re-acceleration

Michaël Tandecki - Werkbespreking – 09/12/2009 High voltage / re-acceleration Optimal settings normal settings Recently obtained SPACCE01 -2 kV-1.4 kV -2 kV SPACCE kV -2 kV -8 kV SPEINZ V -500 V -500V SPDRIF kV -550 V -8 kV SPDRIF kV -7 kV -9 kV SPACCE01 SPACCE02 SPEINZ01 SPDRIF01 SPDRIF02 Detector MCP Compensation magnet

Simon Van Gorp – TCP Saariselkä /12 Simbuca overview Simonion is a modular Penning Trap simulation package. Reading external fieldmaps Trap excitations 3 different integrators 2 buffergas routines Can run on CPU and GPU Compile with g++ or icpc A root analysis file is provided A Makefile is provided