NEWS: measurements at sub keV energies with spherical detectors

1. NEWS: measurementsatsubkeVenergieswithspherical detectors G Gerbier + I Giomataris, J Derre, P Magnier, A Dastgheibi, D. Jourde, M Gros, E Bougamont, XF Navick, TPapaevangelou, J Galan, G TsiledakisIRFU–Saclay on behalf of NEWS collaboration Introduction to the detector Lowenergy investigations -preliminary- Calibrations, characterisation Measurementsat LSM NEWS : neutrino coherentscatteringmeasurement 6th TPC Symposium- Paris-2012

2. SphericalProportionalCounters Drift region • Spherecavity + sphericalsensor + HT • Lowthreshold (low C) • Fiducialselection by risetime • Flexible (P, gaz) • Large mass / large volume • Robust, simple, cheap, sealedmode • Digitisation @ 1 MHz, soft trigger • 2 LEP cavity130 cm Øtested • 1 lowactivity 60 cm Ø in operation @ LSM Amplregion

3. RunwithAr/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM NB: no start => risetime records place and/or history of energydeposition 210Po 5.3 MeV If localisedenergydeposition, rise time depends of radius (diffusion) n capt on 3He 764 keV Rise time (s) alpha If track, rise time depends on orientation of track (different drift times) 222Rn 218Po 214Po derivative de/dx Amplitude

4. RunwithAr/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM 210Po 5.3 MeV from 210Pb @ Cu surface R = 15 cm 210Po 5.3 MeV Taux 400 capt/j n capt on 3He 764 keV Rise time (s) n capt on 3He => p + T 3 2 1 Unwanted Radon daughter deposit on surface 222Rn 218Po 214Po Amplitude 2 : fast neutron expected here

5. Calibrations with (external) sources • Saclay SPC, Ar/CH4, 500 mb, 16 mm ball • Calibration with 22 keVfrom 109Cd => Illustration of volume/surface identification Periph interactions Latt 8 keV= 10 cm Volume interactions Latt 22 keV= 190 cm 22 keV 8keV 8.1 keVfrom fluorescence of Cu

6. Calibration with UV flash lampfor single electronresponse 250 mb, Ar/2%CH4 ms Digitisedregionaroundwhere UV induced pulse expected=> Look for pulse in 200-260 ms window About 1 in 10 => single electronresponse 1 electron 16 ADU => Trigger efficiency for single electron = 54 % Single electron distribution Trigger @ 10 ADU

7. Volume calibration with37Ar source • 37Ar, 35 dayslifetime, Ka 2.6 keV and Lb 260 ev • Can be made with Calcium irradiatedwithfast neutrons • => first experimentssuccessful ! 2.6 keV Behaviourat E<300 eV

8. Spectrum atlowenergy in surface lab Saclay Ar/2%CH4 250 mb Exponentialriseatlowenergy 106evts/keV.d adu 20 eV thresh 600 eV

9. Spectrum atlowenergy in surface lab Simulatedspectrumshapewith flat + 1.3 electronmeanexponential adu 20 eV thresh 600 eV => Source of single electrons ? Many…

10. Detectingcoherent neutrino scattering ? • Simulation of expectedspectrumfromnuclearreactor, on Ar, withquenching factor and instrumental response • Normalisation to experimentalreactor 70 MW • Sphere of 2 m diam, 5 bars >30 eV Equivalent to 120 daysexposure If background is 500 evts/kg.d.keV Nbackev= 500*37*120*0.22= 500 000 evts S/N = 1/20, Ns = 30 80 ev/keV.kg.d 20 ev/keV.kg.d eV 30 eV

11. Data with « SEDINE » the 60 cm lowactivity detector @ LSM Rate Hz Tot rate surface SPC 130 cm Tot rate @LSM Ar CH4(2%) SEDINE @LSM In shield Alpha’s (Po 210 + Rn induced) Argon 39 (1 Bq/kg) Residual e rate Pressure mb

12. Data with « SEDINE » the 60 cm lowactivity detector @ LSM Stability of gain : 4 days ok

13. Data with « SEDINE » the 60 cm lowactivity detector @ LSM – « High energy » 210Po 214Po Corrected for gain loss (1 % in 4 days) 218Po ? In volume 222Rn h Inventory of alpha rates Po210 peak 0.090 Hz  1300/m2.d (« EDW » 400) Rn222 peak0.011 Hz Po214 peak 0.006 Hz Po218 peak 0.012 Hz Tail 0.054 Hz in vol « Bi-Po » event on surf in vol Degasing of valves ? NB : 2009 measurementwith 130 cm SPC => 0.045 Hz Po210

14. Data with « SEDINE » the 60 cm lowactivity detector @ LSM – « Lowenergy » • Example of two 50 mb & 300 mb runs (<24h, non stable conditions) evts/kev.d « Electron track » spectrum (high RT) 50 mb 3keV • Localisedenergydeposition in volume • Need volume calibration to estimatecuts and background level • Needbetterestimator for rejection keV evts/kev.d 23 keV 300 mb eV Monte carlo simulations on going : see G Tsiledakis talk

15. DetectingALPs ? • AxionLikeParticles KK postulated to explainhightemperature corona of sun (Zioutas/di Lella, 0207073v1) • => shoulddecay in 2 gammas withspectra < 3 keV @ rate = 200 /d/m3 • Analysis of pulse shapeprovide signature • Tests runs in Saclay with 130 cm SPC on-going Pulse of 6 keV 55Fe source a1/a2 a1 derivative a2 Working on background rejection and simulation : J Galan and TPapaevangelou GG IG

16. NewExperiments With Spheres NeutrinoExperiments With Spheres New Experiments forWimps with Spheres CEA-IRFU/Saclay (GG,IG) ,LSM (F Piquemal), Aristotle University of Tessaloniki (I Savvidis), University of Ioannina (I Vergados), NCSR DemoKritos (G Fanourakis), Hellenic Open University(S Tzamaria) University of Tsinghua Beijing (C Tao), Shanghai Jiao Tong University (K Ni), IHEP-Beijing ( C Yang) University of Saragoza (I Irastorza), Livermore (JR Armendariz) • F : R&D at Saclay and LSM, sensors, high P • F : Coherent neutrino scatteringexperimentfeasibility (ERC submitted by IG/GG) • G : Neutron monitor (I Savvidisnext talk) • C : R&D with SPC 130 cm shipped to Beijing, investigating large sphere building / tests • F G C : SN monitor, DM … Tessaloniki 2012