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NEWS: measurements at sub keV energies with spherical detectors

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1 NEWS: measurements at sub keV energies with spherical detectors
G Gerbier + I Giomataris, J Derre, P Magnier, A Dastgheibi, D. Jourde, M Gros, E Bougamont, XF Navick, T Papaevangelou, J Galan, G Tsiledakis IRFU–Saclay on behalf of NEWS collaboration Introduction to the detector Low energy investigations -preliminary- Calibrations, characterisation Measurements at LSM NEWS : neutrino coherent scattering measurement 6th TPC Symposium- Paris-2012

2 Spherical Proportional Counters
Sphere cavity + spherical sensor + HT Low threshold (low C) Fiducial selection by risetime Flexible (P, gaz) Large mass / large volume Robust, simple, cheap, sealed mode 1 MHz, soft trigger 2 LEP cavity 130 cm Ø tested 1 low activity 60 cm Ø in LSM Drift region Ampl region

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

4 Run with Ar/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 Rise time (s) n capt on 3He 764 keV n capt on 3He => p + T 3 1 2 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 keV from 109Cd => Illustration of volume/surface identification Periph interactions Latt 8 keV= 10 cm Volume interactions Latt 22 keV= 190 cm 8 keV 22 keV 8.1 keV from fluorescence of Cu

6 Calibration with UV flash lamp for single electron response
250 mb, Ar/2%CH4 ms Digitised region around where UV induced pulse expected => Look for pulse in ms window About 1 in 10 => single electron response => Trigger efficiency for single electron = 54 % 1 electron 16 ADU Single electron distribution 10 ADU

7 Volume calibration with 37Ar source
37Ar, 35 days lifetime, Ka 2.6 keV and Lb 260 ev Can be made with Calcium irradiated with fast neutrons => first experiments successful ! 2.6 keV Behaviour at E<300 eV

8 Spectrum at low energy in surface lab
Saclay Ar/2%CH4 250 mb Exponential rise at low energy 106evts/keV.d adu 20 eV thresh 600 eV

9 Spectrum at low energy in surface lab
Simulated spectrum shape with flat electron mean exponential 20 eV thresh adu 600 eV => Source of single electrons ? Many…

10 Detecting coherent neutrino scattering ?
Simulation of expected spectrum from nuclear reactor, on Ar, with quenching factor and instrumental response Normalisation to experimental reactor 70 MW Sphere of 2 m diam, 5 bars >30 eV Equivalent to 120 days exposure If background is 500 evts/kg.d.keV Nbackev= 500*37*120*0.22= evts S/N = 1/20 , Ns = 30 80 ev/ 20 ev/ eV 30 eV

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

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

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

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

15 Detecting ALPs ? Axion Like Particles KK postulated to explain high temperature corona of sun (Zioutas/di Lella, v1) => should decay in 2 gammas with spectra < 3 rate = 200 /d/m3 Analysis of pulse shape provide 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 T Papaevangelou GG IG

16 New Experiments With Spheres Neutrino Experiments With Spheres
New Experiments for Wimps 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 scattering experiment feasibility (ERC submitted by IG/GG) G : Neutron monitor (I Savvidis next talk) C : R&D with SPC 130 cm shipped to Beijing, investigating large sphere building / tests F G C : SN monitor, DM … Tessaloniki 2012

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