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/keV.kg.d
20 ev/keV.kg.d 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