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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–Saclayon behalf of NEWS collaboration

Introduction to the detectorLow energy investigations -preliminary-

Calibrations, characterisationMeasurements at LSM

NEWS : neutrino coherent scattering measurement 6th TPC Symposium- Paris-2012

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Drift region

Ampl region

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• Digitisation @ 1 MHz, soft trigger• 2 LEP cavity 130 cm Ø tested• 1 low activity 60 cm Ø in operation @ LSM

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Run with Ar/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM

Rise

tim

e (

s)

Amplitude

210Po5.3 MeV

n capt on 3He 764 keV

222Rn 218Po 214Po

If localised energy deposition, rise time depends of radius(diffusion)

If track, rise time depends on orientation of track(different drift times)

NB: no start=> risetime records place and/or history of energy deposition

derivative

alpha

de/dx

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Rise

tim

e (

s)

Amplitude

210Po5.3 MeV

n capt on 3He 764 keV

210Po5.3 MeV

from 210Pb @ Cu surface

R = 15 cm

n capt on 3He => p + T

222Rn 218Po 214Po Unwanted Radon daughter deposit on surface

1 23

2 : fast neutron expected here

Taux 400 capt/j

Run with Ar/CH4 + 3g 3He @ 200 mb SPC 130cm Ø @ LSM

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Calibrations with (external) sources• Saclay SPC, Ar/CH4, 500 mb, 16 mm ball • Calibration with 22 keV from 109Cd => Illustration of volume/surface

identification

8.1 keV from fluorescence of Cu

22 keV8 keV

Volume interactionsLatt 22 keV= 190 cm

Latt 8 keV= 10 cm

Periph interactions

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Calibration with UV flash lampfor single electron response

Digitised region around where UV induced pulse expected => Look for pulse in 200-260 ms windowAbout 1 in 10 => single electron response

Trigger @ 10 ADU

=> Trigger efficiency for single electron = 54 %

1 electron16 ADU

ms

Single electrondistribution

250 mb, Ar/2%CH4

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• 37Ar, 35 days lifetime, K a 2.6 keV and Lb 260 ev

• Can be made with Calcium irradiated with fast neutrons

• => first experiments successful !

Volume calibration with 37Ar source

Behaviour at E<300 eV

2.6 keV

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Spectrum at low energy in surface lab

adu20 eVthresh

600 eV

Exponential rise at low energy

Saclay Ar/2%CH4250 mb

106evts/keV.d

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Spectrum at low energy in surface lab

adu

Simulated spectrum shape with flat + 1.3 electron mean exponential

=> Source of single electrons ? Many…

600 eV20 eVthresh

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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

20 ev/keV.kg.d

80 ev/keV.kg.d

>30 eV

30 eV

Equivalent to 120 days exposure

If background is 500 evts/kg.d.keVNbackev= 500*37*120*0.22= 500 000 evtsS/N = 1/20 , N s = 30

eV

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Data with « SEDINE » the 60 cm low activity detector @ LSM

Argon 39 (1 Bq/kg)

Alpha’s (Po 210 + Rn induced)SEDINE@LSMIn shield

Tot rate surface

Tot rate @LSM

Ar CH4(2%)

SPC130 cm

Pressure mb

Rate Hz

Residual e rate

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Data with « SEDINE » the 60 cm low activity detector @ LSM

Stability of gain : 4 days ok

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Data with « SEDINE » the 60 cm low activity detector @ LSM – « High energy »

h

222Rn

210Po

In volume

?

in vol

on surf

in vol

Corrected for gain loss (1 % in 4 days)

Inventory of alpha ratesPo210 peak 0.090 Hz 1300/m2.d (« EDW » 400)Rn222 peak 0.011 HzPo214 peak 0.006 HzPo218 peak 0.012 HzTail 0.054 Hz

« Bi-Po » event

NB : 2009 measurement with 130 cm SPC => 0.045 Hz Po210

Degasing of valves ?

218Po

214Po

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• Example of two 50 mb & 300 mb runs (<24h, non stable conditions)

Data with « SEDINE » the 60 cm low activity detector @ LSM – « Low energy »

Monte carlo simulations on going : see G Tsiledakis talk

eV

keV

« Electron track » spectrum (high RT) evts/kev.d

23 keV

3 keV

300 mb

50 mb

Localised energy deposition in volume Need volume calibration to estimate

cuts and background level Need better estimator for rejectionevts/kev.d

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Detecting ALPs ?• Axion Like Particles KK postulated to explain high

temperature corona of sun (Zioutas/di Lella, 0207073v1)

• => should decay in 2 gammas with spectra < 3 keV @ rate = 200 /d/m3

• Analysis of pulse shape provide signature• Tests runs in Saclay with 130 cm SPC on-going

derivative

Pulse of 6 keV 55Fe source

Working on background rejection and simulation : J Galan and T Papaevangelou GG IG

a1/a2a1

a2

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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)

New Experiments With SpheresNeutrino Experiments With SpheresNew Experiments for Wimps with Spheres

• 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