I. Giomataris

NOSTOSNeutrino studies with a tritium source

• Neutrino Oscillations with triton neutrinos

• The concept of a spherical TPC• Measurement of the angle ,Neutrino magnetic moment,

Neutrino decay, Weinberg angle measurement at low energy, Supernova sensitivity

• The first prototype

• Conclusions

I. Giomataris

Tritium

• Produced by neutrons on Li6 or He3

• Half life 12.26 years, Energy Maximum 18.6 keV, Average energy 5.7 keV, power 4 kWatt/20 Kgr

Neutrino production: 7x1018/s/20 Kgr

T → He

3

+ e

−

+ v

0

1000000

2000000

3000000

4000000

5000000

6000000

7000000

8000000

0 2 4 6 8 10 12 14 16 18 20

dN/dT

T(keV)

electronneutrino

I. Giomataris

The idea

Study neutrino-electron elastic scattering with very-low energy neutrinos from a strong tritium source (E ≈14 keV)

Detect low energy electron recoils (Tmax = 1.27 keV) by a spherical gaseous TPC surrounding the tritium source

The oscillation length is shorter than the length of the detector

The modulation will be contained and seen in the TPC

Reconstruction of the relevant oscillation parameters by a single experiment

I. Giomataris, J. Vergados, hep-ex/0303045

J. Bouchez, I Giomataris DAPNIA-01-07

I. Giomataris

The new strategy(I. Giomataris, J. Vergados, hep-ex/0303045 )

L32 = 4/m232 m2

32= 2.510-3, keVL13 = L12/50 = 13 m fully contained in the TPC (radius=10m)

€

P(ν e → ν e) ≈ 1 − sin2 2θ13

× sin2 (πL /L13)

New challenge : measurement The sensitivity depends on statistics, backgrounds and systematics >104 neutrino-electron interactions must be detected and localized Tritium source activity can be measured on-line at <1% Background level can be measured and subtracted (source on-off) Fitting the oscillation will suppress systematics

I. Giomataris

• 200 Mcurie T2 source

• 3000 m3 spherical TPC volume

• 5x1030 e- with Xe at p=1 bar

NOSTOS Neutrino OScillation Tritium Outgoing Source

I. Giomataris

The advantages of the spherical TPC• Natural focusing system reasonable size detector

• Provides a full 4 coverage enhancement of the detected signal

• Allows a good determination of the depth of the interaction point by measuring the time dispersion of the signal:The electric field is V0 = the applied high voltage,

R1= the internal radius, R2 = the external radius

t = L/vd, L = D√r

At low fields: vd ≈ E and D ≈1/√ E t ≈ 1/E3/2 ≈ r3

The time dispersion is highly enhanced in the spherical case

Estimation of the depth of the interaction < 10 cm

€

E = V0

r2

R1R2

R2 − R1

I. Giomataris

QuickTime™ and aGraphics decompressorare needed to see this picture.

-0.2

-0.15

-0.1

-0.05

0

0.05

-200 -100 0 100 200 300 400Time (ns)

Two Micromegas signals at 3 mm distance in depth

3 mm drift

Precise determination of the depth

I. Giomataris

Cu

Cuescape

Fe

Feescape Ar

Low energy spectrum from Micromegas in CAST

I. Giomataris

Energy distribution of detected neutrinos,

Eth = 200 eV 14 keV

I. Giomataris

Detected neutrinos-versus distance, sin2213=.17, Eth=200 eVThe effect of the unknown neutrino energy distribution is small

Fitting the curve we extract the oscillation parameters with a single experiment

I. Giomataris

Neutrino-electron elastic scattering cross section

€

e + e− → ν e + e−

e e

e e

e-e-

e- e-

w-

z0

G.’t Hooft, Phys. Lett. B37,195(1971)

€

dσ /dT =1.710−47(gL2 + gR

2 (1− T / Eν )2 − gLgR meT / Eν2)

€

gL = sin2 θW ,gR = sin2 θW +1/2,T ≈ 2(Eν cosθ)2 /me,Tmax =1.27keV

For T<<1 keV d/dT = a(2sin4w+sin2w +1/4)High accuracy measurement of the Weinberg angle at very-low energy!!Test the weak interaction at long distances

I. Giomataris

0

0.5

1

1.5

2

2.5

3

0.01 0.1 1 2

d/dT(cm2/keV)

T (keV)

weak

*10-47

10-12B

Neutrino magnetic moment sensitivity

d/dT ≈ ()2(1-T/E)/T

<< 10-12 B

Actual limit 10-10 B

I. Giomataris

Low cost

Very high pressure

None4127He

Moderate costNone365.4Ne

Low cost42Ar activity: <1000/y below 1keV

42ArT=33y,Emax=565keV

263Ar

It needs high purification

Expensive

85Kr161Xe

CommentsRadioactivityW(eV)Pressure

(bar)

Noble gas

Target properties with 5.1030 electrons, 1000 events/year

Reasonable goal: operate with Ar or Ne at pressures >10 bars

>104 events/year to tackle a total number of events of 105

Good news : The HELLAZ prototype provide gains of about 106 with He at 20 bar

I. Giomataris

Supernova sensitivity

Detect recoils from coherent neutrino-nucleus interaction High cross section: ≈N2E 2 ≈ 2.5x10-39 cm2, Xe and E=10 MeVand 1.5x10-38 cm2 at 25 MeV For a a typical supernova explosion and the spherical TPC deterctor:≈ 15,000 detected with Xe at 1 bar for a distance of 10kpc ≈ 15,000 at 10 bar pressure !!!≈ 30 at 700 kpc (Extragalactic detection !!!) The challenge is again at the low-energy threshold detection Tmax = 1500 eV for E = 10 MeV Detection efficiency independent of the neutrino flavor

I. Giomataris

Plans• 1.3 m prototype is under construction

- Laboratory study of the radial spatial accuracy

- Laboratory study of the electron attenuation length

• First investigations on the availability of the tritium source

• High gain operation of the detector at high pressure operation must be investigated with various gas candidates

I. Giomataris

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

NOSTOS 1rst prototype

Schedule• 2003-2004Laboratory tests• From 2004Operation in underground laboratory

I. Giomataris

I. Giomataris

I. Giomataris

Tests and studies with the 1.3 m prototype

• Laboratory tests with various gas mixtures up to 5 bar Total mass 1 - 25 Kgr (He, Ne, Ar, Xe, CF4)

• First underground investigations1. Measure the background level in the sub-keV range2. Optimize the detector parameters, pitch, pulse shaping, gas

mixture etc..• If the background level is satisfactory

1. Search for low mass dark matter candidates2. Search for WIMPs trapped in the solar system3. WIMP search in spin dependant interactions (CF4 target) Possible investigations with reactor neutrinos : coherent neutrino-nucleon scattering (>100/day detected neutrinos)

I. Giomataris

Summary and Outlook

• The purpose of the new experiment is to establish the phenomenon of neutrino oscillations with a different experimental technique and measure the angle

• High sensitivity measurement of the neutrino magnetic moment

• Measurement of the Weinberg angle at very-low energy

• High sensitivity for supernova neutrinos

• Increase as much as possible the gas pressure will provide very-high statistics