I. Giomataris

NOSTOS a new low energy neutrino experiment

• Detect low energy neutrinos from a tritium source using a spherical gaseous TPC

• Study neutrino oscillations, magnetic moment, Weinberg angle at low energy

• The first Saclay prototype

• Preliminary results and short term experimental program• SUPERNOVA detection sensitivity

• Conclusions

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

• Use a large spherical TPC surrounding the tritium source• Detect low energy electron recoils (Tmax=1.27keV) produced by neutrino-electron scattering

• L13 = L12/50 = 13 m E=14 keV• The oscillation length is comparable to the radius of the TPC• Measure 13 and m2 by a single experiment• The background level can be measured and subtracted• The neutrino flux can be measured with a high accuracy <1%

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P(ν e → ν e) ≈ 1 − sin2 2θ13

× sin2 (πL /L13)

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

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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

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E = V0

r2

R1R2

R2 − R1

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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

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Detected neutrinos-versus distance, sin2213=.17, Eth=200 eV3 years of running at p= 1 bar of Xenon

The effect of the unknown neutrino energy distribution is small

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

Preliminary

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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 5x1030 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

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Neutrino-electron elastic scattering cross section

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ν e + e− → ν e + e−

νe νe

νe νe

e-e-

e- e-

w-

z0

G.’t Hooft, Phys. Lett. B37,195(1971)

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dσ /dT =1.710−47(gL2 + gR

2 (1− T / Eν )2 − gLgR meT / Eν2)

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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

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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=cons(ν)2(1-T/Eν)/T<< 10-12 B

Actual limit 10-10 B

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1st Saclay prototype

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are needed to see this picture.

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1.3 m

Volume = 1 m3 P=5 bars

Cu 6 mm

1st prototype

• Gas leak < 5x10-9mbar/s

• Gas mixture Argon + 10%CO2 (5.7)

• Pressure up to 5 bar (26.5 kgr Xe)

• Internal electrode at high voltage

• Read-out of the internal electrode

10 mm

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First results• Low pressure operation 250 mbar - 1100 mbar

• High voltage 7 kV- 15 kV• X-ray and cosmic ray signals well observed

• Satisfactory gain > 5x104

• Signal stable during 1 month

55Fe 5.9 keV signal

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0

50

100

150

200

250

300

350

0 0,1 0,2 0,3 0,4 0,5 0,6Energy (arb.units)

Counts

STA047P=208 mbarRFe55=42 cmHV=95

30%

55Fe x-rays

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I. Giomataris

I. Giomataris

Future short-term investigations• Tests of the 1st prototype and optimize the amplification structure • Optimize the detector for very-high gain operation• Measure the attenuation length of drifting electrons• Optimize the energy resolution• Measure the accuracy of the depth measurement by the time dispersion of the signal• Optimize mechanics and electronics, use low-radioactivity materials• Improve the simulation program•Calculate (or measure?) the quenching factor in various gases (Xe, Ar..).

• Underground measurement of the background level at low energyIf satisfactory measure the neutrino-nucleus

coherent scattering with reactor neutrinos

• Design a 4-m in diameter demonstrator and evaluate it as Supernova detector

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Supernova sensitivity

Detect recoils from coherent neutrino-nucleus interaction High cross section in Xenon:

For Eν = 10 MeV ≈ N2E 2 ≈ 2.5x10-39 cm2, Tmax = 1.500 keV For Eν = 25 MeV ≈ 1.5x10-38 cm2, Tmax = 9 keV

Using a 4-m spherical TPC detectorFilled with Xe at 10 bar we expect :

≈ 1,000 events at 10 kpc (105 events for the big TPC!!)

Detection efficiency independent of the neutrino flavor

The challenge is again at the low-energy threshold detection

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4-m

2nd 4-m demonstratorA simple and cheap Galactic supernova detector

Xe Pmax=10 bars 1000 events/explosion50 m shield is enough (deploy in the see or lake?)

We should assure stability for 100 yearsCost estimate : 300k€ (with Xe)

<100k€ (with Ar)

1 channel read-out

To be operated and maintained by UniversitiesTo be operated and maintained by UniversitiesSeveral such detectors are neededSeveral such detectors are needed

I. Giomataris

CONCLUSIONS

• The spherical TPC project allows a simple and low cost detection scheme and offers an ambitious experimental program :

• Neutrino oscillations, neutrino magnetic moment studies with measurement of the Weinberg angle at low energy using an intense tritium source

• A first prototype is operating in Saclay as a first step to NOSTOS

• A low-cost dedicated Supernova detector is proposed