P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 NOSTOS a new low energy neutrino experiment Detect low energy neutrinos from

P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005

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

• SUPERNOVA detection sensitivity• The first Saclay prototype• Preliminary results and short term experimental program• HELLAZ?• Conclusions

An idea by I. Giomataris from Saclay (France)


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%

€

P(ν e → ν e) ≈ 1 − sin2 2θ13

× sin2 (πL /L13)


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


• 200 Mcurie T2 source

• 3000 m3 spherical TPC volume

• 5x1030 e- with Xe at p=1 bar

NOSTOS Neutrino OScillation Tritium Outgoing Source


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


Energy distribution of detected neutrinos,

Recoil energy threshold Eth = 200 eV

Neutrino energy (keV)

14 keV


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


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


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()2(1-T/E)/T<< 10-12 B

Actual limit 10-10 B


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

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

For a a typical supernova explosion and the spherical TPC detectorFilled with Xe at 10 bar we expect :

≈ 100,000 events at 10 kpc!!!≈ 20 at 700 kpc (Extragalactic sensitivity !!!)

Detection efficiency independent of the neutrino flavor

The challenge is again at the low-energy threshold detection

Supernova sensitivity


1st challenge : low background level in the sub-keV rangeGood news from the Micromegas-CAST detector

Cu

Fe

Ar

Low energy spectrum from Micromegas in CAST

escape

Same detector in MODANE underground :Few counts/day (100 eV threshold)


2nd challenge : high gain at high gas pressure

- Good news from the Micromegas of the HELLAZ projectSingle electron detection with high time resolution with Micromegas. They reached gains of >105 at p=20 bars in helium !!

- High gain at high pressure Xenon is challenging

ISSUES

• Use a low ionization potential quencher (C6H8, TEA, TMAE..)

• Double amplification

• Resistive anode


1.3 m

Volume = 1 m3 P=5 bars

Cu 6 mm

1st prototype (old LEP cavity)

• 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


First results• Low pressure operation 250 mbar - 1100 mbar

• High voltage 7 kV- 15 kV

• Cosmic ray signals well observed

• Low energy x-ray signals observed

• Satisfactory gain > 5x104

• Signal stable during 1 week


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


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€ (2/3 Xe) ==> Ar: 100 k€ (60 bar)

1 channel read-out

Maybe no active detector (field big enough if central ball small enough)

The idea is to provide these cheap detectors to receptive universities. They would be maintained by the faculty and their students. The resulting network would tell not only WHEN Supernovae happen, but also WHERE.

For that, 5 to 10 spheres have to be installed around the world

First sphere: here underwater in Pylos at 600 m depth, hence no security problem?


HELLAZ?

Hellaz was T. Ypsilantis idea to measure solar neutrinos in a cylindrical TPC filled with 20 bar He. Solar neutrinos (pp and Be7) would elastically scatter the He nuclei, produce e- whose energy and direction relative to the sun would be measured. Then the neutrino energy can be reconstructed. Monte-Carlo showed that with 2000 m3 we had 1000 events / year. The energy threshold had to do with the e - track length that had to be > 2 cm at the beginning, hence 100 keV e-, that is around 200 keV neutrinos.To get the angular resolution, all possible information had to be gathered, hence the “digital” TPC where each individual ionisation e- was identified. The end-detector best suited is Giomataris parallel plate Micromegas (160 m2). But it was difficult to get Micromegas to have single electron gain at 20 bar. This was finally solved, together with getting X-Y information.

Here, instead of a 20 m long, 5 m in diameter constant E TPC, we think of the tritium 8.5 m radius TPC where the field would be reversed: the anode would be the external sphere, covered by Micromegas (300 m2).

Advantages: - best volume per surface ratio (less background)- best mechanical strength (thinner ==> less background)- good information on the interaction positionéz@”dzxz

mailto:position%8Ez@%D3dzxz


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

• Low-cost Supernova detector

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

• Conference in Paris 9 & 10 dec 2004. Interested people should contact [email protected]

Documents

P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005 NOSTOS a new low energy neutrino experiment Detect low energy neutrinos from