NOSTOS a new low energy neutrino experiment

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NOSTOS a new low energy neutrino experiment
An idea by I. Giomataris from Saclay (France)

• 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

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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
  (Tmax1.27keV) produced by neutrino-electron
  scattering
• L13 L12/50 13 m E14 keV
• The oscillation length is comparable to the
  radius of the TPC
• Measure q13 and dm2 by a single experiment
• The background level can be measured and
  subtracted
• The neutrino flux can be measured with a high
  accuracy lt1

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• 200 Mcurie T2 source
• 3000 m3 spherical TPC volume
• 5x1030 e- with Xe at p1 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 4p 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
• st sL/vd, sL Dvr
• At low fields vdE and D1/v E
  st1/E3/2 r3
• The time dispersion is highly enhanced in the
  spherical case
• Estimation of the depth of the interaction ltlt
  10 cm

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Energy distribution of detected neutrinos,
Recoil energy threshold Eth 200 eV
14 keV
Neutrino energy (keV)
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Detected neutrinos-versus distance, sin22q13.17,
Eth200 eV 3 years of running at p 1 bar of
Xenon The effect of the unknown neutrino energy
distribution is small
Preliminary
Fitting the curve we extract the oscillation
parameters with a single experiment
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Target properties with 5x1030 electrons, 1000
events/year
Reasonable goal operate with Ar or Ne at
pressures gt10 bars gt104 events/year to tackle a
total number of events of 105
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Neutrino magnetic moment sensitivity ds/dTcons(
mn)2(1-T/En)/T
ltlt 10-12 mB


Actual limit 10-10 mB
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Supernova sensitivity
Detect recoils from coherent neutrino-nucleus
interaction High cross section in Xenon For En
10 MeV s N2E 2 2.5x10-39 cm2, Tmax 1.500
keV For En 25 MeV s 1.5x10-38 cm2, Tmax 9
keV
For a a typical supernova explosion and the
spherical TPC detector Filled 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
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1st challenge low background level in the
sub-keV range Good news from the Micromegas-CAST
detector
Low energy spectrum from Micromegas in CAST
Cu
Fe
escape
Ar
Same detector in MODANE underground Few
counts/day (100 eV threshold)
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2nd challenge high gain at high gas pressure

• - Good news from the Micromegas of the HELLAZ
  project
• Single electron detection with high time
  resolution with
• Micromegas. They reached gains of gt105 at p20
  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

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1st prototype (old LEP cavity)
1.3 m

• Gas leak lt 5x10-9mbar/s
• Gas mixture Argon 10CO2 (5.7)
• Pressure up to 5 bar (26.5 kgr Xe)
• Internal electrode at high voltage
• Read-out of the internal electrode

Cu 6 mm
10 mm
Volume 1 m3 P5 bars
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• 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 gt 5x104
• Signal stable during 1 week

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• 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 energy
• If 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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2nd 4-m demonstrator A simple and cheap Galactic
supernova detector Xe Pmax10 bars 1000
events/explosion 50 m shield is enough (deploy in
the see or lake?) We should assure stability for
100 years Cost estimate 300k (2/3 Xe) gt
Ar 100 k (60 bar)
4-m
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?
1 channel read-out Maybe no active detector
(field big enough if central ball small enough)
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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 gt 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 gt less background) - good
information on the interaction positionéz_at_dzxz
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• 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 philippe.gorodetzky_at_cern.ch