NOSTOS Neutrino studies with a tritium source
description
Transcript of NOSTOS Neutrino studies with a tritium source
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
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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
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+ e
−
+ v
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dN/dT
T(keV)
electronneutrino
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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
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The new strategy(I. Giomataris, J. Vergados, hep-ex/0303045 )
L13 = 4/m232 m2
32= 2.510-3, keVL13 = L12/50 = 13 m fully contained in the TPC (radius=10m)
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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
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• 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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Two Micromegas signals at 3 mm distance in depth
3 mm drift
Precise determination of the depth
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Cu
Cuescape
Fe
Feescape Ar
Low energy spectrum from Micromegas in CAST
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Energy distribution of detected neutrinos,
Eth = 200 eV 14 keV
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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
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Neutrino-electron elastic scattering cross section
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e + e− → ν e + e−
e e
e e
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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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
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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 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
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Supernova sensitivity
Detect recoils from coherent neutrino-nucleus interaction High cross section: ≈N2E 2 ≈ 2.5x10-39 cm2, Xe and E=10 MeV Assuming a flux of 1012/cm2 of a typical supernova and the spherical TPC filled with Xe : ≈ 280 detected with Xe at 1 bar ≈ 2,800 at 10 bar pressure!!! The challenge is again the low-energy threshold detection Tmax = 1500 eV Tmean = 508 eV Detection efficiency independent of the neutrino flavor Extra galactic supernova detection ? To be studied
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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
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NOSTOS 1rst prototype
Schedule• 2003-2004Laboratory tests• From 2004Operation in underground laboratory
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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)
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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 supervova neutrinos
• Increase as much as possible the gas pressure will provide very-high statistics