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

I. Giomataris The idea (I. Giomataris, J. Vergados, hep-ex/ ) Use a large spherical TPC surrounding the tritium source Detect low energy electron recoils (T max =1.27keV) produced by neutrino-electron scattering L 13 = L 12 /50 = 13 mE=14 keV The oscillation length is comparable to the radius of the TPC Measure  13 and  m 2 by a single experiment The background level can be measured and subtracted The neutrino flux can be measured with a high accuracy <1%

I. Giomataris 200 Mcurie T 2 source 3000 m 3 spherical TPC volume 5x10 30 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 V 0 = the applied high voltage, R 1 = the internal radius, R 2 = the external radius  t =  L/ v d,  L = D√r At low fields: v d ≈E and D≈1/√ E  t ≈1/E 3/2 ≈ r 3 The time dispersion is highly enhanced in the spherical case Estimation of the depth of the interaction << 10 cm

I. Giomataris Two Micromegas signals at 3 mm distance in depth 3 mm drift Precise determination of the depth

I. Giomataris Detected neutrinos-versus distance, sin 2 2  13 =.17, E th =200 eV 3 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

I. Giomataris Low cost Very high pressure None4127He Moderate costNone365.4Ne Low cost 42 Ar activity: <1000/y below 1keV 42 Ar T=33y,E max =565keV 263Ar It needs high purification Expensive 85 Kr161Xe CommentsRadioactivityW(eV)Pressure (bar) Noble gas Target properties with 5x10 30 electrons, 1000 events/year Reasonable goal: operate with Ar or Ne at pressures >10 bars >10 4 events/year to tackle a total number of events of 10 5

I. Giomataris Neutrino-electron elastic scattering cross section e e e e e-e- e-e- e-e- e-e- w-w- z0z0 G.’t Hooft, Phys. Lett. B37,195(1971) For T<<1 keV d  /dT = a(2sin 4  w +sin 2  w +1/4) High accuracy measurement of the Weinberg angle at very-low energy!! Test the weak interaction at long distances

I. Giomataris  Neutrino magnetic moment sensitivity d  /dT=cons(  ) 2 (1-T/E )/T <<  B Actual limit  B

I. Giomataris 1 st Saclay prototype

I. Giomataris 1.3 m Volume = 1 m 3 P=5 bars Cu 6 mm 1 st prototype Gas leak < 5x10 -9 mbar/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

I. Giomataris First results Low pressure operation 250 mbar mbar High voltage 7 kV- 15 kV X-ray and cosmic ray signals well observed Satisfactory gain > 5x10 4 Signal stable during 1 month 55 Fe 5.9 keV signal

I. Giomataris 55 Fe x-rays

I. Giomataris

Future short-term investigations Tests of the 1 st 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 satisfactorymeasure the neutrino-nucleus coherent scattering with reactor neutrinos Design a 4-m in diameter demonstrator and evaluate it as Supernova detector

I. Giomataris Supernova sensitivity Detect recoils from coherent neutrino-nucleus interaction High cross section in Xenon: For E = 10 MeV  ≈  N 2 E 2 ≈ 2.5x cm 2, T max = keV For E = 25 MeV  ≈ 1.5x cm 2, T max = 9 keV Using a 4-m spherical TPC detector Filled with Xe at 10 bar we expect : ≈ 1,000 events at 10 kpc (10 5 events for the big TPC!!) Detection efficiency independent of the neutrino flavor The challenge is again at the low-energy threshold detection

I. Giomataris 4-m 2 nd 4-m demonstrator A simple and cheap Galactic supernova detector Xe P max =10 bars1000 events/explosion 50 m shield is enough (deploy in the see or lake?) We should assure stability for 100 years Cost estimate : 300k€ (with Xe) <100k€ (with Ar) 1 channel read-out To be operated and maintained by Universities Several 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