p. gorodetzky pcc-collège de france xiii isvhecri pylos september 6-12 2005 nostos a new low energy...
TRANSCRIPT
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)
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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)
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
• 200 Mcurie T2 source
• 3000 m3 spherical TPC volume
• 5x1030 e- with Xe at p=1 bar
NOSTOS Neutrino OScillation Tritium Outgoing Source
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
Energy distribution of detected neutrinos,
Recoil energy threshold Eth = 200 eV
Neutrino energy (keV)
14 keV
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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)
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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?
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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]