Transcript NOSTOS A novel low-energy neutrino experiment

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
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
2
2
P( e   e )  1  sin 2q  sin (L /L13)
13
• L13 = L12/50 = 13 m
E=14 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 <1%
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  He3  e   v
8000000
electron
neutrino
7000000
6000000
dN/dT
5000000
4000000
3000000
2000000
1000000
0
0
2
4
6
8
10
T (keV)
12
14
16
18
20
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
NOSTOS
Neutrino OScillation
Tritium Outgoing Source
• 200 Mcurie T2 source
• 3000 m3 spherical TPC volume
• 5x1030 e- with Xe at p=1 bar
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 R1R2
E 2
r R2  R1
V0 = the applied high voltage,
R1= the internal radius,
R2 = the external radius
st = sL/vd, sL = D√r
At low fields: vd≈E and D≈1/√ E
st≈1/E3/2 ≈ r3
The
time dispersion is highly enhanced in the spherical case
Estimation of the depth of the interaction << 10 cm
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
Energy distribution of detected neutrinos,
Recoil energy threshold Eth = 200 eV
14 keV
Neutrino energy (keV)
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
Detected neutrinos-versus distance, sin22q13=.17, Eth=200 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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
Target properties with 5x1030 electrons, 1000 events/year
Noble gas
Pressure
(bar)
W(eV) Radioactivity
Comments
Xe
1
16
85Kr
It needs high purification
Expensive
Ar
3
26
42Ar
Low cost
T=33y,Emax=565keV
42Ar
activity: <1000/y below 1keV
Ne
5.4
36
None
Moderate cost
He
27
41
None
Low cost
Very high pressure
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
Neutrino magnetic moment sensitivity
<< 10-12 mB
ds/dT=cons(m)2(1-T/E)/T
3
Actual limit 10-10 mB
2.5
*10-47
2
ds/dT(cm2/keV)
10 -12mB
1.5
1
weak
0.5
0
0.01
0.1
T (keV)
1
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
2
Supernova sensitivity
Detect recoils from coherent neutrino-nucleus interaction
High cross section in Xenon:
For E = 10 MeV s≈ N2E 2 ≈ 2.5x10-39 cm2, Tmax = 1.500 keV
For E = 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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
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
escape Fe
Ar
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 project
Single 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
1st prototype (old LEP cavity)
1.3 m
• Gas leak < 5x10-9mbar/s
• Gas mixture Argon + 10%CO2 (5.7)
Cu 6 mm
• Pressure up to 5 bar (26.5 kgr Xe)
10 mm
• Internal electrode at high voltage
• Read-out of the internal electrode
Volume = 1 m3 P=5 bars
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 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
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005
2nd 4-m demonstrator
A simple and cheap Galactic supernova detector
Xe Pmax=10 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) ==> 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.
1 channel read-out
Maybe no active detector
(field big enough if central
ball small enough)
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]
P. Gorodetzky PCC-Collège de France XIII ISVHECRI Pylos September 6-12 2005