Transcript NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay NOSTOS  A new concept: the spherical TPC.  A first prototype: the Saclay sphere. 

NOSTOS: a spherical TPC
to detect low energy neutrinos
Igor G. Irastorza
CEA/Saclay
NOSTOS
 A new concept: the
spherical TPC.
 A first prototype: the
Saclay sphere.
 Results and prospects.
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LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
NOSTOS Scheme
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Large Spherical TPC
10 m radius
200 MCi tritium
source in the center
Neutrinos oscillate
inside detector
volume L23=13 m
Measure q13 and
more…
LRT2004 Sudbury, 12-14
December 2004
High
Voltage
Shield
E
10 m
Tritium
Source
Igor G. Irastorza, CEA Saclay
Drift
Gaseous
Volume
Shield
The spherical TPC concept
(I. Giomataris, J. Vergados, NIM A530 (04) 330-358 [hep-ex/0303045] )
Drift
Gaseous
Volume
E
10 m
Tritium
Source
LRT2004 Sudbury, 12-14
December 2004
MICROMEGAS
readout
Igor G. Irastorza, CEA Saclay
(max E=1.27 keV)
The spherical TPC concept:
Advantages
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Natural focusing:

– large volumes can be
instrumented with a small
readout surface and few (or
even one) readout lines
4p coverage: better signal
 Still some spatial
information achievable:
Other practical
advantages:
– Symmetry: lower noise and
threshold
– Low capacity
– No field cage
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– Signal time dispersion
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Simplicity: few materials.
They can be optimized for
low radioactivity.
Low cost
The way to obtain large detector volumes
keeping low background and threshold
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Source & Target
Source: 200MCi (20 kg) Tritium
 Target: Several possibilities as target gas:
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Detailed calculation/simulation in progress to assess
expected signal/sensitivity, taking into account atomic
effects (Gounaris et al. hep-ex/0409053)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Experimental challenges: within reach
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Threshold  easily achievable, to be
demonstrated with underground tests
Background  simulations planned, to be
demonstrated with underground tests
Radial resolution  being demonstrated by
Saclay sphere
Stability  first results positive, more planned
Scaling up  intermediate size prototypes
being designed
Electrostatics  some ideas being
demonstrated by Saclay sphere
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First prototype:
the Saclay sphere
D=1.3 m
 V=1 m3
 Spherical vessel
made of Cu (6
mm thick)
 P up to 5 bar
possible (up to 1.5
tested up to now)
 Vacuum tight:
~10-6 mbar
(outgassing: ~10-9
mbar/s)
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LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First prototype: the Saclay sphere
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Simple multiplication structure: small
(10 mm Ø) sphere
10 mm
Internal electrode at HV
 Readout of the internal electrode
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LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First tests
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Mixtures tested:
– Ar+10% CO2
– Ar+2% Isobutane
Pressures from 0.25 up to
1.5 bar tested up to now
 High gains (>104)
achieved with simple
spherical electrode
 No need to go to very
high V (better for minimizing
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absorption)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First results

5.9 keV
55Fe
signal
• Very low electronic
noise: low threshold
• Fit to theoretical curve
including avalanche
induction and electronics:
system well understood
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First results
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Runs of 55Fe, 109Cd
and Cosmic Rays
55Fe
spectrum
with Ar+CO2
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Better resolution
obtained in more
recent tests with
Isobutane (analysis in
progress)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Ar
escape
55Fe
5.9 keV
Pulse deconvolution
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Response function
including the ion
induction + electronics
effects associated to one
single point charge.
Remove the slow tail of
the pulses
Recover the time
(=radial) structure of the
primary e- cloud
This analysis will not be
needed when a fast
readout (MICROMEGAS)
will be available
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
First results
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Clear time
dispersion effect
observed in
deconvoluted
pulses correlated
with distance
drifted
60 cm
drift
50 cm
drift
40 cm
drift
30 cm
drift
20 cm
drift
10 cm
drift
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Template
pulses
(average of 20
sample pulses)
In Ar+CO2
P=0.25 bar
First results
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Even with a very
simple (and slow)
readout, we have
proved the use of
dispersion effects to
estimate the position
of the interation (at
least at ~10 cm
level).
Further test are
under preparation to
better calibrate
(external trigger from
Am source )
LRT2004 Sudbury, 12-14
December 2004
Average time dispersion of 5.9
keV deconvoluted events
VS.
Distance drifted
No source run
(cosmics)
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Ar+CO2
P=0.25 bar
Igor G. Irastorza, CEA Saclay
First results
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Stability:
– tested up to ~2 months.
– No circulation of gas. Detector working in
sealed mode. (1 pass through an oxysorb
filter)
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No absorption observed
– Signal integrity preserved after 60 cm drift.
– Not high E needed to achieve high gain.
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Next steps
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Electrostatics
– Field shaping rings
– More ambitious ideas in mind for the future:
charging systems without electrical contact
(like the ones in electrostatic accelerators)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
Next steps:
Micromegas as NOSTOS readout
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Very fast signals: will allow to measure precisely time
(and space) dispersion, i.e. radial coordinate of event.
2 Typical
MICROMEGAS
pulses
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Spherical MICROMEGAS (?) (or series of flat elements)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay
NOSTOS Additional Physics
Neutrino magnetic
moment
 Test of weak
interaction at low
energy (Weinberg
angle)
 Supernovae
(neutrino-nucleus
scattering)
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LRT2004 Sudbury, 12-14
December 2004
10-12mB
10-11mB
NO MM
McLaughlin & Volpe PLB 591 (04) 229
Igor G. Irastorza, CEA Saclay
Conclusions
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Spherical TPC concept introduced in the
framework of NOSTOS proposal
Promising as a simple way to obtain large
detector volumes, keeping low background and
low threshold
First prototype already working in Saclay
First encouraging results: low threshold, stability,
no absorption, dispersion vs. drift observed.
To be done next: optimize electrostatics, develop
more calibration systems, assess background
(test underground)
LRT2004 Sudbury, 12-14
December 2004
Igor G. Irastorza, CEA Saclay