LRT2004 Sudbury, 12-14 December 2004Igor G. Irastorza, CEA Saclay NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay NOSTOS

LRT2004 Sudbury, 12-14 LRT2004 Sudbury, 12-14 December 2004December 2004

Igor G. Irastorza, CEA SaclayIgor G. Irastorza, CEA Saclay

NOSTOS:NOSTOS: a spherical TPC a spherical TPC to detect low energy neutrinosto detect low energy neutrinos

Igor G. Irastorza Igor G. Irastorza CEA/SaclayCEA/Saclay

NOSTOSNOSTOS A new concept: the A new concept: the

spherical TPC.spherical TPC. A first prototype: the A first prototype: the

Saclay sphere.Saclay sphere. Results and Results and

prospects.prospects.

Igor G. Irastorza, CEA SaclayIgor G. Irastorza, CEA SaclayLRT2004 Sudbury, 12-14 LRT2004 Sudbury, 12-14 December 2004December 2004

NOSTOS SchemeNOSTOS Scheme

Large Spherical TPCLarge Spherical TPC 10 m radius10 m radius 200 MCi tritium 200 MCi tritium

source in the centersource in the center Neutrinos oscillate Neutrinos oscillate

inside detector inside detector volume Lvolume L2323=13 m=13 m

Measure Measure 1313 and and more…more…

10m

E

Shield

HighVoltage

DriftGaseousVolume

TritiumSource



10m

E

Shield

HighVoltage

DriftGaseousVolume

TritiumSource

The spherical TPC conceptThe spherical TPC concept(I. Giomataris, J. Vergados, NIM A530 (04) 330-358 [hep-ex/0303045] )

Drifting charges

MICROMEGASreadout

(max E=1.27 keV)(max E=1.27 keV)



The spherical TPC concept: The spherical TPC concept: AdvantagesAdvantages

Natural focusing: Natural focusing: – large volumes can be large volumes can be

instrumented with a small instrumented with a small readout surface and few readout surface and few (or even one) readout (or even one) readout lineslines

44 coverage: better coverage: better signalsignal

Still some spatial Still some spatial information information achievable: achievable: – Signal time dispersionSignal time dispersion

Other practical Other practical advantages:advantages:– Symmetry: lower noise Symmetry: lower noise

and thresholdand threshold– Low capacityLow capacity– No field cageNo field cage

Simplicity: few Simplicity: few materials. They can be materials. They can be optimized for low optimized for low radioactivity. radioactivity.

Low costLow cost

The way to obtain large detector The way to obtain large detector volumes keeping low background and volumes keeping low background and

thresholdthreshold


SourceSource & Target & Target SourceSource: 200MCi (20 kg) Tritium: 200MCi (20 kg) Tritium TargetTarget: Several possibilities as target gas:: Several possibilities as target gas:

Detailed calculation/simulation in progress to Detailed calculation/simulation in progress to assess expected signal/sensitivity, taking into assess expected signal/sensitivity, taking into account atomic effects (Gounaris account atomic effects (Gounaris et al.et al. hep-ex/0409053)hep-ex/0409053)



Experimental challenges: Experimental challenges: within within

reachreach ThresholdThreshold easily achievable, to be easily achievable, to be

demonstrated with underground tests demonstrated with underground tests BackgroundBackground simulations planned, to be simulations planned, to be

demonstrated with underground testsdemonstrated with underground tests Radial resolutionRadial resolution being demonstrated being demonstrated

by Saclay sphereby Saclay sphere StabilityStability first results positive, more first results positive, more

plannedplanned Scaling upScaling up intermediate size prototypes intermediate size prototypes

being designedbeing designed ElectrostaticsElectrostatics some ideas being some ideas being

demonstrated by Saclay spheredemonstrated by Saclay sphere



First prototype: First prototype: the Saclay spherethe Saclay sphere

D=1.3 m D=1.3 m V=1 mV=1 m3 3

Spherical vessel Spherical vessel made of Cu (6 made of Cu (6 mm thick)mm thick)

P up to 5 bar P up to 5 bar possible (up to possible (up to 1.5 tested up to 1.5 tested up to now)now)

Vacuum tight: Vacuum tight: ~10~10-6-6 mbar mbar (outgassing: (outgassing: ~10~10-9-9 mbar/s) mbar/s)


First prototype: the Saclay First prototype: the Saclay spheresphere

Simple multiplication structure: Simple multiplication structure: small (10 mm small (10 mm Ø) Ø) spheresphere

Internal electrode at HVInternal electrode at HV Readout of the internal electrodeReadout of the internal electrode

10 mm10 mm



First testsFirst tests Mixtures tested: Mixtures tested:

– Ar+10% COAr+10% CO22

– Ar+2% IsobutaneAr+2% Isobutane Pressures from 0.25 Pressures from 0.25

up to 1.5 bar tested up to 1.5 bar tested up to nowup to now

High gains (>10High gains (>1044) ) achieved with simple achieved with simple spherical electrodespherical electrode

No need to go to very No need to go to very high V high V (better for (better for minimizing absorption)minimizing absorption)



First resultsFirst results 5.9 keV 5.9 keV 5555Fe signalFe signal

• Very low electronic noise: low threshold

• Fit to theoretical curve including

avalanche induction and electronics: system

well understood



First resultsFirst results

Runs of Runs of 5555Fe, Fe, 109109Cd Cd and Cosmic Raysand Cosmic Rays

Better resolution Better resolution obtained in more obtained in more recent tests with recent tests with Isobutane Isobutane (analysis in (analysis in progress)progress)

55Fe55Fe 5.9 keV5.9 keV

Ar Ar escapeescape

5555Fe Fe spectrum spectrum

with Ar+COwith Ar+CO22



Pulse deconvolutionPulse deconvolution

Response function Response function including the ion including the ion induction + electronics induction + electronics effects associated to effects associated to one single point charge.one single point charge.

Remove the slow tail of Remove the slow tail of the pulsesthe pulses

Recover the time Recover the time (=radial) structure of (=radial) structure of the primary ethe primary e-- cloud cloud

This analysis will not be This analysis will not be needed when a fast needed when a fast readout (MICROMEGAS) readout (MICROMEGAS) will be availablewill be available




Clear time Clear time dispersion effect dispersion effect observed in observed in deconvoluted deconvoluted pulses correlated pulses correlated with distance with distance drifteddrifted

60 cm drift

50 cm drift

40 cm drift

30 cm drift

20 cm drift

10 cm drift

Template pulses

(average of 20 sample

pulses)

In Ar+CO2

P=0.25 bar



First resultsFirst results Even with a very Even with a very

simple (and slow) simple (and slow) readout, we have readout, we have proved the use of proved the use of dispersion effects dispersion effects to estimate the to estimate the position of the position of the interation (at least interation (at least at ~10 cm level).at ~10 cm level).

Further test are Further test are under preparation under preparation to better calibrate to better calibrate (external trigger (external trigger from Am source )from Am source )

Average time dispersion of 5.9 keV deconvoluted events

VS.

Distance drifted

No s

ou

rce r

un

(c

osm

ics)

Ar+CO2P=0.25 bar




Stability: Stability: – tested up to ~2 months.tested up to ~2 months.– No circulation of gas. Detector working No circulation of gas. Detector working

in sealed mode. (1 pass through an in sealed mode. (1 pass through an oxysorb filter)oxysorb filter)

No absorption observedNo absorption observed– Signal integrity preserved after 60 cm Signal integrity preserved after 60 cm

drift.drift.– Not high E needed to achieve high gain.Not high E needed to achieve high gain.



Next stepsNext steps

ElectrostaticsElectrostatics

– Field shaping ringsField shaping rings

– More ambitious ideas in mind for the More ambitious ideas in mind for the future: charging systems without electrical future: charging systems without electrical contact contact (like the ones in electrostatic (like the ones in electrostatic accelerators)accelerators)



Next stepsNext steps: : Micromegas as NOSTOS Micromegas as NOSTOS

readoutreadout Very fast signals: will allow to measure precisely time Very fast signals: will allow to measure precisely time

(and space) dispersion, i.e. radial coordinate of event.(and space) dispersion, i.e. radial coordinate of event.

Spherical MICROMEGAS (?) (or series of flat elements)Spherical MICROMEGAS (?) (or series of flat elements)

2 Typical MICROMEGAS

pulses



NOSTOS Additional PhysicsNOSTOS Additional Physics

Neutrino Neutrino magnetic magnetic momentmoment

Test of weak Test of weak interaction at low interaction at low energy energy (Weinberg angle)(Weinberg angle)

Supernovae Supernovae (neutrino-nucleus (neutrino-nucleus scattering)scattering) McLaughlin & Volpe PLB 591 (04) 229

10-12B10-11B

NO MM



ConclusionsConclusions Spherical TPC concept introduced in the Spherical TPC concept introduced in the

framework of NOSTOS proposalframework of NOSTOS proposal Promising as a simple way to obtain large Promising as a simple way to obtain large

detector volumes, keeping low background detector volumes, keeping low background and low threshold and low threshold

First prototype already working in SaclayFirst prototype already working in Saclay First encouraging results: low threshold, First encouraging results: low threshold,

stability, no absorption, dispersion vs. drift stability, no absorption, dispersion vs. drift observed.observed.

To be done next: optimize electrostatics, To be done next: optimize electrostatics, develop more calibration systems, assess develop more calibration systems, assess background (test underground)background (test underground)

Documents

LRT2004 Sudbury, 12-14 December 2004Igor G. Irastorza, CEA Saclay NOSTOS: a spherical TPC to detect low energy neutrinos Igor G. Irastorza CEA/Saclay NOSTOS