Transcript Slide 1

Enriched Xenon Observatory
for double beta decay
Z.Djurcic, D.Leonard, A.Piepke
Physics Dept, University of Alabama, Tuscaloosa AL
P.Vogel
Physics Dept Caltech, Pasadena CA
A. Bellerive, M. Dixit, C. Hargrove, D. Sinclair
Carleton University, Ottawa, Canada
W.Fairbank Jr., S.Jeng, K.Hall
Colorado State University, Fort Collins CO
M.Moe
Physics Dept UC Irvine, Irvine CA
D.Akimov, A.Burenkov, M.Danilov, A.Dolgolenko, A.Kovalenko, D.Kovalenko, G.Smirnov, V.Stekhanov
ITEP Moscow, Russia
J. Farine, D. Hallman, C. Virtue
Laurentian University, Canada
M.Hauger, F.Juget, L.Ounalli, D.Schenker, J-L.Vuilleumier, J-M.Vuilleumier, P.Weber
Physics Dept University of Neuchatel, Neuchatel Switzerland
M.Breidenbach, R.Conley, C.Hall, A.Odian, C.Prescott, P.Rowson, J.Sevilla, K.Skarpaas, K.Wamba,
SLAC, Menlo Park CA
E.Conti, R.DeVoe, G.Gratta, M.Green, T.Koffas, R.Leon, F.LePort, R.Neilson, S.Waldman, J.Wodin
Physics Dept Stanford University, Stanford CA
Last decade: the age of ν physics
Discovery of ν flavor change:
• Solar neutrinos (MSW effect)
• Reactor neutrinos (vacuum oscillation)
• Atmospheric neutrinos (vacuum oscillation)
• Loose ends: LSND results
So assuming that MiniBoone sees no oscillations,
we know that:
•ν masses are non-zero,
•There are 2.981±0.008 v (Z lineshape),
•3 ν flavors were active in Big bang Nucleosynthesis
Drastically different mass scenarios are still
allowed by the data
From WMAP
From 0νββ if ν is Majorana
From tritium endpoint
(Maintz and Troitsk)
~0.3 eV
~1 eV
No real understanding why M so small
Dirac vs Majorana neutrinos?
Need a lepton number violating process…
Time of flight from SN1987A
(PDG 2002)
~2.8 eV
23 eV
 decay can occur in two modes
a) Via the emission of 2’s:
A typical 2nd order
nuclear process
b) A neutrinoless mode:
Requires both
M0 and 
2nd
 decay a standard but small
order correction to regular  decay
BUT in some cases is the only
energetically allowed
2 has been
observed
experimentally
0 has never
been observed
experimentally
0 sensitive to all
neutrino masses
For 0 decay due to light Majorana ν masses:
mee
2
where,
2

 g A  0
 0 0
0
  T1/ 2 G E, Z  M GT    M F

 gV 

3
mee   U e,i mi  i
2
i 1
M F and M GT
G
0
T10/ 
2
2





1
the effective Majorana neutrino
mass,
nuclear matrix elements that can
be calculated,
a known phase-space factor,
the half-life time to be measured
Detection of 0νββ Decay
The two e- energy sum is the primary tool
2 spectrum
(normalized to 1)
0 peak (5% FWHM)
(normalized to 10-6)
0 peak (5% FWHM)
(normalized to 10-2)
Summed electron energy in units of the kinematic endpoint (Q)
from S.R. Elliott and P. Vogel, Ann.Rev.Nucl.Part.Sci. 52 (2002) 115.
For further substantial progress we need tons of an
appropriate isotope exposed for a long time
BUT there are problems
•In a bkgnd free environment mass sensitivity scales as
m  1 / T10/ 
 1 / Nt
2
•If bkgnd scales like Nt mass sensitivity scales as
m  1 / T10/ 
 1 / Nt 
2
1/ 4
Qualitatively new means are needed to suppress
bkgnds and fully utilize the large fiducial mass
Xe is ideal for such a measurement
• It is one of the easiest isotopes to enrich;
• Like argon, it represents a good ionization detecting
medium;
• It exhibits substantial scintillation that can be used
to complement the ionization detection;
• Can be re-purified during the experiment;
• No long lived Xe isotopes to activate;
• Its  decay results in 136Ba that can be identified
in its atomic form via techniques of high resolution
optical spectroscopy.
Optical detection of a
Ba+ atom (M. Moe PRC44(1991)931)
136
2P
1/2
Resonant laser detection is:
•Highly sensitive, yielding >107
photons per atom;
•Highly selective;
•Extensively used in the
atomic physics community.
Provides additional
constraint
Huge bkgnd reduction
650nm
493nm
4D
2S
metastable 47s
3/2
1/2
pump
probe
Detector R&D Program
• Single ion Ba+ tagging at different Xe pressures;
• LXe energy resolution;
• LXe purification for long e- lifetime and
radioimpurities;
• Ba ion lifetime and grabbing from LXe;
•
136Xe
Isotopic enrichment;
• Procurement and characterization of low radioactivity
materials;
• Construction/operation of a 200kg enriched 136Xe
prototype detector;
EXO spectroscopy lab
Ion Trap
493nm laser
650nm laser
CCD Image of Ba+ ions in the trap
Trap
edge
Millikan type experiment with the ion trap
Zero ion background
All above in UHV;
Perform the same
experiment in noble
gas atmosphere
Energy Resolution Measurement Setup
Reconstruct energy as linear
combination of ionization and
scintillation signals
Ionization Readout
Preamplifier
There are indications that
correlations between the two
variables help improve energy
resolution; J.Seguinot et al.
1Lt Test Chamber
NIM A354 (1995) 280
PMT
Clear anti-correlation on event-to-event basis is seen…
A linear combination of ionization and scintillation
WILL optimize resolution
Resolution is optimized by a ~100-150 ‘mixing angle’
Ionization only
Ionization combined
with scintillation
E.Conti et al Phys. Rev. B 68 (2003) 054201
3.3%@570keV
or 1.6%@2.5MeV
Xe purification studies-Continuous Xe Recirculation
First 200 kg pilot production started in the Summer of 2001
and was successfully completed in May 2003
Xe leak monitoring
station
This is already the
largest non-fissile isotope
enrichment program ever
entertained!
200kg 136Xe Prototype is an important step
• Need to test the detector technology, particularly
the LXe option;
• Essential to understand backgrounds from
radioactivity;
• Necessary to measure the 2 “background” mode;
• Test the production logistics and quality of 136Xe;
• 2000kg of natural Xe are already available by our
collaborators at ITEP;
• Already a respectable (20x)  decay experiment
(no Ba-ion tagging at this stage);
Detector
• ~60 liters enriched liquid 136Xe,
– In low background teflon vessel
– Surrounded and shielded by ~50 cm radially low background
thermal transfer fluid
– Contained in a low background Cu double walled vacuum
insulated cryostat
– Shielded by ~ 5 cm very low background Pb
– Further shielded by ~20 cm low background Pb
– Located ~800 m below ground in NaCl deposit – WIPP in
Carlsbad, New Mexico.
• Detector is a liquid TPC with photo-detectors to provide start
time and improve energy resolution of the β’s.
Detector
APD plane below crossed wire array
2D Detector schematic
Cryostat Cross Section
Refrigerant feedthroughs
Heat Transfer Fluid In/Out
Outer Door
Condenser
Xenon
Chamber
Support
FC-87
Inner Door
Xenon Heater
should be
on this area
1” thick Thermal Insulation (MLIvacuum), not shown to scale
FC-87
Inner Copper Vessel
Outer Copper Vessel
Xenon
Chamber
Detector Full View
Simplified xenon handling system diagram
An experimental facility for EXO
WIPP : Waste Isolation Pilot Plant
Carlsbad NM
Status
•Enriched Xe in hand.
•Clean rooms in commercial production.
•WIPP agreement, including Environmental Impact,
complete.
•Swiss collaborators building cryostat.
•Xe purification and refrigeration issues through
R&D, purchasing of components.
•Detector vessel, readout, and electronics being
engineered.
•EXO could be in WIPP by Summer 2005, if
technically limited.
EXO 200kg prototype mass sensitivity
Assumptions:
1) 200kg of Xe enriched to 80% in 136
2) σ(E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 054201
3) Low but finite radioactive background:
20 events/year in the ±2σ interval centered around the 2.481MeV endpoint
4) Negligible background from 2νββ (T1/2>1·1022yr R.Bernabei et al. measurement)
Case
Prototype
Mass Eff.
(ton) (%)
0.2
70
Run
Time
(yr)
2
σE/E @ Radioactive
2.5MeV Background
(%)
(events)
1.6*
40
T1/20ν
(yr,
90%CL)
6.4*1025
Majorana mass
(eV)
QRPA (NSM)
0.18
(0.53)
EXO neutrino effective mass sensitivity
Assumptions:
1) 80% enrichment in 136
2) Intrinsic low background + Ba tagging eliminate all radioactive background
3) Energy res only used to separate the 0ν from 2ν modes:
Select 0ν events in a ±2σ interval centered around the 2.481MeV endpoint
4) Use for 2νββ T1/2>1·1022yr (Bernabei et al. measurement)
Case
Mass
(ton)
Eff.
(%)
Run
Time
(yr)
σE/E @
2νββ
2.5MeV Background
(%)
(events)
Conserva
tive
1
70
5
1.6*
Aggressi
ve
10
70
10
1†
0.5 (use 1)
T1/20ν
(yr,
90%CL)
2*1027
0.7 (use 1) 4.1*1028
Majorana mass
(meV)
QRPA‡ (NSM)#
33
(95)
7.3
(21)
s(E)/E = 1.6% obtained in EXO R&D, Conti et al Phys Rev B 68 (2003) 054201
† s(E)/E = 1.0% considered as an aggressive but realistic guess with large light
collection area
‡ QRPA: A.Staudt et al. Europhys. Lett.13 (1990) 31; Phys. Lett. B268 (1991) 312
# NSM: E.Caurier et al. Phys Rev Lett 77 (1996) 1954
*