Post on 28-Aug-2018
Measuring the neutrino Measuring the neutrino mass…mass…
one atom at the timeone atom at the time
Giorgio GrattaPhysics Dept, Stanford
Columbia, SC, May 15, 2008 Giorgio Gratta 2
ββββ
decay experiments are at the leadingdecay experiments are at the leadingedge of edge of ““low backgroundlow background””
techniquestechniques
•• Final state ID: Final state ID: 1) “Geochemical”: search 1) “Geochemical”: search for an abnormal abundancefor an abnormal abundanceof (A,Z+2) in a material contaiof (A,Z+2) in a material containing (A,Z)ning (A,Z)
2) “Radiochemical”: store in a mine some m2) “Radiochemical”: store in a mine some material (A,Z)aterial (A,Z)and after some time try to findand after some time try to find
(A,Z+2) in it(A,Z+2) in it+ Very specific signature+ Very specific signature+ Large live times (particularly for 1)+ Large live times (particularly for 1)+ Large masses+ Large masses--
Possible only for a few isotopes (in the case of 1)Possible only for a few isotopes (in the case of 1)--
No distinction between 0No distinction between 0νν, , 22νν
or other modesor other modes•• “Real time”: “Real time”: ionization or scintillation is detected in the decayionization or scintillation is detected in the decay
a) “Homogeneous”: source=detectora) “Homogeneous”: source=detectorb) “Heterogeneous”: b) “Heterogeneous”: sourcesource≠≠detectordetector
+ Energy/some tracking available (can distinguish modes)+ Energy/some tracking available (can distinguish modes)+ In principle universal (b)+ In principle universal (b)--
Many Many γγ
backgrounds can fake signaturebackgrounds can fake signature--
Exposure is limited by human patienceExposure is limited by human patience
Columbia, SC, May 15, 2008 Giorgio Gratta 3
ββββ
decay experiments are at the leadingdecay experiments are at the leadingedge of edge of ““low backgroundlow background””
techniquestechniques
•• Final state ID: Final state ID: 1) “Geochemical”: search 1) “Geochemical”: search for an abnormal abundancefor an abnormal abundanceof (A,Z+2) in a material contaiof (A,Z+2) in a material containing (A,Z)ning (A,Z)
2) “Radiochemical”: store in a mine some m2) “Radiochemical”: store in a mine some material (A,Z)aterial (A,Z)and after some time try to findand after some time try to find
(A,Z+2) in it(A,Z+2) in it+ Very specific signature+ Very specific signature+ Large live times (particularly for 1)+ Large live times (particularly for 1)+ Large masses+ Large masses--
Possible only for a few isotopes (in the case of 1)Possible only for a few isotopes (in the case of 1)--
No distinction between 0No distinction between 0νν, , 22νν
or other modesor other modes•• “Real time”: “Real time”: ionization or scintillation is detected in the decayionization or scintillation is detected in the decay
a) “Homogeneous”: source=detectora) “Homogeneous”: source=detectorb) “Heterogeneous”: b) “Heterogeneous”: sourcesource≠≠detectordetector
+ Energy/some tracking available (can distinguish modes)+ Energy/some tracking available (can distinguish modes)+ In principle universal (b)+ In principle universal (b)--
Many Many γγ
backgrounds can fake signaturebackgrounds can fake signature--
Exposure is limited by human patienceExposure is limited by human patience
EXO wa
nts it
both w
ays!
We want
to de
velop a
very
clean
experim
ent us
ing bot
h thes
e tech
niques!
Columbia, SC, May 15, 2008 Giorgio Gratta 4
To reach <mν
> ~ 10 meV
very large fiducial
mass (tons)(except for Te) need massive isotopic enrichment
Need to reduce and control backgrounds in qualitatively new waysthese are the lowest background experiment ever built
For no For no bkgndbkgnd
Scaling with Scaling with bkgdbkgdgoes like goes like NtNt
NtTm /1/1 02/1 ∝∝ νββ
ν
( ) 4/102/1 /1/1 NtTm ∝∝ νββ
ν
In addition a multiIn addition a multi--parameter experiment, if feasible,parameter experiment, if feasible,would provide information for cross checks withwould provide information for cross checks with
more than one single variable, if a discovery is made.more than one single variable, if a discovery is made.
Columbia, SC, May 15, 2008 Giorgio Gratta 5
XeXe
is ideal for a large experimentis ideal for a large experiment••No need to grow crystalsNo need to grow crystals••Can be reCan be re--purified during the experimentpurified during the experiment••No long lived No long lived XeXe
isotopes to activateisotopes to activate
••Can be easily transferred from one detector to Can be easily transferred from one detector to another if new technologies become availableanother if new technologies become available
••Noble gas: Noble gas: easy(ereasy(er) to purify) to purify••136136Xe enrichment easier and safer:Xe enrichment easier and safer:
--
noble gas (no chemistry involved)noble gas (no chemistry involved)--
centrifuge feed rate in gram/s, all mass usefulcentrifuge feed rate in gram/s, all mass useful
--
centrifuge efficiency centrifuge efficiency ~~
ΔΔm.m.
For For XeXe
4.7 4.7 amuamu••129129Xe is a Xe is a hyperpolarizablehyperpolarizable
nucleus, under study for NMR nucleus, under study for NMR tomography… a joint enrichment program ?tomography… a joint enrichment program ?
Columbia, SC, May 15, 2008 Giorgio Gratta 6
XeXe
offers a qualitatively new tool against background:offers a qualitatively new tool against background:136136Xe Xe 136136BaBa++++
ee--
ee--
final state can be identified final state can be identified
using optical spectroscopyusing optical spectroscopy
((M.MoeM.Moe
PRC44 (1991) 931)PRC44 (1991) 931)
BaBa++
system best studiedsystem best studied((NeuhauserNeuhauser, , HohenstattHohenstatt,,ToshekToshek, , DehmeltDehmelt
1980)1980)Very specific signatureVery specific signature
“shelving”“shelving”Single ions can be detectedSingle ions can be detectedfrom a photon rate of 10from a photon rate of 1077/s/s
••Important additionalImportant additionalconstraintconstraint
••Drastic backgroundDrastic backgroundreductionreduction
22PP1/21/2
44DD3/23/2
22SS1/21/2
493nm493nm
650nm650nm
metastablemetastable
47s47s
Columbia, SC, May 15, 2008 Giorgio Gratta 7
The The BaBa--tagging, added to a high resolution tagging, added to a high resolution XeXe
imagingimagingdetector provides the tools to develop a backgrounddetector provides the tools to develop a background--freefree
nextnext--generation generation ββββ
experimentexperiment
Assume an “asymptotic” Assume an “asymptotic” fiducialfiducial
mass of mass of 10 tons of 10 tons of 136136Xe at 80%Xe at 80%
A somewhat natural scale:A somewhat natural scale:•• World production of World production of XeXe
is ~45 ton/yris ~45 ton/yr
•• Detector sizeDetector size•• 22••101033
size increase: good match to the size increase: good match to the 1010--22
eVeV
mass regionmass region
Mainly going inMainly going inlight bulbs, plasma light bulbs, plasma
displays anddisplays andsatellite propulsionsatellite propulsion
Columbia, SC, May 15, 2008 Giorgio Gratta 8
The roadmap to the background-free discoveryof Majorana
neutrinos and the neutrino mass scale
Gain practicewith Batrapping andspectroscopyin Xe
and other gases
Learn about physicsand economics of Xe
enrichmenton a grand scale
Enrich a large amountof Xe
(200 kg)
Design and build a large, ton scaleexperiment with Ba
tagging
Improve the energyresolution in LXe
Design & build alarge size, lowbackground prototypeLXe
0νββ
detector
Measure 2νββ
in136Xe, gain operationalexperience, reach thebest 0νββ
sensitivity
Build a fully functionalion grab, transfer,trap, spectroscopy cell
Gain practicewith Bagrabbing and release
DoneIn progressTo do
Investigatedirect taggingin LXe
Columbia, SC, May 15, 2008 Giorgio Gratta 9Plot from Plot from AvignoneAvignone, Elliott, Engel arXiv:0708.1033 (2007), Elliott, Engel arXiv:0708.1033 (2007)
100kg-class detectors~100-200 meV
sensit.
Klapdor
et al. 0.24 –
0.58 eV
Full-EXO sensitivity
1 ton, 5yr, 28 meV
1 ton, 10yr, 6 meV
Assumptions:
Majorana
neutrinosNo cancellations
For the first time there is a clear opportunity to make an importantdiscovery if one pusheddthe
<m> sensitivity to the 0.01 -
1 eV
region
Columbia, SC, May 15, 2008 Giorgio Gratta 10
EXOEXO--200:200:an intermediate detector an intermediate detector withoutwithout BaBa taggingtagging
••Need to test detector technology, particularly the Need to test detector technology, particularly the LXeLXe
option:option:A 200 kg chamber is close to the largest A 200 kg chamber is close to the largest XeXe detector ever built detector ever built and hence good training groundand hence good training ground
••Essential to understand backgrounds from radioactivity:Essential to understand backgrounds from radioactivity:200 kg is the minimum size for which the self200 kg is the minimum size for which the self--shielding is shielding is important and there is negligible surface inefficiencyimportant and there is negligible surface inefficiency
••Using Using 136136Xe can hope to measure the “background” Xe can hope to measure the “background” 2νββ2νββ
mode:mode:200 kg is needed to have a chance (if do not see the mode the200 kg is needed to have a chance (if do not see the mode thennis really good news for the large experiment !!)is really good news for the large experiment !!)
••The production logistics and quality of The production logistics and quality of 136136Xe need to be tested:Xe need to be tested:Need a reasonably large quantity to test productionNeed a reasonably large quantity to test production
••Already a respectable (20x) Already a respectable (20x) ββββ
decay experiment decay experiment ••No need for No need for BaBa
tagging at this scaletagging at this scale
Columbia, SC, May 15, 2008 Giorgio Gratta 11
200 kg 200 kg 136136Xe test production completed in spring ’03 (80% enrichment)Xe test production completed in spring ’03 (80% enrichment)
••Largest highly enriched stockpileLargest highly enriched stockpilenot related to nuclear industrynot related to nuclear industry
••Largest sample of separated Largest sample of separated ββββisotope (by ~factor of 10)isotope (by ~factor of 10)
from
S.R
. Elli
ott
and
P. V
ogel
, Ann
.Rev
.Nuc
l.Par
t.Sc
i. 52
(200
2) 1
15.
2νββ
spectrum(normalized to 1)
0νββ
peak (5% FWHM)(normalized to 10-6)
Summed electron energy in units of the kinematic endpoint (Q)
Background due to the Standard Model 2νββ
decay
The two can be separated in a detector withgood energy resolution
0νββ
peak (5% FWHM)(normalized to 10-2)
Columbia, SC, May 15, 2008 Giorgio Gratta 13
1 kV/cm
~570 ~570 keVkeV
EXO R&D showed the way to improved energy resolution in LXe: Use (anti)correlations between
ionization and scintillation signals
Columbia, SC, May 15, 2008 Giorgio Gratta 14
Anti-correlated ionization and scintillation improves the energy resolution in LXe
Ionization alone:σ(E)/E = 3.8% @ 570 keV
or 1.8% @ Qββ
Ionization & Scintillation:σ(E)/E = 3.0% @ 570 keV
or 1.4% @ Qββ(a factor of 2 better than the
Gotthard TPC)
Drift Field [kV/cm]0 2 4 6 8 10
%]
σR
eso
luti
on
[
0
2
4
6
8
10
12Aprile xxxx
Aprile xxxx
Barabash xxxx
Lindblad xxxx
Mel xxxx
Ionization Signal
Correlated Signal
Compilationof Xe
resolution results
EXO ioniz
+ scintE.Conti et al. Phys. Rev. B: 68 054201
EXO-200 will collect 3-4 timesas much scintillation…
further improvement possible
EXO ioniz
only
Columbia, SC, May 15, 2008 Giorgio Gratta 16
EXO chamber “hugs” the fiducial
volume very closely!
2x300 large area(1.6cm active diameter)unmounted
APDs
228.6mm
170.8mm186.2mm
Mechanical supports and cable/Xe
conduits
Inductive and chargecollecting wire planes
Cathode grid
Columbia, SC, May 15, 2008 Giorgio Gratta 17
Ultra-low activity Cu vessel
• Very light (~1.5mm thin, ~15kg)to minimize materials
•Different parts e-beam weldedtogether
• Field TIG weld(s) to seal the vessel after assembly (TIG technology tested for radioactivity)
• All machining done by in theCR-shielded HEPL building)
Columbia, SC, May 15, 2008 Giorgio Gratta 18
EXO-200 LXe
TPC field cage & readout planes
flex cables on back of APD plane
acrylic supportsCentral HV plane (photo-etched phosphor bronze)
~40cm
~500 “Bare” LAAPD
QE > 1 at 175nm
Gain set at 100-150
V~1500V∆V < ±0.5V ∆T < ±1K APD is the driver
for temperature stabilityLeakage current OK cold
APDs
are ideal for ourapplication:
-
very clean & light-weight, -
very sensitive to VUV
Columbia, SC, May 15, 2008 Giorgio Gratta 20
APDs
are ideal for our application: -
very clean & light-weight, -
QE>1 @ 175nm
Gain set at 100-150
V~1500V∆V < ±0.5V ∆T < ±1K APD is the driver
for temperature stabilityLeakage current OK cold
APD testing rig to measure16 APDs
at the time in vacuumAt -100C.Readout using production EXO-200 electronics (one card)
All APDs are in han
d
Columbia, SC, May 15, 2008 Giorgio Gratta 23
Low activity Copper arriving fromGermany in a shielded container
Columbia, SC, May 15, 2008 Giorgio Gratta 24
Massive effort on material radioactive qualification using:
• NAA (MIT-Alabama)• Low background γ-spectroscopy (Neuchatel, Alabama)• α-counting (Alabama, Stanford, SLAC, Carleton)• Radon counting (Laurentian)• High performance GD-MS and ICP-MS (Canadian Inst. Standards)
At present the database of characterized materialsincludes >300 entries
MC simulation of backgrounds at Alabama and Stanford/SLAC
The impact of every screw within the Pb
shielding is evaluatedbefore acceptance
NIM article published on the subject with entries for 225 materials[D.Leonard et al., arXiv:0709.4524 to appear on NIM A]
Columbia, SC, May 15, 2008 Giorgio Gratta 25underground at WIPP
★
muon flux at WIPP(~ 1700 m.w.e.):
4.77×10-3 m-2 s-1
(3.10×10-3 m-2 s-1sr-1, ~15 m-2 h-1)
[E.-I.Esch et al., Nucl. Instr. Meth. A 538(2005)516]
Mod 1 ready to shipJun 2007
Columbia, SC, May 15, 2008 Giorgio Gratta 32
BaBa++
Tagging R&DTagging R&D
Vcos(Vcos(ΩΩt) + Ut) + U
UU
Ba ovenBa oven
DC
pote
ntial [V
]DC
pote
ntial [V
]
0 Volts0 Volts
--5 Volts5 Volts
BaBaBuffer gasBuffer gas
CCD
ee--
gungun
Spectroscopy Spectroscopy laserslasers
ScopeScope
Columbia, SC, May 15, 2008 Giorgio Gratta 33
Electrode structure being prepared
Loading region inthe vacuum tank
e-gun
Ba
oven
Tip loading access Main turboport
Differentiallypumped aperture
Fluorescence from 1, 2, 3
Ba-ions
Columbia, SC, May 15, 2008 Giorgio Gratta 34
M.Green et al. arXiv:0702122, Phys Rev A 76 (2007) 023404B.Flatt et al. arXiv:0704.1646, NIM A 578 (2007) 409
~9σ
disciminationin 25s integration
First single ion detection in high pressure gas (He, Ar)
Columbia, SC, May 15, 2008 Giorgio Gratta 35
Single ion spectroscopy & identification possible in some Xeatmosphere provided He is added to the trap
p=10-4 torr
Cryogenic dipstick• Capture ion on SXe
coating• LHe
cooling (~20K) tomaintain stable SXe
coatingin 10-8 torr
vacuum• Microcapacitor
used to measure and stabilize
SXe
with accuracy ofa few monolayers
in LXe
andvacuum
Remaining challenge is the efficient transferof single Ba
ions from LXe
to the ion trap
Columbia, SC, May 15, 2008 Giorgio Gratta 37
LHe
cryostat
SXe-coatedtip
LXe
cell
Actuator
Complete setupComplete setup
Columbia, SC, May 15, 2008 Giorgio Gratta 38
from LXe
Growing SXe
layers from meteredamounts of GXe
in the vacuum chamber
Growing and maintainingSXe
layers in a LXe
bathwith active feedback
P.Fierlinger et al, arXiv:0706.0540Rev. Sci. Instr. 79, 045101 (2008)
Columbia, SC, May 15, 2008 Giorgio Gratta 39
In parallelengineerthe second version ofthe cryotip
Next StepsShoot ions from the traponto the cryotip
and backinto the ion trap
Columbia, SC, May 15, 2008 Giorgio Gratta 40
Ba
atomon tip
Semitransparent metallic coating absorbs desorption
λ, transmits RIS lasers
Ba+
ion in vacuum/gas
UV multimodeoptical fiber(~200μm core)
~200μm
~200μm
1.
Pulsed desorption
laser: Nd:YAG2.
~10ns delay to allow Ba
neutral atom to leave the surface
3.
-Resonant step: pulsed laser @ 413nm
-Autoionizing
step: pulsed laser @ 481nm
RIS tipRIS tip
In this case each step can be documented to work with high efficiency in the literature !
R&D on this has started (have YAG + 2 dye lasers, test cellbeing commissioned, fiber coating facility ready)
Columbia, SC, May 15, 2008 Giorgio Gratta 41
Gas phase R&D in progress mostly by EXO- Canada (Carleton + Laurentian)
Columbia, SC, May 15, 2008 Giorgio Gratta 42
In this case Ba
tagging will occur directly in a region of the chamber
Columbia, SC, May 15, 2008 Giorgio Gratta 43
EXO really belongs to this tradition!
Isotope enrichment at an unprecedented scale (for science) is a reality
EXO-200 is going underground!
Ba
tagging for EXO is using bag of tricks borrowed fromnuclear and particle physics, AMO and surface science
EXO is ramping up GXe
R&D to arrive to the technologydecision point with all of the information needed
ConclusionsOver its glorious history neutrino physics has providedplenty of surprises and has required forays in many different areas of science and technology
Columbia, SC, May 15, 2008 Giorgio Gratta 46
The EXO Collaboration
K.Barry, D.Leonard, E.Niner, A.Piepke
Physics Dept, University of Alabama, Tuscaloosa AL
P.Vogel
Physics Dept Caltech, Pasadena CA
A.Bellerive, M.Bowcock,
M.Dixit, C.Hargrove, E.Rollin, D.Sinclair, V.Strickland
Carleton University, Ottawa, Canada
C. Benitez-Medina, S.Cook, W.Fairbank
Jr., K.Hall, B.Mong
Colorado State University, Fort Collins CO
M.Moe
Physics Dept UC Irvine, Irvine CA
D.Akimov, I.Alexandrov, A.Burenkov, M.Danilov, A.Dolgolenko, A.Kovalenko, V.Stekhanov
ITEP Moscow, Russia
J.Farine, D.Hallman, C.Virtue, U.Wichoski
Laurentian University, Canada
H.Breuer, C.Hall, L.Kaufman, S. Slutsky, Y-R. YenUniversity of Maryland, College Park MD
K.Kumar
U. of Massachusetts, Amherst
M.Auger, R.Gornea, D.Schenker, J-L.Vuilleumier, J-M.Vuilleumier
Physics Dept University of Neuchatel, Switzerland
N.Ackerman, M.Breidenbach, R.Conley, W.Craddock, J.Hodgson, D.McKay, A.Odian, C.Prescott, P.Rowson, K.Skarpaas, J.Wodin, L.Yang, S.Zalog
SLAC, Menlo Park CA
J.Anthony, L.Bartoszek, R.DeVoe, P.Fierlinger, B.Flatt, G.Gratta, M.Green, S.Kolkowitz, F.LePort, M.Montero-Diez, R.Neilson, M. Noske, K.O’Sullivan, A.Pocar, K.Twilker
Physics Dept Stanford U., Stanford CA