Transcript Sub-MeV solar neutrinos: experimental techniques and
Sub-MeV solar neutrinos: experimental techniques and backgrounds
Aldo Ianni Gran Sasso Laboratory, INFN
Stockholm, May 2-6, 2006 SNOW 2006 1
Why do we need to measure sub-MeV solar neutrinos?
Neutrino physics Astrophysics
How can they be observed?
Upcoming: 100-ton scale
ultra-pure organic Liquid Scintillator
photon yield below 1 MeV)
Elastic Scattering
Future:
liquid noble gases
,
metal loaded LS
,
TPC ES + Inverse Electron Capture
(high Stockholm, May 2-6, 2006 SNOW 2006 2
Why?
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Only 0.01% of solar neutrino spectrum measured in real time
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Measurements vs unknowns
R
radiochemi cal experiment s i
i
observed sources
SNO CC
B
P ee B
i
SNO NC
Super
ES K
B
B
P ee B
1
P ee B
B
P ee i
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MSW-LMA to explain observations Stockholm, May 2-6, 2006
Obtained with SSM constraints!
SNOW 2006
Transition of P ee
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What do we want to measure and why do it?
measure/SS
Be
,
pp
M
ES
f Be
,
pp
measure/SS
Be
,
pp
M
CC
f Be
,
pp
measure
f pep P ee Be
,
pp P ee Be
,
pp
1
P ee Be
,
pp
f Be
,
pp
astrophysics
f Be f pp
0 .
91 0 .
24 0 .
62 1 .
07 0 .
05 0 .
07 1 .
02 0 .
02 1.010
0.005
L L 1 .
4 0 .
0 .
2 3 0 .
99 0 .
02
Neutrino physics
Non standard physics such as 0 , l q f q and a light sterile neutrino might shows up at middle or low energies Stockholm, May 2-6, 2006 SNOW 2006 7
How difficult is it going to be?
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• What detection channel
– ES : not a specific signature, better with Be and pep + asks for a ultra-pure Fiducial Mass – CC : strong signature via inverse electron capture. Internal background may become less important Stockholm, May 2-6, 2006 SNOW 2006 9
Signatures and requirements for the ES channel
With U,Th at 10 -16 g/g and 40 K at 10 -14 g/g • internal backg. ~ 20 cpd/100 tons in [0.25,0.8]MeV 100
Simulated seasonal Signal Background in BOREXINO
95 90 S 0 B 33 counts day 50 counts day 85 80 75 200 400 600 time days 800 1000
10 -16 g/g
6 5 2 1 4 3 0 20 40 60 80 100 120 Background events day 140 2yr 3yr 5yr 3 level Stockholm, May 2-6, 2006 SNOW 2006 10
•
ES + Ultra-pure liquid scintillators
– First thoughts/tests ~1988 to address radiopurity issues • High photon yield (10 4 /MeV) allows to perform spectroscopic measurements • SSM predicts ~ 0.5 cpd/ton for Be with ES => 100t FM – Borexino a pioneer experiment with a 4-ton prototype showed (1997): • that
238 U
and
232 Th
can be
below
or on the order of
10 -16 g/g
–
(~10 -6 Bq/ton)
• that
14 C/ 12 C ~ 10 -18
allows to set a
thereshold
at
250 keV
• that (
self-shielding design
~ 1 g/cm 3 ) to works with organic scintillator
reduce external background
for ES KamLAND (2002) with a 500 ton-scale mass has measured 238 U and 232 Th at the level of
10 -17 -10 -18 g/g
=> pep meas. opportunity Stockholm, May 2-6, 2006 SNOW 2006 11
All spectra normalized to 1 Stockholm, May 2-6, 2006
Beyond U and Th
Asking for 1cpd/100tons [0.1 Bq/m 3 PC] it implies: 1.
2.
3.
System sealed against 222 Rn ~10 -5 Bq/ton 0.4 ppm 39 Ar in N 2 0.2 ppt 85 Kr in N 2 210 Pb and 210 Po are often found not in equlibrium due to a different chemistry SNOW 2006 12
Beyond U and Th
Removing/Reducing 210 Bi, 210 Po, 85 Kr, 39 Ar • High level of cleanliness • Purification of scintillator – Distillation (thought to be the best method on the basis of small set-up tests) – Water extraction – High level nitrogen sparging Check radioisotope impurities before filling!
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What about pep neutrinos?
• • • Cosmogenic background:
11 C
• Possible
11 C background reduction
capture + 11 by tagging the sequence (in Borexino and KamLAND): muon + neutron C decay [see Galbiati et al, PRC, 71, 055805 (2005)]
Method
already
Borexino prototype
ex/0601035 ]
tested with
[see hep-
SNO+ main goal
depth due to SNOlab Stockholm, May 2-6, 2006 SNOW 2006 14
Reduction of background for pep neutrinos
Muon going through Spherical cut around neutron capture vertex to reject 11 C event correlated in time and space Cylindrical cut Around muon-track Neutron production vertex In 95% of cases a neutron is produced together with a 11 C Signal/Noise as large as 2 with only 3% of data rejected @ Gran Sasso Stockholm, May 2-6, 2006 SNOW 2006 15
11
C tagged with the Borexino prototype
11 C decays b + with Q b ~1MeV and t~30 min Measured production rate ~0.14 events/day/ton at Gran Sasso depth
Taken from Borexino coll. hep-ex/0601035
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Backgrounds for pep besides U,Th,
11
C
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Next generation projects
Goals
• real-time observation of pp (CC/ ES ) • real-time observation of Be with a CC channel
Projects XMASS : LXe, ES CLEAN : LNe, ES
(see D. McKinsey this workshop)
MOON :
100
Mo CC LENS :
115
In CC
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Liquid Xe [XMASS]
• Multi-purpose detector • Channel: ES • No 14 C!
• Target: 23t [10t FV] of LXe • Design: use of 30cm self shielding ( = 3.06 g/cm 3 ) • Backgrounds (main tasks): – – 85 Kr: to be reduced to 4x10 -15 g/g from 10ppm (by distillation) 136 Xe 0 bb : isotope separation (<1/100 of natural) • 100kg(NOW)->1E3->1E4 Stockholm, May 2-6, 2006 SNOW 2006 2.5 m 19
LENS
e
115
In
e
[prompt] 2 [delayed, t 4.5
s] 115
Sn
• 115 In abundance = 95.7% •Threshold of capture = 0.114 MeV •B(GT) = 0.17 [precise measurement with neutrino source in TF] •LS stability tested : > 2yr •Backgrounds: b decay of 115 In + following Bremsstrahlung Multiple In b decay •Desing: high segmentation with 125t on LS [10t of In] Stockholm, May 2-6, 2006 SNOW 2006 ~4% pp meas. in 5yr 20
• Multi-purpose detector [0 bb , supernova ’s] • Channel: inverse e- capture (prompt) + delayed b decay •Threshold of capture = 0.168
•(g A /g V ) 2 B(GT) = 0.52
•Backgrounds: • U,Th at 10 -3 ±0.06
Bq/ton MeV • 214 Pb-> 214 Bi-> 214 Po • •2 bb •Surface contamination •Design:
3.3ton 100 Mo
•module 6m x 6m x 5m •Mo foils 0.05 g/cm 2 •x, y reading with scintillators •
~10 -9 spatial resolution required
•Signal: • pp: ~337 events/yr/3.3tons
•Be: ~167 events/yr/3.3tons
•Test Facility in operation since April 2005 @ Oto underground lab.
MOON
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Conclusions
• • • It is
great opportunity
solar neutrinos • First thoughts: 1988!
When to measure low energy : Borexino and KamLAND-> 2007 10% Be meas. [5%] gives 10%Be,1%pp [5%Be,0.5%pp] • New goal: pep neutrinos . Precise meas. @ SNO+ • Complementary projects under-way >=2010(?) Stockholm, May 2-6, 2006 SNOW 2006 22
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From Galbiati et al, PRC, 71, 055805 (2005) Stockholm, May 2-6, 2006 SNOW 2006 25
From Galbiati et al, PRC, 71, 055805 (2005) Stockholm, May 2-6, 2006 SNOW 2006 26
From Galbiati et al, PRC, 71, 055805 (2005) Stockholm, May 2-6, 2006 SNOW 2006 27
From Galbiati et al, PRC, 71, 055805 (2005) Stockholm, May 2-6, 2006 SNOW 2006 28
A He 2 Ne 10 Ar 18 Kr 36 Xe 54 Ion. Potent. (eV) Boiling point (K) p.e./MeV 24.6
4.2
21.6
27 15.7
87 14 Stockholm, May 2-6, 2006 4E4 long lived isotopes Density (g/cm 3 ) Rad. Length (cm) 0.125
756 1.2
24 4E4 39 1.4
14 Ar, 42 Ar 85 2.6
From hep-ph/0008296 SNOW 2006 Kr 12.1
119.8 165 4.3E4
3.06
2.4
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XMASS Program with LXe
100kg Prototype 800kg detector With light guide ～ 30cm R&D 10 ton detector ～ 80cm ～ 2.5m
Dark Matter Search SNOW 2006 Multipurpose Detector (DM, Solar Neutrino, bb ) 30 2006
Coded Aperture Wafer Array
R. Lanou Stockholm, May 2-6, 2006
General Properties
x + e →
x + e in 22 tonnes Helium
Ultra-pure (superfluid self-cleaning)
Scintillation + rotons or e-bubbles
Event discrimination Position & energy reconstruction Progress
Frozen N 2 + acrylic to replace graphite moderator
Successful extraction of electrons from drifted e-bubbles …
more powerful than rotons Prospects
Technique & physics potential established
SNOW 2006
… Requires large scale prototyping
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