Search for 0νββ decay with EXO-200 and prospects with nEXO...Search for 0νββdecay with EXO-200...
Transcript of Search for 0νββ decay with EXO-200 and prospects with nEXO...Search for 0νββdecay with EXO-200...
Search for 0νββ decay with EXO-200
and nEXO
Guofu Cao
Institute of High Energy Physics, Beijing, China
On behalf of the EXO-200 and nEXO Collaborations
XIV International Conference on Heavy Quarks and Leptons
May 27 – June 1, 2018, Yamagata, Japan
Neutrinoless Double Beta Decays
Two types of double beta decay Ordinary double beta decay (2νββ, with
two anti-neutrinos)
Neutrinoless double beta decay (0νββ), takes place between two even-even nuclei.
Observation of 0νββ decay = Discovery of NEW PHYSICS Antineutrino and neutrino are the same
particle – Majorana particle
Lepton number violation
Constrain neutrino mass scale
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2νββ decay 0νββ
Single β decay is forbidden
Requirements of 0νββ Detection 3
2νββ
0νββ(A,Z) (A,Z+2) + 2e–
(A,Z) (A,Z+2) + 2e– + 2ne
For a one dimensional 0νββ search by using energy, the only way to enhance the sensitivity is to reduce the background and improve the energy resolution. This is the case for a small detector.
However, a more powerful detector should provide more parameters used to reject background and simultaneously fit signal and background.
Use liquid Xenon TPC to search for 0νββ 4
- 8kVCharge collection
e-
e-
e-e-
e-e-
e-e-
e-
e-
e-
e-
e-
Ionization Scintillation
Example of TPC schematics (EXO-200)
Advantage of Xenon: Xenon is used both as the source
and detection medium.
136Xe enrichment is easier and safer. Easily scale to tonne scale. Low background -- No long lived
radioactive isotopes and can be continuously purified.
Advantage of liquid Xenon TPC: Simultaneous collection of both
ionization and scintillation signals. Full 3D reconstruction of all energy
depositions in LXe.Monolithic detector structure with
excellent background rejection capabilities.
Combine all parameters, processing a simultaneously fitting for signal and background.
EXO-200 is a running LXe detector,
the first 100 kg-class experiment to
produce results and has demonstrated
key technologies for 0νββ search.
nEXO is a proposed 5 tonne detector,
will take full advantage of LXe TPC to
reach T1/2 ~ 1028 yrs and entirely cover
the Inverted Hierarchy.
Energy measurement
Combine light and ionization to enhance energy resolution
(E.Conti et al. Phys Rev B 68 (2003) 054201)
EXO-200 has achieved ~1.23% energy resolution at the Q value.
nEXO will reach resolution < 1%, sufficient to suppress background from 2νββ.
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228Th source
Again, LXe TPC IS NOT A PURE CALORIMETER, it can use optimally more than just the energy. Event multiplicity (SS/MS in EXO-200)Distance from the TPC surface Particle ID (α-electron)
Event multiplicity information 6
Low
bac
kgro
un
dd
ata
228Th
cal
ibra
tio
nso
urc
e
2νββ
Low
bac
kgro
un
dd
ata
228Th
cal
ibra
tio
nso
urc
e
γ γ
multiple site events (MS)
2νββ
single site events (SS)
SS/MS discrimination is a very powerful tool to reject gamma backgrounds, because Compton scattering results in multiple energy deposits. This is well demonstrated in EXO-200.
EXO-200 Liquid 136Xe TPC 7
EXO-200 Most Recent 0νββ Results 8
“Blind” analysis (box opened on July 1st, 2017)
Background model + data maximum likelihood fit
Combine Phase I + Phase II profiles
No statistically significant excess: combined p-value ~ 1.5σ
From EXO-200 to nEXO (~200kg to 5000 kg) 9
EXO-200
Detector
From EXO-200 to nEXO (~200kg to 5000 kg) 10
EXO-200
Detector
From EXO-200 to nEXO (~200kg to 5000 kg) 11
EXO-200 Detector
nEXO Detector
1.3 m
A 5000 kg enriched LXe TPC, directly extrapolated from EXO-200.
A monolithic detector is essential!!
Monolithic Detectors 12
LXe mass (kg) Diam. or length (cm)
5000 130
150 40
5 13
5kg
150kg
5000kg
2.5MeV gamma ray attenuation
length 8.5 cm =
Monolithic detector is essential for background rejection:
• Rejection of surface background
• Self-shielding, containment of Compton scattering
• Inner fiducial volume extremely clean
EXO-200nEXO
View of conceptual design of nEXO 13
Ø 13 m
14 m
14m
6,000 m.w.e. depth sufficient to shield cosmogenic background.
SNOLAB’s cryopit
Optimizations from EXO-200 to nEXO 14
nEXO TPC Conceptual Design 15
Cathode is located at the bottom of TPC.
A pad-like charge readout tile is on top of TPC.
Photo-sensors are behind the field shaping rings and will operate in a high field region.
Photo-detector System in nEXO 16
VUV sensitive SiPMsThe overall photon detection efficiency is crucial for nEXO, which is determined by PDE of SiPM and light transport efficiency in TPC.
Copper vessel24 staves, 4-5m2
R&D items:
SiPM characterization Reflectivity on SiPM (>50% VUV lights
reflected) SiPM performance in external high E
field Silicon/quartz interposer Large area test …
Highlights of part of R&D progresses 17
FBK SiPM
PreliminarynEXO
goal
Preliminary
Preliminary
Preliminary
In Vacuum
Charge Readout Tile 18
Prototype charge readout tile
In nEXO, a modular and pad-like charge collection scheme is under study.
A 10cm x 10cm prototype has been made by IHEP/IME in China.
The prototype is tested at Stanford.
JINST 13 P01006 (2018)
nEXO Sensitivity 19
Summary
It will be a great discovery, if 0νββ decay is observed.
EXO-200 achieved 0νββ half-life sensitivity of 3.7×1025 yrs (90% CL), and will further improve to 5×1025 yrs after Phase II running, which is one of most competitive experiments in the field.
nEXO is extrapolated from EXO-200, and aiming to reach 0νββhalf-life sensitivity of 1028 yrs by using 5 tonne liquid 136Xe TPC, which can entirely cover inverted hierarchy region.
Lots of R&D work is ongoing in nEXO, in order to enhance TPC performance.
We are ready to enter the world of ton scale.
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University of Alabama, Tuscaloosa AL, USA —M Hughes, O Nusair, I Ostrovskiy, A Piepke, AK Soma, V VeeraraghavanUniversity of Bern, Switzerland — J-L VuilleumierUniversity of California, Irvine, Irvine CA, USA — M MoeCalifornia Institute of Technology, Pasadena CA, USA — P VogelCarleton University, Ottawa ON, Canada — I Badhrees, R Gornea, C Jessiman, T Koffas, D Sinclair, B Veenstra, J WatkinsColorado State University, Fort Collins CO, USA —C Chambers, A Craycraft, D Fairbank, W Fairbank Jr, A Iverson, J ToddDrexel University, Philadelphia PA, USA —MJ Dolinski, P Gautam, EV Hansen, YH Lin, Y-R YenDuke University, Durham NC, USA — PS BarbeauFriedrich-Alexander-University Erlangen, Nuremberg, Germany —G Anton, J Hoessl, P Hufschmidt, T Michel, M Wagenpfeil, S Schmidt, G Wrede, T ZieglerIBS Center for Underground Physics, Daejeon, South Korea —DS LeonardIHEP Beijing, People’s Republic of China —G Cao, W Cen, T Tolba, L Wen, J ZhaoITEP Moscow, Russia —V Belov, A Burenkov, M Danilov, A Dolgolenko, A Karelin, A Kuchenkov, V Stekhanov, O Zeldovich
University of Illinois, Urbana-Champaign IL, USA —D Beck, M Coon, J Echevers, S Li, L YangIndiana University, Bloomington IN, USA — JB Albert, SJ DaughertyLaurentian University, Sudbury ON, Canada —B Cleveland, A Der Mesrobian-Kabakian, J Farine, C Licciardi, A Robinson, U WichoskiUniversity of Maryland, College Park MD, USA — C HallUniversity of Massachusetts, Amherst MA, USA — S Feyzbakhsh, A Pocar, M TarkaMcGill University, Montreal QC, Canada — T Brunner, L Darroch, K MurrayUniversity of North Carolina, Wilmington NC, USA — T DanielsSLAC National Accelerator Laboratory, Menlo Park CA, USA —M Breidenbach, R Conley, J Davis, S Delaquis, A Johnson, LJ Kaufman,
B Mong, A Odian, CY Prescott, PC Rowson, JJ Russell, K Skarpaas, A Waite, M WittgenUniversity of South Dakota, Vermillion SD, USA — A Larson, R MacLellanStanford University, Stanford CA, USA — J Dalmasson, R DeVoe, D Fudenberg, G Gratta, M Jewell, S Kravitz, G Li, A Schubert, M Weber, S WuStony Brook University, SUNY, Stony Brook, NY, USA — K Kumar, O NjoyaTechnical University of Munich, Garching, Germany — W Feldmeier, P Fierlinger, M MarinoTRIUMF, Vancouver BC, Canada — J Dilling, R Krücken, Y Lan, F Retière, V StricklandYale University, New Haven CT, USA —A Jamil, Z Li, D Moore, Q Xia
The EXO-200 Collaboration
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Backup
EXO-200 Detector 24
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The power of homogeneous detector.
The background is constrained by outer part of detector, and keeping inner part clean.
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Background Assumption 27
Background index 28