NEXT Searching for the 0 decay with a HPGXe TPC Pau Novella - - PowerPoint PPT Presentation
NEXT Searching for the 0 decay with a HPGXe TPC Pau Novella (CIEMAT) On behalf of the NEXT Collaboration TAUP09, Rome. Pau Novella [CIEMAT]. 1 Overview The NEXT experiment The SOFT TPC Concept Energy and tracking functions
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Pau Novella (CIEMAT) On behalf of the NEXT Collaboration
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Search for the ββ0ν process with a high pressure gas xenon (HPGXe) TPC Measure the ββ2ν decay of 136Xe T2ν
1/2 > 1022 year
T0ν
1/2 > 1.2 1024 year
HPGXe Energy Resolution BKG rejection NEXT-100: 100 kg 136Xe @ LSC Degenerate region: <mν >~ 100 meV Scalability to 1-ton detector
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The NEXT experiment
136Xe
High Qββ: 2480 keV Scintillation/Ionization Purification, reusability Easy to enrich Long ββ2ν mode Liquid xenon Gas xenon YES Scalability YES YES Compactness NO
Cryogenics Complexity H.P.
YES Fully Active YES NO Topology YES YES E. resolution YES
The Gothard experiment
Gas Xe TPC 3.3 kg 136Xe 5 bars 6.6% FWHM @ Qββ
95.6% rejection of single e
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Separated-Optimized Function for Tracking: a TPC with separately optimized technical solutions for energy and tracking
Energy function
Cathode: E measurement T0 measurement (scin.) Optimized for E resolution and T0 efficiency
Tracking function
Anode: tracking Optimized for fine pixelization Totally active detector Two different readout planes Inner walls with reflective material
How do we implement such energy and tracking functions in the NEXT TPC?
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The SOFT Concept
Energy resolution: a must for ββ0ν experiments Bolotnikov et Al. Nucl. Ins. Meth A 396 (1997) HPGXe Lxe T=-30ºC Lxe T=-110ºC
136Xe Intrinsic energy resolution:
δE/E ~ 3·10-3 FWHM @ Qββ Ionization only Intrinsic resolution worsens due to technical factors... NEXT target: 1% FWHM @ Qββ
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Electroluminiscence
EL amplification is lineal Small fluctuations (no gain) Better resolution than Q amplification Xe
Secondary scintillation
NEXT PMT: Hamamatsu R8520-06SEL (modified version of the XENON PMT) Fit Width Pressure up to 10 bars
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The SOFT Concept
A gas TPC provides also event topology information... ββ0ν event visualization Tracking: random walk, ionization Single e ββ signature: twisted track connected to 2 blobs BKG signature: any other topology topology:
Width: ~ 1cm Length ~ 30-40 cm
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Charge amplification
Alternative: Micromegas Hybrid TPC: gain-EL Operation in pure Xe with EL grid Radiopure device Low cost per unit of sensitive area Small size suitable for tracking
Requirements
Electroluminiscence
SiPM (MPPC) Wave length shifter APD (LAPD) Gain, dark current
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The SOFT Concept Drift lenght: 140 cm Diameter: 140 cm Pressure: 10 bars 108 kg of xenon e γ Cathode Sparse PMT plane E, t0
Reflective material TTX
1% FWHM @ Qββ Anode EL grid SiPM/APD/MM tracking 5mm gap ~20 kV 106 γ/e Pitch ~1.5 cm Steel vessel
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ββ2ν background is negligible for 1% FWHM @ Qbb 214Bi, 208Tl: mimic the ββ signal if a second e is generated γ interact with Xe via Photoelectric and Compton Neither double Compton nor pair are bkg in our ROI NEXT will measure the backgrounds with depleted xenon
Main background: 2.6 γ from 208Tl
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Physics Case
Fully active detector: External backgrounds can be rejected defining a fiducial volume tracks fully contained may become a bkg
208Tl and 214Bi decays in vessel/RO
Event topology: Events with more than one track Tracks with only one blob
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Physics Case
Expected number of bkg events (Bi,Tl) Event Selection cuts: contained in fiducial volume
ββ topology
F.Iguaz, University of Zaragoza
Rejection factors (1% FWHM):
214Bi in vessel: 3.5·10-7 214Bi in RO plane: 3.7·10-7 208Tl in vessel: 3.5·10-6 208Tl in RO plane: 4·10-6
Gothard experiment: ββ topology lead to 1/30 rejection factor.
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Physics Case
Most conservative scenario: Contamination in vessel and readout planes according market Minimum set of cuts on topology 1% FWHM @ Qbb
QRPA (V.A. Rodin et Al., Nuc.
T0ν
1/2 = 1.8·1026 year @ 90% C.L.
For 500 kg·year: Background: <10-3 count/keV/kg/year
Just to show the physics potential of the NEXT-100 detector...
To be improved: more radiopure materials for vessel and readout fully exploiting topological signature Improving energy resolution
<mν> <100 meV
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Institutional Support: Approved by the Scientific Committee of the LSC Partially funded by MICINN
LBNL, USA CEA, IRFU, Saclay, France
Portugal Spain: IFAE, CIEMAT, U. Santiago, IFIC, ITACA, UPV, U. Zaragoza
The NEXT Collaboration:
New collaborators welcome!
Spokesperson: J.J. Gómez Cadenas (gomez@mail.cern.ch)
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The NEXT project
Milestones:
NEXT-1 (2009-2011): Demonstrate the technology NEXT-10 (2011-2013): Radiopure 1/10 scale detector @ LSC NEXT-100 (2013-2018): 100 kg 136Xe detector @ LSC LOI submitted to the Scientific Committee. NEXT project is approved.
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NEXT project is meant to search for the ββ0ν decay with a HPGXe TPC The TPC is defined according to the SOFT concept: good energy resolution and track reconstruction NEXT-100 will explore the degenerate region of neutrino masses. Very promising physics potential A LOI has been submitted and NEXT has been approved by the LSC This is a first step towards a 1-ton detector, but NEXT Collaboration needs to grow up with new members from all over the world!
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