The search for Majorana neutrinos with a background-free gaseous Xenon TPC at the tonne scale F . Monrabal on behalf The NEXT coll. � 1
The Majorana neutrino challenge Lifetime ~10 27 -10 28 years 1 signal event in a tonne of active volume per year Lifetime ~10 30 years 1 signal event in a 100 tonne of active volume per year � 2
The Majorana neutrino challenge counts/ Experiment counts/(ROI·ton·year) (keV·kg·year) Gerda 1.0x10 -3 4 Phys. Rev. Lett 120 , 132503 Kamland-Zen 1.18x10 -2 40 Conf. Series 888 (2017) 012031 EXO 1.7x10 -3 255 Nature, 510, 229-234 CUORE 1.4x10 -2 107 arXiv:1905.07667v1 JHEP05 (2016) 159 NEXT 4x10 -4 10 � 3
Gas phase detectors: NEXT Prototypes NEXT-100 (100 kg) NEW (~10kg) NEXT (~1000 kg) See J.M. Benlloch talk! � 4
The NEXT incremental approach: NEXT-HD Extrapolation of the current NEXT-100 concept Symmetric TPC Reduced radioactive budget by replacing the PMTs with SiPM. Energy and tracking functions remain independent � 5
Solutions to be implemented in NEXT-100 Design voltage of cathode and EL mesh HVFT is very close to NEXT-100 SiPM radio-pure substrates already in hand. � 6
The NEXT incremental approach: NEXT-HD Di ff erences with NEXT-100 Symmetric detector: Two sizes of SiPMs in the same plane, need to develop an integrated electronics. Operation with cold Xenon: Gas mixtures to reduce We need to reduce SiPM dark di ff usion current � 7
Current R&D: Symetric detector We will use a vertical symmetric detector with the cathode in the center. This simplifies the design of the high voltage E feedthrough and reduces total drift length. E Sensor planes will have two SiPMs sizes. Similar dynamic range Energy function implemented in the opposite size of the amplification (as usual) � 8
Current R&D: Gas mixtures Xenon-CH4 mixtures could provide very small 2016 JINST 11 C02007 electron di ff usion At low concentrations (<1%) resolution is maintained Xenon-Helium mixtures have a similar e ff ect on Much smaller e ff ect on di ff usion but for a larger He concentrations. light production � 9 JINST 14 (2019) no.08, P08009 arXiv:1906.03984 [physics.ins-det] Nucl.Instrum.Meth. A905 (2018) 82-90.
Current R&D: Cold Xenon We need to reduce the SiPM dark current Operation at lower temperatures! We still want to operate in the gas phase, and we have a large phase space for that! � 10
Current R&D: FAT-GEMs FAT-GEM: Field Assisted Transparent ‘Super-thick’ (5mm) acrylic GEM Gas electroluminescenceMultiplier with semitransparent electrodes Energy resolution still limited by the number of photoelectrons arXiv:1907.03292v1 [physics.ins-det] � 11
The aggressive approach: NEXT-BOLD Detecting “tagging” the Ba++ signaling a ββ 0 ν process has been a long sought holy grail of xenon chambers. � 12
Single Molecule Imaging comes back to physics! Noble price in Chemistry 2014: Development of super- resolved fluorescence microscopy by D. Nygren J.Phys.Conf.Ser. 650 (2015) no.1, 012002 Demonstration of Single-Barium-Ion Sensitivity for Neutrinoless Double-Beta Decay Using Single-Molecule Fluorescence Imaging A. D. McDonald et al. (NEXT Collaboration) Phys. Rev. Lett. 120 , 132504 � 13
From biology to physics Biology Physics Wet medium Dry phase Molecules that Molecules that fluoresce in wet fluoresce in dry Small density of Dense target with only molecules 1 active molecule Small surrounding Large, but measurable background background Large numerical Limited numerical apertures thanks to aperture immersion oil techniques 14
From biology to physics Biology Physics Wet medium Dry phase All that already demonstrated for Ba++ Molecules that Molecules that in the proof of concept! fluoresce in wet fluoresce in dry A. D. McDonald et al. (NEXT Collaboration) Small density of Dense target with only Phys. Rev. Lett. 120 , 132504 molecules 1 active molecule Small surrounding Large background background Large numerical Limited numerical apertures thanks to aperture immersion oil techniques 15
Dry molecules Based on aza-crowns. • Development at DIPC based • Development at UTA based on on bicolor molecules. monocolor molecules: on/o ff • Enhance fluorescence and • Enhanced fluorescence. spectra separation. Single detected Ba 2+ Fluorescence Intensity ion per Pixel (arb) 16
Bi-color molecules FBI molecule developed at DIPC/EHU by the F . Cossio group Density functional theory gas phase structures Frontier molecular orbital energy diagram the torsion of the phenyl group allowing $\pi$-coordination breaks the planarity with the rest of the fluorophore, modifying HOMO and LUMO energy levels https://arxiv.org/abs/1909.02782 17
NEXT steps In order to maximise the e ffi ciency of capturing the Ba 2+ ion we should create a dens monolayer of molecules and be able to scan all of it after a candidate event. We should be able to find 1 molecule in a sensor of ~10x10mm 2 ~10 6 molecules/um 2 Large background from the Optimal packaging and sensor non-chelated molecules. size is still being studied 18
NEXT steps One possibility is to adapt the TIRF technique to the dry phase A di ff erent approach is the use of two photon absorption technique that allows for self-focusing 19
Scanning the whole sample When focusing our laser to minimise background we need to move our focusing spot to scan the whole sample Interesing possibilities like wide-field microscopy or espacio-temporal focusing allow for sampling larger surfaces on every laser pulse. 20
Ba++ open questions and R&D • Ion transport in gas: Decelerated beams. • Ion capture: preparing proof-of-concept experiments to demonstrate/measure ion capture. • Applications to radio purity measurements using SMFI techniques. (Collaboration with LSC) • Ion transport to the sensor: RF carpets, mechanical intercepts. • Target density: Study of targets of di ff erent density, e ffi ciency of ion capture, collective e ff ects,… • Optical laser scanning technique: TIRF , TPA,… � 21
Conclusions • Next generation of double beta experiments target to reach ~10 27 years lifetime. Background rates at 1 evt/tonne·year. • NEXT-HD incremental approach. • R&D in the crucial parts already on-going. • The next step requires background rates at the 0.1 evt/tonne·year level. • NEXT-BOLD with barium tagging may be a back free experiment. • Very active R&D e ff ort with great progress in the last year! � 22
Back-up � 23
Sensitivity � 24
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