Prospects of neutrinoless double beta decay search with PandaX-4T and beyond

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Prospects of neutrinoless double beta decay search with PandaX-4T and beyond

HAN, Ke (

^{韩柯}

)

Shanghai Jiao Tong University

On Behalf of the PandaX Collaboration Aug 31, 2021

17th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2021)

PandaX Double Beta Decay Program HAN, Ke (Shanghai Jiao Tong University) 1

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PandaX: Particle and Astrophysical Xenon TPC

PandaX-I: 120kg LXe

(2009 – 2014) PandaX-II: 500kg LXe

(2014 – 2018) PandaX-4T LXe

(2019-)

WIMP searches (0νββ as well)

PRL 117, 121303 (2016)

…

… PandaX-III: HPXe for 0νββ (future)

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CJPL: Deepest underground lab

2430m

8750m

• Deepest (6800 m.w.e): < 0.2 muons/m

²

/day

• Horizontal access with ~9 km long tunnel

• National key science research facility for dark matter searches, neutrino physics, and

astroparticle physics, etc.

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PandaX-4T

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PandaX-4T major milestones

• Apr. 2, 2018, permission from CJPL management to start construction in B2 hall

• Aug. 19, 2019, infrastructure completed, detector installation in CJPL-II started

• Mar 6, 2020, offline distillation of xenon completed

• May 28, 2020, installation completed

• Nov. 28, 2020 – Apr. 16, 2021, commissioning run

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Commissioning onsite

Ultra-pure water system

Electronics and DAQ TPC and PMT Distillation Tower

Cooling Bus Lowering TPC to

Inner Vessel

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Data taking during TPC commissioning

7

Set 1 2 3 4 5

Gate(kV) -4.9 -5 -5

Cathode (kV) -20 -18.6 -18 -16

During the run, HV set at a few different values to avoid excessive discharges.

• Electron lifetime: in situ S2 vertical uniformity calibration

• Maximum drift time ~ 840 µs (field dependent)

• Stable data running period: 95.0 calendar days (86 days after selection)

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PandaX-4T for 0νββ

• ~350 kg of ¹³⁶Xe; 400 kg of ¹³⁴Xe; 4 kg of ¹²⁴Xe for rich double-beta-decay related physics

• Excellent single-site and multi-site event discrimination with precise 3D reconstruction

• Large monolithic target with effective self-shielding; fiducialization to optimize search sensitivity

• High signal efficiency (~90%) and good energy resolution at Q-Value

0 500 1000 1500 2000 2500

ER Energy [keV]

−3

10

−2

10

−1

10 1 10 102

ER Rate [mDRU]

Total Materials ⁸⁵Kr ²²²Rn ¹³⁶Xe DBD Neutrino ¹³⁶Xe NLDBD (Assumed 3E25 y half-life for visual guide)

For PandaX-4T:

• Energy resolution improved w.r.t. PandaX-II

• Material background still dominate

• 0νββ sensitivity approaches EXO-200 at 10²⁵ yr level

• 0νββ search is a key component for multi-physics approach at LXe TPC

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Mitigating electronics and PMT saturation with offline analysis

• PandaX-4T installed newly designed PMT readout bases; dual-readout for top/bottom center 7 PMTs

• S1 signals may be out of the dynamic range of digitizers and clipped; a few channels per event at MeV

• S2 signals may saturate the PMT and/or base and the pulses are distorted

• De-saturation: align rising edge of waveform and a template constructed from non-saturated PMTs

• For 2.6 MeV event, the average correction factor for top (bottom) PMT array is >2 (~1.04)

1344 1346 1348 1350 1352 1354

Time [us]

0 20 40 60 80 100

Area-normalized Pulse

Scale Saturated pulses

Template (<500 B), 193 PMT, 32943.4 PE Scaled Pulse for PMT 10614

Scale Alignment Range

Scale Factor: 0.411 +/- 0.008 Scaling Chi2: 118.1

Original PE: 2150.8 Scaled PE: 7227.6

Scale Saturated pulses

Clipped S1 signal

Saturated S2 signal (blue) vs. template (red)

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−600 −400 −200 0 200 400 600

−600

−400

−200 0 200 400 600

Y [mm]

0 50 100 150 200 250 300 350 400

Position reconstruction at HE is greatly improved

• XY position reconstruction suffered from saturated PMTs on the top

• Many events are reconstructed wrongly in between PMTs

• Position reconstruction greatly improved after desaturation

• Events are still incorrectly clustered more around center 7 PMTs with dual-readout bases

−600 −400 −200 0 200 400 600

X[mm]

−600

−400

−200 0 200 400 600

Y[mm]

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Before After

Calibration run with an external thorium source

PRELIMINARY

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Energy resolution in calibration runs

• Original PMT waveforms at high energy have a long tail due to the constant threshold

• Forcing the window to 16 μs for single-site events imrpoves energy resolution

• With new position reconstruction, XY mapping correction improved and so is energy resolution

• For ²³²Th calibration run, energy resolution at 2.6 MeV is 1.5% (σ/E)

1600 1800 2000 2200 2400 2600 2800 3000

Energy[keV]

0 0.01 0.02 0.03 0.04 Counts 0.05

Original: 4.8%

16us window: 2.1%

+ Single-Site: 1.8%

+ New Position Recon: 1.5%

Energy Spectrum of GT 1MeV Events

PRELIMINARY

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0 500 1000 1500 2000 2500 3000 3500 Energy [keV]

−4

10

−3

10

−2

10

−1

10 1 10 102

Rate [mDRU]

Energy spectrum at HE

• Very preliminary HE spectrum reconstructed from S1 signal only without single-site cut

• Select the most central volume of ~0.5 ton of xenon

• 2νββ spectrum (half-life 2.165E21 yr) becomes prominent

PRELIMINARY

Green: data Blue: 2νββ spectrum

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Ongoing effort to further improve HE analysis at PandaX

• Fine tune charge calculation algorithm: effects of waveform width and impact of de- saturation

• Improve single-site and multi-site event discrimination

• Detailed background budget analysis at high energy with MC and calibration data inputs

• Exploit the advantage of natural xenon TPC:

• Double beta decay of

¹³⁴

Xe

• Double EC related physics of

¹²⁴

Xe

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Beyond PandaX-4T

• Active R&D on new generation of liquid xenon TPC at CJPL

• Exploring options for better ββ physics:

• New PMT for low radioactivity, better position recon, fast timing, no saturation

• New vessel materials/designs for background control

• Enrichment with cryogenic distillation

R11410 R12699

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Summary

• PandaX-4T started commissioning run last November

• Detector performance in MeV energy range has been improved significantly compared to PandaX-II

• Active R&D on-going for next generation multi-physics LXe TPC at CJPL with the aim to establish PandaX as a competative 0νββ experiment

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PandaX Collaboration

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0νββ search at PandaX-II

arXiv:1906.11457; Chinese Physics C 43, 113001 (2019)

• 580 kg natural xenon; ~50 kg of ¹³⁶Xe.

• 403.1 day of dark matter physics data

• Null results; Lower limit for decay half-life:

2.4×10²³ yr at 90% CL

• Effective Majorana mass upper limit: 1.3-3.5 eV.

• First 0νββ result reported from a dual-phase xenon experiment

• Proof of Principle Saturated pulses