High-pressure xenon gas TPC for neutrino-less double-beta decay in 136Xe: Progress toward the

goal of 1% FWHM energy resolution

Azriel Goldschmidt1, Tom Miller1, David Nygren1, Joshua Renner1,2, Derek Shuman1, Helmuth Spieler1, James White3

1Lawrence Berkeley National Laboratory2University of California, Berkeley

3Texas A&M University

IEEE Nuclear Science SymposiumOctober 26, 2011

for the NEXT Collaboration

Neutrinoless Double-Beta Decay (0νββ)

136 Xe 136 Ba2e-

Would establish Majorana nature of neutrinos

Would violate conservation of lepton number

Detection requires good energy resolution and background elimination

LBNL prototype to establish proof of concept for the 0νββ experiment NEXT; uses electroluminescent readout

An electroluminescent TPC is divided into several key regions

Electroluminescence

Drift EL

Buffer Regions

Incident particle deposits energy, producing ionization (S2) and scintillation (S1)

Electroluminescence

Ed

Electrons drift in an electric field to a narrow region of high field

E EL

Electroluminescence

Ed

The xenon medium scintillates as the electrons traverse the EL gap; electrons gain enough energy to excite but not ionize xenon atoms

E EL

Electroluminescence

Ed

The amount of light (S2) detected determines the energy of the incident particle

E EL

Electroluminescence

A High-Pressure Xenon TPC

19-PMT Array

3mm EL Gap8cm Drift

Region

10L Stainless Steel Vessel

*Drawing by Robin LaFever

A High-Pressure Xenon TPC

EL Grid

PMT Array Full Chamber and Gas System

- PMTs are read out by 3 Struck SIS3302 ADCs

Waveforms

S1 S2

Waveforms

S1 S2

P ~16 bar, calibrated to 662 keV Cs peak

137Cs Energy Spectrum

Drift time determined as delay between S1 start time and averaged S2 time

Corrected by applying an exponential factor exp(t/τ)

Attachment Losses (O2, H

2O)

τ = 5.8 ms

PMT signals weighted according to location to determine x-y position

Axis calibrated according to size of hexagonal pattern of events (inset)

Select by cutting on radius

Spatial Response

Energy Resolution

Approx. 10 photons per ionized electron

E/P = 2.96 kV/cm-bar

Small central region radial cut

τ = 7.72 ms drift correction

0.7 kV/cm drift field

Energy Resolution

Expected resolution[1]: Fano factor + photon statistics Approximately:

E = 662 keV, η = 1431, σ2

PMT = 2, n

pe = 10,

w = 21.9 eV, F = 0.14 (from [2])

EE

%FWHM =235 FGwE

G=1/1PMT2 /npe

EE

%FWHM ≈0.9 %

[1] D. Nygren. Nucl. Instr. Meth. A, vol 603, 337 (2009).[2] A. Bolotnikov and B. Ramsey. Nucl. Instr. Meth. A, vol 396, 360 (1997).

Compare with 1.04% fit

Search for neutrinoless double-beta decay

100 kg of xenon, enriched to 90% 136Xe

To operate with EL + Si photomultiplier tracking(see poster by M. Ball in session NP5.S)

To be stationed at Canfranc Underground Laboratory (LSC), Spain

NEXT: Neutrino Experiment with a Xenon TPC

This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

J. Renner acknowledges the support of a DOE NNSA SSGF Fellowship, grant number DE-FC52-08NA28752.

Acknowledgements