Prakash Gautam | publications

2020

Measurement of the Spectral Shape of the β-decay of ^137Xe to the Ground State of ^137Cs in EXO-200 and Comparison with Theory

Kharusi, S. Al, Gautam, P., Yen, Y.-R., Zeldovich, O. Ya, Ziegler, T., and nEXO-Collaboration,

arXiv:2002.00108 [nucl-ex, physics:nucl-th] 2020

Abs arXiv

We report on a comparison between the theoretically predicted and experimentally measured spectra of the first-forbidden non-unique β-decay transition ^137\textrmXe(7/2^-)\to\,^137\textrmCs(7/2^+). The experimental data were acquired by the EXO-200 experiment during a deployment of an AmBe neutron source. The ultra-low background environment of EXO-200, together with dedicated source deployment and analysis procedures, allowed for collection of a pure sample of the decays, with an estimated signal-to-background ratio of more than 99-to-1 in the energy range from 1075 to 4175 keV. In addition to providing a rare and accurate measurement of the first-forbidden non-unique β-decay shape, this work constitutes a novel test of the calculated electron spectral shapes in the context of the reactor antineutrino anomaly and spectral bump.

2019

Characterization of the Hamamatsu VUV4 MPPCs for nEXO

Collaboration, , Dolinski, M. J., and Gautam, P.et. al

arXiv:1903.03663 [astro-ph, physics:physics] 2019

Abs arXiv

In this paper we report on the characterization of the Hamamatsu VUV4 Vacuum Ultra-Violet (VUV) sensitive Silicon Photo-Multipliers (SiPMs) as part of the development of a solution for the detection of liquid xenon scintillation light for the nEXO experiment. Various SiPM features, such as: dark noise, gain, correlated avalanches, direct crosstalk and Photon Detection Efficiency (PDE) were measured in a dedicated setup at TRIUMF. SiPMs were characterized in the range $163 \text \textK ≤\textT≤233 \text \textK. We report a PDE of 13.4\pm2.6% for 189\pm 7 nm light at a SiPM over voltage of 3.6\pm0.2\text V and at \textT=233 \text \textK. Within systematic uncertainties, this value meets nEXO requirements. At an over voltage of 3.1\pm0.2 V and at \textT=163 \text \textK the number of Correlated Avalanches (CAs) per pulse in the 1 \upmu\texts interval following the trigger pulse is 0.161\pm0.005. At the same settings the Dark-Noise (DN) rate is 0.137\pm0.002 \text Hz/mm^2$. Both the number of CAs and the DN rate are within nEXO specifications.
Search for Neutrinoless Double-Beta Decay with the Complete EXO-200 Dataset

Anton, G., Dolinski, M. J., Gautam, P., Ziegler, T., and al,

arXiv:1906.02723 [hep-ex, physics:nucl-ex] 2019

Abs arXiv

A search for neutrinoless double-beta decay (0νββ) in ^136Xe is performed with the full EXO-200 dataset using a deep neural network to discriminate between 0νββand background events. Relative to previous analyses, the signal detection efficiency has been raised from 80.8% to 96.4\pm3.0% and the energy resolution of the detector at the Q-value of ^136Xe 0νββhas been improved from σ/E=1.23% to 1.15\pm0.02% with the upgraded detector. Accounting for the new data, the median 90% confidence level 0νββhalf-life sensitivity for this analysis is 5.0 ⋅10^25 yr with a total ^136Xe exposure of 234.1 kg\cdotyr. No statistically significant evidence for 0νββis observed, leading to a lower limit on the 0νββhalf-life of 3.5⋅10^25 yr at the 90% confidence level.
Measurement of the scintillation and ionization response of liquid xenon at MeV energies in the EXO-200 experiment

Collaboration, EXO-200, Anton, G., Badhrees, I., Barbeau, D., Gautam, P., Gornea, R., Gratta, G., Hall, C., Hansen, L., Yen, Y.-R., Zeldovich, O. Ya, and Ziegle, T.

arXiv:1908.04128 [hep-ex, physics:physics] 2019

Abs arXiv

Liquid xenon (LXe) is employed in a number of current and future detectors for rare event searches. We use the EXO-200 experimental data to measure the absolute scintillation and ionization yields generated by γinteractions from ^228Th (2615 keV), ^226Ra (1764 keV) and ^60Co (1332 keV and 1173 keV) calibration sources, over a range of electric fields. The measured W-value, defined as the energy required to produce either an electron-ion pair or a photon in the LXe is 11.5 \pm 0.5 (syst.) \pm 0.1 (stat.) eV. These data are also used to measure the recombination fluctuations in the number of electrons and photons produced by the calibration sources at the MeV-scale, which deviate from extrapolations of lower-energy data. Additionally, a semi-empirical model for the energy resolution of the detector is developed, which is used to constrain the recombination efficiency, i.e., the fraction of recombined electrons that result in the emission of a detectable photon. Detailed measurements of the absolute charge and light yields for MeV-scale electron recoils are important for predicting the performance of future neutrinoless double beta decay detectors.
Calibration of nEXO Light Response

Gautam, Prakash, and nEXO Collaboration,

2019

Abs

nEXO is a proposed 5 tonne liquid xenon experiment which seeks to detect neutrinoless double beta decay(0 νββ) in Xe-136 using Time Projection Chamber(TPC) technology. The experiment will use the combination of scintillation and ionization signals to reconstruct events with an energy resolution of 1% σ / E at the 0 νββ Q-value. The scintillation light will be collected by silicon photomultipliers (SiPMs) around the sides of the detector, and their collection efficiency will vary as a function of event position. In this talk, we present the strategy for calibrating light response in the nEXO detector. We will deploy a suite of calibration sources, including external γ-ray sources and internal sources dissolved in the liquid xenon. Using nEXO Monte Carlo data, we have demonstrated the use of machine learning techniques to effectively map the light response of the detector while minimizing calibration time.
Measurements of Electron Transport in Liquid and Gas Xenon Using a Laser-Driven Photocathode

Njoya, O., Tsang, T., Tarka, M., Fairbank, W., Gautam, P., and al,

arXiv:1911.11580 [nucl-ex, physics:physics] 2019

Abs arXiv

Measurements of electron drift properties in liquid and gaseous xenon are reported. The electrons are generated by the photoelectric effect in a semi-transparent gold photocathode driven in transmission mode with a pulsed ultraviolet laser. The charges drift and diffuse in a small chamber at various electric fields and a fixed drift distance of 2.0 cm. At an electric field of 0.5 kV/cm, the measured drift velocities and corresponding temperature coefficients respectively are \1.97 \pm 0.04 mm/\μ\s and \(-0.69\pm0.05)\\%/K for liquid xenon, and \1.42 \pm 0.03 mm/\μ\s and \(+0.11\pm0.01)\\%/K for gaseous xenon at 1.5 bar. In addition, we measure longitudinal diffusion coefficients of \25.7 \pm 4.6 cm\\^2\/s and \149 \pm 23 cm\\^2\/s, for liquid and gas, respectively. The quantum efficiency of the gold photocathode is studied at the photon energy of 4.73 eV in liquid and gaseous xenon, and vacuum. These charge transport properties and the behavior of photocathodes in a xenon environment are important in designing and calibrating future large scale noble liquid detectors.
Measurements of Electron Transport in Liquid and Gas Xenon Using a Laser-Driven Photocathode

Njoya, O., Tsang, T., Dolinski, P., and et., al

arXiv:1911.11580 [nucl-ex, physics:physics] 2019

Abs arXiv

Measurements of electron drift properties in liquid and gaseous xenon are reported. The electrons are generated by the photoelectric effect in a semi-transparent gold photocathode driven in transmission mode with a pulsed ultraviolet laser. The charges drift and diffuse in a small chamber at various electric fields and a fixed drift distance of 2.0 cm. At an electric field of 0.5 kV/cm, the measured drift velocities and corresponding temperature coefficients respectively are \1.97 \pm 0.04 mm/\μ\s and \(-0.69\pm0.05)\\%/K for liquid xenon, and \1.42 \pm 0.03 mm/\μ\s and \(+0.11\pm0.01)\\%/K for gaseous xenon at 1.5 bar. In addition, we measure longitudinal diffusion coefficients of \25.7 \pm 4.6 cm\\^2\/s and \149 \pm 23 cm\\^2\/s, for liquid and gas, respectively. The quantum efficiency of the gold photocathode is studied at the photon energy of 4.73 eV in liquid and gaseous xenon, and vacuum. These charge transport properties and the behavior of photocathodes in a xenon environment are important in designing and calibrating future large scale noble liquid detectors.
Simulation of charge readout with segmented tiles in nEXO

Li, Z., Cen, W. R., Robinson, M. J., Gautam, P., Zhao, J., Zhou, Y., and Ziegler, T.

Journal of Instrumentation 2019

Abs arXiv

nEXO is a proposed experiment to search for the neutrino-less double beta decay (0νββ) of ^136Xe in a tonne-scale liquid xenon time projection chamber (TPC). The nEXO TPC will be equipped with charge collection tiles to form the anode. In this work, the charge reconstruction performance of this anode design is studied with a dedicated simulation package. A multi-variate method and a deep neural network are developed to distinguish simulated 0νββsignals from backgrounds arising from trace levels of natural radioactivity in the detector materials. These simulations indicate that the nEXO TPC with charge-collection tiles shows promising capability to discriminate the 0νββsignal from backgrounds. The estimated half-life sensitivity for 0νββdecay is improved by \sim20 (32)% with the multi-variate (deep neural network) methods considered here, relative to the sensitivity estimated in the nEXO pre-conceptual design report.