Reactor Antineutrino Spectrum Research Articles

Design of the ASIC readout scheme for the JUNO-TAO experiment

The Taishan Antineutrino Observatory (TAO) has been proposed to precisely measure the reactor antineutrino spectrum with an energy resolution better than 2% at 1 MeV. It can provide a reference spectrum to the Jiangmen Underground Neutrino Observatory (JUNO) to enhance its sensitivity to the neutrino mass ordering measurement. In addition, TAO can also provide a benchmark to verify the nuclear database and conduct new physics searches. The TAO detector is a 2.8-ton liquid scintillator detector equipped with a 10 m2 silicon photomultiplier (SiPM) array to collect the light with a coverage of 94%. The TAO detector will be operated at -50 °C to suppress the SiPM dark count rate. In this work, we report on the design of a readout system based on the KLauS6 chip to handle the outputs from the SiPMs, which exhibits advantages of high granularity (potentially good particle identification) and large dynamic range. A dedicated mockup system has been built and its performance carefully evaluated both at room and low temperatures, measuring gain, charge linearity, signal-to-noise ratio, and dead time. The testing results show that the performance of this system can meet the requirements of TAO. However, an abnormal increase in current at 1.8 V analog power of the KLauS6 chip has been observed when operating it at temperatures below -20 °C, resulting in a potential risk on the long-term reliability. Therefore, the KLauS-based readout design is considered as an alternative option for the future upgrading of the TAO's readout system. This study also provides a reference and guidance for other relevant applications.

First measurements with a new β-electron detector for spectral shape studies

The shape of the electron spectrum emitted in β decay carries a wealth of information about nuclear structure and fundamental physics. In spite of that, few dedicated measurements have been made of β-spectrum shapes. In this work we present a newly developed detector for β electrons based on a telescope concept. A thick plastic scintillator is employed in coincidence with a thin silicon detector. The first measurements employing this detector have been carried out with mono-energetic electrons from the high-energy resolution electron-beam spectrometer at Bordeaux. Here we report on the good reproduction of the experimental spectra of mono-energetic electrons using Monte Carlo simulations. This is a crucial step for future experiments, where a detailed Monte Carlo characterization of the detector is needed to determine the shape of the β-electron spectra by deconvolution of the measured spectra with the response function of the detector. A chamber to contain two telescope assemblies has been designed for future β-decay experiments at the Ion Guide Isotope Separator On-Line facility in Jyväskylä, aimed at improving our understanding of reactor antineutrino spectra.

JUNO Experiment: Current Status and Physics

JUNO is a 20 kt liquid scintillator detector located ∼650 m underground in Jiangmen, China. The construction will be finished in 2023. Its energy resolution can reach 3% at 1 MeV, which allows it to realize its main goal of determining the neutrino mass ordering (NMO) detecting antineutrinos from two nuclear power plants at 53 km baseline. Mass ordering is expected to have 3 σ of significance in 6 years of data taking. Meanwhile the measurement of oscillation parameters sin2 θ 12, , and will reach sub-percent precision. The Taishan Antineutrino Observatory will be placed ∼30 m from the core of one power plant, in order to measure the reactor antineutrino spectrum, as a reference spectrum for the determination of NMO in JUNO, with resolution better than 2% at 1 MeV. The OSIRIS pre-detector is designed to monitor the LS of JUNO during the several months of filling. With its massive LS volume and excellent energy resolution, JUNO will be able to explore many other neutrino, astro, and particle physics topics. For example, detection of supernova neutrinos, atmospheric neutrinos, solar neutrinos, and geoneutrinos. This paper reviews the current status of JUNO and introduces recent studies on JUNO’s potential in many different physics topics.

Improved Measurement of the Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay.

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the ^{239}Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from ^{239}Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to ^{235}U fission is changed or the predicted ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu spectra are changed in equal measure.

Towards a sub-percent precision measurement of sin2θ13 with reactor antineutrinos

Measuring the neutrino mixing parameter sin2θ13 to the sub-percent precision level could be necessary in the next ten years for the precision unitary test of the PMNS matrix. In this work, we discuss the possibility of such a measurement with reactor antineutrinos. We find that a single liquid scintillator detector on a reasonable scale could achieve the goal. We propose to install a detector of ∼ 10% energy resolution at about 2.0 km from the reactors with a JUNO-like overburden. The integrated luminosity requirement is about 150 kton · GW · year, corresponding to 4 years’ operation of a 4 kton detector near a reactor complex of 9.2 GW thermal power like Taishan reactor. Unlike the previous θ13 experiments with identical near and far detectors, which can suppress the systematics especially the rate uncertainty by the near-far relative measurement and the optimal baseline is at the first oscillation maximum of about 1.8 km, a single-detector measurement prefers to offset the baseline from the oscillation maximum. At low statistics ≲ 10 kton · GW · year, the rate uncertainty dominates the systematics, and the optimal baseline is about 1.3 km. At higher statistics, the spectral shape uncertainty becomes dominant, and the optimal baseline shifts to about 2.0 km. The optimal baseline keeps being ∼ 2.0 km for an integrated luminosity up to 106 kton · GW · year. Impacts of other factors on the precision sin2θ13 measurement are also discussed. We have assumed that the TAO experiment will improve our understanding of the spectral shape uncertainty, which gives the highest precision measurement of reactor antineutrino spectrum for neutrino energy in the range of 3–6 MeV. We find that the optimal baseline is ∼ 2.9 km with a flat input spectral shape uncertainty provided by the future summation or conversion methods’ prediction. The shape uncertainty would be the bottleneck of the sin2θ13 precision measurement. The sin2θ13 precision is not sensitive to the detector energy resolution and the precision of other oscillation parameters.

Overview of the JUNO-TAO detector

The JUNO-TAO is a liquid scintillator detector that will be placed near one core of the Taishan nuclear power plant of China. It is a satellite detector of the Jiangmen Underground Neutrino Observatory (JUNO) and will provide a precise measurement of the reactor antineutrino spectra with unprecedented accuracy in energy resolution, improving the sensitivity of JUNO on mass hierarchy study. Furthermore, JUNO-TAO will provide benchmark tests on nuclear database.In this proceeding, JUNO-TAO’s design, the status of its R&D program, and its physics potential, will be presented.

Total Absorption Spectroscopy of Fission Fragments Relevant for Reactor Physics and Nuclear Structure and Astrophysics

The accurate determination of reactor antineutrino spectra remains a very hot research topic, where new questions have emerged in recent years. Indeed, after the “reactor anomaly” – a deficit of measured antineutrinos at short baseline reactor experiments with respect to spectral predictions – the three international reactor neutrino experiments Double Chooz, Daya Bay and Reno have evidenced spectral distortions in their measurements with respect to the same spectral predictions. This puzzle is called the “shape anomaly”. Recently summation calculations of reactor antineutrino spectra based on the use of nuclear data have obtained the best agreement to date with the reactor neutrino flux measurements at the level of 2% thanks to a decade of Total Absorption Gamma-ray Spectroscopy (TAGS) measurements at the radioactive beam facility of the University of Jyväskylä in two experimental campaigns. A selection of the results obtained so far is presented.

Improvements in Antineutrino Spectrum by Including Fission Product Corrections and Calculation of Scatter-Based Pulse Height Distributions

Modeling a reactor’s antineutrino flux spectrum is a critical step in studying its detector response. The first objective of this paper is to study the importance of fission product libraries in the construction of the antineutrino spectrum using the summation method and with various other corrections, including excited states in fission products, finite size, weak magnetism, and radiative corrections. We have used the ENDF/B-VIII.0 and JEFF-3.3 nuclear libraries as our base data to model the antineutrino spectrum. We have also included the total absorption gamma spectroscopy (TAGS) data, which is free from the pandemonium effect, when such data are available. Our analysis includes the newest TAGS data sets from Gombas et al. [Phys. Rev. C, Vol. 103, p. 35803 (2021)] with additions made after the Estienne et al. [EPJ Web Conf., Vol. 211, p. 01001 (2019)] reactor antineutrino spectra study involving TAGS data. The excited state correction has the highest impact on the antineutrino energy spectra, increasing the values 29% to 37% on average in the energy range of 0.5 to 2 MeV. This antineutrino spectra correction also shows an increase of 4.71% to 7.13% in the range of 0 to 2 MeV, with improving excited states using the TAGS data from published literature. Next, antineutrino spectra including the excited state correction using the Gross Theory causes reduction by 11.56% to 69.46% for all four fissionable isotopes in the range of 6 to 8 MeV. The finite size correction, radiative correction, and weak magnetism corrections cause no more than a 3.27% difference between the corrected and uncorrected spectra. We studied the impact of various corrections to the antineutrino spectra and quantified the improvements made in the antineutrino spectrum calculation due to these changes. However, we have not included forbidden decays to simplify the calculations. The second objective of this work is to determine the impact of spectrum improvements on the coherent-elastic-neutrino-nucleus-scatter (CEνNS)-based detector response because this detection mechanism is more sensitive to lower energy antineutrinos, as expected from a nuclear reactor. We calculate pulse height distributions of Ge- and Si-based CEνNS sensors assuming a 20-eV nuclear recoil threshold. Toward this objective, we formulate pulse height distribution probabilities for different incident antineutrino energies in Ge and Si for a 100-kg detector placed 10 m away from the 1-MW TRIGA reactor with a 20-eV nuclear recoil energy threshold. Our results show that the reaction rate with corrected spectra for a CEνNS-based natural Ge detector is 20.6 events/day and a natural Si detector is 7.18 events/day. The biggest impact on the reaction rates between 38% and 41% is observed due to the excited state corrections. To benchmark our results, we show excellent agreement with the previous antineutrino spectrum calculated by Huber [Phys. Rev. C, Vo. 84, p. 24617 (2011)] and Hayes et al. [Phys. Rev. Lett., Vol. 112, p. 202501 (2014)].

β decay of Ba141

The $\ensuremath{\beta}$-decay strength function of nuclides produced in fission is important as it dictates the distribution of decay energy between electrons, neutrinos, and $\ensuremath{\gamma}$ rays and so is critical for calculating decay heat in reactors and for estimating the reactor antineutrino spectrum. Several experimental techniques are available to determine this strength function, including electron spectroscopy, $\ensuremath{\gamma}$-ray calorimetry (TAGS spectroscopy), and detailed, high-resolution spectroscopy with modern large high-purity germanium arrays. This work investigates the decay of the well-known and strongly produced fission fragment $^{141}\mathrm{Ba}$. A beam of $^{141}\mathrm{Cs}$ was implanted at the target position of the Gammasphere and the subsequent decay of the daughter $^{141}\mathrm{Ba}$ was studied. Extensive decay spectroscopy was possible up to the decay $Q$ value of 3.197(7) MeV, including a significant extension of the level scheme and detailed angular correlation measurements for all levels with greater than $0.25%\phantom{\rule{4pt}{0ex}}\ensuremath{\beta}$ feeding. The distribution of the $\ensuremath{\beta}$-decay strength was then inferred and compared to previous calorimetric studies. The agreement was excellent and provides a benchmark for comparing strength function methods and data for a more detailed understanding of the structure of $^{141}\mathrm{La}$.

Detector optimization to reduce the cosmogenic neutron backgrounds in the TAO experiment

Short-baseline reactor antineutrino experiments with shallow overburden usually have large cosmogenic neutron backgrounds. The Taishan Antineutrino Observatory (TAO) is a ton-level liquid scintillator detector located at about 30 m from a core of the Taishan Nuclear Power Plant. It will measure the reactor antineutrino spectrum with high precision and high energy resolution to provide a reference spectrum for JUNO and other reactor antineutrino experiments, and provide a benchmark measurement to test nuclear databases. Background is one of the critical concerns of TAO since the overburden is just 10 meter-water-equivalent. The cosmogenic neutron background was estimated to be ∼10% of signals [1]. With detailed Monte Carlo simulations, we propose several measures in this work to reduce the neutron backgrounds, including doping Gadolinium in the buffer liquid, adding a polyethylene layer above the bottom lead shield, and optimization of the veto strategy. With these improvements, the neutron background-to-signal ratio can be reduced to ∼2%, and might be further suppressed with pulse shape discrimination.

Total absorption γ -ray spectroscopy of the β decays of Y96gs,m

The $\beta$ decays of the ground state (gs) and isomeric state (m) of $^{96}$Y have been studied with the total absorption $\gamma$-ray spectroscopy technique at the Ion Guide Isotope Separator On-Line facility. The separation of the 8$^{+}$ isomeric state from the 0$^{-}$ ground state was achieved thanks to the purification capabilities of the JYFLTRAP double Penning trap system. The $\beta$-intensity distributions of both decays have been independently determined. In the analyses the de-excitation of the 1581.6 keV level in $^{96}$Zr, in which conversion electron emission competes with pair production, has been carefully considered and found to have significant impact on the $\beta$-detector efficiency, influencing the $\beta$-intensity distribution obtained. Our results for $^{96\text{gs}}$Y (0$^+$) confirm the large ground state to ground state $\beta$-intensity probability, although a slightly larger value than reported in previous studies was obtained, amounting to $96.6_{-2.1}^{+0.3}\%$ of the total $\beta$ intensity. Given that the decay of $^{96\text{gs}}$Y is the second most important contributor to the reactor antineutrino spectrum between 5 and 7 MeV, the impact of the present results on reactor antineutrino summation calculations has been evaluated. In the decay of $^{96\text{m}}$Y (8$^{+}$), previously undetected $\beta$ intensity in transitions to states above 6 MeV has been observed. This shows the importance of total absorption $\gamma$-ray spectroscopy measurements of $\beta$ decays with highly fragmented de-excitation patterns. $^{96\text{m}}$Y (8$^{+}$) is a major contributor to reactor decay heat in uranium-plutonium and thorium-uranium fuels around 10 s after fission pulses, and the newly measured average $\beta$ and $\gamma$ energies differ significantly from the previous values in evaluated databases (...)

Search for sterile neutrino oscillations using RENO and NEOS data

We present a reactor model independent search for sterile neutrino oscillation using 2\,509\,days of RENO near detector data and 180 days of NEOS data. The reactor related systematic uncertainties are significantly suppressed as both detectors are located at the same reactor complex of Hanbit Nuclear Power Plant. The search is performed by electron antineutrino\,($\overline{\nu}_e$) disappearance between six reactors and two detectors with baselines of 294\,m\,(RENO) and 24\,m\,(NEOS). A spectral comparison of the NEOS prompt-energy spectrum with a no-oscillation prediction from the RENO measurement can explore reactor $\overline{\nu}_e$ oscillations to sterile neutrino. Based on the comparison, we obtain a 95\% C.L. excluded region of $0.1<|\Delta m_{41}^2|<7$\,eV$^2$. We also obtain a 68\% C.L. allowed region with the best fit of $|\Delta m_{41}^2|=2.41\,\pm\,0.03\,$\,eV$^2$ and $\sin^2 2\theta_{14}$=0.08$\,\pm\,$0.03 with a p-value of 8.2\%. Comparisons of obtained reactor antineutrino spectra at reactor sources are made among RENO, NEOS, and Daya Bay to find a possible spectral variation.

PROSPECT-II physics opportunities

The precision reactor oscillation and spectrum experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eV-scale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from 235U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the reactor antineutrino anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the world’s most precise measurement of the 235U antineutrino spectrum and measuring the absolute flux of antineutrinos from 235U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.

Joint Determination of Reactor Antineutrino Spectra from ^{235}U and ^{239}Pu Fission by Daya Bay and PROSPECT.

A joint determination of the reactor antineutrino spectra resulting from the fission of ^{235}U and ^{239}Pu has been carried out by the Daya Bay and PROSPECT Collaborations. This Letter reports the level of consistency of ^{235}U spectrum measurements from the two experiments and presents new results from a joint analysis of both data sets. The measurements are found to be consistent. The combined analysis reduces the degeneracy between the dominant ^{235}U and ^{239}Pu isotopes and improves the uncertainty of the ^{235}U spectral shape to about 3%. The ^{235}U and ^{239}Pu antineutrino energy spectra are unfolded from the jointly deconvolved reactor spectra using the Wiener-SVD unfolding method, providing a data-based reference for other reactor antineutrino experiments and other applications. This is the first measurement of the ^{235}U and ^{239}Pu spectra based on the combination of experiments at low- and highly enriched uranium reactors.

Antineutrino detection for temporal monitoring of fuel burnup in a large nuclear reactor

The objective of this work is to determine if coherent-elastic-neutrino-nucleus scatter (CEνNS) in natural germanium detectors can be used to detect antineutrinos from an AP1000-type fission reactor. In this work, we first modeled the AP1000 core using Monte Carlo N-Particle Transport Code 6.2 (MCNP) to estimate the number of fissions from each fissile isotope in the core. Next, the reactor antineutrino spectrum was computed using the summation method for fuel burnup from 10 to 60 GWd/MTU. It was found that with the increasing fuel burnup, as the 239Pu inventory builds-up in the fuel and the 235U inventory depletes, the contributions from 239Pu to fission is enhanced. Thus, the antineutrino energy spectrum begins to skew more towards lower energies as seen by the quantification of third and fourth central moments. Increased fuel burnup also results in greater antineutrino production. The detection setup assumes a 100-kg CEνNS based natural germanium detector, which is placed outside the reactor containment, 25 m away from the core. The detector has a 100-eV nuclear recoil (NR) threshold and experiences a background level of 100 differential rate units (DRU), per kg.keV.day, due to surrounding radiation interacting in the detector. We then computed the differential pulse height distribution responses for two 235U enrichment cases: 3.3-wt-% and 4.4-wt-% at burnup levels of 10, 20, 40, and 60 GWd/MTU. Overall, the detection rate decreases when the burnup increases. This study indicates that germanium pulse height distribution end-point energies decrease with increasing fuel burnup and become less separable. Thus, we note that the CEνNS detector resolution would need to be higher for more burned fuel. A 16-eV NR is sufficient for distinguishing fresh fuel from that burned to 20 GWd/MTU. We also investigate the ability to detect a difference between burnups: 10 and 20 GWd/MTU, 10 and 40 GWd/MTU, 10 and 60 GWd/MTU, based on the integral detector counts after accounting for background and detection threshold. We determined that fuel burnup deviations can be detected with confidence much greater than 20%, as required by the IAEA, for low likelihood events. For 3.3-wt-% 235U enrichment, the confidence levels to distinguish burnup between 10 and 20 GWd/MTU, 10 and 40 GWd/MTU, 10 and 60 GWd/MTU are 80.60%, 100%, and 100%, respectively. For 4.4-wt% 235U enrichment, but the same three burnup comparisons, the confidence levels decreased marginally to 65.52%, 100%, and 100%, respectively.

Measurement of reactor antineutrino flux and spectrum at RENO

The RENO experiment reports measured flux and energy spectrum of reactor electron antineutrinos\,($\overline{\nu}_e$) from the six reactors at Hanbit Nuclear Power Plant. The measurements use 966\,094\,(116\,111)\,$\overline{\nu}_e$ candidate events with a background fraction of 2.39\%\,(5.13\%), acquired in the near\,(far) detector, from August 2011 to March 2020. The inverse beta decay (IBD) yield is measured as (5.852$\,\pm\,$0.124$) \times 10^{-43}$\,cm$^2$/fission, corresponding to 0.941\,$\pm$ 0.019 of the prediction by the Huber and Mueller (HM) model. A reactor $\overline{\nu}_e$ spectrum is obtained by unfolding a measured IBD prompt spectrum. The obtained neutrino spectrum shows a clear excess around 6\,MeV relative to the HM prediction. The obtained reactor $\overline{\nu}_e$ spectrum will be useful for understanding unknown neutrino properties and reactor models. The observed discrepancies suggest the next round of precision measurements and modification of the current reactor $\overline{\nu}_e$ models.

Structure of high-lying levels populated in the 96Y →96Zr β decay

The nature of the high-lying final levels of the 96Ygsβ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements.

Antineutrino energy spectrum unfolding based on the Daya Bay measurement and its applications * *Supported in part by the Ministry of Science and Technology of China, the U.S. Department of Energy, the Chinese Academy of Sciences, the CAS Center for Excellence in Particle Physics, the National Natural Science Foundation of China, the Guangdong provincial government, the Shenzhen municipal government, the

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era. The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment, in combination with the fission rates of fissile isotopes in the reactor, is used to extract the positron energy spectra resulting from the fission of specific isotopes. This information can be used to produce a precise, data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay. The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method. Consistent results are obtained with other unfolding methods. A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated. Given the reactor fission fractions, the technique can predict the energy spectrum to a 2% precision. In addition, we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.

A liquid scintillator for a neutrino detector working at −50 degree

A liquid scintillator (LS) is developed for the Taishan Antineutrino Observatory (TAO), a ton-level neutrino detector to measure the reactor antineutrino spectrum with sub-percent energy resolution by adopting Silicon Photomultipliers (SiPMs) as photosensors. To reduce the dark noise of SiPMs to an acceptable level, the LS has to work at −50 °C or lower. A customized apparatus based on a charge-coupled device (CCD) is developed to study the liquid samples’ transparency in a cryostat. We find that the water content in LS results in transparency degradation at low temperatures, which can be cured by bubbling dry nitrogen to remove water. Adding 0.43 g/L ethanol as co-solvent cures the solubility decrease problem of the fluors PPO and bis-MSB at low temperature. Finally, a Gadolinium-doped liquid scintillator (GdLS), with 0.1% Gd by weight, 2 g/L PPO, 1 mg/L bis-MSB, and 0.43 g/L ethanol in the solvent LAB, shows good transparency at −50 °C and also good light yield.

Evaluation of the KLauS ASIC at low temperature

The Taishan Antineutrino Observatory (TAO) is proposed to first use a cold liquid scintillator detector (−50 °C) equipped with large-area silicon photomultipliers (SiPMs) (∼10 m2) to precisely measure the reactor antineutrino spectrum with a record energy resolution of ¡ 2% at 1 MeV. The KLauS ASIC shows excellent performance at room temperature and is a potential readout solution for TAO. In this work, we report evaluations of the fifth version of the KLauS ASIC (KLauS5) from room temperature to -50 °C with inputs of injected charge or SiPMs. Our results show that KLauS5 has good performance at the tested temperatures with no significant degradation of the charge noise, charge linearity, gain uniformity or recovery time. Meanwhile, we also observe that several key parameters degrade when the chip operates in cold conditions, including the dynamic range and power consumption. However, even with this degradation, a good signal-to-noise ratio and good resolution of a single photoelectron can still be achieved for the tested SiPM with a gain of greater than 1.5 × 106 and even an area of SiPM up to 1 cm2 in one channel, corresponding to an input capacitance of approximately 5 nF. Thus, we conclude that KLauS5 can fulfill the TAO requirements for precise charge measurement.