# Optimization of a BEGe Detector Setup for Testing Quantum Foundations in the Underground LNGS Laboratory

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## Abstract

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## 1. Scientific Motivation

#### 1.1. Spin-Statistics Violation and Quantum Gravity Models

_{α}and K

_{β}PEP-violating transitions in an ultra-radio-pure Roman lead target surrounding a High-Purity Germanium detector (HPGe).

_{α}and K

_{β}PEP-violating transitions in the Ge crystal itself, thus exploiting a gain of about four orders of magnitude in the detection efficiency. Considered that the standard K

_{α}transitions in Ge are located around 9.9 keV and the corresponding PEP-violating transitions are shifted downwards in energy by about 0.3 keV, a lower energy threshold of about 6 keV is needed. Moreover, performing a scan of the (limits of the) spin-statistics violation probability over the periodic table is an important task in general [7], not only for testing predictions in the quantum gravity framework (where the probability explicitly depends on the energy of the atomic transition under test) but also for testing other types of PEP violations. A discussion of other PEP violation models and related experimental tests is given in ref. [8]. Important recent research in these directions has been performed (see, e.g., [9,10,11]), and new research is under development [12].

#### 1.2. Spontaneous Radiation from Wave Function Collapse Search in the Few-keV Regime

- The general spontaneous emission rate differs from the approximated one in the range (1–100) keV;
- In the same energy range, the spontaneous radiation energy spectra also depend on the atomic structure of the emitter;
- The CSL and the DP rates significantly differ (relative difference of more than 10%) in the range (1–10) keV.

## 2. The Experimental Setup

^{2}). A section of the detector is schematically represented in Figure 4, top left. The acquisition and elaboration of the signals generated by the BEGe detector are performed by means of a CAEN Flash-ADC (FADC), model DT 5743, with the following main features: resolution of 12 bits, maximum sampling rate of 3.2 GS/s, analog input impedance of 50 Ω, and a 2.55 Vpp dynamic range.

#### 2.1. Pulse Shape Discrimination Analysis

- first, a comparison of the fluctuations mean values at pulse beginning and end is performed (i.e., the mean value of the first and the last 100 points of the pulse). Moreover, the maximum pulse height is compared with the mean value at the end of the pulse.
- The second step consists of ${\chi}^{2}$ discrimination, with respect to linear behavior, at the end of the pulse.
- As a third step, pulse derivative selection is performed, which rejects multi-site events based on both the width and discrimination (using the error function template).

^{238}U and

^{232}Th and are

^{210}Pb at 46 keV,

^{212}Pb at 239 keV,

^{214}Pb at 295 keV, and 352 keV,

^{214}Bi at 609 keV. The calibration line is shown in Figure 2 left. The energy resolution was determined to be 2.2 keV (FWHM) at the

^{210}Pb peak.

_{α}transition in Ge requires a lower energy threshold of at least 6 keV (corresponding to about 3 mV), the Data Acquisition (DAQ) system was improved as described in Section 2.2.

#### 2.2. Upgrade of the the Data Acquisition System

- A careful analysis of the sources of electrical noise highlighted that the connection via USB cable between the computer and Fast ADC is the main origin. To address this problem, we decided to replace the USB cable connection with a fiber optic connection. Moreover, in order to further reduce the noise coming from the power supplies, the power supplies provided with the instrumentation (Fast ADC and preamplifier) were replaced with special power supplies with very low residual noise. And finally, careful distribution of the electrical grounding was also studied.
- A second step was the installation of a very-low-noise broadband amplifier (CAEN A1423B) with a voltage gain of 10 at the input of the Fast ADC to further improve the overall behavior of the DAQ system.

#### 2.3. Analysis of the Microphonic Background

## 3. Conclusions and Perspectives

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Top panel: a typical multi-site event that would survive selection cut 2 but not selection cut 3. Bottom panel: a signal event that has been selected by the algorithm. Figures on the right correspond to the derivatives of the corresponding curves on the left. The full acquisition time window is 2560 ns, one acquisition corresponds to 1024 samples, and the sampling rate is 400 MHz, so one sample corresponds to 2.5 ns.

**Figure 3.**An event corresponding to the data-taking period of July–September 2021 is shown, in which the intrinsic noise of the digitizer at 4 mV is evident.

**Figure 5.**An event acquired during the 2022 data-taking period is shown: the peak-to-peak electronic noise corresponds to about 0.5 mV.

**Figure 6.**

**Left**: a microphonic noise event is shown.

**Right**: a signal event is represented with the microphonic background superimposed.

**Figure 7.**The results of a long-term measurement of the environmental noise in the laboratory is shown. The plot reports multiple measurements performed with one accelerometer and taken at consecutive times.

**Figure 8.**The attenuation curve of the optimized isolation system is shown in dB and is a function of the ratio between the mechanical excitation frequency and the resonance frequency of the system which is 1.5 Hz. The curve is theoretical and is taken from an application note present in the Angst + Pfister pneumatic suspension catalog.

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**MDPI and ACS Style**

Piscicchia, K.; Clozza, A.; Sirghi, D.L.; Bazzi, M.; Bortolotti, N.; Bragadireanu, M.; Cargnelli, M.; De Paolis, L.; Del Grande, R.; Guaraldo, C.;
et al. Optimization of a BEGe Detector Setup for Testing Quantum Foundations in the Underground LNGS Laboratory. *Condens. Matter* **2024**, *9*, 22.
https://doi.org/10.3390/condmat9020022

**AMA Style**

Piscicchia K, Clozza A, Sirghi DL, Bazzi M, Bortolotti N, Bragadireanu M, Cargnelli M, De Paolis L, Del Grande R, Guaraldo C,
et al. Optimization of a BEGe Detector Setup for Testing Quantum Foundations in the Underground LNGS Laboratory. *Condensed Matter*. 2024; 9(2):22.
https://doi.org/10.3390/condmat9020022

**Chicago/Turabian Style**

Piscicchia, Kristian, Alberto Clozza, Diana Laura Sirghi, Massimiliano Bazzi, Nicola Bortolotti, Mario Bragadireanu, Michael Cargnelli, Luca De Paolis, Raffaele Del Grande, Carlo Guaraldo,
and et al. 2024. "Optimization of a BEGe Detector Setup for Testing Quantum Foundations in the Underground LNGS Laboratory" *Condensed Matter* 9, no. 2: 22.
https://doi.org/10.3390/condmat9020022