Novel technique for the study of pileup events in cryogenic bolometers

A. Armatol et al. (CUPID Collaboration)

Phys. Rev. C 104, 015501 – Published 2 July 2021

Abstract

Precise characterization of detector time resolution is of crucial importance for next-generation cryogenic-bolometer experiments searching for neutrinoless double-beta decay, such as CUPID, in order to reject background due to pileup of two-neutrino double-beta decay events. In this paper, we describe a technique developed to study the pileup rejection capability of cryogenic bolometers. Our approach, which consists of producing controlled pileup events with a programmable wave-form generator, has the benefit that we can reliably and reproducibly control the time separation and relative energy of the individual components of the generated pileup events. The resulting data allow us to optimize and benchmark analysis strategies to discriminate between individual and pileup pulses. We describe a test of this technique performed with a small array of detectors at the Laboratori Nazionali del Gran Sasso, in Italy; we obtain a $90 %$ rejection efficiency against pulser-generated pileup events with rise time of $\sim 15 ms$ down to time separation between the individual events of about $2 ms$ .

Received 25 November 2020
Accepted 28 April 2021

DOI:https://doi.org/10.1103/PhysRevC.104.015501

Physics Subject Headings (PhySH)

Double beta decay Nuclear tests of fundamental interactions Particle decays

Calorimeters Radiation detectors

Particles & FieldsNuclear Physics

Authors & Affiliations

Click to Expand

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 104, Iss. 1 — July 2021

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Overlay of the rising edge and initial part of the decay for heater pulses excited by rectangular (blue, short-dashed), exponential (green, long-dashed), and sawtooth (red, dot-dashed) wave forms and a particle pulse (black). Particle pulses have a similar shape, despite the different origin and entity of the energy deposition; quantitatively, the width of the distribution of rise and decay time is close to $3 %$ .
Reuse & Permissions
Figure 2
Examples of heater-induced pileup pulses excited by two sawtooth wave forms with amplitude ratio $α あるふぁ = 1.4$ close in time. It can be seen that the time separations between the two pulses (the begin of the rise is taken as a reference) reflects that of the original wave forms ( $Δ でるた t$ ). A time-isolated reference pulse is shown for comparison.
Reuse & Permissions
Figure 3
Time distribution of the events in one of the pileup runs. Each interval corresponds to a different $α あるふぁ / Δ でるた t$ configuration. In this sequence, $α あるふぁ$ is fixed to 0.24 while $Δ でるた t$ goes from 1 to $11 ms$ (from left to right). The gray dots represent the events selected as heater pulses, the red dots the discarded ones. To avoid an excessive statistics loss, we accepted events affected by a rather high noise level and by instability of the baseline, that would be otherwise discarded in a physics run. It is thus possible that some events in the various intervals deviate from the average behavior, despite the identical settings of the input wave forms.
Reuse & Permissions
Figure 4
Comparison between the discrimination power ( $D$ ) obtained with the ${TVL}^{2} + {TVR}^{2}$ and delay variables for the configuration $α あるふぁ = 0.24$ of Channel 03. The value $D = 3$ for both variables is indicated with a dashed line. The configuration with $Δ でるた t = 5 ms$ has been tested in two different runs; the different values of discrimination power are likely due to the different detector noise (see the discussion in the text).
Reuse & Permissions
Figure 5
Pileup rejection efficiency ( $ɛ_{rej}$ ) as a function of $Δ でるた t$ for the configuration $α あるふぁ = 0.24$ of Channel 03. The solid line is the best-fit error function described in the text. The dashed horizontal line marks $ɛ_{rej} = 90 %$ .
Reuse & Permissions
Figure 6
$Δ でるた t$ thresholds corresponding to $ɛ_{rej} = 90 %$ for each configuration of $α あるふぁ$ obtained for the three channels. The two outliers at $α あるふぁ = 1.12$ for Channel 04 and $α あるふぁ = 1.41$ for Channel 03 are likely due to suboptimal detector conditions while collecting data for $Δ でるた t = 1 ms$ .
Reuse & Permissions

Physical Review C

covering nuclear physics