https://doi.org/10.1140/epjc/s10052-026-15318-7
Regular Article - Experimental Physics
Modeling the light response of an optically readout GEM based TPC for the CYGNO experiment
1
LIBPhys, Department of Physics, University of Coimbra, 3004-516, Coimbra, Portugal
2
Istituto Nazionale di Fisica Nucleare, Sezione di Roma TRE, 00146, Roma, Italy
3
Dipartimento di Matematica e Fisica, Università Roma TRE, 00146, Roma, Italy
4
Gran Sasso Science Institute, 67100, L’Aquila, Italy
5
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso, 67100, Assergi, Italy
6
Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati, 00044, Frascati, Italy
7
Istituto Nazionale di Fisica Nucleare, Sezione di Roma, 00185, Rome, Italy
8
Dipartimento di Fisica, Sapienza Università di Roma, 00185, Roma, Italy
9
ENEA Centro Ricerche Frascati, 00044, Frascati, Italy
10
Universidade Estadual de Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil
11
Department of Physics and Astronomy, University of Sheffield, S3 7RH, Sheffield, UK
12
Universidade Federal de Juiz de Fora, Faculdade de Engenharia, 36036-900, Juiz de Fora, MG, Brasil
13
Dipartimento di Ingegneria Chimica, Materiali e Ambiente, Sapienza Università di Roma, 00185, Roma, Italy
a
This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
13
May
2025
Accepted:
14
January
2026
Published online:
7
February
2026
Abstract
The use of gaseous Time Projection Chambers enables the detection and the detailed study of rare events due to particles interactions with the atoms of the gas with energy releases as low as a few keV. Due to this capability, these instruments are being developed for applications in the field of astroparticle physics, such as the study of dark matter and neutrinos. To acquire events occurring in the sensitive volume with a high granularity, the Cygno collaboration is developing a solution where the light generated during the avalanche processes occurring in a multiplication stage based on Gas Electron Multiplier (GEM) is read out by optical sensors with very high sensitivity and spatial resolution. To achieve a high light output, gas gain values of the order of 
are needed. In this working condition, a dependence of the detector response on the spatial density of the charge collected in the GEM holes has been observed, indicating a gain-reduction effect likely caused by space-charge buildup within the multiplication channels. This paper presents data collected with a prototype featuring a sensitive volume of about two liters, together with a model developed by the collaboration to describe and predict the gain dependence on charge density. A comparison with experimental data shows that the model reproduces, with a percent-level precision, the gain behaviour over nearly one order of magnitude.
© The Author(s) 2026
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
Funded by SCOAP3.
