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Design and performance of a large-area scintillator-based chamber for the MID subsystem of ALICE 3

Ruben Alfaro Molina, Juan Carlos Cabanillas Noris, Edmundo García Solis, Laura Helena González Trueba, Varlen Grabski, Gerardo Herrera Corral, Jesús Eduardo Muñoz Méndez, Ildefonso León Monzón, Antonio Ortiz, Antonio Paz, Ian Pérez García, Ricardo Rodríguez Pineda, Solangel Rojas Torres, Guillermo Tejeda Muñoz, Paola Vargas Torres, Victor Vázquez Campos, Yael Antonio Vásquez Beltran

Abstract

This paper reports on the design and construction of a chamber for the muon identifier detector (MID) of the ALICE 3 upgrade project. The chamber consists of two sensitive layers separated by a 1 cm air gap. Each layer holds 24 scintillator bars ($1\times4\times100$ cm$^3$) manufactured by FNAL-NICADD. The bars are equipped with Kuraray wavelength shifting fibers and the readout is provided by a silicon photomultiplier from Hamamatsu. The bars in the second layer are orthogonal to the bars in the first layer, thus providing an overlapping cell size of 4$\times$4 cm$^{2}$. The bar assembly as well as the design of the mechanical structure is described. The design of the chamber is close to that considered in the ALICE 3 letter of intent. The chamber was tested at the CERN T10 beamline using 3 GeV/$c$ pion-enriched and muon beams. The chamber was placed behind an iron absorber, with different absorber lengths considered in the test. The muon identification is performed using a Machine Learning algorithm, which was trained and tested using muon (signal) and pion (background) data (50% of the available statistics). The trained ML algorithm was applied to muon data, yielding a muon efficiency above 99% for the OR condition (detection in either layer 1 or 2). The implementation in the pion-beam data gives the fake-muon efficiency as a function of the absorber length that is well described by an exponential function with a slope parameter of 18.79 cm. The next steps towards finalizing the optimization are outlined.

Design and performance of a large-area scintillator-based chamber for the MID subsystem of ALICE 3

Abstract

This paper reports on the design and construction of a chamber for the muon identifier detector (MID) of the ALICE 3 upgrade project. The chamber consists of two sensitive layers separated by a 1 cm air gap. Each layer holds 24 scintillator bars ( cm) manufactured by FNAL-NICADD. The bars are equipped with Kuraray wavelength shifting fibers and the readout is provided by a silicon photomultiplier from Hamamatsu. The bars in the second layer are orthogonal to the bars in the first layer, thus providing an overlapping cell size of 44 cm. The bar assembly as well as the design of the mechanical structure is described. The design of the chamber is close to that considered in the ALICE 3 letter of intent. The chamber was tested at the CERN T10 beamline using 3 GeV/ pion-enriched and muon beams. The chamber was placed behind an iron absorber, with different absorber lengths considered in the test. The muon identification is performed using a Machine Learning algorithm, which was trained and tested using muon (signal) and pion (background) data (50% of the available statistics). The trained ML algorithm was applied to muon data, yielding a muon efficiency above 99% for the OR condition (detection in either layer 1 or 2). The implementation in the pion-beam data gives the fake-muon efficiency as a function of the absorber length that is well described by an exponential function with a slope parameter of 18.79 cm. The next steps towards finalizing the optimization are outlined.

Paper Structure

This paper contains 8 sections, 11 figures.

Table of Contents

  1. Introduction
  2. Prototype construction
  3. Paddle assembly
  4. Mechanical structure
  5. Experimental setup
  6. Data analysis
  7. Results
  8. Summary and outlook

Figures (11)

  • Figure 1: The polished surfaces for the 2.0 mm (left) and 1.5 mm (right) WLS fibers already attached to the scintillator.
  • Figure 2: (Left) Assembly steps for the bars from left to right: from a bar without a fiber to the bar already wrapped with the SiPM holder. (Right) 48 assembled bars with their snap-fit holders for SiPMs, ready to be introduced to the mechanical structure.
  • Figure 3: Mechanical structure for the $1\times1$m$^2$ prototype, where N2 and N4 are the scintillator layers separated by N3 by 1 cm.
  • Figure 4: Complete design for the mechanical structure, showing how each bar is arranged in its place, with the SiPM protection holders.
  • Figure 5: Simulation of the mechanical stress for the top and bottom aluminum cover (left), and for the intermediate aluminum plate (right).
  • ...and 6 more figures