Studies of Hadronic Showers in SND@LHC

TL;DR

This work addresses calibrating the hadronic shower energy reconstruction for SND@LHC by measuring how energy is deposited in the target and HCAL using a detector replica exposed to 100–300 GeV hadrons. It introduces a shower tagging approach based on in-time SciFi hit density to locate the shower origin along the target and combines calibrated SciFi and HCAL signals to estimate the total shower energy. The study provides quantitative results: ordinary showers achieve energy resolutions around 22% at 100 GeV improving to about 12% at 300 GeV, with a validated Monte Carlo that reproduces data after tuning. These findings support accurate neutrino energy reconstruction in SND@LHC and guide Run3 extrapolations, while highlighting limitations for late showers and the need for region-specific corrections.

Abstract

The SND@LHC experiment was built for observing neutrinos arising from LHC pp collisions. The detector consists of two sections: a target instrumented with SciFi modules and a hadronic calorimeter/muon detector. Energetic $ν$N collisions in the target produce hadronic showers. Reconstruction of the shower total energy requires an estimate of the fractions deposited in both the target and the calorimeter. In order to calibrate the SND@LHC response, a replica of the detector was exposed to hadron beams with 100 to 300 GeV in the CERN SPS H8 test beam line in Summer 2023. This report describes the methods developed to tag the presence of a shower, to locate the shower origin in the target, and to combine the target SciFi and the calorimeter signals so to measure the shower total energy.

Figures (29)

• Figure 1: Detector setup in the SPS H8 test beam line with the beam coming from the right. From right to left: (i) small-size Beam Counter scintillators, (ii) three target walls interleaved with four SciFi X-Y detectors, and (iii) the hadronic calorimeter (HCAL), consisting of planes of scintillating bars interspaced with (grey) iron walls.
• Figure 2: PCB hosting the SiPMs that read-out the bars on one side of a US station.
• Figure 3: Hit frequency as function of the signal thresholds (T1) in both TOFPETs (0 and 1) of both PCBs (Left and Right) in US0, the most upstream HCAL station in the test beam. On the Left side of US0 a silicon gel pad was used to make contact between scintillating bars and the SiPMs. Each plot maps 30 "large" SiPMs and 10 "small" SiPMs. A few slightly noisier channels show up in the bottom left plot. The T1 threshold is set at 30 DAC counts.
• Figure 4: Sketch of the detector on the beam line. From left to right: the Target (three 10 cm thick iron walls interleaved with four SciFi X and Y planes) and the hadronic calorimeter (HCAL) (five US planes of scintillating bars interspaced with 20 cm thick iron walls, and a DS plane of thin scintillating bars). The pion interaction length in iron is $20.4\ \rm cm$.
• Figure 5: Beam profiles recorded in the most upstream SciFi 1 X and Y planes for positive hadron beams.