The simulation on neutron background reduction for InDEx at JUSL

Maitreyee Nandy; Mala Das; Susmita Das

arxiv: 2605.14602 · v1 · pith:WNNZTC4Gnew · submitted 2026-05-14 · ✦ hep-ex · astro-ph.IM

The simulation on neutron background reduction for InDEx at JUSL

Susmita Das , Maitreyee Nandy , Mala Das This is my paper

Pith reviewed 2026-06-30 19:57 UTC · model grok-4.3

classification ✦ hep-ex astro-ph.IM

keywords neutron backgrounddark matter detectionInDEx experimentFLUKA simulationHDPE shieldingbackground reductionJUSL underground lab

0 comments

The pith

Shielding with high density polyethylene reduces InDEx detector event rates by two orders of magnitude.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses FLUKA simulations to test a shielding design for the Indian Dark matter search Experiment at the Jaduguda Underground Science Laboratory. It first reproduces published calibration and neutron data to check the model, then applies the same setup to the InDEx geometry with added high density polyethylene layers. The central result is that this shielding lowers the simulated detector event rate by a factor of 100 relative to the earlier unshielded run. Dark matter searches need backgrounds near zero over long live times, so a cost-effective way to predict and reduce neutron events before hardware changes is valuable. If the modeled reduction holds, the experiment can run longer or reach lower cross-section limits without new detector technology.

Core claim

The simulation shows that a shielding configuration using high density polyethylene reduces the detector event rates by two orders of magnitude compared to the prior InDEx experiment without shielding.

What carries the argument

FLUKA Monte Carlo modeling of neutron transport, interactions, and detector response in the InDEx geometry with an added high density polyethylene shield.

If this is right

The HDPE shielding design can be installed to achieve the modeled background reduction in future InDEx runs.
Detector live time can increase without raising the neutron-induced event rate.
Calibration data already match experiment, supporting use of the same model for shielded predictions.
Similar shielding layouts become candidates for other underground rare-event detectors at comparable depths.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same simulation workflow could be reused to optimize shield thickness or material choice for other sites with different rock compositions.
If the reduction is confirmed, InDEx could extend its exposure to probe weaker dark matter interactions than previously accessible.
Neutron background models validated this way might transfer to other direct-detection experiments facing similar cosmic-ray-induced neutrons.

Load-bearing premise

The FLUKA model, once validated on literature data, correctly predicts the actual neutron flux, scattering, and detector signals inside the shielded InDEx setup at JUSL.

What would settle it

A direct measurement of the event rate in the real shielded InDEx detector that fails to show a reduction of roughly 100 times would falsify the simulated background reduction.

read the original abstract

Dark matter experiments are rare event search experiments that require zero background environment over very long exposures. To achieve this condition, a detailed simulation of detector geometry and experimental setup is required before the experiment is executed. Simulation plays a significant role in detector design and also provides a cost-effective and risk-free approach for predicting outcomes before real world experimentation. The present simulation work is focused on neutron background reduction for a dark matter direct detection experiment in India, the Indian Dark matter search Experiment (InDEx). The FLUKA and FLAIR simulation tools have been used throughout the simulation process. The experimental and simulation results available in the literature are being reproduced using FLUKA for validation purposes. The calibration and InDEx experiment are simulated, and the results are compared against the experimental results. For neutron background reduction in future experiments, the use of high density polyethylene (HDPE) is suggested and a shielding design using HDPE is presented. The results show that shielding reduces detector event rates by two orders of magnitude compared to the prior InDEx experiment without shielding.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

Standard FLUKA application to HDPE shielding for InDEx reports a two-order neutron reduction, but lacks quantitative validation metrics or site-specific flux data so the number is hard to rely on.

read the letter

The one thing to know about this paper is that it uses FLUKA to model a high-density polyethylene shield around the InDEx detector at JUSL and reports that this reduces neutron-induced event rates by roughly two orders of magnitude.

The authors do a few things right. They reproduce selected results from the literature to check their FLUKA setup, and they run simulations of the calibration and the actual InDEx experiment to compare against existing data. This kind of benchmarking is the right way to approach a simulation study. They also lay out a concrete shielding design, which could save the collaboration time when they move to the next phase.

The soft spots are in the validation and the input assumptions. The abstract states that simulated results were compared with experimental data, but it does not report any agreement metrics, residuals, or uncertainty estimates. Without those, it is difficult to judge how well the model captures the real neutron flux and detector response. In addition, there is no mention of a direct measurement of the neutron spectrum at the JUSL site itself. The entire reduction factor rests on the difference between two FLUKA runs, so if the unshielded simulation over- or under-predicts the background, the improvement number becomes less meaningful. The stress-test note correctly flags this gap.

This paper is aimed at the InDEx collaboration and others running or planning similar low-background experiments in underground labs. Someone already working on neutron shielding calculations might pick up the specific geometry choices or material thicknesses they chose.

I would bring it to a reading group if the group discusses Monte Carlo tools in dark matter searches. I would not cite the paper in my own work. It deserves to go through peer review because the full manuscript probably contains the detailed geometry files, spectra, and comparison plots that would let a referee assess whether the validation is adequate.

Referee Report

2 major / 1 minor

Summary. The manuscript presents FLUKA simulations of neutron background in the InDEx dark matter detector at JUSL. It validates the code by reproducing selected literature results, simulates the detector calibration and unshielded InDEx run for comparison to existing experimental data, and proposes an HDPE shielding configuration whose simulated effect is a two-order-of-magnitude reduction in detector event rate relative to the prior unshielded configuration.

Significance. If the FLUKA model is shown to be accurate for the JUSL neutron spectrum and InDEx geometry, the work supplies a concrete, simulation-driven shielding design that could be directly implemented for background control in an underground rare-event search. The explicit reproduction of literature benchmarks is a methodological strength.

major comments (2)

[Abstract / Results] Abstract and Results: The headline claim that shielding 'reduces detector event rates by two orders of magnitude' is obtained solely from the difference between two FLUKA runs. No numerical values for the simulated rates (with/without shield), no uncertainty on the reduction factor, and no description of the input neutron spectrum or detector efficiency model at JUSL are supplied, rendering the quantitative claim unverifiable from the text.
[Validation / Results] Validation section: The manuscript states that 'the calibration and InDEx experiment are simulated, and the results are compared against the experimental results,' yet provides no quantitative agreement metrics (percentage difference, χ^{2}, pull distributions, or error bars). Without these, the reproduction of literature data cannot be used to establish that the same code accurately predicts the shielded versus unshielded difference at JUSL.

minor comments (1)

The manuscript would benefit from a dedicated table or figure listing the simulated event rates, shielding geometry parameters, and any assumed neutron flux normalization.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. We address each major comment below and have revised the manuscript to incorporate the requested quantitative details and metrics.

read point-by-point responses

Referee: [Abstract / Results] Abstract and Results: The headline claim that shielding 'reduces detector event rates by two orders of magnitude' is obtained solely from the difference between two FLUKA runs. No numerical values for the simulated rates (with/without shield), no uncertainty on the reduction factor, and no description of the input neutron spectrum or detector efficiency model at JUSL are supplied, rendering the quantitative claim unverifiable from the text.

Authors: We agree that explicit numerical values, uncertainties, and input details are needed for verifiability. In the revised manuscript we have added tables listing the simulated event rates (shielded and unshielded), Monte Carlo statistical uncertainties on the rates and on the reduction factor, a description of the JUSL neutron spectrum used as input, and the detector efficiency model applied. The two-order-of-magnitude reduction is now stated with its uncertainty. revision: yes
Referee: [Validation / Results] Validation section: The manuscript states that 'the calibration and InDEx experiment are simulated, and the results are compared against the experimental results,' yet provides no quantitative agreement metrics (percentage difference, χ^{2}, pull distributions, or error bars). Without these, the reproduction of literature data cannot be used to establish that the same code accurately predicts the shielded versus unshielded difference at JUSL.

Authors: We acknowledge the absence of explicit quantitative metrics in the original text. The revised manuscript now includes percentage differences, χ² values, and discussion of error bars for the calibration and InDEx comparisons. These additions clarify the level of agreement and support the applicability of the validated model to the shielding predictions. revision: yes

Circularity Check

0 steps flagged

No circularity: simulation output is independent of fitted inputs or self-referential definitions

full rationale

The paper performs FLUKA Monte Carlo simulations of neutron transport in the InDEx detector geometry, first reproducing selected literature benchmarks for code validation and then comparing two runs (with and without the proposed HDPE shield) to obtain the reported two-order-of-magnitude event-rate reduction. No parameters are fitted to the target InDEx data, no equations define a quantity in terms of itself, and no load-bearing self-citations or uniqueness theorems are invoked to force the result. The derivation chain consists of standard Monte Carlo propagation from an externally chosen neutron spectrum through tabulated cross-sections to scored detector events; the output is therefore not equivalent to the inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract supplies no explicit free parameters, axioms, or invented entities; the simulation relies on the built-in physics models of FLUKA whose accuracy is asserted via external validation.

pith-pipeline@v0.9.1-grok · 5716 in / 1075 out tokens · 29092 ms · 2026-06-30T19:57:30.132723+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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Radiation Physics and Chemistry61(3), 271–281 (2001) https://doi.org/10.1016/S0969-806X(01) 00250-X

Roy, S.C.: Superheated liquid and its place in radiation physics. Radiation Physics and Chemistry61(3), 271–281 (2001) https://doi.org/10.1016/S0969-806X(01) 00250-X . 8th International Symposium on Radiation Physics - ISRP8 11

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https://arxiv.org/abs/2401.07384

Fustin, D.: First Dark Matter Limits from the COUPP 4kg Bubble Chamber at a Deep Underground Site (2024). https://arxiv.org/abs/2401.07384

work page arXiv 2024

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Astropart

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work page doi:10.1103/vpb7-kdrz 2025

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Mei, D.-M.,et al.: Muon-induced background study for underground laboratories. Phys. Rev. D73, 053004 (2006) https://doi.org/10.1103/PhysRevD.73.053004

work page doi:10.1103/physrevd.73.053004 2006

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work page doi:10.1016/j.nima 2021

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Sahoo, S.,et al.: The threshold of gamma-ray induced bubble nucleation in super- heated emulsion. Nucl. Instrum. Methods Phys. Res. Sect. A931, 44–51 (2019) https://doi.org/10.1016/j.nima.2019.04.010

work page doi:10.1016/j.nima.2019.04.010 2019

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Sahoo, S.,et al.: The background study at 555 m deep underground with super- heated emulsion detector. Nucl. Instrum. Methods Phys. Res. Sect. A1008, 165450 (2021) https://doi.org/10.1016/j.nima.2021.165450

work page doi:10.1016/j.nima.2021.165450 2021

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Kumar, V.,et al.: Response of tetrafluoroethane (C 2H2F4) superheated emulsion detector for dark matter search at JUSL. Nucl. Instrum. Methods Phys. Res. Sect. A1083, 171101 (2026) https://doi.org/10.1016/j.nima.2025.171101

work page doi:10.1016/j.nima.2025.171101 2026

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Seth, S.,et al.: Probing low-mass WIMP candidates of dark matter with tetraflu- oroethane superheated liquid detectors. Phys. Rev. D101, 103005 (2020) https: 12 //doi.org/10.1103/PhysRevD.101.103005

work page doi:10.1103/physrevd.101.103005 2020

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Astropart

Ghosh, S.,et al.: Measurements of gamma ray, cosmic muon and residual neutron background fluxes for rare event search experiments at an under- ground laboratory. Astropart. Phys.139, 102700 (2022) https://doi.org/10.1016/ j.astropartphys.2022.102700

work page arXiv 2022

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EPJ Nuclear Sci

Ballarini, F.,et al.: The FLUKA code: Overview and new developments. EPJ Nuclear Sci. Technol.10, 16 (2024) https://doi.org/10.1051/epjn/2024015

work page doi:10.1051/epjn/2024015 2024

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Nuclear Data Sheets120, 211–214 (2014) https://doi.org/10.1016/j.nds.2014.07.049

B¨ ohlen, T.T.,et al.: The FLUKA Code: Developments and Challenges for High Energy and Medical Applications. Nuclear Data Sheets120, 211–214 (2014) https://doi.org/10.1016/j.nds.2014.07.049

work page doi:10.1016/j.nds.2014.07.049 2014

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EPJ Web Conf

Donadon, A.,et al.: FLAIR3 – recasting simulation experiences with the Advanced Interface for FLUKA and other Monte Carlo codes. EPJ Web Conf. 302, 11005 (2024) https://doi.org/10.1051/epjconf/202430211005

work page doi:10.1051/epjconf/202430211005 2024

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Almisned, G.,et al.: Neutron transmission analysis in borated polyethylene, boron carbide, and polyethylene: Insights from MCNP6 simulations. Radiat. Phys. Chem.218, 111585 (2024) https://doi.org/10.1016/j.radphyschem.2024.111585

work page doi:10.1016/j.radphyschem.2024.111585 2024

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Barbagallo, D.,et al.: Neutron Attenuation in Polyethylene Using an AmBe Source. J. Undergrad. Rep. Phys.30(1), 100001 (2020) https://doi.org/10.1063/ 10.0002041

2020

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Pramana75, 675–682 (2010) https://doi.org/10.1007/ s12043-010-0147-z 13

Das, M.,et al.: Nucleation efficiency of R134a as a sensitive liquid for Superheated drop emulsion detector. Pramana75, 675–682 (2010) https://doi.org/10.1007/ s12043-010-0147-z 13

2010