SIREN

SIREN (Sampling and Injection for Rare EveNts) is a framework for injecting and weighting interaction final states of complex topology, with specific concern for the detector geometry. SIREN is designed to support a wide variety of neutrino experimental setups, including atmospheric neutrinos, accelerator beam decay-in-flight neutrinos, and neutrinos from decay-at-rest sources. SIREN grew out of LeptonInjector, a neutrino injection code developed within the IceCube collaboration to study atmospheric and astrophysical neutrino interactions in the IceCube detector.

SIREN provides a generic interface for user-defined BSM processes (and includes several pre-defined processes). It also supports generation of any number of secondary processes, e.g. the decay of a BSM particle after it has been created by an initial process.

Quick start

pip install siren

See Installation for other options, including building from source or as a C++ library.

The following example injects 1e4 muon-neutrino DIS events in IceCube and computes their physical weights:

import siren

# Load detector geometry and interaction cross sections
detector_model = siren.utilities.load_detector("IceCube")
primary_type = siren.dataclasses.Particle.ParticleType.NuMu
primary_processes, _ = siren.utilities.load_processes(
    "CSMSDISSplines",
    primary_types=[primary_type],
    target_types=[siren.dataclasses.Particle.ParticleType.Nucleon],
    isoscalar=True,
    process_types=["CC"],
)

# Configure the injector: energy spectrum, direction, and position
injector = siren.injection.Injector()
injector.number_of_events = int(1e4)
injector.detector_model = detector_model
injector.primary_type = primary_type
injector.primary_interactions = primary_processes[primary_type]
injector.primary_injection_distributions = [
    siren.distributions.PrimaryMass(0),
    siren.distributions.PowerLaw(2, 1e3, 1e6),
    siren.distributions.IsotropicDirection(),
    siren.distributions.ColumnDepthPositionDistribution(
        600, 600.0, siren.distributions.LeptonDepthFunction()
    ),
]

# Generate events
from siren._util import GenerateEvents, SaveEvents
events, gen_times = GenerateEvents(injector)

# Weight events using physical distributions
weighter = siren.injection.Weighter()
weighter.injectors = [injector]
weighter.detector_model = detector_model
weighter.primary_type = primary_type
weighter.primary_interactions = primary_processes[primary_type]
weighter.primary_physical_distributions = [
    siren.distributions.PowerLaw(2, 1e3, 1e6),
    siren.distributions.IsotropicDirection(),
]

weights = [weighter(event) for event in events]

# Save results to HDF5 and Parquet
SaveEvents(events, weighter, gen_times, output_filename="my_output")

More examples — including BSM dipole-portal injection and MARLEY low-energy interactions — are in resources/examples/.

How it works

A SIREN workflow has two phases: injection and weighting.

During injection, SIREN samples interaction vertices inside a detector geometry according to user-specified distributions (energy spectrum, direction, position). Each call to injector.generate_event() produces an interaction tree — a primary interaction and any secondary processes (e.g. the decay of a BSM particle produced in the primary interaction).

During weighting, SIREN computes a physical weight for each injected event. The Weighter takes the injection configuration and a set of physical distributions (the true flux and cross sections) and returns a weight that corrects for the difference between the injection and physical distributions. This importance-sampling approach allows a single injection run to be reweighted against different physical models without regenerating events.

Supported detectors

SIREN includes detector geometry definitions for the following experiments:

Experiment	Model name
ATLAS	ATLAS
CCM	CCM
DUNE Far Detector	DUNEFD
Hyper-Kamiokande	HyperK
IceCube	IceCube
KM3NeT/ORCA	KM3NeTORCA
MINERvA	MINERvA
MiniBooNE	MiniBooNE
ND280	ND280
ND280 Upgrade	ND280UPGRD
SINE	SINE
UNDINE	UNDINE

Each detector is defined by a materials file and a density profile. To load one:

detector_model = siren.utilities.load_detector("IceCube")

Contributions of new detector geometries are welcome.

Supported process models

Model	Description
CSMSDISSplines	Deep inelastic scattering (CC and NC) on nucleons, using photospline cross-section tables
MarleyCrossSection	Low-energy neutrino interactions via MARLEY
DarkNewsTables	BSM processes (dark photons, dipole portal, HNLs) via DarkNews — see example2
HNLDISSplines	Heavy neutral lepton (HNL) production via neutrino neutral current deep inelastic scattering on nucleons, using photospline cross-section tables
DipoleHNLDISSplines	Heavy neutral lepton (HNL) production via neutrino dipole-portal (i.e., via a transition magnetic moment) deep inelastic scattering on nucleons, using photospline cross-section tables

Supported flux models

Model	Description
BNB	Booster Neutrino Beam (FHC and RHC modes)
NUMI	NuMI beamline (low-energy and medium-energy)
T2K_NEAR	T2K near detector flux
HE_SN	Supernova neutrino flux
Atmospheric	A suite of atmospheric neutrino flux models

To load a flux model:

flux = siren.utilities.load_flux("BNB", tag="FHC_numu")

Installation

Python (pip)

pip install siren

Requires Python >= 3.8. Dependencies (numpy, scipy, awkward, pyarrow, h5py) are installed automatically.

For optional BSM support via DarkNews:

pip install siren DarkNews>=0.4.2

Python (from source)

git clone https://github.com/Harvard-Neutrino/SIREN.git
cd SIREN
pip install . --config-settings='build-dir=build'

C++ library

SIREN can also be built and installed as a standalone C++ shared library using CMake. This is useful when integrating SIREN into a larger C++ project.

Prerequisites

• A C++ compiler with C++17 support
• CMake >= 3.20
• CFITSIO
• SuiteSparse

CFITSIO and SuiteSparse are required by photospline for reading cross-section spline tables.

Workspace layout

We recommend keeping source, build, and install directories separate. A typical workspace looks like:

workspace/
├── env.sh              # environment setup script
├── local/              # install prefix
│   ├── bin/
│   ├── include/
│   └── lib/
└── sources/
    ├── SIREN/
    │   └── build/      # out-of-source build directory
    └── (other projects that depend on SIREN)

Environment setup

Create an env.sh script that configures your compiler and paths. This script should be sourced before building or running anything in the workspace.

#!/bin/bash

export WORKSPACE=/path/to/workspace
export PREFIX=$WORKSPACE/local

export CC=gcc
export CXX=g++

export PATH=$PREFIX/bin:$PATH
export LD_LIBRARY_PATH=$PREFIX/lib:$LD_LIBRARY_PATH
export C_INCLUDE_PATH=$PREFIX/include:$C_INCLUDE_PATH
export CPLUS_INCLUDE_PATH=$PREFIX/include:$CPLUS_INCLUDE_PATH
export PKG_CONFIG_PATH=$PREFIX/lib/pkgconfig:$PKG_CONFIG_PATH
PY_SITE_DIR="$(python3 -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])')"
export PYTHONPATH="$PY_SITE_DIR${PYTHONPATH:+:$PYTHONPATH}"

On macOS, use DYLD_FALLBACK_LIBRARY_PATH instead of LD_LIBRARY_PATH.

Build and install

source env.sh

git clone https://github.com/Harvard-Neutrino/SIREN.git $WORKSPACE/sources/SIREN
cd $WORKSPACE/sources/SIREN
git submodule update --init

mkdir -p build && cd build
cmake .. -DCMAKE_INSTALL_PREFIX=$PREFIX
cmake --build . --parallel && cmake --install .

After the initial build, only the last line (cmake --build . --parallel && cmake --install .) needs to be rerun when source files change. Rerun the first cmake step if CMakeLists.txt files change or new source files are added.

CMake options

Option	Default	Description
CMAKE_INSTALL_PREFIX	—	Install destination for libraries, headers, and binaries
SIREN_PYTHON_PACKAGE	ON	Build and install the Python package
SIREN_WITH_MARLEY	ON	Enable MARLEY support (used if found)
SIREN_REQUIRE_MARLEY	OFF	Fail the build if MARLEY is not found

Dataset download

SIREN uses external datasets that need to be downloaded separately, including neutrino flux models and cross-section tables. To do this, after installing SIREN , run the following commands:

siren-download --processes
siren-download --flux

These commands will download the necessary datasets to the resources/processes and resources/fluxes directories in the SIREN installation.

Project structure

SIREN/
├── projects/              # C++ source modules
│   ├── utilities/         # Interpolation, random numbers, string utilities
│   ├── serialization/     # Serialization support
│   ├── math/              # Vector3D, Matrix3D, Quaternion, interpolation
│   ├── dataclasses/       # Particle, InteractionRecord, InteractionTree
│   ├── geometry/          # Geometric primitives and operations
│   ├── detector/          # Detector geometry and density profiles
│   ├── interactions/      # Cross section and decay implementations
│   ├── distributions/     # Probability distributions for sampling
│   └── injection/         # Injector and Weighter
├── python/                # Python API (Injector, Weighter, utilities)
├── vendor/                # Vendored dependencies (git submodules)
│   ├── cereal             # Serialization
│   ├── delabella          # Delaunay triangulation
│   ├── googletest         # Unit testing
│   ├── pybind11           # Python bindings
│   ├── rk                 # Relativistic kinematics
│   ├── photospline        # B-spline cross-section tables
│   └── NamedType          # Type-safe wrappers
├── resources/
│   ├── detectors/         # Detector geometry definitions
│   ├── fluxes/            # Neutrino flux models
│   ├── processes/         # Cross-section and decay data
│   └── examples/          # Example scripts and notebooks
└── cmake/Packages/        # CMake find-modules for dependencies

Contributing

Create a branch off of main named $GitHubUsername/$YourSubProject. When your changes are stable, pull from main and open a pull request.

Citing SIREN

If you use SIREN in your research, please cite the repository:

https://github.com/Harvard-Neutrino/SIREN

License

SIREN is licensed under the GNU Lesser General Public License v3.0.