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Documentation Index

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The SHiP experiment at CERN is designed to search for hidden particles produced by 400 GeV proton interactions on a dense tungsten target. Particles travel downstream through a sequence of purpose-built detectors, each with a distinct role: suppressing the dominant muon background, identifying neutrino interactions, spotting hidden-particle decays inside an evacuated vessel, and precisely reconstructing the final-state tracks and energy deposits. This page maps the full chain from the proton beam target to the timing detector, giving the C++ geometry class and Python digitiser for every element so you can quickly locate the relevant source when debugging a simulation or adding a new detector feature.

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Detector chain

The coordinate origin (z = 0) sits at the upstream face of the proton target. All positions downstream increase in z. 
z = 0                  z ≈ 0.5 m               z ≈ 10 – 50 m
|--- Target/Absorber ---|--- Muon Shield ---|--- SND ---|
                                                        |
                        z ≈ 58 m             z ≈ 84 m  |
--- Decay Vessel (helium) ---|--- Upstream Tagger ------|
                                                        |
z ≈ 86 m     z ≈ 90 m     z ≈ 92 m    z ≈ 93 m        |
|--- T1 ---|--- T2 ---|Magnet|--- T3 ---|--- T4 --------|
                                                        |
z ≈ 97 m          z ≈ 99 – 102 m       z ≈ 103 m       |
|--- SplitCal ---|--- Muon/SBT Veto ---|--- TimeDet ----|

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Sub-detector reference table

#Sub-detectorC++ classPython digitiserSource directory
1Proton target / hadron absorberShipTargetStation—passive/
2Muon shieldShipMuonShield—passive/
3SND (NuTau target)Target + TargetTracker—SND/EmulsionTarget/
3SND (MTC)MTCDetectorMTCDetectorSND/MTC/
3SND (SiliconTarget)SiliconTarget—SND/SiliconTarget/
4Decay vessel / SBT vetovetoSBTDetectorveto/
5Upstream TaggerUpstreamTaggerUpstreamTaggerDetectorUpstreamTagger/
6Straw Tube SpectrometerstrawtubesstrawtubesDetectorstrawtubes/
7Split-Cal (ECAL)splitcalsplitcalDetectorsplitcal/
8Timing detector (TimeDet)TimeDettimeDetectorTimeDet/

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Component descriptions

1
Proton target and hadron absorber
2
The upstream anchor of the experiment. ShipTargetStation (passive/ShipTargetStation.h) builds a multi-slice tungsten target whose material, thickness, and gaps are read from geometry/target_config.yaml. The hadron absorber downstream suppresses secondary hadrons so that only muons (and long-lived hidden particles) emerge. The geometry is configured in geometry_config.py under c.target and c.hadronAbsorber.
3
# excerpt from geometry_config.py
c.target.z0 = 0          # coordinate origin, upstream face of target
c.target.z  = c.target.z0 + c.target.length / 2.0
4
Muon shield
5
A large, magnetised iron shield that bends the intense muon flux away from the detector acceptance. ShipMuonShield (passive/ShipMuonShield.h) consumes a flat parameter list—15 numbers per magnet section—encoding the longitudinal offset, half-length, inner and outer transverse dimensions, gap sizes, and field goal. The named geometry TRY_2025 in shield_db is the current baseline. See the Muon Shield page for full parameter documentation.
6
SND — Scattering and Neutrino Detector
7
Placed immediately upstream of the decay vessel, the SND searches for neutrino interactions and hidden-particle scattering signatures. Design 1 (configure_snd_old) builds an emulsion-brick wall (Target) interleaved with SciFi tracking planes (TargetTracker). Design 2 (configure_snd_mtc) builds the Muon Tracker for Charm (MTCDetector) and optional silicon strip tracking (SiliconTarget). See the SND page for details.
8
Decay vessel and Surrounding Background Tagger
9
A 50 m helium-filled (or evacuated) cylindrical vessel where hidden particles produced at the target decay to visible final states. The veto class (veto/veto.h) implements the vessel walls and the liquid-scintillator Surrounding Background Tagger (SBT). The medium (helium or vacuum) is set by DecayVolumeMedium and drives which YAML configuration is loaded:
10
configure_veto(
    f"$FAIRSHIP/geometry/veto_config_{ship_geo.DecayVolumeMedium}.yaml",
    ship_geo.decayVolume.z0,
)
11
The Python digitiser for the SBT is SBTDetector in python/detectors/SBTDetector.py.
12
Upstream Tagger (UBT)
13
A thin vacuum-box scoring plane (UpstreamTagger, UpstreamTagger/UpstreamTagger.h) placed ~25 m upstream of the decay-vessel centre. It tags charged particles entering the vessel, providing a key handle for rejecting muon-induced backgrounds. Position smearing is ±1 cm; time resolution is 0.3 ns. Digitisation is performed by UpstreamTaggerDetector in python/detectors/UpstreamTaggerDetector.py.
14
Straw Tube Spectrometer (T1–T4)
15
Four straw-tube tracking stations straddle a dipole spectrometer magnet. The strawtubes class (strawtubes/strawtubes.h) inherits from SHiP::Detector<strawtubesPoint> and places 2 cm diameter aluminium or steel-framed drift tubes in four views (two axial, two ±4.57° stereo). The strawtubesDetector Python class converts strawtubesPoint MC hits to strawtubesHits. See the Spectrometer page for parameter details.
16
Split-Cal (electromagnetic calorimeter)
17
An electromagnetic sampling calorimeter (splitcal, splitcal/splitcal.h) with 50 ECAL samplings of 2.8 mm lead filter + 5.6 mm scintillator active layers, covering a 4 m × 6 m aperture. Precision layers at fixed depths provide pointing information. Configuration is entirely driven by the c.SplitCal AttrDict in geometry_config.py.
18
Muon system / veto (SBT extension)
19
Iron-scintillator muon stations (MuonStation0–3) behind the calorimeter identify muons and provide the last line of background suppression. Stations are spaced 1 m apart starting from c.MuonStation0.z; iron filter slabs of 30 cm thickness sit between stations.
20
Timing detector (TimeDet)
21
A thin scintillator-bar detector (TimeDet, TimeDet/TimeDet.h) just upstream of the spectrometer magnet. Two orthogonal bar layers (1.2 cm and 2.4 cm z-spacing) each cover a 4.5 m × 6.5 m aperture. The timeDetector Python digitiser converts TimeDetPoint MC hits to TimeDetHit objects, selecting the earliest valid hit per cell. Timing is used to associate reconstructed tracks with interaction vertices.

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Key pages

Muon Shield

Magnetised shield geometry, named configurations in shield_db, parameter format, and field-map classes.

Straw Tube Spectrometer

Four-station drift-tube tracker: geometry options, digitisation, ACTS digi config, and field map.

SND Detector

Scattering and Neutrino Detector: emulsion target, SciFi tracker, silicon strips, and MTC sub-systems.

Running a Simulation

How to run run_simScript.py and choose geometry options for the full detector chain.

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Configuration entry point

All detector objects are instantiated in python/shipDet_conf.py::configure(). This function reads the geometry AttrDict produced by geometry_config.py::create_config(), constructs each ROOT detector object, and registers it with the FairRunSim instance via run.AddModule(). 
# Minimal usage pattern (python/shipDet_conf.py)
from geometry_config import create_config
import shipDet_conf

ship_geo = create_config(shieldName="TRY_2025", strawDesign=10, SND=True)
det_elements = shipDet_conf.configure(run, ship_geo)
# det_elements is a dict: {"TargetStation": ..., "MuonShield": ..., ...}
The detectorList module-level list in shipDet_conf.py accumulates detector objects in the order they must be registered with FairRoot. Do not reorder entries — FairRoot processes them sequentially during geometry construction.

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