Neutrinos · D11 · Catch the first message

Supernova Neutrino Burst Observatory

Catch a simulated burst in a spherical scintillation detector. Freeze its event times, scan a trigger window, and follow one interaction from a light flash to the collection sphere.

Recorded interactions $\text{—}$

Peak window count $\text{—}$

Scan tail upper bound $\text{—}$

Teaching simulation, not SN 1987A data or a replica of JUNO, SNO+ or SNEWS. Prescribed Poisson time profiles and illustrative yield; distance and exposure scale counts. Ideal isotropic point flashes, fixed refractive index and full spherical collection. No energy, flavor, direction or distance inference. The trigger uses timestamps only. Scan probabilities are conservative bounds for a known stationary background, not calibrated discovery significance or operational alerts. Sources and assumptions below.

Recorded event timeline

Show injected expectation

Mint bars: sampled counts. Shading: peak window. Solid line: selected event; dashed line: replay clock. Optional gold line: injected expectation, not recovered luminosity. Zero is the prescribed arrival onset at Earth.

The sliding-window scan

Every full window is evaluated on a fixed quarter-second grid. The first crossing is a simulated decision time, not a fitted stellar collapse time.

INSPECT ONE INTERACTION

From a point flash to the sphere

Event index

Ideal prompt isotropic light; 64 rays are geometric samples, not photoelectron yield. The full 5 m collection sphere and fixed index 1.5 omit scintillation delay, absorption, scattering and sensor response.

Model assumptions & primary sources

Illustrative mean: 120 detected candidates at 10 kpc and exposure one, scaled by exposure and inverse square of distance. Exposure changes candidate yield only; it does not resize the schematic sphere or scale the independently controlled background. Cooling is a truncated exponential over 30 seconds; Fast onset mixes 30% of a 0.4 second component and 70% cooling. Background is stationary Poisson. Uniform vertices fill the inner 4 m sphere, carry no sky direction and do not enter the trigger. No energy, cross-section, efficiency or flavor model; no SN 1987A events are reproduced.

Read SN 1987A →Explore the global history →

CONTINUE EXPLORING

From flavor to evidence

Propagation predicts a flavor probability. Which parts of the experiment turn an interaction into a usable record?

Physics tutorial

A trigger is a decision, not a discovery.

BackgroundSN 1987A connected short neutrino bursts in independent underground instruments with a visible stellar explosion. Today, SNEWS combines detector reports to support early warning. Each detector must first decide whether its own event stream is unusual.

Why it mattersA nearby source can produce a rush of interactions while a distant source leaves only a few. Lowering a count threshold catches more weak bursts, but stationary background can also cross it. This Lab separates sampling, replay and that decision.

Start with the essentials

Focus question: How much does a convincing-looking cluster depend on your window, threshold and assumed background?
One-sentence intuition: The same timestamps can yield different trigger decisions. A peak found by scanning many windows needs a scan-level probability bound; its single-window tail alone is not the false-alarm probability.

Core mathematical model

Distance and relative exposure

\bar N_s=120\,a\left(\frac{10\,\mathrm{kpc}}{d}\right)^2

The normalization is illustrative, not a prediction for a named instrument. Relative exposure changes signal yield only; the background has an independent control and the schematic chamber stays the same size.

A prescribed cooling profile

F(t)=\frac{1-e^{-t/\tau}}{1-e^{-30\,\mathrm{s}/\tau}},\qquad 0\le t\le30\,\mathrm{s}

Signal is a nonhomogeneous Poisson process whose integrated intensity is mean yield times this cumulative profile. Fast onset adds a 30% short component. This is not a hydrodynamic supernova or flavor-evolution calculation.

Count a full window

C_j=\sum_i\mathbf 1\{u_j-W<t_i\le u_j\},\qquad C_j\ge k\ \Rightarrow\ \text{candidate trigger}

Window ends are fixed on a quarter-second grid. Only observed timestamps enter this rule. The model origin labels, spatial vertices and injected onset are not trigger inputs.

Account for the scan

p_k=\Pr\{\mathrm{Poisson}(bW)\ge k\},\quad\Pr\{\max_j C_j\ge k\}\le\min(1,Mp_k)

The union bound is conservative even though windows overlap. It assumes a known stationary Poisson background. It covers one fixed window and threshold choice, not repeated tuning after viewing the record or continuous year-long monitoring.

One flash, a different clock

L=-\mathbf r\cdot\hat{\mathbf q}+\sqrt{(\mathbf r\cdot\hat{\mathbf q})^2+R^2-|\mathbf r|^2},\qquad t_{\mathrm{hit}}=\frac{nL}{c}

Each representative ray starts at the selected event vertex and intersects the same ideal 5 m collection sphere. The index is 1.5; coordinates are meters and optical time is nanoseconds. Ray count is not photoelectron yield. Scintillation emission delay and detector response are omitted.

Common difficulties

A local tail is not the whole search

Typical misconceptionThe smallest single-window tail is the false-alarm probability for the entire scan.

Better mental modelSelecting the peak creates multiple opportunities for a fluctuation. The scan bound includes every prescribed grid window; additional model or setting choices require further treatment.

Uniform vertices do not point to a star

Typical misconceptionThe bright pattern inside the sphere reconstructs a supernova direction.

Better mental modelThese are prescribed uniform deposits for optical illustration. There is no directional interaction model, triangulation or sky reconstruction.

Run the experiment

01
Catch a burst
Acquire Galactic burst and replay the event clock. Inspect the half-second counts and the first threshold crossing.
What to observe: The clock reveals an existing frozen record; it does not generate new events. Gold marks the selected vertex and recent interactions; mint marks the accumulated sample.
02
Keep the record, change the decision
Change window duration and count threshold in the analysis panel.
What to observe: The event times stay fixed, but peak count, candidate crossing and false-trigger bound change together.
03
Try only background
Acquire Background only, restore this record’s background assumption, then lower the threshold.
What to observe: A background fluctuation can trigger. The probability bound states its conditional rarity rather than calling it a stellar discovery.
04
Enter one interaction
Select an event on the timeline, then Follow this flash in 3D. Scrub the optical clock.
What to observe: Representative light rays stop on the collection sphere. Their histogram is computed from those same path lengths; the burst clock and optical clock describe different scales.