---
title: ESSnuSBplus Setup Overview
url: https://www.emergentmind.com/topics/essnusbplus-setup
type: topic
---

# ESSnuSBplus Setup Overview

The ESSnuSBplus (ESSnuSB⁺) setup is an advanced extension to the European Spallation Source neutrino Super Beam (ESSnuSB) project. It is designed as a precision, low-energy neutrino cross-section and oscillation complex, integrating multiple neutrino beamlines and state-of-the-art detector systems. ESSnuSB⁺ aims to deliver world-leading measurements of leptonic CP violation and detailed neutrino–nucleus cross sections by leveraging the exceptionally high-power ESS linear accelerator and optimized detector suites. The program also incorporates facilities for new-physics searches, short-baseline oscillation studies, and systematic control at the percent level [2501.12297, 2601.10271, 2303.17356].

## 1. Accelerator Architecture and Beam Generation

ESSnuSB⁺ builds on major upgrades to the ESS linac, deploying a high-power H⁻ ion source, a chopper system, and a new accumulator ring. Key parameters include:

- **Linac output:** Kinetic energy $E_p = 2.0$–$2.5\,\mathrm{GeV}$, peak current $62.5\,\mathrm{mA}$, pulse length $2.86\,\mathrm{ms}$, repetition rate $14\text{–}28\,\mathrm{Hz}$, average beam power $5\,\mathrm{MW}$ [2303.17356, 2501.12297].
- **Pulse compression:** The H⁻ pulse is chopped into four $560\,\mu\mathrm{s}$ sub-pulses, each injected and accumulated, then fast extracted in $1.3\,\mu\mathrm{s}$ micro-bunches for target delivery [2303.17356].
- **Switchyard distribution:** Fast-extraction kickers dispatch pulses to four separate target/horn systems, each handling $1.25\,\mathrm{MW}$, to optimize target longevity and flexibility.
- **R&D target station:** A $1.25\,\mathrm{MW}$ titanium-sphere target with helium gas cooling is the prototype for full operations. Horn focusing employs $350\,\mathrm{kA}$, $100\,\mu\mathrm{s}$ pulses, optimized to focus pions in the $200\text{–}600\,\mathrm{MeV}/c$ range [2303.17356].

These innovations enable pulse structures and instantaneous power necessary for high-intensity, narrow-band neutrino beams with suppressed background.

## 2. ESSnuSBplus Beamline Complex

ESSnuSB⁺ comprises three main neutrino production facilities:

**a) Main ESS linac–based Superbeam:**  
- Generates a high-intensity, predominantly $\nu_\mu$ ($\bar\nu_\mu$) beam from $\pi^+$ ($\pi^-$) decays, focused and sign-selected by dual magnetic horns.  
- Typical flux composition at 100 km: $97.6\,\%\,\nu_\mu$, $1.7\,\%\,\bar\nu_\mu$, $0.67\,\%\,\nu_e$, $0.03\,\%\,\bar\nu_e$ in $\nu$ mode [2303.17356].  
- Neutrino energy spectrum is broadly peaked near $0.3$–$0.4\,\mathrm{GeV}$, with rapid suppression beyond $0.6\,\mathrm{GeV}$.

**b) Low-Energy Monitored Neutrino Beam (LEMNB):**  
- Features an instrumented decay tunnel, with calorimeters and trackers surrounding the active region, capable of $1\%$-level flux monitoring.  
- Delivers neutrinos from monitored $\pi$ and $K$ decays in the $0.2$–$0.6\,\mathrm{GeV}$ window, with sharply peaked spectra and controlled systematics [2501.12297].

**c) Low-Energy nuSTORM (LEnuSTORM):**  
- Employs a compact muon storage ring ($p_\mu\sim300\,\mathrm{MeV}/c$; $C_\text{ring}\approx150\,\mathrm{m}$), storing $\mu^-$ or $\mu^+$ for decay-in-flight to yield well-understood $\nu_e$, $\bar\nu_\mu$ spectra [2501.12297].
- Delivers fluxes at $L=50\,\mathrm{m}$ of order $10^{12}\text{--}10^{13}/(\mathrm{cm}^2\,\mathrm{yr})$.

All beamlines are co-located at the ESS site (Lund, Sweden), enabling synchronized operation and systematic intercomparison.

## 3. Detector Systems and Configurations

ESSnuSB⁺ incorporates a hierarchical detector suite, designed for both near and far applications:

**Far Detector:**  
- Two water Cherenkov tanks, each $78\,\mathrm{m}\times78\,\mathrm{m}$, $\sim270\,\mathrm{kt}$ fiducial mass, $30\%$ PMT coverage [2303.17356].
- Sited at Zinkgruvan mine, $360\,\mathrm{km}$ (second oscillation maximum), $\approx1\,\mathrm{km}$ underground, with active and passive cosmic-ray suppression.
- Achieves energy resolution $\sigma_E/E\simeq15\%/\sqrt{E[\mathrm{GeV}]}$, angular resolution $O(1^\circ)$, background rejection (NC $\pi^0$ mis-ID $<1\%$).

**Near Detector Complex:**  
- Comprised of a $0.75$–$1\,\mathrm{kt}$ water Cherenkov detector, a Super-Fine-Grained Detector (SFGD-$\sim1\,\mathrm{t}$ $CH$), and an Emulsion Cloud Chamber ("$\nu$iking", $\sim1\,\mathrm{t}$ $H_2O$) [2303.17356, 2111.05550].
- Delivers $>10^6$ $\nu_\mu$ CC and $\sim10^4$ $\nu_e$ CC events/year in WC, providing $<3\%$ flux normalization, with flavor ID $\epsilon(e\rightarrow e)=46.3\%$, $\text{misID}(\mu\rightarrow e)=1.6\%$ [2111.05550].
- Energy reconstruction to $<5\%$ for lepton tracks in SFGD; emulsion for hadronic and MEC topologies.

**LEMNB and LEnuSTORM Detectors:**  
- Cylindrical water Cherenkov ("LEMMOND"): $5\,\mathrm{m}$ diameter, $10\,\mathrm{m}$ length, $200\,\mathrm{t}$ total mass ($150\,\mathrm{t}$ fiducial), $25\%$ SiPMT coverage ($QE=25\%$), energy threshold $5\,\mathrm{MeV}$ [2501.12297].
- Placed at $L=50$–$500\,\mathrm{m}$, measures cross sections and monitors $\nu$ fluxes with $O(10^4)$ CC events/year per tonne.

| Detector   | Location / Baseline | Mass (fiducial) | Technology/Role                                   |
|------------|---------------------|-----------------|---------------------------------------------------|
| WC (far)   | Zinkgruvan/360 km   | 2 × 270 kt      | CPV, oscillations, atmospheric neutrinos           |
| WC (near)  | ESS site/0.2–0.5 km | 0.75–1 kt       | Flux/cross-section constraint                     |
| SFGD       | ESS site/0.2–0.5 km | 1 t             | Tracking, energy calibration, nuclear effects      |
| Emulsion   | ESS site/0.2–0.5 km | 1 t             | Topology (MEC), hadronic system                   |
| LEMMOND    | LEMNB/LEnuSTORM     | 150 t           | $\nu$ cross sections, sterile $\nu$ searches      |

## 4. Oscillation Physics and Secondary Measurements

ESSnuSB⁺ is optimized to exploit the second oscillation maximum ($L=360\,\mathrm{km}$, $E_\nu\sim0.3\,\mathrm{GeV}$), where the oscillation probability

$$
P_{\mu e}(E,L)\simeq\sin^2\theta_{23}\sin^22\theta_{13}\sin^2(\Delta_{31}) + J_{CP}\sin(\Delta_{21})\sin(\Delta_{31})\sin(\Delta_{32})
$$

(with $J_{CP} = \frac{1}{2}\cos\theta_{13}\sin2\theta_{12}\sin2\theta_{23}\sin2\theta_{13}\sin\delta_{CP}$, $\Delta_{ij}\equiv\Delta m^2_{ij}L/(4E)$) is especially sensitive to $\delta_{CP}$ due to an enhancement factor $\approx2.5$ vs.\ the first maximum. Matter effects remain subdominant ($< 5\%$), minimizing theoretical systematics [2501.12297, 2303.17356]. The far detector expects $\sim1.2\times10^4$ $\nu_e$ appearance and $3\times10^4$ $\nu_\mu$ disappearance events/year, with signal efficiency $\sim70\%$ in the QE peak region [2601.10271].

**Sterile Neutrino and BSM Searches:**  
- LEMNB and LEnuSTORM enable short-baseline disappearance studies, probing $\Delta m^2\sim1\,\mathrm{eV}^2$,
- 5$\sigma$ sensitivity to LSND/MiniBooNE-parameter regions, advanced evaluation of invisible decay, scalar NSI, and decoherence scenarios [2501.12297, 2303.17356].

**Cross Section Precision:**  
- $\nu$–nucleus ($^{16}$O, C) cross sections in the $0.1$–$1\,\mathrm{GeV}$ band are targeted for $3$–$5\%$ uncertainty, benefitting from controlled flux and novel beam monitoring. The generic cross-section relation is:

$$
\sigma(E_\nu) = \frac{N_{\text{obs}}(E_\nu)}{\phi(E_\nu)\,N_{\text{target}}\,\epsilon_{\text{det}}}
$$

where $N_{\text{obs}}$ is background-subtracted yield, $\phi$ the known flux, $N_{\text{target}}$ the number of targets, and $\epsilon_{\text{det}}$ the detection efficiency [2501.12297].

## 5. Systematic Uncertainties and Performance Metrics

ESSnuSB⁺ achieves systematic control at the percent level by leveraging:

- **Flux normalization:** $3$–$5\%$ (main beam), $<3\%$ (ND, LEMNB), $O(1\%)$ (LEnuSTORM, monitored beams).
- **Cross-section modeling:** $10\%$ (QE), down to $5\%$ (RES channels).
- **Detector normalization:** $2$–$3\%$ (efficiencies, volumes).
- **Energy scale:** $1\%$ correlated uncertainty at the far detector.
- **Background rejection:** Intrinsic beam $\nu_e$ and NC $\pi^0$ backgrounds are suppressed below $5\%$ of signal in appearance channels [2601.10271, 2110.14276].

Expected event rates and signal/background ratios are derived with these uncertainties, employing full MC or parametric GLoBES simulations [2110.14276]. Statistical precision is dominant; e.g., near detectors attain $O(1\%)$ precision on $\sigma_{\nu_e}$ with $10^4$ events per year [2111.05550].

## 6. Projected Physics Reach and Extended Program

ESSnuSB⁺ is projected to provide:

- **CP violation coverage:** $5\sigma$ rejection of no-CPV hypothesis in $\sim72\%$ of the allowed $\delta_{CP}$ range after $10$ years; precision on $\delta_{CP}$ better than $8$–$9^\circ$ for all values [2501.12297, 2303.17356].
- **Atmospheric parameters:** Moderate–good sensitivity to the neutrino mass ordering and atmospheric mixing parameters; limited sensitivity to $\theta_{23}$ octant [2110.14276, 1909.13746].
- **Cross section systematics:** Measured to the few-percent level, providing essential input for next-generation oscillation experiments.
- **Astroparticle and non-standard physics:** Atmospheric, solar, supernova, and proton-decay studies become feasible by virtue of the water Cherenkov’s high mass and low threshold. Short-baseline BSM searches are enabled by the closely integrated low-energy beamlines and multiple detector technologies [2303.17356].

| Attribute                        | Value or Range                                |
|-----------------------------------|-----------------------------------------------|
| Beam power (linac)                | $5\,\mathrm{MW}$                             |
| Main baseline                     | $360\,\mathrm{km}$ (Zinkgruvan)              |
| Far detector mass                 | $2\times270\,\mathrm{kt}$ (water Cherenkov)  |
| Near detector distance            | $0.2$–$0.5\,\mathrm{km}$                     |
| Cross-section precision           | $3$–$5\%$ in $0.1$–$1\,\mathrm{GeV}$         |
| $\delta_{CP}$ precision           | $<9^\circ$                                   |
| Systematic normalization          | $3$–$5\%$ (flux), $2$–$3\%$ (detector)       |

## 7. Significance in the Neutrino Physics Landscape

The ESSnuSB⁺ setup operationalizes a phased, systematic-reduction strategy. By co-siting multiple precisely monitored beamlines and a diverse detector suite, the program achieves:

- Maximized sensitivity to leptonic CP violation by exploiting the second oscillation maximum, where the CP-odd oscillation amplitude is enhanced by a factor $\sim2.5$ compared to the first maximum, and matter effects are suppressed [2501.12297, 2303.17356].
- Reduction and calibration of key systematics (flux, cross-section, detector) to levels required for the next generation of precision oscillation physics and new physics searches.
- Direct investigation of sterile neutrino anomalies, as well as non-standard interactions, invisible decay modes, and decoherence effects, leveraging the coordinated short- and long-baseline configurations.

The ESSnuSB⁺ design and its associated experimental program set a technical benchmark for precision long-baseline and short-baseline neutrino oscillation studies, cross-section measurements, and systematic control [2501.12297, 2601.10271, 2303.17356].

Source: https://www.emergentmind.com/topics/essnusbplus-setup