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Oscillation physics with reactor neutrinos in JUNO Han Zhang Institute of High Energy Physics, CAS On behalf of the JUNO collaboration Neutel, Padova, Sep. 30, 2025 2025/9/29 Han Zhang, IHEP 1
Jiangmen Underground Neutrino Observatory 2025/9/29 Han Zhang, IHEP 2 ØLocated at a baseline of ~52.5 km from 8 reactors in Yangjiang and Taishan NPPs Ø35 m diameter sphere with 20 ktons of liquid scintillator (LS) surrounded by water Cherenkov detector JUNO is a large multi-purpose liquid-scintillator neutrino experiment in Southern China Yangjiang NPP 17.4 GW Taishan NPP 9.2 GW Daya Bay NPP 52.5 km 52.5 km JUNO Shen Zhen Zhu Hai JUNO-TAO 9.6m underground 2.8 tons Gd-LS Hong Kong
JUNO detector 2025/9/30 Han Zhang, IHEP 3 Key parameters: ØLarge statistics: • Huge target mass – 20 ktons LS ØEnergy resolution: •17,612 20-inch PMTs and 25,600 3-inch PMTs à Large PMT coverage (~78%) • Designed for unprecedented energy resolution (~3% at 1MeV) •Control of energy response systematics (≤ 1%) ØPowerful nuclear reactors (26.6 GW!") ØOptimized baseline (~52.5 km) ØLow background •~650m overburden for cosmic background suppression • LS purification and screening of materials See detail in Guanda‘s talk on Oct. 2 See detector detail in Monica‘s talk on Oct. 2
JUNO status 2025/9/29 Han Zhang, IHEP 4 JUNO Timeline:
Status of 𝜈 oscillation physics ØNeutrino oscillation implies non-zero neutrino mass: beyond Standard Model 2025/9/29 Han Zhang, IHEP 5 Main goals of JUNO: Determine the neutrino mass ordering (NMO), and measure Δ𝑚!" #, Δ𝑚#" #, and sin#𝜃"# at <1% level via reactor antineutrinos ØKnown: ØUnknown: • sign of Δ𝑚!" #, 𝛿$%, octant of 𝜃#! • Dirac or Majorana particle, absolute mass scale Normal ordering Inverted ordering Δ𝑚#$ %~2.5×10&#eV%Δ𝑚%$ %~7.5×10&'eV% sin%𝜃%# ~0.5 sin%𝜃$% ~0.3 sin%𝜃$# ~0.02 𝑚#> 𝑚%> 𝑚$𝑚%> 𝑚$> 𝑚#
JUNO physics program 2025/9/29 Han Zhang, IHEP 6 ~50/day >100/year >100/day ~10(/10 s @ 10kpc ~400/year ØJUNO can detect neutrinos and antineutrinos coming from several sources: Neutrino oscillation properties Neutrinos as a probe Covered in this talk See Vannesa’s talk
Reactor oscillations in JUNO 2025/9/29 Han Zhang, IHEP 7 𝑃 𝜈)→ 𝜈)= 1 − cos(𝜃$# sin%2𝜃$% sin%*+!" !, (- −sin%2𝜃$# cos%𝜃$% sin%*+#" !, (- +sin%𝜃$% sin%*+#! !, (- Oscillation: slow fast ØSimultaneously probe two oscillation frequencies, no dependence on 𝛿./ and 𝜃%# ØOptimized baseline at first solar oscillation maximum for NMO determination Daya Bay JUNO (quasi-vacuum) Chinese Phys. C 46 123001
Antineutrino detection in JUNO 2025/9/29 Han Zhang, IHEP 8 ØMeasure neutrinos from fissions of 4 main isotopes in reactor via Inverse Beta Decay (IBD) •Prompt: kinetic energy loss of e& and e&e' annihilation 𝛾𝑠 • Delayed: n-capture on H (2.2 MeV) or $%C (4.95 MeV) ØTime-space coincidence between prompt positron and delayed neutron signals àpowerful background suppression ØRelation of positron energy and neutrino energy E()* 𝑒&~𝐸+!− 0.78 𝑀𝑒𝑉 IBD threshold 1.8 MeV 𝜏~200𝜇𝑠
Event display of reactor neutrino 2025/9/30 9 Han Zhang, IHEP Prompt 𝑒0signal Delayed neutron signal
Conclusion ØJUNO is a multi-purpose large liquid scintillator experiment ØGreat physics potential using reactor 𝜈Fdataset: •Δ𝑚*+ *, Δ𝑚,+ *, and sin*𝜃+* measurements with < 0.5% precision in 6 years • NMO sensitivity via oscillation interference in vacuum: 𝟑𝝈 in 7.1 years of data taking ØJUNO detector has been fully constructed, and LS filling has been completed. ØThe physics data taking began at the end of August • Results from reactor neutrinos will come soon ! 2025/9/29 16 Han Zhang, IHEP
Backup 2025/9/29 17 Han Zhang, IHEP
18 ØMeasured light yield better than expectations based on simulation: •>1600 PE/MeV for 68Ge, >1800 PE/MeV for neutron capture (~1785 PE/MeV in expectations) ØEnergy resolution for alpha from 214Po gives ~3% @0.92MeV ØEnergy resolution for 68Ge ~3.4%@2×0.511 MeV, close and worse than expectation 3.1% ØFurther improvement coming: more calibration data, noise/flasher removal, reconstruction and fit, … Chinese Phys. C 49 (2025) 013003 Light yield for 68Ge and neutron Detector performance
Detector performance 2025/9/29 19 Han Zhang, IHEP
Spectral shape uncertainty from TAO 2025/9/30 20 Han Zhang, IHEP
