1950s 2020s Reactor neutrino experiments · PDF file...

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  • Reactor neutrino experiments Zeyuan Yu, IHEP, CAS

    yuzy@ihep.ac.cn

    June 25, SJTU

    1950s 2000s 2010s 2020s

  • Nuclear reactor as antineutrino source

    • Nuclear reactors produce pure

    νe from beta decays of fission

    daughters

    • 6 νe per fission

    • 2*1020 νe per second per GWth

    • Commercial reactor: ~ 3 GWth

    • Free, huge flux

    • Research reactor: ~ MWth

    2

  • Beta decay in 1920s

    • Why the beta decay spectrum is

    continuous?

    • Break of energy conservation law?

    3

    ZX -> β + Z+1X

  • Pauli

    • Why the beta decay spectrum is

    continuous?

    4

    ZX -> β + Z+1X + ν

  • Fermi

    • In 1932, Chadwick discovered neutron, then Fermi proposed to change

    Pauli’s ‘neutron’ to ‘neutrino’ – a minor neutron

    • In 1933, Fermi proposed β-decay results from some sort of interaction

    between the nucleons, the electron and the neutrino

    • This interaction is different from all other forces and will be called the weak

    interaction

    • But the paper was rejected by Nature

    • “Because it contained speculations too

    remote from reality to be of interest

    to the reader”

    5

  • How to detect neutrino

    • ν + 37Cl  37Ar + β • Used by Raymond Davis

    6

    • ν + p  n + e+

    • Used by Reines and Cowan

    Since 1953

    Hanford reactor

    0.3m3 liquid scintillator

    90 2” PMTs

    Since 1948

    CCl4 detector

    BNL reactor

  • Neutrino discovery

    • Reines and Cowan moved the experiment to Savannah River reactor plants

    • In 1956, the neutrino was observed

    • Nobel Prize of physics, 1995

    7

  • Solar neutrino

    • Raymond Davis moved the CCl4 detector to Homestake in 1960s

    • ν + 37Cl  37Ar + β

    • ν + 37Cl  37Ar + β

    • The observation of solar neutrinos, Nobel Prize of 2002

    8

  • What we learned from Reines and Cowan

    • Detection principles

    • Inverse beta decay in CdCl3 water solution  coincidence of prompt and delayed signal

    • Liquid scintillator + PMTs

    • Underground

    • Modern experiments are still quite similar, except

    • Loading Gd into liquid scintillator

    • Larger, better detector

    • Deeper underground, better shielding

    9

  • CHOOZ and Paolo Verde

    10

    • They were built around 1997 with ~ 1 km reactor to detector distance

    • Aimed to search for the neutrino oscillation with Δm2 ~ 10-3 eV2

    1998-1999, US

    11.6 GWth

    Segmented detector

    12 ton 0.1% Gd-LS

    Shallow overburden

    32 mwe

    1997-1998, France

    8.5 GWth

    300 mwe

    5 ton 0.1% Gd-LS

    Bad Gd-LS

    R=1.012.8%(stat) 2.7%(syst), sin2213

  • KamLAND

    11

    2002-, Japan, 53 reactors, 80 GWth

    1000 ton LS, 2700 mwe

    Radioactivity  fiducial cut, Energy threshold

    Baseline 180 km

  • KamLAND

    12

    The first observation of reactor antineutrino disappearance

    Confirmed antineutrino disappearance at 99.998% CL

    Excluded neutrino decay at 99.7% CL

    Excluded decoherence at 94% CL

    R=0.6580.044(stat) 0.047(syst)

  • Neutrino oscillation @ 2003

    13

    1 2 3

    1 2 3

    1 2 3

    1

    2

    3

      

      

    

         

       

          

      

      

          

    e e ee U U U

    U U U

    U U U

    1 13 13

    13 13

    23 23

    23 23

    2 12

    12 12

    1 0 0

    0 0

    0

    0 0

    0 c s

    0 s c 0

    c s 0

    s c 0

    0 0 1

    c 0 s

    0 0

    s 0 c 1

    

          

            

        

       

          

        

    i

    iiU ee

    e

    23 ~ 45

    Atmospheric

    Accelerator

    12 ~ 34

    Solar

    Reactor

    0

    13 = ?

    Reactor

    Accelerator

    In a 3- framework

  • θ13 = ?

    • Reactor neutrino experiments use ν disappearance • Clean in physics, only related to 13

    14

     

     

    2

    4 2 2

    1

    2

    3 12

    2

    13 31

    2

    21

    1 sin / 4

    cos si

    sin

    n 2 sin / 4

    2 

     

    

     

     e e

    m

    m

    P L E

    L E

  • “New generation” θ13 experiments

    15

    Parameter Error Near-far

    Reaction cross section 1.9 % 0

    Energy released per fission 0.6 % 0

    Reactor power 0.7 % ~0.1%

    Number of protons 0.8 % < 0.3%

    Detection efficiency 1.5 % 0.2~0.6%

    CHOOZ Combined 2.7 % < 0.6%

    Major sources of uncertainties:

    • Reactor related ~2%

    • Detector related ~2%

    • Background 1~3%

    Lessons from past experience:

     CHOOZ: Good Gd-LS

     Palo Verde: Better shielding

     KamLAND: No fiducial cut

    Near-far relative measurement

    Mikaelyan and Sinev, hep-ex/9908047

  • 16

    Angra, Brazil

    Diablo Canyon, USA

    Braidwood, USA

    Double Chooz, France

    Krasnoyarsk, Russia

    KASKA, Japan

    Daya Bay, China

    RENO, Korea

    8 proposals, most in 2003 (3 on-going) • Fundamental parameter • Gateway to -CPV and Mass Hierachy measurements • Less expensive

  • Reactor antineutrino detection

    17

    Capture on H

    Capture on Gd

  • Daya Bay experiment

    • 6 reactor cores, 17.4 GWth

    • Relative measurement

    – 2 near sites, 1 far site

    • Multiple detector modules

    • Good cosmic shielding

    – 250 m.w.e @ near sites

    – 860 m.w.e @ far site

    18

  • Three on-going experiment @ 2009

    19

    Experiment Power

    (GW)

    Detector(t)

    Near/Far

    Overburden (m.w.e.)

    Near/Far

    Sensitivity

    (3y,90%CL)

    Daya Bay 17.4 40 / 80 250 / 860 ~ 0.008

    Double Chooz 8.5 8 / 8 120 / 300 ~ 0.03

    RENO 16.5 16 / 16 120 / 450 ~ 0.02

    Huber et al. JHEP 0911:044, 2009

  • Daya Bay

    20

  • Three on-going experiment @ 2018

    • Daya Bay: running to Dec. 2020, sin22θ13 precision better than 3%

    • RENO: running to 2020

    • Double Chooz: data taking stopped in Dec. 2017 21

    3.4%

    2.8%

  • Neutrino flux measurements

    • The neutrino oscillation study is a near and far relative measurement

    • The absolute neutrino flux can also be measured

    22

  • Reactor neutrino predictions

    • Summation method: 10% uncertainty • Sum over the fission products’ νe spectra

    from the nuclear database

    • 235U, 239Pu, 241Pu: conversion method, ~2.7% uncertainty • Convert ILL’s measured beta spectra to νe

    ones with virtual beta-decay branches

    • ILL + Vogel model since 1980s • Predicted flux was consistent with Bugey-3

    and other short baseline experiments

    • Huber + Mueller Model • In 2011, two conversion re-analyses increased

    the predicted flux by ~5%

    23

  • Flux measurements @ 2011

    • Measured flux is 6% higher than the Huber-Mueller model prediction

    • eV scale sterile neutrino?

    • A lot of short baseline experiments were proposed

    24 G. Mention et al.

    Phys.Rev. D83 (2011) 073006

    fit with sterile 𝜈 Δ𝑚2 ≈ 1 𝑒𝑉2

  • Daya Bay measurement

    • The 6% flux deficit is confirmed

    • 5 sigma discrepancies are found in the

    neutrino spectra

    25

    1904.07812

    1808.10836

    https://arxiv.org/abs/1904.07812 https://arxiv.org/abs/1808.10836

  • Fuel evolution study

    • With nuclear fuel burning, larger 239Pu fission fraction  smaller

    neutrino yield

    26

  • Fuel evolution study

    • With nuclear fuel burning, larger 239Pu fission fraction  smaller

    neutrino yield

    27PRL118, 251801 (2017)

  • Fuel evolution study

    • Combined fit for major fission isotopes 235U and 239Pu

    • σ235 is 7.8% lower than Huber-Mueller model (2.7% meas. uncertainty)

    • σ239 is consistent with the prediction (6% meas. uncertainty)

    • 2.8σ disfavor equal deficit (H-M model & sterile hypothesis)

    28PRL118, 251801 (2017)

  • Isotropic neutrino spectra

    • Daya Bay