Sterile Neutrino Experiments at Accelerator

Transcription

1 Sterile Neutrino Experiments at Accelerator Takeo Kawasaki Kitasato University Rencontres du Vietnam, Neutrinos, Quy Nhon, July 16-22,2017 1

2 Outline Neutrino oscillation Sterile neutrino 3+1 model Neutrino oscillation experiments at accelerator Indication of sterile neutrino LSND MiniBooNE Sterile neutrino search at accelerator experiment JSNS 2 SBN NuPRISM Summary 2

3 Matrix elements Neutrino mixing matrix (3 flavors) ν e ν μ ν τ = U e1 U μ1 U τ1 U e2 U μ2 U τ2 U e3 U μ3 U τ3 ν 1 ν 2 ν 3 Ex) P ν μ ν μ Monochromatic energy case 1/Δm 2 ν oscillation is explained by mixing matrix elements and mass difference. Most Exp. Results are consistent with 3 neutrino mixing model. 3

4 Neutrino mixing matrix (4 or more flavors) If there are more generations, it affect to the oscillation ν e ν μ ν τ ν s = U e1 U μ1 U τ1 U s1 U e2 U μ2 U τ2 U s2 U e3 U μ3 U τ3 U s3 U e4 U μ4 U τ4 U s4 ν 1 ν 2 ν 3 ν 4 m 4 2 m 2 ν e ν μ ν τ ν S 2 Δm new For 3(n a ) + 1(n s ) & m 4 >> m 1~3 case, 0 P ν e ν e 1 4 U S4 2 U e4 2 sin 2 m 4 2 L 4E ν P ν μ ν e 4 U μ4 2 Ue4 2 sin 2 m 4 2 L 4E ν P ν μ ν μ 1 4 U S4 2 U μ4 2 sin 2 m 4 2 L 4E ν n e disappearance n m n e appearance n m disappearance Reactor &source Exp. Accelerator Exp. can measure n s may be detected by n oscillations 4

5 Reactor/RI source Accelerator Exp. E-L relation of n oscillation experiments Suekane@HINT2016 P ν α ν β = sin 2 2θ sin 2 Δm ij 2 L 4E ν There are indications of 3 rd Dm 2 which requires 4 or more n s. 2 Dm 2 s are confirmed Solar n 5

6 Reactor/RI source Accelerator Exp. E-L relation of n oscillation experiments Suekane@HINT2016 P ν α ν β = sin 2 2θ sin 2 Δm ij 2 L 4E ν There are indications of 3 rd Dm 2 which requires 4 or more n s. SBN NuPRISM 2 Dm 2 s are confirmed JSNS2 Solar n 6

7 How to make neutrino beam Decay in Flight Proton beam Target π π ± π + Horn magnet Choose flavor K + π ± (in flight) μ ± + ν μ μ + Decay volume ν μ Off-Axis On-Axis ν e ~0.5% contamination Decay at Rest Proton beam π ± ν μ π + μ + νμ Stopper π and μ captured in the beam stopper material ν e 7

8 Indications of Sterile neutrinos Experiment ν source Mode Significance LSND Decay-At-Rest ν μ ν e 3.8σ MiniBooNE Decay-In-Flight ν μ ν e 3.4σ νμ νe 2.8σ combined 3.8σ Ga-Solar e capture n e n x 2.7σ Reactor b-decay n e n x 3.0σ Strong indication at Appearance modes at Accelerator experiment Reactor/source experiments show indication at Disappearance mode. However, no positive result at Dis-appearance mode at Accelerator Exp. 8

9 LSND experiment The most significant indication of the sterile n Decay At Rest 800MeV, proton beam 120Hz, 600ms Duty factor= 6% Inverse b decay (ν e only) Neutron capture Liquid Scintillator π ± produced at the water Target 9

10 LSND Results Phys. Rev. D64, (2001) Oscillation Parameter νe excess = 87.9 ± 22.4 ± 6.0 events To reject beam/cosmic related BG, many complicated cut were applied. Unknown systematics may have been introduced. 10

11 MiniBooNE experiment MiniBooNE Detector Placed at 500m to preserve LSND results with similar L/E 800-ton mineral oil Cherenkov/Scintillation Ring topology to separate e, μ and π 0 Can t distinguish e from γ π ± (in flight) μ ± + ν μ ν μ energy 400/600MeV Oscillation ν μ ν e νμ νe Detection mode: ν e + n e + p νe + p e + + n 11

12 MiniBooNE results Phys. Rev. Lett.110, (2013) 2.8σ Event excess ν mode: 78.4 ± σ ν mode: ± σ 3.4σ ν mode case; Large excess at low energy <475MeV But no excess at higher energy. The fit result doesn t explain it? Due to miss-id γ as electron? 12

13 MiniBooNE/LSND Results Comparison Phys Rev. D80, (2009) Phys. Rev. Lett.110, (2013) MiniBooNE ν mode is more compatible with LSND result compared with ν mode. How the difference is explained? 13

14 Short baseline accelerator experiments in preparation LSND/MiniBooNE results should be checked by accelerator experiment for Appearance/Dis-Appearance mode. J-PARC(Japan Accelerator Research Complex) Fermilab Booster n beam NuPrism SBN program JSNS 2 n Beam To Kamioka JSNS DAR/Appearance SBN program@fermilab BNB NuPrism@J-PARC /n -beam line DIF/Appearance/Dis-appearance 14

15 Direct test of LSND result JSNS Life science Facility Stage-1 approved. Funded for 1 detector TDR released on May 2017 arxiv: Members experienced at Reactor Exps. (Daya-Bay, DoubleChooz,RENO) Consists of -21 institutes -53 collaborators -Japan/US/Korea MLF Exp. Hall JSNS 2 : J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source. 15

16 Experimental site: J-PARC MLF Use existing building and beam facility Detector positon : 3 rd floor (L=24m) Mercury target (neutron&neutrino source) p + Hg π ± + X π + stop μ + + ν μ (t=2.2ms) μ + stop e + + ν e + νμ n source and oscillation mode are same as LSND Oscillation 3GeV, 1MW Proton beam νe Thanks to high-z of Hg, νe from μ decays are suppressed to 1/1,

17 ν beam DT=40ms(25Hz) Expected spectrum observed for L=24m 0.5eV 2 Δm 2 = 2.5eV 2 3.5eV 2 4.5eV 2 n from p & K decays n from m decay. n timing window =1~10ms - Signal - νefrom μ (normalized) Pulsed beam can reduce beam BKG and accidental BKG drastically Cosmic-ray and accidental BG: suppression factor= 9ms/40ms~2x

18 JSNS 2 :Detector Gd-loaded Liq. Scintillator 17 tons 2 (Established for reactor Exp.) νe + p n + e + (prompt) Depends on Gd concentration n Gd 158 Gd + γs (delayed; Q~8MeV, t cap ~30ms) 253,000b for thermal n Delayed coincidence Prompt; t e =1~10ms, E e =20~60MeV Delayed; t g =t p ~100ms, E g =7~12MeV Surface level without overburden Further BG suppression with PSD (Pulse shape discrimination) Use 2 of them. (1 detector funded) 18

19 JSNS 2 :Detector Normal LS Gd-LS 3 rd Floor for MLF maintenance work Use 2 of them. The detector size is limited by Facility requirement. Well established technology for reactor experiments. Gd loaded LS in transparent Acrylic tank Normal LS in Stainless Tank inch PMTs to ensure good Energy resolution Huge cosmic induced BG at surface level. LS region is divided to make Veto region. Neutron beam lines 19

20 Comparison with LSND Neutrino beam Detector Facility Beam Pow. [MW] Rep. Rate [Hz] Pulse Width [ns] Duty Factor JSNS 2 J-PARC/MLF e-5 LSND LANL/LAMPF e Type Mass [t] L [m] JSNS 2 Gd-LS with PSD LSND LS JSNS 2 : S/N > 1,000 LSND 20

21 JSNS 2 sensitivity (3y, 1 MW, 17 tons) Expected spectrum Case Δm 2 = 2.5eV 2, sin 2 2θ = Case Δm 2 = 1.2eV 2, sin 2 2θ =

22 Schedule for the 1st Detector (17-ton) JSNS2 group is now preparing for the 1 st detector construction Japan Fiscal Year (April March) JFY S.S/Acrylic Tank PMT install LS production Dry run LS filling Start Exp. Run Now Continuous work for 2 nd detector (17t) for increase of statistics and measurement with different baseline. The bidding of Stainless tank was started on June, 2017! 22

23 JSNS 2 status We have experiences at reactor Expetiments Work for Detector construction (from TDR) Stainless/Acrylic Tank design (inner)pmt location Consideration on Acrylic tank and PMTinstallation to S.S tank. 23

24 Compatibility tests of material inside Liquid Scintillators. It is Important to chose the material installed into LS (LAB Check attenuation length of the liquids and the condition of the material surface/weight after long soak. FINEMET for PMT magnetic shield LUIREMIRROR for light reflection at veto region 24

25 PMT Gain and P/V ratio were measured for PMT candidate. 25

26 SBN Address MiniBooNE anomaly Funded Booster neutrino Beam ~700MeV L/E ~ 1km/GeV Use 3 Liquid Argon TPCs( t) Good separation e/γ Study ν-lar cross section Further development for DUNE Sensitive to sterile oscillation ν μ ν e appearance ν μ ν μ dis-appearance I borrowed the slides from * Neutrino2016 arxive:

27 n-beam penetrates 3 LAr TPCs (soon) (running) 27

28 28

29 Sensitivities for sterile ν oscillations(3yrs) 29

30 neutrino beamline Stage1 approved ~10m Use movable detector in a shaft hole Water Cherenkov, ~1000 ton (depends on baseline) Baseline :1-2km (not fixed yet) Study ν nuclear interaction with various energy ~15m It is sensitive to sterile ν oscillation Both appearance/dis-appearance mode 30

31 θ OA = 4.0 θ OA = 2.5 With Off-axis beam technique. Large angle gives sharp E ν distribution. θ OA = 1.0 Change Off-Axis angle by moving detector in a shaft, 31

32 NuPRISM: sterile n sensitivity T2K II exposure(2e21 POT) ν e appearance mode 32

33 Comparison of the future projects JSNS2 SBND/mBooN/ICARUS nuprism Accelerator J-PARC/MLF Fermilab BnB J-PARC/n E n [MeV] ~50 ~ ~1500 n source m + DAR p + DIF p + DIF L[m] /470/ ~2000 (-) (-) (-) (-) Osc. mode νμ νe n m n e, n m n m n m n e, n m n m Detector Gd-LS LAr-TPC Water Cherenkov Fid. Mass(t) 17(phase0) 112/87/ (depnds on L) Characteristic Status Direct Test of LSND funded for 1detector Full n-ar interaction reconstruction. Near/Far cancellation funded Commissioning 2018~9 2018~9/2015/ Cost $ $$$ $$$ Wide range semimonochromatic n stage-1 approval 33

34 Summary There are some indications of sterile neutrinos Significant at LSND/MiniBooNE: Δm 2 ~O(eV) at ν e appearance mode Reactor/Source Exp. also show it in ν e dis-appearance mode SBL Accelerator experiments are sensitive to ν μ ν e and ν μ ν x Experiments are in preparation JSNS2@J-PARC is funded for 1 detector SBN@FermiLAB is funded and will start soon Those are complementary to the reactor/source experiments The interesting results will appear in a few years. 34