THE JUNO EXPERIMENT. A.Meregaglia - IN2P3/CNRS - IPHC Strasbourg on behalf of the JUNO collaboration. 4 th November Paris NNN 2014

Transcription

1 THE JUNO EXPERIMENT A.Meregaglia - IN2P3/CNRS - IPHC Strasbourg on behalf of the JUNO collaboration 4 th November Paris NNN 2014

2 JUNO COLLABORATION EUROPE (20) APC Paris Charles University Prague CPPM Marseille FZ Julich INFN Frascati INFN Ferrara INFN Milano INFN Padova INFN Perugia INFN Roma3 IPHC Strasbourg JINR Dubna LLR Paris RWTH Aachen Subatech Nantes TUM Munich University of Hambourg University of Mainz University of Oulu University of Tuebingen University of Bruxelles (observer) JUNO international collaboration has recently been established. It consists so far of 45 institutions (most of european ones still subject to founding agency approval). US 10 institutes observers ASIA (25) Beijing University CAGS CIAE DGUT ECUST Guangxi University IHEP Jilin University Nanjing University Nankay University Natl. Chiao-Tung University Natl. Taiwan University Natl. United University NCEPU Pekin University Shandong University Shanghai JT University Sichuan University SYSU Tsinghua University UCAS USTC Wuhan University Wuyi University Xi an University 2

3 INTRODUCTION Recent results of neutrino reactor experiment discovering a non zero value of the mixing angle θ13, opened the way for the CP violation search in the leptonic sector which is the main goal of future long baseline neutrino experiments. Normal Hierarchy (N.H.) An additional goal for next generation neutrino experiment is the mass hierarchy determination. ν e νµ ντ m 2 atm ν 3 Such a measurement could be performed on a shorter time scale with respect to long baseline projects. m 2 sol ν1 ν 2 Δm 2 31 > 0 Exploiting the matter effects in atmospheric neutrino oscillations (e.g. PINGU, ORCA or INO projects). Observing the interference between Δm 2 31 and Δm 2 32 in reactor antineutrino disappearance (e.g. JUNO or RENO50 experiments). ν e ν µ ν τ Inverted Hierarchy (I.H.) m 2 sol m 2 atm ν 3 ν2 ν1 Δm 2 31 < 0 3

4 LOCATION The JUNO (Jiangmen Underground Neutrino Observatory) optimal distance of ~53 km from the reactor cores, is close to the maximum of oscillation of θ12. Note that multiple reactor cores may cancel the oscillation structure: the baseline difference should be below 500 m. Kaiping, Jiang Men city, Guangdong Province Guang Zhou Phys.Rev. D88 (2013) h drive Shen Zhen Huizhou NPP Lufeng NPP 700 m overburden Zhu Hai Daya Bay NPP Hong Kong 53 km 53 km Yangjiang NPP Taishan NPP Macau by 2020: 26.6 GW NPP Daya Bay Huizhou Lufeng Yangjiang Taishan Status Operational Planned Planned Under construction Under construction Power 17.4 GW 17.4 GW 17.4 GW 17.4 GW 18.4 GW 4

5 NEUTRINO DETECTION Neutrinos are observed via Inverse Beta Decay (IBD): νe + p e + + n e The energy spectrum is a convolution of flux and cross section (threshold at 1.8 MeV). Thr=1.8MeV The signal signature is given by: 1. Prompt photons from e + ionisation and annihilation (1-8 MeV). 2. Delayed photons from n capture on Hydrogen (2.2 MeV). 3. Time (Δt ~200 µs) correlation. 5

6 SIGNAL AND BACKGROUND The estimated IBD event rate is 80 events per day before selections cuts (estimated efficiency 83%). The background can be divided into accidental and correlated. Accidental BG e + -like signal: radioactivity from materials, PMTs, surrounding rock. n signal: n from cosmic µ spallation, thermalised in detector and captured on H or radioactivity gamma. Correlated BG Fast n (by cosmic µ) gives recoil protons (low energy) and are captured on H. γ from radioactivity γ from radioactivity Accidental BG H n capture on H Correlated BG µ 9 Li->e+n Spallation neutron µ µ Long-lived ( 9 Li, 8 He) β+n-decaying isotopes induced by µ. Type of BG Rate/day Reduction methods Accidental 1.1 Low radioactivity PMT, LS purification and prompt delayed distance cut (1.5 m) Fast n 0.01 High muon detection efficiency (99.5%) 9 Li/ 8 He PRELIMINARY 1.8 Depending on muon tracking results: distance to muon track < 3 m and veto 1.2 s or full volume veto 1.2 s H n capture on H electron H n capture on H Recoil p Spallation fast neutron 6

7 DETECTOR CONCEPT The experiment consists of a very large 20 kton liquid scintillator detector. Given the energy resolution requirements of 3%/ (E) (see later), such a large detector would require particular attention to the scintillator attenuation length and on the detected p.e. per MeV. Top muon veto: plastic scintillator strips + RPC? 20 kt LS PMT support:φ39.9m LS:Φ35.4m LS: 20 kton LAB based LS container: acrylic or balloon? Buffer: 6 kton mineral oil or water? PMTs: PMTs for a 80% coverage Buffer/PMT support: Stainless steel structure or sphere? Water Cherenkov veto: 20 kton water PMTs: veto PMTs 7

8 MASS HIERARCHY DETERMINATION FCT(ω) = The neutrino oscillation probability can be written as: P ee (L/E) = 1 P 21 P 31 P 32 P 21 = cos 4 (θ 13 )sin 2 (2θ 12 )sin 2 ( 21 ) P 31 = cos 2 (θ 12 )sin 2 (2θ 13 )sin 2 ( 31 ) P 32 = sin 2 (θ 12 )sin 2 (2θ 13 )sin 2 ( 32 ) ij =1.27 m 2 ij L/E, 2 3σ 0.6 According to the mass hierarchy No oscillationone oscillation frequency 0.5 ω is larger than the other: 1-P 21 oscillation a global fit, upross section [17] s 0.3 m 2 31 = m m2 21 NH : m 2 31 = m m 2 21 IH : m 2 31 = m2 32 m2 21 ωp31 > ωp32 ωp31 < ωp32 Fourier analysis 10 can 15 be applied to the 30 L/E (km/mev) reconstructed energy spectrum to discriminate between the two FIG. 1: Reactor neutrino spectra at a baseline of 60 km hierarchies. in L/E space for no oscillation (dashed dotted line), 1 P 21 1MeV 2 ) (3) positronenergy, and p (0) e is the ability of ν e can oscillation (dotted line) and P ee oscillation in the cases of NH and IH, assuming sin 2 (2θ 13 tmax )=0.1. FST(ω) = F (t)sin(ωt)dt t min P ee P ee for NH for IH 2 tmax t min F (t)cos(ωt)dt (5) where ω is the frequency, ω =2.54 m 2 ij ; t = L E is the variable in L/E space, varying from t min = L E max to t max = L E min. Phys.Rev. D78 (2008) Since P 0.6 ee is a linear combination of 1 P 21, P 31 No and oscillation P 32, FST and FCT spectra can be divided into three components corresponding 0.5 to 1 P 1-P 21 oscillation 21, P 31 and P 32 respectively. Fig.2 shows the three components of thep FST for NH 0.4 ee and FCT spectra together with full P ee oscillation for P ee for IH both NH and IH cases. The oscillation frequency is proportional to m0.3 2 ij,sowecanscalethefrequencytobe δm 2 and plot the spectra in axis of δm 2 in the interested frequency range 0.2 of ev 2 < δm 2 < ev 2. From Fig.2, we know that: P 31 and P 32 components dominate the FCT and FST spectra0 in the 10 interested 15 frequency 20 range 25 of ev 2 < δm 2 < ev 2 since m 2 31 L/E (km/mev) and m 2 32 are in this range, while 1 P 21 is very weak since its oscillation Phys.Rev. frequency D78 (2008) is in a much lower range. The FST and FCT spectra of P ee are approximately the sum of FCT Pspectrum NH and P 32 components which are sensitive to mass hierarchy. IH The peak of FCT spectrum corresponds to the zero FST spectrum knowing their accurate values apriori For NH, the P 32 FCT and FST spectra are leftshifted with respect to the P 31 spectra because 0 m 2 32 < m 2 31 ; while for IN, the P 32 spectra are right-shifted because m 2 32 > m2 31. δm /ev point of FST spectrum. This feature is helpful to identify the position of m 2 32 and m 2 31, without 4. For FCT spectrum, P 32 and P 31 components have similar shapes with the 0 peak around m 2 32 and NH IH 2 sin 2 ( 21 ) sin 2 ( 31 ) sin 2 ( 32 ) (4) FCT(ω) = tmax t min F (t)cos(ωt)dt (5) where ω is the frequency, ω =2.54 m 2 ij ; t = L E is the variable in L/E space, varying from t min = L to E max δm /ev 8

9 MASS HIERARCHY SENSITIVITY The energy resolution is a critical parameter in the achievable sensitivity. The goal is to achieve 3%/ E (see later). Phys.Rev. D88 (2013) The baseline is optimized to 53 km with a difference to reactor cores of less than 500 m. The energy scale require calibration at the sub-percent level and it can be achieved with a comprehensive calibration program. We can perform a relative measurement (no constraint on Δm 2 31) or an absolute measurement accounting for constraints from external experiments in particular on Δm 2 µµ (from long baseline experiments). m 2 µµ sin 2 θ 12 m cos 2 θ 12 m sin 2θ 12 sin θ 13 tan θ 23 cos δ m 2 21 m 2 ee cos 2 θ 12 m sin 2 θ 12 m 2 32 Figure 6: the reactor-only (dashed) and combin in Eq. (11) Sensitivity and Eq. for (17), 100k whereibds a 1% (left pan m 2 µµ is assumed ( 6 years and at the36 CP-violating GW) phase for illustration. The black and red lines are f neutrino Relative MH, respectively. measurement: TheΔχ non-linearity 2 >9 size 0 = 2% and size 1 =4%. Absolute measurement: Δχ 2 >16 non-zero contribution to the discriminator χ χ 2 pull (MH) [2 m2 21 (cos 2θ 12 9σ

10 ADDITIONAL PHYSICS REACH Beside the mass hierarchy determination, JUNO has a broad physics program. Precision measurement of mixing parameters could be performed. Parameter Current precision JUNO Δm 2 21 Δm 2 32 sin 2 θ12 3% 0.6% 5% 0.6% 6% 0.7% High statistics supernova neutrino observation: about 5000 IBD events and 2000 events from other channels are expected for a SN explosion at 10 kpc. Geo-neutrino observation: about 2 events per day expected. Proton decay, solar and atmospheric neutrinos. Yellow book of JUNO physics in preparation 10

11 TIMESCALE Civil engineering Civil construction Detector components production PMT production Detector assembly and installation Filling and start data taking. 11

12 CIVIL CONSTRUCTION The civil engineering design is nearly finished. The expected construction time is 3 years m tun nel (42 %s lop e) 580 m vertical shaft Cavern (50 m diameter, 80 m high) Tunnel entrance 12

13 CENTRAL DETECTOR The central detector is a very large (diameter larger than 35 m) liquid scintillator detector in the water pool. Two options are considered: 1. Acrylic tank plus a stainless steel structure. 2. Stainless steel sphere plus acrylic structure and a balloon. The choice will be based on: 1. Engineering: mechanics, safety and lifetime. 2. Physics: cleanness and light collection. 3. Assembly and installation. Prototypes studies are ongoing. 13

14 VETO The veto will be critical to reduce all sources of background. 1. Cosmogenic isotopes rejection: good reconstruction of muon tracks and 1.2 s veto around them. Top Tracker 2. Neutrons rejection: passive shielding and possible tagging when multiple proton recoils are detected. Rock 9 Li n 3. Gamma rejection: passive shielding. To achieve the desired background reduction two sub-detectors are used: a water Cherenkov veto and a Top Tracker veto. Water Cherenkov Detector Water Cherenkov Water pool containing the inner detector kton ultrapure water PMTs. Top Tracker OPERA Target Tracker (plastic scintillator strips) will be used on top of the detector. Optimization of the geometry (number of planes and layout) ongoing to maximise efficiency and surface area covered. Additional options (e.g. RPCs) are considered to increase the coverage. 14

15 REQUIREMENTS Probably the most critical requirement of the experiment to reach the desired physics goals is given by the energy resolution. Phys.Rev. D88 (2013) The goal is to achieve a resolution of 3%/ E i.e. a light yield of about 1200 p.e./mev. Such an energy resolution is possible but it requires some improvements with respect to the actual performances of PMTs and liquid scintillator: 1. PMT coverage of 80%. 2. PMT QE increased from the actual 25% to 35%. 3. Light attenuation length from 15 to 20 m. Experiment Daya Bay KamLAND JUNO LS mass 20 ton 1 kton 20 kton Coverage 12% 34% 80% Energy resolution 7.5%/ E 6%/ E 3%/ E Light yield 160 p.e. / MeV 250 p.e. / MeV 1200 p.e. / MeV 15

16 LIQUID SCINTILLATOR The chosen liquid scintillator is a LAB doped with PPO and Bis-MSB. The foreseen amount of 5g/l of PPO results in a high light yield. Absence of Gd to have better optics and long term stability. LIght output, relative units 1,0 0,8 0,6 0,4 0,2 KamLAND Daya Bay JUNO 0,0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 PPO mass fraction, % The absence of Gd allows for a low radioactivity scintillator reducing dramatically the accidental background (factor of 10 4 ). LAB Attenuation length (m) at 430 nm Ongoing R&D Improve raw materials. Improve production and purification process. Study the aging. Study the engineering for the mass production. RAW 14.2 Vacuum distillation 19.5 SiO 2 column Al 2 O 3 column LAB from Nanjing RAW LAB from Nanjing Al 2 O 3 column

17 PMT At the moment 3 types of 20 high QE PMTs are considered: 20 MCT-PMT 1. New design MCP-PMT with Chinese industry (dynodes replaced by micro channels plates). 2. HZC Photonics PMT ( ). 3. Hamamatsu PMT with SBA photocathode (8 20 ). Technical issues related to MCP-PMT are mostly solved, 8 prototype were successfully produced and a few 20 prototypes exist. 40% 20% 30% Insulated trestle table Anode MCP module Brackets of the cables Trasmission photocathode Glass shell Reflection photocathode PMT 8 R R MCP-PMT QE at 410 nm 25% 35% 20% Rise time 3 ns 3.4 ns 5 ns SPE amplitude 8 mv 8 mv 8 mv P/V of SPE > 2.5 > TTS 5.5 ns 2.4 ns 3.5 ns Values at gain = 10 7 Glass joint 20% Quantum Efficiency 40% Glass Transmission 70% Collection Efficiency 17

18 CONCLUSIONS The JUNO international collaboration was established in July The civil construction has started and the laboratory should be ready in about 3 years. Detector optimization studies are ongoing to finalize the layout. R&D is ongoing in particular on the liquid scintillator and on the PMTs. Data taking should start in In 6 years a sensitivity of Δχ 2 >9 (relative measurement) and Δχ 2 >16 (absolute measurement with σ µµ =1%) could be reached on the mass hierarchy discrimination. 18