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中微子振荡 — 大亚湾实验及其未来发展

中微子振荡 — 大亚湾实验及其未来发展. 王贻芳 中国科学院高能物理研究所. 物质世界最基本的单元之一： 中微子. 中微子是构成物质世界的最基本单元之一： 中微子质量极轻，不带电荷，与物质的相互作用十分微弱 , 极难探测  需要用体积庞大的探测器 宇宙中的中微子与光子一样多，~ 100/ cm 3 大多数粒子物理和核物理反应都有中微子产生： 粒子和原子核衰变, 核反应堆,太阳的热核反应, 超新星爆发,加速器， g- 暴，宇宙线 …… 奇怪的中微子：只有左旋中微子  弱作用宇称不守恒的原因. 中微子研究的中心议题：质量.

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中微子振荡 — 大亚湾实验及其未来发展

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  1. 中微子振荡 —大亚湾实验及其未来发展 王贻芳 中国科学院高能物理研究所

  2. 物质世界最基本的单元之一：中微子 • 中微子是构成物质世界的最基本单元之一： • 中微子质量极轻，不带电荷，与物质的相互作用十分微弱,极难探测 需要用体积庞大的探测器 • 宇宙中的中微子与光子一样多，~ 100/cm3 • 大多数粒子物理和核物理反应都有中微子产生：粒子和原子核衰变, 核反应堆,太阳的热核反应, 超新星爆发,加速器，g-暴，宇宙线 …… • 奇怪的中微子：只有左旋中微子 弱作用宇称不守恒的原因

  3. 中微子研究的中心议题：质量 • 由于数目巨大，中微子质量对宇宙的形成与演化有重要影响 • 卫星实验测得： Σi mvi < 0.7 eV • 粒子物理标准模型认为中微子质量为零 • 中微子质量不为零 ==》超出标准模型的新物理 • 如何在标准模型中赋予中微子质量 ？ • Option 1: Dirac 中微子 • Option 2: Majorana中微子 • 中微子是Dirac或Majorana，即中微子与反中微子是否同一个粒子是粒子物理的一个根本问题 • 中微子与宇宙学关系密切： • 构成宇宙中的暗物质 • 中微子振荡与宇宙中物质与反物质不对称有关 • 中微子与大尺度宇宙结构的形成有关 中微子是粒子物理，天体物理与宇宙学研究中的热点与交叉

  4. 中微子振荡 • 1962年，因信仰共产主义而逃到前苏联的Bruno Pontecorvo 提出如果中微子质量不严格为零，且中微子的质量本征态与弱作用本征态不同，根据量子力学，不同的中微子之间可以相互转换 • 判断中微子质量是否为零的方法 Rome, Cimitero Acattolico Dubna， Pontecorvo’s ofice

  5. nm nm ne ne 两种中微子之间的振荡 振荡几率 振荡频率

  6. 三种中微子振荡 • A mixing matrix: CP phase & q13 Majorana phase Atmospheric Solar Atmospheric accelerator reactor accelerator solar reactor Double beta decays • Unknown parameters in neutrino oscillation: • q13 , mass hierarchy, CP phase d+ Majorana phase

  7. 大气中微子振荡 60年代，印度的宇宙线实验中发现大气中微子反常 1985年，美国IMB和日本神岗实验证实大气中微子反常 1998年, 日本超级神岗实验证实大气中微子振荡 小柴昌俊 2001Nobel price

  8. Theoretical Predictions 太阳中微子振荡 60年代，R. Davis发现到达地球的太阳中微子数只有理论预期值的1/3 • 1500米深的矿井中 • 615吨四氯乙烯 • 在30年中一共探测到约2000个中微子 R. Davis 2001 Nobel price e + 37Cl  37Ar + e-

  9. 太阳中微子振荡: SNO实验 • 2001年, 加拿大的SNO实验发现太阳中微子(ne)在飞向地球的过程中变为另一种中微子(nm或nt)

  10. 太阳中微子振荡: KamLAND实验 • 2001年, 日本的KamLAND实验发现反应堆中微子(ne)与太阳中微子(ne)有相同的消失性能, 证明太阳和反应堆中微子确实是发生了振荡

  11. 中微子振荡及其未解决的问题 • 中微子振荡： • 中微子振荡与中微子质量相关联，是中微子研究中的核心问题 • 中微子振荡于1998年被证实，获2001年 诺贝尔奖 • 已发现的中微子振荡有两种：大气中微子振荡和太阳中微子振荡 • 中微子振荡三个未解决的问题： • 寻找第三种振荡，用q13表示  大亚湾中微子实验 • 质量顺序问题 大亚湾中微子实验二期 ？ • (类似于夸克)对称性破缺？  未来的加速器实验 n1 n2 n3 q12太阳中微子振荡 q13 ? mi ? q23大气中微子振荡

  12. Current Knowledge of 13 Direct search PRD 62, 072002 M.C. Gonzalez-Garcia et al., JHEP1004:056,2010 Allowed region G.L.Fogli et al., J.Phys.Conf.Ser.203:012103

  13. No good reason(symmetry) for sin22q13 =0 • Even if sin22q13 =0 at tree level, sin22q13 will not vanish at low energies with radiative corrections • Theoretical models predict sin22q13 ~ 0.1-10 % model prediction of sin22q13 Experimentally allowed at 3s level An experiment with a precision for sin22q13 less than 1% is desired

  14. 大亚湾反应堆中微子实验 • 用大亚湾反应堆测量 q13是我国粒子物理发展的一个重大机遇： • 功率高（世界第二） • 周围有山，便于建设地下实验室以屏蔽宇宙线本底 • 造价较低，没有根本的技术困难 • 世界各国共有8个实验建议，三个正在进行中 • 难点：精度较过去提高一个量级 • 我们的突破：独特设计+环境优势  达到精度要求

  15. Reactor neutrino exp. • Clean signal, no cross talk with d and matter effects • Relatively cheap compare to accelerator based experiments • Can be very quick • Provides the direction to the future of neutrino physics Reactor experiments: Pee  1 sin22q13sin2 (1.27Dm213L/E)  cos4q13sin22q12sin2 (1.27Dm212L/E) Long baseline accelerator experiments: Pme ≈ sin2q23sin22q13sin2(1.27Dm223L/E) + cos2q23sin22q12sin2(1.27Dm212L/E)  A(r)cos2q13sinq13sin(d)

  16. How Neutrinos are produced in reactors ? The most likely fission products have a total of 98 protons and 136 neutrons, hence on average there are 6 n which will decay to 6p, producing 6 neutrinos Neutrino flux of a commercial reactor with 3 GWthermal : 6 1020 /s

  17. Neutrino detection: Inverse-β reaction in liquid scintillator t  28 ms(0.1% Gd) n + p  d + g (2.2 MeV) n + Gd  Gd* + g (8 MeV) Neutrino Event: coincidence intime, space and energy Neutrino energy: 10-40 keV 1.8 MeV: Threshold

  18. Reactor Experiment: comparing observed/expected neutrinos: Typical precision: 3-6% Precision of past exp. • Reactor power: ~ 1% • Spectrum: ~ 0.3% • Fission rate: 2% • Backgrounds: ~1-3% • Target mass: ~1-2% • Efficiency: ~ 2-3% We need a precision of ~ 0.4%

  19. Currently Proposed sites/experiments

  20. How to reach 1% precision ? • Increase statistics: • Powerful nuclear reactors(1 GWth: 6 x 1020e/s) • Larger target mass • Reduce systematic uncertainties: • Reactor-related: • Optimize baseline for best sensitivity and smaller residual errors • Near and far detectors to minimize reactor-related errors • Detector-related: • Use “Identical” pairs of detectors to do relative measurement • Comprehensive program in calibration/monitoring of detectors • Interchange near and far detectors (optional) • Background-related • Go deep to reduce cosmic-induced backgrounds • Enough active and passive shielding

  21. Ling-Ao near： 2 modules, 40 t target 500m to Ling-Ao overburden: 112m far: 4 modules, 80t target 1600m to Ling-Ao 1900m to Daya Bay overburden： 350m 0% slope 0% slope 0% slope entrance entrance Daya Bay near： 2 modules, 40 t target 360m to Daya Bay overburden: 98m 8% slope Layout • Near-far cancellation • Two near sites and one far sites connected by ~3000 tunnel • Event rate： ~1200/day near ~350/day far • backgrounds： B/S ~0.4% near B/S ~0.2% far

  22. Detector design: multiple detector modules and multiple VETO • Multiple detector modules to reuce errors and cross check • Multiple muon veto: • Two-layers of cerenkov detector • RPC at the top • Total efficiency > (99.5  0.25) % Redundancy is a key for the success of this experiment

  23. Central Detector modules • Three zones modular structure: I. target: Gd-loaded scintillator II. g-catcher: normal scintillator III. Buffer shielding: oil • 192 8”PMT/module • Reflector at top and bottom to ease engineering difficulties and save cost: Photocathode coverage 5.6 %  12%(with reflector) sE/E = 12%/E sr = 13 cm Target: 20 t, 1.6m g-catcher: 20t, 45cm Buffer: 40t, 45cm Total weight: ~100 t

  24. Water Buffer & VETO • At least 2m water buffer to shield backgrounds from neutrons and g’s from lab walls • Cosmic-muon VETO Requirement: • Inefficiency < 0.5% • known to <0.25% • Solution: Two active vetos • Active water buffer, Eff.>95% • Muon tracker, Eff. > 90% • RPC • total ineff. = 10%*5% = 0.5% • Two vetos to cross check each other and control uncertainty

  25. Background related error • Uncorrelated backgrounds: U/Th/K/Rn/neutron Single gamma rate @ 0.9MeV < 50Hz Single neutron rate < 1000/day 2m water + 50 cm oil shielding • Correlated backgrounds: n  Em0.75 Neutrons:>100 MWE + 2m water Y.F. Wang et al., PRD64(2001)0013012 8He/9Li: > 250 MWE(near), >1000 MWE(far) T. Hagner et al., Astroparticle. Phys. 14(2000) 33

  26. 其他物理目标 首次测量DM213 测量超新星中微子 寻找不活跃的中微子 大亚湾实验测量 Sin22q13的灵敏度

  27. Sensitivity: important to constraint models • A very interesting seesaw model: almost model independent S.F. Ge, H.J. He, F.R. Yin, JCAP05(2010)017

  28. Civil construction • Tunnel length: ~ 3100m • three experimental halls • One assembly hall • Water purification hall

  29. 大亚湾土建进展 • 3号厅（远厅） • 隧道开挖完成，开始大厅挖掘 • 2号厅（岭澳近厅） • 隧道与实验大厅开挖完成，正在进行水池建造与大厅装修 • 4号厅（纯水厅）已完工 • 5号厅（液闪厅）已完工，交付使用 • 1号厅（大亚湾近厅） • 已完成，即将交付使用。

  30. 地面安装大厅投入使用，正在进行中心探测器装配地面安装大厅投入使用，正在进行中心探测器装配 控制室投入使用 隧道入口 隧道内

  31. 实验大厅

  32. 探测器部件生产：大部分已完成 完成了满载与负压测试、激光形位测量、喷涂、真空检漏后的钢罐运抵现场 RPC 裸室 完成制造与测试 支撑平台已完工，进行了满载测试、测量、喷涂 反射板生产

  33. 探测器装配：完成了试安装，通过了检漏。两个正式探测器的安装正在进行，即将完成。探测器装配：完成了试安装，通过了检漏。两个正式探测器的安装正在进行，即将完成。 中心探测器顶部 反射板与洁净间 中心探测器装配，吊装3米罐 中心探测器装配，吊装反射板

  34. 液闪混制 200吨液袋检漏 液闪厅及混制设备 液闪的寿命与稳定性是最大的技术挑战 完成了设备工艺实验 液闪寿命经过了长期考验 200吨存储池，完成安装

  35. PMT readout and trigger PMT readout Prototype system test Trigger board FADC Fan-out • 清华大学负责的触发板，已与前端电子学完成了联调 • 最近在大亚湾现场完成了Mini Dry Run，成功实现了探测器-->前端电子学-->触发-->数据获取-->数据因特网传输-->离线分析的全流程

  36. Daya Bay collaboration Europe (3) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (14) BNL, Caltech, George Mason Univ., LBNL, Iowa state Univ. Illinois Inst. Tech., Princeton, RPI, UC-Berkeley, UCLA, Univ. of Houston, Univ. of Wisconsin, Virginia Tech., Univ. of Illinois-Urbana-Champaign, Asia (15) IHEP, Beijing Normal Univ., Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ.,Nankai Univ., Shenzhen Univ., Tsinghua Univ., USTC, Zhongshan Univ., Hong Kong Univ. Chinese Hong Kong Univ., Taiwan Univ., Chiao Tung Univ., National United Univ. ~ 200 collaborators

  37. What we can do after Daya Bay ?

  38. 下一代中微子实验：大亚湾二期 • 中微子振荡三个未解决的问题： • 寻找第三种振荡，用q13表示  大亚湾中微子实验 • 质量顺序问题 大亚湾中微子实验二期 • CP对称破缺角  未来的加速器实验 • 为什么反应堆中微子： • 1）加速器中微子实验：造价昂贵 （探测器+加速器） • 2）双β实验：造价昂贵，技术困难，科学风险大 • 3）中微子绝对质量测量：造价昂贵，技术困难 • 4）反应堆中微子实验：意义重大、风险小、条件优越、造价低、技术可行 • 测量磁矩：可能的未来，科学风险大 • 精确测量混合参数：大亚湾、大亚湾二期 n1 n2 n3 q12太阳中微子振荡 q13 ? mi ? q23大气中微子振荡

  39. Neutrino Mass hierarchy • Mass Hierarchy: • Fundamental to the Standard Model • Fundamental to models beyond SM • Most GUTs predict a normal mass hierarchy  a discriminator of different GUTs and/or neutrino mass models • Fundamental to many issues: • Matter-antimatter asymmetry via leptogenesis in specific seesaw models: hierarchy related • Supernova neutrinos: collective flavor transitions due to inverted mass hierarchy • Radiative corrections to mn and qij are more sensitive to the inverted hierarchy But even more important…

  40. Dirac or Majorana ? • Neutrino oscillation: beyond SM in a way of Dirac or Majorana mode ? • bb exp. may never give positive results • If mass hierarchy is known, together with next generation bb exp., the neutrino Dirac or Majorana nature can be determined. next gen. bb exp.

  41. Measuring mass hierarchy • Long baseline accelerator neutrinos • Through Matter effects • Expensive, project-X/LBNE in Fermilab/BNL • Atmospheric neutrinos • Very weak signal • Huge detector, Expensive • Reactor neutrinos • Method: distortion of energy spectrum • Enhance signature: Transform reactor neutrino L/E spectrum to frequency regime using Fourier formalism • need Sin2(2q13) > 0.02 • Need to know DM223 S.T. Petcov et al., PLB533(2002)94 S.Choubey et al., PRD68(2003)113006 J. Learned, PRD 78(2008)071302

  42. Fourier transformation of L/E spectrum L/E spectrum • Frequency regime is in fact the DM2 regime  enhance the visible features in DM2 regime • Take DM232 as reference • NH: DM231 > DM232 , DM231 peak at the right of DM232 • IH: DM231 < DM232 , DM231 peak at the left of DM232 42

  43. Our efforts • Clear distinctive features: • FCT: • NH: peak before valley • IH: valley before peak • FST: • NH: prominent peak • IH: prominent valley • Better than power spectrum • No pre-condition of Dm223 L. Zhan et al., PRD78:111103,2008 43

  44. Quantify Features of FCT and FST Baseline: 46-72 km Sin2(2q13): 0.005-0.05 Others from global fit Two clusters of RL and PV values show the sensitivity of mass hierarchy determination • To quantify the symmetry breaking, we define: RV/LV: amplitude of the right/left valley in FCT P/V: amplitude of the peak/valley in FST • For asymmetric Pee • NH: RL>0 and PV>0 • IH: RL<0 and PV<0 L. Zhan et al., PRD78:111103,2008 2008-07-17 44

  45. In reality Unfortunately, DM221 / DM223 ~ 3% L. Zhan, et. al., Phys.Rev.D79:073007,2009

  46. Requirement • Todetermine mass hierarchy at > 90% CL: • Baseline: ~ 58 km, determined by q12 • Reactor power > 24 GWth • Flux and detector size: ~ (250-700) ktyear • Ideally, sin22q13 > 0.02 & energy resolution < 2% • IF sin22q13=0.01, energy resolution < 2% & 700 ktyear • For sin22q13=0.02 , energy resolution < 3% & 700 ktyear • Overburden > 1000 MWE • ~ 60 km from Daya Bay • A huge ne detector with mass >20kt • currently the largest on is 1kt (KamLAND & LVD) 

  47. Scientific goal: a l0-50kt underground LS detector 60km from reactor • Neutrino Mass hierarchy • Precision mixing para. measurement: q12, D M212, DM231 Unitarity of the mixing matrix • Supernova neutrinos==〉betterthanSuperK • Geo-neutrinos==〉10 betterthanKamLAND • Atmospheric neutrinos==〉 SuperK • Solar neutrinos ? • High energy neutrinos • Point source: GRB, AGN, BH, … • Diffused neutrinos • High energy cosmic-muons • Point source: GRB, AGN, BH, … • Dark matter • Exotics • Sterile neutrinos • Monopoles, Fractionalchargedparticles,…. LVD+MACRO+KamLAND+ SuperK

  48. Precision measurement of mixing parameter • Fundamental to the Standard Model and beyond • Similarities point to a Grand unification of leptons and quarks • Constrain all PMNS matrix elements to < 1% ! Probing Unitarity of UPMNS to <1% level ! If we can spend (0.1-0.5)B$ for each B/C/superB factories to understand UCKM (~ 1-2 elements for each factory), why not a super-reactor neutrino experiment(~ 3 elements) to understand UPMNS ?

  49. Supernova neutrinos • Less than 20 events observed so far (2001 Noble prize) • Assumptions: • Distance: 10 kpc (our Galaxy center) • Energy: 31053 erg • Ln the same for all types • Tem. & energy • Many types of events: • ne + p  n + e+, ~ 3000 correlated events • ne+ 12C  13B* + e+, ~ 10-100 correlated events • ne + 12C  11N* + e-, ~ 10-100 correlated events • nx+ 12C nｘ+ 12C*, ~ 600 correlated events • nx + p  nｘ+ p, single events • ne + e-  ne + e-, single events • nx + e- nｘ+ e-, single events • T(ne) = 3.5 MeV, <E(ne)> = 11 MeV • T(ne) = 5 MeV, <E(ne)> = 16 MeV • T(nx) = 8 MeV, <E(nx)> = 25 MeV SuperK can not see these correlated events

  50. What to do with Supernova neutrinos • Energy spectra & fluxes of all types of neutrinos • tem. and average energy of neutrinos • Understand Supernovae • neutrino properties: mass, mixing, … • Earth tomography • Neutrino models • … • Arrival time of all types of neutrinos  absolute neutrino mass

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