1. Searching for an underground national lab in China Yifang Wang July 23, 2008

2. Motivation for an underground lab • Particle physics • Double beta decays • Nucleon decays • Atmospheric/solar neutrinos • Reactor neutrinos • Long baseline neutrino oscillations • Cosmic-rays • ….. • Gravitational waves • Environment • Geology • …

3. A few ideas discussed in the community • Very long baseline neutrino oscillation • Beams from J-PARC to Beijing, L~ 2000 km • A (0.1-1.0)Mt water Cerenkov Detector • Very very long baseline neutrino oscillation • Beams from Fermilab to Beijing • Gravitational waves • Dark matters

4. Measure CP, sin22q13 and Dm223 sign— very long baseline experiment

5. J-PARC to BeijingL=2100 km, 1300 events/100kt-Yr

6. Study of density effects: Lian-You Shan et al., Phys. Rev. D 68 (2003) 013002

7. A typical nm CC event

8. 1m*1m*13m尺寸的水箱模型

10. A candidate underground lab • An aviation museum near Beijing • Total Volume: 250K m3 • Overburden: 150 m Good enough for accelerator based neutrino experiments but not deep enough for a general purpose low background underground lab.

11. Requirements for a general purpose underground lab • Overburden > 1000 MWE • Size of the underground lab > (0.1-1.0) Mt • Rock quality: good easy construction • Tunnel length: short enough to have acceptable cost • Traffic: easy enough • Logistics: obvious

12. Possibilities and (failed) experience • Existing underground, abandoned military facilities: for its good infrastructure, usually large underground halls • Next to traffic tunnels: to save money of tunneling, similar to that of Gran Sasso • Brand new underground experimental halls

13. Change the direction: look at physics opportunities first • Double beta decays • Nucleon decays • Atmospheric/solar neutrinos • Reactor neutrinos: CP, theta_13, mass hierarchy • Long baseline neutrino oscillations • Cosmic-rays • ….. • Gravitational waves

14. Neutrino mass hierarchy • Three unknowns in neutrino oscillation: • 1. delta-CP phase • 2. theta13 value • 3. mass hierarchy 2008-07-17 14

15. Principle L/E spectrum E spectrum EL/E Three lines, one is for 1 – P21 oscillation, the other two are Pee oscillation with NH and IH. difficult to discriminate using L/E spectrum 2008-07-17 15

16. First attempt: power spectrum of Fourier transform • Conclusion: need Sin2(2q13) > 0.02 • J. Learned et al., HEP-ex/0612022

17. Fourier transform L. Zhan et al., hep-ex/0807.3203 • t = L/E, F(L/E) is neutrino spectrum in L/E space. • Pee is a periodic function in L/E space with oscillation frequency proportional to • In the range the P31 and P32 component is distinctive in the FCT and FST spectrum. 2008-07-17 17

18. FCT and FST spectrum Baseline = 60 km Best fit neutrino mixing paras • Distinctive features: • 1 – P21 is weak • P31 and P32 • Symmetric P31 and P32 are broken in Pee • FCT: • NH: peak before valley • IH: valley before peak • FST: • NH: prominent peak • IH: prominent valley 2008-07-17 18

19. Quantify Features of FCT and FST • To quantify the symmetry breaking, we define: RV and LV: the amplitude of the right and left valley in FCT spectrum. P and V: the amplitude of the peak and valley in FST spectrum. • For symmetric P31 and P32 RL = 0, PV = 0 • For asymmetric Pee • NH: RL>0 and PV>0 • IH: RL<0 and PV<0 2008-07-17 19

20. Baseline and theta13 Baseline: 46-72 km Sin2(2q13): 0.005-0.05 Other mixing parameters from global fit Two clusters of RL and PV values show the sensitivity of mass hierarchy determination. 2008-07-17 20

21. Limit of sin2(2q13) Clear distinctive features Better than power spectrum 2008-07-17 21

22. Best location: Daya Bay • Th. power: 12 GW ~ now, 18 GW ~ 2010, 24 GW ~ 2015

23. Detector: Huizhou - Baiyunzhang Altitude: ~ 1000 m, highest in Dongguan/Huizhou

25. 1.6 km tunnel

27. A promising underground lab • Ideal location for a (1-10)kt reactor neutrino experiment: • Mass hierarchy • Precision q12 measurement • Supernova neutrinos • Geoneutrinos • Sterile neutrinos • …. • Enough overburden as a generic underground national lab for many other applications • A detailed study and detector design will be carried out in the next few months

28. Summary • Searches Starting from a generic underground lab not successful in the past • JPARC-Beijing long baseline exp. uncertain • A neutral continuation of Daya Bay: • Using Daya Bay as the world largest reactor complex as the neutrino source • Using current Daya Bay exp. as the near detector • Construct a generic underground lab at Baiyunzhang • Construct an (1-10) kt electron antineutrino detector A bright future of particle physics in China