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

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 …

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

Measure CP, sin 2 2  13 and  m 2 23 sign — very long baseline experiment

J-PARC to Beijing L=2100 km, 1300 events/100kt-Yr

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

A typical  CC event

1m*1m*13m 尺寸的水箱模型

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.

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

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

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

Neutrino mass hierarchy Three unknowns in neutrino oscillation: –1. delta-CP phase –2. theta13 value –3. mass hierarchy

Principle E  L/E E spectrum L/E spectrum Three lines, one is for 1 – P 21 oscillation, the other two are P ee oscillation with NH and IH.  difficult to discriminate using L/E spectrum

First attempt: power spectrum of Fourier transform Conclusion: need Sin 2 (2  13 ) > 0.02 J. Learned et al., HEP- ex/

Fourier transform t = L/E, F(L/E) is neutrino spectrum in L/E space. P ee is a periodic function in L/E space with oscillation frequency proportional to In the range the P 31 and P 32 component is distinctive in the FCT and FST spectrum L. Zhan et al., hep-ex/

FCT and FST spectrum Distinctive features: –1 – P 21 is weak –P 31 and P 32 Symmetric P 31 and P 32 are broken in P ee FCT: –NH: peak before valley –IH: valley before peak FST: –NH: prominent peak –IH: prominent valley Baseline = 60 km Best fit neutrino mixing paras

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<

Baseline and theta13 Baseline: km Sin 2 (2  13 ): Other mixing parameters from global fit Two clusters of RL and PV values show the sensitivity of mass hierarchy determination

Limit of sin 2 (2  13 ) Clear distinctive features Better than power spectrum

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

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

1.6 km tunnel

A promising underground lab Ideal location for a (1-10)kt reactor neutrino experiment:  Mass hierarchy  Precision  12 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

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