Physics Potential of a Liquid Shield Steve Biller

Physics Potential of a Liquid Shield Steve Biller, Oxford

1) Statistical determination of 9 Li/8 He Background Correlated backgrounds with large uncertainties in production rates (0. 016 – 0. 07 per day per tonne at 450 mwe from Project Description) 9 Li : t 1/2 = 0. 18 s, Q=13. 6 Me. V 8 He: t 1/2 = 0. 12 s, Q=10. 7 Me. V So, with a muon rate of 5. 4 Hz in the fiducial volume, a simple time-cut is not possible

However, “actual” muon time distribution: time production more likely production less likely time DT

~50% of neutrino events ~75% of spallation events

Assume neutrino event rate at far site is 1. 8 per tonne per day Assume 9 Li/8 He event rate at far site is 0. 016 per tonne per day (lower end of prediction) For each 65 tonne volume: In 1 year, we would expect to see a total of: (1. 8)(65)(365) = 42705 neutrino events and (0. 016)(65)(365) = 380 9 Li/8 He events Total number of coincident events expected for DT < 0. 14 s : (0. 5)(42705) + (0. 75)(380) = 21638 Total number of coincident events expected for DT > 0. 14 s : (0. 5)(42705) + (0. 25)(380) = 21448 0. 9 s difference… not much!

Impose energy cut, run with both far detectors for 2 years… this goes to about 2. 5 s (somewhat more interesting) HOWEVER Silo design consists of 9 tanks, each with ~70 tonnes of liquid. If filled with mineral oil + scintillator + Gd, (don’t need as much scint, need very little Gd, so could be done economically) This would give an order of magnitude more statistics: With 2 silos in 1 year 4. 5 s (much better!)

2) Braidwood as a supernova detector Basic supernova neutrino interactions in mineral oil: ne + p ne + 12 C e+ + n 12 B + e+ 12 C ne + 12 C 12 N Q=1. 8 Me. V + e - + ne + e 12 C + e + + ne Q=14. 4 Me. V t 1/2(12 B) = 20 ms Q=17. 3 Me. V t 1/2(12 N) = 11 ms

n. X + p n. X + 12 C not well-defined signature, very low KE (~ke. V) n. X + p 12 C* + n. X 12 C ne + e - Q=15. 1 Me. V + g (15. 1 Me. V) plenty at energies > 20 Me. V, which would stand out well directional information if we can pick out Cherenkov light

Consider silo design (again, filled with oil+scint+Gd mixture) for the 4 -detector baseline 3. 15 kilotonnes! For supernova at 10 kpc: (>20 Me. V) Numbers in brackets are for an inverted mass heirarchy

• Signal are very large and distinct • Sensitivity to VERY small q 13 (constrained by 12 C interactions) • Some sensitivity to earth matter effects, but difficult… needs more work • Mass heirarchy should be easily distinguished for tan(q 13 ) > 10 -5 • Better than Kam. LAND, perhaps crucially so if supernova occurs at, say, 20 kpc • VERY distinct coincident trigger with Braidwood alone (extremely rapid alert? )

Exactly what unique measurements could Braidwood give? If a supernova went off with Super. K, Kam. LAND & Braidwood running: Super. K would have the best measurement of the flux, direction, time profile and, probably, spectrum for ne Braidwood would have the best measurement (by a factor of 3 over Kam. LAND) of the flux, time profile and spectrum ne and n. X along with kinematic threshold measurements of ne and likely better information at lower energies. for