Background Rejection and Alternative ScintillatorPMT Configurations Steve Biller

Background Rejection and Alternative Scintillator/PMT Configurations Steve Biller, Oxford

e- ne g e-e+ g e+ e- p n n n Problematic Backgrounds Cherenk/Scint Discrimination ? p ne 9 Li (Qb = 13. 6 Me. V) e 8 Be* (35%) n a a Accidentals from Fiducial cuts plus SOME Cherenk/Scint Discrimination ? (2. 5 Me. V) e- and/or g (Various Decays) For ES, troublesome, low E, long-lived, muon spallation products mostly involve e+ Cherenk/Scint Discrimination ?

Cherenkov Light: ~50% “SNO-equivalent” Photocathode Coverage (light concentrators) ~25 hits/Me. V + ‘fast’ Wavelength Shifter (scaling from SNO) Scintillation Light: Slooooow Scintillator Tune chemistry to yield (pure pseudocumine: t ~ 28 ns) ~25 -50 hits/Me. V (Energy resolution based on total of 50 -75 hits/Me. V)

PC + SMALL amount of PPO

Also add bis-MSB to shift Cherenkov light?

Why Not Use Concentrators Anyway? ? Degradation? 1 -2% per year in water for SNO… should be much better for mineral oil PLUS neutron peak continually calibrates energy scale Advantages: Less scint for same light yield – better attenuation length OR Increased light for same scint – pulse-shape discrimination OR Can pursue Cherenk/scint by just changing the chemistry More options !! (“What’s not to like? ”)

Plan of Attack: • Benchtop tests being constructed to measure light yield and time spectrum for various mixtures (Gabriel Orebi-Gann) • Identify supplier of Al strips for concentrators • Start accelerated ageing tests for strips in mineral oil • Input will be used for detailed simulations (SNOMAN) SNOMAN Update Completed: Nearly Completed: Added mineral oil as medium; Gd cascade modelled (Nick); PMT geometry reconfigured More detailed handling of additives; Reactor “Event Generator”; Official policy on external distribution.

And Now For Something Completely Different…

Rejection of 9 Li and 8 He (Using spatial and timing information) Half-lives: 0. 1 -0. 2 sec Muon rate at far site: ~5 Hz (0. 2 sec between muons) Need to deal with ~2 muon tracks on average for each candidate neutrino event (~100/day) Fiducial cut needs to include up to ½ meter from muon tack

Fraction of fiducial volume: 2 x [p (0. 5 m)2] x 5 m = 0. 10 3 4/3 p (2. 6 m) Thus, need to know systematics on fiducial cut to better then ~5%

Handles 1) Direct calibration corresponds to a vertex reconstruction systematic of 1 -2%, which about what we have for SNO 2) Comparison in limit of ‘identical’ detectors apply same cuts to near detector – dominated by neutrino interactions, so indicates what’s been thrown out 3) Use Spallation Products particularly 12 B, which can be tagged with muon (0. 02 s half-life) and produces electrons in same energy range 4) Compare with applying the “right cuts at the wrong time” to try to assess the contamination based on the difference, then just model this without making any ‘cuts’ in neutrino analysis

Summary A separated Cherenkov measurement would be VERY nice (and maybe we could even do this… work in progress) We should SERIOUSLY consider using light concentrators in any case (preserves flexibility) 9 Li and 8 He should not really be a problem for us