neutrino hierarchy determination from a galactic supernova burst

Neutrino hierarchy determination from a galactic supernova burst

David WebberAugust 20, 2010

H. Duan and A. Friedland, http://arxiv.org/abs/1006.2359

Neutrino energies at infinity(1 second time-slice of 10-second burst spectrum?)

Consider 3 detector possibilities

• Water Cherenkov (WC) with 30% phototube coverage and high quantum-efficiency tubes– This is roughly equivalent to Super-K’s coverage

• WC, 15% coverage, HQE• Liquid Argon

n reaction cross-sections

https://wiki.bnl.gov/dusel/index.php/Event_Rate_Calculations

nepe nDominant reaction:

Water Argon

Dominant reaction:KeAr 40-40 en

Normal Hierarchy: Observed Spectra(accounts for detector acceptance)

WC 30% coverage

n flux at detector

WC 15% coverage Liquid Ar

Inverted Hierarchy: Observed Spectra(accounts for detector acceptance)

WC 30% coverage

n flux at detector

WC 15% coverage Liquid Ar

How many events are needed to distinguish normal from inverted hierarchy in water?

Normal Hierarchy Inverted Hierarchy

102 eventsindistinguishable

•Water Detector•30% PMT coverage•HQE tubes•IBD reaction•c2 shown for “wrong” fit

105 eventsclearly distinguishable

How many events for 3 sigma exclusion?

• Note: c2 is not the same as Gaussian• “3 sigma” = 99.73% confidence• 99.73% confidence is…– c2/NDF of 1.6 for 57 degrees of freedom– c2/NDF of 1.8 for 34 degrees of freedom

c2 vs. events, WC, 30% coverage

Normalhierarchy

Invertedhierarchy

Normal fit Inverted fit

•Water Detector•30% PMT coverage•HQE tubes•IBD reaction ~103.5-3.6 = 3200-4000 events are needed

c2 vs. events, WC, 15% coverage

Normalhierarchy

Invertedhierarchy

Normal fit Inverted fit

•Water Detector•15% PMT coverage•HQE tubes•IBD reaction ~103.5-3.6 = 3200-4000 events are needed

How many events are needed to distinguish normal from inverted hierarchy in argon?

Normal Hierarchy Inverted Hierarchy

102 eventsindistinguishable

105 eventsclearly distinguishable

•Liquid Argon•c2 shown for “wrong” fit

c2 vs. events, liquid argon

Normalhierarchy

Invertedhierarchy

Normal fit Inverted fit

~102.7-2.8 = 500-630 events are needed

Normal and inverted hierarchy neutrino spectra for 99.7% confidence.

Normal Hierarchy Inverted Hierarchy

Water Cherenkov30% PMT coverage4000 events

Liquid Argon630 events

Summary• WC phototube coverage has little impact on resolving the

hierarchy.– 15% is as good as 30%

• To resolve the hierarchy…– ~4000 events must be observed in water, or– ~630 events must be observed in argon

• If a SNB occurs at 8.5 kpc…– Need 18.3 kT water– Need 7.6 kT Ar– a 100kT water module would have better statistics than a 17 kT LAr

module– The LAr module would show more interesting spectral features

Volume estimates based on http://arxiv.org/abs/astro-ph/0701081This study was based on repository revision 754