1. Mass Hierarchy Determination with WATCHMAN
R.Svoboda, Va. Tech., May

2. While we know neutrinos have mass from oscillation experiments, we still don’t know the neutrino mass ordering or absolute scale
KATRIN: sensitivity to 0.2 eV for mixture of masses corresponding ne
Similar limits on sum of neutrino masses from CMB measurements,
but indirect and very model dependent. Many Experiments propose
to try and measure mass hierarchy.

3. Dirac or
Majorana??!!

4. Are Neutrinos Majorana or Dirac?
2nd order nuclear double
beta decay – with no neutrinos!

5. The rate of the rare
neutrinoless double
beta decay process
depends critically on
the mass hierarchy.
Many experiments
worldwide need to
know this to fully
interpret their
results

6. Experiments Being Proposed
Long Baseline Neutrino Experiment (LBNE) $867M project in HEP
PINGU proposed NSF experiment in ICE CUBE
Hyper-Kamiokande in Japan
JUNO reactor experiment in China

7. <- Oscillation length of about 50 km
<-Oscillation lengths of about 2 km,
but slightly different!
Relative size of wavelength
(or frequency) depends
on hierarchy

8. Fourier Analysis to Determine the Mass Hierarchy

9. En (MeV) Rate (arbitrary units) q12 dip infinite statistics
perfect resolution
50 km
Normal Hierarchy
"classic" setup
for reactor MH
determination
small wiggles due
to q13
q12 dip
Rate (arbitrary units)
En (MeV)

10. En (MeV) NH IH Rate (arbitrary units) infinite statistics
perfect resolution
50 km NH IH
Rate (arbitrary units)
En (MeV)

11. Rate (arbitrary units)
infinite statistics
perfect resolution
50 km
Rate (arbitrary units)
L/E (m/MeV)

12. Power (arbitrary units)
infinite statistics
perfect resolution
50 km
Power (arbitrary units)
Dm2 (eV2)

13. Power (relative to peak)
infinite statistics
perfect resolution
50 km
Power (relative to peak)
Dm2 (eV2) relative to peak

14. Effects of Energy Resolution are very significant
Rate (arbitrary units)
L/E (m/MeV)
L/E (m/MeV)

15. Power (relative to peak)
infinite statistics
3.5% resolution
50 km
Power (relative to peak)
Dm2 (eV2) relative to peak

16. Rate (arbitrary units)
infinite statistics
perfect resolution
13 km
WATCHMAN with
Liquid Scintillator
Rate (arbitrary units)
L/E (m/MeV)

17. Power (arbitrary units)
infinite statistics
perfect resolution
13 km
Power (arbitrary units)
Dm2 (eV2)

18. Power (relative to peak)
infinite statistics
perfect resolution
13 km
Power (relative to peak)
Dm2 (eV2) relative to peak

19. Effects of Energy Resolution NOT significant
at 13 km due to much broader wiggles.
3.5% Energy Resolution
0% Energy Resolution
Rate (arbitrary units)
L/E (m/MeV)
L/E (m/MeV)

20. Test Statistic: Independent of absolute value of Dm2
(L-H)/(H+L)
A<0 for "IH-like"
A>0 for "NH-like"
LOW
HIGH

21. overlap region A Perry to Fairport 100 years 3.5% smearing
includes statistical uncertainty
no osc param uncertainty
100 fake experiments of each
Normal Hierarchy (NH)
Inverted
Hierarchy (IH)
overlap region A

22. A (modified scale) Perry to Fairport 100 years no energy smearing
include statistics
no osc param uncertainty
1000 fake experiments
Nature chooses ONE
set of oscillation
parameters – so need
to look at possible
universes and ask in how
many the hierarchy is
resolved to 95% c.l. or better
A (modified scale)

23. Perry to Fairport
100 years
no energy smearing
include statistics
no osc param uncertainty
100 universes each with
1000 experiments
Universes where
NH is correct
In this case, WATCHMAN+LS
can determine the mass hierarchy
99% (97%) of the time if the
hierarchy is Normal (Inverted)
Universes where
IH is correct

24. Perry to Fairport
100 years
no energy smearing
include statistics
oscillation params smeared
100 universes each with
2000 experiments
Universes where
NH is correct
In this case, WATCHMAN+LS
can determine the mass hierarchy
19% (23%) of the time if the
hierarchy is Normal (Inverted)
clear dependence on exact
combinations of oscillation
parameters – UNDER
INVESTIGATION
Universes where
IH is correct

25. C.Golzales-Garcia, TAUP 2013

26. Possible improvements in parameter measurements from JUNO

27. Conclusions
WATCHMAN sensitivity depends on exact configuration of oscillation parameters – maybe present as function of two most sensitive?
Need to study more realistic exposures. WATCHMAN+LS may have to be larger.
Need to optimize test statistics test