1. KM3NeT Collaboration meeting, Marseille, 29-31 January 2013
ORCA Summary
Uli Katz
ECAP / Univ. Erlangen

2. Preamble
We will have to take a difficult, far-reaching and irreversible decision in a few months. This decision will impact on our future and possibly that of other science communities.
Ultimate scientific rigor will be required, preoccupations must be avoided.
Please don’t take the fat that I am presenting the ORCA summary as any sort of bias or indication for this decision.
U. Katz: ORCA,

3. In a nutshell …
Exciting possibility: Measure neutrino mass hierarchy using oscillations of atmospheric neutrinos in Earth matter (Akhmedov, Razzaque, Smirnov, arXiv: )
Requires measuring precisely zenith angle and energy of νe and νμ in energy range 5-20 GeV  Densely instrumented detector  Can we do it with KM3NeT technology?
Feasibility study: ORCA = Oscillation Research with Cosmics in the Abyss
U. Katz: ORCA,

4. Neutrino oscillation parameters
Parameters: 3 mixing angles known (θ13 first measured 2012) 2 Δm2 values 1 sign unknown 1 absolute mass not measurable from oscillations
Unknown: Mass hierarchy
Can only be determined from neutrino oscillations in matter  atmospheric neutrinos with Eν=3–20eV through Earth
normal
hierarchy
(NH)
„one of the most
important measurements
in particle physics“
inverted
hierarchy
(IH)
U. Katz: ORCA,

5. U. Katz: ORCA,

6. The Akhmedov/Razzaque/Smirnov paper (1)
U. Katz: ORCA,

7. The Akhmedov/Razzaque/Smirnov paper (1)
U. Katz: ORCA,

8. What needs to be done to scrutinise this?
Check phenomenology and dependence on parameter uncertainties
Devise suitable simulation, trigger, event classification and reconstruction algorithms
Assess:
statistics
resolutions and efficiencies
significance of measurement
systematics
Determine detector size required
U. Katz: ORCA,

9. Actions and objectives
Involved in KM3NeT: APC, Bologna, Catania, CPPM, ECAP, HOU, Nikhef, … Coordinator: Antoine Kouchner
Parallel: PINGU in IceCube cooperation, common meetings, exchange of tools
For several reasons: Decision whether to go forward latest fall 2013  Detailed Report by summer 2013
May severely impact on our plans: can be a chance, may be a curse …
U. Katz: ORCA,

10. Some (preliminary) results
All plots shown in the following are preliminary but public (plus several more, to be disseminated asap)
A few examples of studies performed in the past months:
Impact of uncertainties of oscillation and Earth density profile parameters
Simulations
Reconstruction approaches
First sensitivity estimate
U. Katz: ORCA,

11. New plots... cos(q) = -1 dominant source of uncertainty
… like Fig 2 of Akhmedov et al …. but with error bands
dominant
source of
uncertainty
U. Katz: ORCA, 11

12. New plots... cos(q) = -0.8 source of uncertainty 12
U. Katz: ORCA, 12

13. New plots... cos(q) = -0.6 source of uncertainty 13
U. Katz: ORCA, 13

14. New plots... cos(q) = -0.4 source of uncertainty 14
U. Katz: ORCA, 14

15. Effect of 1s parameter uncertainties on relative rate (NH)
Dm2 solarl
Dm2 atm.
q23
cos(zenith)
negligible
log(E/GeV)
q13
q12
negligible
U. Katz: ORCA, 15

16. Earth density profile.
50 km limit shift – no impact
assumption of the flat density profile – no impact (p=0.999 at 3 σ)
reducing the overall density by 10% - p=0.996
density is increased by 10% - p=0.872
varying the overall density factor by 1% - no effect
Second the Earth density profile was studied.
50km layers shift has no impact on the p-value
assumption of the flat density profile – no impact as well
reducing the overall density by 10% no impact
increasing the density by the same value – small impact
and finally varying the overall density factor by 1% - no impact
4 different biases were introduced which are basically larger than known uncertainties or even unphysical.
PAUSE
introduced biases are larger than the known uncertainties or even unphysical
U. Katz: ORCA, 16

17. U. Katz: ORCA,

18. Simulation chain
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19. Detector
U. Katz: ORCA,

20. Effective volume?
Zenith angle.
U. Katz: ORCA,

21. Muon energy resolution
BBfit - vertex contained – timing
Similar results from other studies (Catania, HOU)
Energy from range
Quantiles 16%-84% (~rms)
Function of muon energy
U. Katz: ORCA,

22. Mass hierarchy significance
– NH
– IH
U. Katz: ORCA, 22

23. Results of parameter fit
1 Mton*year ( NHtrue, NHfit )
parameter central sigma sigma sigma
name now now 1 Mtonyr Mtonyr
delta_m2_large e e e e-5
theta23 (deg)
theta13 (deg)
Fit working well.
Good sensitivity
to Dm2large & q23 !
nb: parameter fit is for one assumed MH
U. Katz: ORCA, 23

24. Conclusion
The measurement of the neutrino mass hierarchy with atmospheric neutrinos is difficult but not hopeless
Very quick ramp-up of activities, lots of progress
Energy reconstruction and event classification difficult, new/refined methods and algorithms are needed
Open questions and concerns:
Intrinsic limitations, e.g. due to different kinematics of neutrino/antineutrino interactions, multiple scattering in water, missing light from hadronic shower?
Required resolutions achievable?
Need for atmospheric muon veto?
My plea: Perseverance pays out, we must not give up too early.
U. Katz: ORCA,