KM3NeT Collaboration meeting, Marseille, 29-31 January 2013 ORCA Summary Uli Katz ECAP / Univ. Erlangen 31.01.2013

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, 31.01.2013

In a nutshell … Exciting possibility: Measure neutrino mass hierarchy using oscillations of atmospheric neutrinos in Earth matter (Akhmedov, Razzaque, Smirnov, arXiv:1205.7071) 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, 31.01.2013

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, 31.01.2013

U. Katz: ORCA, 31.01.2013

The Akhmedov/Razzaque/Smirnov paper (1) U. Katz: ORCA, 31.01.2013

The Akhmedov/Razzaque/Smirnov paper (1) U. Katz: ORCA, 31.01.2013

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, 31.01.2013

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, 31.01.2013

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, 31.01.2013

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, 31.01.2013 11

New plots... cos(q) = -0.8 source of uncertainty 12 U. Katz: ORCA, 31.01.2013 12

New plots... cos(q) = -0.6 source of uncertainty 13 U. Katz: ORCA, 31.01.2013 13

New plots... cos(q) = -0.4 source of uncertainty 14 U. Katz: ORCA, 31.01.2013 14

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, 31.01.2013 15

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, 31.01.2013 16

U. Katz: ORCA, 31.01.2013

Simulation chain U. Katz: ORCA, 31.01.2013

Detector U. Katz: ORCA, 31.01.2013

Effective volume? Zenith angle. U. Katz: ORCA, 31.01.2013

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, 31.01.2013

Mass hierarchy significance – NH – IH U. Katz: ORCA, 31.01.2013 22

Results of parameter fit 1 Mton*year ( NHtrue, NHfit ) --------------------------------------------------------------------------------------------------------- parameter central sigma sigma sigma name now now 1 Mtonyr 10 Mtonyr delta_m2_large 2.43e-3 8.0e-5 4.3e-5 1.8e-5 theta23 (deg) 38.4103 1.3 0.66 0.23 theta13 (deg) 8.93082 0.45 0.45 0.41 Fit working well. Good sensitivity to Dm2large & q23 ! nb: parameter fit is for one assumed MH U. Katz: ORCA, 31.01.2013 23

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, 31.01.2013