Measuring the neutrino mass hierarchy with PINGU Justin Evans 11th - PowerPoint PPT Presentation

Measuring the neutrino mass hierarchy with PINGU Justin Evans 11th May 2012

Oscillation parameters Smallest mass splitting Ø ‘ Solar ’ mass splitting Require L/E ~ O (10 5 km/GeV) Solar neutrinos Ø SNO, Borexino, etc Reactor neutrinos over O (100 km) Ø KamLAND 8.0x10 -5 eV 2 2

Oscillation parameters Largest mass splitting Ø ‘ Atmospheric ’ mass splitting Require L/E ~ O (10 3 km/GeV) Atmospheric neutrinos 2.3x10 -3 eV 2 Ø Super-K, MACRO, Soudan2, etc Accelerator neutrinos Ø MINOS, T2K, NO ν A, etc 3

The PMNS matrix ⎛ ⎞ ⎛ ⎞ ⎛ ⎞ cos θ 13 sin θ 13 e − i δ cos θ 12 sin θ 12 1 0 0 0 0 ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ cos θ 23 sin θ 23 U = 0 − sin θ 12 cos θ 12 ⎜ ⎟ 0 1 0 0 ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ ⎜ ⎟ − sin θ 23 cos θ 23 − sin θ 13 e i δ cos θ 13 0 ⎝ ⎠ ⎝ ⎠ 0 ⎝ ⎠ 0 0 1 Reactor & Atmospheric & Solar & reactor accelerator accelerator θ 12 ~ 34 o θ 13 ~ 9 o θ 23 ~ 45 o θ 13 was measured in 2012 Ø Daya Bay, Reno, T2K, Double Chooz, MINOS Three unknowns remain Ø CP violating phase δ Ø Octant of θ 23 : only sin 2 (2 θ 23 ) has been measured; θ 23 < 45 o or θ 23 > 45 o ? Ø Mass hierarchy: the sign of Δ m 2 32 4

The mass hierarchy m 2 ν µ ν e ν τ m 2 ν µ ν e ν τ ν 2 ν 3 21 = 7 . 8 × 10 − 5 eV 2 ∆ m 2 ν 1 32 = 2 . 4 × 10 − 3 eV 2 ∆ m 2 32 = 2 . 4 × 10 − 3 eV 2 ∆ m 2 ν 2 21 = 7 . 8 × 10 − 5 eV 2 ∆ m 2 ν 3 ν 1 Normal Inverted 5

Neutrino mass Why are neutrinos so light? Ø Orders of magnitude lighter than all other massive particles What is the mass generation mechanism? Ø See-saw model? 6

Neutrino mass 1 Neutrinoless double beta decay disfavoured by 0 n 2 b Disfavoured by EXO and KamLAND-Zen can tell us about neutrino mass Ø What is the absolute mass? 10 - 1 Ø Are neutrinos Majorana 2 < 0 D m 23 » m ee » in eV disfavoured by cosmology Majorana mass opens the way to 10 - 2 see-saw models 2 > 0 D m 23 Knowledge of the mass 10 - 3 hierarchy is a key ingredient in this search 99 % CL H 1 dof L 10 - 4 10 - 4 10 - 3 10 - 2 10 - 1 1 lightest neutrino mass in eV 7

Neutrino mass 1 Neutrinoless double beta decay disfavoured by 0 n 2 b Disfavoured by EXO and KamLAND-Zen can tell us about neutrino mass Ø What is the absolute mass? 10 - 1 Ø Are neutrinos Majorana Current experiments 2 < 0 D m 23 » m ee » in eV disfavoured by cosmology Future experiments Majorana mass opens the way to 10 - 2 see-saw models 2 > 0 D m 23 Knowledge of the mass 10 - 3 hierarchy is a key ingredient in this search 99 % CL H 1 dof L 10 - 4 10 - 4 10 - 3 10 - 2 10 - 1 1 lightest neutrino mass in eV 8

MINOS measurements 9

Neutrino Reactor neutrinos sources Atmospheric neutrinos Beam neutrinos 10

Massive detectors The challenge in neutrino physics is statistics Ø We need to instrument kiloton or even megaton detectors H 2 O is an excellent detection medium Ø Huge natural bodies of water and ice exist if we can make use of them 11

IceCube Ø The world’s biggest neutrino detector Ø 1 km 3 of ice 12

IceCube Cerenkov light µ ν µ 13

Highest energy neutrinos IceCube has observed two PeV- energy neutrino candidates Ø Highest energy neutrinos ever observed Events 26 more high-energy candidates at lower energies Inconsistent with standard atmospheric neutrino backgrounds at 4.1 σ 14 Total collected PMT charge

A high energy IceCube event 15

Neutrinos from the sky 10 MeV 100 MeV 1 GeV 10 GeV 100 GeV 1 TeV 10 TeV 100 TeV 1 PeV 10 PeV Deep Super-K IceCube ANITA Core PINGU Borexino ORCA SNO PINGU will study atmospheric neutrino oscillations in the 10-20 GeV region Ø Providing megaton-scale statistics Ø ORCA is a similar proposed extension to ANTARES in the Mediterranean

PINGU 40 new strings in the central region of IceCube & DeepCore Ø 20 m between strings Ø 5 m vertically between DOMs Energy threshold down to a few GeV 17

A megaton detector 4 4 Effective mass / MTon 3.5 eff 3 3 2.5 2 Preliminary 2 1.5 1 1 0.5 0 5 10 15 20 25 30 Energy (GeV) Energy / GeV Ø E fg ective volume for muon neutrinos 18

Cosmic muon veto IceCube surrounds PINGU Ø This can be used to veto cosmic Muon intensity muons The resulting cosmic muon rate is comparable to that of deep mines Depth 19

Atmospheric neutrinos Cosmic rays strike the upper atmosphere Ø Neutrinos produced from pion and muon decay Produces a 2:1 ν µ : ν e ratio Ø Fewer ν e at higher energies when muons hit the ground before decaying Antineutrino interaction cross section is a factor of ~2 lower than for neutrinos

Neutrino oscillations 7 MINOS, 2012 90% best fit ANTARES Super-K, 2012, 90% ANTARES, 68% 6 best fit IceCube ANTARES, 90% IceCube-79, 68% best fit MINOS IceCube-79, 90% ) 5 2 eV -3 | (10 4 2 m Δ | 3 2 0.4 0.5 0.6 0.7 0.8 0.9 1 2 sin (2 ) θ 23 Ø DeepCore has already been used to measure the atmospheric neutrino oscillation parameters 21

The MSW e fg ect Atmospheric neutrinos pass through the Earth Ø Feel an interaction with the Earth’s matter Electron neutrinos feel an additional interaction Ø Acts like a refractive index Ø This e fg ectively changes the mixing angles ν x ν x ν x x - ν e e - W Z W e - ν e e - e - ν e e - Electron flavour All flavours 22

Preliminary Reference Earth Model (PREM) Phys. Earth. Plan. Int. 25 , 297 (1981) The Earth Transition zone & outer mantle Inner mantle Inner core Outer core Three distinct zones of density Ø Sharp changes in density between the zones 23

The Earth Radius / km Radius / km Ø The di fg erent regions can be probed by measuring the zenith angle of the neutrino 24

Neutrino oscillations in vacuum ✓ ∆ m 2 L ◆ P ( ν α → ν β ) = sin 2 (2 θ ) sin 2 4 E 32 = 2 . 32 × 10 − 3 eV 2 ∆ m 2 sin 2 (2 θ 23 ) = π 4 Lines of constant L/E 25

Neutrino oscillations in matter cos θ z = -0.84 Increasing Outer core density 32 = 2 . 32 × 10 − 3 eV 2 ∆ m 2 sin 2 (2 θ 23 ) = π 4 Neutrinos Normal hierarchy 26

Neutrino oscillations in matter cos θ z = -0.84 Increasing Outer core density 32 = 2 . 32 × 10 − 3 eV 2 ∆ m 2 sin 2 (2 θ 23 ) = π 4 Neutrinos Inverted hierarchy 27

Antineutrinos Neutrinos Normal hierarchy Inverted hierarchy 28

Why does this happen? + for neutrinos CC interactions of - for antineutrinos ν e with matter ! ✓ ◆ √ − ∆ m 2 ∆ m 2 i d ✓ ◆ 4 E cos(2 θ ) ± 2 G F N e 4 E sin(2 θ ) ν e ν e = ∆ m 2 ∆ m 2 ν x d t 4 E sin(2 θ ) 4 E cos(2 θ ) ν x This modifies the neutrino mixing, producing effective mixing angles in matter: ∆ m 2 2 E sin(2 θ ) tan(2 θ m ) = p ∆ m 2 2 E cos(2 θ ) ⌥ 2 G F N e - for neutrinos + for antineutrinos This has a resonance condition for neutrinos in the normal hierarchy or antineutrinos in the inverted hierarchy 29

Neutrinos, NH PINGU PINGU cannot distinguish neutrinos from antineutrinos Ø No magnetic field But the neutrino and antineutrino cross sections di fg er by a factor of two Antineutrinos, NH Ø Statistically, there will be an observable di fg erence between the hierarchies Ø And at the megatonne scale, PINGU will have plenty of statistics 30

Sample reconstructed events ν true direction µ true direction 1.7 GeV ν µ 4.4 GeV ν µ µ fitted direction Size of circles: N γ . 31 Color: t γ . 4.7 GeV ν e 11.8 GeV ν µ

Energy resolutions 2200 Energy 1 2400 Energy 1 2200 2000 2000 1800 0.8 0.8 ν µ ν e 1800 1600 ν ν 1600 1400 Frac. resolution on Frac. resolution on 0.6 0.6 1400 1200 Preliminary Preliminary 1200 1000 1000 0.4 0.4 800 800 600 600 0.2 0.2 400 400 200 200 0 0 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 True neutrino Energy (GeV) True neutrino Energy (GeV) Red line is median Red line is median Red line shows median resolutions Reconstruction subdivides the DOM readout pattern as a function of time Ø Fits to a number of parameters: interaction position and time, μ track length and direction, hadronic cascade energy 32

Zenith angle resolutions 90 90 2500 ) ) ° 2200 ° Zenith ( Zenith ( 80 80 2000 2000 1800 70 70 ν µ ν e 1600 60 60 1400 1500 ν ν 50 50 Resolution on Resolution on 1200 Preliminary Preliminary 40 40 1000 1000 30 800 30 600 20 20 500 400 10 10 200 0 0 0 0 0 5 10 15 20 25 30 0 5 10 15 20 25 30 True neutrino Energy (GeV) True neutrino Energy (GeV) Red line is median Red line is median Red line shows median resolutions Reconstruction subdivides the DOM readout pattern as a function of time Ø Fits to a number of parameters: interaction position and time, μ track length and direction, hadronic cascade energy 33