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

ν Ultra high energy cosmic particles Protons Ø Relatively abundant Ø No directional information due to galactic magnetic fields Photons Ø Good directionality !"#$%&'&%('%)*"+,-)." /&'01%(%&*'%+ Ø Above TeV energies, absorbed 21-+#"3'0-+($4."* on cosmic background radiation Neutrinos Ø Good directionality Ø Free to propagate at high energies Ø Di ffj cult to detect 2

Ultra high energy neutrinos Detecting UHE neutrinos requires massive detectors Ø Megatonnes Ø At PeV energies, you can a fg ord to instrument coarsely as the events are large 3

IceCube Ø The world’s biggest neutrino detector Ø 1 km 3 of ice 4

IceCube Cerenkov light µ ν µ 5

ANTARES 6

ANTARES PMT array Cerenkov light Mediterranean sea Sea floor µ ν µ 7

Highest energy neutrinos IceCube has observed two PeV- energy neutrino candidates IceCube Preliminary Ø Highest energy neutrinos ever observed 26 more high-energy candidates at lower energies Inconsistent with standard atmospheric neutrino backgrounds at 4.1 σ 8

A high energy IceCube event 9

Lower energy neutrinos 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 KamLAND Double Chooz Daya Bay SNO Historically, the focus has been on increasing sensitivity to high energy neutrinos Now, these experiments are focusing on lowering the energy threshold Ø Meeting the atmospheric neutrino oscillation experiments The 1—20 GeV region is where precision atmospheric neutrino oscillation physics can be done Ø PINGU and ORCA can provide megaton-scale statistics

Neutrino oscillations 11

PINGU 100 PINGU Geometry V6 (Dozier) PINGU Geometry V6 (Dozier) Y (m) IceCube DeepCore 50 PINGU (HQE) 0 -50 26m -100 75m 125m -150 2 season deployment w/ additional ~1.5 years -100 -50 0 50 100 150 200 , estimate, to first order, X (m) 20—40 additional strings in the central region of IceCube Ø ~25 m spacing (c.f. 125 m for IceCube) Ø 60—100 PMT modules per string Principle already demonstrated by DeepCore ORCA is a similar extension planned for ANTARES 12

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 Approximately equal neutrino and antineutrino production Ø Antineutrino interaction cross section is a factor of ~2 lower

Matter e fg ects ν ν ν ν ν ν Atmospheric neutrinos interact with the Earth’s matter • MSW effect • Alters oscillation probabilities 14

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 15

The Earth Radius / km Radius / km Ø The di fg erent regions can be probed by measuring the zenith angle of the neutrino 16

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 17

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 18

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 19

Antineutrinos Neutrinos Normal hierarchy Inverted hierarchy 20

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 21

INO A detector that can distinguish neutrinos from antineutrinos can use this information to disentangle the mass hierarchy INO is a proposal that can do this Ø Magnetised iron calorimeter Ø The proposed mass is 50 kt, so the statistics are much smaller than PINGU or ORCA 22

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 23

Hierarchy determination This figure shows the situation for a perfect detector Ø Perfect angle and energy Significance ( σ ) resolution With neutrinos and antineutrinos combined, the oscillogram di fg ers significantly between the hierarchies Akhmedov et al., JHEP 02 , 082 (2013) 24

Finite detector resolution This figure includes a smearing to account for detector resolution Ø 3 GeV energy resolution Significance ( σ ) Ø 15 o angle resolution A di fg erence between the two hierarchies is still visible Akhmedov et al., JHEP 02 , 082 (2013) 25

Detector performance PINGU performance simulated using DeepCore algorithms Ø Energy resolution: ~(0.7 GeV + 0.2E ν ) Ø Angular resolution: 15 o to 8 o as energy increases from 5 GeV to 20 GeV More computationally intensive algorithms can improve on this 26

PINGU sensitivity 8 ) σ significance ( - 40 strings, 7 - high efficiency Preliminary 6 - 20 strings, prelim. event selection 5 of - 4 g- 20 strings, low efficiency 3 . 2 1 - 0 0 1 2 3 4 5 - Years of data Sensitivity depends on e ffj ciency, resolution, background, etc Even with pessimistic assumptions, the hierarchy can be determined at 3 σ after two years Ø 5 σ within five years 27

Advantages of PINGU Relatively cheap Ø Startup cost of $8M-$12M, then $1.25M per string Well understood technology Ø IceCube and DeepCore have been very successful Relatively fast Ø Could start deployment in 2016, working over 2—3 years Ø 3 σ hierarchy determination by 2020? Ø LBNE can then focus on CP violation 28

Summary Ultra high energy neutrino detectors are now looking at lower energies Ø Precision atmospheric neutrino studies with megatonne fiducial masses PINGU is an extension of IceCube Ø Taking the energy threshold well below 10 GeV Neutrinos passing through the Earth interact via the MSW e fg ect Ø ν µ disappearance probability depends on the mass hierarchy PINGU could determine the mass hierarchy at 3 σ by 2020 Ø ORCA is a similar extension to ANTARES 29