Exploring neutrino & antineutrino oscillations with NOvA J. Wolcott Tufts University Imperial College London – High Energy Physics Seminar May 29, 2019
Neutrino oscillations and what we can learn from them 2 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations μ ν μ ν e W W e Source Detector Create neutrinos in one lepton flavor state, observe in another (possibly different) state 3 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations μ ν μ ν e W W e Source Detector Create neutrinos in one lepton flavor state, observe in another (possibly different) state U e 1 U e 2 U e 3 ν τ ] = [ U τ 3 ] [ ν e ν 1 [ ν 3 ] U μ 1 U μ 2 U μ 3 ν 2 ν μ U τ 1 U τ 2 nonzero transition probabilities Flavor states are not energy since masses are different (mass) eigenstates 4 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations μ ν μ ν e W W e Source Detector Create neutrinos in one lepton flavor state, Not predicted by the observe in another (possibly different) state Standard Model! U e 1 U e 2 U e 3 ν τ ] = [ U τ 3 ] [ ν e ν 1 [ ν 3 ] Neutrino oscillations can potentially ask U μ 1 U μ 2 U μ 3 ν 2 ν μ and answer BSM questions... U τ 1 U τ 2 nonzero transition probabilities Flavor states are not energy since masses are different (mass) eigenstates 5 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations μ ν μ ν e W W e Source Detector Create neutrinos in one lepton flavor state, observe in another (possibly different) state ν μ ν τ ν e ν 1 ν e [ ν 3 ] [ ν τ ] = ν 2 ν μ arXiv:1212.6374 Flavor states are not energy (mass) eigentstates L/E (arb. units) 6 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations: mixing parameters ν 1 ν e [ ν 3 ] [ ν τ ] = ν 2 ν μ − i δ 1 0 0 cos (θ 13 ) 0 sin (θ 13 ) e cos (θ 12 ) sin (θ 12 ) 0 [ cos (θ 13 ) ] [ cos (θ 23 ) ] [ 1 ] U = 0 cos (θ 23 ) sin (θ 23 ) 0 1 0 − sin (θ 12 ) cos (θ 12 ) 0 0 − sin (θ 23 ) i δ − sin (θ 13 ) e 0 0 0 “Atmospheric” sector: “Reactor” sector: “Solar” sector: best measured in experiments θ 13 best measured in experiments best measured in experiments where ν μ disappearance where ν e disappearance where ν e disappearance dominates dominates: νs from cosmic ray dominates over long distances: over short distances: νs from nuclear muon decays; accelerators νs from solar nuclear fusion reactors (more on δ shortly) 7 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations: mixing parameters ν 1 ν e [ ν 3 ] [ ν τ ] = ν 2 ν μ − i δ 1 0 0 cos (θ 13 ) 0 sin (θ 13 ) e cos (θ 12 ) sin (θ 12 ) 0 [ cos (θ 13 ) ] [ cos (θ 23 ) ] [ 1 ] U = 0 cos (θ 23 ) sin (θ 23 ) 0 1 0 − sin (θ 12 ) cos (θ 12 ) 0 i δ 0 − sin (θ 23 ) − sin (θ 13 ) e 0 0 0 “Reactor” sector: δ accessible via ν e appearance in accelerator expts. 8 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations: mixing parameters ν 1 ν e [ ν 3 ] [ ν τ ] = ν 2 ν μ − i δ 1 0 0 cos (θ 13 ) 0 sin (θ 13 ) e cos (θ 12 ) sin (θ 12 ) 0 [ cos (θ 13 ) ] [ cos (θ 23 ) ] [ 1 ] U = 0 cos (θ 23 ) sin (θ 23 ) 0 1 0 − sin (θ 12 ) cos (θ 12 ) 0 i δ 0 − sin (θ 23 ) − sin (θ 13 ) e 0 0 0 Big question: “Reactor” sector: Is δ nonzero? δ accessible (If it is, neutrinos—and thus leptons—violate CP symmetry ! via ν e appearance … leptogenesis??) in accelerator expts. 9 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations: mixing parameters ν 1 ν e [ ν 3 ] [ ν τ ] = ν 2 ν μ − i δ 1 0 0 cos (θ 13 ) 0 sin (θ 13 ) e cos (θ 12 ) sin (θ 12 ) 0 [ cos (θ 13 ) ] [ [ cos (θ 23 ) ] 1 ] U = 0 cos (θ 23 ) sin (θ 23 ) 0 1 0 − sin (θ 12 ) cos (θ 12 ) 0 0 − sin (θ 23 ) i δ − sin (θ 13 ) e 0 0 0 Big question: Is there a symmetry governing the ν μ /ν τ “Atmospheric” sector: mixing into the 2 nd and 3 rd mass states? best measured in (Is θ 23 “maximal” = 45º?*º?) experiments where ν μ disappearance ? ν 3 = dominates: νs from cosmic ray muon decays; ν τ ν e ν μ accelerators 10 J. Wolcott / Tufts University Imperial / May 29, 2019
Neutrino oscillations: mass splittings ν 3 ν 2 2 Δ m 21 ν 1 ? ⇔ 2 Δ m 32 2 “Normal Hierarchy” Δ m 32 “Inverted Hierarchy” (most electron-like state lightest) ν 2 2 Δ m 21 ν 3 ν 1 Big question : Which way around are the mass states ordered? ν e appearance from accelerator νs, also possibly reactor disappearance 11 J. Wolcott / Tufts University Imperial / May 29, 2019
Measuring neutrino oscillation parameters with NOvA 12 J. Wolcott / Tufts University Imperial / May 29, 2019
Long-baseline neutrino experiments Imagine for a moment you're only oscillating between two flavors. Then: How far away from the source 2 L you build your detector 2 ( Δ m 4 E ) 2 2 θ sin P ν α →ν β ≈ sin Energy spectrum of your neutrino beam 2 L | Δ m 4 E | = π 2 Arbitrary units 2 2 θ sin 13 J. Wolcott / Tufts University Imperial / May 29, 2019
Long-baseline neutrino experiments Because ν μ /ν τ is nearly 5º?*0/5º?*0 in all the mass states, 2 L | Δ m 4 E | = π 2 ν 3 = 2 2 θ sin ν τ ν e ν μ this is nearly exactly what you get when you start with ν μ of a few GeV at distances of a few hundred km from the source. Paradigm for modern “long-baseline” expts. 14 J. Wolcott / Tufts University Imperial / May 29, 2019
Long-baseline neutrino experiments is quite a bit harder because θ 13 is small... sin 2 2 θ 23 in ν μ disappearance... note sign flip for antineutrinos … but if you can measure it well (for ν and ν), you gain access to both δ and the mass hierarchy . (Hierarchy dependence enters through matter effects ...) 15 J. Wolcott / Tufts University Imperial / May 29, 2019
Long-baseline neutrino experiments is quite a bit harder because θ 13 is small... CP conserved CP conserved δ = π /2 δ = π /2 δ = 3 π /2 δ = 3 π /2 … but if you can measure it well (for ν and ν), you gain access to both δ and the mass hierarchy . (Hierarchy dependence enters through matter effects ...) 16 J. Wolcott / Tufts University Imperial / May 29, 2019
Long-baseline neutrino experiments is quite a bit harder because θ 13 is small... Normal Hierarchy Normal Hierarchy Vacuum Vacuum Inverted Hierarchy Inverted Hierarchy … but if you can measure it well (for ν and ν), you gain access to both δ and the mass hierarchy . (Hierarchy dependence enters through matter effects ...) 17 J. Wolcott / Tufts University Imperial / May 29, 2019
The NOvA experiment Ash N uMI O ff-axis 𝝃 e A ppearance River Experiment NuMI = N eutrinos at the M ain I njector 8 1 0 ● Long-baseline (anti-)neutrino k m oscillation experiment ● Two functionally identical detectors, optimized for ν e identification Fermilab Bloomington 18 J. Wolcott / Tufts University Imperial / May 29, 2019
The NuMI beam Focusing Horns Decay Pipe Target ν μ /ν μ π - p π + “Neutrino mode” Magnetic “horns” focus mesons from proton beam- 12 C target interactions Detectors are 14mrad off main beam axis: Results in narrow energy spectrum around 2 GeV ● Reduces “wrong-sign” (ν in ν beam and vice versa) ● component → 3% (5º?*%) contamination for ν (ν) Focusing Horns Decay Pipe “Antineutrino Target ν μ /ν μ π - mode” p π + 19 J. Wolcott / Tufts University Imperial / May 29, 2019
The NOvA detectors Detectors differ mainly in size ● Near Detector: 300 ton, 1 km from source (FNAL) (otherwise functionally identical) ● 100m underground, 20,000 channels ● Far Detector: 14 kton, 810 km from source (Ash River, MN) ● On the surface, 3m concrete+barite overburden; 344,000 channels 20 J. Wolcott / Tufts University Imperial / May 29, 2019
The NOvA detectors 1 Channel APD xz -view 32 Channels yz -view y z x (~20K 4cm × 6cm) ● Good energy resolution for muons, electromagnetic & hadron showers: Detectors differ ● Mostly (65%) active detector mainly in size ● Radiation length ~ 40 cm → 6 samples per (otherwise functionally identical) radiation length 21 J. Wolcott / Tufts University Imperial / May 29, 2019
Strategy Main idea: ν μ disappearance example Compare predicted spectrum at FD to observed spectrum at FD to extract oscillation parameters Discuss in two steps: building the spectrum, then details of prediction 22 J. Wolcott / Tufts University Imperial / May 29, 2019
Spectrum construction (1) Event selection (2) Reconstruction & observables 23 J. Wolcott / Tufts University Imperial / May 29, 2019
Spectrum construction: identifying neutrino events l - ν l Q: How do you identify a ν μ or ν e ? W A: Look for charged-current reactions p , π ± , … ( charged leptons differ & backgrounds have no primary charged lepton ) N Selections share many ingredients; will discuss in parallel. Illustrate using neutrino mode (antineutrinos shown where different) 24 J. Wolcott / Tufts University Imperial / May 29, 2019
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