Oscillations on Ice Tyce DeYoung Department of Physics Pennsylvania State University Exotic Physics with Neutrino Telescopes Marseilles April 5, 2013
IceCube DeepCore Original IceCube design focused on neutrinos with energies above a few hundred GeV DeepCore provides reduced volume with lower energy threshold Higher efficiency far outweighs reduced geometrical volume Note: comparison at trigger level analysis efficiencies not included (typically ~%) (megaton) V effectice ρ ice 50 40 30 20 DeepCore Trigger IceCube Trigger w/o DC 1.0 0.8 0.6 0.4 0.2 O( 5 ) atmospheric neutrino triggers per year 1.0 0 1.2 1.4 1.6 1.8 2.0 ν µ Energy (Log GeV) 0.0
IceCube DeepCore A more densely instrumented region at the bottom center of IceCube Eight special strings plus 12 nearest standard strings High Q.E. PMTs ~5x higher effective photocathode density In the clearest ice, below 20 m λatten 45-50 m IceCube provides an active veto against cosmic ray muon background (around 6 times atmospheric neutrino rate) scattering IceCube extra veto cap 350 m 250 m AMANDA Deep Core
Oscillations with Atmospheric Neutrinos Neutrinos oscillating over one Earth diameter have a νμ survival minimum at ~25 GeV Corresponding maximum in ντ appearance probability Neutrinos from all terrestrial baselines are available for free Compare observations from different baselines to mitigate impact of systematics νµ νµ νµ ~12,700km νµ νµ Hierarchy-dependent matter effects below ~-20 GeV IceCube DeepCore PINGU Tyce DeYoung EPNT 2013 April 5, 2013
Muon Disappearance As a first step, compare zenith-dependent response of standard IceCube muon analysis (high energy) to a modified version for DeepCore Look for oscillation signature in event rate suppression at low energies Detector systematics reduced by comparing HE and LE rates Based on traditional muon analysis, no new techniques designed for DeepCore lower efficiency accepted Tyce DeYoung EPNT 2013 April 5, 2013
Muon Neutrino Disappearance Statistically significant angle-dependent suppression at low energy Shaded bands show range of uncorrelated systematic uncertainties; overall normalization uncertainty shown at right
Muon Neutrino Disappearance Oscillation parameter allowed regions extracted from zenith distributions Systematics included Preliminary results in excellent agreement with world average measurements (with large uncertainties) Potential for significant improvement with inclusion of energy estimators, more advanced reconstructions and event selections
Ongoing Improvements Parallel analysis of first year of data from DeepCore Introduce specialized data analysis and background rejection techniques for DeepCore Low energy event yield improved by almost an order of magnitude Also including an energy estimator based on track length of contained neutrino-induced muons, 2 more DeepCore strings Potentially substantial improvements in precision, depending on impact of systematics
Toward Measurement of Tau Appearance In the standard oscillation scenario, the disappearing νμ are being converted to ντ Confirmation of tau appearance and verification of the tau neutrino rate, are an interesting test Oscillation effects scale as L/Eν, so longer baselines move effect to higher energy Mena, Mocioiu & Razzaque, Phys. Rev. D78, 093003 (2008) ντ appearance νμ disappearance Leads to substantial increases in event rate, since kinematic suppression of tau neutrino cross section is reduced Tyce DeYoung EPNT 2013 April 5, 2013
Toward Measurement of Tau Appearance IceCube/DeepCore will not have the precision for eventwise tau neutrino identification (Lτ ~ 1 mm) Rely instead on statistical observation via modification of cascade energy spectrum Cascades include νe, ντ, νx NC First step: observation of low energy atmospheric neutrino cascades With DeepCore, achieved statistically significant observation (on substantial νμ CC and atmospheric μ backgrounds) Events (281 days) Bartol Honda Data Tyce DeYoung EPNT 2013 April 5, 2013 1200 00 800 600 400 200 0 e (CC) µ (NC) µ (CC) e (NC) e (CC) µ (NC) µ (CC) µ µ PRELIMINARY e (NC) Observed
Toward Measurement of Tau Appearance Energy range of current measurement above oscillation region Limited by current flavor tagging algorithms (track detection) νμ CC the main problem, not μ Work in progress Events (281 days) 450 400 350 300 250 200 150 Data Total Predicted (Bartol) Total Predicted (Honda) Atm. e (Bartol) Atm. e (Honda) Atm. µ (Bartol) Atm. µ (Honda) Atm. µ Two additional DeepCore strings deployed in late 20 will help 0 50 0 1 1.5 2 2.5 3 3.5 4 4.5 reco log ( E [GeV] ) Tyce DeYoung EPNT 2013 April 5, 2013
DeepCore Atmospheric νe Spectrum Statistical subtraction of contributions from NC, νμ CC, and atmospheric μ First measurement in the energy range 80 GeV 6 TeV In agreement with both Honda and Bartol flux calculations, within current uncertainties [GeV cm 2 s 1 sr 1 ] 2 E 1 2 3 4 5 6 7 8 9 conventional e This Work e conventional µ prompt µ, e 1 0 1 2 3 4 5 6 7 log Super K µ Frejus µ Frejus e AMANDA µ unfolding forward folding IceCube µ unfolding forward folding (E [GeV]) Tyce DeYoung EPNT 2013 April 5, 2013
Future Directions Assessment of feasibility of tau appearance measurement is now underway Signature is distortion of neutrino-induced cascade spectrum tough Better event reconstructions, including muon tagging, will likely be needed Better understanding of systematics also important Also studying possibility of extending low energy reach of IceCube with an even denser infill array PINGU Enhancement of all DeepCore physics topics Possibility of exploiting neutrino/anti-neutrino asymmetries and matter oscillation effects to measure neutrino mass hierarchy, given the large θ13 Feasibility studies now underway Tyce DeYoung EPNT 2013 April 5, 2013
PINGU One of several candidate geometries under investigation Exploring requirements for mass hierarchy measurement additional strings could be added if better angular and energy resolution is needed Systematics can be addressed with additional in situ calibration devices Y (m) 0 50 PINGU Geometry V6 (Dozier) IceCube DeepCore PINGU (HQE) 0-50 -0 125m 75m 26m s er, -150-0 -50 0 50 0 150 200 X (m)
Signature of the Mass Hierarchy Idealized case with no background, perfect flavor ID, 0% signal efficiency Different assumed resolutions smear the signature but do not eliminate it NB: angular resolution is for muon kinematic effects are included Expected efficiencies and resolutions under investigation now Energy (GeV) 20 18 16 14 Energy (GeV) 12 8 6 4 20 18 16 14 12 NH ( N IH -N ) /(N NH 1/2 ) [PINGU 1 Year] 8 2-1 6-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.1 0 Cos(Zenith Angle) 4 2 NH ( N IH -N ) /(N NH 1/2 ) [PINGU 1 Year] -1-0.9-0.8-0.7-0.6-0.5-0.4-0.3-0.2-0.1 0 Cos(Zenith Angle) smeared: 3 GeV in νµ energy and 11.25 in µ zenith resolution 3 2 1 0.8 0.60 0.4-1 0.2 0-2 -0.2-3 -0.4-0.6-0.8
Sensitivity vs. Performance Start with perfect resolution and 0% efficiency Apply a 20 DOMs reconstructibility cut to mimic analysis efficiency Apply an assumed detector energy resolution Repeat for various assumed resolutions Distinguishability 120 0 80 60 40 20 0 Distinguishability with Time σ(e)=0 GeV, σ(θ)=0, 0 Hits σ(e)=0 GeV, σ(θ)=0, 20 Hits σ(e)=3 GeV, σ(θ)=, 0 Hits σ(e)=3 GeV, σ(θ)=, 20 Hits 1 1.5 2 2.5 3 3.5 4 4.5 5 Time (years)
Sensitivity vs. Performance Require 20 DOMs hit in PINGU, and evaluate expected distinguishability after (1 year x 0% efficiency above 20 nch) as a function of assumed energy and muon angular resolution Required performance parameters will drive detector design Distinguishability for PINGU 26m Spacing - 1 Year Data Taking, 20 Hit Cut Need to fold in systematics and physics degeneracies (e.g. Δm31 2 ) More sophisticated resolution models will also be evaluated (e.g. energy/inelasticity dependence, biases, etc.) Distinguishability 14 12 8 6 4 2 0 2 4 6 Neutrino Energy Resolution (GeV) 8 12 14 20 18 16 14 12 Muon Zenith Angle Resolution (deg) 8 6 4 2
Advantages of PINGU Well-established detector and construction technology Relatively low cost: ~$M design/startup plus ~$1.25M per string Rapid schedule: deployment could be complete by 2017-18, depending on final scope Quick accumulation of statistics once complete Provides a platform for more detailed calibration systems to reduce detector systematics Enhance physics at PINGU energies e.g. hierarchy, ντ appearance Opportunity for R&D toward other future ice/water Cherenkov detectors Working toward a Letter of Intent now