Neutrino Mass Hierarchy and Mixing Parameters: Long-baseline Measurements with IceCube Laura Bodine

Transcription

1 Neutrino Mass Hierarchy and Mixing Parameters: Long-baseline Measurements with IceCube Laura Bodine Mass Hierarchy Observables Matter Effects Feasibility University of Washington

2 Neutrino Mass: Current status Most oscillation parameters: known Reactor, Atmospheric & Solar expt 13 small, exact value unknown Overall mass scale: limited Small allowed region Beta decay expt Nature of neutrino: unknown Double-beta decay expt Mass hierarchy: unknown Matter enhanced oscillations? Implications for physics beyond the Standard Model as well as Cosmology 2

3 Neutrino Mass Hierarchy atmospheric ~310-3 ev 2 solar ~ ev 2 solar ~ ev 2 atmospheric ~310-3 ev 2 Sign of m 2 21 known from matter effects Charged current Similar experiment may be possible for m 2 32 Requires large 13 What if 13 = 0? Normal Inverted 3

4 3 Flavor Neutrino Oscillations Interaction eigenstates Unitary matrix Mass eigenstates Probability exists for neutrino to transition from state to Matrix elements are functions of mixing angles The survival probability depends on 3 matrix elements, 3 mass gaps, the distance traveled and the neutrino energy All terms contribute, even if 13 = 0 4

5 Basic Experimental Setup source very long baseline detector Look at muon neutrino probability to transition to electron neutrino or tau neutrino The survival probability depends on the mass gaps, the distance traveled and the energy Only sensitive to 13 via the matrix elements 5

6 P Survival Probability First Solar Minimum Threshold for Čerenkov light in water 6

7 Oscillation Maxima Both look like straight lines 7

8 Linearity of Oscillation Maxima Observable difference between normal and inverted hierarchies! 8

9 Adding Matter Effects I Much smaller effect 9

10 Adding Matter Effects II Matter effects reduce sensitivity to hierarchy 10

11 Requirements Ability to resolve the solar and atmospheric mass gaps simultaneously Scan large a range of L/E Ultra-narrowband neutrino beam Put energy selection on beam side A few percent energy spread Ability to scan energies in 100s MeV-GeV range Efficient counting detector Use beam timing information to lower threshold Huge detector very far from the source 11

12 Huge, Faraway Detector: IceCube at the South Pole km from Fermilab 12

13 IC as a Low-Energy Counter 100 GeV std threshold, ~500 Hz dark noise rate But we re looking for neutrinos in 100s MeV- GeV range Look for small amounts of light in time with beam Typical spill times of s occurring every ~2 sec Expect 10-3 counts/spill background May be able to use single count data for after the fact reconstruction Large trigger update may not be necessary Could run in parallel with other missions Photon transport is the dominant open question Need to see small numbers of photons Deep Core may be the right venue 13

14 Beam Prospects Basic method employed in off-axis beams Improve energy spread by filtering pions in-flight Tune by movement of horn and filters Can lower energy spread at expense of flux Recover event rate by use of large detector This is a difficult task But NuMI upgrade plans for 10% energy spread when optimized for NOA which has limited sensitivity to low flux 14

15 Other Mixing Parameters Amplitude of oscillations depends on the mixing angles. Use peak heights to extract information Frequency provide information on m 2 atm Unknown sensitivity to CP 13 -dependent, but we are planning to investigate Could provide simultaneous measurements of several mixing parameters 15

16 Summary It is possible, at least in principle, to measure the hierarchy even if 13 = 0 Long baseline muon neutrino survival provides sensitivity to the mass hierarchy and other neutrino mixing parameters New techniques would be necessary Ultra-narrowband neutrino beams from monochromatic pion beams Alternative use of modern detector, like IceCube 16

17 Acknowledgements University of Washington Work done in collaboration with Hamish Robertson Supported by DOE Grant #DE-FG02-97ER41020 Thank you for listening! 17

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19 Matter Effects in More Detail PREM was used to calculate the average density MSW potential, with average density used in A Parameterize in terms of shifted m 2 21 mass gap 19