Neutrino Decoherence Phys. Rev. Lett. 118, 221801 (2017) Joo Coelho - - PowerPoint PPT Presentation

Nonmaximal θ23 Mixing at NOvA from Neutrino Decoherence

João Coelho

APC Laboratory

22 June 2017

22 Jun 2017 1

• Phys. Rev. Lett. 118, 221801 (2017)

Quantum System

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2 2 1 1

  

  

U U  

2 2 1 1

  

  

U U  

2 2 * 2 1 * 1 2       

  U U U U P   

1 * 1 2 * 2 2 * 2 1 * 1 2 2 2 2 2 1 2 1             

U U U U U U U U U U U U P    

Classical Probability Quantum Interference

Decoherence

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2 2 2 1 1 1

,      

  

U U  

2 2 * 2 2 1 * 1 2 2 2 1

, , , ,

        

        U U U U P    

2 2 2 2 2 1 2 1    

U U U U  

 

   

   2 2 1 1

U U  

i i i i

U    

 

 ,

Entanglement Measurement coupled to environment Only Classical Probability

Density Matrix

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2 2 1 1

  

  

U U  

2 2 1 1

  

  

U U  

   

    P          

2 2 1 * 2 2 * 1 2 1

| | | |

        

   U U U U U U

• Better framework to describe loss of coherence

Quantum Terms Classical Terms Unitary Evolution (Shcroedinger)

Modeling Decoherence

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• What causes decoherence?
• Coupling to an environment
• Neutrino interactions with matter?
• Vacuum fluctuation? (Quantum Gravity)
• Very model dependent!
• Phenomenological approach:

Unitary Non-Unitary

Lindblad Equation:

Most general Markovian evolution that preserves probabilities even in the environment system

Neutrino Oscillations





i i i

U  

 

 

2    

   

iHt

e P



  E L m L E t H 2 ~ . ~ .

2

   

Simple QM

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• Neutrinos are created in a superposition of mass states
• Time evolution generates flavour oscillations

Neutrino Decoherence

Open QM

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• Interaction with some environment → Mixed states
• Time evolution given by Lindblad equation
• Complete Positivity
• Trace Preserving
• Increasing Entropy
• Energy Conserving

Effect On Disappearance

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Nonmaximal Mixing?

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• NOvA sees nonmaximal mixing with 2.6 sigma
• All others are consistent with maximal
• T2K especially is in mild tension with NOvA

3x3 Systems

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• Neutrinos come in 3 flavours
• Hilbert space can be describe by SU(3)
• Expand all operators in generators of SU(3) (Gell-Mann Matrices)

Operators as sum SU(3) of generators System of 9 coupled equations Simple block-diagonal form

3x3 Systems

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• Neutrinos come in 3 flavours
• Hilbert space can be describe by SU(3)
• Expand all operators in generators of SU(3) (Gell-Mann Matrices)

Operators as sum SU(3) of generators System of 9 coupled equations Diagonal w/ energy conserv.

In general* 36 parameters!

*But already assuming increasing entropy (Aj

† = Aj)

3 Formulas

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ORCA T2K NOvA DUNE q12 q13 q23 JUNO

G21 Constraints

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• Solar scale oscillations strongly constrain G21
• Under our assumptions, this implies G31 ≈ G32 = G

G21 < 5.5×10-25 GeV at 90% C.L.

Mimicking Nonmaximal Mixing

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NOvA

Mimicking Nonmaximal Mixing

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Given Solve

G-1 ~ 8600 km

Global Fit

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• MINOS: Neutrino 2012 talk*
• NOvA: PRL 118, 151802 (2017)
• T2K: arXiv:1704.06409 [hep-ex]

* No new MINOS result has LBL-only values that would be relevant to this analysis

• Current LBL global fit agrees

with NOvA-only prediction

Global Fit

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• MINOS: Neutrino 2012 talk*
• NOvA: PRL 118, 151802 (2017)
• T2K: arXiv:1704.06409 [hep-ex]

* No new MINOS result has LBL-only values that would be relevant to this analysis

• Current LBL global fit agrees

with NOvA-only prediction

• Still weak preference for

nonzero decoherence

What About Super-K?

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• Lisi et al.: PRL 85, 1166 (2000)
• Not a lot has been published since early 2000’s
• Strongest limits we found: G < 3.5 x 10-23 GeV at 90% CL
• Effect mostly on up-going muon neutrinos

What About MINOS at HE?

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• Oliveira et al.: PRD 89, 053002 (2014)
• Not a lot of power from MINOS so far, but UNICAMP Group

published some positive results in 2014…

However…

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• R. Oliveira: EPJC 76, 417 (2016)
• Strong matter effects may

not be trivial to understand

• Oliveira’s paper shows some

funky behaviour at the reso- nance for some decoherence models

• Important questions on usual

assumptions of energy con- servation, especially with res- pect to the underlying mech- anism for decoherence

• Mass Hierarchy may also play

a very important role

Energy Conservation

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• Simple constraint equation:
• But which H is conserved?

– Vacuum? Decoherence is due to neutrino mass measurement (QG-like) – Matter? Decoherence is due to effective neutrino energy (EW-like)

• In the paper we assume the latter, but effect is small so both scenarios

are reasonably described

• Important consequences when matter effects are large

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Summary

• NOvA’s new results indicate some tension in LBL exps
• Could this be a sign of decoherence?
• Our paper shows there’s still room for speculation
• New analyses of existing data at higher energies needed
• More studies of relationship with matter effects are likely

to be required before looking at atmospheric neutrinos

• Read our paper at: PRL 118, 221801 (2017)
• r https://arxiv.org/abs/1702.04738

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Thank you!

João Coelho Tony Mann Saqib Bashar

Cauchy-Schwarz

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• Gij are not independent
• Related by Cauchy-Schwarz inequalities

= Any permutation of

32 31 21

G  G   G

Matter Effects

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H0 V

Matter Effects w/o Deco.

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Heff = H0 + V Heff = H0 - V

Matter Effects w/ Deco.

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Heff = H0 + V Heff = H0 - V

Matter Effects

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Resonances

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q12 q13 q23 m2

21 cos2q12

m2

31 cos2q13

Resonances

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IH NH q12 q13 q23

Resonances

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ORCA ARCA T2K NOvA DUNE q12 q13 q23 JUNO

Resonance Formulas

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Depends on sign of m2

31 (MH)