Tests of non-standard neutrino interactions (NSI)

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Tests of non-standard neutrino interactions (NSI)

• Cecilia Lunardini
• Institute for Nuclear Theory
• University of Washington, Seattle

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Menu

• Non Standard neutrino-matter Interactions
• Accelerator limits
• Neutrino oscillation sensitivity
• NSI effects on solar neutrinos
• Ideas for low energy experiments

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New interactions a possibility

• Not excluded by neutrino coupling measurements
• Theoretically sensible
• New physics ? new couplings (new gauge bosons, )

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Neutral current, low energy

• Neutral current
• neutrino q,e ? neutrino q,e
• Low energy
• Momentum transfer ltlt new physics scale
• 4-fermion interactions
• Flavor changingflavor preserving NSI

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Accelerator limits (direct only)

• Direct bounds CHARM, NuTeV
• no SU(2) charged lepton data
• Strong in muon sector
• Weak in e-tau sector

Zeller et al., PRL 88, 2002 Vilain et al.,
PLB335, 1994
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Neutrino oscillation sensitivity

• NSI contribute to matter effects (MSW)!
• Example solar neutrinos
• NSI in e-tau sector only

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Understanding the survival probability

• Regimes
• Vacuum dominates ? vacuum mixing
• Matter dominates ? NSI mixing
• Not zero if NSI are flavor-changing!

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The survival probability
E/MeV
NSI on quarks only, same couplings for u and d
Positive coupling longer step
Negative coupling Flattening
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Regeneration in the Earth day/night

• If Earth effect can be suppressed
  by small
• Large flavor changing NSI needed

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Fit to the data?

• Good fit needs
• 30 survival of 8B
• Flat SK and SNO spectrum
• No indication of upturn at lower E
• No evidence of Earth matter effect (lt 7)

favored
Small mass splitting possible for small
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Results of data analysis/1

• Bounds on NSI
• NSI on quarks.
• Fit of
• 2002 KamLAND data
• BP04 model solar Cl, Ga rates, SK-ES, SNO
  day-night (phase I) SNO rates (phase II),
• neutral current SNO free parameter (modified by
  NSI)
• e110, -0.32 lteu12lt0.14 90 C.L.
• A1 , -0.19 lteu12lt0.11 90 C.L.
• eu12 lt -0.08 new solution!

Best for flat spectrum
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Results/2 a new solution!

• LMA-0 Day/Night suppressed by (q - a) 0.15
  eu11ed11-0.065 eu12 ed12-0.15

90,95,99,99.73 C.L.
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LMA-1 and LMA-0

• Large effects at medium energy!

(Best-fit parameters taken)
8 B
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Update with KamLAND 2004 data

• Only minor changes
• LMA-D excluded by atmospheric neutrinos

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LMA-1 and LMA-0 compatible with
atmosphericK2KMINOS

• Section of 3D region at eee-0.15 (others
  marginalized) inverted hierarchy
• c2min48.50 for no NSI
• Contours c2 - c2min7.81,
  11.35, 18.80 (95,99, 3.6 s)

LMA-0
LMA-1
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Potential for low energy experiments!

• Look for suppression of Be7 and pep fluxes

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NSI at LENS
Plot courtesy of C. Grieb
See Grieb Raghavan, hep-ph/0609030
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• Look for distortions in the shape of the survival
  probability at intermediate E
• Lack of upturn below SK/SNO threshold

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FAQs

• How large NSI are needed?
• About 10 of standard coupling per each component
  of matter (electrons, u,d, quarks)
• Are these values natural?
• Not very but possible
• Can these effects be mimicked by other physics?
• yes sterile neutrinos, noise in solar matter,
  mass varying neutrinos
• Can other experiments test this?
• Neutrino factories, LBL beams, KamLAND high
  statistics (LMA-0)

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Conclusions

• Possible large neutral current NSI of neutrinos
  in the e-tau sector
• allowed by all existing experiments
  (accelerators, neutrino oscillations exp.)
• Large NSI could have tiny effects where we have
  looked so far!
• little effect on current solar data (8B), on
  atmospheric neutrinos and on short-medium
  baseline neutrino beams (MINOS)

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• But could appear dramatically in lower energy
  solar neutrino data!
• Different shape of probability
• Suppression of 7Be, pep
• Win-win game for low energy detectors!
• Negative result? ? best constraint on NSI
• Positive result? ? Another evidence of new
  physics in neutrinos
• Different vacuum oscillations parameters (solar
  mass splitting smaller, atmospheric mixing not
  maximal)?