Solar Neutrino Detection in Solar Neutrino Detection in SNO, SNO+, - - PowerPoint PPT Presentation

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Solar Neutrino Detection in Solar Neutrino Detection in SNO, SNO+, and Theia SNO, SNO+, and Theia Benjamin Land Benjamin Land 290E / Oct 19, 2016 290E / Oct 19, 2016 1 10/19/2016 B. Land - 290E Outline Solar neutrino introduction

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Solar Neutrino Detection in Solar Neutrino Detection in SNO, SNO+, and Theia SNO, SNO+, and Theia

Benjamin Land Benjamin Land 290E / Oct 19, 2016 290E / Oct 19, 2016

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Outline

  • Solar neutrino introduction

– Where they come from – Standard solar models

  • The solar neutrino problem

– How it was identifjed and solved – Detection and analysis methods in SNO – Neutrino oscillations in vacuum and matter

  • Solar neutrino physics

– What physics can solar neutrinos probe

  • Current plans: SNO+
  • Future Plans: Tʜᴇɪᴀ
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Solar Neutrino Overview

  • Stars are powered by fusion reaction chains
  • Fusion products are unstable, will decay

– β decays produce νe

  • Neutrinos escape the star largely* unhindered
  • Eventually arrive at Earth to be studied
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Proton-Proton Chain

https://en.wikipedia.org/wiki/Proton%E2%80%93proton_chain_reaction#/media/File:Proton_proton_cycle.svg (modified)

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CNO Cycle

+ variations

https://en.wikipedia.org/wiki/CNO_cycle#/media/File:CNO_Cycle.svg (modified)

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Standard Solar Models

  • SSM spearheaded by John Bahcall
  • Goal: predict internal structure of the sun

– Radial profjle of neutrino production – Rates of neutrino production (fusion reactions)

  • Utilizes best available information

– Helioseismology, metallicity measurements – Solar luminosity/mass/size – Theory predictions (cross sections)

  • Still, large theoretical uncertainties

– Neutrinos can probe directly for precision measurements

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SSM Neutrino Fluxes

  • J. Bahcall et al. (plot by B. Land)
  • J. Bahcall et al. http://www.kip.uni-heidelberg.de/tt_detektoren/neutrinos.php?lang=en
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  • First measurement from

Homestake experiment

  • Large tank of tetrachloroethylene

–

Neutrinos (νe specifjcally) capture on Cl νe + 37Cl → 37Ar + e-

–

Count the Ar → determine the fmux

  • Measured a fmux about

⅓ of SSM predictions

–

The solar neutrino problem

–

Confjrmed by GALLEX, GNO, SAGE, (gallium); Kamiokande

Early Measurements

  • J. Bahcall et al. http://www.kip.uni-heidelberg.de/tt_detektoren/neutrinos.php?lang=en
  • J. Bahcall
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Missing Neutrinos?

  • Early experiments were only sensitive to νe

– Could a mechanism convert νe to νμ / ντ ?

  • Herb Chen proposed using a heavy water target

– Deuterium has a large neutral current (NC) cross section – Would be sensitive to all fmavors of neutrinos

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Interactions in Heavy Water

  • νe will undergo elastic scatter (ES) as usual

–

Other fmavors also ES but factor of ~6 less likely

–

Detect Cherenkov light from scattered electron

https://physics.carleton.ca/sno/about-sno-project/neutrino-reactions

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Interactions in Heavy Water

  • νe will undergo and charged current (CC)

–

Deuterium has a suffjciently large CC cross section

–

Detect Cherenkov light from scattered electron

https://physics.carleton.ca/sno/about-sno-project/neutrino-reactions

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Interactions in Heavy Water

  • All fmavors undergo neutral current (NC) interactions

–

Deuterium disassociated producing a free neutron

–

Neutron captures producing gamma(s)

  • Add a nucleus to capture neutrons
  • Chlorine (from salt) works well

–

Gamma(s) scatter producing energetic electrons

–

Detect Cherenkov light from scattered electrons

https://physics.carleton.ca/sno/about-sno-project/neutrino-reactions

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The SNO Detector

  • SNO realized H. Chen’s proposal

–

12m diameter acrylic vessel

–

1kT of heavy water, ultrapure water bufger

–

Instrumented with ~9500 8” PMT s

–

2km underground in Sudbury, CA

  • Primarily sensitive to 8B neutrinos

The SNO Collaboration

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SNO Analysis

  • Raw data is from photomultiplier tubes (PMTs)

–

Photon strikes photocathode, liberated electron amplifjed, charge collected

–

Hit time, integrated charge

  • Reconstruction algorithms fjt observables

from raw data event by event

–

Energy from number of detected photons

–

Image cherenkov ring for direction of event

–

Position from minimizing hit time residuals

  • Used a statistical fjt to disentangle

signal and background with observables

–

Also used a metric of hit isotropy

The SNO Collaboration http://natefinney.com/images_large/figure1.jpg

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SNO Analysis

  • Monte-carlo predictions generated PDFs

–

For signal and background classes

  • Fit out number of NC, CC, ES events

–

Disentangle contributions from νe,νμ,ντ

–

Use livetime, cross sections to extract fmux

  • B. Land
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SNO Results

  • Sum agreed well with

SSM predictions!

–

Confjrms that neutrinos do change forms

  • Relative proportions

require more explanation

The SNO Collaboration

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Neutrino (Vacuum) Oscillation

  • Proposed method to explain neutrino mutation
  • Mass basis rotated relative to fmavor basis

–

Requires that neutrinos have mass

  • The solar core is large relative to oscillation lengths

–

Oscillations would be averaged out

–

Easy to compute electron neutrino “survival probability”

  • Vacuum oscillations are not the whole story!
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The Mikheyev–Smirnov– Wolfenstein (MSW) Efgect

  • *Solar core densities are high

enough to matter

  • νe selectively experience CC

–

Many e, virtually no τ or μ

–

Gives a potential energy to νe

  • Coherent forward scatter
  • c.f. refractive index of light
  • Short version: initial νe exits as ν2

–

For high energy neutrinos (8B)

–

MSW prediction matches SNO data well

–

Agrees with many other measurements

  • B. Land
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The Mikheyev–Smirnov– Wolfenstein (MSW) Efgect

Plot by LBNE Collaboration

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Solar Neutrino Problem Solar Neutrino Problem == == Solved! Solved! What else can we do? What else can we do?

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Solar Neutrino Physics

  • Studying the solar core

–

Neutrino rates are direct measure of fusion rates

–

Difgerent neutrinos produced in difgerent regions

–

Highly dependent on properties of the core

–

Directly related to metalicity, resolve tensions in other measurement

  • Constrain mixing angles,

squared mass difgerences

–

Primarily θ12 and Δm2

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  • J. Bahcall et al. (plot by B. Land)
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Solar Neutrino Physics

  • Neutrino lifetime

–

Neutinos have mass, could decay

–

Solar provides long baseline, constrained initial fmux

–

Probes beyond standard model physics

  • Sterile neutrinos

–

Would lack potential present for other fmavors

–

Solar densities uniquely sensitive to MSW-like resonances

  • B. Land
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Solar Neutrino Physics

  • Fundamental symmetry violation

–

Long baseline that rotates yearly (earth orbit)

–

Perfect for looking for Lorentz violations

  • Other beyond standard

model efgects

–

Look for distortions in energy spectrums

  • M. Maltoni and A. Smirnov
  • J. Bernhard
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Moving Forward: SNO+

  • Upgrade of the SNO detector
  • Replaces heavy water with

liquid scintillator

–

Linear alkylbenzene(LAB)+PPO

–

Loses sensitivity to NC, CC

–

Otherwise similar detection methods as SNO, just with isotropic scintillation

  • Primarily a 0νββ experiment

–

Starting with a water commissioning phase (fjlling now!)

–

Followed by pure scintillator phase

  • Potentially great for solar neutrinos (demonstrated by Borexino), other physics

–

Finally loading 130T e into the scintillator for 0νββ

SNO+ Collaboration

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Scintillator Detection

Pros

  • Greater light yield

–

~500 hits/MeV vs ~10 hits/MeV

–

Improved energy resolution

–

Lower thresholds

–

No cutofg for light production

  • Demonstrated by Borexino

Cons

  • Loses directionality

–

Scintillation is inherently isotropic, no ring or similar directionality

–

Cherenkov intensity lost in scintillation fmuctuations

  • Shorter scattering lengths

–

Modifjes hit time residuals, hinders reconstruction

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SNO+ Solar Neutrinos

  • Monte-carlo predictions

–

Similar analysis to SNO, without directionality

–

Sensitivity to 8B, 7Be, pep, CNO

  • Backgrounds are an issue

–

Scintillator can be made ultra clean

–

Acrylic vessel is comparatively dirty

–

Efgort underway to estimate impact

  • Directionality would help

–

Backgrounds should not change with solar direction

–

Far easier to fjt out solar neutrinos

SNO+ Collaboration

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The Future: Cherenkov+Scintillation

  • Combination potentially has

the best of both worlds

–

Directional rejection

  • f backgrounds

–

High light yield → better energy resolution

  • Make it BIG

–

More interactions

–

Better self-shielding of backgrounds

  • Load it with something

–

e.g. 7Li has a large CC cross section, sharply peaked response

–

Very precise spectral measurement possible

  • B. Land

G.D. Orebi Gann G.D. Orebi Gann

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The Future: Tʜᴇɪᴀ

  • Proposed experiment to realize combined

Cherenkov and Scintillation detection

  • Uses water based liquid

scintillator (WbLS)

–

Developed by Minfang Yeh

–

Scintillator suspended water

–

T une loading fraction of scintillator to tune scintillation light yield

  • Broad physics program, and great for solar
  • B. Land
  • B. Land
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Tʜᴇɪᴀ MC Predictions

30-kT WbLS Tʜᴇɪᴀ detector loaded with 1% 7Li

Tʜᴇɪᴀ Interest Group

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Questions?

References

–

  • J. Bahcall Scientifjc American, Volume 221, Number 1, July 1969, pp. 28-37

–

  • J. Bahcall ApJ, 621, L85 (2005), astro-ph/0412440

–

B.T. Cleveland, et al. Astrophys.J. 496 (1998) 505-526

–

The SNO Collaboration, Phys. Rev. C 88, 025501 (2013)

–

G.D. Orebi Gann, arXiv:1504.02154v2 [nucl-ex]

–

J.R. Alonso, et al., arXiv:1409.5864v3 [physics.ins-det]

–

Theia Interest Group arXiv:1504.08284v1 [physics.ins-det]

–

  • M. Yeh, et al., Nucl. Inst. & Meth. A 660 51 (2011)

–

  • M. Maltoni and A. Smirnov, arXiv:1507.05287v3 [hep-ph]

–

  • J. Bernhard, arXiv:1009.4717 [hep-ph]