Looking for New Physics in Neutrino Experiments Morgan Wascko Imperial College London

Looking for New Physics in Neutrino Experiments

Morgan Wascko

Imperial College London

Morgan Wascko, Aspen 2007 Page 211 January, 2007

The Open Questions of Neutrino Physics

1. What else can neutrinos reveal beyond the Standard Model?

2. How does the mixing really work?

3. What is the nature of neutrino mass?

4. What do neutrinos tell us about cosmology? (I won’t actually cover this today.)


Comment on the open questions

• The open questions I listed are all motivated by experimental results– You might say that some results are more compelling than

others, but they’re all worth pursuing

• Answering these questions will at least give us a more precise picture of neutrino masses and mixings

• This is so far the only observation of physics beyond the Standard Model

• If nature is kind, the next generation of neutrino experiments will tear the roof off of the Standard Model!


Comment on the open questions

• The open questions I listed are all motivated by experimental results– You might say that some results are more compelling than

others, but they’re all worth pursuing

• Answering these questions will at least give us a more precise picture of neutrino masses and mixings

• This is so far the only observation of physics beyond the Standard Model

• If nature is kind, the next generation of neutrino experiments will tear the roof off of the Standard Model!




A. How many generations?

2. How does the mixing really work?



Nu Oscillation HOWTO

• Neutrinos oscillate their flavour with distance travelled (time)

• Ideally, one measures neutrino flux at birth in a near detector

• Then measure flux after ’s have time to oscillate

• Can measure appearance and disappearance

MINOS near detector data


Nu Oscillation HOWTO

• Neutrinos oscillate their flavour with distance travelled (time)

• Ideally, one measures neutrino flux at birth in a near detector

• Then measure flux after ’s have time to oscillate

• Can measure appearance and disappearance

MINOS far detector data


Neutrino Oscillations Current Situation

• Three oscillation signals• Allowed regions indicated

– Note: The true answers are actually single points!

• Only mass differences, not absolute scale

• For 3 neutrinos, should find: m2

12 + m2

23 = m2

13

Reactor Limit

LSNDe

Sorel


LSND Signal & MiniBooNE

• LSND observed 3.8 excess

– e

• Taken with atmospheric and solar oscillations, the oscillation hypothesis implies additional neutrino flavours– Sterile!

• MiniBooNE is sensitive to the same parameter space

• See J. Monroe’s MiniBooNE talk in today’s evening session


Post MiniBooNE

• If MiniBooNE sees a signal, build BooNE– Second detector– Precise measurement

• Near term: ICARUS– LAr detector in Gran Sasso

– Great /e PID

• Longer Term:– OscSNS at Oak Ridge– T2K 2km detector

• Future currently uncertain

– NOvA near detector


Post MiniBooNE

• If MiniBooNE sees a signal, build BooNE– Second detector– Precise Measurement

• Near term: ICARUS– LAr detector in Gran Sasso

– Great /e PID

• Longer Term:– OscSNS at Oak Ridge– T2K 2km detector

• Future currently uncertain

– NOvA near detector


Sterile Neutrinos: Solar Hints

• MSW model predicts upturn in spectrum at low energy

• SNO and Super-K data do not show it!

• Sterile neutrino mixing models give best global fits to data

• Reducing threshold should resolve the question

• SNO is doing just that with LETA

Smirnov




A. How many generations? (MiniBooNE)

2. How does the mixing really work?A. Is 23 maximal?

B. What is the value of 13?C. Mass hierarchy?D. Do leptons violate CP?


Accelerator neutrino beams

And reactor neutrinos


Neutrino Flavour Mixing

ATMOSPHERIC

SK, K2K, MINOS

23 =~45

m223 = ~2.5E-3 eV2

CROSS MIXING

CHOOZ, Bugey

13 <~12

is unknown

SOLAR

SNO, others, KamLAND

12 =~32

m212 = ~8E-5 eV2

Flavour Mass


Neutrino Flavour Mixing

ATMOSPHERIC

SK, K2K, MINOS

23 =~45

m223 = ~2.5E-3 eV2

SOLAR

SNO, others, KamLAND

12 =~32

m212 = ~8E-5 eV2

Flavour Mass

0.7 0.7 <0.12 0.5 -0.5 0.7-0.5 0.5 0.7

Neutrino mixing matrix values are large!

But so are the uncertainties…


Improving Precision for Oscillations: Off-Axis Beams

• Use kinematics of pion decay to tune the neutrino energy

• Flux peak at target energy for desired value of L/E– L is often constrained by

geographic considerations…


T2K:Tokai-to-Kamioka

• Start with world’s largest detector: Super-Kamiokande– Super-K III (50kt) is running now

• Build new neutrino beam– J-PARC facility in Tokai

• Off-axis beam to Super-K– L = 295 km

– E = 0.7 GeV

• Near detector at 280m to constrain beam flux

• Beam should be running in April 2009

• Expect 5E21 POT in 5 yearsNishikawa



• Start with world’s largest detector: Super-Kamiokande– Super-K III is running now



– E = 0.7 GeV



• Expect 5E21 POT in 5 years



• Start with world’s largest detector: Super-Kamiokande– Super-K III is running now



– E = 0.7 GeV



• Expect 5E21 POT in 5 years


NOA:

(NuMI Off-axis e Appearance)

• Start with world’s (current) most powerful beam– NuMI facility at Fermilab

• Build new detectors in off-axis locations– FNAL & Ash River, MN (810 km)

• 25 kton far detector

• Program of beam upgrades– Goal: 6E21POT

– 50% , 50%

• NOvA turn-on as early as 2011

—NUMI-On-axis beam—14mrad off-axis beam

(no oscillation)

Mualem


NOA:

(NuMI Off-axis e Appearance)

• Start with world’s (current) most powerful beam– NuMI facility at Fermilab

• Build new detectors in off-axis locations– FNAL & Ash River, MN (810 km)

• 25 kton far detector

• Program of beam upgrades– Goal: 6E21POT

– 50% , 50%

• NOvA turn-on as early as 2011

Ash River

Minneapolis

Duluth

International Falls

Fermilab

Ash River

Minneapolis

Duluth

International Falls

Fermilab


• disappearance• T2K and NOvA have same

goal for 23

(sin2223) ~ 0.01

• Problem: Background estimate uncertainties due to neutrino cross section are large

• Example: T2K uncertainties in atmospheric parameters– stat. Only– (nQE/QE)= 5%– (nQE/QE)=20%

• Need better data for physics input!

Is 23 Maximal?NovA

(sin2 2) (m2)

Hiraide

Mualem


Reducing Cross Section Uncertainties• Two FNAL experiments

embarking on campaigns to bring uncertainties down to needed levels

• Both experiments will have high statistics data sets with fine-grained detectors

• SciBooNE (E-954)– Near detector in Booster beam– Energy perfect for T2K– Antineutrino data!– Will be running this spring (07)

• MINERA (E-938)– Near detector in NuMI beam– Wide range of energies– Different nuclear targets– Data in 2009

Eve

nts

K. Hiraide

SciBooNE detector

assembly

MINERvA design MINERvA detector protoyping


Measuring 13: Current Situation

• Reminder: 13 is how CP violation enters the mixing matrices – We hope it’s large enough!

• To measure 13, must observe e appearance

• Want sensitivities to sin2213>0.01

• Most troublesome BG: mis-identified NC0– SciBooNE and MINERvA data will

solve that!

• Accelerator experiments have ambiguities in measuring 13

Reactor Limit

LSNDe

Sorel


Measuring 13: Accelerators




• Most troublesome BG: mis-identified NC0– SciBooNE and MINERvA

data will solve that!


Erec

m2=2.5x10-3eV2,sin2213=0.1

even

ts/2

2.5k

t/5y

rs

T2K Simulated e Appearance Signal

Mine



—Statistics only—(BG) = 10%—(BG) = 20%




• Most troublesome BG: mis-identified NC0– SciBooNE and MINERvA data will

solve that!


T2K Simulated e Appearance Sensitivity

Mine






• Most troublesome BG: mis-identified NC0– SciBooNE and MINERvA data

will solve that!


– Tied to atmospheric parameters– CP violation?


Measuring 13: Reactors

• Use near/far detectors to search for e disappearance

• Use inverse decay– Well know cross section– Great BG rejection

13

2

ReactorNear Detector

ee?

Far Detector



• Double CHOOZ– Build two detectors at

CHOOZ site– First data in 2008

• Daya Bay– Two detectors at Daya

Bay reactor site in China– First data in 2011

• Unambiguous sensitivity to sin2213

– DC: ~0.03– DB: ~0.01

Double CHOOZ

(France)

Daya Bay (China)



• Double CHOOZ– Build two detectors at

CHOOZ site– First data in 2008

• Daya Bay– Two detectors at Daya

Bay reactor site in China– First data in 2011

• Unambiguous sensitivity to sin2213

– DC: ~0.03– DB: ~0.01

Double CHOOZ

Daya Bay

Wang

Tonazzo


Mass Hierarchy

• Is m3>m2? m2

atm ~10-3

m2sol ~10-5

e and e scatter with different rates in matter– Raises effective mass of e

– Lowers effective mass of e

• Changes oscillation probabilities!– P(e) P (e)

Diagram taken from Boris Kayser

e

We


Mass Hierarchy

• Matter effects change oscillation probabilities!– P(e) P (e)– If neutrinos oscillate more, it’s a

normal hierarchy– If antineutrinos oscillate more,

it’s an inverted hierarchy

• Effect grows with energy

• Two experiments at fixed L/E– R>1 Normal– R<1 Inverted

• NOvA, with higher L and E, will see a much larger effect than T2K

Where S = Sign(m223)


CP Violation via Oscillation Measurements

• The Holy Grail of oscillations • Further ambiguities:

– P(e) P (e) is also the signature for CP violation

• Because of the need to know 13, and disentangle matter effects, observing CP violation requires a broad program of experiments– Want a reactor to measure 13

– Want an accelerator that will see matter effects– Want an accelerator that will NOT see matter effects– Need a lot of statistics in both neutrino and

antineutrinos!



1. What else can neutrinos reveal beyond the Standard Model?A. How many generations? MiniBooNE

2. How does the mixing really work?A. Is 23 maximal?

B. What is the value of 13?

C. Mass hierarchy?

D. Do leptons violate CP?

3. What is the nature of neutrinos?A. What is the absolute scale?

B. Majorana or Dirac?

C. Are neutrino interactions different?

Accelerator neutrino beams

And reactor neutrinos


Absolute Mass Scale

• Why so light?• Can use kinematics to determine the mass of

neutrinos directly e: m < ~2 eV ( decay) : m < 0.19 MeV ( decay) : m < 18.2 MeV ( decay (hadronic))

• Best limits come from tritium decay• 2 main experimental techniques

– Spectrometers• Measure energy of emitted electron

– Calorimeters• Measure heat increase due to emitted electron


Tritium Decay Experiments

• Measure tritium decay spectrum

• Look at endpoint for evidence of neutrino mass

• Detector resolution sets mass sensitivity

-3 -2 -1 0E - E0 [eV]

E0 E0 of fit

undisturbed spectrum

spectrum with additional energy loss

3H3He e

Elliot

Bornschein


SourceElectron analyzer

Electron counter

T2

Tritium Decay: Spectrometers

• Best existing limits come from spectrometer experiments– “MAC-E filter”

• Magnetic Adiabatic Collimation with Electrostatic Filter

– Integrating high pass filter

• Troitsk– m2() = -2.3 ± 2.5 ± 2.0 eV2

m()< 2.2 eV (95% C.L.)

• Mainz– m2() = -0.6 ± 2.2 ± 2.1 eV2

m()< 2.3 eV (95% C.L.)

Troitsk Detector

Mainz Detector


Next Generation Tritium Decay: KATRIN

• Combine best of Mainz and Troitsk techniques

• Much larger experiment!• Aim: improve mass reach by

one order of magnitude– sensitivity

• m() < 0.2 eV (90% CL)

– discovery potential• m() = 0.35 eV (5)

• Will observe Heidelberg-Moscow size mass neutrino if it exists!

• Installation in progress…

70 m



Majorana Mass?

• Use rare nuclear transitions that emit 2 s

• “Line” detected at the endpoint energy indicates neutrinoless double

• Can only happen if neutrinos are Majorana particles

• 2 primary experimental approaches:– Source = Detector (SED)– Tracker-Calorimeters (TC)

• Search for decays; limits on half-life for decays yield limits on neutrino mass

2.01.51.00.50.0Sum Energy for the Two Electrons (MeV)

Two Neutrino Spectrum Zero Neutrino Spectrum

1% resolutionΓ(2 )=100* Γ(0 )

P

P

nn

Left

Left

C

e1

e2

Thomas

Gomez Cadenas


Experimental Techniques 1: SED• Examples:

– Ge detectors– Bolometers

• Excellent energy resolution, efficiency– No pattern in signal, just

energy deposit• Limited to single

isotope per experiment• Dominant BG: External

radioactivity• Current limits:

– CUORICINO:– m < (0.18-0.94) eV

Cuoricino detector block

Cuoricino dataBellini


Experimental Techniques 2: TC• Example: NEMO-3• “Pattern” signature observed• Multiple sources in same

detector • Modest energy resolution

– Resolution of calorimeter– Energy loss in foils

• Dominant BG: internal double decays– 82Se: m < 1.3 – 3.6 eV– 100Mo: m < 0.7 – 1.2 eV

• Expected Reach in 5 years after RadonPurification– 100Mo: m < 0.2 – 0.35 eV– 82Se: m < 0.65 – 1.8 eV

Top viewSide view

3 m

4 mB (25 G)

Source foils + tracker+ calorimeter


0: Possible Signal?

• Heidelberg-Moscow experiment (Ge) has published a signal claim

• Enriched 76Ge detector

• Total mass 10.9 kg

• m = 0.39 eV (95% CL)

• Controversial

• Needs confirmation!


0: Next Generation

• Many next generation experiment proposals

• 4 that are most on mass shell:– CUORE

– EXO

– MAJORANA

– Super NEMO

• Broad program using different isotopes

• Will reach sensitivities sufficient to confirm or refute the Heidelberg-Moscow result Bellini

Thomas


The NuTev Result

• Measurement of sin2W differs by 3 from SM!– Find: sin2W=0.2277

0.00130.0009

– cf. sin2W=0.22270.0003

• Precise measurement uses Paschos-Wolfenstein relation

• Clean and beams– SSQT

• Recall LEP result favors N = 2.9841 0.0083


Addressing NuTeV

• Reactor elastic scattering can be used to measure weak angle

• Total event rate is sensitive to sin2W

• Normalize rate using inverse decay– Cross section known to 0.2%

• Address the mixing angle with neutrinos at low Q2

• Main BGs come from other decays and neutron spallation

e

Z

e

e

We

Conrad


Addressing NuTeV

• Reactor elastic scattering can be used to measure weak angle

• Total event rate is sensitive to sin2W

• Normalize rate using inverse decay– Cross section known to 0.2%

• Address the mixing angle with neutrinos at low Q2

• Main BGs come from other decays and neutron spallation

e

Z

e

e

We


Best Bets For New Physics “Soon”(N.B.: I bet on the USA to win the World Cup)

• MiniBooNE– Could reveal new generations

• Neutrinoless Double Decay– Majorana neutrinos?

• Absolute mass scale– Maybe not “NEW PHYSICSNEW PHYSICS”, but it would set the

scale for neutrino masses

Documents

Looking for New Physics in Neutrino Experiments Morgan Wascko Imperial College London