IceCube’s Sensitivity to Sterile Neutrinos€¦ · SNAC 2011, Virginia Tech S. Razzaque, slide...

IceCubeIceCube’’s s Sensitivity toSensitivity toSterile NeutrinosSterile Neutrinos

Soebur RazzaqueSoebur RazzaqueGeorge Mason University,George Mason University, Fairfax, VirginiaFairfax, Virginia

U.S. Naval Research Laboratory, Washington, DCU.S. Naval Research Laboratory, Washington, DC

arXivarXiv:1104.1390v4 [:1104.1390v4 [hep-phhep-ph]]JHEP 07, 084 (2011)JHEP 07, 084 (2011)

In collaboration withIn collaboration with

Alexei Yu. SmirnovAlexei Yu. SmirnovAbdus Salam Abdus Salam ICTP, ICTP, Trieste, ItalyTrieste, Italy

Sterile Neutrinos at the Crossroads, September 25-28, Virginia Tech, USA

Sterile Sterile νν MixingMixing with Active with Active νν's'sMixing of sterile Mixing of sterile νν's's with active with active νν's's affectaffectprobabilities of active-to-active probabilities of active-to-active νν-flavor conversions-flavor conversions

It was realized soonIt was realized soon after LSND that the MSW resonances are atafter LSND that the MSW resonances are at very high energiesvery high energies

•• MSW resonance effect appears in the antineutrino channel (MSW resonance effect appears in the antineutrino channel (‘‘--’’ potential) potential)

Resonance condition

SNAC 2011, Virginia Tech S. Razzaque, slide 02/23

LSND, MiniBooNE

!

"m032

2Ecos2# = $

12GF nn

H. Nunokawa, O.L.G. Peres and R. Zunkanovich Funchal (2003), S. Choubey (2007)

South Pole

TeV resonace energy for ~1 eV ν

Neutrino telescopes Neutrino telescopes may probe sterile may probe sterile νν signatures signatures

IceCubeIceCube’’s s Sensitivity toSensitivity to Sterile Sterile νν's's

The number ofThe number of ννµµ events scales as events scales as

1 TeVlog E

NE


3500 kmCore

6371 km

PreliminaryReferenceEarth Model(PREM)

Mantle

ν

IceCube

EarthEarth’’ssdensitydensityprofileprofile

MSW resonance energies forMSW resonance energies forearth-crossing sterile earth-crossing sterile νν‘‘ss

!

" E ~ (2 # 5) TeV ($m032 /1eV2)

Details depend on the zenithangle (θz) of the arrival direction

!

Veff " Rµ3 "

E 3 ;<1TeVln3;>1TeV

# $ %

!

NE ~ Aeff E"#

!

Veff nN "nN # det

!

E "3.7

!

E1



1 TeVlog E

NE


3500 kmCore

6371 km


Mantle

ν

IceCube



!

" E ~ (2 # 5) TeV ($m032 /1eV2)


!

Veff " Rµ3 "

E 3 ;<1TeVln3;>1TeV

# $ %

!

NE ~ Aeff E"#

!

Veff nN "nN # det

!

E "3.7

!

E1



1 TeVlog E

NE


3500 kmCore

6371 km


Mantle

ν

IceCube



!

" E ~ (2 # 5) TeV ($m032 /1eV2)


!

Veff " Rµ3 "

E 3 ;<1TeVln3;>1TeV

# $ %

!

NE ~ Aeff E"#

!

Veff nN "nN # det

!

E "3.7

!

E1

IceCube energy range is well-suited to explore sterile ν

IceCube IceCube Neutrino ObservatoryNeutrino ObservatoryCompleted in December 2010


Atmospheric NeutrinoAtmospheric Neutrino Flux DataFlux Data

Precise measurement of high-Precise measurement of high-energy atmospheric neutrino fluxenergy atmospheric neutrino fluxdata can be used todata can be used to probe theprobe theexistence of sterile neutrinosexistence of sterile neutrinos

Recently published data onatmospheric muon neutrino fluxAMANDA IIIceCube 40 string

IceCube Collab. [Abbasi et al.] 2010

IceCube Collab.[Abbasi et al.] 2010


Model of Model of ννs s MixingMixing with Active with Active νν's's

•• ν νss mixes with mixes with ννµµ and and ννττ via massvia mass eigenstates eigenstates mm0 0 , , mm33

We consider only 1 sterile neutrino species and normal hierarchyWe consider only 1 sterile neutrino species and normal hierarchy

m1

m2

m3

m0

νs mass-mixing scheme

!

˜ " =

"s"#

' $ c23"# % s23" µ

" µ' $ c23" µ + s23"#

&

'

( ( (

)

*

+ + +

•• Mixing with Mixing with mm22 is suppressed by is suppressed by

•• Mixing with Mixing with ννee (via (via mm11)) can becan be neglectedneglected

!

"0 = cos# "s $ sin# "%'

"3 = cos# "%' $ sin# "s

"2 =" µ' Mixing matrixMixing matrix

Propagation basisPropagation basisEvolution Evolution eqeq. .

!

sin" (#m322 /2E) γγ--additional mixing angleadditional mixing angle


Uµ0

ννµµ−ν−νµµ Oscillation ProbabilityOscillation ProbabilityAntineutrinos Neutrinos


IceCube Collab. [R. Abbasi et al. 2010]

Atmospheric Atmospheric Muon Muon Neutrino FluxNeutrino Flux

!

N = dE d"## [$µ (E,% z)Aeff (E,% z) +$ µ (E,% z)A eff (E,% z)]Number ofNumber ofmuon muon eventsevents

Flux at the detector

With known With known NN and and AAeff eff , invert to calculate flux , invert to calculate flux

Effective area

Originalflux

Oscillationprobability!

"µ ="µ0 Pµµ +"e

0 Peµ # "µ0 Pµµ

For 3-flavor oscillationFor 3-flavor oscillationproperties (without sterileproperties (without sterileνν mixing) mixing) PPµµµµ ~ 1~ 1

Zenith angle (97-180 deg.)Zenith angle (97-180 deg.)averaged fluxaveraged flux


!

N = dE d"## [$µ (E,% z)Aeff (E,% z) +$ µ (E,% z)A eff (E,% z)]

SR & A.Yu. Smirnov, JHEP (2011)

Atmospheric Atmospheric Muon Muon Neutrino FluxNeutrino Flux

Number ofNumber ofmuon muon eventsevents

Flux at the detector

With known With known NN and and AAeff eff , invert to calculate flux , invert to calculate flux

Effective area

Originalflux

Oscillationprobability

For 3-flavor oscillationFor 3-flavor oscillationproperties (without sterileproperties (without sterileνν mixing) mixing) PPµµµµ ~ 1~ 1

Zenith angle (97-180 deg.)Zenith angle (97-180 deg.)averaged fluxaveraged flux

For sterile For sterile νν mixing mixing PPµµµµ ≠≠ 1 1

!

"µ ="µ0 Pµµ +"e

0 Peµ # "µ0 Pµµ


Sterile Sterile νν Mixing Effect on Flux Mixing Effect on Flux

Varying sterileVarying sterile νν mass shifts inmass shifts inenergy the dip in the flux,energy the dip in the flux,EE ~ ( ~ (ΔΔmm0303))22

IceCube IceCube is well-suited tois well-suited to probeprobethe the allowed sterileallowed sterile νν mass rangemass range(~0.5-3 (~0.5-3 eVeV))

Maximum effect is ~40% Maximum effect is ~40% sincesince Φ(νΦ(νµµ)) = 1.4 x = 1.4 x Φ(Φ(ννµ µ barbar))Averaging over half of the skyAveraging over half of the skyreduces it to ~20%reduces it to ~20%

Averaging over near-vertical smallAveraging over near-vertical smallzenith angle can enhance the sterilezenith angle can enhance the sterileνν effecteffect

At the cost of reduced numberAt the cost of reduced numberof events and increased errorof events and increased error


Sterile Sterile νν Mixing Effect on Flux Mixing Effect on Flux


Varying sterileVarying sterile νν mass shifts inmass shifts inenergy the dip in the flux,energy the dip in the flux,EE ~ ( ~ (ΔΔmm0303))22

IceCube IceCube is well-suited tois well-suited to probeprobethe the allowed sterileallowed sterile νν mass rangemass range(~0.5-3 (~0.5-3 eVeV))

Maximum effect is ~40% Maximum effect is ~40% sincesince Φ(νΦ(νµµ)) = 1.4 x = 1.4 x Φ(Φ(ννµ µ barbar))Averaging over half of the skyAveraging over half of the skyreduces it to ~20%reduces it to ~20%

Averaging over near-vertical smallAveraging over near-vertical smallzenith angle can enhance the sterilezenith angle can enhance the sterileνν effecteffect

At the cost of reduced numberAt the cost of reduced numberof events and increased errorof events and increased error

Zenith Angle Event DistributionZenith Angle Event Distribution


Integrated over E > 100 GeV in each bin

Ice properties notIce properties notwell-understoodwell-understood


Zenith Angle Event DistributionZenith Angle Event Distribution


Integrated over E > 100 GeV in each bin

Ice properties notIce properties notwell-understoodwell-understood

Sterile Sterile νν mixing mixingshifts the eventsshifts the eventsup/downup/down

Simulate events withSimulate events withsterile sterile νν mixing and mixing andcompare with datacompare with data


EventEvent Suppression FactorSuppression Factor

Number of events in each zenith binNumber of events in each zenith bin

Suppression factor inSuppression factor in individual zenith binindividual zenith bin Indicate effect of sterileIndicate effect of sterile ν ν mixing mixing Strong effect in near vertical binsStrong effect in near vertical bins

With sterile With sterile νν mixing mixing No sterile No sterile νν mixing mixing

Expected events for sterileExpected events for sterile νν mixingmixing casecase

IceCubeIceCubesimulationsimulation

!

N j = 2" dcos# dE$% µ

0 (E,# z)Pµµ (E,# z)Aeff (E,# z)Eth

&' j cos# z

&+ antineutrinos

!

S j =N j (Pµµ "1)N j0 (Pµµ #1)

!

N j = S j N jMC


!

"2(C,# ;$m032 ,sin2%) =

(N j

dat & N jmod (C,# ;$m03

2 ,sin2%))2

(' jdat )2

j(

Event Distribution with Sterile Event Distribution with Sterile ννRenormalized model of sterile Renormalized model of sterile νν mixing mixing

Chi-squareChi-square analysisanalysis

Overall normalization and tilt

Null hypothesisNull hypothesis

No νs mixing

Minimize for Minimize for CC and and ττ (leave out last 2 bins) (leave out last 2 bins)

Best-fit models and null distributionBest-fit models and null distribution

!

N jmod (C," ;#m03

2 ,sin2$) =

C[1+" (cos% z + 0.5)]N jMCS j (#m03

2 ,sin2$)

!

N jnull (C," ;#m03

2 ,0)


Bounds on Sterile Bounds on Sterile νν Parameters ParametersNull hypothesis (without sterile Null hypothesis (without sterile νν mixing) fits data rater well mixing) fits data rater well

Reject sterile Reject sterile νν mixing models: mixing models:

Null (MC) modelNull (MC) model

!

" #2 = #min,model2 $ #min,null

2

!

"min,null2 =14.16 (20 dof);C = 0.98,# = 0.04


Bounds on Sterile Bounds on Sterile νν Parameters ParametersNull hypothesis (without sterile Null hypothesis (without sterile νν mixing) fits data rater well mixing) fits data rater well

Reject sterile Reject sterile νν mixing models: mixing models:

Null (MC) modelNull (MC) model

Models with large mixing of sterile Models with large mixing of sterile ννwith active with active νν''s s can be constrainedcan be constrained

!

" #2 = #min,model2 $ #min,null

2

!

"min,null2 =14.16 (20 dof);C = 0.98,# = 0.04


!

|Uµ0 |2= sin2"23 sin

2# $ 12 sin

2#

|Uµ0 |2 ~ 0.02 % 0.04

ννs s MixingMixing with Active with Active νν's's

•• ν νss mixes with mixes with ννµµ only and only and flavor states are propagation statesflavor states are propagation states

We consider only 1 sterile neutrino species and normal hierarchyWe consider only 1 sterile neutrino species and normal hierarchy

m1

m2

m3

m0

νs - νµ flavor-mixing scheme

!

"s"#" µ

$

%

& & &

'

(

) ) )

=Uf

"0"3"2

$

%

& & &

'

(

) ) ) Mixing matrixMixing matrix

Evolution equation Evolution equation

!

id"dx

= H" = (UfHdiagU f

T +V )"!

|Uµ0 |2= sin2"24 = sin2"23 sin

2# correspondence with mass-mixing schemecorrespondence with mass-mixing scheme


ννµµ−ν−νµµ Oscillation ProbabilityOscillation Probabilityνs mass mixing νs - νµ flavor mixing Antineutrinos


ννµµ−ν−νµµ Oscillation ProbabilityOscillation Probabilityνs mass mixing νs - νµ flavor mixing Neutrinos


EventEvent Suppression FactorSuppression Factorν s

mas

s m

ixin

g

ν s - ν µ

flav

or m

ixin

g


Event Distribution with Sterile Event Distribution with Sterile νν







Sterile ν model fits data better than thenull hypothesis of no sterile ν mixing!



Future expanded data set from Future expanded data set from IceCube IceCube cancanpotentially rule out or discover sterile potentially rule out or discover sterile νν's's



Sterile ν model fits data better than thenull hypothesis of no sterile ν mixing!


Understanding the detector betterUnderstanding the detector better


After all After all IceCube IceCube is not builtis not builtfor sterile neutrino search orfor sterile neutrino search oreven to do oscillation physics,even to do oscillation physics,but to search for astrophysicalbut to search for astrophysicalneutrino sourcesneutrino sources

•• Muon Muon energy resolutionenergy resolution•• Simulation of the detectorSimulation of the detector•• Atmospheric Atmospheric muon muon backgroundbackground

Need to be understood betterNeed to be understood better



Upcoming data release fromUpcoming data release fromIceCube IceCube 59 strings and the full59 strings and the fulldetector (86 strings) willdetector (86 strings) willenhance sterile neutrino searchenhance sterile neutrino search

How to distinguish mixing schemes?How to distinguish mixing schemes?

νs - νµ flavor mixingνs mass mixing


Summary and OutlookSummary and Outlook•• Atmospheric high-energy (Atmospheric high-energy (TeVTeV) neutrinos can be used to probe) neutrinos can be used to probe

fundamental neutrino physicsfundamental neutrino physics

•• IceCube IceCube provides the largest sample of data to probe existence ofprovides the largest sample of data to probe existence of~1 ~1 eV eV sterile neutrinos in naturesterile neutrinos in nature through through muon muon neutrinoneutrinodisappearance at the MSW resonancedisappearance at the MSW resonance

•• A signature of sterile neutrino effect, however, depends on theA signature of sterile neutrino effect, however, depends on themixing model with active neutrinosmixing model with active neutrinos

•• Currently available Currently available IceCube IceCube 40 string data can bound the sterile40 string data can bound the sterileneutrino model parameters in the mass-mixing modelneutrino model parameters in the mass-mixing model

•• A discovery of sterile neutrino is not ruled-out, however, in theA discovery of sterile neutrino is not ruled-out, however, in theflavor-mixing modelflavor-mixing model

•• Expanded data set from Expanded data set from IceCube IceCube with better understanding of thewith better understanding of thedetector willdetector will be crucial to probe sterile neutrinosbe crucial to probe sterile neutrinos

•• Tau Tau neutrino measurement may be able to distinguish betweenneutrino measurement may be able to distinguish betweensterile neutrino mixing modelssterile neutrino mixing models


Backup SlidesBackup Slides

ννµµ−ν−νµµ ProbProb. in other mixing schemes. in other mixing schemes

SNAC 2011, Virginia Tech S. Razzaque, extra slide 1

Supp. Factor in other mixing schemesSupp. Factor in other mixing schemes

SNAC 2011, Virginia Tech S. Razzaque, extra slide 2

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IceCube’s Sensitivity to Sterile Neutrinos€¦ · SNAC 2011, Virginia Tech S. Razzaque, slide...

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