padova, 11 may 2012 thomas...

Sterile neutrinos at the eV scale?Padova, 11 May 2012

Thomas Schwetz-Mangold

Max-Planck-Institut für KernphysikHeidelberg

T. Schwetz 1

Outline

Introduction

Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data

Active-sterile mixing

Can we explain all the hints together?

More exotic proposals

Cosmology

How to proceed?

Conclusions

T. Schwetz 2

Introduction

Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 3

Introduction

Global fit within three-flavour framework

Gonzalez-Garcia, Maltoni, Salvado, TS, in prep.

with SBL reactor data:

sin2 θ13 = 0.022+0.0033−0.0030

sin2 2θ13 = 0.086± 0.012

θ13 = (8.5+0.62−0.61)

6.9σ significance

without SBL data using2011 flux prediction:

sin2 θ13 = 0.026+0.0034−0.0032

sin2 2θ13 = 0.101+0.013−0.012

θ13 = (9.3± 0.59)

8.0σ significance

T. Schwetz 4

Introduction

Let us consider the existence of “sterile neutrinos”

“sterile neutrinos”: fermionic gauge singlets or right-handed neutrinos

Yukawa term:LY = −yLLφNR + h.c.

bare Majorana mass term:

12

NTR C−1M∗

RNR + h.c.

we have no (very little) guidance about their mass (y and MR)

T. Schwetz 5

Introduction

Sterile neutrinos at which scale?

I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)

I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al

I maybe they have mass in the keV range (warm dark matter)

I maybe they have mass in the eV range (SBL neutrino oscillations)

I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov

T. Schwetz 6

Introduction

4-neutrino schemes

3+1: small perturbation to 3-active case

T. Schwetz 7

Introduction

5-neutrino schemes

(3+2) scheme∆m

2

LSND

∆m2

sol

∆m2

atm

∆m2

LSND

νe

νµ ντ νs

m2

i

Peres, Smirnov, hep-ph/0011054; Sorel, Conrad, Shaevitz, hep-ph/0305255

T. Schwetz 8

Hints for sterile neutrinos

Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 9

Hints for sterile neutrinos The reactor anomaly

New reactor flux calculationsI to predict the νe flux from nuclear reactors one has to convert the

measured e− spectra from 235U, 239Pu, 241Pu into neutrino spectraSchreckenbach et al., 82, 85, 89

I recent improved calculation Mueller et al., 1101.2663

(ab initio calculations + virtual branches for missing part)∼ 3% higher fluxes

T. Schwetz 10


New reactor flux calculations

I confirmed by independent calculation P. Huber, 1106.0687

(virtual branches)

I increase of predicted number of neutrino-induced events compared toold flux calculations:

235U 239Pu 241Pu 238U3.7% 4.2% 4.7% 9.8%

T. Schwetz 11


New reactor flux calculations

data from short-baseline reactorexperiments:

µ = 0.927± 0.023

2.9σ away from 1

Mention et al, 1101.2755 (2012 upd)

T. Schwetz 12


New reactor fluxes and reactor dataMention et al., 1101.2755 (2012 upd)

I non-zero θ13 can reduce flux at L & 1 km but not shorter baselinesI sterile neutrino with ∆m2 ∼ 1 eV2 can account for rate reduction at

L & 10− 100 mI all based on ILL electron spectrum measurement

systematic error...?

T. Schwetz 13


Reactor data and sterile neutrinos

3 4 5 6 7 8E

pos [MeV]

0.8

0.9

1

1.1

obse

rved

/ pr

edic

ted

rate

3 4 5 6 7 8E

pos [MeV]

0.9

1

Bugey3 15 m Bugey3 40 m

Bugey4

χ2

no osc = 59.0/69

χ2

3+1 = 50.1/67

χ2

3+2 = 46.5/65

10-2

10-1

100

sin22θ

react

10-1

100

101

∆m2 41

[eV

2 ]

90%, 99% CL (2 dof)

curves: old fluxescolors: new fluxes

sin2 2θreact = 4|U2e4|(1 − |U2

e4|) ≈ 4|U2e4|

∆m241 [eV2] |Ue4| ∆m2

51 [eV2] |Ue5| ∆χ2(no osc)3+1 1.78 0.151 8.5 (98% CL 2 dof)3+2 0.46 0.108 0.89 0.124 12.1 (98% CL 4 dof)

bounds on Ue4,5 become “preferred regions” with new reactor fluxesMention et al., 11; Kopp, Maltoni, TS, 11

T. Schwetz 14


3+1 and 3+2 fit to SBL reactor data

0.1 1 10

∆m2

41 [eV

2]

50

55

60

65

χ2

0.1 1 1050

55

60

65

dashed:old fluxsolid:new fluxSBL reactor data (84 data points)

(3+1)

(3+2)

preference for sterile neutrino oscillations with new fluxes

I ∆χ2(3 + 1/no-osc) = 8.5 → 98.6% CL (2 dof)I ∆χ2(3 + 2/no-osc) = 12.1 → 98.3% CL (4 dof)I old flux: ∆χ2 = 3.6(4.4) for 3+1 (3+2)I further improvement of fit for 3+2 wrt 3+1 with new fluxes

Kopp, Maltoni, TS, 11

T. Schwetz 15

Hints for sterile neutrinos Gallium anomaly

The Gallium anomaly

callibration data in galliumsolar neutrino experimentsνe +71 Ga →71 Ge + e−

ratio of measured topredicted rate:

RBahcall = 0.86± 0.05 (2.8σ)

RHaxton = 0.76± 0.09 (2.7σ)

Acero, Giunti, Laveder, 0711.4222; Giunti, Laveder, 1006.3244

T. Schwetz 16


The Gallium anomaly

comparing Gallium and reactor anomalies:

T. Schwetz 17


Constraint from LSND and KARMENLSND and KARMEN measure the cross section for νe +12 C →12 N + e−

consistent with expectations → limit on νe disappearance

Conrad, Shaevitz, 1106.5552

T. Schwetz 18


Constraint from LSND and KARMEN

T. Schwetz 19

Hints for sterile neutrinos SBL appearance data

νµ → νe data at the E/L ∼ 1 eV2 scale

I LSND νµ → νe , 87.9± 22.4± 6.0 excess eventsP = (0.264± 0.067± 0.045)% ∼ 3.8σ away from zero

I MiniBooNE νµ → νeE > 475: no excess, E < 475: ∼ 3σ excess

I MiniBooNE νµ → νe , inconclusiveconsistent with MBν as well as with LSND in 2ν framework

I KARMEN νµ → νe , tight constraint on LSND region(slightly smaller L/E than LSND)

T. Schwetz 20

Hints for sterile neutrinos SBL appearance data

Latest MiniBooNE results Z. Djurcic @ NuFact11

T. Schwetz 21


Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 22


What do we know about active-sterile mixing?

U =

Ue1 Ue2 Ue3 Ue4Uµ1 Uµ2 Uµ3 Uµ4Uτ1 Uτ2 Uτ3 Uτ4Us1 Us2 Us3 Us4

independent information on Uα4 mainly from disappearance exps

T. Schwetz 23


Ue4

from reactor and Gallium anomalies: Ue4 ≈ 0.15

T. Schwetz 24


Uµ4

H

10-3 10-2 10-1

|Uµ4|2

10-2

10-1

100

101

∆m2 41

[eV

2 ]

atmospheric

CDHS

Kopp, Maltoni, TS, in prepMiniBooNE, 1106.5685

sin2 2θ = 4|U2µ4|(1 − |U2

µ4|)

I νµ disappearance CDHS (and also MiniBooNE)I atmospheric neutrinos Bilenky, Giunti, Grimus, TS 99; Maltoni, TS, Valle 01

I MINOS CC/NC data 1001.0336, 1104.3922

I additional constraints from MiniB νµ(νµ) at ∆m2 & 1 eV2

T. Schwetz 25


Uτ4

|U2µ4| = sin2 θ24 < 0.03 |U2

τ4| = cos2 θ24 sin2 θ34 < 0.16

T. Schwetz 26


What do we know about active-sterile mixing?

U =

Ue1 Ue2 Ue3 ≈ 0.15Uµ1 Uµ2 Uµ3 < 0.17Uτ1 Uτ2 Uτ3 < 0.4Us1 Us2 Us3 Us4

|U2

e4| ≈ 0.025|U2

µ4| < 0.03|U2

τ4| < 0.16

for 3+n:

limit on |U2α4| → limit on

3+n∑i=4

|U2αi |

T. Schwetz 27


Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 28


Short-baseline (SBL) experiments

I νµ → νe , νµ → νe appearance searchesLSND, MiniBooNE, KARMEN, NOMAD

I νe disappearance experiments (reactors)Bugey-3 (15, 40, 95), Bugey-4, Goessgen, Krasnoyarsk, Rovno, ILL,Chooz, Palo Verde

I νµ disappearanceCDHS, MiniBooNE, atmospheric neutrinos, MINOS CC/NC

SBL: E/L ∼ eV2 → set ∆m221 ≈ ∆m2

31 ≈ 0exceptions: Chooz, Palo Verde, atmospheric, MINOS

T. Schwetz 29


3+1 SBL oscillations

appearance

Pµe = sin2 2θapp sin2 ∆m241L

4Esin2 2θapp = 4|Ue4|2|Uµ4|2

disappearance

Pαα = 1− sin2 2θdis sin2 ∆m241L

4Esin2 2θdis = 4|Uα4|2(1− |Uα4|2)

I effective 2-flavour oscillationsI no CP violation → can’t reconcile ν (LSND, MB) and ν (MB) dataI constraints from νe (νµ) disappearance experiments on Ue4 (Uµ4)

appearance mixing angle quadratically suppressed

T. Schwetz 30


3+2 SBL oscillationsappearance:

Pνµ→νe = 4 |Ue4|2|Uµ4|2 sin2 φ41 + 4 |Ue5|2|Uµ5|2 sin2 φ51

+ 8 |Ue4Uµ4Ue5Uµ5| sin φ41 sin φ51 cos(φ54 − δ)

disappearance:

Pνα→να ≈ 1− 4∑i=4,5

|Uαi |2 sin2 φi1 − 4 |Uα4|2|Uα5|2 sin2 φ54

[φĳ ≡ ∆m2

ĳL/4E]

I phase δ ≡ arg(

U∗e4Uµ4Ue5U∗

µ5

)→ CP violation Karagiorgi et al. 06; Maltoni, TS 07

I BUT: constrain |Uei | and |Uµi | (i = 4, 5) from disappearanceto be reconciled with appearance amplitudes |UeiUµi |

T. Schwetz 31


3+1 global fit

10-4

10-3

10-2

10-1

sin22θ

SBL

10-1

100

101

∆m2 41

[eV

2 ]

99% CL (2 dof)

LSND + MBν−

MBνKARMENNOMAD

disappearance90, 99% CL

Kopp, Maltoni, TS, 11

Giunti, Laveder, 1109.4033

I no CP violation → LSND versus MBν

I despite relaxed constraints on Ue4 no improvement of global 3+1 fitI LSND+MBν versus rest → compatibility of less than 10−5

T. Schwetz 32


3+1 global fit

10-4

10-3

10-2

10-1

sin22θ

SBL

10-1

100

101

∆m2 41

[eV

2 ]

99% CL (2 dof)

LSND + MBν−

MBνKARMENNOMAD

disappearance90, 99% CL

Kopp, Maltoni, TS, 11 Giunti, Laveder, 1109.4033

I no CP violation → LSND versus MBν

I despite relaxed constraints on Ue4 no improvement of global 3+1 fitI LSND+MBν versus rest → compatibility of less than 10−5

T. Schwetz 32


3+2 global fit

Kopp, Machado, Maltoni, TS, work in prep. Giunti, Laveder, 1109.4033

T. Schwetz 33


3+2 global fit

3 4 5 6 7 8Epos [MeV]

0.8

0.9

1

1.1

obse

rved

/ pr

edic

ted

rate

3 4 5 6 7 8Epos [MeV]

0.9

1

Bugey3 15 m Bugey3 40 m

Bugey4

3+2 react3+2 global

0.3 0.6 0.9 1.2 1.5 3

EνCCQE [GeV]

0

0.2

0.4

0.6

0.8

1

exce

ss e

vent

s

MiniBooNE(neutrinos)

LSND

0.3 0.6 0.9 1.2 1.5 3

EνCCQE [GeV]

0

0.1

0.2

0.3

MiniBooNE(anti-neutrinos)

0.1

0.2

0.3

0.4

PL

SND

[%

]

I 3+2 fit to appearance data only (LSND, MBν, MBν, KARMEN,NOMAD) allows for explanation of MB low energy excess Maltoni, TS, 07

I BUT: this requires large Ue4, Ue5, Uµ4, Uµ5 in sever disagreement withdisappearance bounds

I MB low-E excess cannot be explained using global data

T. Schwetz 34


Have we already discovered CP violation?

90

100

110

90

100

110

0 0.5 1 1.5 2δ [π]

10

20

30

χ2

0 0.5 1 1.5 2

MB475

MB300

MB300

MB475

global data

appearance data

Maltoni, TS 07 Giunti, Laveder, 1109.4033

T. Schwetz 35


There is severe tension in the 3+2 fit

Giunti, Laveder, 1109.4033

T. Schwetz 36


There is severe tension in the 3+2 fit

LSND+MB(ν) vs rest appearance vs disapp.old new old new

χ2PG/dof 25.1/5 19.9/5 19.9/4 14.7/4PG 10−4 0.13% 5× 10−4 0.53%adding MINOS CC/NC Kopp, Machado, Maltoni, TS, work in prep.

χ2PG/dof 30.0/5 24.8/5 24.7/4 19.5/4PG 10−5 10−4 5× 10−5 6× 10−4

I explanation of appearance signal requires Uei and Uµi (i = 4, 5)I no hint for oscillations seen in νµ disappearance⇒ constraints on Uµi in tension with signals

I MINOS data make compatibility worse by one order of magnitude

T. Schwetz 37


Summary so-far

I If we assume that the 3+n oscillation scenario is correct there issevere tension in the global fit and not all data can be explained.

I If we neglect LSND, the hint for νe disappearance from the reactorand Gallium anomalies remain, not in direct conflict with other data(relies on complicated theoretical calculations, uncertainties difficultto estimate)

I If we stick to LSND, probably we have to discard more than one otherexperiment (several experiments constrain νµ disappearance)

T. Schwetz 38


Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 39



I 3-neutrinos and CPT violation Murayama, Yanagida 01;Barenboim, Borissov, Lykken 02; Gonzalez-Garcia, Maltoni, TS 03

I 4-neutrinos and CPT violation Barger, Marfatia, Whisnant 03

I Exotic muon-decay Babu, Pakvasa 02

I CPT viol. quantum decoherence Barenboim, Mavromatos 04

I Lorentz violation Kostelecky et al., 04, 06; Gouvea, Grossman 06

I mass varying ν Kaplan,Nelson,Weiner 04; Zurek 04; Barger,Marfatia,Whisnant 05

I shortcuts of sterile νs in extra dim Paes, Pakvasa, Weiler 05

I decaying sterile neutrino Palomares-Riuz, Pascoli, TS 05; Gninenko 10

I 2 decaying sterile neutrinos with CPVI energy dependent quantum decoherence Farzan, TS, Smirnov 07

I sterile neutrinos and new gauge boson Nelson, Walsh 07

I sterile ν with energy dep. mass or mixing TS 07

I sterile ν with nonstandard interactions Akhmedov, TS 10

most of these proposals

T. Schwetz 40















most of these proposals involve sterile neutrinos

T. Schwetz 40















most of these proposals have problems with some data

T. Schwetz 40

More exotic proposals Sterile neutrino + NSI

3+1 + NSI Akhmedov, TS 10

assume

I a 4th neutrino with ∆m241 ∼ 1 eV2

I a new type of CC-like interaction

LNSI = −2√

2GF∑α,β

εff ′αβ(f PL,Rγµf ′)(lαPLγµνβ) + h.c.

f , f ′ fermions depending on production or detection process

(NC-like NSI will have no relevant effect in short-baseline experimentssince matter effect is very small)

T. Schwetz 41


3+1 + NSI

I zero-distance effects and CPV (NSI-oscillation interference)I can decouple LSND/KARMEN from the rest:

source detectionLSND/KARMEN µ decay ν-nucl CC (e)MiniB/NOMAD π decay ν-nucl CC (e)

CDHS (atm) π decay ν-nucl CC (µ)Bugey/Chooz ν-nucl CC (e) ν-nucl CC (e)

|αLKµe |, |βLK

µe |, δLK, αe , αµ, |βµe |, δ, ∆m241

→ 8 parameters (7 for 3+2 osc)

T. Schwetz 42


3+1 + NSI

I χ2(3+1)osc − χ2

(3+1)NSI = 18.5(5 dof) → 99.76% CLappearance versus disappearance: PG compatibility of 15%

I |Ue4| ≈ 0.116, |Uµ4| ≈ 0.205 (more freedom from new react flux)|εud

µs | ≈ 0.05, |εudeµ| ≈ 0.011, |εeν

µs | ≈ 0.03, |εeνµe | ≈ 0.01

strength of new interactions at the level of few % compared to GFin agreement with bounds Biggio, Blennow, Fernandez-Martinez, 0907.0097

I if due to dim-6 operator εGF (f f ′)(¯ν) expect a charged mediatorwith mφ ∼ mW /

√ε ∼ TeV → excellent prospect at LHC

I BUT: seems difficult (impossible?) to obtain such operators at dim-6in gauge invariant way → go to dim-8 and involve some fine tuningGavela, Hernandez, Ota, Winter, 0809.3451; Antusch, Baumann, Fernandez, 0807.1003

severe constraints from colliders Davidson, Sanz, 1108.5320

T. Schwetz 43

More exotic proposals Soft decoherence

Energy dependent quantum decoherence Farzan, TS, Smirnov 07

I no sterile neutrino needed

I postulate quantum-decoherence of the mass states ⇒damping of the interference terms in the oscillation probabilities.

I damping affects only oscillations with ∆m231 and rapidly decreases

with the neutrino energy

I reconcile LSND signal with MBν and other null-result exps.

I standard explanations of solar, atmos, KamL, MINOS not affected

I LSND signal controlled by the 1-3 mixing: 0.0014 < sin2 θ13 < 0.034

I consistent with reactor anomaly

I positive signal for θ13 in long-baseline accelerator experimentsBUT: near/far comparisonat reactors: null-result →Excluded by Daya Bay/RENO!

T. Schwetz 44

Cosmology

Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 45

Cosmology

eV sterile neutrinos and cosmologyHamann et al., 1006.5276

68, 95, 99% CL

I CMB, SDSS, HST: prefer some extra radiation, but limit on HDMexcludes two eV-scale neutrinos

I BBN: Ns < 1.2 (95% CL) Mangano, Serpico, 1103.1261

I PLANCK: obtain δNs ≈ 0.1 very soon

How bad is the fit if eV-scale neutrinos are imposed?

T. Schwetz 46

Cosmology

eV sterile neutrinos and cosmologyHamann et al., 1006.5276

68, 95, 99% CL

I CMB, SDSS, HST: prefer some extra radiation, but limit on HDMexcludes two eV-scale neutrinos

I BBN: Ns < 1.2 (95% CL) Mangano, Serpico, 1103.1261

I PLANCK: obtain δNs ≈ 0.1 very soon

How bad is the fit if eV-scale neutrinos are imposed?T. Schwetz 46

Cosmology

eV sterile neutrinos and cosmology

bounds assume full equilibration of sterile neutrinos

Hannestad, Tamborra, Tram, 1204.5861

... typically fulfilled for LSND-like mass/mixingEnqvist, Kainulainen, Thomson, NPB92; Shi, Schramm, Fields, astro-ph/9307027; Okada, Yasuda, hep-ph/9606411;

Bilenky, Giunti, Grimus, TS, hep-ph/9804421; DiBari, hep-ph/0108182

T. Schwetz 47

Cosmology

How to accommodate eV sterile neutrinos with cosmology?

invent a mechanism to avoid thermalization

I large chemical potential: Lµ = 10−2

Hannestad, Tamborra, Tram, 1204.5861

Foot, Volkas, hep-ph/9508275; Chu, Cirelli, astro-ph/0608206; Smith, Fuller, Kishimoto, Abazajian, astro-ph/0608377

I assume very low re-heating temperature (dangerously close to BBN)Gelmini, Palomares-Ruiz, Pascoli, astro-ph/0403323

T. Schwetz 48

Cosmology

How to accommodate eV sterile neutrinos with cosmology?

Hamann, Hannestad, Raffelt, Wong, 1108.4136

I limit on neutrino mass (HDM) can be evaded by allowing extraradiation ∆Nml ' 1− 2 and/or DE equation of statew < −1 Elgaroy, Kristiansen, 1104.0704

I BBN constraints on extra radiation can be avoided by introducing achemical potential of νe .

I modifies other cosmological parameters, e.g. ΩCDM (+20%-75%)

⇒ all those options require substantial modification of standard cosmology

T. Schwetz 49

How to proceed?

Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 50

How to proceed?

Many ideas to test eV sterile neutrinos

I radioactive source experiments to test reactor and Gallium anomalies(e.g., in Borexino, SNO+, KamLAND) Cribier et al, 1107.2335; Garvin et al, 1006.2103;

Vergados, Novikov, 1006.3862; Grieb, Link, Raghavan, hep-ph/0611178,...

I several ideas at FNAL (MINOS+, MicroBooNE, MiniBooNEextensions, very-low-E NuFact) B. Louis @ NuFact11

I ICARUS at CERN PS C. Rubbia et al. 0909.0355

I experiments with ∼100 kW proton synchrotronsConrad, Shaevitz 09; Huber, Agarwalla 10; Agarwalla, Conrad, Shaevitz, 11

I signatures in IceCube (Deep Core)Nunokawa, Peres, Zukanovich, hep-ph/0302039; Coubey, 0709.1937; Razzaque, Smirnov, 1104.1390; 1203.5406

T. Schwetz 51

How to proceed?

Many ideas to test eV sterile neutrinos

2011 sterile neutrino workshops:

I LNGS, Italy, May 2011

I FNAL, USA, May 2011

I Virginia Tech, Blacksburg, USA, Sept 2011

White paper on sterile neutrinos published on arxiv: 1204.5379

T. Schwetz 52

Conclusions

Outline

Introduction





Cosmology

How to proceed?

Conclusions

T. Schwetz 53

Conclusions

Conclusions

I There are a couple of "hints" for sterile neutrinos at the eV scale

I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)

I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.

I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)

I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.

Thank you for your attention!

T. Schwetz 54

Conclusions

Conclusions

I There are a couple of "hints" for sterile neutrinos at the eV scale

I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)

I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.

I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)

I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.

Thank you for your attention!T. Schwetz 54

padova, 11 may 2012 thomas...

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