Status of Light Sterile Neutrinos Carlo Giunti

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1 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 /5 Status of Light Sterile Neutrinos Carlo Giunti INFN, Sezione di Torino and Dipartimento di Fisica, Università di Torino giunti@to.infn.it Neutrino Unbound: EPS-HEP 05 Vienna, Austria -9 July 05

2 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 /5 Indications of Short-Baseline Oscillations Reactor Electron Antineutrino Anomaly: ν e ν e deficit L 0m E 4MeV m 0.5eV [Mention et al, PRD 83 (0) ; Mueller et al, PRC 83 (0) 05465; Huber, PRC 84 (0) 0467; Sinev, arxiv:3.45; Ciuffoli, Evslin, Li, JHEP (0) ; Zhang, Qian, Vogel, PRD 87 (03) 07308; Ivanov et al, PRC 88 (03) 05550] Gallium Anomaly: ν e ν e deficit L m E MeV m ev [SAGE, PRC 73 (006) , PRC 80 (009) 05807; Laveder et al, Nucl.Phys.Proc.Suppl. 68 (007) 344, MPLA (007) 499, PRD 78 (008) , PRC 83 (0) ] LSND: Accelerator ν µ ν e 4σ excess L 30m E 50MeV m 0.eV [LSND, PRL 75 (995) 650, PRC 54 (996) 685, PRL 77 (996) 308, PRD 64 (00) 07]

3 Beyond Three-Neutrino Mixing: Sterile Neutrinos C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 3/5 ν τ ν s ν µ ν e ν ν 3 ν 4 ν 5 ν m 3 m m m 4 m 5 logm ν s m SOL 3ν-mixing m ATM m SBL Terminology: a ev-scale sterile neutrino means: a ev-scale massive neutrino which is mainly sterile

4 Sterile Neutrinos from Physics Beyond the SM Neutrinos are special in the Standard Model: the only neutral fermions Active left-handed neutrinos can mix with non-sm singlet fermions often called right-handed neutrinos Neutrino Portal [A. Smirnov, arxiv: ] Light anti-ν R are light sterile neutrinos ν c R ν sl (left-handed) Sterile means no standard model interactions [Pontecorvo, Sov. Phys. JETP 6 (968) 984] Active neutrinos (ν e,ν µ,ν τ ) can oscillate into light sterile neutrinos (ν s ) Observables: Disappearance of active neutrinos (neutral current deficit) Indirect evidence through combined fit of data (current indication) Short-baseline anomalies + 3ν-mixing: m m 3 m 4... ν ν ν 3 ν 4... ν e ν µ ν τ ν s... C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 4/5

5 Effective SBL Oscillation Probabilities in 3+ Schemes ( ) m P SBL ( ) sin ϑ ν ( ) αβ sin 4 L α ν β 4E sin ϑ αβ = 4 U α4 U β4 ( ) m P SBL ( ) sin ϑ ν ( ) αα sin 4 L α ν α 4E sin ϑ αα = 4 U α4 ( U α4 ) Perturbation of 3ν Mixing: U e4, U µ4, U τ4, U s4 6 mixing angles U = U e U µ U τ U s U e U µ U τ U s U e3 U µ3 U τ3 U s3 U e4 U µ4 U τ4 U s4 SBL 3 Dirac CP phases 3 Majorana CP phases But CP violation is not observable in current SBL experiments! Observable in LBL accelerator exp. sensitive to matm [de Gouvea, Kelly, Kobach, PRD 9 (05) ; Klop, Palazzo, PRD 9 (05) 07307; Berryman, de Gouvea, Kelly, Kobach, arxiv: ] and solar exp. sensitive to msol [Long, Li, Giunti, PRD 87, 3004 (03) 3004] C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 5/5

6 3+: Appearance vs Disappearance C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 6/5 Amplitude of ν e disappearance: sin ϑ ee = 4 U e4 ( U e4 ) 4 U e4 Amplitude of ν µ disappearance: sin ϑ µµ = 4 U µ4 ( U µ4 ) 4 U µ4 Amplitude of ν µ ν e transitions: sin ϑ eµ = 4 U e4 U µ4 4 sin ϑ ee sin ϑ µµ Upper bounds on ν e and ν µ disappearance strong limit on ν µ ν e [Okada, Yasuda, IJMPA (997) 3669; Bilenky, Giunti, Grimus, EPJC (998) 47] Similar constraint in 3+, 3+3,..., 3+N s!

7 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 7/5 3+ Our Fit Global 3+ Fit Kopp, Machado, Maltoni, Schwetz 68.7% CL 90.00% CL 95.45% CL 99.00% CL 99.73% CL [ev ] m ν e DIS ν µ DIS DIS APP [04 update of Giunti, Laveder, Li, Long, PRD 88 (03) ] 4 3 sin ϑ eµ GoF = 5% PGoF = 0.% GoF = 9% PGoF = 0.0% [Kopp, Machado, Maltoni, Schwetz, JHEP 305 (03) 050]

8 MiniBooNE Low-Energy Excess? [ev ] m 4 ν e&ν µdis MiniBooNE 68.7% CL (σ) 95.45% CL (σ) 99.73% CL () OPERA ATM+SUN ICARUS 4 3 sin ϑ eµ ν edis ν µdis * Excess Events / MeV E MiniBooNE ν e Data Expected Background sin ϑ = 0.98, m = 0.04 ev (bf) sin ϑ = 0.007, m = 0.5 ev sin ϑ = 0.00, m = 0.9 ev sin ϑ = 0.003, m = 3 ev [MeV] No fit of low-energy excess for realistic sin ϑ eµ 3 3 Neutrino energy reconstruction problem? [Martini, Ericson, Chanfray, PRD 87 (03) 03009] MB low-energy excess is the main cause of bad APP-DIS PGoF = 0.% Pragmatic Approach: discard the Low-Energy Excess because it is very likely not due to oscillations C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 8/5

9 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 9/5 [ev ] m 4 3+ GLO 68.7% CL 90.00% CL 95.45% CL 99.00% CL 99.73% CL + + [04 update of Giunti, Laveder, Li, Long, PRD 88 (03) ] Pragmatic 3+ Fit [Giunti, Laveder, Y.F. Li, H.W. Long, PRD 88 (03) ] 4 3 sin ϑ eµ MiniBooNE E > 475MeV GoF = 6% PGoF = 7% 3+ ν e DIS ν µ DIS DIS APP APP ν µ ν e & ν µ ν e : LSND (ν s ), MiniBooNE (?), OPERA ( ν s), ICARUS ( ν s), KARMEN ( ν s), NOMAD ( ν s), BNL-E776 ( ν s) DIS ν e & ν e : Reactors (ν s ), Gallium (ν s ), ν e C ( ν s), Solar ( ν s) DIS ν µ & ν µ : CDHSW ( ν s), MINOS ( ν s), Atmospheric ( ν s), MiniBooNE/SciBooNE ( ν s) No Osc. nominally disfavored at 6. χ /NDF = 47.7/3

10 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 /5 ν e and ν µ Disappearance 3+ GLO 3+ GLO 68.7% CL 90.00% CL 95.45% CL 99.00% CL 99.73% CL 68.7% CL 90.00% CL 95.45% CL 99.00% CL 99.73% CL [ev ] m 4 + [ev ] m 4 + ν e DIS ν µ DIS ν e DIS 95.45% CL (σ) 99.73% CL () sin ϑ ee ν µ DIS 95.45% CL (σ) 99.73% CL () sin ϑ µµ

11 Neutrinoless Double-β Decay m ββ = U e m + U e e iα m + U e3 e iα 3 m 3 + U e4 e iα 4 m 4 χ % 99% 95.45% 90% 68.7% SBL GERDA, EXO, KLZ, CUOR 90% CL 3 (4) m ββ Pragmatic 3+ Fit [Giunti, Laveder, Li, Long, 04] m (k) ββ = U ek m k m m 4 m (4) ββ U e4 m 4 surprise: possible cancellation with m (3ν) ββ [Barry et al, JHEP 07 (0) 09] [Li, Liu, PLB 706 (0) 406] [Rodejohann, JPG 39 (0) 4008] [Girardi, Meroni, Petcov, JHEP 3 (03) 46] C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 /5

12 3ν Normal Ordering 3ν Inverted Ordering σ σ σ σ µ µ µk µk µ µ3 3 3 µ3 µ Lightest mass: m 4 Lightest mass: 3ν Normal Ordering m3 3ν Inverted Ordering (+,+) (+, ) (,+) (, ) σ σ CPV 3 (+,+) (+, ) (,+) (, ) σ σ CPV mββ mββ Lightest mass: m 3 Lightest mass: m3 C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 /5

13 ν4 ν4 σ σ µ4 µ4 µ µ µk µk σ σ µ µ3 3 3 µ3 3+ Normal 3ν Ordering 3+ Inverted 3ν Ordering σ σ µ σ σ Lightest mass: m 4 Lightest mass: 3+ Normal 3ν Ordering m3 3+ Inverted 3ν Ordering σ σ CPV σ σ CPV mββ mββ (+,+,+) (+,+, ) (+,,+) (+,, ) (,+,+) (,+, ) (,,+) (,, ) 4 4 (+,+,+) (+,+, ) (+,,+) (+,, ) (,+,+) (,+, ) (,,+) (,, ) 4 3 Lightest mass: m 3 Lightest mass: m3 [Giunti, Zavanin, arxiv: ] C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 3/5

14 Normal 3ν Ordering Inverted 3ν Ordering 3ν 3+ 3ν 3+ m ββ m ββ m β Normal 3ν Ordering 4 m β Inverted 3ν Ordering 3ν 3+ 3ν 3+ m ββ m ββ Σ [Giunti, Zavanin, arxiv: ] Σ C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 4/5 4

15 Conclusions C. Giunti Status of Light Sterile Neutrinos EPS-HEP 05 3 July 05 5/5 Short-Baseline ν e and ν e Disappearance: Experimental data agree on Reactor νe and Gallium ν e anomalies. Problem: unknown systematic uncertainties (Reactor νe flux). Many promising projects to test unambiguously short-baseline νe and ν e disappearance in a few years with reactors and radioactive sources. Independent tests through effect of m4 in β-decay and ββ 0ν -decay. Short-Baseline ν µ ν e LSND Signal: ( ) Not seen by other SBL ν µ ( ) ν e experiments. MiniBooNE experiment has been inconclusive. Experiments with near detector are needed to check LSND signal! If Ue4 > 0 why not U µ4 > 0? = sin ϑ eµ = 4 U e4 U µ4 > 0 Pragmatic 3+ Fit is fine: moderate APP-DIS tension. 3+ is not needed: same APP-DIS tension as 3+ and no evidence of CP violation. Cosmology: Tension between Neff = and m s ev. Cosmological and oscillation data may be reconciled by a non-standard cosmological mechanism.