Sterile Neutrinos in July 2010

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1 Sterile Neutrinos in July 0 Carlo Giunti INFN, Sezione di Torino Presidenza INFN, Roma, 19 July 0 Collaboration with Marco Laveder (Padova University) C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 1

2 Standard Model: Massless Neutrinos Standard Model: L c R =µ no Dirac mass term Ä D = m D ( L R + R L ) Majorana Neutrino: c = c R = R =µ Majorana mass term Ä M = 1 mm L R c + c R L Standard Model: Majorana mass term not allowed by SU() L U(1) Y (no Higgs triplet) C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0

3 Neutrinos are special in the Standard Model: the only neutral fermions In extensions of SM neutrinos can mix with non-sm fermions L «L = «L Φ = i Φ = 0 Ô Symmetry v «L Breaking 0 («= e ) L «L Φ can be coupled to new non-sm chiral fermion fields f R Dirac mass terms L «L Φf R + Majorana mass terms f C R f R f R are often called Right-Handed Neutrinos: f R R If f R are light, they are called Sterile Neutrinos: s L = f C R C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 3

4 Sterile Neutrinos Sterile means No Standard Model Interactions Obviously no electromagnetic interactions as normal active neutrinos Thus Sterile means No Standard Weak Interactions But Sterile Neutrinos are not absolutely sterile: Gravitational Interactions New Non-Standard Interactions of the Physics Beyond the Standard Model which generates the masses of sterile neutrinos Extremely interesting and powerful window on Physics Beyond the SM Active Neutrinos ( e ) can oscillate into Sterile Neutrinos ( s ) Observable: disappearance of Active Neutrinos or indirect evidence through combined fit of data C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 4

5 How many Sterile Neutrinos? e + e Z µ e 3 active flavor neutrinos mixing µ «L = N k=1 U «k kl «= e N 3 no upper limit! Mass Basis: Flavor Basis: e s1 s ACTIVE STERILE C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 5

6 Experimental Evidences of Neutrino Oscillations ¼ ½ Homestake Kamiokande Solar GALLEX/GNO & SAGE e Super-Kamiokande msol ³ ev Reactor e disappearance Atmospheric Accelerator disappearance ¼ SNO BOREXino (KamLAND) Kamiokande IMB Super-Kamiokande MACRO Soudan- (KK & MINOS) ½ sin SOL ³ 0 3 m ATM ³ 4 3 ev sin ATM ³ 0 50 Two scales of m : m ATM ³ 30 m SOL Large mixings: ATM ³ 45 Æ SOL ³ 34 Æ C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 6

7 Three-Neutrino Mixing «L = 3 k=1 U «k kl («= e ) three flavor fields: e,, three massive fields: 1,, 3 m 1 + m 3 + m 13 = m m 1 +m 3 m +m 1 m 3 = 0 m SOL = m 1 ³ ev m ATM ³ m 31 ³ m 3 ³ 4 3 ev C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 7

8 Allowed Three-Neutrino Schemes m m ν 3 ν m SOL ν 1 m ATM m ATM ν m SOL ν 1 ν 3 normal inverted different signs of m 31 ³ m 3 absolute scale is not determined by neutrino oscillation data C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 8

9 Interesting possibility: a new msbl 1eV It has been studied in connection with searches of neutrino oscillations in Short-BaseLine Experiments L E 1 m MeV =µ m SBL 1eV Necessary introduction of at least one new massive neutrino: 4- Mixing m SBL = m 41 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 9

10 Four-Neutrino Schemes: + and 3+1 m m ν 4 ν 4 ν 3 m SBL m SBL ν 3 ν ν + ν ν 1 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0

11 LSND [PRL 75 (1995) 650; PRC 54 (1996) 685; PRL 77 (1996) 308; PRD 64 (001) 11007] e L ³ 30m 0MeV E 00MeV Beam Excess Beam Excess p(ν _ µ ν_ e,e+ )n p(ν _ e,e+ )n other L/E ν (meters/mev) m (ev /c 4 ) Karmen Bugey 90% (L max -L <.3) 99% (L max -L < 4.6) CCFR NOMAD sin θ m LSND 0 ev ( m ATM m SOL ) C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 11

12 + Four-Neutrino Schemes m m ν 4 ν m ATM ν 3 m SOL ν 1 m SBL m SBL ν m SOL ν 1 normal ν 4 m ATM ν 3 inverted C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 1

13 + Schemes are strongly disfavored by solar and atmospheric data 50 χ solar + KamLAND solar solar (pre SNO salt) global solar + KamLAND χ PG χ PC 99% CL (1 dof) atm + KK + SBL η s η s s = U s1 + U s [Maltoni, Schwetz, Tortola, Valle, New J. Phys. 6 (004) 1, arxiv:hep-ph/040517] 99% CL: s 0 5 (solar + KamLAND) s 0 75 (atmospheric + KK) C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 13

14 3+1 Four-Neutrino Schemes m m m m ν ν 4 ν 4 ν 3 m SOL m ATM ν m ATM ν 1 m SOL ν 1 ν 3 m SBL m SBL m SBL m SBL ν 3 ν m SOL m ATM ν m ATM ν 1 m SOL ν 4 ν 4 ν 1 ν 3 normal 3 -inverted 4 -inverted fully-inverted Perturbation of 3- Mixing U e4 1 U 4 1 U 4 1 U s4 ³ 1 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 14

15 Effective SBL Oscillation Probability in 3+1 Schemes P «= sin «sin m L 4E sin «= 4 U «4 U 4 («= ) No CP Violation! P ««= 1 sin ««sin m L 4E sin ««= 4 U «4 1 U «4 U e1 U e U e3 U e4 sin ««1 U = U µ1 U τ1 U µ U τ U µ3 U τ3 U µ4 U τ4 U s1 U s U s3 U s4 SBL U «4 ³ sin ««4 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 15

16 e disappearance experiments: sin ee = 4 U e4 1 U e4 ³ 4 U e4 disappearance experiments: sin = 4 U 4 1 U 4 ³ 4 U 4 e experiments: sin e = 4 U e4 U 4 ³ 1 4 sin ee sin Upper bounds on sin ee and sin imply strong limit on sin e C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 16

17 e Disappearance [Savannah River (SRP), PRD 53 (1996) 6054] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 17

18 ( ) Disappearance [CCFR, Z. Phys. C 7 (1985) 53] [CDHSW, PLB 134 (1984) 81] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 18

19 99% CL ( ) ( ) e 1 NEV + atm + KK NEV + atm(1d) m LSND [ev ] 0 LSND global LSND DAR -1 95% CL sin θ LSND [Maltoni, Schwetz, Tortola, Valle, New J. Phys. 6 (004) 1, arxiv:hep-ph/040517] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 19

20 MiniBooNE Neutrinos [PRL 98 (007) 31801] e L ³ 541m 475MeV E 3GeV Events / MeV Data ν e from µ + ν e from K 0 ν e from K π 0 misid Nγ dirt other Total Background QE E ν (GeV) Excess Events / MeV 0.8 data - expected background best-fit ν µ ν e 0.6 sin θ=0.004, m =1.0eV 0.4 sin θ=0., m =0.1eV QE E ν (GeV) [PRL (009) 180, arxiv:081.43] Low-Energy Anomaly! [arxiv: ] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 0

21 MiniBooNE Antineutrinos [arxiv: ] e L ³ 541m 475MeV E 3GeV Events/MeV 0.6 +/- ν e & ν e from µ Fit Region +/- ν e & ν e from K 0 ν e & ν e from K 0 π misid 0.4 Nγ dirt Events/MeV other Constr. Syst. Error Best Fit (E>475MeV) Data - expected background Best Fit sin θ=0.004, m =1.0eV ) 4 /c (ev m 1 68% CL 90% CL 99% CL KARMEN 90% CL BUGEY 90% CL sin θ=0.03, m =0.3eV -1 LSND 90% CL QE E ν (GeV) - -3 LSND 99% CL Agreement with LSND e signal! - sin (θ) Similar L E but different L and E =µ Oscillations! C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July

22 68% CL 90% CL 1 NEV + atm + KK NEV + atm(1d) 99% CL KARMEN 90% CL BUGEY 90% CL m LSND [ev ] 0 LSND global LSND DAR ) 4 /c (ev m % CL 99% CL LSND 90% CL LSND 99% CL sin θ LSND sin (θ) -1 1 Most of LSND and MiniBooNE e allowed region excluded by MiniBooNE e Tension between LSND and MiniBooNE e appearance and e (Bugey) + ( ) (CDHSW+CCFR) disappearance limits Marginally preferred: msbl ³ 0 9eV sin e ³ 3 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0

23 Õ m 1 m m 3 m 4 =µ m 4 ³ m41 = m SBL m SBL ³ 0 9eV =µ m 4 ³ 0 9eV Marginally allowed by cosmological limit in ΛCDM (thermalized s s) [Hamann, Hannestad, Raffelt, Tamborra, Wong, arxiv:06.576] Note preference for N s 0 indicated also by BBN C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 3

24 The primordial abundance of 4 He: evidence for non-standard BBN [Izotov, Thuan, Astrophysical Journal Letters 7 (0) L67, arxiv: ] N = N = ( ) C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 4

25 3+ Five-Neutrino Mixing? [Georgia Karagiorgi, Neutrino 0, 14 June 0] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 5

26 CPT Violation? Masses and mixing of neutrinos and antineutrinos may be different 68% CL 90% CL 99% CL KARMEN 90% CL BUGEY 90% CL In CDHSW mainly s ) 4 /c No limit on SBL e transitions from disappearance experiments [Barger, Marfatia, Whisnant, PLB 576 (003) 303] LSND and MiniBooNE allowed regions are limited only by KARMEN and Bugey (ev m LSND 90% CL LSND 99% CL - sin (θ) -1 1 C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 6

27 Gallium Anomaly Gallium Radioactive Source Experiments Tests of the solar neutrino detectors GALLEX (Cr1, Cr) and SAGE (Cr, Ar) Detection Process: e + 71 Ga 71 Ge+e e Sources: e + 51 Cr 51 V+ e e + 37 Ar 37 Cl+ e 37Ar (35.04 days) 37Cl (stable) 813 kev ν ( 9.8%) 811 kev ν (90.%) [SAGE, PRC 73 (006) , nucl-ex/051041] [SAGE, PRC 59 (1999) 46, hep-ph/ ] R Ga = [Giunti, Laveder, arxiv:06.344] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 7

28 Re + 3 H 68.7% C.L. (1σ) 95.45% C.L. (σ) 99.73% C.L. (3σ) m [ev ] + m [ev ] Gallium 68.7% C.L. (1σ) 95.45% C.L. (σ) 99.73% C.L. (3σ) 1 1 sin ϑ [Giunti, Laveder, arxiv:06.344] sin ϑ [Giunti, Laveder, arxiv: ] m SBL ³ 0 9eV sin sin is OK CPT violation? C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 8

29 MINOS Hint of CPT Violation LBL disappearance E 3GeV Near Detector at 1.04 km Far Detector at 734 km [MINOS, Neutrino 0, 14 June 0] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 9

30 Conclusions Existence of sterile neutrinos is possible and likely connected with neutrino mass generation Impressive LSND and MiniBooNE agreement on e signal Three experimental tensions: LSND and MiniBooNE e vs MiniBooNE e LSND and MiniBooNE e vs e and ( ) disappearance limits Gallium Anomaly ( e disappearance) vs Bugey ( e disappearance) Interpretation of experimental results is difficult: 3+1 Four-Neutrino Mixing or more? CPT violation?...? ΛCDM cosmology and BBN indicate N s 0 New experiments are needed! C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 30

31 MiniBooNE Low-Energy Anomaly Events / MeV Data ν e from µ + ν e from K 0 ν e from K π 0 misid Nγ dirt other Total Background [PRL (009) 180, arxiv:081.43] Our Hypothesis: N the j = f P e en cal e j +N cal j QE E ν [Giunti, Laveder, PRD 77 (008) 09300, arxiv: ; PRD 80 (009) , arxiv: ] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 31 (GeV)

32 N j the = f P e en cal e j +Ncal j Estimated 15% uncertainty of the calculated neutrino flux [MiniBooNE, PRD 79 (009) 0700, arxiv: ] is consistent with measured ratio of detected and predicted charged-current quasi-elastic events [MiniBooNE, PRL 0 (008) 03301, arxiv: ] We fit MiniBooNE e and data using the info at C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 3

33 events / MeV E [MeV] MiniBooNE ν e N νe,the (j) νe,cal νe,j = f ν P νe νe N νe,j νµ,the νµ,cal N νe,j = f ν N νe,j N the νe,j = N νe,the νµ,the νe,j + N νe,j (b) No Osc. & f = 1 min = NdF = 3+16 GoF = 41% Our Hypothesis min = NdF = 16 GoF = 89% f = 1 6 sin = 0 3 m = 1 84eV [Giunti, Laveder, 0, arxiv: ] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 33

34 Note similar best-fit values of sin and m Gallium best fit: sin = 0 7 and m = 09eV MiniBooNE best fit: sin = 0 3 and m = 1 84eV Parameter Goodness of Fit of combined analysis: min = 0 14 NDF = GoF = 93% C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 34

35 MiniBooNE + Gallium m [ev ] χ MB + Ga 68.7% C.L. (1σ) 95.45% C.L. (σ) 99.73% C.L. (3σ) min = 3+9 NdF = 0 GoF = 93% sin = m = 1 9eV sin ϑ χ [Giunti, Laveder, 0, arxiv: ] C. Giunti Sterile Neutrinos in July 0 Presidenza INFN, Roma, 19 July 0 35

Carlo Giunti. CERN Particle and Astro-Particle Physics Seminar. work in collaboration with Mario Acero Marco Laveder Walter Winter

Carlo Giunti. CERN Particle and Astro-Particle Physics Seminar. work in collaboration with Mario Acero Marco Laveder Walter Winter Very-Short-BaseLine Electron Neutrino Disappearance Carlo Giunti INFN, Sezione di Torino, and Dipartimento di Fisica Teorica, Università di Torino mailto://giunti@to.infn.it Neutrino Unbound: http://www.nu.to.infn.it