Phenomenology of Sterile Neutrinos 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 NUFACT 11 XIII th International Workshop on Neutrino Factories, Super-Beams and Beta-Beams 1-6 August 2011, CERN and UNIGE C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 1/35
LSND [LSND, PRL 75 (1995) 2650; PRC 54 (1996) 2685; PRL 77 (1996) 3082; PRD 64 (2001) 112007] e L ³ 30m 20MeV E 200MeV Beam Excess 17.5 15 12.5 7.5 5 2.5 Beam Excess p(ν _ µ ν_ e,e+ )n p(ν _ e,e+ )n other 2 1-1 0 0.4 0.6 0.8 1 1.2 1.4-2 L/E ν (meters/mev) m 2 (ev 2 /c 4 ) Karmen Bugey 90% (L max -L < 2.3) 99% (L max -L < 4.6) CCFR NOMAD -3-2 -1 1 sin 2 2θ m 2 LSND 0 2eV 2 ( m 2 ATM m 2 SOL) C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 2/35
MiniBooNE Neutrinos [PRL 98 (2007) 231801; PRL 2 (2009) 1802] e L ³ 541m 475MeV E 3GeV Events / MeV 3 2.5 2 1.5 1 Data ν e from µ + ν e from K 0 ν e from K π 0 misid Nγ dirt other Total Background 0.5 0.2 0.4 0.6 0.8 1 1.2 1.4 1.5 1.6 3. QE E ν (GeV) Excess Events / MeV 0.8 data - expected background best-fit ν µ ν e 0.6 2 2 2 sin 2θ=0.004, m =1.0eV 0.4 2 2 2 sin 2θ=0.2, m =0.1eV 0.2 0-0.2 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.5 3. QE E ν (GeV) [MiniBooNE, PRL 2 (2009) 1802, arxiv:0812.2243] Low-Energy Anomaly! [Djurcic, arxiv:0901.1648] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 3/35
MiniBooNE Antineutrinos [PRL 3 (2009) 111801; PRL 5 (20) 181801] 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 0.2 other Constr. Syst. Error Best Fit (E>475MeV) 4 ) 2 68% CL 90% CL 99% CL KARMEN2 90% CL BUGEY 90% CL /c Events/MeV 0.3 0.2 Data - expected background Best Fit 2 2 2 sin 2θ=0.004, m =1.0eV 2 (ev 2 m 1 0.1 2 2 2 sin 2θ=0.03, m =0.3eV 0.0-1 LSND 90% CL -0.1 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.5 1.6 3.0 QE E ν (GeV) [MiniBooNE, PRL 5 (20) 181801, arxiv:07.1150] -2-3 LSND 99% CL Agreement with LSND e signal! -2 2 sin (2θ) Similar L E but different L and E =µ Oscillations! -1 1 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 4/35
!" # $ $ % & ' $ ( )*+,- ),-". %$" /$/ /0!!1 23 0+1 23" 2 4/ 3567 / 00*1" 8 9 : ;1!1" 69 :!*01!1" 34 $ 4 / ( <*+,-. :;! (. :++ " 6 4,86 4 //! " 4 /=! > / " ( 4 3567 / ; from M. Shaevitz, PANIC11, 26 July 2011 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 5/35
Beyond Three-Neutrino Mixing ν τ ν s1 ν µ ν e ν 2 ν 3 ν 4 ν 5 ν 1 m 2 1 m 2 2 m 2 3 ν s2 m 2 4 m 2 5 logm 2 m 2 SOL 3ν-mixing m 2 ATM m 2 SBL C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 6/35
Standard Model Neutrinos are the only massless fermions Neutrinos are the only fermions with only left-handed component L Extension of the SM: Massive Neutrinos Simplest extension: introduce right-handed component R Dirac mass m D R L + Majorana mass m M c R R el L L + er R R =µ 6 massive Majorana neutrinos C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 7/35
Sterile Neutrinos Light anti- R are called sterile neutrinos c R sl (left-handed) Sterile means no standard model interactions Active neutrinos ( e ) can oscillate into sterile neutrinos ( s ) Observables: Disappearance of active neutrinos (neutral current deficit) Indirect evidence through combined fit of data (current indication) Powerful window on new physics beyond the Standard Model C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 8/35
In this talk I consider sterile neutrinos with mass scale 1eV in light of LSND, MiniBooNE, Reactor Anomaly, Gallium Anomaly. Other possibilities (not exclusive): Very light sterile neutrinos with mass scale 1eV: important for solar neutrino phenomenology [de Holanda, Smirnov, PRD 83 (2011) 113011, arxiv:12.5627] Heavy sterile neutrinos with mass scale 1eV: could be Warm Dark Matter [Kusenko, Phys. Rept. 481 (2009) 1, arxiv:0906.2968] [Boyarsky, Ruchayskiy, Shaposhnikov, Ann. Rev. Nucl. Part. Sci. 59 (2009) 191, arxiv:0901.0011] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 9/35
Cosmology N s = number of thermalized sterile neutrinos (not necessarily integer) CMB and LSS in ΛCDM: BBN: [Hamann, Hannestad, Raffelt, Tamborra, Wong, PRL 5 (20) 181301, arxiv:06.5276] N s = 1 61 0 92 m s 0 70eV (95% C.L.) [Giusarma, Corsi, Archidiacono, de Putter, Melchiorri, Mena, Pandolfi, arxiv:12.4774] N s = 0 22 0 59 N s = 0 64 +0 40 0 35 [Izotov, Thuan, ApJL 7 (20) L67, arxiv:01.4440] N s 1 at 95% C.L. [Mangano, Serpico, PLB 701 (2011) 296, arxiv:13.1261] [Cyburt, Fields, Olive, Skillman, AP 23 (2005) 313, astro-ph/0408033] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 /35
Direct Searches of Active-Sterile Transitions C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 11/35
CCFR [PRD 59 (1999) 0311, arxiv:hep-ex/9809023] NC interactions E 0GeV L ³ 1 4km C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 12/35
MINOS NC sample: 89% efficiency and 61% purity 97% of e -induced CC events misidentified as NC [arxiv:14.3922] Events/GeV 4 60 50 40 30 20 0 0 2 4 6 8 12 14 16 18 20 (GeV) E reco Near Detector Data Monte Carlo Prediction CC Background ν µ L ND = 1 04km Events/GeV 140 120 0 80 60 40 20 0 0 2 4 6 8 12 14 16 18 20 (GeV) E reco L FD = 735km Far Detector Data θ 13 = 0 2 θ = 11.5, δ = π, m32 >0 13 ν µ CC Background 2-3 2 m 32 = 2.32 ev 2 sin 2θ 23 = 1 13 2 /NDF 23 24 34 0 130.4/122 45 0 +7 7 0 0 +5 0 0 0 0 +17 0 0 11 5 128.5/122 45 6 +7 7 0 0 +5 0 0 0 0 +25 0 0 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 13/35
24 8 Æ at 90% C.L. =µ U 4 2 ³ sin 2 24 0 019 U 4 2 0 035 at 99% C.L. Limit valid for m 2 41 0 5eV2. Hernandez, Smirnov, arxiv:15.5946 For m 2 41 0 5eV2 SBL oscillations at Near Detector. MINOS insensitive to oscillations for m 2 41 15eV2 because oscillations already averaged at Near Detector. Oscillations with m 2 41 = (1 3)eV2 could explain some deficit of events observed in the low energy bins in the near detector and correspondingly the excess of events in the far detector. C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 14/35
Reactor Antineutrino Anomaly [Mention et al, arxiv:11.2755] R 0.7 0.8 0.9 1.0 1.1 1.2 Old Reactor e Fluxes Reactor Rates Average Rate Bugey3 15 Gosgen 45 Bugey3 40 Gosgen 65 Bugey3 95 ILL Bugey4 Krasno 33 ROVNO Krasno 92 Gosgen 38 Krasno 57 0 20 40 60 80 0 L [m] R = 0 992 0 024 R 0.7 0.8 0.9 1.0 1.1 1.2 New Reactor e Fluxes [Mueller et al, arxiv:11.2663] Reactor Rates Average Rate Bugey3 15 Gosgen 45 Bugey3 40 Gosgen 65 Bugey3 95 ILL Bugey4 Krasno 33 ROVNO Krasno 92 Gosgen 38 Krasno 57 0 20 40 60 80 0 L [m] R = 0 946 0 024 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 15/35
P «P ««Effective SBL Oscillation Probabilities in 3+1 Schemes = sin 2 2 «sin 2 m 2 L 4E m = 1 sin 2 2 ««sin 2 2 L 4E Perturbation of 3 Mixing sin 2 2 «= 4 U «4 2 U 4 2 No CP Violation! sin 2 2 ««= 4 U «4 2 1 U «4 2 U e4 2 1 U 4 2 1 U 4 2 1 U s4 2 ³ 1 U e1 U e2 U e3 U e4 sin 2 2 ««1 U = U µ1 U τ1 U µ2 U τ2 U µ3 U τ3 U µ4 U τ4 U s1 U s2 U s3 U s4 SBL U «4 2 ³ sin2 2 ««4 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 16/35
2 m 2 [ev 2 ] 1 3+1 GoF = 32% 1 95.00% C.L. ν µ >ν e: LSND+KARMEN+MiniBooNE ν µ >ν e: MiniBooNE PGoF = 0 89% 2 4 3 2 1 1 sin 2 2ϑ eµ Tension between LSND + KARMEN + MiniBooNE e and MiniBooNE e =µ CP Violation? 3+2 =µ CP Violation OK [Sorel, Conrad, Shaevitz, PRD 70 (2004) 073004, hep-ph/0305255], [Maltoni, Schwetz, PRD 76, 093005 (2007), arxiv:0705.07], [Karagiorgi et al, PRD 80 (2009) 073001, arxiv:0906.1997], [Kopp, Maltoni, Schwetz, arxiv:13.4570], [Giunti, Laveder, arxiv:17.1452] 3+1+NSI =µ CP Violation OK [Akhmedov, Schwetz, JHEP (20) 115, arxiv:07.4171] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 17/35
Effective SBL Oscillation Probabilities in 3+2 Schemes kj = m 2 kj L 4E = arg[u e4u 4U e5 U 5] P ( ) = 4 U ( ) e4 2 U 4 2 sin 2 41 +4 U e5 2 U 5 2 sin 2 51 e (+) +8 U 4U e4 U 5U e5 sin 41 sin 51 cos( 54 ) P ( ) «( ) «= 1 4(1 U «4 2 U «5 2 )( U «4 2 sin 2 41 + U «5 2 sin 2 51 ) 4 U «4 2 U «5 2 sin 2 54 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 18/35
3+2: MiniBooNE e and e P νµ νe 0.005 0.000 0.005 0.0 MiniBooNE ν e exp P νµ νe <P > νµ νe 550 675 800 950 10 1300 1500 3000 E [MeV] P νµ νe 0.005 0.000 0.005 0.0 MiniBooNE ν e exp P νµ νe <P > νµ νe 550 675 800 950 10 1300 1500 3000 E [MeV] P ( ) ( ) e = 4 U e4 2 U 4 2 sin 2 41 +4 U e5 2 U 5 2 sin 2 51 +4 U e4 U 4U e5 U 5 cos sin 2 41 +sin 2 51 sin 2 54 (+) 2 Ue4 U 4U e5 U 5 sin [sin(2 41 ) sin(2 51 )+sin(2 54 )] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 19/35
Disappearance Constraints C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 20/35
e Disappearance and Disappearance 2 99% C.L. Bugey 3 (1995) Bugey 4 (1994) + Rovno (1991) Gosgen (1986) + ILL (1995) Krasnoyarsk (1994) 2 99% C.L. CDHSW (1984): ν µ ATM: ν µ + ν µ MINOS (2011): ν µ m 2 [ev 2 ] 1 m 2 [ev 2 ] 1 1 1 2 2 1 1 sin 2 2ϑ ee New Reactor e Fluxes [Mueller et al., arxiv:11.2663] [Mention et al., arxiv:11.2755] 2 2 1 1 sin 2 2ϑ µµ ATM constraint on U 4 2 [Maltoni, Schwetz, PRD 76 (2007) 093005, arxiv:0705.07] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 21/35
e disappearance experiments: 3+1 sin 2 2 ee = 4 U e4 2 1 U e4 2 ³ 4 U e4 2 disappearance experiments: sin 2 2 = 4 U 4 2 1 U 4 2 ³ 4 U 4 2 e experiments: sin 2 2 e = 4 U e4 2 U 4 2 ³ 1 4 sin2 2 ee sin 2 2 Upper bounds on sin 2 2 ee and sin 2 2 =µ strong limit on sin 2 2 e [Okada, Yasuda, Int. J. Mod. Phys. A12 (1997) 3669-3694, arxiv:hep-ph/9606411] [Bilenky, Giunti, Grimus, Eur. Phys. J. C1 (1998) 247, arxiv:hep-ph/9607372] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 22/35
3+1 2 99% C.L. Reactors CDHSW + Atm Disappearance LSND + MBν m 2 [ev 2 ] 1 1 2 4 3 2 1 1 sin 2 2ϑ eµ C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 23/35
2 99% C.L. MBν + LSNDν Dis + KAR + NOM + MBν m 2 [ev 2 ] 1 3+1 GoF = 98% 1 PGoF = 0 0016% 2 4 3 2 1 1 3+1: strong tension 3+2: next slides sin 2 2ϑ eµ Tension reduced in 3+1+NSI [Akhmedov, Schwetz, JHEP (20) 115, arxiv:07.4171] No tension in 3+1+CPTV [Barger, Marfatia, Whisnant, PLB 576 (2003) 303] [Giunti, Laveder, PRD 82 (20) 093016, PRD 83 (2011) 053006] Sterile neutrino decay? [Gninenko, arxiv:17.0279] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 24/35
Global 3+2 Fits [Kopp, Maltoni, Schwetz, arxiv:13.4570] [Giunti, Laveder, arxiv:17.1452] m 2 51 1 3+2 90%, 95%, 99%, 99.73% CL (2 dof) 0.1 0.1 1 m 2 41 1+3+1 Best Fit: = 1 64 m41 2 = 0 47eV 2 m51 2 = 0 87eV2 U e4 2 = 0 016 U e5 2 = 0 019 U 4 2 = 0 027 U 5 2 = 0 022 2 min NDF = 1 1 130 [ev 2 ] m 51 2 1 1 + 1 1 2 m 41 [ev 2 ] 3+2 68.27% C.L. (1σ) 90.00% C.L. 95.45% C.L. (2σ) 99.00% C.L. 99.73% C.L. (3σ) Best Fit: = 1 52 m41 2 = 0 90eV 2 m51 2 = 1 60eV2 U e4 2 = 0 017 U e5 2 = 0 017 U 4 2 = 0 018 U 5 2 = 0 0064 2 min NDF = 91 6 0 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 25/35
3+2: Persisting Tension 3+1 3+2 2 PG 21 5 19 9 NDF PG 2 5 PGoF 2 5 1 3 3 [Kopp, Maltoni, Schwetz, arxiv:13.4570] 3+1 3+2 2 PG 24 1 22 2 NDF PG 2 5 PGoF 6 6 5 4 [Giunti, Laveder, arxiv:17.1452] 4 U e5 2 U µ5 2 1 2 3 4 + 95% C.L. MBν + LSNDν Dis + KAR + NOM + MBν 4 U e4 2 U µ4 2 + 4 3 2 1 3+2 improvement of PGoF is mainly a statistical effect! 3+2 is preferred to 3+1 only for CP-violating MiniBooNE neutrino antineutrino difference. C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 26/35
Back to 3+1 Simplest scheme beyond standard three-neutrino mixing which can partially explain the data. It corresponds to the natural addition of one new entity (a sterile neutrino) to explain a new effect (short-baseline oscillations). Minimum value of the global 2 is good: 2 min NDF = 0 2 4. Marginal APP-DIS compatibility: 2 PG = 9 2 =µ PGoF = 1 0%. 3+1 68.27% C.L. (1σ) 90.00% C.L. 95.45% C.L. (2σ) 99.00% C.L. 99.73% C.L. (3σ) [ev 2 ] 2 m 41 1 + + + 1 DIS APP 4 3 2 1 DIS 2 1 GAL DIS 1 1 sin 2 2ϑ eµ sin 2 2ϑ ee sin 2 2ϑ µµ C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 27/35
Gallium Anomaly Gallium Radioactive Source Experiments Tests of the solar neutrino detectors GALLEX (Cr1, Cr2) 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 51 Cr 37 Ar E [kev] 747 752 427 432 811 813 B.R. 0 8163 0 0849 0 0895 0 0093 0 902 0 098 37Ar (35.04 days) 37Cl (stable) 813 kev ν ( 9.8%) 811 kev ν (90.2%) [SAGE, PRC 73 (2006) 045805, nucl-ex/0512041] [SAGE, PRC 59 (1999) 2246, hep-ph/9803418] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 28/35
p(measured)/p(predicted) 1.1 1.0 0.9 0.8 0.7 GALLEX Cr1 SAGE Cr GALLEX Cr2 SAGE Ar [SAGE, PRC 73 (2006) 045805, nucl-ex/0512041] R Gallex-Cr1 B = 0 953 0 11 RB Gallex-Cr2 = 0 812 +0 0 11 RB SAGE-Cr = 0 95 0 12 RB SAGE-Ar = 0 791 +0 084 0 078 R Ga B = 0 86 0 05 Bahcall cross section without uncertainty [Bahcall, PRC 56 (1997) 3391, hep-ph/97491] L GALLEX = 1 9m L SAGE = 0 6m R Gallex-Cr1 = 0 84 +0 13 0 12 R Gallex-Cr2 = 0 71 +0 12 0 11 R SAGE-Cr = 0 84 +0 14 0 13 R SAGE-Ar = 0 70 +0 0 09 R Ga = 0 76 +0 09 0 08 [Giunti, Laveder, PRC 83 (2011) 065504, arxiv:06.3244] Haxton cross section and uncertainty [Haxton, PLB 431 (1998) 1, arxiv:nucl-th/9804011] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 29/35
Gallium Anomaly + Reactor Anomaly m 2 [ev 2 ] 1 ++ + 95% C.L. Gallium Reactors Combined 2 min = 29 0 NdF = 40 GoF = 90% sin 2 2 = 0 13 m 2 = 1 95eV 2 PGoF = 7 9% 1 2 1 1 sin 2 2ϑ C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 30/35
Implications of Gallium and Reactor Anomalies Decay ( ) 0 Decay χ 2 0 2 4 6 8 99.73% Gallium Reactors Tritium Combined 99% 95.45% 90% 68.27% 2 1 1 U e4 m 2 [ev] χ 2 0 2 4 6 8 m 2 = U ek 2 mk 2 m = k [Giunti, Laveder, In Preparation] 99.73% Gallium Reactors Tritium Combined 99% 95.45% 90% 68.27% 3 2 1 1 U e4 2 m 2 [ev] U ek 2 m k k C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 31/35
Future MiniBooNE is continuing to take antineutrino data. e + ICARUS@CERN-PS: L 1km E 1GeV [C. Rubbia et al, CERN-SPSC-2011-012] ( ) ( ) e + ( ) ( ) + ( ) e ( ) e MicroBooNE will test the MiniBooNE low-energy anomaly by measuring 0 2 background. LSND reloaded? Super-Kamiokande doped with Gadolinium [Agarwalla, Huber, PLB 696 (2011) 359, arxiv:07.3228.] Reactor Anomaly: Nucifer, small scintillator detector at L = 7m [Lasserre, talk at EPS-HEP 2011] Possible experiment at a small-size fast neutron reactor [Yasuda, arxiv:17.4766] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 32/35
Gallium Anomaly: new SAGE Gallium source experiments with 2 spherical shells [Gavrin et al, arxiv:06.23] e and e radioactive source experiments with low-threshold detectors. Borexino: ( ) e +e ( ) e +e [Cribier et al, arxiv:17.2335] [Pallavicini, talk at BEYOND3NU] [Ianni, Montanino, Scioscia, EPJC 8 (1999) 609, arxiv:hep-ex/99012] LENS (Low Energy Neutrino Spectroscopy): e + 115 In 115 Sn+e +2 e +p n+e + [Agarwalla, Raghavan, arxiv:11.4509] E th = 0 1MeV E th = 1 8MeV Spherical Gaseous TPC: [Vergados, Giomataris, Novikov, arxiv:13.5307] Targets: 131 Xe, 40 Ar, 20 Ne, 4 He. Sources: 37 Ar, 51 Cr, 65 Zn, 32 P. Coherent neutrino-nucleon scattering in low-temperature bolometers [Formaggio, Figueroa-Feliciano, Anderson, arxiv:17.3512] C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 33/35
Near-Detector Beta-Beam experiments: [Agarwalla, Huber, Link, JHEP 01 (20) 071] N(A Z) N(A Z +1)+e + e ( ) N(A Z) N(A Z 1)+e + + e ( + ) ND Neutrino Factory experiments: [Giunti, Laveder, Winter, PRD 80 (2009) 073005] + +e + + e +e + e ND+FD at Low Energy Neutrino Factory (LENF) [poster by Pascoli and Wong] CPT tests: A CPT «= P «P «C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 34/35
PRESENT Conclusions FUTURE? =µ Tetrahedral Double Planetoid Babel Tower e s 1 2 3 4 C. Giunti Phenomenology of Sterile Neutrinos 3 August 2011 35/35