Searching for sterile antineutrinos with SciBooNE & MiniBooNE - PowerPoint PPT Presentation

Joint Search for ν ̅ µ Disappearance at Δ m 2 ~ 1 eV 2 Searching for sterile antineutrinos with SciBooNE & MiniBooNE M.O. Wascko Imperial College London Birmingham HEP Seminar 2013 01 16 Wednesday, 16 January 13 1

Outline • Introduction • Neutrino oscillation • The LSND signal and sterile neutrinos • Experiments: SciBooNE and MiniBooNE • SciBooNE-MiniBooNE joint ν ̅ µ disappearance analysis • Results Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 2

Introduction Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 3

Neutrino oscillation e µ ν W W Maki, Pontecorvo Nakagawa, Sakata Sov.Phys.JETP 6:429,1957 Prog.Theor.Phys. 28, Sov.Phys.JETP 870 (1962) Source Detector 26:984-988,1968 • if neutrinos have mass... • a neutrino that is produced as a ν ̅ µ • (e.g. π − → µ − ν ̅ µ ) • might some time later be observed as a ν ̅ e • (e.g. ν ̅ e n → e + p) Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 4

Neutrino oscillation In a world with 2 neutrinos, if the weak eigenstates ( ν e , ν µ ) ν 1 ν µ are different from the mass eigenstates ( ν 1 , ν 2 ): ν 2 ✓ ◆ ✓ ◆✓ ◆ ν e cos θ sin θ ν 1 ϴ = ν µ − sin θ cos θ ν 2 ν e The weak states are mixtures of the mass states: | ν µ > = − sin θ | ν 1 > + cos θ | ν 2 > | ν µ ( t ) > = − sin θ ( | ν 1 > e − iE 1 t )+ cos θ ( | ν 2 > e − iE 2 t ) The probability to find a ν e when you started with a ν µ is: P oscillation ( ν µ → ν e ) = | < ν e | ν µ ( t ) > | 2 Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 5

• 2 fundamental parameters • Δ m 2 ↔ period • θ 12 ↔ magnitude • 2 experimental parameters • L = distance travelled • E = neutrino energy • Choose L&E to target ranges of Δ m 2 and θ • Neutrinos disappear and appear Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 6

• 2 fundamental parameters • Δ m 2 ↔ period • θ 12 ↔ magnitude • 2 experimental parameters • L = distance travelled • E = neutrino energy • Choose L&E to target ranges of Δ m 2 and θ • Neutrinos disappear and appear Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 7

• 2 fundamental parameters • Δ m 2 ↔ period • θ 12 ↔ magnitude • 2 experimental parameters • L = distance travelled • E = neutrino energy • Choose L&E to target ranges of Δ m 2 and θ • Neutrinos disappear and appear Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 8

• L and E determine Δ m 2 sensitivity • θ 12 sensitivity determined by statistics, backgrounds, and uncertainties • No signal: exclusion curve • Signal: allowed region Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 9

Neutrino Interactions ν µ µ - ν µ ν µ Z0 W+ NC CC CC interactions NC interactions preserve neutrino can happen equally for flavour, but require all flavours because enough energy to there is no energy produce rest mass of requirement charged lepton! Both interaction modes are useful for neutrino oscillation experiments Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 10

Three flavours flavour atmospheric cross-mixing solar mass where c ij =cos θ ij , s ij =sin θ ij Mass (eV) ν e ν µ ν τ ν 3 atmospheric 0.05 ν 2 solar 0.009 ν 1 ? Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 11

Atmospheric Oscillation flavour atmospheric cross-mixing solar mass MINOS Super-K Phys.Rev.Lett.81.1562(1998) PhysRevLett.101.131802 Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 12

Solar Oscillation flavour atmospheric cross-mixing solar mass KamLAND SNO Phys.Rev.Lett.89.011301 (2002) Phys.Rev.Lett.100.221803 (2008) Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 13

Cross Mixing flavour atmospheric cross-mixing solar mass 10-2 Phys.Rev.Lett.107.041801 (2011) Causes ν̅ e disappearance in reactors and ν e appearance in accelerator experiments Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 14

Current picture flavour atmospheric cross-mixing solar mass where cij=cos θ ij, sij=sin θ ij Mass (eV) ν e ν µ ν τ VALUE Δ m 223 2.35E-03 (eV 2 ) ν 3 Δ m 212 7.58E-05 (eV 2 ) Non-zero δ : atmospheric 0.05 sin 2 θ 12 0.306 matter vs antimatter ν 2 sin 2 θ 23 0.42 solar 0.009 sin 2 θ 13 0.02 ν 1 ? δ ? arXiv:1106.6028 [hep-ph] Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 15

Open Questions • What is the value of θ 13 ? δ CP ?? Mass Mass • What is the mass hierarchy? • What is the absolute mass scale? • What is the nature of neutrino Normal Inverted mass? • Dirac or Majorana? Mass Mass • Answers important for theories about origins of neutrino mass • Relations to flavour? GUTs? Quasi-Degenerate Hierarchical • Cosmological and astrophysical implications Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 16

The LSND Signal Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 17

The LSND Signal • The LSND experiment observed a small excess of ν̅ e events in a ν̅ µ beam. Data excess: 87.9 ± 22.4 ± 6.0 (3.8 σ ) Best fit: Δ m 2 ~ 1 eV 2 , sin 2 2 θ ~ 0.003 Phys.Rev.D 64, 112007 (2001) Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 18

Sterile Neutrinos • LEP experiments measured the number of light neutrinos: 3 • Only two independent Δ m 2 values for 3 neutrinos • 2.5 ☓ 10 -3 + 7.6 ☓ 10 -5 ≠ 1 • LSND signal involves sterile neutrinos , if it is due to neutrino oscillation Phys.Lett.B 313 520 (1993) ➡ They do not interact via the weak force Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 19

Active-sterile Neutrino Oscillation? • Sterile neutrinos could still mix with active neutrinos! 3+1 sterile neutrino scheme A simple realisation of the sterile neutrino is 4 a right-handed neutrino ν R , which can be mixed with active ν L . m 2 � LSND 3 � s m 2 � 23 � � 2 � µ m 2 � 12 � e 1 Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 20

ν μ → ν e ν ̅ μ →ν ̅ e MiniBooNE ν e Results • MiniBooNE recently tested the LSND signal. • Ruled out most of LSND region in ν µ → ν e search. • However, observed (small) ν ̅ µ → ν ̅ e excess. • Consistent with LSND??? • We want to test this with disappearance measurements! MiniBooNE 90% C.L. y KARMEN2 90% C.L. Null excluded at 99.4% with 10 Bugey 90% C.L. 10 respect to the two neutrino ) 4 /c 2 | (eV E>475 MeV 1 1 2 m ! | Phys.Rev.Lett. 105 181801(2010) -1 -1 10 10 Phys. Rev. Lett. 98, 231801(2007) LSND 90% C.L. LSND 99% C.L. -2 -2 10 10 -3 -2 -1 10 10 10 1 2 sin (2 " ) Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 21

Indications of Sterile Neutrinos? MiniBooNE Appearance arXiv:1207.4809 Red: Oscillations assuming 3 neutrino mixing Blue: Using a 3+1 (sterile neutrino) model 8 N.B.: several 2-3 σ results don’t constitute compelling evidence... Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 22

Appearance vs. Disappearance Testing appearance signals with disappearance measurements ν µ →ν e appearance � ⇥ L P ( ν µ → ν e ) = 4 | U e 4 | 2 | U µ 4 | 2 sin 2 1 . 27 ∆ m 2 41 E ν e disappearance � ⇥ L P ( ν e → ν x ) = 1 − 4 | U e 4 | 2 (1 − | U e 4 | 2 ) sin 2 1 . 27 ∆ m 2 41 E ν µ disappearance � ⇥ L P ( ν µ → ν x ) = 1 − 4 | U µ 4 | 2 (1 − | U µ 4 | 2 ) sin 2 1 . 27 ∆ m 2 41 E ν µ →ν e appearance probability can be constrained by ν e and ν µ disappearance measurements! Imperial College Morgan O. Birmingham HEP Seminar London Wascko Wednesday, 16 January 13 23