Long baseline neutrino physics: present and future IC-IPPP meeting - PowerPoint PPT Presentation

0 – Long baseline neutrino physics: present and future IC-IPPP meeting London - 28 May 2009 Silvia Pascoli IPPP - Durham University

1 – Outline 1 – Outline • Theoretical aspects of long baseline experiments: Appearance probability Matter effects CP-violation • Present long baseline experiments: OPERA and MINOS and T2K • Future facilities: Superbeams Beta-beams Neutrino factory • Conclusions

2 – ν -oscillations: present status and questions for the future 2 – ν -oscillations: present status and questions for the future The probability of ν a oscillating into ν b is: P ( ν a → ν b ) = |� ν b | ν, t �| 2 ≃ sin 2 2 θ sin 2 � � ∆ m 2 4 E L [T. Schwetz, hep-ph/0606060] • Solar neutrino and KamLAND experiments: ∆ m 2 ⊙ , θ 12 • Atmospheric neutrino, K2K, MINOS experiments: ∆ m 2 atm , θ 23 ⊙ = 8 . 0 × 10 − 5 eV 2 ≪ ∆ m 2 atm = 2 . 5 × 10 − 3 eV 2 ⇒ 3 ν . ∆ m 2

2 – ν -oscillations: present status and questions for the future Neutrino oscillations are crucial in our understanding of neutrino physics as they imply that NEUTRINOS ARE MASSIVE AND THEY MIX. The explanation of neutrino masses requires physics beyond the Standard Model.

2 – ν -oscillations: present status and questions for the future Normal ordering Inverted ordering 2 m ∆ . O 3 2 1 2 2 ∆ m A ∆ m A 2 1 3 2 ∆ m . O m 1 = m MIN m 3 = m MIN � � m MIN2 + ∆ m 2 m MIN2 +∆ m 2 atm − ∆ m 2 m 2 = m 1 = ⊙ ⊙ m MIN2 + ∆ m 2 m MIN2 + ∆ m 2 � � m 3 = m 2 = atm atm Measuring neutrino masses requires to know: • m MIN • sign( ∆ m 2 31 ).

2 – ν -oscillations: present status and questions for the future Mixing is described by a unitary matrix: | ν l � = � i U li | ν i � U is the Pontecorvo-Maki-Nakagawa-Sakata matrix.     c 12 s 12 0 1 0 0     U = − s 12 c 12 c 23 s 23 0 0         − s 23 c 23 0 0 1 0 Solar, reactor θ ⊙ ∼ 30 o Atm, Acc. θ A ∼ 45 o       c 13 s 13 1 0 0 0 1 0 0       e − iα 21 / 2 0 1 0 0 1 0 0 0             e − iδ e − iα 31 / 2+ iδ − s 13 c 13 0 0 0 0 0 Reactor, Acc. θ < 12 o CPV phase CPV Majorana phases

2 – ν -oscillations: present status and questions for the future If U � = U ∗ , there is leptonic CP-violation. P ( ν l → ν l ′ ) � = P (¯ ν l → ¯ ν l ′ ) • Establishing leptonic CP-V is a fundamental and challenging task. • There are: 1 Dirac phase (measurable in long base-line experiments) and 2 Majorana phases (one might be determined in neutrinoless double beta decay). • Leptogenesis takes place in the context of see-saw models, which explain the origin of neutrino masses. The observation of neutrinoless double beta decay ( L violation) and of CPV in the lepton sector would be an indication, even if not a proof, of leptogenesis as the explanation for the observed baryon asymmetry of the Universe.

2 – ν -oscillations: present status and questions for the future Questions for the future • What is the nature of neutrinos ? Whether they Majorana ( ν = ¯ ν ) or Dirac ( ν � = ¯ ν ). Majorana neutrinos violate the lepton number. • Absolute value of neutrino masses ? Needed the type of hierarchy and the mass scale of the lightest neutrino. • Leptonic CP-violation ? δ � = 0 , π and/or α ij � = 0 , π . • Standard scenario ? NSI, sterile neutrinos, violations of unitarity

3 – Long baseline neutrino experiments: theoretical aspects 3 – Long baseline neutrino experiments: theoretical aspects δ and the sign of ∆ m 2 31 can be measured in long baseline appearance ν -oscillation experiments: they use a manmade flux of neutrinos with detectors located at 100s-1000s of km away. These accelerator neutrino experiments search for ν µ ( e ) → ν e ( µ ) appearance: P ( ν µ → ν e ) = sin 2 θ 23 sin 2 2 θ 13 sin 2 ∆ m 2 31 L 4 E for subdominant matter effects and CPV.

3 – Long baseline neutrino experiments: theoretical aspects • MINOS: NUMi beam sourced at Fermilab with iron magnetised detector at 735 km distance. It can improve the present sensitivity on θ 13 . [M. Diwan, 0904.3706]

3 – Long baseline neutrino experiments: theoretical aspects • T2K: ν µ beam sourced at JPARC with Super-K detector at 300 km distance. Aimed at ν e appearance. [T2K LOI]

3 – Long baseline neutrino experiments: theoretical aspects • NO ν A: NUMi beam with scintillator detector at 800 Km distance ( 0 . 85 o OA). Aimed at ν e appearance. [http://www-nova.fnal.gov/] [NOvA proposal]

3 – Long baseline neutrino experiments: theoretical aspects These oscillations take place in matter (Earth), ( e − , p and n ), ⇒ Matter effects violate CP . A potential V in the Hamiltonian √ ( V = 2 G F ( N e − N n / 2) ) describes matter effects. The probability can be approximated as (for no CPV): P ν µ → ν e = sin 2 θ 23 sin 2 2 θ m 13 sin 2 ∆ m 13 L 2 The mixing angle changes with respect to the vacuum case: (∆ m 2 / 2 E ) sin 2 θ sin 2 θ m = �� � 2 � 2 � ∆ m 2 ∆ m 2 sin 2 θ + cos 2 θ − V 2 E 2 E � 2 + �� � 2 � ∆ m 2 ∆ m 2 and ∆ m 13 = 2 E sin 2 θ 2 E cos 2 θ − V .

3 – Long baseline neutrino experiments: theoretical aspects For ∆ m 2 > 0 , the probability gets enhanced for neutrinos and suppressed for antineutrinos. Viceversa, for ∆ m 2 < 0 . Matter effects imply that P ( ν l → ν l ′ ) � = P (¯ ν l → ¯ ν l ′ ) If U is complex ( δ � = 0 , π ), we have CP-violation: P ( ν l → ν l ′ ) � = P (¯ ν l → ¯ ν l ′ ) A measure of CP- violating effects is provided by: A CP = P ( ν l → ν l ′ ) − P (¯ ν l → ¯ ν l ′ ) ν l ′ ) ∝ J CP ∝ sin θ 13 sin δ P ( ν l → ν l ′ )+ P (¯ ν l → ¯ It is necessary to disentangle true CP-V effects due to the δ phase from the ones induced by matter: degeneracies.

3 – Long baseline neutrino experiments: theoretical aspects In the range of energies ( E ∼ 0 . 5 ÷ 4 GeV) and length ( L ∼ 200 ÷ 1500 Km), of interest, the oscillation probability for ν µ → ν e , in 3-neutrino mixing case, is given by: � 2 sin 2 ( A ∓ ∆ 13 ) L 23 sin 2 2 θ 13 P ( ¯ � ∆ 13 s 2 P ) ≃ A ∓ ∆ 13 2 + ˜ � � sin ( A ∓ ∆ 13 ) L J ∆ 12 A ∓ ∆ 13 sin AL ∆ 13 ∓ δ + ∆ 13 L cos A 2 2 2 � 2 sin 2 AL 23 sin 2 2 θ 12 � ∆ 12 + c 2 A 2 with ˜ J ≡ c 13 sin 2 θ 13 sin 2 θ 23 sin 2 θ 12 and ∆ 13 ≡ ∆ m 2 31 / (2 E ) . √ A ≡ 2 G F ¯ n e .

3 – Long baseline neutrino experiments: theoretical aspects In the vacuum case, for simplicity, we identify 2-, 4- and 8- fold degeneracies [Barger, Marfatia, Whisnant] : • ( θ 13 , δ ) degeneracy [Koike, Ota, Sato; Burguet-Castell et al.] : δ ′ = π − δ ∆ m 2 cot θ 23 cot ∆ m 2 12 L 13 L θ ′ = θ 13 + cos δ sin 2 θ 12 13 4 E 4 E • (sign(∆ m 2 13 ) , δ ) degeneracy [Minakata, Nunokawa] : δ ′ π − δ sign ′ (∆ m 2 − sign(∆ m 2 13 ) 13 ) • θ 23 , π/ 2 − θ 23 degeneracy [Fogli, Lisi] .

3 – Long baseline neutrino experiments: theoretical aspects • degeneracies strongly affect the ability to determine the type of hierarchy and CP-violation 150 150 150 100 100 100 50 50 50 δ CP [degrees] δ CP [degrees] δ CP [degrees] 0 0 0 -50 -50 -50 -100 -100 -100 BB (Normal) 99% CL. BB + EC (Normal) 99% CL. BB (With Clon) 99% CL. -150 -150 -150 BB + EC (With Clon) 99% CL. 0 0 1 1 2 2 3 3 4 4 5 5 6 6 1e-05 1e-04 0.001 0.01 0.1 Sin 2 (2 θ 13 ) θ 13 [degrees] θ 13 [degrees] [J. Bernabeu et al., 2009]

4 – Long baseline neutrino experiments: experimental aspects 4 – Long baseline neutrino experiments: experimental aspects Future LBL experiments: 1. Superbeams : a very intense ν µ beam. Intrinsic ν e background. Typical energies: 100 MeV to few GeV → WC, LiAr or scintillator detector. 2. Beta-beams : ν e beams given by the β -decays of high-gamma ions. Same energy and type of detector as for superbeams. 3. Neutrino factories : ν µ - ν e beam from high- γ muons (20 GeV - 50 GeV). The detector needs to be magnetised to distinguish the signal from the background.

4 – Long baseline neutrino experiments: experimental aspects Flux and Baseline • The statistics plays an important role in determining the physics reach. • Backgrounds depend on the type of beam: superbeams have an intrinsic background which limits the reach for very small θ 13 . Betabeams have a very “clean” beam but they might be limited in flux and energy. Neutrino factory beams could be very well controlled. • The longer the baseline the stronger matter effects in the oscillations. This implies an increased sensitivity to the type of neutrino mass spectrum. • The longer the baseline the higher the energy as the experiments try to increase the sensitivity by having the average energy at first oscillation maximum. Higher energy typically implies higher cross section but also impacts on the type of detector used (WC versus LiAr vs scintillator vs iron magnetised).