Neutrino Physics: Lecture 12

Size: px

Start display at page:

Download "Neutrino Physics: Lecture 12"

Douglas Allen
5 years ago
Views:

1 Neutrino Physics: Lecture 12 Sterile neutrinos Amol Dighe Department of Theoretical Physics Tata Institute of Fundamental Research Apr 5, 2010

2 Outline 1 Short baseline experiments and LSND anomaly 2 Adding a fourth neutrino 3 Constraining the sterile neutrino 4 Sterile neutrino in astrophysics and cosmology

3 Outline 1 Short baseline experiments and LSND anomaly 2 Adding a fourth neutrino 3 Constraining the sterile neutrino 4 Sterile neutrino in astrophysics and cosmology

4 SBLs: When only one m 2 matters No CP violation, any number of neutrinos: P αβ = δ αβ i<j 4Re( αβij ) sin 2 ( ji ) αβij U αi U βj Uαj U βi Approximation of single mass-squared dominance All significant ji nearly equal, All other ji negligible, 0 P αα = 1 sin 2 2θ eff sin 2 ( ) P αβ = sin 2 2θ eff sin 2 ( ) (α β)

5 SBLs: When only one m 2 matters No CP violation, any number of neutrinos: P αβ = δ αβ i<j 4Re( αβij ) sin 2 ( ji ) αβij U αi U βj Uαj U βi Approximation of single mass-squared dominance All significant ji nearly equal, All other ji negligible, 0 P αα = 1 sin 2 2θ eff sin 2 ( ) P αβ = sin 2 2θ eff sin 2 ( ) (α β)

6 Equi-probabilty contours sin 2 2θ eff sin 2 ( ) = Constant

7 Short baseline and sensitivity to m 2 Nontrivial P αα or P αβ only when 1 Atmospheric neutrinos: E 1 GeV, L 10 3 km m ev 2 Reactor neutrinos: E 1 MeV, L 1 km m ev 2 Long baseline experiments: E 1 10 GeV, L km m ev 2 Accelerator (short baseline) experiments: E MeV, L 1 km m ev 2

8 Neutrino experiments with 2ν approximation

9 Solar and atmospheric experiments

10 Results from short baseline experiments

11 The LSND excess ν µ ν e oscillations! Excess = 87.9 ± 22.4 ± 6.0 events

12 L/E oscillations in LSND Oscillation probability ± ± m ev 2

13 The LSND parameter space hep-ex/

14 A fourth neutrino? Three independent m 2 : m ev 2 matm ev 2 m ev 2 Not possible with only three neutrino masses! A fourth neutrino species must be present

15 A fourth neutrino? Three independent m 2 : m ev 2 matm ev 2 m ev 2 Not possible with only three neutrino masses! A fourth neutrino species must be present

16 Outline 1 Short baseline experiments and LSND anomaly 2 Adding a fourth neutrino 3 Constraining the sterile neutrino 4 Sterile neutrino in astrophysics and cosmology

17 A fourth generation neutrino? LEP: e + e Z f f Effective number of neutrinos: N ν = ± Only three light neutrinos interact with Z The fourth neutrino has to be sterile!

18 What is a (light) sterile neutrino A fermion without electric charge Does not have electroweak interactions (Does not interact with W, Z, γ) Can have interactions beyond the Standard Model (BSM) Can mix with active neutrinos due to the BSM interactions NOT the right-handed partner of active neutrinos

19 What is a (light) sterile neutrino A fermion without electric charge Does not have electroweak interactions (Does not interact with W, Z, γ) Can have interactions beyond the Standard Model (BSM) Can mix with active neutrinos due to the BSM interactions NOT the right-handed partner of active neutrinos

20 What is a (light) sterile neutrino A fermion without electric charge Does not have electroweak interactions (Does not interact with W, Z, γ) Can have interactions beyond the Standard Model (BSM) Can mix with active neutrinos due to the BSM interactions NOT the right-handed partner of active neutrinos

21 What would the neutrino mass spectrum look like? Mixing matrix: 6 angles and 10 phases U = Φ(χ 1, χ 2, χ 3, χ 4 ) U 14 (θ 14, δ 14 ) U 34 (θ 34, 0) U 24 (θ 24, δ 24 ) U 23 (θ 23, 0) U 13 (θ 13, δ 13 ) U 12 (θ 12, 0) Φ(φ 1, φ 2, φ 3, 0)

22 Outline 1 Short baseline experiments and LSND anomaly 2 Adding a fourth neutrino 3 Constraining the sterile neutrino 4 Sterile neutrino in astrophysics and cosmology

23 Testing the LSND anomaly MiniBOONE: E 1 GeV, L 1 km ν µ as well as ν µ beams

24 Constraining sterile ν from appearance experiments

25 Constraints from disappearance experiments Solar neutrinos SNO indicates that most ν e go to ν µ or ν τ bound on ν e ν s mixing Atmospheric neutrinos Extra contribution to atmospheric oscillations: P µµ P µµ (3ν) 1 2 sin2 2θ µs bound on ν µ ν s mixing Reactor experiments mlsnd 2 would contribute to KamLAND, K2K, MINOS bound on ν e ν s and ν µ ν s mixing mlsnd 2 would contribute to CHOOZ bound on ν e ν s and ν µ ν s mixing

26 Constraints from disappearance experiments Solar neutrinos SNO indicates that most ν e go to ν µ or ν τ bound on ν e ν s mixing Atmospheric neutrinos Extra contribution to atmospheric oscillations: P µµ P µµ (3ν) 1 2 sin2 2θ µs bound on ν µ ν s mixing Reactor experiments mlsnd 2 would contribute to KamLAND, K2K, MINOS bound on ν e ν s and ν µ ν s mixing mlsnd 2 would contribute to CHOOZ bound on ν e ν s and ν µ ν s mixing

27 Constraints from disappearance experiments Solar neutrinos SNO indicates that most ν e go to ν µ or ν τ bound on ν e ν s mixing Atmospheric neutrinos Extra contribution to atmospheric oscillations: P µµ P µµ (3ν) 1 2 sin2 2θ µs bound on ν µ ν s mixing Reactor experiments mlsnd 2 would contribute to KamLAND, K2K, MINOS bound on ν e ν s and ν µ ν s mixing mlsnd 2 would contribute to CHOOZ bound on ν e ν s and ν µ ν s mixing

28 LSND parameter space ruled out ArXiv:

29 Can more than one sterile neutrinos help? Need 2 neutrinos of masses ev Constraints from cosmology

30 Outline 1 Short baseline experiments and LSND anomaly 2 Adding a fourth neutrino 3 Constraining the sterile neutrino 4 Sterile neutrino in astrophysics and cosmology

31 Sterile neutrinos in astrophysics Nucleosynthesis of heavy elements (r-process) Heavy elements need more neutrons ν e tend to reduce number of neutrons: ν e + n e + p ν e ν s conversion can allow heavy elements to be formed, if m ev 2 Supernova explosions Conversions to ν s carry away energy efficiently May affect explosion dynamics Can create large asymmetries in ν emission May explain large pulsar velocities

32 Sterile neutrinos in astrophysics Nucleosynthesis of heavy elements (r-process) Heavy elements need more neutrons ν e tend to reduce number of neutrons: ν e + n e + p ν e ν s conversion can allow heavy elements to be formed, if m ev 2 Supernova explosions Conversions to ν s carry away energy efficiently May affect explosion dynamics Can create large asymmetries in ν emission May explain large pulsar velocities

33 Sterile neutrinos in cosmology kev neutrinos are viable dark matter candidates Can help in producing supermassive black holes Predicted by some models (e.g. νmsm) that explain baryon asymmetry

34 (Not) the last word on sterile neutrinos ev-neutrinos not required for explaining oscillation data, Not ruled out either (only mixing constrained) Can help some astrophysical phenomena if m ev 2, very small mixing kev-neutrinos may play a role in cosmology, structure formation

35 (Not) the last word on sterile neutrinos ev-neutrinos not required for explaining oscillation data, Not ruled out either (only mixing constrained) Can help some astrophysical phenomena if m ev 2, very small mixing kev-neutrinos may play a role in cosmology, structure formation

36 (Not) the last word on sterile neutrinos ev-neutrinos not required for explaining oscillation data, Not ruled out either (only mixing constrained) Can help some astrophysical phenomena if m ev 2, very small mixing kev-neutrinos may play a role in cosmology, structure formation

Neutrino Physics II. Neutrino Phenomenology. Arcadi Santamaria. TAE 2014, Benasque, September 19, IFIC/Univ. València

Neutrino Physics II. Neutrino Phenomenology. Arcadi Santamaria. TAE 2014, Benasque, September 19, IFIC/Univ. València Neutrino Physics II Neutrino Phenomenology Arcadi Santamaria IFIC/Univ. València TAE 2014, Benasque, September 19, 2014 Neutrino Physics II Outline 1 Neutrino oscillations phenomenology Solar neutrinos