Why neutrinos? Patrick Huber. Center for Neutrino Physics at Virginia Tech. KURF Users Meeting June 7, 2013, Virginia Tech. P. Huber VT-CNP p.

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1 Why neutrinos? Patrick Huber Center for Neutrino Physics at Virginia Tech KURF Users Meeting June 7, 2013, Virginia Tech P. Huber VT-CNP p. 1

2 Neutrinos are massive so what? Neutrinos in the Standard Model (SM) are strictly massless, therefore the discovery of neutrino oscillation, which implies non-zero neutrino masses requires the addition of new degrees of freedom. P. Huber VT-CNP p. 2

3 We always knew they are... The SM is an effective field theory, i.e. at some high scaleλnew degrees of freedom will appear L SM + 1 Λ L Λ 2L The first operators sensitive to new physics have dimension 5. It turns out there is only one dimension 5 operator L 5 = 1 Λ (LH)(LH) 1 Λ (L H )(L H ) = m ννν Thus studying neutrino masses is, in principle, the most sensitive probe for new physics at high scales Weinberg P. Huber VT-CNP p. 3

4 Effective theories The problem in effective theories is, that there are a priori unknown pre-factors for each operator L SM + # Λ L 5 + # Λ 2L Typically, one has # = O(1), but there may be reasons for this being wrong lepton number may be conserved no Majorana mass term lepton number may be approximately conserved small pre-factor forl 5 Therefore, we do not know the scale of new physics responsible for neutrino masses. P. Huber VT-CNP p. 4

5 θ 13 is large! The Daya Bay result is sin 2 2θ 13 = 0.089±0.010(stat)±0.005(syst), which translates into a more than 5 σ exclusion of θ 13 = 0, confirmed by RE- NO. NB a year ago we had only 2 σ indications. P. Huber VT-CNP p. 5

6 Implications In general, this raises the following questions Is neutrino physics essentially done? Will the mass hierarchy have been determined before the next generation of long-baseline experiments? Are new experiments beyond NOνA and T2K necessary to discover CP violation? Are superbeams sufficient for precision neutrino physics? Any of this questions is both a challenge and opportunity! P. Huber VT-CNP p. 6

$large fraction$ has been excluded!

7 Model selection a large fraction has been excluded! of a selection of 63 models disfavoured! Figure shows only a small subset of the existing models! disfavoured! based on figure from Albright, Mu-Chun Chen ( 06) Antusch, 2012 P. Huber VT-CNP p. 7

8 Flavor models Simplest un-model anarchy Murayama, Naba, DeGouvea du = ds 2 12 dc4 13 ds2 23 dδ CP dχ 1 dχ 2 predicts flat distribution in δ CP Simplest model Tri-bimaximal mixing Harrison, Perkins, Scott to still fit data, obviously corrections are needed predictivity? P. Huber VT-CNP p. 8

9 Sum rules Θ Θ 13 cos Θ Θ 13 cos Θ Θ 13 cos Θ Θ 13 cos Θ Θ 13 cos Antusch, King current best fit values and errors forθ 12,Θ 13 andθ 23 taken from Fogli et al on sin 2 2Θ on sin 2 Θ 12 current errors 1 on sin 2 2Θ predicted value of CP 3σ resolution of 15 distance requires 5 error. P. Huber VT-CNP p. 9

10 What we want to learn In the context of neutrino oscillation experiments δ CP mass hierarchy θ 23 = π/4, θ 23 < π/4 orθ 23 > π/4? Resolution of LSND and the other short-baseline anomalies New physics vs tests of the three flavor framework Given the current state of the theory of neutrinos we can not say with confidence that any one quantity is more fundamental than any other. P. Huber VT-CNP p. 10

11 LSND and MiniBooNE P( ν µ ν e ) Tension between neutrino and antineutrino signals? P. Huber VT-CNP p. 11

12 Reactor and Gallium anomalies ROVNO88 3S ROVNO88 1S SRP I N OBS /(N EXP ) pred,new ILL Bugey 3 Bugey 4 ROVNO88 2I ROVNO91 ROVNO88 1I SRP II ROVNO88 2S Krasnoyarsk I Bugey 3 Goesgen I Goesgen II Krasnoyarsk III Goesgen III Krasnoyarsk II Bugey 3 PaloVerde CHOOZ DoubleCHOOZ Nucifer (2012) Distance to Reactor (m) P. Huber VT-CNP p. 12

13 Disappearance constraints Absence of effects in - atmospheric - Bugey - CDHS - MINOS -... data creates considerable tension in 3+N sterile neutrino models More details can be found in the sterile neutrino white paper, arxiv: P. Huber VT-CNP p. 13

14 Sterile oscillation In general, in a 3+N sterile neutrino oscillation model one finds that the energy averaged probabilities obey the following inequality P(ν µ ν e ) 4P(ν e ν e )P(ν µ ν µ ) independent of CP transformations. Therefore, a stringent test of the model is to measure P(ν µ ν e ) appearance P( ν µ ν e ) appearance P(ν µ ν µ ) or P( ν µ ν µ ) disappearance P(ν e ν e ) or P( ν e ν e ) disappearance P. Huber VT-CNP p. 14

15 Non-standard interactions NSI are the workhorse of beyond the Standard Model physics in the neutrino sector. Phenomenologically the can be parametrized by terms like this L NSI = 2 2G f ǫ fp αβ ( ν αγ ρ ν β )( fγ ρ Pf), wheref can be any fermion and P is the projection onto right and left-handed components. Wolfenstein, 1978 At higher energy, this contact term has to be replaced with a propagating exchange particle. P. Huber VT-CNP p. 15

16 Simple example Assume a flavor changing interaction with quarks of the typeν e +q ν τ +q, this adds the following term to the Hamiltonian H NSI = 2G f n e E 1 0 ǫ eτ e iδ ν ǫ eτ e +iδ ν 0 0. Typically, ǫ 1 and thus this is a sub-dominant effect. P. Huber VT-CNP p. 16

17 Impact on three flavors Three flavor analysis are not safe from these effects! Especially, global fits for the phase and mass hierarchy need to be aware of NSI. Friedland, 2012 P. Huber VT-CNP p. 17

18 New ideas for mass hierarchy Literature survey The dashed ones are from collaborations phenomenological studies are driving the fieldp. Huber VT-CNP p. 18

19 Early hints for CP? Fogli, et al., 2012 NB 1σ range forδ = P. Huber VT-CNP p. 19

20 Early hints for CP? Double Chooz 2Π T2K 2Π NO A 2Π Daya Bay 2Π Combined 3 2 Π Π Π 3 2 Π 9.7 CP Π CP Π CP Π CP Π Π 2 Π 2 Π 2 Π sin 2 2Θ sin 2 2Θ sin 2 2Θ sin 2 2Θ sin 2 2Θ 13 PH, et al., 2009 At lower confidence levels some indications maybe obtained impact in future program? P. Huber VT-CNP p. 20

21 How much will we gain? Assuming that the combination of T2K+NOνA has seen (or not) a hint for CP violation, what is the probability that a given facility can observe a high significance signal for CP violation? Blennow, Coloma, Donini, Fernandez-Martnez, 2013 P. Huber VT-CNP p. 21

22 Summary Neutrino oscillation is solid evidence for new physics Precision measurements help to exclude a vast number of models Precision measurements have the best potential to uncover even newer physics In combination this warrants a rich experimental program. To be successful, this will require adequate theory support. P. Huber VT-CNP p. 22

Largeθ 13 Challenge and Opportunity

Largeθ 13 Challenge and Opportunity Patrick Huber Center for Neutrino Physics at Virginia Tech Experimental Seminar January 15, 2013, SLAC P. Huber VT-CNP p. 1 θ 13 is large! The Daya Bay result is sin