Impact of light sterile!s in LBL experiments "

Xmas Theory Workshop Bari, 22/12/14 Impact of light sterile!s in LBL experiments " Work done in collaboration with L. Klop (Master Thesis at MPI) (now PhD student @ GRAPPA Institute, Amsterdam) Antonio Palazzo MPI für Physik - Munich

Outline Introduction CP violation in neutrino oscillations Measuring the CP-phases induced by sterile neutrinos at running LBL experiments (T2K) Conclusions 2

3! scheme: knowns & unknowns +%m 2 NH! 3"! 2"! 1"! 3"? IH -%m 2! e! µ"! #" $m 2 = 7.5 x 10-5 ev 2 %m 2 = 2.4 x 10-3 ev 2 $m 2 ' = $m2 = 0.03 %m 2 $ is the Dirac CP-violating phase? & 23 ~ 41 º & 12 ~ 34 º & 13 ~ 9 º 3

CPV is a genuine 3-flavor effect % ij = %m2 ij L 4E A CP αβ P (ν α ν β ) P ( ν β ν α ) A CP αβ = 16J 12 αβ sin 21 sin 13 sin 32 J ij αβ Im [U αiu βj U αju βi] J γ=e,µ,τ αβγ k=1,2,3 J is parameterization independent (Jarlskog invariant) In the standard parameterization: J = 1 8 sin 2θ 12 sin 2θ 23 sin 2θ 13 cos θ 13 sin δ ijk Conditions for CPV: - No degenerate (! i,! j ) - No & ij = (0, (/2) - $ / = (0, ()? 4

Present data are sensitive to $" $ not necessarily has to be extracted from asymmetry A ')" Currently from combination of: { Pee ($-independent), LBL Reactors" Pµe ($-dependent), LBL Accelerators (T2K)" CP 5

Outline of the T2K experiment E = 0.6 GeV L = 295 km %m 2 13 = 2.4 x 10-3 = m2 13L 4E π 2 First oscillation maximum 6

T2K: 3-flavor transition probability P 3ν ν µ ν e = P ATM + P SOL + P INT, P ATM =4s 2 23s 2 13 sin 2 P SOL =4c 2 12c 2 23s 2 12(α ) 2 In vacuum: Pµe ATM INT SOL E = 0.6 GeV best & 13 estimate P INT =8s 23 s 13 c 12 c 23 s 12 (α ) sin cos( + δ CP ). = m2 31L 4E, α = m2 21 m 2 31 % * (/2 ' * 0.03 sin 2& 13 NH P ATM leading! & 13 > 0 P INT subleading! $ dependence P SOL negligible IH Matter effects induce some difference among NH and IH 7

An apparently unrelated issue 8

SBL anomalies point to sterile!s Reactor & Gallium: Pee < 1 N OBS /(N EXP ) pred,new 1.15 1.1 1.05 1 0.95 0.9 0.85 ILL Bugey!3/4 ROVNO Krasnoyarsk Goesgen Bugey3 Goesgen Krasnoyarsk!3 Goesgen Krasnoyarsk!2 Bugey3 PaloVerde CHOOZ 9 Giunti et al., PRD 2013 C. GIUNTI et al. 10 3+1 GLO 68.27% CL 90.00% CL 95.45% CL 99.00% CL 99.73% CL 0.8 0.75 0.7 10 1 10 2 10 3 Distance to Reactor (m) FIG. 4. Illustration of the short baseline reactor antineutrino anomaly. The experimental results are compared to the prediction without oscillation, taking into account the new antineutrino spectra, the corrections of the neutron mean lifetime, and the off-equilibrium effects. Published experimental errors and antineutrino spectra errors are added in quadrature. The LSND mean 1 + averaged ratio including possible correlations is 0.937±0.027. The red line shows a 3 active neutrino mixing solution fitting the data, with sin 2 (2θ13) =0.06. The blue line [LSND, displays a solution PRLincluding 75 (1995) a new neutrino 2650; mass state, PRC such 54 as m(1996) 2 new,r 1 2685; PRL 77 (1996) 3082; PRD 64 (2001) 112007] ev 2 (for illustration) and sin 2 (2θnew,R)=0.16. e L 30 m 20 MeV E 200 MeV noted anomalies affecting other short baseline electron neutrino experiments Gallex, Sage and MiniBooNE, reviewed in Ref. [43]. Experiment(s) sin 2 (2θnew) m 2 new (ev 2 ) C.L. (%) 10 2 17.5 Reactors (no ILL-S,R Beam Our goal is to quantify the compatibility of those anomalies. p(! _ µ ) Excess 0.02-0.23 >0.2 95.0 Gallium (G) 0.06-0.4 >0.3 97.7 MiniBooNE (M) e,e+ )n 15 72.4 We first reanalyzed the Gallex and Sage calibration ILL-S p(! _ 68.2 )n 10 runs with 51 Cr and 37 Ar radioactive sources emitting R e 12.5 +G 0.07-0.24 >1.5 99.7 1 MeV electron neutrinos. [44], following the methodology developed in Ref. 10 [43, 45]. However we decided to R + ILL-S 0.04-0.23 >2.0 97.1 Bugey R other +M 0.04-0.23 >1.4 97.5 Karmen CCFR 3+1 3σ include possible correlations between these four measurements in this present7.5 work. Details are given in in Ap- ν µ DIS ALL 0.06-0.25 >2.0 99.93 1 ν e DIS pendix B. This has the effect of being slightly more conservative, with the no-oscillation TABLE III. Best fit parameter intervals or limits at (95%) NOMAD DIS 5 hypothesis disfavored at for (sin 2 (2θnew), m 2 new) and significance of the sterile neutrino oscillation hypothesis in %, for different combinations of 10 1 APP 97.73% C.L., instead of 98% C.L in Ref. [43]. Gallex and 2.5 10-1 Sage observed an average deficit of RG = 0.86±0.05(1σ). the reactor experiment rates only (R ), the ILL-energy spectrum information (ILL-S), the Gallium experiments (G), and 90% (L max -L < 2.3) Considering the hypothesis of νe disappearance caused by 0 short baseline oscillations we used Eq. (11), neglecting MiniBooNE-ν (M) re-analysis of Ref. [43]. the m 2 31 driven oscillations 0.4because of0.6 the very short0.8 1 1.2 1.4 10-2 baselines of order 1 meter. Fitting the data leads to sin 2 10-3 10-2 10 2ϑ 1 m 2 new,g eµ (95%) and sin 2 L/E (2θnew,G) 0.26.! (meters/mev) sin 2 2# Combining the reactor antineutrino anomaly with the ev 2 and sin 2 (2θnew,MB) 0.2, but are not significant Gallium anomaly gives a good fit to the data and disfavors the no-oscillation hypothesis at 99.7% C.L. Allowed favored LSND 2 0 2eV 2 ( at 95% C.L. The no-oscillation hypothesis is only dis- m at the level of 72.4% C.L., less significant than matm 2 msol) 2 regions in the sin 2 (2θnew) m 2 new plane are displayed the reactor and gallium anomalies. Combining the reactor antineutrino anomaly with our MiniBooNE re- in Figure 5 (left). The associated best-fit parameters are m 2 new,r&g > 0.7 ev2 (95%) and sin 2 C. (2θnew,R&G) analysis Giunti leads to a Phenomenology good fit with the sterile neutrino of Sterile Neutrinos 16 May 2011 5/59 0.16. hypothesis and disfavors the absence of oscillations at We then reanalyzed the MiniBooNE electron neutrino 97.5% C.L., dominated by the reactor experiments data. excess assuming the very short baseline neutrino oscillation explanation of Ref. [43]. Details of our re- displayed in Figure 5 (right). Allowed regions in the sin 2 (2θnew) m 2 new plane are L production of the latter analysis are provided in Appendix parameters are m 2 new,r&mb B. The best fit values are m 2 new,mb =1.9 sin 2 (2θnew,R&MB) 0.1. Beam Excess E Accelerators: Pµe > 0 [ev 2 ] m 41 2 $m 2 (ev 2 /c 4 ) + 10 4 99% (L 10 3 10 2 10 1 max -L < 4.6) 1 FIG. 2 (color online). Allowed region in the sin 2 2# e m 2 41 plane in the global (GLO) 3 þ 1-HIG fit of short-baseline neutrino oscillation data compared with the 3 allowed regions obtained from ð Þ! ð Þ e short-baseline appearance data (APP; inside the solid blue curves) ~ and the 3 constraints obtained from ð Þ e short-baseline disappearance data ( e DIS; left of the dotted dark-red curve), ð Þ short-baseline disappearance data ( DIS; left of the dash-dotted dark-green curve) and the combined short-baseline disappearance data (DIS; left of the 12 0 Need of a new larger %m 2 The associated best-fit > 1.4 ev2 (95%) and 13 0 MeV 1 ev 2 9 FIG. 3 (color and sin 2 2# fit of short-ba the 3 constra ance data (s short-baseline right panel). T crosses.

Introducing a sterile neutrino 3+1 scheme" 3! scheme U s4 ~ 1 2 %m atm 2 %m 14 ~ 1 ev 2 2 %m sol Only small perturbations to the 3! framework However, 3! CP-violation effects are very small Can new 4! CPV effects compete with the 3! ones? 10

An important remark A CP αβ = 16J 12 αβ sin 21 sin 13 sin 32 if 13 23 1 Osc. averaged out by finite E resol. { sin 2 =1/2 It can be: A CP (if sin $ / = 0) αβ = 0 The bottom line is that if one of the three! i is! far from the other two ones this does not erase CPV (relevant for the 4! case) 11

Mixing matrix in 3+1 scheme R ij = U = R 34 R 24 R 14 R 23 R 13 R 12 cij s ij s ij c ij R ij = cij { s ij s ij c ij 3!" s ij =sinθ ij c ij =cosθ ij s ij = s ij e iδ ij {" 6 mixing angles {" 3+3N mixing angles 3+1 3 Dirac CP-phases 3+N 1+2N Dirac phases 3 Majorana phases 2+N Majorana phases & 14 = & 24 = & 34 = 0 3-flavor case 12

T2K: 4-flavor transition probability - %m 2 14 >> %m2 13 : fast oscillations induced by %m2 14 are averaged out - Phase information (value of %m 2 14 ) gets lost in contrast to SBL - Unlike SBL, interf. of %m 2 14 & %m2 13,12 In vacuum, for %m 2 14! P 4ν ν µ ν e =4 U µ3 2 U e3 2 sin 2 +4 U µ2 2 U e2 2 (α ) 2 +8 Uµ3 U e3 U µ2 Ue2 (α )sin cos( + δ 13 ) +4 Uµ3 U e3 U µ4 Ue4 sin sin( + δ 13 δ 14 ) occurs: sensitivity to CP-phases & 13 = 9 o E = 0.6 GeV SBL preferred range P ATM 4 U µ2 U e2 U µ4 U e4 (α )sinδ 14 +2 U µ4 2 U e4 2 Pν 4ν µ ν e (1 U e4 2 U µ4 2 )Pµe 3ν + PII INT + PIII INT + P STR P INT II =2sin2θ µe s 13 s 23 sin sin( + δ 13 δ 14 ) P INT III = 2sin2θ µe c 23 s 12 c 12 (α ) sin δ 14 P STR = 1 2 sin2 2θ µe. sin 2 2θ µe =4 U e4 2 U µ4 2 INT P II can be as large as P I INT P max I 3! limit P max II sin 2& µe P STR P III max P sol 13

Numerical examples of 4! probability (Averaged over fast oscillations) Different line styles Different values of $ 14 14

Results of the 4! analysis (NH) - Big impact on T2K wiggles Similar findings in IH - Comparable sensitivity to $ 13 & $ 14 ~ ~ - Best fit values: $ 13 $ 14 -(/2-4! gives better agreement of T2K & Reactors 15

Summary Neutrino physics is entering a new era (CPV, NMH) Several indications of light sterile neutrinos Sterile neutrinos are sources of additional CPV LBL experiments can give info on new CP-phases The running exp T2K has already some sensitivity Ours is the first quantitative study of such effects 16