Chasing the light sterile neutrino Status of the STEREO experiment Alessandro Minotti (IRFU - CEA Saclay) on behalf of the STEREO collaboration 16/03/2017 Outlook • Neutrino physics and oscillation • Reactor neutrinos and the Reactor Antineutrino Anomaly • The STEREO experiment: principle, configuration, and timeline of the installation and commissioning phase • The STEREO experiment: status of the analysis of first collected data Alessandro Minotti (CEA - IRFU) Outlook • Neutrino physics and oscillation • Reactor neutrinos and the Reactor Antineutrino Anomaly • The STEREO experiment: principle, configuration, and timeline of the installation and commissioning phase • The STEREO experiment: status of the analysis of first collected data Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) The Neutrino • Neutrinos (ν) = neutral leptons - A wide range of sources and energies - Standard Model: 3 massless and only LH ν (RH ν̄) νe νμ ντ W+ e+ W+ μ+ W+ τ+ • Neutrinos oscillate (change flavour) propagating α+ β+ - Energy-dependent deficit in solar ν flux να Flavour changing νβ W+ - Distance-dependent deficit for atmospheric ν’s KOSMISK Electron-neutrinosSUN STRÅLNING are produced in the ATMOSFÄR Sun center. SUPER- KAMIOKANDE 2015 SNO Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #4 Oscillation Formalism • Neutrinos oscillate (change flavour) propagating α+ β+ να Flavour changing νβ Very small but non-zero different massesAs you can see, theW oscillatory+ behaviour comes from the difference in the energy eigenvalues of ν > and ν > (E WeakE ), Hamiltonian which we interpretFree Hamiltonian as coming fromWeak di Hamiltonianfferent masses for each of themass | 1 | 2 2 − 1 + Flavour eigenstates are a mix of eigenvalues.mass eigenstates A plot of this function is shown in Figure 7 for a particular setUnitary of parameters : ∆m2 =3 10−3eV 2, (like K̄ ⁰ K⁰ and KS KL) 2 × sin (2θ)=0.8andEν =1GeV.AtL = 0, the oscillation probability is zero and the corresponding 2 L π survival probability is one. As L increases the oscillatios begin to switch on until 1.27∆m E = 2 = Relative phases change while propagatingor L = 400 km. At this point the oscillation is a maximum. However, the mixing angle is just Two-Flavor mixingsin2 (2(forθ)=0 simplicity).8 so at maximal mixing, only 80% of the initial neutrinos have oscillated away. As L increases furthur, the oscillation dies down until, around L = 820 km, the beam is entirely composed 2 ! of the initial! neutrino flavour. If sin (2θ)=1.0, the oscillations would be referred to as maximal, " "#$$ $%&meaning$ that' at some point on the path to the detector 100% of the neutrinos have oscillated. • E.g.: 2 families ! $ Definite momentum p; same for ! # !#$%& $ "#$$ " ! ( all mass eigenstate components ! " ! " ( Time development for an initially pure |να> beam: ( ( ) # #$ ! $ #! . &)# ! .& Δm² = 0.003 eV² Amplitude Oscillation##$ % ! # & ) (, Eν = 1 GeV %!" ! ! " !"#$$ " %!' &$%& $ " %!( ( ( ( )'#)( %) ##$ ! ##$ ! $ # $ ! * ( % ( & ( ' (, ( $ ! " "#$ $ " &$%& $ " #$% !" ! -$$./%&0!, !%$!123!$-/3" ##$ ! ##$ ! # Squared mass % & ! !45 # 65 #*' / & "#$2 $2$%& $ ! " # " " $% ! # splitting m" 1 -m2 # ( Baseline, ν energy %) $ #$ !! * ! ( ' " ($ Mixing probability: • Sensitive to oscillation if L/E is ~ ΔmFigure2 7: The oscillation probability as a function of the baseline, L, for a given set of parameters : 2 ( −3 2 (2 ( $(#$' ' ! ! ' ! (!"!%(! %!∆!m! "=3% !(!10"#$$eV$%&, $sin" (2'#θ)=0"#$ .8andEν !=1GeV. " # # " × " ( # Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #5 As a side( comment, the derivation of the oscillation( probability depends on two assumptions : that ( ( %) ( ( '*(+$%) " "+ # ' ! ! (! $%& (the! $%& neutrino flavour* $%& and( mass! $%& states are mixed and* that-) we create a coherent superposition of mass ! ! " ' # "! ! ! " # states at! ) the$ weak" vertex. This! coherent) $ " superposition,"+ # reflects" the fact that we can’t experimentally resolve which mass state was created at the vertex. One might ask oneself what we would expect to see if we did know which mass state was created at the vertex. If we knew that, we would know the mass of the neutrino state that propagates to the detector. There would be no superposition, no phase difference and no flavour oscillation. However there would be flavour change. Suppose that at the vertex we create a lepton of flavour α and a specific mass state, νk >. Mixing implies that we’ve picked out the kth mass state from the α flavour state. The probability| of doing this is just Search for Neutrino Oscillations (PDG 1996)< ν ν > 2 = U 2 (47) | k| α | kα ( Exclusion plots ( ( %This) mass state then propagates to the detector, and is detected as a neutrino of flavour β with ' ! !" ' ! # (!"!$%& (! $%&probability* < ν ν > 2 = U 2. The flavour change probability is then the incoherent sum ! ) $ " | β| k | | βk| P (ν ν )mixing = < ν ν >e−iφk < ν ν > 2 = U 2 U 2 (48) • Disappearance: reactor experiments. α → β | β| k k| α | | αk| | βk| Nuclear reactors are most intensive More k k statistics ! ! – In the two-flavour approximation, we would have a ν flavour transition probability of sources of νe on Eearth. e (I) With known neutrino flux: measure flux at distance L. excluded Only – flux is measured via νe 16 – + νe + p ' e + n (II) Measure neutrino flux at position 1 and verify flux after distance L. More sensitive to small ∆m2 , as longer L can be used due to high flux Baseline longer • Appearance: (–) Use neutrino beam of type A (νµ) and (–) search at distance L for neutrinos of type B (νe). More! sensitive to small sinθ due to appearance! Neutrino Oscillation • Real three-families case: PMNS matrix (3 mixing angles, 1 CP-violating phase) Majorana neutrino? • 2 mass-squared differences: solar (Δm²₁₂) and atmospheric (Δm²₂₃), with |Δm²₂₃|≫|Δm²₁₂| Atmospheric sector Super-Kamiokande 848 days Preliminary 2 4 2 4 • For atmospheric/accelerator ν, (L~10 -10 km, Eν~10 -10 MeV)" - " 2 ➡ sin (2θ23) > 0.92 (90% CL)" 2 -3 2 ➡ |'m 23| = (2.44±0.06)x10 eV Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #6 Neutrino Oscillation • Real three-families case: PMNS matrix (3 mixing angles, 1 CP-violating phase)" • 2 mass-squared di$erences: solar ('m()*) and atmospheric ('m(*+), with |'m(*+|≫|'m()*| Solar sector 2 • For solar νe and medium-baseline reactor ν̄e (L~10 km, Eν~MeV)" 2 ➡ sin (2θ12) = 0.846 ± 0.021" 2 -5 2 ➡ 'm 12 = (7.53±0.18)x10 eV Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #7 Neutrino Oscillation • Real three-families case: PMNS matrix (3 mixing angles, 1 CP-violating phase) 64 our @CERN result vs the world… DC-IV-PRELIMINARY @ CERN • 2 mass-squared differences: solar (Δm²₁₂) and atmospheric (Δm²₂₃), with |Δm²₂₃|≫|Δm²₁₂ MORIOND superseds CERN 64 our @CERN result vs the world… DC-IV-PRELIMINARY @ CERN CERN superseds MORIOND superseds CERN 13 sector 2 Δ σ (~+45%) θ sin (2θ13)=(0.119±0.016) (DYB:DC) ~2.2 ’s • For short-baseline reactor ν̄e (L~km, Eν~MeV) 2 Δ(DYB:DC) ~2.2σ’s (~+45%) sin (2θ13)=(0.119±0.016) 3 • …and for accelerator νμ (L~10 km, Eν~GeV) NOvA Reactors PDG DC-IV @ CERN ➡ 2 Up to 2010: best limit by CHOOZ (sin (2θ13) < 0.14) NOvA Reactors PDG (Many thanks to NOvA: latest reference) Example:DC-IV NOvA @ CERN Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #8 arXiv:1601.05522 DC & beams might prefer a higher θ13? (accepted by PRL) (Many thanks to NOvA: latest reference) (beam “handicapped” by unknowns(δCP) / uncertainties)Example: NOvA reactor-θ13 key to solve CP-violation & mass hierarchy→ redundancy fundamentalarXiv:1601.05522 DC & beams might prefer a higher θ13? (accepted by PRL) (reactor-(beam “handicapped”θ13 experiments by unknowns( work togetherδCP) / uncertainties) to resolve) Anatael Cabrera (CNRS-IN2P3 & APC) reactor-θ13 key to solve CP-violation & mass hierarchy→ redundancy fundamental (reactor-θ13 experiments work together to resolve) Anatael Cabrera (CNRS-IN2P3 & APC) PMNS and Beyond • Standard 3-families oscillation now well-established - Mixing angles known @ ≲10%, 'm2 @ ~2%: now in the precision era" 2 - Still need to find the sign of Δm 13 (mass hierarchy), δCP, octant of θ23" • Neutrino masses call for physics beyond the Standard Model - Light right-handed neutrinos and Dirac mass terms" - Majorana mass terms, possibly with very heavy neutrinos + see-saw mechanism" • Moreover, some experimental anomalies in the standard neutrino oscillation" - Some quite old (Gallium anomaly, LSND-MiniBooNe results)" - Some more recent (reactor antineutrino anomaly) Neutrino Physics and Oscillation Alessandro Minotti (CEA - IRFU) #9 Outlook • Neutrino physics and oscillation" • Reactor neutrinos and the Reactor Antineutrino Anomaly" • The STEREO experiment: principle, configuration, and timeline of the installation and commissioning phase" • The STEREO experiment: status of the analysis of first collected data Reactor Antineutrino Anomaly Alessandro Minotti (CEA - IRFU) #10 Reactor Antineutrinos 2 -5 2 2 2 20 ∆ m = 8×10 , sin (2θ ) = 0.9, ∆ m = 0.0025, sin (2θ ) = 0.1 • 12 12 13 13 Reactor neutrinos: 2⋅10 /s⋅GW pure ν̄ -" e ν 1 → e ν P 0.8 • Long baseline (~50 km)" 0.6 Far detector - “Measure” the oscillation around the Near detector 0.4 first global minimum to determine θ12 ν̄ ₑ ν̄ ₑ 2 ν̄ ₑ and Δm 12 (KamLAND)" 0.2 0 3 4 5 10 10 10 • Short baseline (~1 km)" L/EL/E (m/eV) (m/MeV) - Compare oscillated and un-oscillated ν̄ - rate/spectrum (disappearance) at first local minimum to measure θ13 (Double Chooz, Daya Bay, RENO)" • Very short baseline (~10 m)? Study sterile neutrinos Reactor Antineutrino Anomaly Alessandro Minotti (CEA - IRFU) #11 Reactor Antineutrino Anomaly • New computation of ν̄ spectrum for Double Chooz RAA 2011: Phys.Rev.D83, 073006 (2011) → 6% excess wrt results from previous reactor experiments • Results confirmed by Double Chooz, RENO, Daya Bay near detectors Daya Bay 2016: Phys.Rev.Lett.116, 061801 (2016)" Global fit 3+1 arXiv:1703.00860 • Possible explanations" - Problems in the anti-neutrino spectrum prediction" - Oscillation with a sterile neutrino in the eV Δm² scale Reactor Antineutrino Anomaly Alessandro Minotti (CEA - IRFU) #12 Chinese Physics C Vol.