Probing Neutrino Masses and Mixings with Probing Neutrino Masses and - PowerPoint PPT Presentation

1 Probing Neutrino Masses and Mixings with Probing Neutrino Masses and Mixings with Accelerator and Reactor Neutrinos Accelerator and Reactor Neutrinos Mike Shaevitz Shaevitz - Columbia University - Columbia University Mike Particles and Nuclei International Conference Particles and Nuclei International Conference (PANIC11) July, 2011 (PANIC11) July, 2011

2 Outline • Introduction to Neutrino Mass and Mixing • Neutrino Oscillations among ν e , ν µ , and ν τ – The “Hunt” for the Little Mixing Angle θ 13 • New T2K and MINOS results – Plans and Prospects for Measuring CP Violation • Possible Oscillations to Sterile Neutrinos – Current Hints and Anomalies • Updated MiniBooNE ν e appearance results – Ideas for Future Searches • Final Comments

3 Absolute Mass Scale Determinations Current limit (Mainz): m ν < 2.2 eV @ 95% CL KATRIN Sensitivity: m ν < 0.2 eV @ 90% CL See J. Formaggio talk on Thurs. If detect 0 ν 2 β decay ⇒ Neutrinos are Majoranna particles and information on m ν at 0.1eV scale Limits sum of neutrino masses: Σ m ν < ~0.7 eV

Neutrino Oscillations 4 The observation of neutrino oscillations where one type of neutrino can change (oscillate) into another type implies: 1. Neutrinos have mass and 2. Lepton number (electron, muon, tau) is not conserved ( ν e →ν µ , ν µ →ν τ , ν e →ν τ ) • The phenomena comes about because the mass and flavor states are different as parameterized by a mixing matrix More details on osc theory ( ) ( ) = sin 2 2 # sin 2 1.27 $ m 2 L / E Osc ! a " ! b see Boris Kayser talk yesterday P and J. Diaz on Thurs.. where # = mixing angle; $ m 2 = m b 2 % m a 2 ; L = travel distance; E = neutrino energy • Two types of oscillation searches: – Appearance Experiment: Look for appearance of ν e or ν τ in a pure ν µ beam vs. L and E – Disappearance Experiment: Look for a change in ν e/ µ flux as a function of L and E

5 Oscillations Parameterized by 3x3 Unitary Mixing Matrix solar atmospheric ! ! " = # " $ " = # 2 5 2 2 2 3 2 m 8 10 eV , m m 2.5 10 eV Current Measurements: 12 13 23 $ % " " " # ! " i $ cos sin 0 % cos 0 e sin $ 1 0 0 % CP 12 12 13 13 & ' & ' & ' = # " " ( ( " " U sin cos 0 0 1 0 0 cos sin & ' & ' & ' 12 12 23 23 & ' & ' & ' ! # " " # " " i 0 0 1 e sin 0 cos 0 sin cos ) * ) * CP ) * 13 13 23 23 “Little mixing angle, θ 13 ” 3-mixing Solar: θ 12 ~ 33° Atmospheric: θ 23 ~ 45° sin 2 2 θ 13 < 0.14 at 90% CL angles (or θ 13 < 11°) and δ = ??

6 Oscillation Summary Before PANIC11 New MiniBooNE ν µ consistent OPERA : ν µ →ν →ν τ ⇒ Confirmed by K2K and & ICARUS Minos accelerator neutrino exps ν e →ν →ν µ / ν τ ⇒ Confirmed by Kamland reactor neutrino exp

7 Big Questions in (3x3) Neutrino Mixing 1. What is ν e component in the ν 3 mass eigenstate? θ 13 ⇒ The size of the “little mixing angle”, θ 13 ? Only know θ 13 <11 0 – 8 2. What is the mass hierarchy? − Is the solar pair the least massive or not? 8 3. Do neutrinos exhibit CP violation, i.e. is δ≠ 0? Normal Hierarchy Inverted Hierarchy

8 The Search for the “Little Mixing Angle” ( θ 13 )

9 Experimental Limits before PANIC11 on θ 13 • Chooz Reactor Experiment – sin 2 2 θ < 0.14 90% CL • MINOS previous longbaseline appearance limits • Solar neutrino agreement including KAMLAND Global Fits: sin 2 2 ! 13 < 0.12@95% CL

10 Experimental Methods to Measure the “Little Mixing Angle”, θ 13 13 • Long-Baseline Accelerators: Appearance ( ν µ →ν e ) at Δ m 2 ≈ 2.5 × 10 -3 eV 2 – Look for appearance of ν e in a pure ν µ beam vs. L and E • Use near detector to measure background ν e 's (beam and misid) MINOS: <E ν > = 3.0 GeV T2K: L = 735 km <E ν > = 0.7 GeV NO ν A: L = 295 km <E ν > = 2.3 GeV L = 810 km ( See J. Nowak NOvA talk on Tuesday afternoon ) • Reactors: Disappearance ( ν e →ν e ) at Δ m 2 ≈ 2.5 × 10 -3 eV 2 – Look for a change in ν e flux as a function of L and E • Look for a non- 1/r 2 behavior of the ν e rate • Use near detector to measure the un-oscillated flux Double Chooz, RENO, Daya Bay: <E ν > = 3.5 MeV L = ~1100 m

11 Long-Baseline Accelerator Appearance Experiments Oscillation probability complicated and dependent not only on θ 13 but also: • 1. CP violation parameter ( δ ) 2. Mass hierarchy (sign of Δ m 31 2 ) “Matter Effects” 3. Size of sin 2 θ 23 ⇒ These extra dependencies are both a “curse” and a “blessing” Reactor Disappearance Experiments • Reactor disappearance measurements provide a straight forward method to measure θ 13 with no dependence on matter effects and CP violation

12 Long-baseline ν e Appearance Program

Big News: T2K Sees Indication of 13 ν µ →ν e Oscillations! See K. Okumura talk yesterday for more details Far Detector Near Detector Delivered ¡protons ¡for ¡analysis ¡ RUN1 ¡(Jan. ¡2010 ¡~ ¡Jun. ¡2010) ¡ ¡ ¡3.23 ¡x ¡10 19 ¡p.o.t. ¡achieved ¡ave. ¡50 ¡kW ¡running RUN2 ¡(Nov. ¡2010 ¡~ ¡Mar. ¡2011) ¡ ¡11.09 ¡x ¡10 19 ¡p.o.t. ¡achieved ¡ave. ¡145 ¡kW ¡running ¡ ¡ ¡ ¡ ¡ à ¡ ¡ ¡ RUN1+RUN2total ¡ ¡ ¡ ¡1.43 ¡x ¡10 20 ¡p.o.t. ¡ ¡ ¡ (2% ¡of ¡final ¡goal) Select signal events and compare to 1.5 ± 0.3 event expected background BG ¡(NC ¡ π 0 ¡ ) ¡-­‑ ¡0.6 ¡events Signal ¡( ν e ¡ ¡CCQE) (Also intrinsic ν e in beam - 0.8 events)

14 Observe Six Events with 1.5 ± 0.3 Background Reconst. ¡ ν ¡energy 6 ¡candidate ¡events ¡observed Invariant ¡mass ¡ a?er ¡all ¡cuts Null ¡hypothesis ¡( θ 13 =0): ¡1.5 ¡±0.3 ¡(syst.) Null ¡Prob. ¡= ¡0.7% ¡corresponding ¡to ¡2.5 σ ν ¡beam Beam ¡coordinate out ¡of ¡FV in ¡bo[om

New T2K Results for sin 2 2 θ 13 15 From ¡6 ¡events ¡versus ¡1.5 ± 0.3 ¡backgnd ¡(2.5 σ ) 90% ¡C.L. ¡allowed ¡regions ¡ ¡and ¡best ¡fit (for Δ m 223 =2.4 x 10 -3 eV 2 , δ CP =0) 0.03 < sin 2 2 θ 13 < 0.28 sin 2 2 θ 13 =0.11 (normal hierarchy) 0.04 < sin 2 2 θ 13 < 0.34 sin 2 2 θ 13 =0.14 (inverted hierarchy) March 11 Earthquake caused damage to J-PARC but not too extensive (See K.Tanaka plenary talk) Plan to resume J-PARC operation in Dec. 2011 and restart T2K data taking as soon as possible Published ¡in ¡Phys. ¡Rev. ¡Le[. ¡107, ¡041801 ¡(2011) after that. Could triple data set by Summer 2012 15

16 New MINOS ν µ →ν e Oscillation Search and Results for sin 2 2 θ 13 See L. Whitehead talk on Thurs. for more details • New selection criteria for ν e candidates – MINOS not optimized for isolating ν e – Developed new type of “library event matching” technique • Use nearly identical Near detector to make background prediction in Far detector. – Using Near detector is essential for the search • Look for an excess of Far detector events over background – Use MC to predict Far/Near ratio Best Fit: sin 2 2 ! 13 = 0.04(0.08) for normal (inverted) hierarchy Null (sin 2 2 ! 13 = 0.0) hypothesis excluded at 89% CL

17 Comparisons of T2K and MINOS sin 2 2 θ 13 Results Expected signal from T2K Best Fit value • Good compatibility between two results: – MINOS consistent with T2K best fit value – MINOS upper limit cuts into T2K larger allowed values ⇒ Need combined fit to establish the best sin 2 2 θ 13 range

18 Global Fits with New T2K and MINOS Results “Evidence of θ 13 > 0 from global neutrino data analysis”, Fogli et al. (arXiv:1106.6028v1 [hep-ph])) Greater than 3 ! evidence for " 13 > 0 # 0.084 ± 0.028 , old reactor fluxes % sin 2 2 " 13 = (1 ! ) $ 0.100 ± 0.028 , new reactor fluxes % &

19 Reactor Neutrino Experiments

Reactor Measurements of θ 13 20 • Nuclear reactors are very intense sources of  ν e with a well understood spectrum – 3 GW → 6 × 10 20 ν e /s 700 events / yr / ton at 1500 m away – Reactor spectrum peaks at ~3.7 MeV – Oscillation Max. for Δ m 2 =2.5 × 10 -3 eV 2 at L near 1500 m 35 " m 2 = 2.5 # 10 -3 eV 2 Full Mixing 30 25 Disappearance Measurement: Observed Events Look for small rate deviation from 1/r 2 No Osc. 20 measured at near and far baselines 15 10 1500 m 5 0 1.50 2.50 3.50 4.50 5.50 6.50 7.50 8.50 E ! (MeV)

21 How to do better than previous CHOOZ reactor experiment? ⇒ Better detectors with reduced systematic uncertainties Gd ⇒ Use larger detectors ⇒ Reduce and control backgrounds ⇒ Use Near/Far Detectors ν e ν e ν e ν e oil - buffer γ - catcher ν e ν - target ν ~ 8 m ν e with Gd sin 2 2 2 Unoscillated Unoscillated sin 2 θ θ 13 13 flux flux ~7 m

Double Chooz Reactor Experiment 22 in Ardennes, France See M. Kuse Talk yesterday for details

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