Precision Measurement of Muon Neutrino Disappearance with T2K Alex Himmel Duke University for the The T2K Collaboration 37 th International Conference on High Energy Physics Valencia, Spain July 3 rd, 2014

New: Study effects of multi- nucleon interactions Neutrino Physics at T2K Alex Himmel2 Neutrino Interactions Next Talk See Posters from E. Scantamburlo and L. Haegel Talk from A. Hillairet on Saturday

The T2K Experiment Alex Himmel3 J-PARC ND280, INGRID Super-K ν N 295 km

J-PARC Neutrino Beam 2.5° off-axis angle – Peak at oscillation minimum – Fewer backgrounds from high energy – Monitored by the INGRID on-axis detector Alex Himmel4 p π+π+ µ+µ+ νµνµ Graphite Target 3 Focusing Horns Decay Volume Beam Dump Muon Monitors to SK 2.5° off-axis On-axis 2°

Accumulated POT Alex Himmel5 Runs ×10 20 POT Run 5: Includes 0.5×10 20 POT ν-mode beam (8% of our goal)

Analysis Step 1: Flux simulation in Fluka and Geant Constrain with NA61 hadron production data 10-15% flux uncertainty at SK Alex Himmel6 Flux and cross section models, constrained by external data E ν (GeV) σ/E ( cm 2 /GeV) T2K Peak E NEUT simulation with nuclear effects Constrain effective parameters to external data (mostly MiniBooNE) ~15% uncertainty in CCQE rate

Analysis Step 2: Alex Himmel7 Fit ND280 data to constrain flux and cross section parameters Multi-function detector – Trackers, TPCs, EM calorimeters, µ detector and π 0 detector – Magnetized with UA1 magnet – 280 m from target, 2.5° off-axis Posters from E. Scantamburlo and L. Haegel

Analysis Step 2: Alex Himmel8 Fit ND280 data to constrain flux and cross section parameters CC 0π64% QE CC 1π + 40% Resonance CC other68% DIS – Fit for p and θ in CCν µ samples – Use exclusive subsamples to isolate cross section components MC Pre-fit MC post-fit Data ND280 CC 0π A. Hillairet’s talk on Saturday

Alex Himmel9 Flux Error Before Fit Flux Error After Fit Xsec Error Before Fit Xsec Error After Fit Flux and cross section errors at SK reduced from > 20% to 2.7% Total Error on SK expectation: 8.1%* Analysis Step 2: Fit ND280 data to constrain flux and cross section parameters *Now reduced to 7.6% in joint analyses

Analysis Step 3: Alex Himmel10 Select ν μ CCQE events at Super-K Use ring shape to separate µ and e Select for CCQE final states – 1 ring – ≤ 1 decay electron Use p µ and θ beam to reconstruct E ν Water Cherenkov Detector 50 ktonnes of ultrapure water 40% photocoverage

Alex Himmel11 Analysis Step 3: Select ν μ CCQE events at SuperK 120 Events 98.5% CC ν μ Data 81.0%ν μ CCQE 17.5% ν μ CC non-QE 1.5%NC

Alex Himmel12 Fit for oscillations Extract θ 23, Δm 2 32 Analysis Step 4: Normal HierarchyInverted Hierarchy Maximal Disappearance Data (120 events) – No oscillations (446 events) – Best oscillation fit Data/No osc. – Best fit/No osc.

Alex Himmel Best fit at maximal disappearance – Result narrower than sensitivity by 0.04 in sin 2 (θ 23 ) Most precise measurement of sin 2 (θ 23 )! Normal Hierarchy T2K68% dashed, 90% solid SK90% MINOS90% 13 Analysis Step 4: Fit for oscillations Extract θ 23, Δm 2 32

Alex Himmel14 Multinucleon Interactions Neutrinos may interact with multiple nucleons – Looks CCQE, but has different kinematics – Potential explanation for discrepancies in M A measurements Studied potential for bias in our result from neglecting multinucleon interactions νμνμ μ-μ- p p

Alex Himmel15 Multinucleon Interactions For the current analysis, the effect is small relative to our total error – Mean biases were small (<1%) – However, there is the potential for biases in sin 2 θ 23 similar in size to our current systematic error Future analyses will include multinucleon interactions in the default cross-section model with systematic uncertainties Bias in sin 2 θ 23 from fake experiments Bias in Δm 2 32 from fake experiments Mean bias: -0.2% RMS bias:0.6% Mean bias: 0.3% RMS bias:3.6%

Conclusions Alex Himmel Analyzed 6.57×10 20 POT of neutrino data – Accumulated our first 0.5×10 20 POT of antineutrino data Made the most precise measurement of sin 2 θ 23 and favor maximal disappearance Only 8% of our goal POT accumulated so far 16 Dashed:current systematics Solid: no systematics

Backup Slides Alex Himmel17

Alex Himmel18 Error on # of ν µ Events ND280-constrained Φ & σ2.7% Unconstrained cross section 4.9% SK efficiency & hadronic interactions in water 5.6% Other oscillation parameters 0.2% Total8.1% Flux Error Before Fit Flux Error After Fit Xsec Error After Fit Xsec Error Before Fit Flux and cross section would be > 20% without ND280 constraint Analysis Step 2: Fit ND280 data to constrain flux and cross section parameters

Analysis Structure Alex Himmel19 Flux Simulation Cross section model External σ data Hadron prod. from NA61 Initial Φ estimate, and errors Initial σ estimate, and errors Fit to ND280 data Post-fit Φ, σ estimate, errors Fit to SK data

Sensitivity vs. Data Fit Alex Himmel20

Multinucleon Interactions Long-standing tension over M A in CCQE interactions – “Natural” value of 1.0 GeV from e-scattering – >1.2 GeV in ν scattering New models involving 2p-2h/np-nh interactions have been proposed to reconcile the tension Several papers have investigated the possible effect on T2K or a T2K-like experiment Alex Himmel21 O. Lalakulich and U. Mosel, Phys. Rev. C 86, (2012). D. Meloni and M. Martini, Phys. Lett. B 716, 186 (2012). P. Coloma, et al, arXiv: (2013).

Multinucleon Study in T2K Multi-nucleon interactions: – increase the CCQE-like cross-section and – introduce energy reconstruction biases (no longer 2 body QE kinematics) MC study to investigate this possible bias directly – ν µ disappearance – more sensitive to the spectral shape – We introduce a 2p-2h model into both ND280 and SK fake data – Replace π-less Δ decay already in NEUT Alex Himmel22 J. Nieves et. al., PRC83, (2011) for lepton kinematics J. Sobczyk, PRC86, (2012) for nucleon ejection (ND280-only)

Biases in Oscillation Fits Alex Himmel23 Nieves Nominal BiasRMSData Fit Errors Δm 2 32 (10 -3 eV 2 ) (-0.2%)0.014(0.6%)±0.10 sin 2 θ (0.3%)0.016(3.6%)±0.055