Neutrino-Nucleus Scattering at MINERvA

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1 1 Neutrino-Nucleus Scattering at MINERvA Elba XIII Workshop: Neutrino Physics IV Tammy Walton Fermilab June 26, 2014

2 2 MINERvA Motivation Big Picture Enter an era of precision neutrino oscillation measurements. Determine if CP-invariance is violated in the lepton sector (δ CP 0, π, 2π, ). What is the neutrino mass hierarchy? Are there more than three generations of neutrinos, sterile neutrino?

3 3 MINERvA Motivation The energy of the neutrino beam is unknown. Must reconstruct the neutrino energy. Make various assumptions about the neutrino interaction. Projected Sys & Stats Errors LBNF Neutrino detectors are composed of nuclei with A > 2. Understanding neutrino-nucleus interactions is critical for precision neutrino oscillation measurements. LBNE CDR, arxiv: NOvA Projected Sys & Stats Errors J. Thomas, European ICFA Panel 2014

4 4 MINERvA Motivation J.A. Formaggio and G.P. Zeller, Rev. Mod. Phys. 84 (2012) T2K LBNE NoVA LBNF

5 5 MINERvA Motivation Models that are currently implemented in neutrino event generators do not describe the data for neutrino-nucleus measurements. Slide courtesy of P. Rodrigues (NeutrinoInt2014)

6 6 How well do oscillation measurements need to understand the neutrino energy? Martini et al. arxiv: Solid lines: multi-nucleon contributions Dashed lines: genuine QE Non quasi-elastic interactions can resemble QE like topology, if there are no pions observed in the FS. The uncertainties on the various components of the inelastic crosssection are large. QE event selection usually consists of significant fraction of resonant production where the pion has been absorbed in the nucleus. These inelastic events also contribute to the incorrect reconstruction of the neutrino energy. Simulated LBNE ν μ disappearance Use an on-shell equation assuming QE scattering to calculate off-shell processes (two-body meson exchange currents). The low-side tail of the reconstructed neutrino energy is dramatically smeared due to the multi-nucleon contributions. J. Sobczyk arxiv: , Lalakulich et al. arxiv: , Nieves et al. arxiv:1204:5404 Mosel et al: arxiv Solid: true E ν Dashed: rec. E ν No pion events At 3 GeV: ~50% QE ~20% Δ excitation ~30% DIS and 2p-2h

7 7 Main INjector ExpeRiment n-a Dedicated neutrino-nucleus cross section experiment. Produce measurements in the neutrino energy range that is essential for neutrino oscillation experiments. High precision data will be use to constrain the models in neutrino event generators.

8 8 Neutrinos at the Main Injector Beam Line Fermi National Laboratory Main Injector Apparatus Ring to MINERvA NuMI Hall 120 GeV proton beam graphite target (Carbon) produces hadrons, primary pions and kaons Magnetic horn focus the positive or negative charged pions and kaons down the beam line. Delivers a 120 GeV/c proton beam with ~ protons on targets (POT) per beam spill at ~0.5 Hz. Pions and kaons decay into muon and neutrinos. Any remaining hadrons are absorbed. The event rate of the muons from the meson decay are measured. The remaining muons stop in the rock downstream of the muon monitors.

9 9 The MINERvA Detector Composed of 120 modules stacked along the beam direction. Fine-grained scintillator core surround by electromagnetic and hadronic calorimeters. MINOS near detector serves as the muon spectrometer. 3 orientations 0, +60, 60 Nucl.Instrum.Meth. A694 (2012)

10 10 Recent and Current Cross section Results from MINERvA

11 Strip Number Events ν beam Quasi-elastic Scattering μ enters MINOS Neutrino event generators use the conventional relativistic Fermi gas for modeling QE scattering on nuclei. -q Utilized as a vertex blackout region GeV 2 c 2 4-momentum transfer: q = Q 2 -q Nucl.Inst.Meth. 676 (2012) Q 2 ( GeV 2 c 2 ) The initial-state nucleon momentum distribution does account for nucleon-nucleon short range correlations via the Bodek-Ritchie model. Module Number

12 Phys. Rev. Lett. 111, (2013) Phys. Rev. Lett. 111, (2013) 12 Reconstruct only the muon track. Use the lepton kinematics to characterize the nuclear effects. Shape Measurements Results: Quasi-elastic Scattering Courtesy of J. Sobczyk ν μ ν μ Analyses are relatively insensitive to the nucleon transportation through the nucleus. However, the uncertainty on the hadron propagation through the nucleus enters through background subtraction. Best interpretation of the data is given by a data-driven two-body meson exchange current model.

13 13 The Nuclear Environment Makes Detecting the Correct Neutrino Process Not so Easy Final state interactions (FSI) alter the kinematic distributions of the recoil nucleon. Final state interactions: the recoil hadrons interaction with spectator nucleons in the nucleus. FSIs can lead to many nucleons in the final state. Looks like a 2particle 2hole excitation. Non-QE neutrino scattering processes can look like a QE process QE-like.

14 14 Results: Quasi-elastic Scattering Reconstruct both the muon and proton tracks. Use the proton kinematics to characterize both nuclear effects and final state interactions. Side of the Detector p Analysis does NOT use any kinematic variables to isolate the signal! Side of the Detector μ 2 Q QE,p = M 2 M 2 p + 2M T p + M p M Event selection includes both the quasi-elastic and inelastic ( no pions in the final state) components. Data is best interpreted by the Fermi gas model convoluted with FSI effects that modeled using a particle cascade algorithm.

15 15 Resonant Pion Production Courtesy of P. Rodrigues theoretical predictions event-generator predictions Recent data (E ν ~ 1 GeV) show discrepancies between models. Possible due to the modeling of FSIs? MiniBooNE, Ref Phys.Rev.D83:052007,2011

16 16 Result: Resonant Pion Production The shape comparison shows that the data and event-generator models that include effects of FSI have relatively good agreement. μ π p

17 17 Coherent Pion Scattering t = (q p π ) 2 Previous experiments show no evidence of Coherent pion production for E ν ~ 1 GeV.

18 18 Coherent Pion Scattering Utilized to a cut on the energy around the vertex. μ π ν μ MINERvA sees Coherent pion scattering for both neutrinos and anti-neutrinos for E ν ~ 3.5 GeV. ν μ

19 19 Results : Coherent Pion Production Analyses cut on t to isolate the signal events. ν μ ν μ The predominate background is from the resonant pion production. ν μ ν μ A detail study was performed on the kinematic variable, t for the backgrounds. Measurements show evidence that Rein-Seghal model of coherent scattering does not describe the data.

20 20 Inclusive Ratios on Carbon, Iron, and Lead Courtesy of B. Tice Charged-current neutrino interactions on pure nuclear targets. Study the A-dependence of nuclear effects.

21 21 Results: Inclusive Target Ratios Heavier Nucleus Data agrees with the reference eventgenerator modeling of neutrino interactions for the neutrino energy, E ν. E ν = E μ + E H Muon energy Energy of the hadronic system Systematic uncertainty on the neutrino flux cancels for the ratio

22 Phys. Rev. Lett. 112, (2014) 22 Results: Inclusive Target Ratios Heavier Nucleus Ratio measurements presented as function of the dimensional kinematic variable, Bjorken x. x B = Muon scattering angle Q 2 2M N E H, Q 2 = 4E ν E μ sin 2 θ μ 2 The discrepancy between data and simulation grows dramatically with A in the elastic region. Relative depletion in the cross-section at low x.

23 23 Future Measurements from MINERvA Kaon Production CC Neutral Pion Production Electron Neutrino QE Scattering MINERvA is currently extending the Quasi-elastic program. Updated results on ν μ and ν μ QE measurements compare to more microscopic models. Double differential cross-sections as function of the muon energy and scattering angle. QE on Lead and Iron.

24 24 Summary MINERvA is producing many exciting neutrino cross section measurements!

25 25 Back-up Slides