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Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA

Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA. Jaewon Park University of Rochester On behalf of MINERvA Collaboration December 20, 2013 Fermilab Joint Experimental-Theoretical Seminar. Outline. Neutrino experiments and their fluxes

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Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA

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  1. Direct Measurement of the NuMI Flux with Neutrino-Electron Scattering in MINERvA Jaewon Park University of Rochester On behalf of MINERvA Collaboration December 20, 2013 Fermilab Joint Experimental-Theoretical Seminar

  2. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  3. Oscillation Experiment Strategy N: events in data B: Background e: Efficiency A: Acceptance s: Cross section or ? Near Detector (ND) • In fact the flux doesn’t just decrease like 1/L2 • Oscillations • Near detector sees line source, far detector sees point source • Far detector sample is always very different from near detector sample Far Detector (FD) Isn’t this just 1/L2? Jaewon Park, U. of Rochester FNAL JETP

  4. Needs of Precision Oscillation Experiments • Precise measurement of oscillation parameters is the key to answer important questions like neutrino mass hierarchy and CP violation • To achieve the highest precision, we need: • (High intensity beam) × (big detector) × (long operation) • Low uncertainties on flux prediction • Better understanding of neutrino interactions • More accurate cross-section (May 10 JETP by MINERvA) • Understanding nuclear effects (October 11 JETP by MINERvA) • Detailed understanding of background interactions • This talk is about a method to constrain or measure the neutrino flux using neutrino-electron scattering • This helps to reduce flux normalization uncertainties on MINERvA’s absolute cross-section measurements • This technique can be used in future high intensity beam experiments to measure the flux Jaewon Park, U. of Rochester FNAL JETP

  5. Neutrinos from an Accelerator Decay pipe Rock Near Detector Far Detector Horn 2 Target Horn 1 proton • Neutrino beam is generated from a decay of secondary or tertiary particles  Hard to control beam itself, too hot to measure in situ • Flux has large uncertainties due to poor knowledge of hadron production • Non-perturbative QCD governs it  Difficult to calculate from basic principles • ~15-30% normalization uncertainties on flux Jaewon Park, U. of Rochester FNAL JETP

  6. Neutrinos from an Accelerator Decay pipe Rock Near Detector Far Detector Horn 2 Target Horn 1 proton • Kaon and muon decays are main source of electron neutrinos Jaewon Park, U. of Rochester FNAL JETP

  7. decay pipe n ν π p target Constraining flux with Hadron Production Data • Hadron production primarily function of xF=pion/proton momentum ratio and ptransverse • Use NA49 measurements • Scale to 120 GeV using FLUKA (simulation) • Check by comparing to NA61 data at 31 GeV/c [Phys.Rev. C84 (2011)034604] • Use MIPP (120GeV protons) for K/π ratio Jaewon Park, U. of Rochester FNAL JETP

  8. NA49: pC → π,K,p @ 158 GeV f(xF,pT) = E d3σ/dp3 = invariant production cross-section π+ which makea νμ in MINERvA NA49 data vs. GEANT4 focusing peak high energy tail Uncertainties 7.5% systematic 2-10% statistical Jaewon Park, U. of Rochester FNAL JETP

  9. Need more than Hadron Production Measurements • Hadron Production measurements don’t tell the whole story, only 70% • Some pion production is out of range of Hadron Production data • Tertiary production of neutrinos also important (n, h, KL,S) • Beamline geometry and focusing elements contribute uncertainties Jaewon Park, U. of Rochester FNAL JETP

  10. Special Runs to Understand Flux Normal Running Pt (GeV/c) xF Neutrinos at MINERvA Target Moved upstream Pt (GeV/c) Inclusive Event Spectra xF • MINERvA integrated 10% of our total neutrino beam exposure in alternate focusing geometries: • Changed horn current • Changed Target Position • Purpose is to disentangle focusing uncertainties from hadron production uncertainties • Different geometry focuses different parts of xFpT space, but same horn geometry and current • MINERvA does this by using low hadron energy nm charged current events, where energy dependence of cross section is very well understood Jaewon Park, U. of Rochester FNAL JETP Pion Phase Space

  11. Neutrino Flux and Cross-section Measurement Flux and cross-section are anti-correlated with given Near Detector constraint MINERvA Flux uncertainty goes into cross-section uncertainty Measurement uncertainty Φ (Flux) Flux constraint using Near Detector Cross-section uncertainty goes into flux uncertainty σ (Cross Section) N: Events e: Efficiency A: Acceptance s: signal cross section 20 December 2013 Jaewon Park, U. of Rochester FNAL JETP

  12. Known Interaction (Standard Candle) • ν-e scattering is well known interaction we can use to constrain the neutrino flux Φ (Flux) Flux constraint using ND Cross-section uncertainty goes into flux uncertainty σ (Cross Section) ν-e Scattering Jaewon Park, U. of Rochester FNAL JETP

  13. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal • Event reconstruction • Event selection • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  14. ν-e Scattering History First unambiguous neutral current (Gargamelle) Electroweak theory Solar ν oscillation measurement using ν-e scattering (SNO) Additional interaction for All flavor Matter effect is due to charged current νe scattering on electrons, only for νe Coherent forward scatterings Jaewon Park, U. of Rochester FNAL JETP

  15. Neutrino Scattering on Nucleon Electron Very forward single electron final state • Let’s use well-known reaction to measure the flux • Standard electroweak theory predicts it precisely • Point-like scattering • Very small cross section (~1/2000 of ν-nucleon scattering) • Low center of mass energy due to light electron • Very forward electron final state (Experimental signature) • Good angular resolution is important to isolate the signal νe→ νe candidate event Jaewon Park, U. of Rochester FNAL JETP

  16. ν-e Scattering GF and θW: well-known electroweak parameters • E > 0.8 GeV • High background rate and tough reconstruction at low energy • Predict 147 signal events for 3.43×1020 Protons On Target (POT) • ~100 events when you fold in (reconstruction + selection) efficiency of ~ 70% • Not a large sample in low energy run but still useful to constrain absolute flux ne Scattering Events ne Scattering Events FLUX Jaewon Park, U. of Rochester FNAL JETP

  17. Signal Events E<0.8 GeV is not used • Large background • Tough reconstruction E>0.8 GeV • Signal is mixture of in LE-FHC (neutrino beam) • ~100 signal events for 3.43E20 POT • Can’t distinguish neutrino type • Still useful to constrain the flux • Total events: Constraint for integrated flux • Electron spectrum: Constraint for flux shape For remainder of talk, means and Jaewon Park, U. of Rochester FNAL JETP

  18. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  19. Thank you! for the excellent ν beam Data and Simulation Samples MINERvA ran in three kinds of beam: Low Energy neutrino Low energy anti-neutrino “Special Runs”: higher energy runs to constrain flux model • All Low Energy neutrino data is used for the analysis: more than previous analyses shown to date (3.43 × 1020 Protons on Target) • Time-dependent effects (calibrations, accidental activity) included in the simulation Jaewon Park, U. of Rochester FNAL JETP

  20. Outer Detector (steel + scintillator) 4m 5m 3.5m Hadronic Calorimetry Electromagnetic Calorimetry Nuclear Targets (C, Pb, Fe, H2O) Tracker (Active target) MINERvA Detector Inner Detector Jaewon Park, U. of Rochester FNAL JETP

  21. Inside the Detector MINOS Near Detector (muon spectrometer) Scintillator plane (X, U, V stereo angle) Hcal Ecal Tracker Nuclear Target −60° +60° Number of channels: ~31k Number of scintillator plane: 128 u x Pb Fe v x Tracking Ecal (lead absorber + tracking plane) Tracking Hcal (steel absorber + tracking plane)

  22. 127 strips into a plane 17 mm 2.1m 16 mm Position resolution: ~3mm 2.5 m Detector Technology 64 channel multi-anode PMT 8×8 pixels Scintillator strip Wavelength shifting fiber • Extruded plastic scintillator with wavelength shifting fiber readout • 64 channel multi-anode PMT for photo-sensor Jaewon Park, U. of Rochester FNAL JETP

  23. Fiducial volume ν + e- → ν + e- candidate event X-View U-View V-View Data run: 2157/12/1270/2 Jaewon Park, U. of Rochester FNAL JETP

  24. Single Electron Reconstruction Nuclear Target Region (He,C/H2O/Pb/Fe) HCAL ECAL Shower-like Track-like Track-like part (beginning of electron shower) gives good direction Jaewon Park, U. of Rochester FNAL JETP

  25. Single Electron Reconstruction Nuclear Target Region (He,C/H2O/Pb/Fe) HCAL ECAL Shower cone Track-like part (beginning of electron shower) gives good direction Jaewon Park, U. of Rochester FNAL JETP

  26. Critical Variables for Signal • Electron Identification • Must discriminate from photons • Electron Energy Measurement • Electron Angular Measurement Jaewon Park, U. of Rochester FNAL JETP

  27. Electron Photon Discrimination using dE/dx Electron-induced electromagnetic shower Photon -induced electromagnetic shower MINERvA Preliminary • Electromagnetic shower process is stochastic • Electron and photon showers look very similar • Photon shower has twice energy loss per length (dE/dx) at the beginning of shower than electron shower • Photon shower starts with electron and positron Jaewon Park, U. of Rochester FNAL JETP

  28. Energy and Angle Reconstruction Using simulated signal Using simulated signal MINERvA Preliminary MINERvA Preliminary • Energy resolution ~ 5% • Projected angle resolution ~ 0.3 degree (2 sigma truncated RMS) • Precise angle reconstruction is critical to separate νe elastic scattering from background • Lower energy angular resolution is worse due to multiple scattering Jaewon Park, U. of Rochester FNAL JETP

  29. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal and backgrounds • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  30. Initial Background Rejection Rare but hard to reject: • n-e scattering is very rare, even for n interactions: • Simple cuts can eliminate most background events while keeping high fraction of signal events • Obvious muon-like event rejection • Upstream energy rejection • Removes neutrino interactions upstream of detector that make m Most Events (nm Charged or neutral Current) Coherent p0 ne Quasi-elastic (CCQE) Jaewon Park, U. of Rochester FNAL JETP

  31. 8 6 4 2 0 x z Background Events MeV proton MC Electron neutrino fraction in flux is small ~ 1%. electron • If recoil nucleon is not observed, it looks similar to signal • Angles of electron have wide spread while signal is very forward Use Eθ2to select very forward signal Neutral current single π0 Also, photon has wide spread of angle In addition, use dE/dx to reject NC-coherent π0 2. One of gammas is not observed in the detector NC-resonant π0 1. Small opening angle between two gammas γ (67 MeV ) π0 (7.5 GeV) π0 (1.1 GeV) Simulated event Simulated event Jaewon Park, U. of Rochester FNAL JETP

  32. Example: Neighborhood Energy MINERvA Preliminary • Neighborhood energy = energy around shower cone • Small neighborhood energy means isolated shower Not Full Sample Signal × 200 MINERvA Preliminary 5 cm Shower cone Neighborhood Jaewon Park, U. of Rochester FNAL JETP

  33. Event Selection Other reconstruction quality cuts • Electron Energy>0.8GeV • Fiducial cut Shower cone Reconstruction • Eθ2 • dE/dx Signal sample Kinematic constraint on ne scattering, using Mandelstam variables: in CM frame in lab frame Jaewon Park, U. of Rochester FNAL JETP

  34. dE/dx<4.5MeV/1.7cm dE/dx Cut MINERvA Preliminary • All cuts made on this sample except for the dE/dx cut • Neutrino interaction doesn’t always produce only single electron or single photon (from π0) • Non-single particle activity affects dE/dx MINERvA Preliminary tuned tuned Jaewon Park, U. of Rochester FNAL JETP

  35. Eθ2 Cut • All cuts but Eq2 cut • Kinematic limit for signal • Eθ2 < 2me • Clean separation of signal tuned tuned MINERvA Preliminary MINERvA Preliminary Jaewon Park, U. of Rochester FNAL JETP

  36. Electron Spectrum after all cuts tuned MINERvA Preliminary MINERvA Preliminary True electron energy (signal only) Reconstructed electron energy Jaewon Park, U. of Rochester FNAL JETP

  37. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal and backgrounds • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  38. Backgrounds after all Cuts MINERvA Preliminary MINERvA Preliminary Signal Need to know energy spectrum of background Sideband • Background prediction is affected by the flux and physics model • Cross-section of various neutrino reactions are uncertain • That’s what MINERvA is trying to measure • Data-driven background prediction tuning is used to handle the uncertainty of predicted background Jaewon Park, U. of Rochester FNAL JETP

  39. 4 Background Processes, 4 Sidebands Eθ2(GeV∙rad 2) • No side-exiting muon • Narrow shower at beginning • Eθ2<0.1 Sideband 4 (Coherent π0 rich region) (a) Sideband Energy 0.005 Sideband 1, 2, 3 (not sideband 4) 0.0032 (b) Unused Sideband 3 signal Sideband 1 1.2 4.5 20 Sideband 2 0.8 dE/dx (MeV/1.7cm) 3 Min dE/dx • Sideband = Outside of major Eθ2 and dE/dx cuts • (b) region is not used because there are not many events for tuning • Further, cut is slightly loosened on sideband so it gets some νμ CC for tuning purpose Jaewon Park, U. of Rochester FNAL JETP

  40. Sideband Populations Most Events (nmCharged or Neutral Current ) Rare but hard to reject: ne Charged Current Coherent p0 Jaewon Park, U. of Rochester FNAL JETP

  41. Sideband Tuning Scale three MC components to match to data Minimize χ2 across 7 histograms 3 parameters tuned in this step Minimize χ2 across 2 histograms 1 parameter tuned in this step Before tuning MINERvA Preliminary After tuning Track Length in HCAL (modules) MINERvA Preliminary Events with tracks in downstream Hadron Calorimeter are mostly νμ CC Track Length in HCAL (modules) νe νμ NC νμ CC COH π0 20 December 2013 Jaewon Park, U. of Rochester FNAL JETP

  42. dE/dx and Eq2 in Sidebands after tuning Eθ2 (GeV∙rad 2) # Events (Eθ2 < 0.2) Sideband (b) 0.005 0.0032 Signal (c) Unused (a) MINERvA Preliminary 4.5 dE/dx (MeV/1.7cm) Eθ2 (GeV∙radians 2) • Both dE/dx and Eθ2 are well simulated in the sideband region after fitting MINERvA Preliminary dE/dx (MeV/1.7cm) Jaewon Park, U. of Rochester FNAL JETP

  43. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal and backgrounds • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  44. Systematic Uncertainties N: events in data B: Background e: Efficiency A: Acceptance s: signal cross section • Error in background contribution • Flux uncertainties • Cross Section Uncertainties • Error in efficiency and Acceptance Jaewon Park, U. of Rochester FNAL JETP

  45. Uncertainty in neCCQE extrapolation from sideband Previous MINERvA results on nm Quasi-elastic process shows that momentum transfer squared (Q2QE) distribution is not what GENIE predicts Phys. Rev. Lett. 111, 022502 (2013), Phys. Rev. Lett. 111, 022501 (2013). Q2QE and Eθ2 are highly correlated Compare nebackground prediction Eq2 extrapolation with two different models: one is GENIE, the other is one inspired by MINERvA nm data: systematic uncertainty: 3.3% Jaewon Park, U. of Rochester FNAL JETP

  46. Flux and Cross Section Systematic Uncertainties on MC Background Sideband tuning reduced systematic uncertainty on predicted background Predicted background (before tuning): 38.9 ± 6.2 (stat) ± 10.3 (sys) Predicted background (after tuning): 32.9 ± 5.3 (stat) ± 5.7 (sys) The tuning didn’t eliminate systematic uncertainty but it gives confidence on background prediction 20 December 2013 Jaewon Park, U. of Rochester FNAL JETP

  47. Reconstruction Systematic Uncertainties • Angular Alignment: look at data-simulation differences in m angles for nm CC events with low hadron energy • 3 (1) mrad correction in y (x) • uncertainty is ±1mrad MINERvA Preliminary MINERvA Preliminary nmCharged Current Events with hadron energy<100MeV Electromagnetic Energy Scale: look at electrons from stopped m decays (Michel): see agreement at 4.2% level, add as systematic uncertainty Jaewon Park, U. of Rochester FNAL JETP

  48. Reconstruction Uncertainties Jaewon Park, U. of Rochester FNAL JETP

  49. Outline • Neutrino experiments and their fluxes • ν-e scattering: signal and backgrounds • Event reconstruction • Backgrounds and how to remove them • Background Prediction • Systematic uncertainty • Result and Conclusions Jaewon Park, U. of Rochester FNAL JETP

  50. Result • Found: 121 events before background subtraction • n-e scattering events after background subtraction and efficiency correction: 123.8 ± 17.0 (stat) ± 9.1 (sys)total uncertainty: 15% • Prediction from Simulation: 147.5 ± 22.9 (flux) • Flux uncertainty: 15.5% Observed ν-e scattering events give a constraint on flux with similar uncertainty as current flux uncertainty, consistent with prediction Jaewon Park, U. of Rochester FNAL JETP

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